Removed openssl, and curl, and added mbedded tls.curl-removal

Almost fully removed curl, needs more testing.

Fixed most issues, now trying to cross compile.

Fix?

Sigh.

1 files changed, 6071 insertions, 0 deletions

diff --git a/lib/mbedtls-2.27.0/library/ssl_msg.c b/lib/mbedtls-2.27.0/library/ssl_msg.c
new file mode 100644
index 0000000..1352b49
--- /dev/null
+++ b/lib/mbedtls-2.27.0/library/ssl_msg.c
@@ -0,0 +1,6071 @@
+/*
+ *  Generic SSL/TLS messaging layer functions
+ *  (record layer + retransmission state machine)
+ *
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+/*
+ *  The SSL 3.0 specification was drafted by Netscape in 1996,
+ *  and became an IETF standard in 1999.
+ *
+ *  http://wp.netscape.com/eng/ssl3/
+ *  http://www.ietf.org/rfc/rfc2246.txt
+ *  http://www.ietf.org/rfc/rfc4346.txt
+ */
+
+#include "common.h"
+
+#if defined(MBEDTLS_SSL_TLS_C)
+
+#if defined(MBEDTLS_PLATFORM_C)
+#include "mbedtls/platform.h"
+#else
+#include <stdlib.h>
+#define mbedtls_calloc    calloc
+#define mbedtls_free      free
+#endif
+
+#include "mbedtls/ssl.h"
+#include "mbedtls/ssl_internal.h"
+#include "mbedtls/debug.h"
+#include "mbedtls/error.h"
+#include "mbedtls/platform_util.h"
+#include "mbedtls/version.h"
+
+#include "ssl_invasive.h"
+
+#include <string.h>
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+#include "mbedtls/psa_util.h"
+#include "psa/crypto.h"
+#endif
+
+#if defined(MBEDTLS_X509_CRT_PARSE_C)
+#include "mbedtls/oid.h"
+#endif
+
+static uint32_t ssl_get_hs_total_len( mbedtls_ssl_context const *ssl );
+
+/*
+ * Start a timer.
+ * Passing millisecs = 0 cancels a running timer.
+ */
+void mbedtls_ssl_set_timer( mbedtls_ssl_context *ssl, uint32_t millisecs )
+{
+    if( ssl->f_set_timer == NULL )
+        return;
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "set_timer to %d ms", (int) millisecs ) );
+    ssl->f_set_timer( ssl->p_timer, millisecs / 4, millisecs );
+}
+
+/*
+ * Return -1 is timer is expired, 0 if it isn't.
+ */
+int mbedtls_ssl_check_timer( mbedtls_ssl_context *ssl )
+{
+    if( ssl->f_get_timer == NULL )
+        return( 0 );
+
+    if( ssl->f_get_timer( ssl->p_timer ) == 2 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "timer expired" ) );
+        return( -1 );
+    }
+
+    return( 0 );
+}
+
+#if defined(MBEDTLS_SSL_RECORD_CHECKING)
+static int ssl_parse_record_header( mbedtls_ssl_context const *ssl,
+                                    unsigned char *buf,
+                                    size_t len,
+                                    mbedtls_record *rec );
+
+int mbedtls_ssl_check_record( mbedtls_ssl_context const *ssl,
+                              unsigned char *buf,
+                              size_t buflen )
+{
+    int ret = 0;
+    MBEDTLS_SSL_DEBUG_MSG( 1, ( "=> mbedtls_ssl_check_record" ) );
+    MBEDTLS_SSL_DEBUG_BUF( 3, "record buffer", buf, buflen );
+
+    /* We don't support record checking in TLS because
+     * (a) there doesn't seem to be a usecase for it, and
+     * (b) In SSLv3 and TLS 1.0, CBC record decryption has state
+     *     and we'd need to backup the transform here.
+     */
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_STREAM )
+    {
+        ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
+        goto exit;
+    }
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    else
+    {
+        mbedtls_record rec;
+
+        ret = ssl_parse_record_header( ssl, buf, buflen, &rec );
+        if( ret != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 3, "ssl_parse_record_header", ret );
+            goto exit;
+        }
+
+        if( ssl->transform_in != NULL )
+        {
+            ret = mbedtls_ssl_decrypt_buf( ssl, ssl->transform_in, &rec );
+            if( ret != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_RET( 3, "mbedtls_ssl_decrypt_buf", ret );
+                goto exit;
+            }
+        }
+    }
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+exit:
+    /* On success, we have decrypted the buffer in-place, so make
+     * sure we don't leak any plaintext data. */
+    mbedtls_platform_zeroize( buf, buflen );
+
+    /* For the purpose of this API, treat messages with unexpected CID
+     * as well as such from future epochs as unexpected. */
+    if( ret == MBEDTLS_ERR_SSL_UNEXPECTED_CID ||
+        ret == MBEDTLS_ERR_SSL_EARLY_MESSAGE )
+    {
+        ret = MBEDTLS_ERR_SSL_UNEXPECTED_RECORD;
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 1, ( "<= mbedtls_ssl_check_record" ) );
+    return( ret );
+}
+#endif /* MBEDTLS_SSL_RECORD_CHECKING */
+
+#define SSL_DONT_FORCE_FLUSH 0
+#define SSL_FORCE_FLUSH      1
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+
+/* Forward declarations for functions related to message buffering. */
+static void ssl_buffering_free_slot( mbedtls_ssl_context *ssl,
+                                     uint8_t slot );
+static void ssl_free_buffered_record( mbedtls_ssl_context *ssl );
+static int ssl_load_buffered_message( mbedtls_ssl_context *ssl );
+static int ssl_load_buffered_record( mbedtls_ssl_context *ssl );
+static int ssl_buffer_message( mbedtls_ssl_context *ssl );
+static int ssl_buffer_future_record( mbedtls_ssl_context *ssl,
+                                     mbedtls_record const *rec );
+static int ssl_next_record_is_in_datagram( mbedtls_ssl_context *ssl );
+
+static size_t ssl_get_maximum_datagram_size( mbedtls_ssl_context const *ssl )
+{
+    size_t mtu = mbedtls_ssl_get_current_mtu( ssl );
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t out_buf_len = ssl->out_buf_len;
+#else
+    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
+#endif
+
+    if( mtu != 0 && mtu < out_buf_len )
+        return( mtu );
+
+    return( out_buf_len );
+}
+
+static int ssl_get_remaining_space_in_datagram( mbedtls_ssl_context const *ssl )
+{
+    size_t const bytes_written = ssl->out_left;
+    size_t const mtu           = ssl_get_maximum_datagram_size( ssl );
+
+    /* Double-check that the write-index hasn't gone
+     * past what we can transmit in a single datagram. */
+    if( bytes_written > mtu )
+    {
+        /* Should never happen... */
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    return( (int) ( mtu - bytes_written ) );
+}
+
+static int ssl_get_remaining_payload_in_datagram( mbedtls_ssl_context const *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t remaining, expansion;
+    size_t max_len = MBEDTLS_SSL_OUT_CONTENT_LEN;
+
+#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
+    const size_t mfl = mbedtls_ssl_get_output_max_frag_len( ssl );
+
+    if( max_len > mfl )
+        max_len = mfl;
+
+    /* By the standard (RFC 6066 Sect. 4), the MFL extension
+     * only limits the maximum record payload size, so in theory
+     * we would be allowed to pack multiple records of payload size
+     * MFL into a single datagram. However, this would mean that there's
+     * no way to explicitly communicate MTU restrictions to the peer.
+     *
+     * The following reduction of max_len makes sure that we never
+     * write datagrams larger than MFL + Record Expansion Overhead.
+     */
+    if( max_len <= ssl->out_left )
+        return( 0 );
+
+    max_len -= ssl->out_left;
+#endif
+
+    ret = ssl_get_remaining_space_in_datagram( ssl );
+    if( ret < 0 )
+        return( ret );
+    remaining = (size_t) ret;
+
+    ret = mbedtls_ssl_get_record_expansion( ssl );
+    if( ret < 0 )
+        return( ret );
+    expansion = (size_t) ret;
+
+    if( remaining <= expansion )
+        return( 0 );
+
+    remaining -= expansion;
+    if( remaining >= max_len )
+        remaining = max_len;
+
+    return( (int) remaining );
+}
+
+/*
+ * Double the retransmit timeout value, within the allowed range,
+ * returning -1 if the maximum value has already been reached.
+ */
+static int ssl_double_retransmit_timeout( mbedtls_ssl_context *ssl )
+{
+    uint32_t new_timeout;
+
+    if( ssl->handshake->retransmit_timeout >= ssl->conf->hs_timeout_max )
+        return( -1 );
+
+    /* Implement the final paragraph of RFC 6347 section 4.1.1.1
+     * in the following way: after the initial transmission and a first
+     * retransmission, back off to a temporary estimated MTU of 508 bytes.
+     * This value is guaranteed to be deliverable (if not guaranteed to be
+     * delivered) of any compliant IPv4 (and IPv6) network, and should work
+     * on most non-IP stacks too. */
+    if( ssl->handshake->retransmit_timeout != ssl->conf->hs_timeout_min )
+    {
+        ssl->handshake->mtu = 508;
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "mtu autoreduction to %d bytes", ssl->handshake->mtu ) );
+    }
+
+    new_timeout = 2 * ssl->handshake->retransmit_timeout;
+
+    /* Avoid arithmetic overflow and range overflow */
+    if( new_timeout < ssl->handshake->retransmit_timeout ||
+        new_timeout > ssl->conf->hs_timeout_max )
+    {
+        new_timeout = ssl->conf->hs_timeout_max;
+    }
+
+    ssl->handshake->retransmit_timeout = new_timeout;
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "update timeout value to %lu millisecs",
+                        (unsigned long) ssl->handshake->retransmit_timeout ) );
+
+    return( 0 );
+}
+
+static void ssl_reset_retransmit_timeout( mbedtls_ssl_context *ssl )
+{
+    ssl->handshake->retransmit_timeout = ssl->conf->hs_timeout_min;
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "update timeout value to %lu millisecs",
+                        (unsigned long) ssl->handshake->retransmit_timeout ) );
+}
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
+int (*mbedtls_ssl_hw_record_init)( mbedtls_ssl_context *ssl,
+                     const unsigned char *key_enc, const unsigned char *key_dec,
+                     size_t keylen,
+                     const unsigned char *iv_enc,  const unsigned char *iv_dec,
+                     size_t ivlen,
+                     const unsigned char *mac_enc, const unsigned char *mac_dec,
+                     size_t maclen ) = NULL;
+int (*mbedtls_ssl_hw_record_activate)( mbedtls_ssl_context *ssl, int direction) = NULL;
+int (*mbedtls_ssl_hw_record_reset)( mbedtls_ssl_context *ssl ) = NULL;
+int (*mbedtls_ssl_hw_record_write)( mbedtls_ssl_context *ssl ) = NULL;
+int (*mbedtls_ssl_hw_record_read)( mbedtls_ssl_context *ssl ) = NULL;
+int (*mbedtls_ssl_hw_record_finish)( mbedtls_ssl_context *ssl ) = NULL;
+#endif /* MBEDTLS_SSL_HW_RECORD_ACCEL */
+
+/*
+ * Encryption/decryption functions
+ */
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID) ||  \
+    defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
+
+static size_t ssl_compute_padding_length( size_t len,
+                                          size_t granularity )
+{
+    return( ( granularity - ( len + 1 ) % granularity ) % granularity );
+}
+
+/* This functions transforms a (D)TLS plaintext fragment and a record content
+ * type into an instance of the (D)TLSInnerPlaintext structure. This is used
+ * in DTLS 1.2 + CID and within TLS 1.3 to allow flexible padding and to protect
+ * a record's content type.
+ *
+ *        struct {
+ *            opaque content[DTLSPlaintext.length];
+ *            ContentType real_type;
+ *            uint8 zeros[length_of_padding];
+ *        } (D)TLSInnerPlaintext;
+ *
+ *  Input:
+ *  - `content`: The beginning of the buffer holding the
+ *               plaintext to be wrapped.
+ *  - `*content_size`: The length of the plaintext in Bytes.
+ *  - `max_len`: The number of Bytes available starting from
+ *               `content`. This must be `>= *content_size`.
+ *  - `rec_type`: The desired record content type.
+ *
+ *  Output:
+ *  - `content`: The beginning of the resulting (D)TLSInnerPlaintext structure.
+ *  - `*content_size`: The length of the resulting (D)TLSInnerPlaintext structure.
+ *
+ *  Returns:
+ *  - `0` on success.
+ *  - A negative error code if `max_len` didn't offer enough space
+ *    for the expansion.
+ */
+static int ssl_build_inner_plaintext( unsigned char *content,
+                                      size_t *content_size,
+                                      size_t remaining,
+                                      uint8_t rec_type,
+                                      size_t pad )
+{
+    size_t len = *content_size;
+
+    /* Write real content type */
+    if( remaining == 0 )
+        return( -1 );
+    content[ len ] = rec_type;
+    len++;
+    remaining--;
+
+    if( remaining < pad )
+        return( -1 );
+    memset( content + len, 0, pad );
+    len += pad;
+    remaining -= pad;
+
+    *content_size = len;
+    return( 0 );
+}
+
+/* This function parses a (D)TLSInnerPlaintext structure.
+ * See ssl_build_inner_plaintext() for details. */
+static int ssl_parse_inner_plaintext( unsigned char const *content,
+                                          size_t *content_size,
+                                          uint8_t *rec_type )
+{
+    size_t remaining = *content_size;
+
+    /* Determine length of padding by skipping zeroes from the back. */
+    do
+    {
+        if( remaining == 0 )
+            return( -1 );
+        remaining--;
+    } while( content[ remaining ] == 0 );
+
+    *content_size = remaining;
+    *rec_type = content[ remaining ];
+
+    return( 0 );
+}
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID ||
+          MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
+
+/* `add_data` must have size 13 Bytes if the CID extension is disabled,
+ * and 13 + 1 + CID-length Bytes if the CID extension is enabled. */
+static void ssl_extract_add_data_from_record( unsigned char* add_data,
+                                              size_t *add_data_len,
+                                              mbedtls_record *rec,
+                                              unsigned minor_ver )
+{
+    /* Quoting RFC 5246 (TLS 1.2):
+     *
+     *    additional_data = seq_num + TLSCompressed.type +
+     *                      TLSCompressed.version + TLSCompressed.length;
+     *
+     * For the CID extension, this is extended as follows
+     * (quoting draft-ietf-tls-dtls-connection-id-05,
+     *  https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-05):
+     *
+     *       additional_data = seq_num + DTLSPlaintext.type +
+     *                         DTLSPlaintext.version +
+     *                         cid +
+     *                         cid_length +
+     *                         length_of_DTLSInnerPlaintext;
+     *
+     * For TLS 1.3, the record sequence number is dropped from the AAD
+     * and encoded within the nonce of the AEAD operation instead.
+     */
+
+    unsigned char *cur = add_data;
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
+    if( minor_ver != MBEDTLS_SSL_MINOR_VERSION_4 )
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
+    {
+        ((void) minor_ver);
+        memcpy( cur, rec->ctr, sizeof( rec->ctr ) );
+        cur += sizeof( rec->ctr );
+    }
+
+    *cur = rec->type;
+    cur++;
+
+    memcpy( cur, rec->ver, sizeof( rec->ver ) );
+    cur += sizeof( rec->ver );
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    if( rec->cid_len != 0 )
+    {
+        memcpy( cur, rec->cid, rec->cid_len );
+        cur += rec->cid_len;
+
+        *cur = rec->cid_len;
+        cur++;
+
+        cur[0] = ( rec->data_len >> 8 ) & 0xFF;
+        cur[1] = ( rec->data_len >> 0 ) & 0xFF;
+        cur += 2;
+    }
+    else
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+    {
+        cur[0] = ( rec->data_len >> 8 ) & 0xFF;
+        cur[1] = ( rec->data_len >> 0 ) & 0xFF;
+        cur += 2;
+    }
+
+    *add_data_len = cur - add_data;
+}
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+
+#define SSL3_MAC_MAX_BYTES   20  /* MD-5 or SHA-1 */
+
+/*
+ * SSLv3.0 MAC functions
+ */
+static void ssl_mac( mbedtls_md_context_t *md_ctx,
+                     const unsigned char *secret,
+                     const unsigned char *buf, size_t len,
+                     const unsigned char *ctr, int type,
+                     unsigned char out[SSL3_MAC_MAX_BYTES] )
+{
+    unsigned char header[11];
+    unsigned char padding[48];
+    int padlen;
+    int md_size = mbedtls_md_get_size( md_ctx->md_info );
+    int md_type = mbedtls_md_get_type( md_ctx->md_info );
+
+    /* Only MD5 and SHA-1 supported */
+    if( md_type == MBEDTLS_MD_MD5 )
+        padlen = 48;
+    else
+        padlen = 40;
+
+    memcpy( header, ctr, 8 );
+    header[ 8] = (unsigned char)  type;
+    header[ 9] = (unsigned char)( len >> 8 );
+    header[10] = (unsigned char)( len      );
+
+    memset( padding, 0x36, padlen );
+    mbedtls_md_starts( md_ctx );
+    mbedtls_md_update( md_ctx, secret,  md_size );
+    mbedtls_md_update( md_ctx, padding, padlen  );
+    mbedtls_md_update( md_ctx, header,  11      );
+    mbedtls_md_update( md_ctx, buf,     len     );
+    mbedtls_md_finish( md_ctx, out              );
+
+    memset( padding, 0x5C, padlen );
+    mbedtls_md_starts( md_ctx );
+    mbedtls_md_update( md_ctx, secret,    md_size );
+    mbedtls_md_update( md_ctx, padding,   padlen  );
+    mbedtls_md_update( md_ctx, out,       md_size );
+    mbedtls_md_finish( md_ctx, out                );
+}
+#endif /* MBEDTLS_SSL_PROTO_SSL3 */
+
+#if defined(MBEDTLS_GCM_C) || \
+    defined(MBEDTLS_CCM_C) || \
+    defined(MBEDTLS_CHACHAPOLY_C)
+static int ssl_transform_aead_dynamic_iv_is_explicit(
+                                mbedtls_ssl_transform const *transform )
+{
+    return( transform->ivlen != transform->fixed_ivlen );
+}
+
+/* Compute IV := ( fixed_iv || 0 ) XOR ( 0 || dynamic_IV )
+ *
+ * Concretely, this occurs in two variants:
+ *
+ * a) Fixed and dynamic IV lengths add up to total IV length, giving
+ *       IV = fixed_iv || dynamic_iv
+ *
+ *    This variant is used in TLS 1.2 when used with GCM or CCM.
+ *
+ * b) Fixed IV lengths matches total IV length, giving
+ *       IV = fixed_iv XOR ( 0 || dynamic_iv )
+ *
+ *    This variant occurs in TLS 1.3 and for TLS 1.2 when using ChaChaPoly.
+ *
+ * See also the documentation of mbedtls_ssl_transform.
+ *
+ * This function has the precondition that
+ *
+ *     dst_iv_len >= max( fixed_iv_len, dynamic_iv_len )
+ *
+ * which has to be ensured by the caller. If this precondition
+ * violated, the behavior of this function is undefined.
+ */
+static void ssl_build_record_nonce( unsigned char *dst_iv,
+                                    size_t dst_iv_len,
+                                    unsigned char const *fixed_iv,
+                                    size_t fixed_iv_len,
+                                    unsigned char const *dynamic_iv,
+                                    size_t dynamic_iv_len )
+{
+    size_t i;
+
+    /* Start with Fixed IV || 0 */
+    memset( dst_iv, 0, dst_iv_len );
+    memcpy( dst_iv, fixed_iv, fixed_iv_len );
+
+    dst_iv += dst_iv_len - dynamic_iv_len;
+    for( i = 0; i < dynamic_iv_len; i++ )
+        dst_iv[i] ^= dynamic_iv[i];
+}
+#endif /* MBEDTLS_GCM_C || MBEDTLS_CCM_C || MBEDTLS_CHACHAPOLY_C */
+
+int mbedtls_ssl_encrypt_buf( mbedtls_ssl_context *ssl,
+                             mbedtls_ssl_transform *transform,
+                             mbedtls_record *rec,
+                             int (*f_rng)(void *, unsigned char *, size_t),
+                             void *p_rng )
+{
+    mbedtls_cipher_mode_t mode;
+    int auth_done = 0;
+    unsigned char * data;
+    unsigned char add_data[13 + 1 + MBEDTLS_SSL_CID_OUT_LEN_MAX ];
+    size_t add_data_len;
+    size_t post_avail;
+
+    /* The SSL context is only used for debugging purposes! */
+#if !defined(MBEDTLS_DEBUG_C)
+    ssl = NULL; /* make sure we don't use it except for debug */
+    ((void) ssl);
+#endif
+
+    /* The PRNG is used for dynamic IV generation that's used
+     * for CBC transformations in TLS 1.1 and TLS 1.2. */
+#if !( defined(MBEDTLS_SSL_SOME_SUITES_USE_CBC) && \
+       ( defined(MBEDTLS_SSL_PROTO_TLS1_1) || defined(MBEDTLS_SSL_PROTO_TLS1_2) ) )
+    ((void) f_rng);
+    ((void) p_rng);
+#endif
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> encrypt buf" ) );
+
+    if( transform == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "no transform provided to encrypt_buf" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+    if( rec == NULL
+        || rec->buf == NULL
+        || rec->buf_len < rec->data_offset
+        || rec->buf_len - rec->data_offset < rec->data_len
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+        || rec->cid_len != 0
+#endif
+        )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad record structure provided to encrypt_buf" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    data = rec->buf + rec->data_offset;
+    post_avail = rec->buf_len - ( rec->data_len + rec->data_offset );
+    MBEDTLS_SSL_DEBUG_BUF( 4, "before encrypt: output payload",
+                           data, rec->data_len );
+
+    mode = mbedtls_cipher_get_cipher_mode( &transform->cipher_ctx_enc );
+
+    if( rec->data_len > MBEDTLS_SSL_OUT_CONTENT_LEN )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Record content %" MBEDTLS_PRINTF_SIZET
+                                    " too large, maximum %" MBEDTLS_PRINTF_SIZET,
+                                    rec->data_len,
+                                    (size_t) MBEDTLS_SSL_OUT_CONTENT_LEN ) );
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+    }
+
+    /* The following two code paths implement the (D)TLSInnerPlaintext
+     * structure present in TLS 1.3 and DTLS 1.2 + CID.
+     *
+     * See ssl_build_inner_plaintext() for more information.
+     *
+     * Note that this changes `rec->data_len`, and hence
+     * `post_avail` needs to be recalculated afterwards.
+     *
+     * Note also that the two code paths cannot occur simultaneously
+     * since they apply to different versions of the protocol. There
+     * is hence no risk of double-addition of the inner plaintext.
+     */
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
+    if( transform->minor_ver == MBEDTLS_SSL_MINOR_VERSION_4 )
+    {
+        size_t padding =
+            ssl_compute_padding_length( rec->data_len,
+                                        MBEDTLS_SSL_TLS1_3_PADDING_GRANULARITY );
+        if( ssl_build_inner_plaintext( data,
+                                       &rec->data_len,
+                                       post_avail,
+                                       rec->type,
+                                       padding ) != 0 )
+        {
+            return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+        }
+
+        rec->type = MBEDTLS_SSL_MSG_APPLICATION_DATA;
+    }
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    /*
+     * Add CID information
+     */
+    rec->cid_len = transform->out_cid_len;
+    memcpy( rec->cid, transform->out_cid, transform->out_cid_len );
+    MBEDTLS_SSL_DEBUG_BUF( 3, "CID", rec->cid, rec->cid_len );
+
+    if( rec->cid_len != 0 )
+    {
+        size_t padding =
+            ssl_compute_padding_length( rec->data_len,
+                                        MBEDTLS_SSL_CID_PADDING_GRANULARITY );
+        /*
+         * Wrap plaintext into DTLSInnerPlaintext structure.
+         * See ssl_build_inner_plaintext() for more information.
+         *
+         * Note that this changes `rec->data_len`, and hence
+         * `post_avail` needs to be recalculated afterwards.
+         */
+        if( ssl_build_inner_plaintext( data,
+                        &rec->data_len,
+                        post_avail,
+                        rec->type,
+                        padding ) != 0 )
+        {
+            return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+        }
+
+        rec->type = MBEDTLS_SSL_MSG_CID;
+    }
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+    post_avail = rec->buf_len - ( rec->data_len + rec->data_offset );
+
+    /*
+     * Add MAC before if needed
+     */
+#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
+    if( mode == MBEDTLS_MODE_STREAM ||
+        ( mode == MBEDTLS_MODE_CBC
+#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
+          && transform->encrypt_then_mac == MBEDTLS_SSL_ETM_DISABLED
+#endif
+        ) )
+    {
+        if( post_avail < transform->maclen )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "Buffer provided for encrypted record not large enough" ) );
+            return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+        }
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+        if( transform->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
+        {
+            unsigned char mac[SSL3_MAC_MAX_BYTES];
+            ssl_mac( &transform->md_ctx_enc, transform->mac_enc,
+                     data, rec->data_len, rec->ctr, rec->type, mac );
+            memcpy( data + rec->data_len, mac, transform->maclen );
+        }
+        else
+#endif
+#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
+        defined(MBEDTLS_SSL_PROTO_TLS1_2)
+        if( transform->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_1 )
+        {
+            unsigned char mac[MBEDTLS_SSL_MAC_ADD];
+
+            ssl_extract_add_data_from_record( add_data, &add_data_len, rec,
+                                              transform->minor_ver );
+
+            mbedtls_md_hmac_update( &transform->md_ctx_enc, add_data,
+                                    add_data_len );
+            mbedtls_md_hmac_update( &transform->md_ctx_enc,
+                                    data, rec->data_len );
+            mbedtls_md_hmac_finish( &transform->md_ctx_enc, mac );
+            mbedtls_md_hmac_reset( &transform->md_ctx_enc );
+
+            memcpy( data + rec->data_len, mac, transform->maclen );
+        }
+        else
+#endif
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+
+        MBEDTLS_SSL_DEBUG_BUF( 4, "computed mac", data + rec->data_len,
+                               transform->maclen );
+
+        rec->data_len += transform->maclen;
+        post_avail -= transform->maclen;
+        auth_done++;
+    }
+#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
+
+    /*
+     * Encrypt
+     */
+#if defined(MBEDTLS_ARC4_C) || defined(MBEDTLS_CIPHER_NULL_CIPHER)
+    if( mode == MBEDTLS_MODE_STREAM )
+    {
+        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+        size_t olen;
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "before encrypt: msglen = %" MBEDTLS_PRINTF_SIZET ", "
+                                    "including %d bytes of padding",
+                                    rec->data_len, 0 ) );
+
+        if( ( ret = mbedtls_cipher_crypt( &transform->cipher_ctx_enc,
+                                   transform->iv_enc, transform->ivlen,
+                                   data, rec->data_len,
+                                   data, &olen ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_crypt", ret );
+            return( ret );
+        }
+
+        if( rec->data_len != olen )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+    }
+    else
+#endif /* MBEDTLS_ARC4_C || MBEDTLS_CIPHER_NULL_CIPHER */
+
+#if defined(MBEDTLS_GCM_C) || \
+    defined(MBEDTLS_CCM_C) || \
+    defined(MBEDTLS_CHACHAPOLY_C)
+    if( mode == MBEDTLS_MODE_GCM ||
+        mode == MBEDTLS_MODE_CCM ||
+        mode == MBEDTLS_MODE_CHACHAPOLY )
+    {
+        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+        unsigned char iv[12];
+        unsigned char *dynamic_iv;
+        size_t dynamic_iv_len;
+        int dynamic_iv_is_explicit =
+            ssl_transform_aead_dynamic_iv_is_explicit( transform );
+
+        /* Check that there's space for the authentication tag. */
+        if( post_avail < transform->taglen )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "Buffer provided for encrypted record not large enough" ) );
+            return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+        }
+
+        /*
+         * Build nonce for AEAD encryption.
+         *
+         * Note: In the case of CCM and GCM in TLS 1.2, the dynamic
+         *       part of the IV is prepended to the ciphertext and
+         *       can be chosen freely - in particular, it need not
+         *       agree with the record sequence number.
+         *       However, since ChaChaPoly as well as all AEAD modes
+         *       in TLS 1.3 use the record sequence number as the
+         *       dynamic part of the nonce, we uniformly use the
+         *       record sequence number here in all cases.
+         */
+        dynamic_iv     = rec->ctr;
+        dynamic_iv_len = sizeof( rec->ctr );
+
+        ssl_build_record_nonce( iv, sizeof( iv ),
+                                transform->iv_enc,
+                                transform->fixed_ivlen,
+                                dynamic_iv,
+                                dynamic_iv_len );
+
+        /*
+         * Build additional data for AEAD encryption.
+         * This depends on the TLS version.
+         */
+        ssl_extract_add_data_from_record( add_data, &add_data_len, rec,
+                                          transform->minor_ver );
+
+        MBEDTLS_SSL_DEBUG_BUF( 4, "IV used (internal)",
+                               iv, transform->ivlen );
+        MBEDTLS_SSL_DEBUG_BUF( 4, "IV used (transmitted)",
+                               dynamic_iv,
+                               dynamic_iv_is_explicit ? dynamic_iv_len : 0 );
+        MBEDTLS_SSL_DEBUG_BUF( 4, "additional data used for AEAD",
+                               add_data, add_data_len );
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "before encrypt: msglen = %" MBEDTLS_PRINTF_SIZET ", "
+                                    "including 0 bytes of padding",
+                                    rec->data_len ) );
+
+        /*
+         * Encrypt and authenticate
+         */
+
+        if( ( ret = mbedtls_cipher_auth_encrypt_ext( &transform->cipher_ctx_enc,
+                   iv, transform->ivlen,
+                   add_data, add_data_len,
+                   data, rec->data_len,                     /* src */
+                   data, rec->buf_len - (data - rec->buf),  /* dst */
+                   &rec->data_len,
+                   transform->taglen ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_auth_encrypt", ret );
+            return( ret );
+        }
+        MBEDTLS_SSL_DEBUG_BUF( 4, "after encrypt: tag",
+                               data + rec->data_len - transform->taglen,
+                               transform->taglen );
+        /* Account for authentication tag. */
+        post_avail -= transform->taglen;
+
+        /*
+         * Prefix record content with dynamic IV in case it is explicit.
+         */
+        if( dynamic_iv_is_explicit != 0 )
+        {
+            if( rec->data_offset < dynamic_iv_len )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "Buffer provided for encrypted record not large enough" ) );
+                return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+            }
+
+            memcpy( data - dynamic_iv_len, dynamic_iv, dynamic_iv_len );
+            rec->data_offset -= dynamic_iv_len;
+            rec->data_len    += dynamic_iv_len;
+        }
+
+        auth_done++;
+    }
+    else
+#endif /* MBEDTLS_GCM_C || MBEDTLS_CCM_C || MBEDTLS_CHACHAPOLY_C */
+#if defined(MBEDTLS_SSL_SOME_SUITES_USE_CBC)
+    if( mode == MBEDTLS_MODE_CBC )
+    {
+        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+        size_t padlen, i;
+        size_t olen;
+
+        /* Currently we're always using minimal padding
+         * (up to 255 bytes would be allowed). */
+        padlen = transform->ivlen - ( rec->data_len + 1 ) % transform->ivlen;
+        if( padlen == transform->ivlen )
+            padlen = 0;
+
+        /* Check there's enough space in the buffer for the padding. */
+        if( post_avail < padlen + 1 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "Buffer provided for encrypted record not large enough" ) );
+            return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+        }
+
+        for( i = 0; i <= padlen; i++ )
+            data[rec->data_len + i] = (unsigned char) padlen;
+
+        rec->data_len += padlen + 1;
+        post_avail -= padlen + 1;
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_1) || defined(MBEDTLS_SSL_PROTO_TLS1_2)
+        /*
+         * Prepend per-record IV for block cipher in TLS v1.1 and up as per
+         * Method 1 (6.2.3.2. in RFC4346 and RFC5246)
+         */
+        if( transform->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 )
+        {
+            if( f_rng == NULL )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "No PRNG provided to encrypt_record routine" ) );
+                return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+            }
+
+            if( rec->data_offset < transform->ivlen )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "Buffer provided for encrypted record not large enough" ) );
+                return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+            }
+
+            /*
+             * Generate IV
+             */
+            ret = f_rng( p_rng, transform->iv_enc, transform->ivlen );
+            if( ret != 0 )
+                return( ret );
+
+            memcpy( data - transform->ivlen, transform->iv_enc,
+                    transform->ivlen );
+
+        }
+#endif /* MBEDTLS_SSL_PROTO_TLS1_1 || MBEDTLS_SSL_PROTO_TLS1_2 */
+
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "before encrypt: msglen = %" MBEDTLS_PRINTF_SIZET ", "
+                            "including %" MBEDTLS_PRINTF_SIZET
+                            " bytes of IV and %" MBEDTLS_PRINTF_SIZET " bytes of padding",
+                            rec->data_len, transform->ivlen,
+                            padlen + 1 ) );
+
+        if( ( ret = mbedtls_cipher_crypt( &transform->cipher_ctx_enc,
+                                   transform->iv_enc,
+                                   transform->ivlen,
+                                   data, rec->data_len,
+                                   data, &olen ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_crypt", ret );
+            return( ret );
+        }
+
+        if( rec->data_len != olen )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1)
+        if( transform->minor_ver < MBEDTLS_SSL_MINOR_VERSION_2 )
+        {
+            /*
+             * Save IV in SSL3 and TLS1
+             */
+            memcpy( transform->iv_enc, transform->cipher_ctx_enc.iv,
+                    transform->ivlen );
+        }
+        else
+#endif
+        {
+            data             -= transform->ivlen;
+            rec->data_offset -= transform->ivlen;
+            rec->data_len    += transform->ivlen;
+        }
+
+#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
+        if( auth_done == 0 )
+        {
+            unsigned char mac[MBEDTLS_SSL_MAC_ADD];
+
+            /*
+             * MAC(MAC_write_key, seq_num +
+             *     TLSCipherText.type +
+             *     TLSCipherText.version +
+             *     length_of( (IV +) ENC(...) ) +
+             *     IV + // except for TLS 1.0
+             *     ENC(content + padding + padding_length));
+             */
+
+            if( post_avail < transform->maclen)
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "Buffer provided for encrypted record not large enough" ) );
+                return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+            }
+
+            ssl_extract_add_data_from_record( add_data, &add_data_len,
+                                              rec, transform->minor_ver );
+
+            MBEDTLS_SSL_DEBUG_MSG( 3, ( "using encrypt then mac" ) );
+            MBEDTLS_SSL_DEBUG_BUF( 4, "MAC'd meta-data", add_data,
+                                   add_data_len );
+
+            mbedtls_md_hmac_update( &transform->md_ctx_enc, add_data,
+                                    add_data_len );
+            mbedtls_md_hmac_update( &transform->md_ctx_enc,
+                                    data, rec->data_len );
+            mbedtls_md_hmac_finish( &transform->md_ctx_enc, mac );
+            mbedtls_md_hmac_reset( &transform->md_ctx_enc );
+
+            memcpy( data + rec->data_len, mac, transform->maclen );
+
+            rec->data_len += transform->maclen;
+            post_avail -= transform->maclen;
+            auth_done++;
+        }
+#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
+    }
+    else
+#endif /* MBEDTLS_SSL_SOME_SUITES_USE_CBC) */
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    /* Make extra sure authentication was performed, exactly once */
+    if( auth_done != 1 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= encrypt buf" ) );
+
+    return( 0 );
+}
+
+#if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC)
+/*
+ * Turn a bit into a mask:
+ * - if bit == 1, return the all-bits 1 mask, aka (size_t) -1
+ * - if bit == 0, return the all-bits 0 mask, aka 0
+ *
+ * This function can be used to write constant-time code by replacing branches
+ * with bit operations using masks.
+ *
+ * This function is implemented without using comparison operators, as those
+ * might be translated to branches by some compilers on some platforms.
+ */
+static size_t mbedtls_ssl_cf_mask_from_bit( size_t bit )
+{
+    /* MSVC has a warning about unary minus on unsigned integer types,
+     * but this is well-defined and precisely what we want to do here. */
+#if defined(_MSC_VER)
+#pragma warning( push )
+#pragma warning( disable : 4146 )
+#endif
+    return -bit;
+#if defined(_MSC_VER)
+#pragma warning( pop )
+#endif
+}
+
+/*
+ * Constant-flow mask generation for "less than" comparison:
+ * - if x < y,  return all bits 1, that is (size_t) -1
+ * - otherwise, return all bits 0, that is 0
+ *
+ * This function can be used to write constant-time code by replacing branches
+ * with bit operations using masks.
+ *
+ * This function is implemented without using comparison operators, as those
+ * might be translated to branches by some compilers on some platforms.
+ */
+static size_t mbedtls_ssl_cf_mask_lt( size_t x, size_t y )
+{
+    /* This has the most significant bit set if and only if x < y */
+    const size_t sub = x - y;
+
+    /* sub1 = (x < y) ? 1 : 0 */
+    const size_t sub1 = sub >> ( sizeof( sub ) * 8 - 1 );
+
+    /* mask = (x < y) ? 0xff... : 0x00... */
+    const size_t mask = mbedtls_ssl_cf_mask_from_bit( sub1 );
+
+    return( mask );
+}
+
+/*
+ * Constant-flow mask generation for "greater or equal" comparison:
+ * - if x >= y, return all bits 1, that is (size_t) -1
+ * - otherwise, return all bits 0, that is 0
+ *
+ * This function can be used to write constant-time code by replacing branches
+ * with bit operations using masks.
+ *
+ * This function is implemented without using comparison operators, as those
+ * might be translated to branches by some compilers on some platforms.
+ */
+static size_t mbedtls_ssl_cf_mask_ge( size_t x, size_t y )
+{
+    return( ~mbedtls_ssl_cf_mask_lt( x, y ) );
+}
+
+/*
+ * Constant-flow boolean "equal" comparison:
+ * return x == y
+ *
+ * This function can be used to write constant-time code by replacing branches
+ * with bit operations - it can be used in conjunction with
+ * mbedtls_ssl_cf_mask_from_bit().
+ *
+ * This function is implemented without using comparison operators, as those
+ * might be translated to branches by some compilers on some platforms.
+ */
+static size_t mbedtls_ssl_cf_bool_eq( size_t x, size_t y )
+{
+    /* diff = 0 if x == y, non-zero otherwise */
+    const size_t diff = x ^ y;
+
+    /* MSVC has a warning about unary minus on unsigned integer types,
+     * but this is well-defined and precisely what we want to do here. */
+#if defined(_MSC_VER)
+#pragma warning( push )
+#pragma warning( disable : 4146 )
+#endif
+
+    /* diff_msb's most significant bit is equal to x != y */
+    const size_t diff_msb = ( diff | -diff );
+
+#if defined(_MSC_VER)
+#pragma warning( pop )
+#endif
+
+    /* diff1 = (x != y) ? 1 : 0 */
+    const size_t diff1 = diff_msb >> ( sizeof( diff_msb ) * 8 - 1 );
+
+    return( 1 ^ diff1 );
+}
+
+/*
+ * Constant-flow conditional memcpy:
+ *  - if c1 == c2, equivalent to memcpy(dst, src, len),
+ *  - otherwise, a no-op,
+ * but with execution flow independent of the values of c1 and c2.
+ *
+ * This function is implemented without using comparison operators, as those
+ * might be translated to branches by some compilers on some platforms.
+ */
+static void mbedtls_ssl_cf_memcpy_if_eq( unsigned char *dst,
+                                         const unsigned char *src,
+                                         size_t len,
+                                         size_t c1, size_t c2 )
+{
+    /* mask = c1 == c2 ? 0xff : 0x00 */
+    const size_t equal = mbedtls_ssl_cf_bool_eq( c1, c2 );
+    const unsigned char mask = (unsigned char) mbedtls_ssl_cf_mask_from_bit( equal );
+
+    /* dst[i] = c1 == c2 ? src[i] : dst[i] */
+    for( size_t i = 0; i < len; i++ )
+        dst[i] = ( src[i] & mask ) | ( dst[i] & ~mask );
+}
+
+/*
+ * Compute HMAC of variable-length data with constant flow.
+ *
+ * Only works with MD-5, SHA-1, SHA-256 and SHA-384.
+ * (Otherwise, computation of block_size needs to be adapted.)
+ */
+MBEDTLS_STATIC_TESTABLE int mbedtls_ssl_cf_hmac(
+        mbedtls_md_context_t *ctx,
+        const unsigned char *add_data, size_t add_data_len,
+        const unsigned char *data, size_t data_len_secret,
+        size_t min_data_len, size_t max_data_len,
+        unsigned char *output )
+{
+    /*
+     * This function breaks the HMAC abstraction and uses the md_clone()
+     * extension to the MD API in order to get constant-flow behaviour.
+     *
+     * HMAC(msg) is defined as HASH(okey + HASH(ikey + msg)) where + means
+     * concatenation, and okey/ikey are the XOR of the key with some fixed bit
+     * patterns (see RFC 2104, sec. 2), which are stored in ctx->hmac_ctx.
+     *
+     * We'll first compute inner_hash = HASH(ikey + msg) by hashing up to
+     * minlen, then cloning the context, and for each byte up to maxlen
+     * finishing up the hash computation, keeping only the correct result.
+     *
+     * Then we only need to compute HASH(okey + inner_hash) and we're done.
+     */
+    const mbedtls_md_type_t md_alg = mbedtls_md_get_type( ctx->md_info );
+    /* TLS 1.0-1.2 only support SHA-384, SHA-256, SHA-1, MD-5,
+     * all of which have the same block size except SHA-384. */
+    const size_t block_size = md_alg == MBEDTLS_MD_SHA384 ? 128 : 64;
+    const unsigned char * const ikey = ctx->hmac_ctx;
+    const unsigned char * const okey = ikey + block_size;
+    const size_t hash_size = mbedtls_md_get_size( ctx->md_info );
+
+    unsigned char aux_out[MBEDTLS_MD_MAX_SIZE];
+    mbedtls_md_context_t aux;
+    size_t offset;
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    mbedtls_md_init( &aux );
+
+#define MD_CHK( func_call ) \
+    do {                    \
+        ret = (func_call);  \
+        if( ret != 0 )      \
+            goto cleanup;   \
+    } while( 0 )
+
+    MD_CHK( mbedtls_md_setup( &aux, ctx->md_info, 0 ) );
+
+    /* After hmac_start() of hmac_reset(), ikey has already been hashed,
+     * so we can start directly with the message */
+    MD_CHK( mbedtls_md_update( ctx, add_data, add_data_len ) );
+    MD_CHK( mbedtls_md_update( ctx, data, min_data_len ) );
+
+    /* For each possible length, compute the hash up to that point */
+    for( offset = min_data_len; offset <= max_data_len; offset++ )
+    {
+        MD_CHK( mbedtls_md_clone( &aux, ctx ) );
+        MD_CHK( mbedtls_md_finish( &aux, aux_out ) );
+        /* Keep only the correct inner_hash in the output buffer */
+        mbedtls_ssl_cf_memcpy_if_eq( output, aux_out, hash_size,
+                                     offset, data_len_secret );
+
+        if( offset < max_data_len )
+            MD_CHK( mbedtls_md_update( ctx, data + offset, 1 ) );
+    }
+
+    /* The context needs to finish() before it starts() again */
+    MD_CHK( mbedtls_md_finish( ctx, aux_out ) );
+
+    /* Now compute HASH(okey + inner_hash) */
+    MD_CHK( mbedtls_md_starts( ctx ) );
+    MD_CHK( mbedtls_md_update( ctx, okey, block_size ) );
+    MD_CHK( mbedtls_md_update( ctx, output, hash_size ) );
+    MD_CHK( mbedtls_md_finish( ctx, output ) );
+
+    /* Done, get ready for next time */
+    MD_CHK( mbedtls_md_hmac_reset( ctx ) );
+
+#undef MD_CHK
+
+cleanup:
+    mbedtls_md_free( &aux );
+    return( ret );
+}
+
+/*
+ * Constant-flow memcpy from variable position in buffer.
+ * - functionally equivalent to memcpy(dst, src + offset_secret, len)
+ * - but with execution flow independent from the value of offset_secret.
+ */
+MBEDTLS_STATIC_TESTABLE void mbedtls_ssl_cf_memcpy_offset(
+                                   unsigned char *dst,
+                                   const unsigned char *src_base,
+                                   size_t offset_secret,
+                                   size_t offset_min, size_t offset_max,
+                                   size_t len )
+{
+    size_t offset;
+
+    for( offset = offset_min; offset <= offset_max; offset++ )
+    {
+        mbedtls_ssl_cf_memcpy_if_eq( dst, src_base + offset, len,
+                                     offset, offset_secret );
+    }
+}
+#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
+
+int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
+                             mbedtls_ssl_transform *transform,
+                             mbedtls_record *rec )
+{
+    size_t olen;
+    mbedtls_cipher_mode_t mode;
+    int ret, auth_done = 0;
+#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
+    size_t padlen = 0, correct = 1;
+#endif
+    unsigned char* data;
+    unsigned char add_data[13 + 1 + MBEDTLS_SSL_CID_IN_LEN_MAX ];
+    size_t add_data_len;
+
+#if !defined(MBEDTLS_DEBUG_C)
+    ssl = NULL; /* make sure we don't use it except for debug */
+    ((void) ssl);
+#endif
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> decrypt buf" ) );
+    if( rec == NULL                     ||
+        rec->buf == NULL                ||
+        rec->buf_len < rec->data_offset ||
+        rec->buf_len - rec->data_offset < rec->data_len )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad record structure provided to decrypt_buf" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    data = rec->buf + rec->data_offset;
+    mode = mbedtls_cipher_get_cipher_mode( &transform->cipher_ctx_dec );
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    /*
+     * Match record's CID with incoming CID.
+     */
+    if( rec->cid_len != transform->in_cid_len ||
+        memcmp( rec->cid, transform->in_cid, rec->cid_len ) != 0 )
+    {
+        return( MBEDTLS_ERR_SSL_UNEXPECTED_CID );
+    }
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+#if defined(MBEDTLS_ARC4_C) || defined(MBEDTLS_CIPHER_NULL_CIPHER)
+    if( mode == MBEDTLS_MODE_STREAM )
+    {
+        padlen = 0;
+        if( ( ret = mbedtls_cipher_crypt( &transform->cipher_ctx_dec,
+                                   transform->iv_dec,
+                                   transform->ivlen,
+                                   data, rec->data_len,
+                                   data, &olen ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_crypt", ret );
+            return( ret );
+        }
+
+        if( rec->data_len != olen )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+    }
+    else
+#endif /* MBEDTLS_ARC4_C || MBEDTLS_CIPHER_NULL_CIPHER */
+#if defined(MBEDTLS_GCM_C) || \
+    defined(MBEDTLS_CCM_C) || \
+    defined(MBEDTLS_CHACHAPOLY_C)
+    if( mode == MBEDTLS_MODE_GCM ||
+        mode == MBEDTLS_MODE_CCM ||
+        mode == MBEDTLS_MODE_CHACHAPOLY )
+    {
+        unsigned char iv[12];
+        unsigned char *dynamic_iv;
+        size_t dynamic_iv_len;
+
+        /*
+         * Extract dynamic part of nonce for AEAD decryption.
+         *
+         * Note: In the case of CCM and GCM in TLS 1.2, the dynamic
+         *       part of the IV is prepended to the ciphertext and
+         *       can be chosen freely - in particular, it need not
+         *       agree with the record sequence number.
+         */
+        dynamic_iv_len = sizeof( rec->ctr );
+        if( ssl_transform_aead_dynamic_iv_is_explicit( transform ) == 1 )
+        {
+            if( rec->data_len < dynamic_iv_len )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "msglen (%" MBEDTLS_PRINTF_SIZET
+                                            " ) < explicit_iv_len (%" MBEDTLS_PRINTF_SIZET ") ",
+                                            rec->data_len,
+                                            dynamic_iv_len ) );
+                return( MBEDTLS_ERR_SSL_INVALID_MAC );
+            }
+            dynamic_iv = data;
+
+            data += dynamic_iv_len;
+            rec->data_offset += dynamic_iv_len;
+            rec->data_len    -= dynamic_iv_len;
+        }
+        else
+        {
+            dynamic_iv = rec->ctr;
+        }
+
+        /* Check that there's space for the authentication tag. */
+        if( rec->data_len < transform->taglen )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "msglen (%" MBEDTLS_PRINTF_SIZET
+                                        ") < taglen (%" MBEDTLS_PRINTF_SIZET ") ",
+                                        rec->data_len,
+                                        transform->taglen ) );
+            return( MBEDTLS_ERR_SSL_INVALID_MAC );
+        }
+        rec->data_len -= transform->taglen;
+
+        /*
+         * Prepare nonce from dynamic and static parts.
+         */
+        ssl_build_record_nonce( iv, sizeof( iv ),
+                                transform->iv_dec,
+                                transform->fixed_ivlen,
+                                dynamic_iv,
+                                dynamic_iv_len );
+
+        /*
+         * Build additional data for AEAD encryption.
+         * This depends on the TLS version.
+         */
+        ssl_extract_add_data_from_record( add_data, &add_data_len, rec,
+                                          transform->minor_ver );
+        MBEDTLS_SSL_DEBUG_BUF( 4, "additional data used for AEAD",
+                               add_data, add_data_len );
+
+        /* Because of the check above, we know that there are
+         * explicit_iv_len Bytes preceeding data, and taglen
+         * bytes following data + data_len. This justifies
+         * the debug message and the invocation of
+         * mbedtls_cipher_auth_decrypt() below. */
+
+        MBEDTLS_SSL_DEBUG_BUF( 4, "IV used", iv, transform->ivlen );
+        MBEDTLS_SSL_DEBUG_BUF( 4, "TAG used", data + rec->data_len,
+                               transform->taglen );
+
+        /*
+         * Decrypt and authenticate
+         */
+        if( ( ret = mbedtls_cipher_auth_decrypt_ext( &transform->cipher_ctx_dec,
+                  iv, transform->ivlen,
+                  add_data, add_data_len,
+                  data, rec->data_len + transform->taglen,          /* src */
+                  data, rec->buf_len - (data - rec->buf), &olen,    /* dst */
+                  transform->taglen ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_auth_decrypt", ret );
+
+            if( ret == MBEDTLS_ERR_CIPHER_AUTH_FAILED )
+                return( MBEDTLS_ERR_SSL_INVALID_MAC );
+
+            return( ret );
+        }
+        auth_done++;
+
+        /* Double-check that AEAD decryption doesn't change content length. */
+        if( olen != rec->data_len )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+    }
+    else
+#endif /* MBEDTLS_GCM_C || MBEDTLS_CCM_C */
+#if defined(MBEDTLS_SSL_SOME_SUITES_USE_CBC)
+    if( mode == MBEDTLS_MODE_CBC )
+    {
+        size_t minlen = 0;
+
+        /*
+         * Check immediate ciphertext sanity
+         */
+#if defined(MBEDTLS_SSL_PROTO_TLS1_1) || defined(MBEDTLS_SSL_PROTO_TLS1_2)
+        if( transform->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 )
+        {
+            /* The ciphertext is prefixed with the CBC IV. */
+            minlen += transform->ivlen;
+        }
+#endif
+
+        /* Size considerations:
+         *
+         * - The CBC cipher text must not be empty and hence
+         *   at least of size transform->ivlen.
+         *
+         * Together with the potential IV-prefix, this explains
+         * the first of the two checks below.
+         *
+         * - The record must contain a MAC, either in plain or
+         *   encrypted, depending on whether Encrypt-then-MAC
+         *   is used or not.
+         *   - If it is, the message contains the IV-prefix,
+         *     the CBC ciphertext, and the MAC.
+         *   - If it is not, the padded plaintext, and hence
+         *     the CBC ciphertext, has at least length maclen + 1
+         *     because there is at least the padding length byte.
+         *
+         * As the CBC ciphertext is not empty, both cases give the
+         * lower bound minlen + maclen + 1 on the record size, which
+         * we test for in the second check below.
+         */
+        if( rec->data_len < minlen + transform->ivlen ||
+            rec->data_len < minlen + transform->maclen + 1 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "msglen (%" MBEDTLS_PRINTF_SIZET
+                                        ") < max( ivlen(%" MBEDTLS_PRINTF_SIZET
+                                        "), maclen (%" MBEDTLS_PRINTF_SIZET ") "
+                                "+ 1 ) ( + expl IV )", rec->data_len,
+                                transform->ivlen,
+                                transform->maclen ) );
+            return( MBEDTLS_ERR_SSL_INVALID_MAC );
+        }
+
+        /*
+         * Authenticate before decrypt if enabled
+         */
+#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
+        if( transform->encrypt_then_mac == MBEDTLS_SSL_ETM_ENABLED )
+        {
+            unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD];
+
+            MBEDTLS_SSL_DEBUG_MSG( 3, ( "using encrypt then mac" ) );
+
+            /* Update data_len in tandem with add_data.
+             *
+             * The subtraction is safe because of the previous check
+             * data_len >= minlen + maclen + 1.
+             *
+             * Afterwards, we know that data + data_len is followed by at
+             * least maclen Bytes, which justifies the call to
+             * mbedtls_ssl_safer_memcmp() below.
+             *
+             * Further, we still know that data_len > minlen */
+            rec->data_len -= transform->maclen;
+            ssl_extract_add_data_from_record( add_data, &add_data_len, rec,
+                                              transform->minor_ver );
+
+            /* Calculate expected MAC. */
+            MBEDTLS_SSL_DEBUG_BUF( 4, "MAC'd meta-data", add_data,
+                                   add_data_len );
+            mbedtls_md_hmac_update( &transform->md_ctx_dec, add_data,
+                                    add_data_len );
+            mbedtls_md_hmac_update( &transform->md_ctx_dec,
+                                    data, rec->data_len );
+            mbedtls_md_hmac_finish( &transform->md_ctx_dec, mac_expect );
+            mbedtls_md_hmac_reset( &transform->md_ctx_dec );
+
+            MBEDTLS_SSL_DEBUG_BUF( 4, "message  mac", data + rec->data_len,
+                                   transform->maclen );
+            MBEDTLS_SSL_DEBUG_BUF( 4, "expected mac", mac_expect,
+                                   transform->maclen );
+
+            /* Compare expected MAC with MAC at the end of the record. */
+            if( mbedtls_ssl_safer_memcmp( data + rec->data_len, mac_expect,
+                                          transform->maclen ) != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "message mac does not match" ) );
+                return( MBEDTLS_ERR_SSL_INVALID_MAC );
+            }
+            auth_done++;
+        }
+#endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
+
+        /*
+         * Check length sanity
+         */
+
+        /* We know from above that data_len > minlen >= 0,
+         * so the following check in particular implies that
+         * data_len >= minlen + ivlen ( = minlen or 2 * minlen ). */
+        if( rec->data_len % transform->ivlen != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "msglen (%" MBEDTLS_PRINTF_SIZET
+                                        ") %% ivlen (%" MBEDTLS_PRINTF_SIZET ") != 0",
+                                        rec->data_len, transform->ivlen ) );
+            return( MBEDTLS_ERR_SSL_INVALID_MAC );
+        }
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_1) || defined(MBEDTLS_SSL_PROTO_TLS1_2)
+        /*
+         * Initialize for prepended IV for block cipher in TLS v1.1 and up
+         */
+        if( transform->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 )
+        {
+            /* Safe because data_len >= minlen + ivlen = 2 * ivlen. */
+            memcpy( transform->iv_dec, data, transform->ivlen );
+
+            data += transform->ivlen;
+            rec->data_offset += transform->ivlen;
+            rec->data_len -= transform->ivlen;
+        }
+#endif /* MBEDTLS_SSL_PROTO_TLS1_1 || MBEDTLS_SSL_PROTO_TLS1_2 */
+
+        /* We still have data_len % ivlen == 0 and data_len >= ivlen here. */
+
+        if( ( ret = mbedtls_cipher_crypt( &transform->cipher_ctx_dec,
+                                   transform->iv_dec, transform->ivlen,
+                                   data, rec->data_len, data, &olen ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_cipher_crypt", ret );
+            return( ret );
+        }
+
+        /* Double-check that length hasn't changed during decryption. */
+        if( rec->data_len != olen )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1)
+        if( transform->minor_ver < MBEDTLS_SSL_MINOR_VERSION_2 )
+        {
+            /*
+             * Save IV in SSL3 and TLS1, where CBC decryption of consecutive
+             * records is equivalent to CBC decryption of the concatenation
+             * of the records; in other words, IVs are maintained across
+             * record decryptions.
+             */
+            memcpy( transform->iv_dec, transform->cipher_ctx_dec.iv,
+                    transform->ivlen );
+        }
+#endif
+
+        /* Safe since data_len >= minlen + maclen + 1, so after having
+         * subtracted at most minlen and maclen up to this point,
+         * data_len > 0 (because of data_len % ivlen == 0, it's actually
+         * >= ivlen ). */
+        padlen = data[rec->data_len - 1];
+
+        if( auth_done == 1 )
+        {
+            const size_t mask = mbedtls_ssl_cf_mask_ge(
+                                rec->data_len,
+                                padlen + 1 );
+            correct &= mask;
+            padlen  &= mask;
+        }
+        else
+        {
+#if defined(MBEDTLS_SSL_DEBUG_ALL)
+            if( rec->data_len < transform->maclen + padlen + 1 )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "msglen (%" MBEDTLS_PRINTF_SIZET
+                                            ") < maclen (%" MBEDTLS_PRINTF_SIZET
+                                            ") + padlen (%" MBEDTLS_PRINTF_SIZET ")",
+                                            rec->data_len,
+                                            transform->maclen,
+                                            padlen + 1 ) );
+            }
+#endif
+
+            const size_t mask = mbedtls_ssl_cf_mask_ge(
+                                rec->data_len,
+                                transform->maclen + padlen + 1 );
+            correct &= mask;
+            padlen  &= mask;
+        }
+
+        padlen++;
+
+        /* Regardless of the validity of the padding,
+         * we have data_len >= padlen here. */
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+        if( transform->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
+        {
+            /* This is the SSL 3.0 path, we don't have to worry about Lucky
+             * 13, because there's a strictly worse padding attack built in
+             * the protocol (known as part of POODLE), so we don't care if the
+             * code is not constant-time, in particular branches are OK. */
+            if( padlen > transform->ivlen )
+            {
+#if defined(MBEDTLS_SSL_DEBUG_ALL)
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad padding length: is %" MBEDTLS_PRINTF_SIZET ", "
+                                            "should be no more than %" MBEDTLS_PRINTF_SIZET,
+                                            padlen, transform->ivlen ) );
+#endif
+                correct = 0;
+            }
+        }
+        else
+#endif /* MBEDTLS_SSL_PROTO_SSL3 */
+#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
+    defined(MBEDTLS_SSL_PROTO_TLS1_2)
+        if( transform->minor_ver > MBEDTLS_SSL_MINOR_VERSION_0 )
+        {
+            /* The padding check involves a series of up to 256
+             * consecutive memory reads at the end of the record
+             * plaintext buffer. In order to hide the length and
+             * validity of the padding, always perform exactly
+             * `min(256,plaintext_len)` reads (but take into account
+             * only the last `padlen` bytes for the padding check). */
+            size_t pad_count = 0;
+            volatile unsigned char* const check = data;
+
+            /* Index of first padding byte; it has been ensured above
+             * that the subtraction is safe. */
+            size_t const padding_idx = rec->data_len - padlen;
+            size_t const num_checks = rec->data_len <= 256 ? rec->data_len : 256;
+            size_t const start_idx = rec->data_len - num_checks;
+            size_t idx;
+
+            for( idx = start_idx; idx < rec->data_len; idx++ )
+            {
+                /* pad_count += (idx >= padding_idx) &&
+                 *              (check[idx] == padlen - 1);
+                 */
+                const size_t mask = mbedtls_ssl_cf_mask_ge( idx, padding_idx );
+                const size_t equal = mbedtls_ssl_cf_bool_eq( check[idx],
+                                                             padlen - 1 );
+                pad_count += mask & equal;
+            }
+            correct &= mbedtls_ssl_cf_bool_eq( pad_count, padlen );
+
+#if defined(MBEDTLS_SSL_DEBUG_ALL)
+            if( padlen > 0 && correct == 0 )
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad padding byte detected" ) );
+#endif
+            padlen &= mbedtls_ssl_cf_mask_from_bit( correct );
+        }
+        else
+#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
+          MBEDTLS_SSL_PROTO_TLS1_2 */
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+
+        /* If the padding was found to be invalid, padlen == 0
+         * and the subtraction is safe. If the padding was found valid,
+         * padlen hasn't been changed and the previous assertion
+         * data_len >= padlen still holds. */
+        rec->data_len -= padlen;
+    }
+    else
+#endif /* MBEDTLS_SSL_SOME_SUITES_USE_CBC */
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+#if defined(MBEDTLS_SSL_DEBUG_ALL)
+    MBEDTLS_SSL_DEBUG_BUF( 4, "raw buffer after decryption",
+                           data, rec->data_len );
+#endif
+
+    /*
+     * Authenticate if not done yet.
+     * Compute the MAC regardless of the padding result (RFC4346, CBCTIME).
+     */
+#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
+    if( auth_done == 0 )
+    {
+        unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD];
+        unsigned char mac_peer[MBEDTLS_SSL_MAC_ADD];
+
+        /* If the initial value of padlen was such that
+         * data_len < maclen + padlen + 1, then padlen
+         * got reset to 1, and the initial check
+         * data_len >= minlen + maclen + 1
+         * guarantees that at this point we still
+         * have at least data_len >= maclen.
+         *
+         * If the initial value of padlen was such that
+         * data_len >= maclen + padlen + 1, then we have
+         * subtracted either padlen + 1 (if the padding was correct)
+         * or 0 (if the padding was incorrect) since then,
+         * hence data_len >= maclen in any case.
+         */
+        rec->data_len -= transform->maclen;
+        ssl_extract_add_data_from_record( add_data, &add_data_len, rec,
+                                          transform->minor_ver );
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+        if( transform->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
+        {
+            ssl_mac( &transform->md_ctx_dec,
+                     transform->mac_dec,
+                     data, rec->data_len,
+                     rec->ctr, rec->type,
+                     mac_expect );
+            memcpy( mac_peer, data + rec->data_len, transform->maclen );
+        }
+        else
+#endif /* MBEDTLS_SSL_PROTO_SSL3 */
+#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
+        defined(MBEDTLS_SSL_PROTO_TLS1_2)
+        if( transform->minor_ver > MBEDTLS_SSL_MINOR_VERSION_0 )
+        {
+            /*
+             * The next two sizes are the minimum and maximum values of
+             * data_len over all padlen values.
+             *
+             * They're independent of padlen, since we previously did
+             * data_len -= padlen.
+             *
+             * Note that max_len + maclen is never more than the buffer
+             * length, as we previously did in_msglen -= maclen too.
+             */
+            const size_t max_len = rec->data_len + padlen;
+            const size_t min_len = ( max_len > 256 ) ? max_len - 256 : 0;
+
+            ret = mbedtls_ssl_cf_hmac( &transform->md_ctx_dec,
+                                       add_data, add_data_len,
+                                       data, rec->data_len, min_len, max_len,
+                                       mac_expect );
+            if( ret != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_cf_hmac", ret );
+                return( ret );
+            }
+
+            mbedtls_ssl_cf_memcpy_offset( mac_peer, data,
+                                          rec->data_len,
+                                          min_len, max_len,
+                                          transform->maclen );
+        }
+        else
+#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
+              MBEDTLS_SSL_PROTO_TLS1_2 */
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+
+#if defined(MBEDTLS_SSL_DEBUG_ALL)
+        MBEDTLS_SSL_DEBUG_BUF( 4, "expected mac", mac_expect, transform->maclen );
+        MBEDTLS_SSL_DEBUG_BUF( 4, "message  mac", mac_peer, transform->maclen );
+#endif
+
+        if( mbedtls_ssl_safer_memcmp( mac_peer, mac_expect,
+                                      transform->maclen ) != 0 )
+        {
+#if defined(MBEDTLS_SSL_DEBUG_ALL)
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "message mac does not match" ) );
+#endif
+            correct = 0;
+        }
+        auth_done++;
+    }
+
+    /*
+     * Finally check the correct flag
+     */
+    if( correct == 0 )
+        return( MBEDTLS_ERR_SSL_INVALID_MAC );
+#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
+
+    /* Make extra sure authentication was performed, exactly once */
+    if( auth_done != 1 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
+    if( transform->minor_ver == MBEDTLS_SSL_MINOR_VERSION_4 )
+    {
+        /* Remove inner padding and infer true content type. */
+        ret = ssl_parse_inner_plaintext( data, &rec->data_len,
+                                         &rec->type );
+
+        if( ret != 0 )
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+    }
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    if( rec->cid_len != 0 )
+    {
+        ret = ssl_parse_inner_plaintext( data, &rec->data_len,
+                                         &rec->type );
+        if( ret != 0 )
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+    }
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= decrypt buf" ) );
+
+    return( 0 );
+}
+
+#undef MAC_NONE
+#undef MAC_PLAINTEXT
+#undef MAC_CIPHERTEXT
+
+#if defined(MBEDTLS_ZLIB_SUPPORT)
+/*
+ * Compression/decompression functions
+ */
+static int ssl_compress_buf( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    unsigned char *msg_post = ssl->out_msg;
+    ptrdiff_t bytes_written = ssl->out_msg - ssl->out_buf;
+    size_t len_pre = ssl->out_msglen;
+    unsigned char *msg_pre = ssl->compress_buf;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t out_buf_len = ssl->out_buf_len;
+#else
+    size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
+#endif
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> compress buf" ) );
+
+    if( len_pre == 0 )
+        return( 0 );
+
+    memcpy( msg_pre, ssl->out_msg, len_pre );
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "before compression: msglen = %" MBEDTLS_PRINTF_SIZET ", ",
+                   ssl->out_msglen ) );
+
+    MBEDTLS_SSL_DEBUG_BUF( 4, "before compression: output payload",
+                   ssl->out_msg, ssl->out_msglen );
+
+    ssl->transform_out->ctx_deflate.next_in = msg_pre;
+    ssl->transform_out->ctx_deflate.avail_in = len_pre;
+    ssl->transform_out->ctx_deflate.next_out = msg_post;
+    ssl->transform_out->ctx_deflate.avail_out = out_buf_len - bytes_written;
+
+    ret = deflate( &ssl->transform_out->ctx_deflate, Z_SYNC_FLUSH );
+    if( ret != Z_OK )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "failed to perform compression (%d)", ret ) );
+        return( MBEDTLS_ERR_SSL_COMPRESSION_FAILED );
+    }
+
+    ssl->out_msglen = out_buf_len -
+                      ssl->transform_out->ctx_deflate.avail_out - bytes_written;
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "after compression: msglen = %" MBEDTLS_PRINTF_SIZET ", ",
+                   ssl->out_msglen ) );
+
+    MBEDTLS_SSL_DEBUG_BUF( 4, "after compression: output payload",
+                   ssl->out_msg, ssl->out_msglen );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= compress buf" ) );
+
+    return( 0 );
+}
+
+static int ssl_decompress_buf( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    unsigned char *msg_post = ssl->in_msg;
+    ptrdiff_t header_bytes = ssl->in_msg - ssl->in_buf;
+    size_t len_pre = ssl->in_msglen;
+    unsigned char *msg_pre = ssl->compress_buf;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len = ssl->in_buf_len;
+#else
+    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+#endif
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> decompress buf" ) );
+
+    if( len_pre == 0 )
+        return( 0 );
+
+    memcpy( msg_pre, ssl->in_msg, len_pre );
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "before decompression: msglen = %" MBEDTLS_PRINTF_SIZET ", ",
+                   ssl->in_msglen ) );
+
+    MBEDTLS_SSL_DEBUG_BUF( 4, "before decompression: input payload",
+                   ssl->in_msg, ssl->in_msglen );
+
+    ssl->transform_in->ctx_inflate.next_in = msg_pre;
+    ssl->transform_in->ctx_inflate.avail_in = len_pre;
+    ssl->transform_in->ctx_inflate.next_out = msg_post;
+    ssl->transform_in->ctx_inflate.avail_out = in_buf_len - header_bytes;
+
+    ret = inflate( &ssl->transform_in->ctx_inflate, Z_SYNC_FLUSH );
+    if( ret != Z_OK )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "failed to perform decompression (%d)", ret ) );
+        return( MBEDTLS_ERR_SSL_COMPRESSION_FAILED );
+    }
+
+    ssl->in_msglen = in_buf_len -
+                     ssl->transform_in->ctx_inflate.avail_out - header_bytes;
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "after decompression: msglen = %" MBEDTLS_PRINTF_SIZET ", ",
+                   ssl->in_msglen ) );
+
+    MBEDTLS_SSL_DEBUG_BUF( 4, "after decompression: input payload",
+                   ssl->in_msg, ssl->in_msglen );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= decompress buf" ) );
+
+    return( 0 );
+}
+#endif /* MBEDTLS_ZLIB_SUPPORT */
+
+/*
+ * Fill the input message buffer by appending data to it.
+ * The amount of data already fetched is in ssl->in_left.
+ *
+ * If we return 0, is it guaranteed that (at least) nb_want bytes are
+ * available (from this read and/or a previous one). Otherwise, an error code
+ * is returned (possibly EOF or WANT_READ).
+ *
+ * With stream transport (TLS) on success ssl->in_left == nb_want, but
+ * with datagram transport (DTLS) on success ssl->in_left >= nb_want,
+ * since we always read a whole datagram at once.
+ *
+ * For DTLS, it is up to the caller to set ssl->next_record_offset when
+ * they're done reading a record.
+ */
+int mbedtls_ssl_fetch_input( mbedtls_ssl_context *ssl, size_t nb_want )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t len;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len = ssl->in_buf_len;
+#else
+    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+#endif
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> fetch input" ) );
+
+    if( ssl->f_recv == NULL && ssl->f_recv_timeout == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Bad usage of mbedtls_ssl_set_bio() "
+                            "or mbedtls_ssl_set_bio()" ) );
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+    }
+
+    if( nb_want > in_buf_len - (size_t)( ssl->in_hdr - ssl->in_buf ) )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "requesting more data than fits" ) );
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+    }
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        uint32_t timeout;
+
+        /*
+         * The point is, we need to always read a full datagram at once, so we
+         * sometimes read more then requested, and handle the additional data.
+         * It could be the rest of the current record (while fetching the
+         * header) and/or some other records in the same datagram.
+         */
+
+        /*
+         * Move to the next record in the already read datagram if applicable
+         */
+        if( ssl->next_record_offset != 0 )
+        {
+            if( ssl->in_left < ssl->next_record_offset )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+                return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+            }
+
+            ssl->in_left -= ssl->next_record_offset;
+
+            if( ssl->in_left != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "next record in same datagram, offset: %"
+                                            MBEDTLS_PRINTF_SIZET,
+                                    ssl->next_record_offset ) );
+                memmove( ssl->in_hdr,
+                         ssl->in_hdr + ssl->next_record_offset,
+                         ssl->in_left );
+            }
+
+            ssl->next_record_offset = 0;
+        }
+
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "in_left: %" MBEDTLS_PRINTF_SIZET
+                                    ", nb_want: %" MBEDTLS_PRINTF_SIZET,
+                       ssl->in_left, nb_want ) );
+
+        /*
+         * Done if we already have enough data.
+         */
+        if( nb_want <= ssl->in_left)
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= fetch input" ) );
+            return( 0 );
+        }
+
+        /*
+         * A record can't be split across datagrams. If we need to read but
+         * are not at the beginning of a new record, the caller did something
+         * wrong.
+         */
+        if( ssl->in_left != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+
+        /*
+         * Don't even try to read if time's out already.
+         * This avoids by-passing the timer when repeatedly receiving messages
+         * that will end up being dropped.
+         */
+        if( mbedtls_ssl_check_timer( ssl ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "timer has expired" ) );
+            ret = MBEDTLS_ERR_SSL_TIMEOUT;
+        }
+        else
+        {
+            len = in_buf_len - ( ssl->in_hdr - ssl->in_buf );
+
+            if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
+                timeout = ssl->handshake->retransmit_timeout;
+            else
+                timeout = ssl->conf->read_timeout;
+
+            MBEDTLS_SSL_DEBUG_MSG( 3, ( "f_recv_timeout: %lu ms", (unsigned long) timeout ) );
+
+            if( ssl->f_recv_timeout != NULL )
+                ret = ssl->f_recv_timeout( ssl->p_bio, ssl->in_hdr, len,
+                                                                    timeout );
+            else
+                ret = ssl->f_recv( ssl->p_bio, ssl->in_hdr, len );
+
+            MBEDTLS_SSL_DEBUG_RET( 2, "ssl->f_recv(_timeout)", ret );
+
+            if( ret == 0 )
+                return( MBEDTLS_ERR_SSL_CONN_EOF );
+        }
+
+        if( ret == MBEDTLS_ERR_SSL_TIMEOUT )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "timeout" ) );
+            mbedtls_ssl_set_timer( ssl, 0 );
+
+            if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
+            {
+                if( ssl_double_retransmit_timeout( ssl ) != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "handshake timeout" ) );
+                    return( MBEDTLS_ERR_SSL_TIMEOUT );
+                }
+
+                if( ( ret = mbedtls_ssl_resend( ssl ) ) != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_resend", ret );
+                    return( ret );
+                }
+
+                return( MBEDTLS_ERR_SSL_WANT_READ );
+            }
+#if defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_SSL_RENEGOTIATION)
+            else if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER &&
+                     ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_PENDING )
+            {
+                if( ( ret = mbedtls_ssl_resend_hello_request( ssl ) ) != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_resend_hello_request",
+                                           ret );
+                    return( ret );
+                }
+
+                return( MBEDTLS_ERR_SSL_WANT_READ );
+            }
+#endif /* MBEDTLS_SSL_SRV_C && MBEDTLS_SSL_RENEGOTIATION */
+        }
+
+        if( ret < 0 )
+            return( ret );
+
+        ssl->in_left = ret;
+    }
+    else
+#endif
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "in_left: %" MBEDTLS_PRINTF_SIZET
+                                    ", nb_want: %" MBEDTLS_PRINTF_SIZET,
+                       ssl->in_left, nb_want ) );
+
+        while( ssl->in_left < nb_want )
+        {
+            len = nb_want - ssl->in_left;
+
+            if( mbedtls_ssl_check_timer( ssl ) != 0 )
+                ret = MBEDTLS_ERR_SSL_TIMEOUT;
+            else
+            {
+                if( ssl->f_recv_timeout != NULL )
+                {
+                    ret = ssl->f_recv_timeout( ssl->p_bio,
+                                               ssl->in_hdr + ssl->in_left, len,
+                                               ssl->conf->read_timeout );
+                }
+                else
+                {
+                    ret = ssl->f_recv( ssl->p_bio,
+                                       ssl->in_hdr + ssl->in_left, len );
+                }
+            }
+
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "in_left: %" MBEDTLS_PRINTF_SIZET
+                                        ", nb_want: %" MBEDTLS_PRINTF_SIZET,
+                                        ssl->in_left, nb_want ) );
+            MBEDTLS_SSL_DEBUG_RET( 2, "ssl->f_recv(_timeout)", ret );
+
+            if( ret == 0 )
+                return( MBEDTLS_ERR_SSL_CONN_EOF );
+
+            if( ret < 0 )
+                return( ret );
+
+            if ( (size_t)ret > len || ( INT_MAX > SIZE_MAX && ret > (int)SIZE_MAX ) )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1,
+                    ( "f_recv returned %d bytes but only %" MBEDTLS_PRINTF_SIZET " were requested",
+                    ret, len ) );
+                return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+            }
+
+            ssl->in_left += ret;
+        }
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= fetch input" ) );
+
+    return( 0 );
+}
+
+/*
+ * Flush any data not yet written
+ */
+int mbedtls_ssl_flush_output( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    unsigned char *buf;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> flush output" ) );
+
+    if( ssl->f_send == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Bad usage of mbedtls_ssl_set_bio() "
+                            "or mbedtls_ssl_set_bio()" ) );
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+    }
+
+    /* Avoid incrementing counter if data is flushed */
+    if( ssl->out_left == 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= flush output" ) );
+        return( 0 );
+    }
+
+    while( ssl->out_left > 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "message length: %" MBEDTLS_PRINTF_SIZET
+                                    ", out_left: %" MBEDTLS_PRINTF_SIZET,
+                       mbedtls_ssl_out_hdr_len( ssl ) + ssl->out_msglen, ssl->out_left ) );
+
+        buf = ssl->out_hdr - ssl->out_left;
+        ret = ssl->f_send( ssl->p_bio, buf, ssl->out_left );
+
+        MBEDTLS_SSL_DEBUG_RET( 2, "ssl->f_send", ret );
+
+        if( ret <= 0 )
+            return( ret );
+
+        if( (size_t)ret > ssl->out_left || ( INT_MAX > SIZE_MAX && ret > (int)SIZE_MAX ) )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1,
+                ( "f_send returned %d bytes but only %" MBEDTLS_PRINTF_SIZET " bytes were sent",
+                ret, ssl->out_left ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+
+        ssl->out_left -= ret;
+    }
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        ssl->out_hdr = ssl->out_buf;
+    }
+    else
+#endif
+    {
+        ssl->out_hdr = ssl->out_buf + 8;
+    }
+    mbedtls_ssl_update_out_pointers( ssl, ssl->transform_out );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= flush output" ) );
+
+    return( 0 );
+}
+
+/*
+ * Functions to handle the DTLS retransmission state machine
+ */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+/*
+ * Append current handshake message to current outgoing flight
+ */
+static int ssl_flight_append( mbedtls_ssl_context *ssl )
+{
+    mbedtls_ssl_flight_item *msg;
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> ssl_flight_append" ) );
+    MBEDTLS_SSL_DEBUG_BUF( 4, "message appended to flight",
+                           ssl->out_msg, ssl->out_msglen );
+
+    /* Allocate space for current message */
+    if( ( msg = mbedtls_calloc( 1, sizeof(  mbedtls_ssl_flight_item ) ) ) == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc %" MBEDTLS_PRINTF_SIZET " bytes failed",
+                            sizeof( mbedtls_ssl_flight_item ) ) );
+        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
+    }
+
+    if( ( msg->p = mbedtls_calloc( 1, ssl->out_msglen ) ) == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "alloc %" MBEDTLS_PRINTF_SIZET " bytes failed",
+                                    ssl->out_msglen ) );
+        mbedtls_free( msg );
+        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
+    }
+
+    /* Copy current handshake message with headers */
+    memcpy( msg->p, ssl->out_msg, ssl->out_msglen );
+    msg->len = ssl->out_msglen;
+    msg->type = ssl->out_msgtype;
+    msg->next = NULL;
+
+    /* Append to the current flight */
+    if( ssl->handshake->flight == NULL )
+        ssl->handshake->flight = msg;
+    else
+    {
+        mbedtls_ssl_flight_item *cur = ssl->handshake->flight;
+        while( cur->next != NULL )
+            cur = cur->next;
+        cur->next = msg;
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= ssl_flight_append" ) );
+    return( 0 );
+}
+
+/*
+ * Free the current flight of handshake messages
+ */
+void mbedtls_ssl_flight_free( mbedtls_ssl_flight_item *flight )
+{
+    mbedtls_ssl_flight_item *cur = flight;
+    mbedtls_ssl_flight_item *next;
+
+    while( cur != NULL )
+    {
+        next = cur->next;
+
+        mbedtls_free( cur->p );
+        mbedtls_free( cur );
+
+        cur = next;
+    }
+}
+
+/*
+ * Swap transform_out and out_ctr with the alternative ones
+ */
+static int ssl_swap_epochs( mbedtls_ssl_context *ssl )
+{
+    mbedtls_ssl_transform *tmp_transform;
+    unsigned char tmp_out_ctr[8];
+
+    if( ssl->transform_out == ssl->handshake->alt_transform_out )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "skip swap epochs" ) );
+        return( 0 );
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "swap epochs" ) );
+
+    /* Swap transforms */
+    tmp_transform                     = ssl->transform_out;
+    ssl->transform_out                = ssl->handshake->alt_transform_out;
+    ssl->handshake->alt_transform_out = tmp_transform;
+
+    /* Swap epoch + sequence_number */
+    memcpy( tmp_out_ctr,                 ssl->cur_out_ctr,            8 );
+    memcpy( ssl->cur_out_ctr,            ssl->handshake->alt_out_ctr, 8 );
+    memcpy( ssl->handshake->alt_out_ctr, tmp_out_ctr,                 8 );
+
+    /* Adjust to the newly activated transform */
+    mbedtls_ssl_update_out_pointers( ssl, ssl->transform_out );
+
+#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
+    if( mbedtls_ssl_hw_record_activate != NULL )
+    {
+        int ret = mbedtls_ssl_hw_record_activate( ssl, MBEDTLS_SSL_CHANNEL_OUTBOUND );
+        if( ret != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_hw_record_activate", ret );
+            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+        }
+    }
+#endif
+
+    return( 0 );
+}
+
+/*
+ * Retransmit the current flight of messages.
+ */
+int mbedtls_ssl_resend( mbedtls_ssl_context *ssl )
+{
+    int ret = 0;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> mbedtls_ssl_resend" ) );
+
+    ret = mbedtls_ssl_flight_transmit( ssl );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= mbedtls_ssl_resend" ) );
+
+    return( ret );
+}
+
+/*
+ * Transmit or retransmit the current flight of messages.
+ *
+ * Need to remember the current message in case flush_output returns
+ * WANT_WRITE, causing us to exit this function and come back later.
+ * This function must be called until state is no longer SENDING.
+ */
+int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> mbedtls_ssl_flight_transmit" ) );
+
+    if( ssl->handshake->retransmit_state != MBEDTLS_SSL_RETRANS_SENDING )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "initialise flight transmission" ) );
+
+        ssl->handshake->cur_msg = ssl->handshake->flight;
+        ssl->handshake->cur_msg_p = ssl->handshake->flight->p + 12;
+        ret = ssl_swap_epochs( ssl );
+        if( ret != 0 )
+            return( ret );
+
+        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_SENDING;
+    }
+
+    while( ssl->handshake->cur_msg != NULL )
+    {
+        size_t max_frag_len;
+        const mbedtls_ssl_flight_item * const cur = ssl->handshake->cur_msg;
+
+        int const is_finished =
+            ( cur->type == MBEDTLS_SSL_MSG_HANDSHAKE &&
+              cur->p[0] == MBEDTLS_SSL_HS_FINISHED );
+
+        uint8_t const force_flush = ssl->disable_datagram_packing == 1 ?
+            SSL_FORCE_FLUSH : SSL_DONT_FORCE_FLUSH;
+
+        /* Swap epochs before sending Finished: we can't do it after
+         * sending ChangeCipherSpec, in case write returns WANT_READ.
+         * Must be done before copying, may change out_msg pointer */
+        if( is_finished && ssl->handshake->cur_msg_p == ( cur->p + 12 ) )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "swap epochs to send finished message" ) );
+            ret = ssl_swap_epochs( ssl );
+            if( ret != 0 )
+                return( ret );
+        }
+
+        ret = ssl_get_remaining_payload_in_datagram( ssl );
+        if( ret < 0 )
+            return( ret );
+        max_frag_len = (size_t) ret;
+
+        /* CCS is copied as is, while HS messages may need fragmentation */
+        if( cur->type == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC )
+        {
+            if( max_frag_len == 0 )
+            {
+                if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
+                    return( ret );
+
+                continue;
+            }
+
+            memcpy( ssl->out_msg, cur->p, cur->len );
+            ssl->out_msglen  = cur->len;
+            ssl->out_msgtype = cur->type;
+
+            /* Update position inside current message */
+            ssl->handshake->cur_msg_p += cur->len;
+        }
+        else
+        {
+            const unsigned char * const p = ssl->handshake->cur_msg_p;
+            const size_t hs_len = cur->len - 12;
+            const size_t frag_off = p - ( cur->p + 12 );
+            const size_t rem_len = hs_len - frag_off;
+            size_t cur_hs_frag_len, max_hs_frag_len;
+
+            if( ( max_frag_len < 12 ) || ( max_frag_len == 12 && hs_len != 0 ) )
+            {
+                if( is_finished )
+                {
+                    ret = ssl_swap_epochs( ssl );
+                    if( ret != 0 )
+                        return( ret );
+                }
+
+                if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
+                    return( ret );
+
+                continue;
+            }
+            max_hs_frag_len = max_frag_len - 12;
+
+            cur_hs_frag_len = rem_len > max_hs_frag_len ?
+                max_hs_frag_len : rem_len;
+
+            if( frag_off == 0 && cur_hs_frag_len != hs_len )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "fragmenting handshake message (%u > %u)",
+                                            (unsigned) cur_hs_frag_len,
+                                            (unsigned) max_hs_frag_len ) );
+            }
+
+            /* Messages are stored with handshake headers as if not fragmented,
+             * copy beginning of headers then fill fragmentation fields.
+             * Handshake headers: type(1) len(3) seq(2) f_off(3) f_len(3) */
+            memcpy( ssl->out_msg, cur->p, 6 );
+
+            ssl->out_msg[6] = ( ( frag_off >> 16 ) & 0xff );
+            ssl->out_msg[7] = ( ( frag_off >>  8 ) & 0xff );
+            ssl->out_msg[8] = ( ( frag_off       ) & 0xff );
+
+            ssl->out_msg[ 9] = ( ( cur_hs_frag_len >> 16 ) & 0xff );
+            ssl->out_msg[10] = ( ( cur_hs_frag_len >>  8 ) & 0xff );
+            ssl->out_msg[11] = ( ( cur_hs_frag_len       ) & 0xff );
+
+            MBEDTLS_SSL_DEBUG_BUF( 3, "handshake header", ssl->out_msg, 12 );
+
+            /* Copy the handshake message content and set records fields */
+            memcpy( ssl->out_msg + 12, p, cur_hs_frag_len );
+            ssl->out_msglen = cur_hs_frag_len + 12;
+            ssl->out_msgtype = cur->type;
+
+            /* Update position inside current message */
+            ssl->handshake->cur_msg_p += cur_hs_frag_len;
+        }
+
+        /* If done with the current message move to the next one if any */
+        if( ssl->handshake->cur_msg_p >= cur->p + cur->len )
+        {
+            if( cur->next != NULL )
+            {
+                ssl->handshake->cur_msg = cur->next;
+                ssl->handshake->cur_msg_p = cur->next->p + 12;
+            }
+            else
+            {
+                ssl->handshake->cur_msg = NULL;
+                ssl->handshake->cur_msg_p = NULL;
+            }
+        }
+
+        /* Actually send the message out */
+        if( ( ret = mbedtls_ssl_write_record( ssl, force_flush ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret );
+            return( ret );
+        }
+    }
+
+    if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
+        return( ret );
+
+    /* Update state and set timer */
+    if( ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER )
+        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_FINISHED;
+    else
+    {
+        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_WAITING;
+        mbedtls_ssl_set_timer( ssl, ssl->handshake->retransmit_timeout );
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= mbedtls_ssl_flight_transmit" ) );
+
+    return( 0 );
+}
+
+/*
+ * To be called when the last message of an incoming flight is received.
+ */
+void mbedtls_ssl_recv_flight_completed( mbedtls_ssl_context *ssl )
+{
+    /* We won't need to resend that one any more */
+    mbedtls_ssl_flight_free( ssl->handshake->flight );
+    ssl->handshake->flight = NULL;
+    ssl->handshake->cur_msg = NULL;
+
+    /* The next incoming flight will start with this msg_seq */
+    ssl->handshake->in_flight_start_seq = ssl->handshake->in_msg_seq;
+
+    /* We don't want to remember CCS's across flight boundaries. */
+    ssl->handshake->buffering.seen_ccs = 0;
+
+    /* Clear future message buffering structure. */
+    mbedtls_ssl_buffering_free( ssl );
+
+    /* Cancel timer */
+    mbedtls_ssl_set_timer( ssl, 0 );
+
+    if( ssl->in_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE &&
+        ssl->in_msg[0] == MBEDTLS_SSL_HS_FINISHED )
+    {
+        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_FINISHED;
+    }
+    else
+        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_PREPARING;
+}
+
+/*
+ * To be called when the last message of an outgoing flight is send.
+ */
+void mbedtls_ssl_send_flight_completed( mbedtls_ssl_context *ssl )
+{
+    ssl_reset_retransmit_timeout( ssl );
+    mbedtls_ssl_set_timer( ssl, ssl->handshake->retransmit_timeout );
+
+    if( ssl->in_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE &&
+        ssl->in_msg[0] == MBEDTLS_SSL_HS_FINISHED )
+    {
+        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_FINISHED;
+    }
+    else
+        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_WAITING;
+}
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+/*
+ * Handshake layer functions
+ */
+
+/*
+ * Write (DTLS: or queue) current handshake (including CCS) message.
+ *
+ *  - fill in handshake headers
+ *  - update handshake checksum
+ *  - DTLS: save message for resending
+ *  - then pass to the record layer
+ *
+ * DTLS: except for HelloRequest, messages are only queued, and will only be
+ * actually sent when calling flight_transmit() or resend().
+ *
+ * Inputs:
+ *  - ssl->out_msglen: 4 + actual handshake message len
+ *      (4 is the size of handshake headers for TLS)
+ *  - ssl->out_msg[0]: the handshake type (ClientHello, ServerHello, etc)
+ *  - ssl->out_msg + 4: the handshake message body
+ *
+ * Outputs, ie state before passing to flight_append() or write_record():
+ *   - ssl->out_msglen: the length of the record contents
+ *      (including handshake headers but excluding record headers)
+ *   - ssl->out_msg: the record contents (handshake headers + content)
+ */
+int mbedtls_ssl_write_handshake_msg( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    const size_t hs_len = ssl->out_msglen - 4;
+    const unsigned char hs_type = ssl->out_msg[0];
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write handshake message" ) );
+
+    /*
+     * Sanity checks
+     */
+    if( ssl->out_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE          &&
+        ssl->out_msgtype != MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC )
+    {
+        /* In SSLv3, the client might send a NoCertificate alert. */
+#if defined(MBEDTLS_SSL_PROTO_SSL3) && defined(MBEDTLS_SSL_CLI_C)
+        if( ! ( ssl->minor_ver      == MBEDTLS_SSL_MINOR_VERSION_0 &&
+                ssl->out_msgtype    == MBEDTLS_SSL_MSG_ALERT       &&
+                ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT ) )
+#endif /* MBEDTLS_SSL_PROTO_SSL3 && MBEDTLS_SSL_SRV_C */
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+    }
+
+    /* Whenever we send anything different from a
+     * HelloRequest we should be in a handshake - double check. */
+    if( ! ( ssl->out_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE &&
+            hs_type          == MBEDTLS_SSL_HS_HELLO_REQUEST ) &&
+        ssl->handshake == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+        ssl->handshake != NULL &&
+        ssl->handshake->retransmit_state == MBEDTLS_SSL_RETRANS_SENDING )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+#endif
+
+    /* Double-check that we did not exceed the bounds
+     * of the outgoing record buffer.
+     * This should never fail as the various message
+     * writing functions must obey the bounds of the
+     * outgoing record buffer, but better be safe.
+     *
+     * Note: We deliberately do not check for the MTU or MFL here.
+     */
+    if( ssl->out_msglen > MBEDTLS_SSL_OUT_CONTENT_LEN )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Record too large: "
+                                    "size %" MBEDTLS_PRINTF_SIZET
+                                    ", maximum %" MBEDTLS_PRINTF_SIZET,
+                                    ssl->out_msglen,
+                                    (size_t) MBEDTLS_SSL_OUT_CONTENT_LEN ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    /*
+     * Fill handshake headers
+     */
+    if( ssl->out_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE )
+    {
+        ssl->out_msg[1] = (unsigned char)( hs_len >> 16 );
+        ssl->out_msg[2] = (unsigned char)( hs_len >>  8 );
+        ssl->out_msg[3] = (unsigned char)( hs_len       );
+
+        /*
+         * DTLS has additional fields in the Handshake layer,
+         * between the length field and the actual payload:
+         *      uint16 message_seq;
+         *      uint24 fragment_offset;
+         *      uint24 fragment_length;
+         */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+        if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+        {
+            /* Make room for the additional DTLS fields */
+            if( MBEDTLS_SSL_OUT_CONTENT_LEN - ssl->out_msglen < 8 )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "DTLS handshake message too large: "
+                              "size %" MBEDTLS_PRINTF_SIZET ", maximum %" MBEDTLS_PRINTF_SIZET,
+                               hs_len,
+                               (size_t) ( MBEDTLS_SSL_OUT_CONTENT_LEN - 12 ) ) );
+                return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+            }
+
+            memmove( ssl->out_msg + 12, ssl->out_msg + 4, hs_len );
+            ssl->out_msglen += 8;
+
+            /* Write message_seq and update it, except for HelloRequest */
+            if( hs_type != MBEDTLS_SSL_HS_HELLO_REQUEST )
+            {
+                ssl->out_msg[4] = ( ssl->handshake->out_msg_seq >> 8 ) & 0xFF;
+                ssl->out_msg[5] = ( ssl->handshake->out_msg_seq      ) & 0xFF;
+                ++( ssl->handshake->out_msg_seq );
+            }
+            else
+            {
+                ssl->out_msg[4] = 0;
+                ssl->out_msg[5] = 0;
+            }
+
+            /* Handshake hashes are computed without fragmentation,
+             * so set frag_offset = 0 and frag_len = hs_len for now */
+            memset( ssl->out_msg + 6, 0x00, 3 );
+            memcpy( ssl->out_msg + 9, ssl->out_msg + 1, 3 );
+        }
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+        /* Update running hashes of handshake messages seen */
+        if( hs_type != MBEDTLS_SSL_HS_HELLO_REQUEST )
+            ssl->handshake->update_checksum( ssl, ssl->out_msg, ssl->out_msglen );
+    }
+
+    /* Either send now, or just save to be sent (and resent) later */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+        ! ( ssl->out_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE &&
+            hs_type          == MBEDTLS_SSL_HS_HELLO_REQUEST ) )
+    {
+        if( ( ret = ssl_flight_append( ssl ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "ssl_flight_append", ret );
+            return( ret );
+        }
+    }
+    else
+#endif
+    {
+        if( ( ret = mbedtls_ssl_write_record( ssl, SSL_FORCE_FLUSH ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "ssl_write_record", ret );
+            return( ret );
+        }
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write handshake message" ) );
+
+    return( 0 );
+}
+
+/*
+ * Record layer functions
+ */
+
+/*
+ * Write current record.
+ *
+ * Uses:
+ *  - ssl->out_msgtype: type of the message (AppData, Handshake, Alert, CCS)
+ *  - ssl->out_msglen: length of the record content (excl headers)
+ *  - ssl->out_msg: record content
+ */
+int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, uint8_t force_flush )
+{
+    int ret, done = 0;
+    size_t len = ssl->out_msglen;
+    uint8_t flush = force_flush;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write record" ) );
+
+#if defined(MBEDTLS_ZLIB_SUPPORT)
+    if( ssl->transform_out != NULL &&
+        ssl->session_out->compression == MBEDTLS_SSL_COMPRESS_DEFLATE )
+    {
+        if( ( ret = ssl_compress_buf( ssl ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "ssl_compress_buf", ret );
+            return( ret );
+        }
+
+        len = ssl->out_msglen;
+    }
+#endif /*MBEDTLS_ZLIB_SUPPORT */
+
+#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
+    if( mbedtls_ssl_hw_record_write != NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "going for mbedtls_ssl_hw_record_write()" ) );
+
+        ret = mbedtls_ssl_hw_record_write( ssl );
+        if( ret != 0 && ret != MBEDTLS_ERR_SSL_HW_ACCEL_FALLTHROUGH )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_hw_record_write", ret );
+            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+        }
+
+        if( ret == 0 )
+            done = 1;
+    }
+#endif /* MBEDTLS_SSL_HW_RECORD_ACCEL */
+    if( !done )
+    {
+        unsigned i;
+        size_t protected_record_size;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+        size_t out_buf_len = ssl->out_buf_len;
+#else
+        size_t out_buf_len = MBEDTLS_SSL_OUT_BUFFER_LEN;
+#endif
+        /* Skip writing the record content type to after the encryption,
+         * as it may change when using the CID extension. */
+
+        mbedtls_ssl_write_version( ssl->major_ver, ssl->minor_ver,
+                           ssl->conf->transport, ssl->out_hdr + 1 );
+
+        memcpy( ssl->out_ctr, ssl->cur_out_ctr, 8 );
+        ssl->out_len[0] = (unsigned char)( len >> 8 );
+        ssl->out_len[1] = (unsigned char)( len      );
+
+        if( ssl->transform_out != NULL )
+        {
+            mbedtls_record rec;
+
+            rec.buf         = ssl->out_iv;
+            rec.buf_len     = out_buf_len - ( ssl->out_iv - ssl->out_buf );
+            rec.data_len    = ssl->out_msglen;
+            rec.data_offset = ssl->out_msg - rec.buf;
+
+            memcpy( &rec.ctr[0], ssl->out_ctr, 8 );
+            mbedtls_ssl_write_version( ssl->major_ver, ssl->minor_ver,
+                                       ssl->conf->transport, rec.ver );
+            rec.type = ssl->out_msgtype;
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+            /* The CID is set by mbedtls_ssl_encrypt_buf(). */
+            rec.cid_len = 0;
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+            if( ( ret = mbedtls_ssl_encrypt_buf( ssl, ssl->transform_out, &rec,
+                                         ssl->conf->f_rng, ssl->conf->p_rng ) ) != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_RET( 1, "ssl_encrypt_buf", ret );
+                return( ret );
+            }
+
+            if( rec.data_offset != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+                return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+            }
+
+            /* Update the record content type and CID. */
+            ssl->out_msgtype = rec.type;
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID )
+            memcpy( ssl->out_cid, rec.cid, rec.cid_len );
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+            ssl->out_msglen = len = rec.data_len;
+            ssl->out_len[0] = (unsigned char)( rec.data_len >> 8 );
+            ssl->out_len[1] = (unsigned char)( rec.data_len      );
+        }
+
+        protected_record_size = len + mbedtls_ssl_out_hdr_len( ssl );
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+        /* In case of DTLS, double-check that we don't exceed
+         * the remaining space in the datagram. */
+        if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+        {
+            ret = ssl_get_remaining_space_in_datagram( ssl );
+            if( ret < 0 )
+                return( ret );
+
+            if( protected_record_size > (size_t) ret )
+            {
+                /* Should never happen */
+                return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+            }
+        }
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+        /* Now write the potentially updated record content type. */
+        ssl->out_hdr[0] = (unsigned char) ssl->out_msgtype;
+
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "output record: msgtype = %u, "
+                                    "version = [%u:%u], msglen = %" MBEDTLS_PRINTF_SIZET,
+                                    ssl->out_hdr[0], ssl->out_hdr[1],
+                                    ssl->out_hdr[2], len ) );
+
+        MBEDTLS_SSL_DEBUG_BUF( 4, "output record sent to network",
+                               ssl->out_hdr, protected_record_size );
+
+        ssl->out_left += protected_record_size;
+        ssl->out_hdr  += protected_record_size;
+        mbedtls_ssl_update_out_pointers( ssl, ssl->transform_out );
+
+        for( i = 8; i > mbedtls_ssl_ep_len( ssl ); i-- )
+            if( ++ssl->cur_out_ctr[i - 1] != 0 )
+                break;
+
+        /* The loop goes to its end iff the counter is wrapping */
+        if( i == mbedtls_ssl_ep_len( ssl ) )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "outgoing message counter would wrap" ) );
+            return( MBEDTLS_ERR_SSL_COUNTER_WRAPPING );
+        }
+    }
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+        flush == SSL_DONT_FORCE_FLUSH )
+    {
+        size_t remaining;
+        ret = ssl_get_remaining_payload_in_datagram( ssl );
+        if( ret < 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "ssl_get_remaining_payload_in_datagram",
+                                   ret );
+            return( ret );
+        }
+
+        remaining = (size_t) ret;
+        if( remaining == 0 )
+        {
+            flush = SSL_FORCE_FLUSH;
+        }
+        else
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "Still %u bytes available in current datagram", (unsigned) remaining ) );
+        }
+    }
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+    if( ( flush == SSL_FORCE_FLUSH ) &&
+        ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flush_output", ret );
+        return( ret );
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write record" ) );
+
+    return( 0 );
+}
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+
+static int ssl_hs_is_proper_fragment( mbedtls_ssl_context *ssl )
+{
+    if( ssl->in_msglen < ssl->in_hslen ||
+        memcmp( ssl->in_msg + 6, "\0\0\0",        3 ) != 0 ||
+        memcmp( ssl->in_msg + 9, ssl->in_msg + 1, 3 ) != 0 )
+    {
+        return( 1 );
+    }
+    return( 0 );
+}
+
+static uint32_t ssl_get_hs_frag_len( mbedtls_ssl_context const *ssl )
+{
+    return( ( ssl->in_msg[9] << 16  ) |
+            ( ssl->in_msg[10] << 8  ) |
+              ssl->in_msg[11] );
+}
+
+static uint32_t ssl_get_hs_frag_off( mbedtls_ssl_context const *ssl )
+{
+    return( ( ssl->in_msg[6] << 16 ) |
+            ( ssl->in_msg[7] << 8  ) |
+              ssl->in_msg[8] );
+}
+
+static int ssl_check_hs_header( mbedtls_ssl_context const *ssl )
+{
+    uint32_t msg_len, frag_off, frag_len;
+
+    msg_len  = ssl_get_hs_total_len( ssl );
+    frag_off = ssl_get_hs_frag_off( ssl );
+    frag_len = ssl_get_hs_frag_len( ssl );
+
+    if( frag_off > msg_len )
+        return( -1 );
+
+    if( frag_len > msg_len - frag_off )
+        return( -1 );
+
+    if( frag_len + 12 > ssl->in_msglen )
+        return( -1 );
+
+    return( 0 );
+}
+
+/*
+ * Mark bits in bitmask (used for DTLS HS reassembly)
+ */
+static void ssl_bitmask_set( unsigned char *mask, size_t offset, size_t len )
+{
+    unsigned int start_bits, end_bits;
+
+    start_bits = 8 - ( offset % 8 );
+    if( start_bits != 8 )
+    {
+        size_t first_byte_idx = offset / 8;
+
+        /* Special case */
+        if( len <= start_bits )
+        {
+            for( ; len != 0; len-- )
+                mask[first_byte_idx] |= 1 << ( start_bits - len );
+
+            /* Avoid potential issues with offset or len becoming invalid */
+            return;
+        }
+
+        offset += start_bits; /* Now offset % 8 == 0 */
+        len -= start_bits;
+
+        for( ; start_bits != 0; start_bits-- )
+            mask[first_byte_idx] |= 1 << ( start_bits - 1 );
+    }
+
+    end_bits = len % 8;
+    if( end_bits != 0 )
+    {
+        size_t last_byte_idx = ( offset + len ) / 8;
+
+        len -= end_bits; /* Now len % 8 == 0 */
+
+        for( ; end_bits != 0; end_bits-- )
+            mask[last_byte_idx] |= 1 << ( 8 - end_bits );
+    }
+
+    memset( mask + offset / 8, 0xFF, len / 8 );
+}
+
+/*
+ * Check that bitmask is full
+ */
+static int ssl_bitmask_check( unsigned char *mask, size_t len )
+{
+    size_t i;
+
+    for( i = 0; i < len / 8; i++ )
+        if( mask[i] != 0xFF )
+            return( -1 );
+
+    for( i = 0; i < len % 8; i++ )
+        if( ( mask[len / 8] & ( 1 << ( 7 - i ) ) ) == 0 )
+            return( -1 );
+
+    return( 0 );
+}
+
+/* msg_len does not include the handshake header */
+static size_t ssl_get_reassembly_buffer_size( size_t msg_len,
+                                              unsigned add_bitmap )
+{
+    size_t alloc_len;
+
+    alloc_len  = 12;                                 /* Handshake header */
+    alloc_len += msg_len;                            /* Content buffer   */
+
+    if( add_bitmap )
+        alloc_len += msg_len / 8 + ( msg_len % 8 != 0 ); /* Bitmap       */
+
+    return( alloc_len );
+}
+
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+static uint32_t ssl_get_hs_total_len( mbedtls_ssl_context const *ssl )
+{
+    return( ( ssl->in_msg[1] << 16 ) |
+            ( ssl->in_msg[2] << 8  ) |
+              ssl->in_msg[3] );
+}
+
+int mbedtls_ssl_prepare_handshake_record( mbedtls_ssl_context *ssl )
+{
+    if( ssl->in_msglen < mbedtls_ssl_hs_hdr_len( ssl ) )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "handshake message too short: %" MBEDTLS_PRINTF_SIZET,
+                            ssl->in_msglen ) );
+        return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+    }
+
+    ssl->in_hslen = mbedtls_ssl_hs_hdr_len( ssl ) + ssl_get_hs_total_len( ssl );
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "handshake message: msglen ="
+                        " %" MBEDTLS_PRINTF_SIZET ", type = %u, hslen = %" MBEDTLS_PRINTF_SIZET,
+                        ssl->in_msglen, ssl->in_msg[0], ssl->in_hslen ) );
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+        unsigned int recv_msg_seq = ( ssl->in_msg[4] << 8 ) | ssl->in_msg[5];
+
+        if( ssl_check_hs_header( ssl ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid handshake header" ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+
+        if( ssl->handshake != NULL &&
+            ( ( ssl->state   != MBEDTLS_SSL_HANDSHAKE_OVER &&
+                recv_msg_seq != ssl->handshake->in_msg_seq ) ||
+              ( ssl->state  == MBEDTLS_SSL_HANDSHAKE_OVER &&
+                ssl->in_msg[0] != MBEDTLS_SSL_HS_CLIENT_HELLO ) ) )
+        {
+            if( recv_msg_seq > ssl->handshake->in_msg_seq )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "received future handshake message of sequence number %u (next %u)",
+                                            recv_msg_seq,
+                                            ssl->handshake->in_msg_seq ) );
+                return( MBEDTLS_ERR_SSL_EARLY_MESSAGE );
+            }
+
+            /* Retransmit only on last message from previous flight, to avoid
+             * too many retransmissions.
+             * Besides, No sane server ever retransmits HelloVerifyRequest */
+            if( recv_msg_seq == ssl->handshake->in_flight_start_seq - 1 &&
+                ssl->in_msg[0] != MBEDTLS_SSL_HS_HELLO_VERIFY_REQUEST )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "received message from last flight, "
+                                    "message_seq = %u, start_of_flight = %u",
+                                    recv_msg_seq,
+                                    ssl->handshake->in_flight_start_seq ) );
+
+                if( ( ret = mbedtls_ssl_resend( ssl ) ) != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_resend", ret );
+                    return( ret );
+                }
+            }
+            else
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "dropping out-of-sequence message: "
+                                    "message_seq = %u, expected = %u",
+                                    recv_msg_seq,
+                                    ssl->handshake->in_msg_seq ) );
+            }
+
+            return( MBEDTLS_ERR_SSL_CONTINUE_PROCESSING );
+        }
+        /* Wait until message completion to increment in_msg_seq */
+
+        /* Message reassembly is handled alongside buffering of future
+         * messages; the commonality is that both handshake fragments and
+         * future messages cannot be forwarded immediately to the
+         * handshake logic layer. */
+        if( ssl_hs_is_proper_fragment( ssl ) == 1 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "found fragmented DTLS handshake message" ) );
+            return( MBEDTLS_ERR_SSL_EARLY_MESSAGE );
+        }
+    }
+    else
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+    /* With TLS we don't handle fragmentation (for now) */
+    if( ssl->in_msglen < ssl->in_hslen )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "TLS handshake fragmentation not supported" ) );
+        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
+    }
+
+    return( 0 );
+}
+
+void mbedtls_ssl_update_handshake_status( mbedtls_ssl_context *ssl )
+{
+    mbedtls_ssl_handshake_params * const hs = ssl->handshake;
+
+    if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER && hs != NULL )
+    {
+        ssl->handshake->update_checksum( ssl, ssl->in_msg, ssl->in_hslen );
+    }
+
+    /* Handshake message is complete, increment counter */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+        ssl->handshake != NULL )
+    {
+        unsigned offset;
+        mbedtls_ssl_hs_buffer *hs_buf;
+
+        /* Increment handshake sequence number */
+        hs->in_msg_seq++;
+
+        /*
+         * Clear up handshake buffering and reassembly structure.
+         */
+
+        /* Free first entry */
+        ssl_buffering_free_slot( ssl, 0 );
+
+        /* Shift all other entries */
+        for( offset = 0, hs_buf = &hs->buffering.hs[0];
+             offset + 1 < MBEDTLS_SSL_MAX_BUFFERED_HS;
+             offset++, hs_buf++ )
+        {
+            *hs_buf = *(hs_buf + 1);
+        }
+
+        /* Create a fresh last entry */
+        memset( hs_buf, 0, sizeof( mbedtls_ssl_hs_buffer ) );
+    }
+#endif
+}
+
+/*
+ * DTLS anti-replay: RFC 6347 4.1.2.6
+ *
+ * in_window is a field of bits numbered from 0 (lsb) to 63 (msb).
+ * Bit n is set iff record number in_window_top - n has been seen.
+ *
+ * Usually, in_window_top is the last record number seen and the lsb of
+ * in_window is set. The only exception is the initial state (record number 0
+ * not seen yet).
+ */
+#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
+void mbedtls_ssl_dtls_replay_reset( mbedtls_ssl_context *ssl )
+{
+    ssl->in_window_top = 0;
+    ssl->in_window = 0;
+}
+
+static inline uint64_t ssl_load_six_bytes( unsigned char *buf )
+{
+    return( ( (uint64_t) buf[0] << 40 ) |
+            ( (uint64_t) buf[1] << 32 ) |
+            ( (uint64_t) buf[2] << 24 ) |
+            ( (uint64_t) buf[3] << 16 ) |
+            ( (uint64_t) buf[4] <<  8 ) |
+            ( (uint64_t) buf[5]       ) );
+}
+
+static int mbedtls_ssl_dtls_record_replay_check( mbedtls_ssl_context *ssl, uint8_t *record_in_ctr )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    unsigned char *original_in_ctr;
+
+    // save original in_ctr
+    original_in_ctr = ssl->in_ctr;
+
+    // use counter from record
+    ssl->in_ctr = record_in_ctr;
+
+    ret = mbedtls_ssl_dtls_replay_check( (mbedtls_ssl_context const *) ssl );
+
+    // restore the counter
+    ssl->in_ctr = original_in_ctr;
+
+    return ret;
+}
+
+/*
+ * Return 0 if sequence number is acceptable, -1 otherwise
+ */
+int mbedtls_ssl_dtls_replay_check( mbedtls_ssl_context const *ssl )
+{
+    uint64_t rec_seqnum = ssl_load_six_bytes( ssl->in_ctr + 2 );
+    uint64_t bit;
+
+    if( ssl->conf->anti_replay == MBEDTLS_SSL_ANTI_REPLAY_DISABLED )
+        return( 0 );
+
+    if( rec_seqnum > ssl->in_window_top )
+        return( 0 );
+
+    bit = ssl->in_window_top - rec_seqnum;
+
+    if( bit >= 64 )
+        return( -1 );
+
+    if( ( ssl->in_window & ( (uint64_t) 1 << bit ) ) != 0 )
+        return( -1 );
+
+    return( 0 );
+}
+
+/*
+ * Update replay window on new validated record
+ */
+void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl )
+{
+    uint64_t rec_seqnum = ssl_load_six_bytes( ssl->in_ctr + 2 );
+
+    if( ssl->conf->anti_replay == MBEDTLS_SSL_ANTI_REPLAY_DISABLED )
+        return;
+
+    if( rec_seqnum > ssl->in_window_top )
+    {
+        /* Update window_top and the contents of the window */
+        uint64_t shift = rec_seqnum - ssl->in_window_top;
+
+        if( shift >= 64 )
+            ssl->in_window = 1;
+        else
+        {
+            ssl->in_window <<= shift;
+            ssl->in_window |= 1;
+        }
+
+        ssl->in_window_top = rec_seqnum;
+    }
+    else
+    {
+        /* Mark that number as seen in the current window */
+        uint64_t bit = ssl->in_window_top - rec_seqnum;
+
+        if( bit < 64 ) /* Always true, but be extra sure */
+            ssl->in_window |= (uint64_t) 1 << bit;
+    }
+}
+#endif /* MBEDTLS_SSL_DTLS_ANTI_REPLAY */
+
+#if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) && defined(MBEDTLS_SSL_SRV_C)
+/*
+ * Without any SSL context, check if a datagram looks like a ClientHello with
+ * a valid cookie, and if it doesn't, generate a HelloVerifyRequest message.
+ * Both input and output include full DTLS headers.
+ *
+ * - if cookie is valid, return 0
+ * - if ClientHello looks superficially valid but cookie is not,
+ *   fill obuf and set olen, then
+ *   return MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED
+ * - otherwise return a specific error code
+ */
+static int ssl_check_dtls_clihlo_cookie(
+                           mbedtls_ssl_cookie_write_t *f_cookie_write,
+                           mbedtls_ssl_cookie_check_t *f_cookie_check,
+                           void *p_cookie,
+                           const unsigned char *cli_id, size_t cli_id_len,
+                           const unsigned char *in, size_t in_len,
+                           unsigned char *obuf, size_t buf_len, size_t *olen )
+{
+    size_t sid_len, cookie_len;
+    unsigned char *p;
+
+    /*
+     * Structure of ClientHello with record and handshake headers,
+     * and expected values. We don't need to check a lot, more checks will be
+     * done when actually parsing the ClientHello - skipping those checks
+     * avoids code duplication and does not make cookie forging any easier.
+     *
+     *  0-0  ContentType type;                  copied, must be handshake
+     *  1-2  ProtocolVersion version;           copied
+     *  3-4  uint16 epoch;                      copied, must be 0
+     *  5-10 uint48 sequence_number;            copied
+     * 11-12 uint16 length;                     (ignored)
+     *
+     * 13-13 HandshakeType msg_type;            (ignored)
+     * 14-16 uint24 length;                     (ignored)
+     * 17-18 uint16 message_seq;                copied
+     * 19-21 uint24 fragment_offset;            copied, must be 0
+     * 22-24 uint24 fragment_length;            (ignored)
+     *
+     * 25-26 ProtocolVersion client_version;    (ignored)
+     * 27-58 Random random;                     (ignored)
+     * 59-xx SessionID session_id;              1 byte len + sid_len content
+     * 60+   opaque cookie<0..2^8-1>;           1 byte len + content
+     *       ...
+     *
+     * Minimum length is 61 bytes.
+     */
+    if( in_len < 61 ||
+        in[0] != MBEDTLS_SSL_MSG_HANDSHAKE ||
+        in[3] != 0 || in[4] != 0 ||
+        in[19] != 0 || in[20] != 0 || in[21] != 0 )
+    {
+        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
+    }
+
+    sid_len = in[59];
+    if( sid_len > in_len - 61 )
+        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
+
+    cookie_len = in[60 + sid_len];
+    if( cookie_len > in_len - 60 )
+        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
+
+    if( f_cookie_check( p_cookie, in + sid_len + 61, cookie_len,
+                        cli_id, cli_id_len ) == 0 )
+    {
+        /* Valid cookie */
+        return( 0 );
+    }
+
+    /*
+     * If we get here, we've got an invalid cookie, let's prepare HVR.
+     *
+     *  0-0  ContentType type;                  copied
+     *  1-2  ProtocolVersion version;           copied
+     *  3-4  uint16 epoch;                      copied
+     *  5-10 uint48 sequence_number;            copied
+     * 11-12 uint16 length;                     olen - 13
+     *
+     * 13-13 HandshakeType msg_type;            hello_verify_request
+     * 14-16 uint24 length;                     olen - 25
+     * 17-18 uint16 message_seq;                copied
+     * 19-21 uint24 fragment_offset;            copied
+     * 22-24 uint24 fragment_length;            olen - 25
+     *
+     * 25-26 ProtocolVersion server_version;    0xfe 0xff
+     * 27-27 opaque cookie<0..2^8-1>;           cookie_len = olen - 27, cookie
+     *
+     * Minimum length is 28.
+     */
+    if( buf_len < 28 )
+        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
+
+    /* Copy most fields and adapt others */
+    memcpy( obuf, in, 25 );
+    obuf[13] = MBEDTLS_SSL_HS_HELLO_VERIFY_REQUEST;
+    obuf[25] = 0xfe;
+    obuf[26] = 0xff;
+
+    /* Generate and write actual cookie */
+    p = obuf + 28;
+    if( f_cookie_write( p_cookie,
+                        &p, obuf + buf_len, cli_id, cli_id_len ) != 0 )
+    {
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    *olen = p - obuf;
+
+    /* Go back and fill length fields */
+    obuf[27] = (unsigned char)( *olen - 28 );
+
+    obuf[14] = obuf[22] = (unsigned char)( ( *olen - 25 ) >> 16 );
+    obuf[15] = obuf[23] = (unsigned char)( ( *olen - 25 ) >>  8 );
+    obuf[16] = obuf[24] = (unsigned char)( ( *olen - 25 )       );
+
+    obuf[11] = (unsigned char)( ( *olen - 13 ) >>  8 );
+    obuf[12] = (unsigned char)( ( *olen - 13 )       );
+
+    return( MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED );
+}
+
+/*
+ * Handle possible client reconnect with the same UDP quadruplet
+ * (RFC 6347 Section 4.2.8).
+ *
+ * Called by ssl_parse_record_header() in case we receive an epoch 0 record
+ * that looks like a ClientHello.
+ *
+ * - if the input looks like a ClientHello without cookies,
+ *   send back HelloVerifyRequest, then return 0
+ * - if the input looks like a ClientHello with a valid cookie,
+ *   reset the session of the current context, and
+ *   return MBEDTLS_ERR_SSL_CLIENT_RECONNECT
+ * - if anything goes wrong, return a specific error code
+ *
+ * This function is called (through ssl_check_client_reconnect()) when an
+ * unexpected record is found in ssl_get_next_record(), which will discard the
+ * record if we return 0, and bubble up the return value otherwise (this
+ * includes the case of MBEDTLS_ERR_SSL_CLIENT_RECONNECT and of unexpected
+ * errors, and is the right thing to do in both cases).
+ */
+static int ssl_handle_possible_reconnect( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t len;
+
+    if( ssl->conf->f_cookie_write == NULL ||
+        ssl->conf->f_cookie_check == NULL )
+    {
+        /* If we can't use cookies to verify reachability of the peer,
+         * drop the record. */
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "no cookie callbacks, "
+                                    "can't check reconnect validity" ) );
+        return( 0 );
+    }
+
+    ret = ssl_check_dtls_clihlo_cookie(
+            ssl->conf->f_cookie_write,
+            ssl->conf->f_cookie_check,
+            ssl->conf->p_cookie,
+            ssl->cli_id, ssl->cli_id_len,
+            ssl->in_buf, ssl->in_left,
+            ssl->out_buf, MBEDTLS_SSL_OUT_CONTENT_LEN, &len );
+
+    MBEDTLS_SSL_DEBUG_RET( 2, "ssl_check_dtls_clihlo_cookie", ret );
+
+    if( ret == MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED )
+    {
+        int send_ret;
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "sending HelloVerifyRequest" ) );
+        MBEDTLS_SSL_DEBUG_BUF( 4, "output record sent to network",
+                                  ssl->out_buf, len );
+        /* Don't check write errors as we can't do anything here.
+         * If the error is permanent we'll catch it later,
+         * if it's not, then hopefully it'll work next time. */
+        send_ret = ssl->f_send( ssl->p_bio, ssl->out_buf, len );
+        MBEDTLS_SSL_DEBUG_RET( 2, "ssl->f_send", send_ret );
+        (void) send_ret;
+
+        return( 0 );
+    }
+
+    if( ret == 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "cookie is valid, resetting context" ) );
+        if( ( ret = mbedtls_ssl_session_reset_int( ssl, 1 ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "reset", ret );
+            return( ret );
+        }
+
+        return( MBEDTLS_ERR_SSL_CLIENT_RECONNECT );
+    }
+
+    return( ret );
+}
+#endif /* MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE && MBEDTLS_SSL_SRV_C */
+
+static int ssl_check_record_type( uint8_t record_type )
+{
+    if( record_type != MBEDTLS_SSL_MSG_HANDSHAKE &&
+        record_type != MBEDTLS_SSL_MSG_ALERT &&
+        record_type != MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC &&
+        record_type != MBEDTLS_SSL_MSG_APPLICATION_DATA )
+    {
+        return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+    }
+
+    return( 0 );
+}
+
+/*
+ * ContentType type;
+ * ProtocolVersion version;
+ * uint16 epoch;            // DTLS only
+ * uint48 sequence_number;  // DTLS only
+ * uint16 length;
+ *
+ * Return 0 if header looks sane (and, for DTLS, the record is expected)
+ * MBEDTLS_ERR_SSL_INVALID_RECORD if the header looks bad,
+ * MBEDTLS_ERR_SSL_UNEXPECTED_RECORD (DTLS only) if sane but unexpected.
+ *
+ * With DTLS, mbedtls_ssl_read_record() will:
+ * 1. proceed with the record if this function returns 0
+ * 2. drop only the current record if this function returns UNEXPECTED_RECORD
+ * 3. return CLIENT_RECONNECT if this function return that value
+ * 4. drop the whole datagram if this function returns anything else.
+ * Point 2 is needed when the peer is resending, and we have already received
+ * the first record from a datagram but are still waiting for the others.
+ */
+static int ssl_parse_record_header( mbedtls_ssl_context const *ssl,
+                                    unsigned char *buf,
+                                    size_t len,
+                                    mbedtls_record *rec )
+{
+    int major_ver, minor_ver;
+
+    size_t const rec_hdr_type_offset    = 0;
+    size_t const rec_hdr_type_len       = 1;
+
+    size_t const rec_hdr_version_offset = rec_hdr_type_offset +
+                                          rec_hdr_type_len;
+    size_t const rec_hdr_version_len    = 2;
+
+    size_t const rec_hdr_ctr_len        = 8;
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    uint32_t     rec_epoch;
+    size_t const rec_hdr_ctr_offset     = rec_hdr_version_offset +
+                                          rec_hdr_version_len;
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    size_t const rec_hdr_cid_offset     = rec_hdr_ctr_offset +
+                                          rec_hdr_ctr_len;
+    size_t       rec_hdr_cid_len        = 0;
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+    size_t       rec_hdr_len_offset; /* To be determined */
+    size_t const rec_hdr_len_len    = 2;
+
+    /*
+     * Check minimum lengths for record header.
+     */
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        rec_hdr_len_offset = rec_hdr_ctr_offset + rec_hdr_ctr_len;
+    }
+    else
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+    {
+        rec_hdr_len_offset = rec_hdr_version_offset + rec_hdr_version_len;
+    }
+
+    if( len < rec_hdr_len_offset + rec_hdr_len_len )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "datagram of length %u too small to hold DTLS record header of length %u",
+                 (unsigned) len,
+                 (unsigned)( rec_hdr_len_len + rec_hdr_len_len ) ) );
+        return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+    }
+
+    /*
+     * Parse and validate record content type
+     */
+
+    rec->type = buf[ rec_hdr_type_offset ];
+
+    /* Check record content type */
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    rec->cid_len = 0;
+
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+        ssl->conf->cid_len != 0                                &&
+        rec->type == MBEDTLS_SSL_MSG_CID )
+    {
+        /* Shift pointers to account for record header including CID
+         * struct {
+         *   ContentType special_type = tls12_cid;
+         *   ProtocolVersion version;
+         *   uint16 epoch;
+         *   uint48 sequence_number;
+         *   opaque cid[cid_length]; // Additional field compared to
+         *                           // default DTLS record format
+         *   uint16 length;
+         *   opaque enc_content[DTLSCiphertext.length];
+         * } DTLSCiphertext;
+         */
+
+        /* So far, we only support static CID lengths
+         * fixed in the configuration. */
+        rec_hdr_cid_len = ssl->conf->cid_len;
+        rec_hdr_len_offset += rec_hdr_cid_len;
+
+        if( len < rec_hdr_len_offset + rec_hdr_len_len )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "datagram of length %u too small to hold DTLS record header including CID, length %u",
+                (unsigned) len,
+                (unsigned)( rec_hdr_len_offset + rec_hdr_len_len ) ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+
+        /* configured CID len is guaranteed at most 255, see
+         * MBEDTLS_SSL_CID_OUT_LEN_MAX in check_config.h */
+        rec->cid_len = (uint8_t) rec_hdr_cid_len;
+        memcpy( rec->cid, buf + rec_hdr_cid_offset, rec_hdr_cid_len );
+    }
+    else
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+    {
+        if( ssl_check_record_type( rec->type ) )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "unknown record type %u",
+                                        (unsigned) rec->type ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+    }
+
+    /*
+     * Parse and validate record version
+     */
+
+    rec->ver[0] = buf[ rec_hdr_version_offset + 0 ];
+    rec->ver[1] = buf[ rec_hdr_version_offset + 1 ];
+    mbedtls_ssl_read_version( &major_ver, &minor_ver,
+                              ssl->conf->transport,
+                              &rec->ver[0] );
+
+    if( major_ver != ssl->major_ver )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "major version mismatch" ) );
+        return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+    }
+
+    if( minor_ver > ssl->conf->max_minor_ver )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "minor version mismatch" ) );
+        return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+    }
+
+    /*
+     * Parse/Copy record sequence number.
+     */
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        /* Copy explicit record sequence number from input buffer. */
+        memcpy( &rec->ctr[0], buf + rec_hdr_ctr_offset,
+                rec_hdr_ctr_len );
+    }
+    else
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+    {
+        /* Copy implicit record sequence number from SSL context structure. */
+        memcpy( &rec->ctr[0], ssl->in_ctr, rec_hdr_ctr_len );
+    }
+
+    /*
+     * Parse record length.
+     */
+
+    rec->data_offset = rec_hdr_len_offset + rec_hdr_len_len;
+    rec->data_len    = ( (size_t) buf[ rec_hdr_len_offset + 0 ] << 8 ) |
+                       ( (size_t) buf[ rec_hdr_len_offset + 1 ] << 0 );
+    MBEDTLS_SSL_DEBUG_BUF( 4, "input record header", buf, rec->data_offset );
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "input record: msgtype = %u, "
+                                "version = [%d:%d], msglen = %" MBEDTLS_PRINTF_SIZET,
+                                rec->type,
+                                major_ver, minor_ver, rec->data_len ) );
+
+    rec->buf     = buf;
+    rec->buf_len = rec->data_offset + rec->data_len;
+
+    if( rec->data_len == 0 )
+        return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+
+    /*
+     * DTLS-related tests.
+     * Check epoch before checking length constraint because
+     * the latter varies with the epoch. E.g., if a ChangeCipherSpec
+     * message gets duplicated before the corresponding Finished message,
+     * the second ChangeCipherSpec should be discarded because it belongs
+     * to an old epoch, but not because its length is shorter than
+     * the minimum record length for packets using the new record transform.
+     * Note that these two kinds of failures are handled differently,
+     * as an unexpected record is silently skipped but an invalid
+     * record leads to the entire datagram being dropped.
+     */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        rec_epoch = ( rec->ctr[0] << 8 ) | rec->ctr[1];
+
+        /* Check that the datagram is large enough to contain a record
+         * of the advertised length. */
+        if( len < rec->data_offset + rec->data_len )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "Datagram of length %u too small to contain record of advertised length %u.",
+                             (unsigned) len,
+                             (unsigned)( rec->data_offset + rec->data_len ) ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+
+        /* Records from other, non-matching epochs are silently discarded.
+         * (The case of same-port Client reconnects must be considered in
+         *  the caller). */
+        if( rec_epoch != ssl->in_epoch )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "record from another epoch: "
+                                        "expected %u, received %lu",
+                                        ssl->in_epoch, (unsigned long) rec_epoch ) );
+
+            /* Records from the next epoch are considered for buffering
+             * (concretely: early Finished messages). */
+            if( rec_epoch == (unsigned) ssl->in_epoch + 1 )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "Consider record for buffering" ) );
+                return( MBEDTLS_ERR_SSL_EARLY_MESSAGE );
+            }
+
+            return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
+        }
+#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
+        /* For records from the correct epoch, check whether their
+         * sequence number has been seen before. */
+        else if( mbedtls_ssl_dtls_record_replay_check( (mbedtls_ssl_context *) ssl,
+            &rec->ctr[0] ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "replayed record" ) );
+            return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
+        }
+#endif
+    }
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+    return( 0 );
+}
+
+
+#if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) && defined(MBEDTLS_SSL_SRV_C)
+static int ssl_check_client_reconnect( mbedtls_ssl_context *ssl )
+{
+    unsigned int rec_epoch = ( ssl->in_ctr[0] << 8 ) | ssl->in_ctr[1];
+
+    /*
+     * Check for an epoch 0 ClientHello. We can't use in_msg here to
+     * access the first byte of record content (handshake type), as we
+     * have an active transform (possibly iv_len != 0), so use the
+     * fact that the record header len is 13 instead.
+     */
+    if( rec_epoch == 0 &&
+        ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER &&
+        ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER &&
+        ssl->in_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE &&
+        ssl->in_left > 13 &&
+        ssl->in_buf[13] == MBEDTLS_SSL_HS_CLIENT_HELLO )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "possible client reconnect "
+                                    "from the same port" ) );
+        return( ssl_handle_possible_reconnect( ssl ) );
+    }
+
+    return( 0 );
+}
+#endif /* MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE && MBEDTLS_SSL_SRV_C */
+
+/*
+ * If applicable, decrypt record content
+ */
+static int ssl_prepare_record_content( mbedtls_ssl_context *ssl,
+                                       mbedtls_record *rec )
+{
+    int ret, done = 0;
+
+    MBEDTLS_SSL_DEBUG_BUF( 4, "input record from network",
+                           rec->buf, rec->buf_len );
+
+#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
+    if( mbedtls_ssl_hw_record_read != NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "going for mbedtls_ssl_hw_record_read()" ) );
+
+        ret = mbedtls_ssl_hw_record_read( ssl );
+        if( ret != 0 && ret != MBEDTLS_ERR_SSL_HW_ACCEL_FALLTHROUGH )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_hw_record_read", ret );
+            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+        }
+
+        if( ret == 0 )
+            done = 1;
+    }
+#endif /* MBEDTLS_SSL_HW_RECORD_ACCEL */
+    if( !done && ssl->transform_in != NULL )
+    {
+        unsigned char const old_msg_type = rec->type;
+
+        if( ( ret = mbedtls_ssl_decrypt_buf( ssl, ssl->transform_in,
+                                             rec ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "ssl_decrypt_buf", ret );
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+            if( ret == MBEDTLS_ERR_SSL_UNEXPECTED_CID &&
+                ssl->conf->ignore_unexpected_cid
+                    == MBEDTLS_SSL_UNEXPECTED_CID_IGNORE )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 3, ( "ignoring unexpected CID" ) );
+                ret = MBEDTLS_ERR_SSL_CONTINUE_PROCESSING;
+            }
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+            return( ret );
+        }
+
+        if( old_msg_type != rec->type )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 4, ( "record type after decrypt (before %d): %d",
+                                        old_msg_type, rec->type ) );
+        }
+
+        MBEDTLS_SSL_DEBUG_BUF( 4, "input payload after decrypt",
+                               rec->buf + rec->data_offset, rec->data_len );
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+        /* We have already checked the record content type
+         * in ssl_parse_record_header(), failing or silently
+         * dropping the record in the case of an unknown type.
+         *
+         * Since with the use of CIDs, the record content type
+         * might change during decryption, re-check the record
+         * content type, but treat a failure as fatal this time. */
+        if( ssl_check_record_type( rec->type ) )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "unknown record type" ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+        if( rec->data_len == 0 )
+        {
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+            if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3
+                && rec->type != MBEDTLS_SSL_MSG_APPLICATION_DATA )
+            {
+                /* TLS v1.2 explicitly disallows zero-length messages which are not application data */
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid zero-length message type: %d", ssl->in_msgtype ) );
+                return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+            }
+#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
+
+            ssl->nb_zero++;
+
+            /*
+             * Three or more empty messages may be a DoS attack
+             * (excessive CPU consumption).
+             */
+            if( ssl->nb_zero > 3 )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "received four consecutive empty "
+                                            "messages, possible DoS attack" ) );
+                /* Treat the records as if they were not properly authenticated,
+                 * thereby failing the connection if we see more than allowed
+                 * by the configured bad MAC threshold. */
+                return( MBEDTLS_ERR_SSL_INVALID_MAC );
+            }
+        }
+        else
+            ssl->nb_zero = 0;
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+        if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+        {
+            ; /* in_ctr read from peer, not maintained internally */
+        }
+        else
+#endif
+        {
+            unsigned i;
+            for( i = 8; i > mbedtls_ssl_ep_len( ssl ); i-- )
+                if( ++ssl->in_ctr[i - 1] != 0 )
+                    break;
+
+            /* The loop goes to its end iff the counter is wrapping */
+            if( i == mbedtls_ssl_ep_len( ssl ) )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "incoming message counter would wrap" ) );
+                return( MBEDTLS_ERR_SSL_COUNTER_WRAPPING );
+            }
+        }
+
+    }
+
+#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        mbedtls_ssl_dtls_replay_update( ssl );
+    }
+#endif
+
+    /* Check actual (decrypted) record content length against
+     * configured maximum. */
+    if( ssl->in_msglen > MBEDTLS_SSL_IN_CONTENT_LEN )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
+        return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+    }
+
+    return( 0 );
+}
+
+/*
+ * Read a record.
+ *
+ * Silently ignore non-fatal alert (and for DTLS, invalid records as well,
+ * RFC 6347 4.1.2.7) and continue reading until a valid record is found.
+ *
+ */
+
+/* Helper functions for mbedtls_ssl_read_record(). */
+static int ssl_consume_current_message( mbedtls_ssl_context *ssl );
+static int ssl_get_next_record( mbedtls_ssl_context *ssl );
+static int ssl_record_is_in_progress( mbedtls_ssl_context *ssl );
+
+int mbedtls_ssl_read_record( mbedtls_ssl_context *ssl,
+                             unsigned update_hs_digest )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> read record" ) );
+
+    if( ssl->keep_current_message == 0 )
+    {
+        do {
+
+            ret = ssl_consume_current_message( ssl );
+            if( ret != 0 )
+                return( ret );
+
+            if( ssl_record_is_in_progress( ssl ) == 0 )
+            {
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+                int have_buffered = 0;
+
+                /* We only check for buffered messages if the
+                 * current datagram is fully consumed. */
+                if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+                    ssl_next_record_is_in_datagram( ssl ) == 0 )
+                {
+                    if( ssl_load_buffered_message( ssl ) == 0 )
+                        have_buffered = 1;
+                }
+
+                if( have_buffered == 0 )
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+                {
+                    ret = ssl_get_next_record( ssl );
+                    if( ret == MBEDTLS_ERR_SSL_CONTINUE_PROCESSING )
+                        continue;
+
+                    if( ret != 0 )
+                    {
+                        MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_get_next_record" ), ret );
+                        return( ret );
+                    }
+                }
+            }
+
+            ret = mbedtls_ssl_handle_message_type( ssl );
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+            if( ret == MBEDTLS_ERR_SSL_EARLY_MESSAGE )
+            {
+                /* Buffer future message */
+                ret = ssl_buffer_message( ssl );
+                if( ret != 0 )
+                    return( ret );
+
+                ret = MBEDTLS_ERR_SSL_CONTINUE_PROCESSING;
+            }
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+        } while( MBEDTLS_ERR_SSL_NON_FATAL           == ret  ||
+                 MBEDTLS_ERR_SSL_CONTINUE_PROCESSING == ret );
+
+        if( 0 != ret )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, ( "mbedtls_ssl_handle_message_type" ), ret );
+            return( ret );
+        }
+
+        if( ssl->in_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE &&
+            update_hs_digest == 1 )
+        {
+            mbedtls_ssl_update_handshake_status( ssl );
+        }
+    }
+    else
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "reuse previously read message" ) );
+        ssl->keep_current_message = 0;
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= read record" ) );
+
+    return( 0 );
+}
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+static int ssl_next_record_is_in_datagram( mbedtls_ssl_context *ssl )
+{
+    if( ssl->in_left > ssl->next_record_offset )
+        return( 1 );
+
+    return( 0 );
+}
+
+static int ssl_load_buffered_message( mbedtls_ssl_context *ssl )
+{
+    mbedtls_ssl_handshake_params * const hs = ssl->handshake;
+    mbedtls_ssl_hs_buffer * hs_buf;
+    int ret = 0;
+
+    if( hs == NULL )
+        return( -1 );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> ssl_load_buffered_messsage" ) );
+
+    if( ssl->state == MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC ||
+        ssl->state == MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC )
+    {
+        /* Check if we have seen a ChangeCipherSpec before.
+         * If yes, synthesize a CCS record. */
+        if( !hs->buffering.seen_ccs )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "CCS not seen in the current flight" ) );
+            ret = -1;
+            goto exit;
+        }
+
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Injecting buffered CCS message" ) );
+        ssl->in_msgtype = MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC;
+        ssl->in_msglen = 1;
+        ssl->in_msg[0] = 1;
+
+        /* As long as they are equal, the exact value doesn't matter. */
+        ssl->in_left            = 0;
+        ssl->next_record_offset = 0;
+
+        hs->buffering.seen_ccs = 0;
+        goto exit;
+    }
+
+#if defined(MBEDTLS_DEBUG_C)
+    /* Debug only */
+    {
+        unsigned offset;
+        for( offset = 1; offset < MBEDTLS_SSL_MAX_BUFFERED_HS; offset++ )
+        {
+            hs_buf = &hs->buffering.hs[offset];
+            if( hs_buf->is_valid == 1 )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "Future message with sequence number %u %s buffered.",
+                            hs->in_msg_seq + offset,
+                            hs_buf->is_complete ? "fully" : "partially" ) );
+            }
+        }
+    }
+#endif /* MBEDTLS_DEBUG_C */
+
+    /* Check if we have buffered and/or fully reassembled the
+     * next handshake message. */
+    hs_buf = &hs->buffering.hs[0];
+    if( ( hs_buf->is_valid == 1 ) && ( hs_buf->is_complete == 1 ) )
+    {
+        /* Synthesize a record containing the buffered HS message. */
+        size_t msg_len = ( hs_buf->data[1] << 16 ) |
+                         ( hs_buf->data[2] << 8  ) |
+                           hs_buf->data[3];
+
+        /* Double-check that we haven't accidentally buffered
+         * a message that doesn't fit into the input buffer. */
+        if( msg_len + 12 > MBEDTLS_SSL_IN_CONTENT_LEN )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Next handshake message has been buffered - load" ) );
+        MBEDTLS_SSL_DEBUG_BUF( 3, "Buffered handshake message (incl. header)",
+                               hs_buf->data, msg_len + 12 );
+
+        ssl->in_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
+        ssl->in_hslen   = msg_len + 12;
+        ssl->in_msglen  = msg_len + 12;
+        memcpy( ssl->in_msg, hs_buf->data, ssl->in_hslen );
+
+        ret = 0;
+        goto exit;
+    }
+    else
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Next handshake message %u not or only partially bufffered",
+                                    hs->in_msg_seq ) );
+    }
+
+    ret = -1;
+
+exit:
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= ssl_load_buffered_message" ) );
+    return( ret );
+}
+
+static int ssl_buffer_make_space( mbedtls_ssl_context *ssl,
+                                  size_t desired )
+{
+    int offset;
+    mbedtls_ssl_handshake_params * const hs = ssl->handshake;
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "Attempt to free buffered messages to have %u bytes available",
+                                (unsigned) desired ) );
+
+    /* Get rid of future records epoch first, if such exist. */
+    ssl_free_buffered_record( ssl );
+
+    /* Check if we have enough space available now. */
+    if( desired <= ( MBEDTLS_SSL_DTLS_MAX_BUFFERING -
+                     hs->buffering.total_bytes_buffered ) )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Enough space available after freeing future epoch record" ) );
+        return( 0 );
+    }
+
+    /* We don't have enough space to buffer the next expected handshake
+     * message. Remove buffers used for future messages to gain space,
+     * starting with the most distant one. */
+    for( offset = MBEDTLS_SSL_MAX_BUFFERED_HS - 1;
+         offset >= 0; offset-- )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Free buffering slot %d to make space for reassembly of next handshake message",
+                                    offset ) );
+
+        ssl_buffering_free_slot( ssl, (uint8_t) offset );
+
+        /* Check if we have enough space available now. */
+        if( desired <= ( MBEDTLS_SSL_DTLS_MAX_BUFFERING -
+                         hs->buffering.total_bytes_buffered ) )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "Enough space available after freeing buffered HS messages" ) );
+            return( 0 );
+        }
+    }
+
+    return( -1 );
+}
+
+static int ssl_buffer_message( mbedtls_ssl_context *ssl )
+{
+    int ret = 0;
+    mbedtls_ssl_handshake_params * const hs = ssl->handshake;
+
+    if( hs == NULL )
+        return( 0 );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> ssl_buffer_message" ) );
+
+    switch( ssl->in_msgtype )
+    {
+        case MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC:
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "Remember CCS message" ) );
+
+            hs->buffering.seen_ccs = 1;
+            break;
+
+        case MBEDTLS_SSL_MSG_HANDSHAKE:
+        {
+            unsigned recv_msg_seq_offset;
+            unsigned recv_msg_seq = ( ssl->in_msg[4] << 8 ) | ssl->in_msg[5];
+            mbedtls_ssl_hs_buffer *hs_buf;
+            size_t msg_len = ssl->in_hslen - 12;
+
+            /* We should never receive an old handshake
+             * message - double-check nonetheless. */
+            if( recv_msg_seq < ssl->handshake->in_msg_seq )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+                return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+            }
+
+            recv_msg_seq_offset = recv_msg_seq - ssl->handshake->in_msg_seq;
+            if( recv_msg_seq_offset >= MBEDTLS_SSL_MAX_BUFFERED_HS )
+            {
+                /* Silently ignore -- message too far in the future */
+                MBEDTLS_SSL_DEBUG_MSG( 2,
+                 ( "Ignore future HS message with sequence number %u, "
+                   "buffering window %u - %u",
+                   recv_msg_seq, ssl->handshake->in_msg_seq,
+                   ssl->handshake->in_msg_seq + MBEDTLS_SSL_MAX_BUFFERED_HS - 1 ) );
+
+                goto exit;
+            }
+
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "Buffering HS message with sequence number %u, offset %u ",
+                                        recv_msg_seq, recv_msg_seq_offset ) );
+
+            hs_buf = &hs->buffering.hs[ recv_msg_seq_offset ];
+
+            /* Check if the buffering for this seq nr has already commenced. */
+            if( !hs_buf->is_valid )
+            {
+                size_t reassembly_buf_sz;
+
+                hs_buf->is_fragmented =
+                    ( ssl_hs_is_proper_fragment( ssl ) == 1 );
+
+                /* We copy the message back into the input buffer
+                 * after reassembly, so check that it's not too large.
+                 * This is an implementation-specific limitation
+                 * and not one from the standard, hence it is not
+                 * checked in ssl_check_hs_header(). */
+                if( msg_len + 12 > MBEDTLS_SSL_IN_CONTENT_LEN )
+                {
+                    /* Ignore message */
+                    goto exit;
+                }
+
+                /* Check if we have enough space to buffer the message. */
+                if( hs->buffering.total_bytes_buffered >
+                    MBEDTLS_SSL_DTLS_MAX_BUFFERING )
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+                    return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+                }
+
+                reassembly_buf_sz = ssl_get_reassembly_buffer_size( msg_len,
+                                                       hs_buf->is_fragmented );
+
+                if( reassembly_buf_sz > ( MBEDTLS_SSL_DTLS_MAX_BUFFERING -
+                                          hs->buffering.total_bytes_buffered ) )
+                {
+                    if( recv_msg_seq_offset > 0 )
+                    {
+                        /* If we can't buffer a future message because
+                         * of space limitations -- ignore. */
+                        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Buffering of future message of size %" MBEDTLS_PRINTF_SIZET
+                                                    " would exceed the compile-time limit %" MBEDTLS_PRINTF_SIZET
+                                                    " (already %" MBEDTLS_PRINTF_SIZET
+                                                    " bytes buffered) -- ignore\n",
+                             msg_len, (size_t) MBEDTLS_SSL_DTLS_MAX_BUFFERING,
+                             hs->buffering.total_bytes_buffered ) );
+                        goto exit;
+                    }
+                    else
+                    {
+                        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Buffering of future message of size %" MBEDTLS_PRINTF_SIZET
+                                                    " would exceed the compile-time limit %" MBEDTLS_PRINTF_SIZET
+                                                    " (already %" MBEDTLS_PRINTF_SIZET
+                                                    " bytes buffered) -- attempt to make space by freeing buffered future messages\n",
+                             msg_len, (size_t) MBEDTLS_SSL_DTLS_MAX_BUFFERING,
+                             hs->buffering.total_bytes_buffered ) );
+                    }
+
+                    if( ssl_buffer_make_space( ssl, reassembly_buf_sz ) != 0 )
+                    {
+                        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Reassembly of next message of size %" MBEDTLS_PRINTF_SIZET
+                                                    " (%" MBEDTLS_PRINTF_SIZET " with bitmap) would exceed"
+                                                    " the compile-time limit %" MBEDTLS_PRINTF_SIZET
+                                                    " (already %" MBEDTLS_PRINTF_SIZET
+                                                    " bytes buffered) -- fail\n",
+                             msg_len,
+                             reassembly_buf_sz,
+                             (size_t) MBEDTLS_SSL_DTLS_MAX_BUFFERING,
+                             hs->buffering.total_bytes_buffered ) );
+                        ret = MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;
+                        goto exit;
+                    }
+                }
+
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "initialize reassembly, total length = %" MBEDTLS_PRINTF_SIZET,
+                                            msg_len ) );
+
+                hs_buf->data = mbedtls_calloc( 1, reassembly_buf_sz );
+                if( hs_buf->data == NULL )
+                {
+                    ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
+                    goto exit;
+                }
+                hs_buf->data_len = reassembly_buf_sz;
+
+                /* Prepare final header: copy msg_type, length and message_seq,
+                 * then add standardised fragment_offset and fragment_length */
+                memcpy( hs_buf->data, ssl->in_msg, 6 );
+                memset( hs_buf->data + 6, 0, 3 );
+                memcpy( hs_buf->data + 9, hs_buf->data + 1, 3 );
+
+                hs_buf->is_valid = 1;
+
+                hs->buffering.total_bytes_buffered += reassembly_buf_sz;
+            }
+            else
+            {
+                /* Make sure msg_type and length are consistent */
+                if( memcmp( hs_buf->data, ssl->in_msg, 4 ) != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "Fragment header mismatch - ignore" ) );
+                    /* Ignore */
+                    goto exit;
+                }
+            }
+
+            if( !hs_buf->is_complete )
+            {
+                size_t frag_len, frag_off;
+                unsigned char * const msg = hs_buf->data + 12;
+
+                /*
+                 * Check and copy current fragment
+                 */
+
+                /* Validation of header fields already done in
+                 * mbedtls_ssl_prepare_handshake_record(). */
+                frag_off = ssl_get_hs_frag_off( ssl );
+                frag_len = ssl_get_hs_frag_len( ssl );
+
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "adding fragment, offset = %" MBEDTLS_PRINTF_SIZET
+                                            ", length = %" MBEDTLS_PRINTF_SIZET,
+                                            frag_off, frag_len ) );
+                memcpy( msg + frag_off, ssl->in_msg + 12, frag_len );
+
+                if( hs_buf->is_fragmented )
+                {
+                    unsigned char * const bitmask = msg + msg_len;
+                    ssl_bitmask_set( bitmask, frag_off, frag_len );
+                    hs_buf->is_complete = ( ssl_bitmask_check( bitmask,
+                                                               msg_len ) == 0 );
+                }
+                else
+                {
+                    hs_buf->is_complete = 1;
+                }
+
+                MBEDTLS_SSL_DEBUG_MSG( 2, ( "message %scomplete",
+                                   hs_buf->is_complete ? "" : "not yet " ) );
+            }
+
+            break;
+        }
+
+        default:
+            /* We don't buffer other types of messages. */
+            break;
+    }
+
+exit:
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= ssl_buffer_message" ) );
+    return( ret );
+}
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+static int ssl_consume_current_message( mbedtls_ssl_context *ssl )
+{
+    /*
+     * Consume last content-layer message and potentially
+     * update in_msglen which keeps track of the contents'
+     * consumption state.
+     *
+     * (1) Handshake messages:
+     *     Remove last handshake message, move content
+     *     and adapt in_msglen.
+     *
+     * (2) Alert messages:
+     *     Consume whole record content, in_msglen = 0.
+     *
+     * (3) Change cipher spec:
+     *     Consume whole record content, in_msglen = 0.
+     *
+     * (4) Application data:
+     *     Don't do anything - the record layer provides
+     *     the application data as a stream transport
+     *     and consumes through mbedtls_ssl_read only.
+     *
+     */
+
+    /* Case (1): Handshake messages */
+    if( ssl->in_hslen != 0 )
+    {
+        /* Hard assertion to be sure that no application data
+         * is in flight, as corrupting ssl->in_msglen during
+         * ssl->in_offt != NULL is fatal. */
+        if( ssl->in_offt != NULL )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+        }
+
+        /*
+         * Get next Handshake message in the current record
+         */
+
+        /* Notes:
+         * (1) in_hslen is not necessarily the size of the
+         *     current handshake content: If DTLS handshake
+         *     fragmentation is used, that's the fragment
+         *     size instead. Using the total handshake message
+         *     size here is faulty and should be changed at
+         *     some point.
+         * (2) While it doesn't seem to cause problems, one
+         *     has to be very careful not to assume that in_hslen
+         *     is always <= in_msglen in a sensible communication.
+         *     Again, it's wrong for DTLS handshake fragmentation.
+         *     The following check is therefore mandatory, and
+         *     should not be treated as a silently corrected assertion.
+         *     Additionally, ssl->in_hslen might be arbitrarily out of
+         *     bounds after handling a DTLS message with an unexpected
+         *     sequence number, see mbedtls_ssl_prepare_handshake_record.
+         */
+        if( ssl->in_hslen < ssl->in_msglen )
+        {
+            ssl->in_msglen -= ssl->in_hslen;
+            memmove( ssl->in_msg, ssl->in_msg + ssl->in_hslen,
+                     ssl->in_msglen );
+
+            MBEDTLS_SSL_DEBUG_BUF( 4, "remaining content in record",
+                                   ssl->in_msg, ssl->in_msglen );
+        }
+        else
+        {
+            ssl->in_msglen = 0;
+        }
+
+        ssl->in_hslen   = 0;
+    }
+    /* Case (4): Application data */
+    else if( ssl->in_offt != NULL )
+    {
+        return( 0 );
+    }
+    /* Everything else (CCS & Alerts) */
+    else
+    {
+        ssl->in_msglen = 0;
+    }
+
+    return( 0 );
+}
+
+static int ssl_record_is_in_progress( mbedtls_ssl_context *ssl )
+{
+    if( ssl->in_msglen > 0 )
+        return( 1 );
+
+    return( 0 );
+}
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+
+static void ssl_free_buffered_record( mbedtls_ssl_context *ssl )
+{
+    mbedtls_ssl_handshake_params * const hs = ssl->handshake;
+    if( hs == NULL )
+        return;
+
+    if( hs->buffering.future_record.data != NULL )
+    {
+        hs->buffering.total_bytes_buffered -=
+            hs->buffering.future_record.len;
+
+        mbedtls_free( hs->buffering.future_record.data );
+        hs->buffering.future_record.data = NULL;
+    }
+}
+
+static int ssl_load_buffered_record( mbedtls_ssl_context *ssl )
+{
+    mbedtls_ssl_handshake_params * const hs = ssl->handshake;
+    unsigned char * rec;
+    size_t rec_len;
+    unsigned rec_epoch;
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len = ssl->in_buf_len;
+#else
+    size_t in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+#endif
+    if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+        return( 0 );
+
+    if( hs == NULL )
+        return( 0 );
+
+    rec       = hs->buffering.future_record.data;
+    rec_len   = hs->buffering.future_record.len;
+    rec_epoch = hs->buffering.future_record.epoch;
+
+    if( rec == NULL )
+        return( 0 );
+
+    /* Only consider loading future records if the
+     * input buffer is empty. */
+    if( ssl_next_record_is_in_datagram( ssl ) == 1 )
+        return( 0 );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> ssl_load_buffered_record" ) );
+
+    if( rec_epoch != ssl->in_epoch )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Buffered record not from current epoch." ) );
+        goto exit;
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "Found buffered record from current epoch - load" ) );
+
+    /* Double-check that the record is not too large */
+    if( rec_len > in_buf_len - (size_t)( ssl->in_hdr - ssl->in_buf ) )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+    memcpy( ssl->in_hdr, rec, rec_len );
+    ssl->in_left = rec_len;
+    ssl->next_record_offset = 0;
+
+    ssl_free_buffered_record( ssl );
+
+exit:
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= ssl_load_buffered_record" ) );
+    return( 0 );
+}
+
+static int ssl_buffer_future_record( mbedtls_ssl_context *ssl,
+                                     mbedtls_record const *rec )
+{
+    mbedtls_ssl_handshake_params * const hs = ssl->handshake;
+
+    /* Don't buffer future records outside handshakes. */
+    if( hs == NULL )
+        return( 0 );
+
+    /* Only buffer handshake records (we are only interested
+     * in Finished messages). */
+    if( rec->type != MBEDTLS_SSL_MSG_HANDSHAKE )
+        return( 0 );
+
+    /* Don't buffer more than one future epoch record. */
+    if( hs->buffering.future_record.data != NULL )
+        return( 0 );
+
+    /* Don't buffer record if there's not enough buffering space remaining. */
+    if( rec->buf_len > ( MBEDTLS_SSL_DTLS_MAX_BUFFERING -
+                         hs->buffering.total_bytes_buffered ) )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "Buffering of future epoch record of size %" MBEDTLS_PRINTF_SIZET
+                                    " would exceed the compile-time limit %" MBEDTLS_PRINTF_SIZET
+                                    " (already %" MBEDTLS_PRINTF_SIZET
+                                    " bytes buffered) -- ignore\n",
+                        rec->buf_len, (size_t) MBEDTLS_SSL_DTLS_MAX_BUFFERING,
+                        hs->buffering.total_bytes_buffered ) );
+        return( 0 );
+    }
+
+    /* Buffer record */
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "Buffer record from epoch %u",
+                                ssl->in_epoch + 1U ) );
+    MBEDTLS_SSL_DEBUG_BUF( 3, "Buffered record", rec->buf, rec->buf_len );
+
+    /* ssl_parse_record_header() only considers records
+     * of the next epoch as candidates for buffering. */
+    hs->buffering.future_record.epoch = ssl->in_epoch + 1;
+    hs->buffering.future_record.len   = rec->buf_len;
+
+    hs->buffering.future_record.data =
+        mbedtls_calloc( 1, hs->buffering.future_record.len );
+    if( hs->buffering.future_record.data == NULL )
+    {
+        /* If we run out of RAM trying to buffer a
+         * record from the next epoch, just ignore. */
+        return( 0 );
+    }
+
+    memcpy( hs->buffering.future_record.data, rec->buf, rec->buf_len );
+
+    hs->buffering.total_bytes_buffered += rec->buf_len;
+    return( 0 );
+}
+
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+static int ssl_get_next_record( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    mbedtls_record rec;
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    /* We might have buffered a future record; if so,
+     * and if the epoch matches now, load it.
+     * On success, this call will set ssl->in_left to
+     * the length of the buffered record, so that
+     * the calls to ssl_fetch_input() below will
+     * essentially be no-ops. */
+    ret = ssl_load_buffered_record( ssl );
+    if( ret != 0 )
+        return( ret );
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+    /* Ensure that we have enough space available for the default form
+     * of TLS / DTLS record headers (5 Bytes for TLS, 13 Bytes for DTLS,
+     * with no space for CIDs counted in). */
+    ret = mbedtls_ssl_fetch_input( ssl, mbedtls_ssl_in_hdr_len( ssl ) );
+    if( ret != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_fetch_input", ret );
+        return( ret );
+    }
+
+    ret = ssl_parse_record_header( ssl, ssl->in_hdr, ssl->in_left, &rec );
+    if( ret != 0 )
+    {
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+        if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+        {
+            if( ret == MBEDTLS_ERR_SSL_EARLY_MESSAGE )
+            {
+                ret = ssl_buffer_future_record( ssl, &rec );
+                if( ret != 0 )
+                    return( ret );
+
+                /* Fall through to handling of unexpected records */
+                ret = MBEDTLS_ERR_SSL_UNEXPECTED_RECORD;
+            }
+
+            if( ret == MBEDTLS_ERR_SSL_UNEXPECTED_RECORD )
+            {
+#if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) && defined(MBEDTLS_SSL_SRV_C)
+                /* Reset in pointers to default state for TLS/DTLS records,
+                 * assuming no CID and no offset between record content and
+                 * record plaintext. */
+                mbedtls_ssl_update_in_pointers( ssl );
+
+                /* Setup internal message pointers from record structure. */
+                ssl->in_msgtype = rec.type;
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+                ssl->in_len = ssl->in_cid + rec.cid_len;
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+                ssl->in_iv  = ssl->in_msg = ssl->in_len + 2;
+                ssl->in_msglen = rec.data_len;
+
+                ret = ssl_check_client_reconnect( ssl );
+                MBEDTLS_SSL_DEBUG_RET( 2, "ssl_check_client_reconnect", ret );
+                if( ret != 0 )
+                    return( ret );
+#endif
+
+                /* Skip unexpected record (but not whole datagram) */
+                ssl->next_record_offset = rec.buf_len;
+
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "discarding unexpected record "
+                                            "(header)" ) );
+            }
+            else
+            {
+                /* Skip invalid record and the rest of the datagram */
+                ssl->next_record_offset = 0;
+                ssl->in_left = 0;
+
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "discarding invalid record "
+                                            "(header)" ) );
+            }
+
+            /* Get next record */
+            return( MBEDTLS_ERR_SSL_CONTINUE_PROCESSING );
+        }
+        else
+#endif
+        {
+            return( ret );
+        }
+    }
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        /* Remember offset of next record within datagram. */
+        ssl->next_record_offset = rec.buf_len;
+        if( ssl->next_record_offset < ssl->in_left )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 3, ( "more than one record within datagram" ) );
+        }
+    }
+    else
+#endif
+    {
+        /*
+         * Fetch record contents from underlying transport.
+         */
+        ret = mbedtls_ssl_fetch_input( ssl, rec.buf_len );
+        if( ret != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_fetch_input", ret );
+            return( ret );
+        }
+
+        ssl->in_left = 0;
+    }
+
+    /*
+     * Decrypt record contents.
+     */
+
+    if( ( ret = ssl_prepare_record_content( ssl, &rec ) ) != 0 )
+    {
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+        if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+        {
+            /* Silently discard invalid records */
+            if( ret == MBEDTLS_ERR_SSL_INVALID_MAC )
+            {
+                /* Except when waiting for Finished as a bad mac here
+                 * probably means something went wrong in the handshake
+                 * (eg wrong psk used, mitm downgrade attempt, etc.) */
+                if( ssl->state == MBEDTLS_SSL_CLIENT_FINISHED ||
+                    ssl->state == MBEDTLS_SSL_SERVER_FINISHED )
+                {
+#if defined(MBEDTLS_SSL_ALL_ALERT_MESSAGES)
+                    if( ret == MBEDTLS_ERR_SSL_INVALID_MAC )
+                    {
+                        mbedtls_ssl_send_alert_message( ssl,
+                                MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                                MBEDTLS_SSL_ALERT_MSG_BAD_RECORD_MAC );
+                    }
+#endif
+                    return( ret );
+                }
+
+#if defined(MBEDTLS_SSL_DTLS_BADMAC_LIMIT)
+                if( ssl->conf->badmac_limit != 0 &&
+                    ++ssl->badmac_seen >= ssl->conf->badmac_limit )
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "too many records with bad MAC" ) );
+                    return( MBEDTLS_ERR_SSL_INVALID_MAC );
+                }
+#endif
+
+                /* As above, invalid records cause
+                 * dismissal of the whole datagram. */
+
+                ssl->next_record_offset = 0;
+                ssl->in_left = 0;
+
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "discarding invalid record (mac)" ) );
+                return( MBEDTLS_ERR_SSL_CONTINUE_PROCESSING );
+            }
+
+            return( ret );
+        }
+        else
+#endif
+        {
+            /* Error out (and send alert) on invalid records */
+#if defined(MBEDTLS_SSL_ALL_ALERT_MESSAGES)
+            if( ret == MBEDTLS_ERR_SSL_INVALID_MAC )
+            {
+                mbedtls_ssl_send_alert_message( ssl,
+                        MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                        MBEDTLS_SSL_ALERT_MSG_BAD_RECORD_MAC );
+            }
+#endif
+            return( ret );
+        }
+    }
+
+
+    /* Reset in pointers to default state for TLS/DTLS records,
+     * assuming no CID and no offset between record content and
+     * record plaintext. */
+    mbedtls_ssl_update_in_pointers( ssl );
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    ssl->in_len = ssl->in_cid + rec.cid_len;
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+    ssl->in_iv  = ssl->in_len + 2;
+
+    /* The record content type may change during decryption,
+     * so re-read it. */
+    ssl->in_msgtype = rec.type;
+    /* Also update the input buffer, because unfortunately
+     * the server-side ssl_parse_client_hello() reparses the
+     * record header when receiving a ClientHello initiating
+     * a renegotiation. */
+    ssl->in_hdr[0] = rec.type;
+    ssl->in_msg    = rec.buf + rec.data_offset;
+    ssl->in_msglen = rec.data_len;
+    ssl->in_len[0] = (unsigned char)( rec.data_len >> 8 );
+    ssl->in_len[1] = (unsigned char)( rec.data_len      );
+
+#if defined(MBEDTLS_ZLIB_SUPPORT)
+    if( ssl->transform_in != NULL &&
+        ssl->session_in->compression == MBEDTLS_SSL_COMPRESS_DEFLATE )
+    {
+        if( ( ret = ssl_decompress_buf( ssl ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "ssl_decompress_buf", ret );
+            return( ret );
+        }
+
+        /* Check actual (decompress) record content length against
+         * configured maximum. */
+        if( ssl->in_msglen > MBEDTLS_SSL_IN_CONTENT_LEN )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+    }
+#endif /* MBEDTLS_ZLIB_SUPPORT */
+
+    return( 0 );
+}
+
+int mbedtls_ssl_handle_message_type( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    /*
+     * Handle particular types of records
+     */
+    if( ssl->in_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE )
+    {
+        if( ( ret = mbedtls_ssl_prepare_handshake_record( ssl ) ) != 0 )
+        {
+            return( ret );
+        }
+    }
+
+    if( ssl->in_msgtype == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC )
+    {
+        if( ssl->in_msglen != 1 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid CCS message, len: %" MBEDTLS_PRINTF_SIZET,
+                           ssl->in_msglen ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+
+        if( ssl->in_msg[0] != 1 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid CCS message, content: %02x",
+                                        ssl->in_msg[0] ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+        if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+            ssl->state != MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC    &&
+            ssl->state != MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC )
+        {
+            if( ssl->handshake == NULL )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping ChangeCipherSpec outside handshake" ) );
+                return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
+            }
+
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "received out-of-order ChangeCipherSpec - remember" ) );
+            return( MBEDTLS_ERR_SSL_EARLY_MESSAGE );
+        }
+#endif
+    }
+
+    if( ssl->in_msgtype == MBEDTLS_SSL_MSG_ALERT )
+    {
+        if( ssl->in_msglen != 2 )
+        {
+            /* Note: Standard allows for more than one 2 byte alert
+               to be packed in a single message, but Mbed TLS doesn't
+               currently support this. */
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid alert message, len: %" MBEDTLS_PRINTF_SIZET,
+                           ssl->in_msglen ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "got an alert message, type: [%u:%u]",
+                       ssl->in_msg[0], ssl->in_msg[1] ) );
+
+        /*
+         * Ignore non-fatal alerts, except close_notify and no_renegotiation
+         */
+        if( ssl->in_msg[0] == MBEDTLS_SSL_ALERT_LEVEL_FATAL )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "is a fatal alert message (msg %d)",
+                           ssl->in_msg[1] ) );
+            return( MBEDTLS_ERR_SSL_FATAL_ALERT_MESSAGE );
+        }
+
+        if( ssl->in_msg[0] == MBEDTLS_SSL_ALERT_LEVEL_WARNING &&
+            ssl->in_msg[1] == MBEDTLS_SSL_ALERT_MSG_CLOSE_NOTIFY )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "is a close notify message" ) );
+            return( MBEDTLS_ERR_SSL_PEER_CLOSE_NOTIFY );
+        }
+
+#if defined(MBEDTLS_SSL_RENEGOTIATION_ENABLED)
+        if( ssl->in_msg[0] == MBEDTLS_SSL_ALERT_LEVEL_WARNING &&
+            ssl->in_msg[1] == MBEDTLS_SSL_ALERT_MSG_NO_RENEGOTIATION )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "is a SSLv3 no renegotiation alert" ) );
+            /* Will be handled when trying to parse ServerHello */
+            return( 0 );
+        }
+#endif
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3) && defined(MBEDTLS_SSL_SRV_C)
+        if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 &&
+            ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER &&
+            ssl->in_msg[0] == MBEDTLS_SSL_ALERT_LEVEL_WARNING &&
+            ssl->in_msg[1] == MBEDTLS_SSL_ALERT_MSG_NO_CERT )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "is a SSLv3 no_cert" ) );
+            /* Will be handled in mbedtls_ssl_parse_certificate() */
+            return( 0 );
+        }
+#endif /* MBEDTLS_SSL_PROTO_SSL3 && MBEDTLS_SSL_SRV_C */
+
+        /* Silently ignore: fetch new message */
+        return MBEDTLS_ERR_SSL_NON_FATAL;
+    }
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        /* Drop unexpected ApplicationData records,
+         * except at the beginning of renegotiations */
+        if( ssl->in_msgtype == MBEDTLS_SSL_MSG_APPLICATION_DATA &&
+            ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
+            && ! ( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS &&
+                   ssl->state == MBEDTLS_SSL_SERVER_HELLO )
+#endif
+            )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping unexpected ApplicationData" ) );
+            return( MBEDTLS_ERR_SSL_NON_FATAL );
+        }
+
+        if( ssl->handshake != NULL &&
+            ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER  )
+        {
+            mbedtls_ssl_handshake_wrapup_free_hs_transform( ssl );
+        }
+    }
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+    return( 0 );
+}
+
+int mbedtls_ssl_send_fatal_handshake_failure( mbedtls_ssl_context *ssl )
+{
+    return( mbedtls_ssl_send_alert_message( ssl,
+                  MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                  MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE ) );
+}
+
+int mbedtls_ssl_send_alert_message( mbedtls_ssl_context *ssl,
+                            unsigned char level,
+                            unsigned char message )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> send alert message" ) );
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "send alert level=%u message=%u", level, message ));
+
+    ssl->out_msgtype = MBEDTLS_SSL_MSG_ALERT;
+    ssl->out_msglen = 2;
+    ssl->out_msg[0] = level;
+    ssl->out_msg[1] = message;
+
+    if( ( ret = mbedtls_ssl_write_record( ssl, SSL_FORCE_FLUSH ) ) != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret );
+        return( ret );
+    }
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= send alert message" ) );
+
+    return( 0 );
+}
+
+int mbedtls_ssl_write_change_cipher_spec( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write change cipher spec" ) );
+
+    ssl->out_msgtype = MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC;
+    ssl->out_msglen  = 1;
+    ssl->out_msg[0]  = 1;
+
+    ssl->state++;
+
+    if( ( ret = mbedtls_ssl_write_handshake_msg( ssl ) ) != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_handshake_msg", ret );
+        return( ret );
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write change cipher spec" ) );
+
+    return( 0 );
+}
+
+int mbedtls_ssl_parse_change_cipher_spec( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse change cipher spec" ) );
+
+    if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
+        return( ret );
+    }
+
+    if( ssl->in_msgtype != MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad change cipher spec message" ) );
+        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                                        MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
+        return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
+    }
+
+    /* CCS records are only accepted if they have length 1 and content '1',
+     * so we don't need to check this here. */
+
+    /*
+     * Switch to our negotiated transform and session parameters for inbound
+     * data.
+     */
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "switching to new transform spec for inbound data" ) );
+    ssl->transform_in = ssl->transform_negotiate;
+    ssl->session_in = ssl->session_negotiate;
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
+        mbedtls_ssl_dtls_replay_reset( ssl );
+#endif
+
+        /* Increment epoch */
+        if( ++ssl->in_epoch == 0 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "DTLS epoch would wrap" ) );
+            /* This is highly unlikely to happen for legitimate reasons, so
+               treat it as an attack and don't send an alert. */
+            return( MBEDTLS_ERR_SSL_COUNTER_WRAPPING );
+        }
+    }
+    else
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+    memset( ssl->in_ctr, 0, 8 );
+
+    mbedtls_ssl_update_in_pointers( ssl );
+
+#if defined(MBEDTLS_SSL_HW_RECORD_ACCEL)
+    if( mbedtls_ssl_hw_record_activate != NULL )
+    {
+        if( ( ret = mbedtls_ssl_hw_record_activate( ssl, MBEDTLS_SSL_CHANNEL_INBOUND ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_hw_record_activate", ret );
+            mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                                            MBEDTLS_SSL_ALERT_MSG_INTERNAL_ERROR );
+            return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
+        }
+    }
+#endif
+
+    ssl->state++;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse change cipher spec" ) );
+
+    return( 0 );
+}
+
+/* Once ssl->out_hdr as the address of the beginning of the
+ * next outgoing record is set, deduce the other pointers.
+ *
+ * Note: For TLS, we save the implicit record sequence number
+ *       (entering MAC computation) in the 8 bytes before ssl->out_hdr,
+ *       and the caller has to make sure there's space for this.
+ */
+
+static size_t ssl_transform_get_explicit_iv_len(
+                        mbedtls_ssl_transform const *transform )
+{
+    if( transform->minor_ver < MBEDTLS_SSL_MINOR_VERSION_2 )
+        return( 0 );
+
+    return( transform->ivlen - transform->fixed_ivlen );
+}
+
+void mbedtls_ssl_update_out_pointers( mbedtls_ssl_context *ssl,
+                                      mbedtls_ssl_transform *transform )
+{
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        ssl->out_ctr = ssl->out_hdr +  3;
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+        ssl->out_cid = ssl->out_ctr +  8;
+        ssl->out_len = ssl->out_cid;
+        if( transform != NULL )
+            ssl->out_len += transform->out_cid_len;
+#else /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+        ssl->out_len = ssl->out_ctr + 8;
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+        ssl->out_iv  = ssl->out_len + 2;
+    }
+    else
+#endif
+    {
+        ssl->out_ctr = ssl->out_hdr - 8;
+        ssl->out_len = ssl->out_hdr + 3;
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+        ssl->out_cid = ssl->out_len;
+#endif
+        ssl->out_iv  = ssl->out_hdr + 5;
+    }
+
+    ssl->out_msg = ssl->out_iv;
+    /* Adjust out_msg to make space for explicit IV, if used. */
+    if( transform != NULL )
+        ssl->out_msg += ssl_transform_get_explicit_iv_len( transform );
+}
+
+/* Once ssl->in_hdr as the address of the beginning of the
+ * next incoming record is set, deduce the other pointers.
+ *
+ * Note: For TLS, we save the implicit record sequence number
+ *       (entering MAC computation) in the 8 bytes before ssl->in_hdr,
+ *       and the caller has to make sure there's space for this.
+ */
+
+void mbedtls_ssl_update_in_pointers( mbedtls_ssl_context *ssl )
+{
+    /* This function sets the pointers to match the case
+     * of unprotected TLS/DTLS records, with both  ssl->in_iv
+     * and ssl->in_msg pointing to the beginning of the record
+     * content.
+     *
+     * When decrypting a protected record, ssl->in_msg
+     * will be shifted to point to the beginning of the
+     * record plaintext.
+     */
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        /* This sets the header pointers to match records
+         * without CID. When we receive a record containing
+         * a CID, the fields are shifted accordingly in
+         * ssl_parse_record_header(). */
+        ssl->in_ctr = ssl->in_hdr +  3;
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+        ssl->in_cid = ssl->in_ctr +  8;
+        ssl->in_len = ssl->in_cid; /* Default: no CID */
+#else /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+        ssl->in_len = ssl->in_ctr + 8;
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+        ssl->in_iv  = ssl->in_len + 2;
+    }
+    else
+#endif
+    {
+        ssl->in_ctr = ssl->in_hdr - 8;
+        ssl->in_len = ssl->in_hdr + 3;
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+        ssl->in_cid = ssl->in_len;
+#endif
+        ssl->in_iv  = ssl->in_hdr + 5;
+    }
+
+    /* This will be adjusted at record decryption time. */
+    ssl->in_msg = ssl->in_iv;
+}
+
+/*
+ * Setup an SSL context
+ */
+
+void mbedtls_ssl_reset_in_out_pointers( mbedtls_ssl_context *ssl )
+{
+    /* Set the incoming and outgoing record pointers. */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        ssl->out_hdr = ssl->out_buf;
+        ssl->in_hdr  = ssl->in_buf;
+    }
+    else
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+    {
+        ssl->out_hdr = ssl->out_buf + 8;
+        ssl->in_hdr  = ssl->in_buf  + 8;
+    }
+
+    /* Derive other internal pointers. */
+    mbedtls_ssl_update_out_pointers( ssl, NULL /* no transform enabled */ );
+    mbedtls_ssl_update_in_pointers ( ssl );
+}
+
+/*
+ * SSL get accessors
+ */
+size_t mbedtls_ssl_get_bytes_avail( const mbedtls_ssl_context *ssl )
+{
+    return( ssl->in_offt == NULL ? 0 : ssl->in_msglen );
+}
+
+int mbedtls_ssl_check_pending( const mbedtls_ssl_context *ssl )
+{
+    /*
+     * Case A: We're currently holding back
+     * a message for further processing.
+     */
+
+    if( ssl->keep_current_message == 1 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "ssl_check_pending: record held back for processing" ) );
+        return( 1 );
+    }
+
+    /*
+     * Case B: Further records are pending in the current datagram.
+     */
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+        ssl->in_left > ssl->next_record_offset )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "ssl_check_pending: more records within current datagram" ) );
+        return( 1 );
+    }
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+    /*
+     * Case C: A handshake message is being processed.
+     */
+
+    if( ssl->in_hslen > 0 && ssl->in_hslen < ssl->in_msglen )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "ssl_check_pending: more handshake messages within current record" ) );
+        return( 1 );
+    }
+
+    /*
+     * Case D: An application data message is being processed
+     */
+    if( ssl->in_offt != NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "ssl_check_pending: application data record is being processed" ) );
+        return( 1 );
+    }
+
+    /*
+     * In all other cases, the rest of the message can be dropped.
+     * As in ssl_get_next_record, this needs to be adapted if
+     * we implement support for multiple alerts in single records.
+     */
+
+    MBEDTLS_SSL_DEBUG_MSG( 3, ( "ssl_check_pending: nothing pending" ) );
+    return( 0 );
+}
+
+
+int mbedtls_ssl_get_record_expansion( const mbedtls_ssl_context *ssl )
+{
+    size_t transform_expansion = 0;
+    const mbedtls_ssl_transform *transform = ssl->transform_out;
+    unsigned block_size;
+
+    size_t out_hdr_len = mbedtls_ssl_out_hdr_len( ssl );
+
+    if( transform == NULL )
+        return( (int) out_hdr_len );
+
+#if defined(MBEDTLS_ZLIB_SUPPORT)
+    if( ssl->session_out->compression != MBEDTLS_SSL_COMPRESS_NULL )
+        return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
+#endif
+
+    switch( mbedtls_cipher_get_cipher_mode( &transform->cipher_ctx_enc ) )
+    {
+        case MBEDTLS_MODE_GCM:
+        case MBEDTLS_MODE_CCM:
+        case MBEDTLS_MODE_CHACHAPOLY:
+        case MBEDTLS_MODE_STREAM:
+            transform_expansion = transform->minlen;
+            break;
+
+        case MBEDTLS_MODE_CBC:
+
+            block_size = mbedtls_cipher_get_block_size(
+                &transform->cipher_ctx_enc );
+
+            /* Expansion due to the addition of the MAC. */
+            transform_expansion += transform->maclen;
+
+            /* Expansion due to the addition of CBC padding;
+             * Theoretically up to 256 bytes, but we never use
+             * more than the block size of the underlying cipher. */
+            transform_expansion += block_size;
+
+            /* For TLS 1.1 or higher, an explicit IV is added
+             * after the record header. */
+#if defined(MBEDTLS_SSL_PROTO_TLS1_1) || defined(MBEDTLS_SSL_PROTO_TLS1_2)
+            if( ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 )
+                transform_expansion += block_size;
+#endif /* MBEDTLS_SSL_PROTO_TLS1_1 || MBEDTLS_SSL_PROTO_TLS1_2 */
+
+            break;
+
+        default:
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+            return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    if( transform->out_cid_len != 0 )
+        transform_expansion += MBEDTLS_SSL_MAX_CID_EXPANSION;
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+    return( (int)( out_hdr_len + transform_expansion ) );
+}
+
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
+/*
+ * Check record counters and renegotiate if they're above the limit.
+ */
+static int ssl_check_ctr_renegotiate( mbedtls_ssl_context *ssl )
+{
+    size_t ep_len = mbedtls_ssl_ep_len( ssl );
+    int in_ctr_cmp;
+    int out_ctr_cmp;
+
+    if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER ||
+        ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_PENDING ||
+        ssl->conf->disable_renegotiation == MBEDTLS_SSL_RENEGOTIATION_DISABLED )
+    {
+        return( 0 );
+    }
+
+    in_ctr_cmp = memcmp( ssl->in_ctr + ep_len,
+                        ssl->conf->renego_period + ep_len, 8 - ep_len );
+    out_ctr_cmp = memcmp( ssl->cur_out_ctr + ep_len,
+                          ssl->conf->renego_period + ep_len, 8 - ep_len );
+
+    if( in_ctr_cmp <= 0 && out_ctr_cmp <= 0 )
+    {
+        return( 0 );
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 1, ( "record counter limit reached: renegotiate" ) );
+    return( mbedtls_ssl_renegotiate( ssl ) );
+}
+#endif /* MBEDTLS_SSL_RENEGOTIATION */
+
+/*
+ * Receive application data decrypted from the SSL layer
+ */
+int mbedtls_ssl_read( mbedtls_ssl_context *ssl, unsigned char *buf, size_t len )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+    size_t n;
+
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> read" ) );
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
+            return( ret );
+
+        if( ssl->handshake != NULL &&
+            ssl->handshake->retransmit_state == MBEDTLS_SSL_RETRANS_SENDING )
+        {
+            if( ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
+                return( ret );
+        }
+    }
+#endif
+
+    /*
+     * Check if renegotiation is necessary and/or handshake is
+     * in process. If yes, perform/continue, and fall through
+     * if an unexpected packet is received while the client
+     * is waiting for the ServerHello.
+     *
+     * (There is no equivalent to the last condition on
+     *  the server-side as it is not treated as within
+     *  a handshake while waiting for the ClientHello
+     *  after a renegotiation request.)
+     */
+
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
+    ret = ssl_check_ctr_renegotiate( ssl );
+    if( ret != MBEDTLS_ERR_SSL_WAITING_SERVER_HELLO_RENEGO &&
+        ret != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "ssl_check_ctr_renegotiate", ret );
+        return( ret );
+    }
+#endif
+
+    if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
+    {
+        ret = mbedtls_ssl_handshake( ssl );
+        if( ret != MBEDTLS_ERR_SSL_WAITING_SERVER_HELLO_RENEGO &&
+            ret != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_handshake", ret );
+            return( ret );
+        }
+    }
+
+    /* Loop as long as no application data record is available */
+    while( ssl->in_offt == NULL )
+    {
+        /* Start timer if not already running */
+        if( ssl->f_get_timer != NULL &&
+            ssl->f_get_timer( ssl->p_timer ) == -1 )
+        {
+            mbedtls_ssl_set_timer( ssl, ssl->conf->read_timeout );
+        }
+
+        if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
+        {
+            if( ret == MBEDTLS_ERR_SSL_CONN_EOF )
+                return( 0 );
+
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
+            return( ret );
+        }
+
+        if( ssl->in_msglen  == 0 &&
+            ssl->in_msgtype == MBEDTLS_SSL_MSG_APPLICATION_DATA )
+        {
+            /*
+             * OpenSSL sends empty messages to randomize the IV
+             */
+            if( ( ret = mbedtls_ssl_read_record( ssl, 1 ) ) != 0 )
+            {
+                if( ret == MBEDTLS_ERR_SSL_CONN_EOF )
+                    return( 0 );
+
+                MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_read_record", ret );
+                return( ret );
+            }
+        }
+
+        if( ssl->in_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "received handshake message" ) );
+
+            /*
+             * - For client-side, expect SERVER_HELLO_REQUEST.
+             * - For server-side, expect CLIENT_HELLO.
+             * - Fail (TLS) or silently drop record (DTLS) in other cases.
+             */
+
+#if defined(MBEDTLS_SSL_CLI_C)
+            if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT &&
+                ( ssl->in_msg[0] != MBEDTLS_SSL_HS_HELLO_REQUEST ||
+                  ssl->in_hslen  != mbedtls_ssl_hs_hdr_len( ssl ) ) )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "handshake received (not HelloRequest)" ) );
+
+                /* With DTLS, drop the packet (probably from last handshake) */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+                if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+                {
+                    continue;
+                }
+#endif
+                return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
+            }
+#endif /* MBEDTLS_SSL_CLI_C */
+
+#if defined(MBEDTLS_SSL_SRV_C)
+            if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER &&
+                ssl->in_msg[0] != MBEDTLS_SSL_HS_CLIENT_HELLO )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "handshake received (not ClientHello)" ) );
+
+                /* With DTLS, drop the packet (probably from last handshake) */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+                if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+                {
+                    continue;
+                }
+#endif
+                return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
+            }
+#endif /* MBEDTLS_SSL_SRV_C */
+
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
+            /* Determine whether renegotiation attempt should be accepted */
+            if( ! ( ssl->conf->disable_renegotiation == MBEDTLS_SSL_RENEGOTIATION_DISABLED ||
+                    ( ssl->secure_renegotiation == MBEDTLS_SSL_LEGACY_RENEGOTIATION &&
+                      ssl->conf->allow_legacy_renegotiation ==
+                                                   MBEDTLS_SSL_LEGACY_NO_RENEGOTIATION ) ) )
+            {
+                /*
+                 * Accept renegotiation request
+                 */
+
+                /* DTLS clients need to know renego is server-initiated */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+                if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
+                    ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
+                {
+                    ssl->renego_status = MBEDTLS_SSL_RENEGOTIATION_PENDING;
+                }
+#endif
+                ret = mbedtls_ssl_start_renegotiation( ssl );
+                if( ret != MBEDTLS_ERR_SSL_WAITING_SERVER_HELLO_RENEGO &&
+                    ret != 0 )
+                {
+                    MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_start_renegotiation",
+                                           ret );
+                    return( ret );
+                }
+            }
+            else
+#endif /* MBEDTLS_SSL_RENEGOTIATION */
+            {
+                /*
+                 * Refuse renegotiation
+                 */
+
+                MBEDTLS_SSL_DEBUG_MSG( 3, ( "refusing renegotiation, sending alert" ) );
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+                if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
+                {
+                    /* SSLv3 does not have a "no_renegotiation" warning, so
+                       we send a fatal alert and abort the connection. */
+                    mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                                                    MBEDTLS_SSL_ALERT_MSG_UNEXPECTED_MESSAGE );
+                    return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
+                }
+                else
+#endif /* MBEDTLS_SSL_PROTO_SSL3 */
+#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
+    defined(MBEDTLS_SSL_PROTO_TLS1_2)
+                if( ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_1 )
+                {
+                    if( ( ret = mbedtls_ssl_send_alert_message( ssl,
+                                    MBEDTLS_SSL_ALERT_LEVEL_WARNING,
+                                    MBEDTLS_SSL_ALERT_MSG_NO_RENEGOTIATION ) ) != 0 )
+                    {
+                        return( ret );
+                    }
+                }
+                else
+#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 ||
+          MBEDTLS_SSL_PROTO_TLS1_2 */
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+                    return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+                }
+            }
+
+            /* At this point, we don't know whether the renegotiation has been
+             * completed or not. The cases to consider are the following:
+             * 1) The renegotiation is complete. In this case, no new record
+             *    has been read yet.
+             * 2) The renegotiation is incomplete because the client received
+             *    an application data record while awaiting the ServerHello.
+             * 3) The renegotiation is incomplete because the client received
+             *    a non-handshake, non-application data message while awaiting
+             *    the ServerHello.
+             * In each of these case, looping will be the proper action:
+             * - For 1), the next iteration will read a new record and check
+             *   if it's application data.
+             * - For 2), the loop condition isn't satisfied as application data
+             *   is present, hence continue is the same as break
+             * - For 3), the loop condition is satisfied and read_record
+             *   will re-deliver the message that was held back by the client
+             *   when expecting the ServerHello.
+             */
+            continue;
+        }
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
+        else if( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_PENDING )
+        {
+            if( ssl->conf->renego_max_records >= 0 )
+            {
+                if( ++ssl->renego_records_seen > ssl->conf->renego_max_records )
+                {
+                    MBEDTLS_SSL_DEBUG_MSG( 1, ( "renegotiation requested, "
+                                        "but not honored by client" ) );
+                    return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
+                }
+            }
+        }
+#endif /* MBEDTLS_SSL_RENEGOTIATION */
+
+        /* Fatal and closure alerts handled by mbedtls_ssl_read_record() */
+        if( ssl->in_msgtype == MBEDTLS_SSL_MSG_ALERT )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "ignoring non-fatal non-closure alert" ) );
+            return( MBEDTLS_ERR_SSL_WANT_READ );
+        }
+
+        if( ssl->in_msgtype != MBEDTLS_SSL_MSG_APPLICATION_DATA )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad application data message" ) );
+            return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
+        }
+
+        ssl->in_offt = ssl->in_msg;
+
+        /* We're going to return something now, cancel timer,
+         * except if handshake (renegotiation) is in progress */
+        if( ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER )
+            mbedtls_ssl_set_timer( ssl, 0 );
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+        /* If we requested renego but received AppData, resend HelloRequest.
+         * Do it now, after setting in_offt, to avoid taking this branch
+         * again if ssl_write_hello_request() returns WANT_WRITE */
+#if defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_SSL_RENEGOTIATION)
+        if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER &&
+            ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_PENDING )
+        {
+            if( ( ret = mbedtls_ssl_resend_hello_request( ssl ) ) != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_resend_hello_request",
+                                       ret );
+                return( ret );
+            }
+        }
+#endif /* MBEDTLS_SSL_SRV_C && MBEDTLS_SSL_RENEGOTIATION */
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+    }
+
+    n = ( len < ssl->in_msglen )
+        ? len : ssl->in_msglen;
+
+    memcpy( buf, ssl->in_offt, n );
+    ssl->in_msglen -= n;
+
+    /* Zeroising the plaintext buffer to erase unused application data
+       from the memory. */
+    mbedtls_platform_zeroize( ssl->in_offt, n );
+
+    if( ssl->in_msglen == 0 )
+    {
+        /* all bytes consumed */
+        ssl->in_offt = NULL;
+        ssl->keep_current_message = 0;
+    }
+    else
+    {
+        /* more data available */
+        ssl->in_offt += n;
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= read" ) );
+
+    return( (int) n );
+}
+
+/*
+ * Send application data to be encrypted by the SSL layer, taking care of max
+ * fragment length and buffer size.
+ *
+ * According to RFC 5246 Section 6.2.1:
+ *
+ *      Zero-length fragments of Application data MAY be sent as they are
+ *      potentially useful as a traffic analysis countermeasure.
+ *
+ * Therefore, it is possible that the input message length is 0 and the
+ * corresponding return code is 0 on success.
+ */
+static int ssl_write_real( mbedtls_ssl_context *ssl,
+                           const unsigned char *buf, size_t len )
+{
+    int ret = mbedtls_ssl_get_max_out_record_payload( ssl );
+    const size_t max_len = (size_t) ret;
+
+    if( ret < 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_get_max_out_record_payload", ret );
+        return( ret );
+    }
+
+    if( len > max_len )
+    {
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+        if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "fragment larger than the (negotiated) "
+                                "maximum fragment length: %" MBEDTLS_PRINTF_SIZET
+                                " > %" MBEDTLS_PRINTF_SIZET,
+                                len, max_len ) );
+            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+        }
+        else
+#endif
+            len = max_len;
+    }
+
+    if( ssl->out_left != 0 )
+    {
+        /*
+         * The user has previously tried to send the data and
+         * MBEDTLS_ERR_SSL_WANT_WRITE or the message was only partially
+         * written. In this case, we expect the high-level write function
+         * (e.g. mbedtls_ssl_write()) to be called with the same parameters
+         */
+        if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flush_output", ret );
+            return( ret );
+        }
+    }
+    else
+    {
+        /*
+         * The user is trying to send a message the first time, so we need to
+         * copy the data into the internal buffers and setup the data structure
+         * to keep track of partial writes
+         */
+        ssl->out_msglen  = len;
+        ssl->out_msgtype = MBEDTLS_SSL_MSG_APPLICATION_DATA;
+        memcpy( ssl->out_msg, buf, len );
+
+        if( ( ret = mbedtls_ssl_write_record( ssl, SSL_FORCE_FLUSH ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret );
+            return( ret );
+        }
+    }
+
+    return( (int) len );
+}
+
+/*
+ * Write application data, doing 1/n-1 splitting if necessary.
+ *
+ * With non-blocking I/O, ssl_write_real() may return WANT_WRITE,
+ * then the caller will call us again with the same arguments, so
+ * remember whether we already did the split or not.
+ */
+#if defined(MBEDTLS_SSL_CBC_RECORD_SPLITTING)
+static int ssl_write_split( mbedtls_ssl_context *ssl,
+                            const unsigned char *buf, size_t len )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    if( ssl->conf->cbc_record_splitting ==
+            MBEDTLS_SSL_CBC_RECORD_SPLITTING_DISABLED ||
+        len <= 1 ||
+        ssl->minor_ver > MBEDTLS_SSL_MINOR_VERSION_1 ||
+        mbedtls_cipher_get_cipher_mode( &ssl->transform_out->cipher_ctx_enc )
+                                != MBEDTLS_MODE_CBC )
+    {
+        return( ssl_write_real( ssl, buf, len ) );
+    }
+
+    if( ssl->split_done == 0 )
+    {
+        if( ( ret = ssl_write_real( ssl, buf, 1 ) ) <= 0 )
+            return( ret );
+        ssl->split_done = 1;
+    }
+
+    if( ( ret = ssl_write_real( ssl, buf + 1, len - 1 ) ) <= 0 )
+        return( ret );
+    ssl->split_done = 0;
+
+    return( ret + 1 );
+}
+#endif /* MBEDTLS_SSL_CBC_RECORD_SPLITTING */
+
+/*
+ * Write application data (public-facing wrapper)
+ */
+int mbedtls_ssl_write( mbedtls_ssl_context *ssl, const unsigned char *buf, size_t len )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write" ) );
+
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
+    if( ( ret = ssl_check_ctr_renegotiate( ssl ) ) != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "ssl_check_ctr_renegotiate", ret );
+        return( ret );
+    }
+#endif
+
+    if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER )
+    {
+        if( ( ret = mbedtls_ssl_handshake( ssl ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_handshake", ret );
+            return( ret );
+        }
+    }
+
+#if defined(MBEDTLS_SSL_CBC_RECORD_SPLITTING)
+    ret = ssl_write_split( ssl, buf, len );
+#else
+    ret = ssl_write_real( ssl, buf, len );
+#endif
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write" ) );
+
+    return( ret );
+}
+
+/*
+ * Notify the peer that the connection is being closed
+ */
+int mbedtls_ssl_close_notify( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    if( ssl == NULL || ssl->conf == NULL )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write close notify" ) );
+
+    if( ssl->out_left != 0 )
+        return( mbedtls_ssl_flush_output( ssl ) );
+
+    if( ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER )
+    {
+        if( ( ret = mbedtls_ssl_send_alert_message( ssl,
+                        MBEDTLS_SSL_ALERT_LEVEL_WARNING,
+                        MBEDTLS_SSL_ALERT_MSG_CLOSE_NOTIFY ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_send_alert_message", ret );
+            return( ret );
+        }
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write close notify" ) );
+
+    return( 0 );
+}
+
+void mbedtls_ssl_transform_free( mbedtls_ssl_transform *transform )
+{
+    if( transform == NULL )
+        return;
+
+#if defined(MBEDTLS_ZLIB_SUPPORT)
+    deflateEnd( &transform->ctx_deflate );
+    inflateEnd( &transform->ctx_inflate );
+#endif
+
+    mbedtls_cipher_free( &transform->cipher_ctx_enc );
+    mbedtls_cipher_free( &transform->cipher_ctx_dec );
+
+#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
+    mbedtls_md_free( &transform->md_ctx_enc );
+    mbedtls_md_free( &transform->md_ctx_dec );
+#endif
+
+    mbedtls_platform_zeroize( transform, sizeof( mbedtls_ssl_transform ) );
+}
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+
+void mbedtls_ssl_buffering_free( mbedtls_ssl_context *ssl )
+{
+    unsigned offset;
+    mbedtls_ssl_handshake_params * const hs = ssl->handshake;
+
+    if( hs == NULL )
+        return;
+
+    ssl_free_buffered_record( ssl );
+
+    for( offset = 0; offset < MBEDTLS_SSL_MAX_BUFFERED_HS; offset++ )
+        ssl_buffering_free_slot( ssl, offset );
+}
+
+static void ssl_buffering_free_slot( mbedtls_ssl_context *ssl,
+                                     uint8_t slot )
+{
+    mbedtls_ssl_handshake_params * const hs = ssl->handshake;
+    mbedtls_ssl_hs_buffer * const hs_buf = &hs->buffering.hs[slot];
+
+    if( slot >= MBEDTLS_SSL_MAX_BUFFERED_HS )
+        return;
+
+    if( hs_buf->is_valid == 1 )
+    {
+        hs->buffering.total_bytes_buffered -= hs_buf->data_len;
+        mbedtls_platform_zeroize( hs_buf->data, hs_buf->data_len );
+        mbedtls_free( hs_buf->data );
+        memset( hs_buf, 0, sizeof( mbedtls_ssl_hs_buffer ) );
+    }
+}
+
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+/*
+ * Convert version numbers to/from wire format
+ * and, for DTLS, to/from TLS equivalent.
+ *
+ * For TLS this is the identity.
+ * For DTLS, use 1's complement (v -> 255 - v, and then map as follows:
+ * 1.0 <-> 3.2      (DTLS 1.0 is based on TLS 1.1)
+ * 1.x <-> 3.x+1    for x != 0 (DTLS 1.2 based on TLS 1.2)
+ */
+void mbedtls_ssl_write_version( int major, int minor, int transport,
+                        unsigned char ver[2] )
+{
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        if( minor == MBEDTLS_SSL_MINOR_VERSION_2 )
+            --minor; /* DTLS 1.0 stored as TLS 1.1 internally */
+
+        ver[0] = (unsigned char)( 255 - ( major - 2 ) );
+        ver[1] = (unsigned char)( 255 - ( minor - 1 ) );
+    }
+    else
+#else
+    ((void) transport);
+#endif
+    {
+        ver[0] = (unsigned char) major;
+        ver[1] = (unsigned char) minor;
+    }
+}
+
+void mbedtls_ssl_read_version( int *major, int *minor, int transport,
+                       const unsigned char ver[2] )
+{
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        *major = 255 - ver[0] + 2;
+        *minor = 255 - ver[1] + 1;
+
+        if( *minor == MBEDTLS_SSL_MINOR_VERSION_1 )
+            ++*minor; /* DTLS 1.0 stored as TLS 1.1 internally */
+    }
+    else
+#else
+    ((void) transport);
+#endif
+    {
+        *major = ver[0];
+        *minor = ver[1];
+    }
+}
+
+#endif /* MBEDTLS_SSL_TLS_C */