mirror of http://git.sairate.top/sairate/doc.git
62 lines
1.9 KiB
Python
62 lines
1.9 KiB
Python
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# This file is dual licensed under the terms of the Apache License, Version
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# 2.0, and the BSD License. See the LICENSE file in the root of this repository
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# for complete details.
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from __future__ import annotations
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import typing
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from cryptography import utils
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from cryptography.exceptions import AlreadyFinalized, InvalidKey
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from cryptography.hazmat.primitives import constant_time, hashes
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from cryptography.hazmat.primitives.kdf import KeyDerivationFunction
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def _int_to_u32be(n: int) -> bytes:
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return n.to_bytes(length=4, byteorder="big")
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class X963KDF(KeyDerivationFunction):
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def __init__(
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self,
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algorithm: hashes.HashAlgorithm,
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length: int,
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sharedinfo: bytes | None,
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backend: typing.Any = None,
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):
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max_len = algorithm.digest_size * (2**32 - 1)
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if length > max_len:
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raise ValueError(f"Cannot derive keys larger than {max_len} bits.")
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if sharedinfo is not None:
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utils._check_bytes("sharedinfo", sharedinfo)
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self._algorithm = algorithm
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self._length = length
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self._sharedinfo = sharedinfo
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self._used = False
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def derive(self, key_material: bytes) -> bytes:
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if self._used:
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raise AlreadyFinalized
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self._used = True
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utils._check_byteslike("key_material", key_material)
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output = [b""]
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outlen = 0
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counter = 1
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while self._length > outlen:
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h = hashes.Hash(self._algorithm)
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h.update(key_material)
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h.update(_int_to_u32be(counter))
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if self._sharedinfo is not None:
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h.update(self._sharedinfo)
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output.append(h.finalize())
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outlen += len(output[-1])
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counter += 1
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return b"".join(output)[: self._length]
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def verify(self, key_material: bytes, expected_key: bytes) -> None:
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if not constant_time.bytes_eq(self.derive(key_material), expected_key):
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raise InvalidKey
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