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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
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, interfaces
@utils.register_interface(interfaces.MACContext)
@utils.register_interface(interfaces.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._ffi.new("HMAC_CTX *")
self._backend._lib.HMAC_CTX_init(ctx)
ctx = self._backend._ffi.gc(
ctx, self._backend._lib.HMAC_CTX_cleanup
)
evp_md = self._backend._lib.EVP_get_digestbyname(
algorithm.name.encode('ascii'))
if evp_md == self._backend._ffi.NULL:
raise UnsupportedAlgorithm(
"{0} is not a supported hash on this backend.".format(
algorithm.name),
_Reasons.UNSUPPORTED_HASH
)
res = self._backend._lib.Cryptography_HMAC_Init_ex(
ctx, key, len(key), evp_md, self._backend._ffi.NULL
)
assert res != 0
self._ctx = ctx
self._key = key
algorithm = utils.read_only_property("_algorithm")
def copy(self):
copied_ctx = self._backend._ffi.new("HMAC_CTX *")
self._backend._lib.HMAC_CTX_init(copied_ctx)
copied_ctx = self._backend._ffi.gc(
copied_ctx, self._backend._lib.HMAC_CTX_cleanup
)
res = self._backend._lib.Cryptography_HMAC_CTX_copy(
copied_ctx, self._ctx
)
assert res != 0
return _HMACContext(
self._backend, self._key, self.algorithm, ctx=copied_ctx
)
def update(self, data):
res = self._backend._lib.Cryptography_HMAC_Update(
self._ctx, data, len(data)
)
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.Cryptography_HMAC_Final(
self._ctx, buf, outlen
)
assert res != 0
assert outlen[0] == self.algorithm.digest_size
self._backend._lib.HMAC_CTX_cleanup(self._ctx)
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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