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# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
from __future__ import absolute_import, division, print_function
from cryptography import utils
from cryptography.exceptions import (
InvalidSignature, UnsupportedAlgorithm, _Reasons
)
from cryptography.hazmat.primitives import constant_time, hashes
@utils.register_interface(hashes.HashContext)
class _HMACContext(object):
def __init__(self, backend, key, algorithm, ctx=None):
self._algorithm = algorithm
self._backend = backend
if ctx is None:
ctx = self._backend._lib.Cryptography_HMAC_CTX_new()
self._backend.openssl_assert(ctx != self._backend._ffi.NULL)
ctx = self._backend._ffi.gc(
ctx, self._backend._lib.Cryptography_HMAC_CTX_free
)
evp_md = self._backend._evp_md_from_algorithm(algorithm)
if evp_md == self._backend._ffi.NULL:
raise UnsupportedAlgorithm(
"{} is not a supported hash on this backend".format(
algorithm.name),
_Reasons.UNSUPPORTED_HASH
)
key_ptr = self._backend._ffi.from_buffer(key)
res = self._backend._lib.HMAC_Init_ex(
ctx, key_ptr, len(key), evp_md, self._backend._ffi.NULL
)
self._backend.openssl_assert(res != 0)
self._ctx = ctx
self._key = key
algorithm = utils.read_only_property("_algorithm")
def copy(self):
copied_ctx = self._backend._lib.Cryptography_HMAC_CTX_new()
self._backend.openssl_assert(copied_ctx != self._backend._ffi.NULL)
copied_ctx = self._backend._ffi.gc(
copied_ctx, self._backend._lib.Cryptography_HMAC_CTX_free
)
res = self._backend._lib.HMAC_CTX_copy(copied_ctx, self._ctx)
self._backend.openssl_assert(res != 0)
return _HMACContext(
self._backend, self._key, self.algorithm, ctx=copied_ctx
)
def update(self, data):
data_ptr = self._backend._ffi.from_buffer(data)
res = self._backend._lib.HMAC_Update(self._ctx, data_ptr, len(data))
self._backend.openssl_assert(res != 0)
def finalize(self):
buf = self._backend._ffi.new("unsigned char[]",
self._backend._lib.EVP_MAX_MD_SIZE)
outlen = self._backend._ffi.new("unsigned int *")
res = self._backend._lib.HMAC_Final(self._ctx, buf, outlen)
self._backend.openssl_assert(res != 0)
self._backend.openssl_assert(outlen[0] == self.algorithm.digest_size)
return self._backend._ffi.buffer(buf)[:outlen[0]]
def verify(self, signature):
digest = self.finalize()
if not constant_time.bytes_eq(digest, signature):
raise InvalidSignature("Signature did not match digest.")
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