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"""Knowledge about cryptographic mechanisms implemented in Mbed TLS.
This module is entirely based on the PSA API.
"""
# 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.
import re
from typing import Dict, Iterable, Optional, Pattern, Tuple
from mbedtls_dev.asymmetric_key_data import ASYMMETRIC_KEY_DATA
class KeyType:
"""Knowledge about a PSA key type."""
def __init__(self, name: str, params: Optional[Iterable[str]] = None):
"""Analyze a key type.
The key type must be specified in PSA syntax. In its simplest form,
`name` is a string 'PSA_KEY_TYPE_xxx' which is the name of a PSA key
type macro. For key types that take arguments, the arguments can
be passed either through the optional argument `params` or by
passing an expression of the form 'PSA_KEY_TYPE_xxx(param1, ...)'
in `name` as a string.
"""
self.name = name.strip()
"""The key type macro name (``PSA_KEY_TYPE_xxx``).
For key types constructed from a macro with arguments, this is the
name of the macro, and the arguments are in `self.params`.
"""
if params is None:
if '(' in self.name:
m = re.match(r'(\w+)\s*\((.*)\)\Z', self.name)
assert m is not None
self.name = m.group(1)
params = m.group(2).split(',')
self.params = (None if params is None else
[param.strip() for param in params])
"""The parameters of the key type, if there are any.
None if the key type is a macro without arguments.
"""
assert re.match(r'PSA_KEY_TYPE_\w+\Z', self.name)
self.expression = self.name
"""A C expression whose value is the key type encoding."""
if self.params is not None:
self.expression += '(' + ', '.join(self.params) + ')'
self.private_type = re.sub(r'_PUBLIC_KEY\Z', r'_KEY_PAIR', self.name)
"""The key type macro name for the corresponding key pair type.
For everything other than a public key type, this is the same as
`self.name`.
"""
ECC_KEY_SIZES = {
'PSA_ECC_FAMILY_SECP_K1': (192, 224, 256),
'PSA_ECC_FAMILY_SECP_R1': (225, 256, 384, 521),
'PSA_ECC_FAMILY_SECP_R2': (160,),
'PSA_ECC_FAMILY_SECT_K1': (163, 233, 239, 283, 409, 571),
'PSA_ECC_FAMILY_SECT_R1': (163, 233, 283, 409, 571),
'PSA_ECC_FAMILY_SECT_R2': (163,),
'PSA_ECC_FAMILY_BRAINPOOL_P_R1': (160, 192, 224, 256, 320, 384, 512),
'PSA_ECC_FAMILY_MONTGOMERY': (255, 448),
'PSA_ECC_FAMILY_TWISTED_EDWARDS': (255, 448),
}
KEY_TYPE_SIZES = {
'PSA_KEY_TYPE_AES': (128, 192, 256), # exhaustive
'PSA_KEY_TYPE_ARC4': (8, 128, 2048), # extremes + sensible
'PSA_KEY_TYPE_ARIA': (128, 192, 256), # exhaustive
'PSA_KEY_TYPE_CAMELLIA': (128, 192, 256), # exhaustive
'PSA_KEY_TYPE_CHACHA20': (256,), # exhaustive
'PSA_KEY_TYPE_DERIVE': (120, 128), # sample
'PSA_KEY_TYPE_DES': (64, 128, 192), # exhaustive
'PSA_KEY_TYPE_HMAC': (128, 160, 224, 256, 384, 512), # standard size for each supported hash
'PSA_KEY_TYPE_RAW_DATA': (8, 40, 128), # sample
'PSA_KEY_TYPE_RSA_KEY_PAIR': (1024, 1536), # small sample
}
def sizes_to_test(self) -> Tuple[int, ...]:
"""Return a tuple of key sizes to test.
For key types that only allow a single size, or only a small set of
sizes, these are all the possible sizes. For key types that allow a
wide range of sizes, these are a representative sample of sizes,
excluding large sizes for which a typical resource-constrained platform
may run out of memory.
"""
if self.private_type == 'PSA_KEY_TYPE_ECC_KEY_PAIR':
assert self.params is not None
return self.ECC_KEY_SIZES[self.params[0]]
return self.KEY_TYPE_SIZES[self.private_type]
# "48657265006973206b6579a064617461"
DATA_BLOCK = b'Here\000is key\240data'
def key_material(self, bits: int) -> bytes:
"""Return a byte string containing suitable key material with the given bit length.
Use the PSA export representation. The resulting byte string is one that
can be obtained with the following code:
```
psa_set_key_type(&attributes, `self.expression`);
psa_set_key_bits(&attributes, `bits`);
psa_set_key_usage_flags(&attributes, PSA_KEY_USAGE_EXPORT);
psa_generate_key(&attributes, &id);
psa_export_key(id, `material`, ...);
```
"""
if self.expression in ASYMMETRIC_KEY_DATA:
if bits not in ASYMMETRIC_KEY_DATA[self.expression]:
raise ValueError('No key data for {}-bit {}'
.format(bits, self.expression))
return ASYMMETRIC_KEY_DATA[self.expression][bits]
if bits % 8 != 0:
raise ValueError('Non-integer number of bytes: {} bits for {}'
.format(bits, self.expression))
length = bits // 8
if self.name == 'PSA_KEY_TYPE_DES':
# "644573206b457901644573206b457902644573206b457904"
des3 = b'dEs kEy\001dEs kEy\002dEs kEy\004'
return des3[:length]
return b''.join([self.DATA_BLOCK] * (length // len(self.DATA_BLOCK)) +
[self.DATA_BLOCK[:length % len(self.DATA_BLOCK)]])
KEY_TYPE_FOR_SIGNATURE = {
'PSA_KEY_USAGE_SIGN_HASH': re.compile('.*KEY_PAIR'),
'PSA_KEY_USAGE_VERIFY_HASH': re.compile('.*KEY.*')
} #type: Dict[str, Pattern]
"""Use a regexp to determine key types for which signature is possible
when using the actual usage flag.
"""
def is_valid_for_signature(self, usage: str) -> bool:
"""Determine if the key type is compatible with the specified
signitute type.
"""
# This is just temporaly solution for the implicit usage flags.
return re.match(self.KEY_TYPE_FOR_SIGNATURE[usage], self.name) is not None
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