updates for review feedback

5 files changed, 23 insertions, 22 deletions

diff --git a/cryptography/hazmat/backends/interfaces.py b/cryptography/hazmat/backends/interfaces.py
index 66ee1e44..e63b079b 100644
--- a/cryptography/hazmat/backends/interfaces.py
+++ b/cryptography/hazmat/backends/interfaces.py
@@ -159,7 +159,7 @@ class DSABackend(object):
         """
 
     @abc.abstractmethod
-    def dsa_parameters_supported(self, p, q):
+    def dsa_parameters_supported(self, p, q, g):
         """
         Return True if the parameters are supported by the backend for DSA.
         """
diff --git a/cryptography/hazmat/backends/openssl/backend.py b/cryptography/hazmat/backends/openssl/backend.py
index ea58d753..37d1c35e 100644
--- a/cryptography/hazmat/backends/openssl/backend.py
+++ b/cryptography/hazmat/backends/openssl/backend.py
@@ -492,20 +492,14 @@ class Backend(object):
         return ctx
 
     def dsa_hash_supported(self, algorithm):
-        if (
-            self._lib.OPENSSL_VERSION_NUMBER < 0x1000000f and
-            not isinstance(algorithm, hashes.SHA1)
-        ):
-            return False
+        if self._lib.OPENSSL_VERSION_NUMBER < 0x1000000f:
+            return isinstance(algorithm, hashes.SHA1)
         else:
             return self.hash_supported(algorithm)
 
-    def dsa_parameters_supported(self, p, q):
-        if (
-            self._lib.OPENSSL_VERSION_NUMBER < 0x1000000f and
-            not (utils.bit_length(p) <= 1024 and utils.bit_length(q) <= 160)
-        ):
-            return False
+    def dsa_parameters_supported(self, p, q, g):
+        if self._lib.OPENSSL_VERSION_NUMBER < 0x1000000f:
+            return (utils.bit_length(p) <= 1024 and utils.bit_length(q) <= 160)
         else:
             return True
 
@@ -1334,8 +1328,7 @@ class _RSAVerificationContext(object):
 
 @utils.register_interface(interfaces.AsymmetricVerificationContext)
 class _DSAVerificationContext(object):
-    def __init__(
-            self, backend, public_key, signature, algorithm):
+    def __init__(self, backend, public_key, signature, algorithm):
         self._backend = backend
         self._public_key = public_key
         self._signature = signature
@@ -1361,6 +1354,8 @@ class _DSAVerificationContext(object):
         data_to_verify = self._hash_ctx.finalize()
         self._hash_ctx = None
 
+        # The first parameter passed to DSA_verify is unused by OpenSSL but
+        # must be an integer.
         res = self._backend._lib.DSA_verify(
             0, data_to_verify, len(data_to_verify), self._signature,
             len(self._signature), self._dsa_cdata)
diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst
index 3b3d5eff..6833f221 100644
--- a/docs/hazmat/backends/interfaces.rst
+++ b/docs/hazmat/backends/interfaces.rst
@@ -351,7 +351,8 @@ A specific ``backend`` may provide one or more of these interfaces.
             :class:`~cryptography.hazmat.primitives.interfaces.DSAPublicKey`
             provider.
 
-        :param bytes signature: The signature to verify.
+        :param bytes signature: The signature to verify. DER encoded as
+            specified in :rfc:`6979`.
 
         :param algorithm: An instance of a
             :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
@@ -369,14 +370,16 @@ A specific ``backend`` may provide one or more of these interfaces.
         :returns: ``True`` if the specified ``algorithm`` is supported by this
             backend, otherwise ``False``.
 
-    .. method:: dsa_parameters_supported(p, q):
+    .. method:: dsa_parameters_supported(p, q, g):
 
         :param int p: The p value of a DSA key.
 
         :param int q: The q value of a DSA key.
 
-        :returns: ``True`` if the given values of ``p`` and ``q`` are supported
-            by this backend, otherwise ``False``.
+        :param int g: The g value of a DSA key.
+
+        :returns: ``True`` if the given values of ``p``, ``q``, and ``g`` are
+            supported by this backend, otherwise ``False``.
 
 
 .. class:: CMACBackend
diff --git a/docs/hazmat/primitives/asymmetric/dsa.rst b/docs/hazmat/primitives/asymmetric/dsa.rst
index 5cee5705..03e476b6 100644
--- a/docs/hazmat/primitives/asymmetric/dsa.rst
+++ b/docs/hazmat/primitives/asymmetric/dsa.rst
@@ -142,7 +142,7 @@ DSA
             ...     hashes.SHA256(),
             ...     default_backend()
             ... )
-            >>> data= b"this is some data I'd like to sign"
+            >>> data = b"this is some data I'd like to sign"
             >>> signer.update(data)
             >>> signature = signer.finalize()
             >>> public_key = private_key.public_key()
@@ -154,7 +154,7 @@ DSA
             >>> verifier.update(data)
             >>> verifier.verify()
 
-        :param bytes signature: The signature to verify in DER encoding as
+        :param bytes signature: The signature to verify. DER encoded as
             specified in :rfc:`6979`.
 
         :param algorithm: An instance of a
diff --git a/tests/hazmat/primitives/test_dsa.py b/tests/hazmat/primitives/test_dsa.py
index 67f90295..c6642e07 100644
--- a/tests/hazmat/primitives/test_dsa.py
+++ b/tests/hazmat/primitives/test_dsa.py
@@ -744,8 +744,11 @@ class TestDSAVerification(object):
     def test_dsa_verification(self, vector, backend):
         digest_algorithm = vector['digest_algorithm'].replace("-", "")
         algorithm = self._algorithms_dict[digest_algorithm]
-        if (not backend.dsa_parameters_supported(vector['p'], vector['q'])
-                or not backend.dsa_hash_supported(algorithm)):
+        if (
+            not backend.dsa_parameters_supported(
+                vector['p'], vector['q'], vector['g']
+            ) or not backend.dsa_hash_supported(algorithm)
+        ):
             pytest.skip(
                 "{0} does not support the provided parameters".format(backend)
             )