Merge pull request #868 from skeuomorf/dsa-parameters

Add DSA parameters api, docs and tests

1 files changed, 74 insertions, 0 deletions

diff --git a/cryptography/hazmat/primitives/asymmetric/dsa.py b/cryptography/hazmat/primitives/asymmetric/dsa.py
new file mode 100644
index 00000000..c368e783
--- /dev/null
+++ b/cryptography/hazmat/primitives/asymmetric/dsa.py
@@ -0,0 +1,74 @@
+# 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.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
+
+    @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