DSA signing support (this is mostly skeuomorf's work, credit to him)

3 files changed, 73 insertions, 0 deletions

diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst
index 6833f221..f363b541 100644
--- a/docs/hazmat/backends/interfaces.rst
+++ b/docs/hazmat/backends/interfaces.rst
@@ -345,6 +345,19 @@ A specific ``backend`` may provide one or more of these interfaces.
             1.0.0 and the key size is larger than 1024; older OpenSSL versions
             do not support keys larger than 1024 bits.
 
+    .. method:: create_dsa_signature_ctx(private_key, algorithm)
+
+        :param private_key: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.DSAPrivateKey`
+            provider.
+
+        :param algorithm: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+            provider
+
+        :returns:
+            :class:`~cryptography.hazmat.primitives.interfaces.AsymmetricSignatureContext`
+
     .. method:: create_dsa_verification_ctx(public_key, signature, algorithm)
 
         :param public_key: An instance of a
diff --git a/docs/hazmat/primitives/asymmetric/dsa.rst b/docs/hazmat/primitives/asymmetric/dsa.rst
index 03e476b6..98aebb6b 100644
--- a/docs/hazmat/primitives/asymmetric/dsa.rst
+++ b/docs/hazmat/primitives/asymmetric/dsa.rst
@@ -97,6 +97,49 @@ DSA
             or if the OpenSSL version is older than 1.0.0 and the key size is larger than 1024
             because older OpenSSL versions don't support a key size larger than 1024.
 
+    .. method:: signer(algorithm, backend)
+
+        .. versionadded:: 0.4
+
+        Sign data which can be verified later by others using the public key.
+
+        .. code-block:: pycon
+
+            >>> from cryptography.hazmat.backends import default_backend
+            >>> from cryptography.hazmat.primitives import hashes
+            >>> from cryptography.hazmat.primitives.asymmetric import dsa
+            >>> parameters = dsa.DSAParameters.generate(
+            ...     key_size=1024,
+            ...     backend=default_backend()
+            ... )
+            >>> private_key = dsa.DSAPrivateKey.generate(
+            ...     parameters=parameters,
+            ...     backend=default_backend()
+            ... )
+            >>> signer = private_key.signer(
+            ...     hashes.SHA256(),
+            ...     default_backend()
+            ... )
+            >>> data= b"this is some data I'd like to sign"
+            >>> signer.update(data)
+            >>> signature = signer.finalize()
+            >>> public_key = private_key.public_key()
+
+        :param algorithm: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+            provider.
+
+        :param backend: A
+            :class:`~cryptography.hazmat.backends.interfaces.RSABackend`
+            provider.
+
+        :returns:
+            :class:`~cryptography.hazmat.primitives.interfaces.AsymmetricSignatureContext`
+
+        :raises cryptography.exceptions.UnsupportedAlgorithm: This is raised if
+            the provided ``backend`` does not implement
+            :class:`~cryptography.hazmat.backends.interfaces.DSABackend`
+
 
 .. class:: DSAPublicKey(modulus, subgroup_order, generator, y)
 
diff --git a/docs/hazmat/primitives/interfaces.rst b/docs/hazmat/primitives/interfaces.rst
index feafe941..dc09a26f 100644
--- a/docs/hazmat/primitives/interfaces.rst
+++ b/docs/hazmat/primitives/interfaces.rst
@@ -381,6 +381,23 @@ Asymmetric interfaces
 
         The DSAParameters object associated with this private key.
 
+    .. method:: signer(algorithm, backend)
+
+        .. versionadded:: 0.4
+
+        Sign data which can be verified later by others using the public key.
+
+        :param algorithm: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+            provider.
+
+        :param backend: A
+            :class:`~cryptography.hazmat.backends.interfaces.DSABackend`
+            provider.
+
+        :returns:
+            :class:`~cryptography.hazmat.primitives.interfaces.AsymmetricSignatureContext`
+
     .. attribute:: key_size
 
         :type: int