diff --git a/cryptography/hazmat/primitives/interfaces.py b/cryptography/hazmat/primitives/interfaces.py
index 49c19d0..217490f 100644
--- a/cryptography/hazmat/primitives/interfaces.py
+++ b/cryptography/hazmat/primitives/interfaces.py
@@ -45,3 +45,17 @@
         """
         finalize return bytes
         """
+
+
+class PaddingContext(six.with_metaclass(abc.ABCMeta)):
+    @abc.abstractmethod
+    def update(self, data):
+        """
+        update takes bytes and return bytes
+        """
+
+    @abc.abstractmethod
+    def finalize(self):
+        """
+        finalize return bytes
+        """
diff --git a/cryptography/hazmat/primitives/padding.py b/cryptography/hazmat/primitives/padding.py
index 09e4b9f..8e2219e 100644
--- a/cryptography/hazmat/primitives/padding.py
+++ b/cryptography/hazmat/primitives/padding.py
@@ -13,6 +13,8 @@
 
 import six
 
+from cryptography.hazmat.primitives import interfaces
+
 
 class PKCS7(object):
     def __init__(self, block_size):
@@ -40,6 +42,7 @@
         return unpadder.update(data) + unpadder.finalize()
 
 
+@interfaces.register(interfaces.PaddingContext)
 class _PaddingContext(object):
     def __init__(self, block_size):
         super(_PaddingContext, self).__init__()
@@ -70,6 +73,7 @@
         return result
 
 
+@interfaces.register(interfaces.PaddingContext)
 class _UnpaddingContext(object):
     def __init__(self, block_size):
         super(_UnpaddingContext, self).__init__()