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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 UnsupportedAlgorithm
from cryptography.hazmat.backends.interfaces import (
CipherBackend, HashBackend, HMACBackend, PBKDF2HMACBackend
)
@utils.register_interface(CipherBackend)
@utils.register_interface(HashBackend)
@utils.register_interface(HMACBackend)
@utils.register_interface(PBKDF2HMACBackend)
class PrioritizedMultiBackend(object):
name = "multibackend"
def __init__(self, backends):
self._backends = backends
def _filtered_backends(self, interface):
for b in self._backends:
if isinstance(b, interface):
yield b
def cipher_supported(self, algorithm, mode):
return any(
b.cipher_supported(algorithm, mode)
for b in self._filtered_backends(CipherBackend)
)
def create_symmetric_encryption_ctx(self, algorithm, mode):
for b in self._filtered_backends(CipherBackend):
try:
return b.create_symmetric_encryption_ctx(algorithm, mode)
except UnsupportedAlgorithm:
pass
raise UnsupportedAlgorithm
def create_symmetric_decryption_ctx(self, algorithm, mode):
for b in self._filtered_backends(CipherBackend):
try:
return b.create_symmetric_decryption_ctx(algorithm, mode)
except UnsupportedAlgorithm:
pass
raise UnsupportedAlgorithm
def hash_supported(self, algorithm):
return any(
b.hash_supported(algorithm)
for b in self._filtered_backends(HashBackend)
)
def create_hash_ctx(self, algorithm):
for b in self._filtered_backends(HashBackend):
try:
return b.create_hash_ctx(algorithm)
except UnsupportedAlgorithm:
pass
raise UnsupportedAlgorithm
def hmac_supported(self, algorithm):
return any(
b.hmac_supported(algorithm)
for b in self._filtered_backends(HMACBackend)
)
def create_hmac_ctx(self, key, algorithm):
for b in self._filtered_backends(HMACBackend):
try:
return b.create_hmac_ctx(key, algorithm)
except UnsupportedAlgorithm:
pass
raise UnsupportedAlgorithm
def pbkdf2_hmac_supported(self, algorithm):
return any(
b.pbkdf2_hmac_supported(algorithm)
for b in self._filtered_backends(PBKDF2HMACBackend)
)
def derive_pbkdf2_hmac(self, algorithm, length, salt, iterations,
key_material):
for b in self._filtered_backends(PBKDF2HMACBackend):
try:
return b.derive_pbkdf2_hmac(
algorithm, length, salt, iterations, key_material
)
except UnsupportedAlgorithm:
pass
raise UnsupportedAlgorithm
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