568 lines
23 KiB
Python
568 lines
23 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 OR GPL-2.0-or-later
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#
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import enum
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import re
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from typing import FrozenSet, Iterable, List, Optional, Tuple, Dict
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from .asymmetric_key_data import ASYMMETRIC_KEY_DATA
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def short_expression(original: str, level: int = 0) -> str:
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"""Abbreviate the expression, keeping it human-readable.
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If `level` is 0, just remove parts that are implicit from context,
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such as a leading ``PSA_KEY_TYPE_``.
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For larger values of `level`, also abbreviate some names in an
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unambiguous, but ad hoc way.
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"""
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short = original
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short = re.sub(r'\bPSA_(?:ALG|DH_FAMILY|ECC_FAMILY|KEY_[A-Z]+)_', r'', short)
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short = re.sub(r' +', r'', short)
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if level >= 1:
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short = re.sub(r'PUBLIC_KEY\b', r'PUB', short)
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short = re.sub(r'KEY_PAIR\b', r'PAIR', short)
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short = re.sub(r'\bBRAINPOOL_P', r'BP', short)
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short = re.sub(r'\bMONTGOMERY\b', r'MGM', short)
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short = re.sub(r'AEAD_WITH_SHORTENED_TAG\b', r'AEAD_SHORT', short)
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short = re.sub(r'\bDETERMINISTIC_', r'DET_', short)
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short = re.sub(r'\bKEY_AGREEMENT\b', r'KA', short)
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short = re.sub(r'_PSK_TO_MS\b', r'_PSK2MS', short)
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return short
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BLOCK_CIPHERS = frozenset(['AES', 'ARIA', 'CAMELLIA', 'DES'])
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BLOCK_MAC_MODES = frozenset(['CBC_MAC', 'CMAC'])
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BLOCK_CIPHER_MODES = frozenset([
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'CTR', 'CFB', 'OFB', 'XTS', 'CCM_STAR_NO_TAG',
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'ECB_NO_PADDING', 'CBC_NO_PADDING', 'CBC_PKCS7',
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])
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BLOCK_AEAD_MODES = frozenset(['CCM', 'GCM'])
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class EllipticCurveCategory(enum.Enum):
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"""Categorization of elliptic curve families.
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The category of a curve determines what algorithms are defined over it.
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"""
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SHORT_WEIERSTRASS = 0
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MONTGOMERY = 1
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TWISTED_EDWARDS = 2
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@staticmethod
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def from_family(family: str) -> 'EllipticCurveCategory':
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if family == 'PSA_ECC_FAMILY_MONTGOMERY':
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return EllipticCurveCategory.MONTGOMERY
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if family == 'PSA_ECC_FAMILY_TWISTED_EDWARDS':
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return EllipticCurveCategory.TWISTED_EDWARDS
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# Default to SW, which most curves belong to.
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return EllipticCurveCategory.SHORT_WEIERSTRASS
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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) -> 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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m = re.match(r'PSA_KEY_TYPE_(\w+)', self.name)
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assert m
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self.head = re.sub(r'_(?:PUBLIC_KEY|KEY_PAIR)\Z', r'', m.group(1))
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"""The key type macro name, with common prefixes and suffixes stripped."""
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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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def short_expression(self, level: int = 0) -> str:
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"""Abbreviate the expression, keeping it human-readable.
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See `crypto_knowledge.short_expression`.
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"""
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return short_expression(self.expression, level=level)
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def is_public(self) -> bool:
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"""Whether the key type is for public keys."""
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return self.name.endswith('_PUBLIC_KEY')
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DH_KEY_SIZES = {
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'PSA_DH_FAMILY_RFC7919': (2048, 3072, 4096, 6144, 8192),
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} # type: Dict[str, Tuple[int, ...]]
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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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} # type: Dict[str, Tuple[int, ...]]
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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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} # type: Dict[str, Tuple[int, ...]]
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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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if self.private_type == 'PSA_KEY_TYPE_DH_KEY_PAIR':
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assert self.params is not None
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return self.DH_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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def can_do(self, alg: 'Algorithm') -> bool:
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"""Whether this key type can be used for operations with the given algorithm.
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This function does not currently handle key derivation or PAKE.
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"""
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#pylint: disable=too-many-branches,too-many-return-statements
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if not alg.is_valid_for_operation():
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return False
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if self.head == 'HMAC' and alg.head == 'HMAC':
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return True
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if self.head == 'DES':
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# 64-bit block ciphers only allow a reduced set of modes.
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return alg.head in [
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'CBC_NO_PADDING', 'CBC_PKCS7',
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'ECB_NO_PADDING',
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]
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if self.head in BLOCK_CIPHERS and \
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alg.head in frozenset.union(BLOCK_MAC_MODES,
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BLOCK_CIPHER_MODES,
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BLOCK_AEAD_MODES):
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if alg.head in ['CMAC', 'OFB'] and \
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self.head in ['ARIA', 'CAMELLIA']:
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return False # not implemented in Mbed TLS
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return True
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if self.head == 'CHACHA20' and alg.head == 'CHACHA20_POLY1305':
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return True
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if self.head in {'ARC4', 'CHACHA20'} and \
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alg.head == 'STREAM_CIPHER':
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return True
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if self.head == 'RSA' and alg.head.startswith('RSA_'):
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return True
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if alg.category == AlgorithmCategory.KEY_AGREEMENT and \
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self.is_public():
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# The PSA API does not use public key objects in key agreement
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# operations: it imports the public key as a formatted byte string.
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# So a public key object with a key agreement algorithm is not
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# a valid combination.
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return False
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if alg.is_invalid_key_agreement_with_derivation():
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return False
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if self.head == 'ECC':
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assert self.params is not None
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eccc = EllipticCurveCategory.from_family(self.params[0])
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if alg.head == 'ECDH' and \
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eccc in {EllipticCurveCategory.SHORT_WEIERSTRASS,
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EllipticCurveCategory.MONTGOMERY}:
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return True
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if alg.head == 'ECDSA' and \
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eccc == EllipticCurveCategory.SHORT_WEIERSTRASS:
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return True
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if alg.head in {'PURE_EDDSA', 'EDDSA_PREHASH'} and \
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eccc == EllipticCurveCategory.TWISTED_EDWARDS:
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return True
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if self.head == 'DH' and alg.head == 'FFDH':
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return True
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return False
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class AlgorithmCategory(enum.Enum):
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"""PSA algorithm categories."""
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# The numbers are aligned with the category bits in numerical values of
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# algorithms.
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HASH = 2
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MAC = 3
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CIPHER = 4
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AEAD = 5
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SIGN = 6
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ASYMMETRIC_ENCRYPTION = 7
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KEY_DERIVATION = 8
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KEY_AGREEMENT = 9
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PAKE = 10
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def requires_key(self) -> bool:
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"""Whether operations in this category are set up with a key."""
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return self not in {self.HASH, self.KEY_DERIVATION}
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def is_asymmetric(self) -> bool:
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"""Whether operations in this category involve asymmetric keys."""
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return self in {
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self.SIGN,
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self.ASYMMETRIC_ENCRYPTION,
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self.KEY_AGREEMENT
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}
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class AlgorithmNotRecognized(Exception):
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def __init__(self, expr: str) -> None:
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super().__init__('Algorithm not recognized: ' + expr)
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self.expr = expr
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class Algorithm:
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"""Knowledge about a PSA algorithm."""
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@staticmethod
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def determine_base(expr: str) -> str:
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"""Return an expression for the "base" of the algorithm.
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This strips off variants of algorithms such as MAC truncation.
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This function does not attempt to detect invalid inputs.
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"""
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m = re.match(r'PSA_ALG_(?:'
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r'(?:TRUNCATED|AT_LEAST_THIS_LENGTH)_MAC|'
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r'AEAD_WITH_(?:SHORTENED|AT_LEAST_THIS_LENGTH)_TAG'
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r')\((.*),[^,]+\)\Z', expr)
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if m:
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expr = m.group(1)
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return expr
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@staticmethod
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def determine_head(expr: str) -> str:
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"""Return the head of an algorithm expression.
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The head is the first (outermost) constructor, without its PSA_ALG_
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prefix, and with some normalization of similar algorithms.
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"""
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m = re.match(r'PSA_ALG_(?:DETERMINISTIC_)?(\w+)', expr)
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if not m:
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raise AlgorithmNotRecognized(expr)
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head = m.group(1)
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if head == 'KEY_AGREEMENT':
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m = re.match(r'PSA_ALG_KEY_AGREEMENT\s*\(\s*PSA_ALG_(\w+)', expr)
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if not m:
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raise AlgorithmNotRecognized(expr)
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head = m.group(1)
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head = re.sub(r'_ANY\Z', r'', head)
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if re.match(r'ED[0-9]+PH\Z', head):
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head = 'EDDSA_PREHASH'
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return head
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CATEGORY_FROM_HEAD = {
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'SHA': AlgorithmCategory.HASH,
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'SHAKE256_512': AlgorithmCategory.HASH,
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'MD': AlgorithmCategory.HASH,
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'RIPEMD': AlgorithmCategory.HASH,
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'ANY_HASH': AlgorithmCategory.HASH,
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'HMAC': AlgorithmCategory.MAC,
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'STREAM_CIPHER': AlgorithmCategory.CIPHER,
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'CHACHA20_POLY1305': AlgorithmCategory.AEAD,
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'DSA': AlgorithmCategory.SIGN,
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'ECDSA': AlgorithmCategory.SIGN,
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'EDDSA': AlgorithmCategory.SIGN,
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'PURE_EDDSA': AlgorithmCategory.SIGN,
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'RSA_PSS': AlgorithmCategory.SIGN,
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'RSA_PKCS1V15_SIGN': AlgorithmCategory.SIGN,
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'RSA_PKCS1V15_CRYPT': AlgorithmCategory.ASYMMETRIC_ENCRYPTION,
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'RSA_OAEP': AlgorithmCategory.ASYMMETRIC_ENCRYPTION,
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'HKDF': AlgorithmCategory.KEY_DERIVATION,
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'TLS12_PRF': AlgorithmCategory.KEY_DERIVATION,
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'TLS12_PSK_TO_MS': AlgorithmCategory.KEY_DERIVATION,
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'TLS12_ECJPAKE_TO_PMS': AlgorithmCategory.KEY_DERIVATION,
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'PBKDF': AlgorithmCategory.KEY_DERIVATION,
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'ECDH': AlgorithmCategory.KEY_AGREEMENT,
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'FFDH': AlgorithmCategory.KEY_AGREEMENT,
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# KEY_AGREEMENT(...) is a key derivation with a key agreement component
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'KEY_AGREEMENT': AlgorithmCategory.KEY_DERIVATION,
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'JPAKE': AlgorithmCategory.PAKE,
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}
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for x in BLOCK_MAC_MODES:
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CATEGORY_FROM_HEAD[x] = AlgorithmCategory.MAC
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for x in BLOCK_CIPHER_MODES:
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CATEGORY_FROM_HEAD[x] = AlgorithmCategory.CIPHER
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for x in BLOCK_AEAD_MODES:
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CATEGORY_FROM_HEAD[x] = AlgorithmCategory.AEAD
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def determine_category(self, expr: str, head: str) -> AlgorithmCategory:
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"""Return the category of the given algorithm expression.
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This function does not attempt to detect invalid inputs.
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"""
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prefix = head
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while prefix:
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if prefix in self.CATEGORY_FROM_HEAD:
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return self.CATEGORY_FROM_HEAD[prefix]
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if re.match(r'.*[0-9]\Z', prefix):
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prefix = re.sub(r'_*[0-9]+\Z', r'', prefix)
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else:
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prefix = re.sub(r'_*[^_]*\Z', r'', prefix)
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raise AlgorithmNotRecognized(expr)
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@staticmethod
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def determine_wildcard(expr) -> bool:
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"""Whether the given algorithm expression is a wildcard.
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This function does not attempt to detect invalid inputs.
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"""
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if re.search(r'\bPSA_ALG_ANY_HASH\b', expr):
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return True
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if re.search(r'_AT_LEAST_', expr):
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return True
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return False
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def __init__(self, expr: str) -> None:
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"""Analyze an algorithm value.
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The algorithm must be expressed as a C expression containing only
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calls to PSA algorithm constructor macros and numeric literals.
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This class is only programmed to handle valid expressions. Invalid
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expressions may result in exceptions or in nonsensical results.
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"""
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self.expression = re.sub(r'\s+', r'', expr)
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self.base_expression = self.determine_base(self.expression)
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self.head = self.determine_head(self.base_expression)
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self.category = self.determine_category(self.base_expression, self.head)
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self.is_wildcard = self.determine_wildcard(self.expression)
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def get_key_agreement_derivation(self) -> Optional[str]:
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"""For a combined key agreement and key derivation algorithm, get the derivation part.
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For anything else, return None.
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"""
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if self.category != AlgorithmCategory.KEY_AGREEMENT:
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return None
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m = re.match(r'PSA_ALG_KEY_AGREEMENT\(\w+,\s*(.*)\)\Z', self.expression)
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if not m:
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return None
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kdf_alg = m.group(1)
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# Assume kdf_alg is either a valid KDF or 0.
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if re.match(r'(?:0[Xx])?0+\s*\Z', kdf_alg):
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return None
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return kdf_alg
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KEY_DERIVATIONS_INCOMPATIBLE_WITH_AGREEMENT = frozenset([
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'PSA_ALG_TLS12_ECJPAKE_TO_PMS', # secret input in specific format
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])
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def is_valid_key_agreement_with_derivation(self) -> bool:
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"""Whether this is a valid combined key agreement and key derivation algorithm."""
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kdf_alg = self.get_key_agreement_derivation()
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if kdf_alg is None:
|
|
return False
|
|
return kdf_alg not in self.KEY_DERIVATIONS_INCOMPATIBLE_WITH_AGREEMENT
|
|
|
|
def is_invalid_key_agreement_with_derivation(self) -> bool:
|
|
"""Whether this is an invalid combined key agreement and key derivation algorithm."""
|
|
kdf_alg = self.get_key_agreement_derivation()
|
|
if kdf_alg is None:
|
|
return False
|
|
return kdf_alg in self.KEY_DERIVATIONS_INCOMPATIBLE_WITH_AGREEMENT
|
|
|
|
def short_expression(self, level: int = 0) -> str:
|
|
"""Abbreviate the expression, keeping it human-readable.
|
|
|
|
See `crypto_knowledge.short_expression`.
|
|
"""
|
|
return short_expression(self.expression, level=level)
|
|
|
|
HASH_LENGTH = {
|
|
'PSA_ALG_MD5': 16,
|
|
'PSA_ALG_SHA_1': 20,
|
|
}
|
|
HASH_LENGTH_BITS_RE = re.compile(r'([0-9]+)\Z')
|
|
@classmethod
|
|
def hash_length(cls, alg: str) -> int:
|
|
"""The length of the given hash algorithm, in bytes."""
|
|
if alg in cls.HASH_LENGTH:
|
|
return cls.HASH_LENGTH[alg]
|
|
m = cls.HASH_LENGTH_BITS_RE.search(alg)
|
|
if m:
|
|
return int(m.group(1)) // 8
|
|
raise ValueError('Unknown hash length for ' + alg)
|
|
|
|
PERMITTED_TAG_LENGTHS = {
|
|
'PSA_ALG_CCM': frozenset([4, 6, 8, 10, 12, 14, 16]),
|
|
'PSA_ALG_CHACHA20_POLY1305': frozenset([16]),
|
|
'PSA_ALG_GCM': frozenset([4, 8, 12, 13, 14, 15, 16]),
|
|
}
|
|
MAC_LENGTH = {
|
|
'PSA_ALG_CBC_MAC': 16, # actually the block cipher length
|
|
'PSA_ALG_CMAC': 16, # actually the block cipher length
|
|
}
|
|
HMAC_RE = re.compile(r'PSA_ALG_HMAC\((.*)\)\Z')
|
|
@classmethod
|
|
def permitted_truncations(cls, base: str) -> FrozenSet[int]:
|
|
"""Permitted output lengths for the given MAC or AEAD base algorithm.
|
|
|
|
For a MAC algorithm, this is the set of truncation lengths that
|
|
Mbed TLS supports.
|
|
For an AEAD algorithm, this is the set of truncation lengths that
|
|
are permitted by the algorithm specification.
|
|
"""
|
|
if base in cls.PERMITTED_TAG_LENGTHS:
|
|
return cls.PERMITTED_TAG_LENGTHS[base]
|
|
max_length = cls.MAC_LENGTH.get(base, None)
|
|
if max_length is None:
|
|
m = cls.HMAC_RE.match(base)
|
|
if m:
|
|
max_length = cls.hash_length(m.group(1))
|
|
if max_length is None:
|
|
raise ValueError('Unknown permitted lengths for ' + base)
|
|
return frozenset(range(4, max_length + 1))
|
|
|
|
TRUNCATED_ALG_RE = re.compile(
|
|
r'(?P<face>PSA_ALG_(?:AEAD_WITH_SHORTENED_TAG|TRUNCATED_MAC))'
|
|
r'\((?P<base>.*),'
|
|
r'(?P<length>0[Xx][0-9A-Fa-f]+|[1-9][0-9]*|0[0-7]*)[LUlu]*\)\Z')
|
|
def is_invalid_truncation(self) -> bool:
|
|
"""False for a MAC or AEAD algorithm truncated to an invalid length.
|
|
|
|
True for a MAC or AEAD algorithm truncated to a valid length or to
|
|
a length that cannot be determined. True for anything other than
|
|
a truncated MAC or AEAD.
|
|
"""
|
|
m = self.TRUNCATED_ALG_RE.match(self.expression)
|
|
if m:
|
|
base = m.group('base')
|
|
to_length = int(m.group('length'), 0)
|
|
permitted_lengths = self.permitted_truncations(base)
|
|
if to_length not in permitted_lengths:
|
|
return True
|
|
return False
|
|
|
|
def is_valid_for_operation(self) -> bool:
|
|
"""Whether this algorithm construction is valid for an operation.
|
|
|
|
This function assumes that the algorithm is constructed in a
|
|
"grammatically" correct way, and only rejects semantically invalid
|
|
combinations.
|
|
"""
|
|
if self.is_wildcard:
|
|
return False
|
|
if self.is_invalid_truncation():
|
|
return False
|
|
return True
|
|
|
|
def can_do(self, category: AlgorithmCategory) -> bool:
|
|
"""Whether this algorithm can perform operations in the given category.
|
|
"""
|
|
if category == self.category:
|
|
return True
|
|
if category == AlgorithmCategory.KEY_DERIVATION and \
|
|
self.is_valid_key_agreement_with_derivation():
|
|
return True
|
|
return False
|
|
|
|
def usage_flags(self, public: bool = False) -> List[str]:
|
|
"""The list of usage flags describing operations that can perform this algorithm.
|
|
|
|
If public is true, only return public-key operations, not private-key operations.
|
|
"""
|
|
if self.category == AlgorithmCategory.HASH:
|
|
flags = []
|
|
elif self.category == AlgorithmCategory.MAC:
|
|
flags = ['SIGN_HASH', 'SIGN_MESSAGE',
|
|
'VERIFY_HASH', 'VERIFY_MESSAGE']
|
|
elif self.category == AlgorithmCategory.CIPHER or \
|
|
self.category == AlgorithmCategory.AEAD:
|
|
flags = ['DECRYPT', 'ENCRYPT']
|
|
elif self.category == AlgorithmCategory.SIGN:
|
|
flags = ['VERIFY_HASH', 'VERIFY_MESSAGE']
|
|
if not public:
|
|
flags += ['SIGN_HASH', 'SIGN_MESSAGE']
|
|
elif self.category == AlgorithmCategory.ASYMMETRIC_ENCRYPTION:
|
|
flags = ['ENCRYPT']
|
|
if not public:
|
|
flags += ['DECRYPT']
|
|
elif self.category == AlgorithmCategory.KEY_DERIVATION or \
|
|
self.category == AlgorithmCategory.KEY_AGREEMENT:
|
|
flags = ['DERIVE']
|
|
else:
|
|
raise AlgorithmNotRecognized(self.expression)
|
|
return ['PSA_KEY_USAGE_' + flag for flag in flags]
|