Merge pull request #338 from reaperhulk/hmac-supported-check

Add hmac_supported method to backend

2 files changed, 10 insertions, 0 deletions

diff --git a/cryptography/hazmat/backends/interfaces.py b/cryptography/hazmat/backends/interfaces.py
index 912476bb..9a570968 100644
--- a/cryptography/hazmat/backends/interfaces.py
+++ b/cryptography/hazmat/backends/interfaces.py
@@ -60,6 +60,13 @@ class HashBackend(six.with_metaclass(abc.ABCMeta)):
 
 class HMACBackend(six.with_metaclass(abc.ABCMeta)):
     @abc.abstractmethod
+    def hmac_supported(self, algorithm):
+        """
+        Return True if the hash algorithm is supported for HMAC by this
+        backend.
+        """
+
+    @abc.abstractmethod
     def create_hmac_ctx(self, key, algorithm):
         """
         Create a HashContext for calculating a message authentication code.
diff --git a/cryptography/hazmat/backends/openssl/backend.py b/cryptography/hazmat/backends/openssl/backend.py
index f11ddf22..7b67fb0b 100644
--- a/cryptography/hazmat/backends/openssl/backend.py
+++ b/cryptography/hazmat/backends/openssl/backend.py
@@ -184,6 +184,9 @@ class Backend(object):
         digest = self.lib.EVP_get_digestbyname(algorithm.name.encode("ascii"))
         return digest != self.ffi.NULL
 
+    def hmac_supported(self, algorithm):
+        return self.hash_supported(algorithm)
+
     def create_hash_ctx(self, algorithm):
         return _HashContext(self, algorithm)