cryptography/hazmat/backends/multibackend.py

# 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
)


@utils.register_interface(CipherBackend)
@utils.register_interface(HashBackend)
@utils.register_interface(HMACBackend)
class PrioritizedMultiBackend(object):
    name = "multibackend"

    def __init__(self, backends):
        self._backends = backends

    def cipher_supported(self, algorithm, mode):
        return any(b.cipher_supported(algorithm, mode) for b in self._backends)

    def create_symmetric_encryption_ctx(self, algorithm, mode):
        for b in self._backends:
            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._backends:
            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._backends)

    def create_hash_ctx(self, algorithm):
        for b in self._backends:
            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._backends)

    def create_hmac_ctx(self, key, algorithm):
        for b in self._backends:
            try:
                return b.create_hmac_ctx(key, algorithm)
            except UnsupportedAlgorithm:
                pass
        raise UnsupportedAlgorithm