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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
import six
from cryptography import utils
from cryptography.exceptions import UnsupportedAlgorithm, _Reasons
from cryptography.hazmat.backends.interfaces import DSABackend
from cryptography.hazmat.primitives import interfaces
def _check_dsa_parameters(modulus, subgroup_order, generator):
if (
not isinstance(modulus, six.integer_types) or
not isinstance(subgroup_order, six.integer_types) or
not isinstance(generator, six.integer_types)
):
raise TypeError("DSA parameters must be integers")
if (utils.bit_length(modulus),
utils.bit_length(subgroup_order)) not in (
(1024, 160),
(2048, 256),
(3072, 256)):
raise ValueError("modulus and subgroup_order lengths must be "
"one of these pairs (1024, 160) or (2048, 256) "
"or (3072, 256)")
if generator <= 1 or generator >= modulus:
raise ValueError("generator must be > 1 and < modulus")
@utils.register_interface(interfaces.DSAParameters)
class DSAParameters(object):
def __init__(self, modulus, subgroup_order, generator):
_check_dsa_parameters(modulus, subgroup_order, generator)
self._modulus = modulus
self._subgroup_order = subgroup_order
self._generator = generator
@classmethod
def generate(cls, key_size, backend):
if not isinstance(backend, DSABackend):
raise UnsupportedAlgorithm(
"Backend object does not implement DSABackend",
_Reasons.BACKEND_MISSING_INTERFACE
)
return backend.generate_dsa_parameters(key_size)
@property
def modulus(self):
return self._modulus
@property
def subgroup_order(self):
return self._subgroup_order
@property
def generator(self):
return self._generator
@property
def p(self):
return self.modulus
@property
def q(self):
return self.subgroup_order
@property
def g(self):
return self.generator
@utils.register_interface(interfaces.DSAPrivateKey)
class DSAPrivateKey(object):
def __init__(self, modulus, subgroup_order, generator, x, y):
_check_dsa_parameters(modulus, subgroup_order, generator)
if (
not isinstance(x, six.integer_types) or
not isinstance(y, six.integer_types)
):
raise TypeError("DSAPrivateKey arguments must be integers")
if x <= 0 or x >= subgroup_order:
raise ValueError("x must be > 0 and < subgroup_order")
if y != pow(generator, x, modulus):
raise ValueError("y must be equal to (generator ** x % modulus)")
self._modulus = modulus
self._subgroup_order = subgroup_order
self._generator = generator
self._x = x
self._y = y
@classmethod
def generate(cls, parameters, backend):
if not isinstance(backend, DSABackend):
raise UnsupportedAlgorithm(
"Backend object does not implement DSABackend",
_Reasons.BACKEND_MISSING_INTERFACE
)
return backend.generate_dsa_private_key(parameters)
def signer(self, algorithm, backend):
if not isinstance(backend, DSABackend):
raise UnsupportedAlgorithm(
"Backend object does not implement DSABackend",
_Reasons.BACKEND_MISSING_INTERFACE
)
return backend.create_dsa_signature_ctx(self, algorithm)
@property
def key_size(self):
return utils.bit_length(self._modulus)
def public_key(self):
return DSAPublicKey(self._modulus, self._subgroup_order,
self._generator, self.y)
@property
def x(self):
return self._x
@property
def y(self):
return self._y
def parameters(self):
return DSAParameters(self._modulus, self._subgroup_order,
self._generator)
@utils.register_interface(interfaces.DSAPublicKey)
class DSAPublicKey(object):
def __init__(self, modulus, subgroup_order, generator, y):
_check_dsa_parameters(modulus, subgroup_order, generator)
if not isinstance(y, six.integer_types):
raise TypeError("y must be an integer")
self._modulus = modulus
self._subgroup_order = subgroup_order
self._generator = generator
self._y = y
def verifier(self, signature, algorithm, backend):
if not isinstance(backend, DSABackend):
raise UnsupportedAlgorithm(
"Backend object does not implement DSABackend",
_Reasons.BACKEND_MISSING_INTERFACE
)
return backend.create_dsa_verification_ctx(self, signature,
algorithm)
@property
def key_size(self):
return utils.bit_length(self._modulus)
@property
def y(self):
return self._y
def parameters(self):
return DSAParameters(self._modulus, self._subgroup_order,
self._generator)
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