111 lines
3.4 KiB
Python
111 lines
3.4 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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import six
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from cryptography import utils
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from cryptography.exceptions import (
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AlreadyFinalized, InvalidKey, UnsupportedAlgorithm, _Reasons
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)
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from cryptography.hazmat.backends.interfaces import HMACBackend
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from cryptography.hazmat.primitives import constant_time, hmac
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from cryptography.hazmat.primitives.kdf import KeyDerivationFunction
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@utils.register_interface(KeyDerivationFunction)
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class HKDF(object):
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def __init__(self, algorithm, length, salt, info, backend):
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if not isinstance(backend, HMACBackend):
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raise UnsupportedAlgorithm(
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"Backend object does not implement HMACBackend.",
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_Reasons.BACKEND_MISSING_INTERFACE
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)
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self._algorithm = algorithm
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if salt is None:
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salt = b"\x00" * self._algorithm.digest_size
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else:
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utils._check_bytes("salt", salt)
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self._salt = salt
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self._backend = backend
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self._hkdf_expand = HKDFExpand(self._algorithm, length, info, backend)
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def _extract(self, key_material):
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h = hmac.HMAC(self._salt, self._algorithm, backend=self._backend)
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h.update(key_material)
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return h.finalize()
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def derive(self, key_material):
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utils._check_byteslike("key_material", key_material)
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return self._hkdf_expand.derive(self._extract(key_material))
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def verify(self, key_material, expected_key):
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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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@utils.register_interface(KeyDerivationFunction)
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class HKDFExpand(object):
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def __init__(self, algorithm, length, info, backend):
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if not isinstance(backend, HMACBackend):
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raise UnsupportedAlgorithm(
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"Backend object does not implement HMACBackend.",
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_Reasons.BACKEND_MISSING_INTERFACE
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)
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self._algorithm = algorithm
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self._backend = backend
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max_length = 255 * algorithm.digest_size
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if length > max_length:
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raise ValueError(
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"Can not derive keys larger than {} octets.".format(
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max_length
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))
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self._length = length
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if info is None:
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info = b""
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else:
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utils._check_bytes("info", info)
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self._info = info
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self._used = False
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def _expand(self, key_material):
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output = [b""]
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counter = 1
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while self._algorithm.digest_size * (len(output) - 1) < self._length:
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h = hmac.HMAC(key_material, self._algorithm, backend=self._backend)
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h.update(output[-1])
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h.update(self._info)
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h.update(six.int2byte(counter))
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output.append(h.finalize())
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counter += 1
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return b"".join(output)[:self._length]
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def derive(self, key_material):
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utils._check_byteslike("key_material", key_material)
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if self._used:
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raise AlreadyFinalized
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self._used = True
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return self._expand(key_material)
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def verify(self, key_material, expected_key):
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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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