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TLS 1.3 Experimental Developments
=================================
Overview
--------
Mbed TLS doesn't support the TLS 1.3 protocol yet, but a prototype is in development.
Stable parts of this prototype that can be independently tested are being successively
upstreamed under the guard of the following macro:
```
MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL
```
This macro will likely be renamed to `MBEDTLS_SSL_PROTO_TLS1_3` once a minimal viable
implementation of the TLS 1.3 protocol is available.
See the [documentation of `MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL`](../../include/mbedtls/config.h)
for more information.
Status
------
The following lists which parts of the TLS 1.3 prototype have already been upstreamed
together with their level of testing:
* TLS 1.3 record protection mechanisms
The record protection routines `mbedtls_ssl_{encrypt|decrypt}_buf()` have been extended
to support the modified TLS 1.3 record protection mechanism, including modified computation
of AAD, IV, and the introduction of a flexible padding.
Those record protection routines have unit tests in `test_suite_ssl` alongside the
tests for the other record protection routines.
TODO: Add some test vectors from RFC 8448.
- The HKDF key derivation function on which the TLS 1.3 key schedule is based,
is already present as an independent module controlled by `MBEDTLS_HKDF_C`
independently of the development of the TLS 1.3 prototype.
- The TLS 1.3-specific HKDF-based key derivation functions (see RFC 8446):
* HKDF-Expand-Label
* Derive-Secret
- Secret evolution
* The traffic {Key,IV} generation from secret
Those functions are implemented in `library/ssl_tls13_keys.c` and
tested in `test_suite_ssl` using test vectors from RFC 8448 and
https://tls13.ulfheim.net/.
- New TLS Message Processing Stack (MPS)
The TLS 1.3 prototype is developed alongside a rewrite of the TLS messaging layer,
encompassing low-level details such as record parsing, handshake reassembly, and
DTLS retransmission state machine.
MPS has the following components:
- Layer 1 (Datagram handling)
- Layer 2 (Record handling)
- Layer 3 (Message handling)
- Layer 4 (Retransmission State Machine)
- Reader (Abstracted pointer arithmetic and reassembly logic for incoming data)
- Writer (Abstracted pointer arithmetic and fragmentation logic for outgoing data)
Of those components, the following have been upstreamed
as part of `MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL`:
- Reader ([`library/mps_reader.h`](../../library/mps_reader.h))
|
