155 lines
6.6 KiB
Python
155 lines
6.6 KiB
Python
"""Knowledge about cryptographic mechanisms implemented in Mbed TLS.
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This module is entirely based on the PSA API.
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"""
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# Copyright The Mbed TLS Contributors
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# SPDX-License-Identifier: Apache-2.0
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import re
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from typing import Dict, Iterable, Optional, Pattern, Tuple
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from mbedtls_dev.asymmetric_key_data import ASYMMETRIC_KEY_DATA
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class KeyType:
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"""Knowledge about a PSA key type."""
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def __init__(self, name: str, params: Optional[Iterable[str]] = None):
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"""Analyze a key type.
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The key type must be specified in PSA syntax. In its simplest form,
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`name` is a string 'PSA_KEY_TYPE_xxx' which is the name of a PSA key
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type macro. For key types that take arguments, the arguments can
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be passed either through the optional argument `params` or by
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passing an expression of the form 'PSA_KEY_TYPE_xxx(param1, ...)'
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in `name` as a string.
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"""
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self.name = name.strip()
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"""The key type macro name (``PSA_KEY_TYPE_xxx``).
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For key types constructed from a macro with arguments, this is the
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name of the macro, and the arguments are in `self.params`.
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"""
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if params is None:
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if '(' in self.name:
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m = re.match(r'(\w+)\s*\((.*)\)\Z', self.name)
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assert m is not None
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self.name = m.group(1)
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params = m.group(2).split(',')
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self.params = (None if params is None else
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[param.strip() for param in params])
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"""The parameters of the key type, if there are any.
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None if the key type is a macro without arguments.
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"""
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assert re.match(r'PSA_KEY_TYPE_\w+\Z', self.name)
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self.expression = self.name
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"""A C expression whose value is the key type encoding."""
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if self.params is not None:
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self.expression += '(' + ', '.join(self.params) + ')'
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self.private_type = re.sub(r'_PUBLIC_KEY\Z', r'_KEY_PAIR', self.name)
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"""The key type macro name for the corresponding key pair type.
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For everything other than a public key type, this is the same as
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`self.name`.
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"""
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ECC_KEY_SIZES = {
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'PSA_ECC_FAMILY_SECP_K1': (192, 224, 256),
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'PSA_ECC_FAMILY_SECP_R1': (225, 256, 384, 521),
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'PSA_ECC_FAMILY_SECP_R2': (160,),
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'PSA_ECC_FAMILY_SECT_K1': (163, 233, 239, 283, 409, 571),
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'PSA_ECC_FAMILY_SECT_R1': (163, 233, 283, 409, 571),
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'PSA_ECC_FAMILY_SECT_R2': (163,),
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'PSA_ECC_FAMILY_BRAINPOOL_P_R1': (160, 192, 224, 256, 320, 384, 512),
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'PSA_ECC_FAMILY_MONTGOMERY': (255, 448),
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'PSA_ECC_FAMILY_TWISTED_EDWARDS': (255, 448),
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}
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KEY_TYPE_SIZES = {
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'PSA_KEY_TYPE_AES': (128, 192, 256), # exhaustive
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'PSA_KEY_TYPE_ARIA': (128, 192, 256), # exhaustive
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'PSA_KEY_TYPE_CAMELLIA': (128, 192, 256), # exhaustive
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'PSA_KEY_TYPE_CHACHA20': (256,), # exhaustive
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'PSA_KEY_TYPE_DERIVE': (120, 128), # sample
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'PSA_KEY_TYPE_DES': (64, 128, 192), # exhaustive
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'PSA_KEY_TYPE_HMAC': (128, 160, 224, 256, 384, 512), # standard size for each supported hash
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'PSA_KEY_TYPE_PASSWORD': (48, 168, 336), # sample
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'PSA_KEY_TYPE_PASSWORD_HASH': (128, 256), # sample
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'PSA_KEY_TYPE_PEPPER': (128, 256), # sample
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'PSA_KEY_TYPE_RAW_DATA': (8, 40, 128), # sample
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'PSA_KEY_TYPE_RSA_KEY_PAIR': (1024, 1536), # small sample
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}
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def sizes_to_test(self) -> Tuple[int, ...]:
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"""Return a tuple of key sizes to test.
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For key types that only allow a single size, or only a small set of
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sizes, these are all the possible sizes. For key types that allow a
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wide range of sizes, these are a representative sample of sizes,
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excluding large sizes for which a typical resource-constrained platform
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may run out of memory.
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"""
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if self.private_type == 'PSA_KEY_TYPE_ECC_KEY_PAIR':
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assert self.params is not None
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return self.ECC_KEY_SIZES[self.params[0]]
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return self.KEY_TYPE_SIZES[self.private_type]
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# "48657265006973206b6579a064617461"
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DATA_BLOCK = b'Here\000is key\240data'
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def key_material(self, bits: int) -> bytes:
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"""Return a byte string containing suitable key material with the given bit length.
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Use the PSA export representation. The resulting byte string is one that
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can be obtained with the following code:
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```
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psa_set_key_type(&attributes, `self.expression`);
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psa_set_key_bits(&attributes, `bits`);
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psa_set_key_usage_flags(&attributes, PSA_KEY_USAGE_EXPORT);
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psa_generate_key(&attributes, &id);
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psa_export_key(id, `material`, ...);
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```
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"""
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if self.expression in ASYMMETRIC_KEY_DATA:
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if bits not in ASYMMETRIC_KEY_DATA[self.expression]:
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raise ValueError('No key data for {}-bit {}'
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.format(bits, self.expression))
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return ASYMMETRIC_KEY_DATA[self.expression][bits]
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if bits % 8 != 0:
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raise ValueError('Non-integer number of bytes: {} bits for {}'
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.format(bits, self.expression))
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length = bits // 8
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if self.name == 'PSA_KEY_TYPE_DES':
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# "644573206b457901644573206b457902644573206b457904"
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des3 = b'dEs kEy\001dEs kEy\002dEs kEy\004'
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return des3[:length]
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return b''.join([self.DATA_BLOCK] * (length // len(self.DATA_BLOCK)) +
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[self.DATA_BLOCK[:length % len(self.DATA_BLOCK)]])
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KEY_TYPE_FOR_SIGNATURE = {
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'PSA_KEY_USAGE_SIGN_HASH': re.compile('.*KEY_PAIR'),
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'PSA_KEY_USAGE_VERIFY_HASH': re.compile('.*KEY.*')
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} #type: Dict[str, Pattern]
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"""Use a regexp to determine key types for which signature is possible
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when using the actual usage flag.
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"""
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def is_valid_for_signature(self, usage: str) -> bool:
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"""Determine if the key type is compatible with the specified
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signitute type.
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"""
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# This is just temporaly solution for the implicit usage flags.
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return re.match(self.KEY_TYPE_FOR_SIGNATURE[usage], self.name) is not None
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