60 lines
2.1 KiB
Python
60 lines
2.1 KiB
Python
# 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 absolute_import, division, print_function
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from cryptography import utils
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from cryptography.exceptions import (
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InvalidSignature, UnsupportedAlgorithm, _Reasons
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)
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from cryptography.hazmat.primitives import constant_time, hashes, interfaces
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@utils.register_interface(interfaces.MACContext)
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@utils.register_interface(hashes.HashContext)
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class _HMACContext(object):
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def __init__(self, backend, key, algorithm, ctx=None):
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self._algorithm = algorithm
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self._backend = backend
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if ctx is None:
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ctx = self._backend._ffi.new("CCHmacContext *")
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try:
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alg = self._backend._supported_hmac_algorithms[algorithm.name]
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except KeyError:
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raise UnsupportedAlgorithm(
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"{0} is not a supported HMAC hash on this backend.".format(
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algorithm.name),
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_Reasons.UNSUPPORTED_HASH
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)
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self._backend._lib.CCHmacInit(ctx, alg, key, len(key))
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self._ctx = ctx
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self._key = key
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algorithm = utils.read_only_property("_algorithm")
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def copy(self):
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copied_ctx = self._backend._ffi.new("CCHmacContext *")
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# CommonCrypto has no APIs for copying HMACs, so we have to copy the
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# underlying struct.
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copied_ctx[0] = self._ctx[0]
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return _HMACContext(
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self._backend, self._key, self.algorithm, ctx=copied_ctx
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)
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def update(self, data):
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self._backend._lib.CCHmacUpdate(self._ctx, data, len(data))
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def finalize(self):
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buf = self._backend._ffi.new("unsigned char[]",
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self.algorithm.digest_size)
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self._backend._lib.CCHmacFinal(self._ctx, buf)
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return self._backend._ffi.buffer(buf)[:]
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def verify(self, signature):
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digest = self.finalize()
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if not constant_time.bytes_eq(digest, signature):
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raise InvalidSignature("Signature did not match digest.")
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