add output feedback mode support + test vectors (aes)

3 files changed, 69 insertions, 0 deletions

diff --git a/cryptography/primitives/block/modes.py b/cryptography/primitives/block/modes.py
index c722e739..70ef8178 100644
--- a/cryptography/primitives/block/modes.py
+++ b/cryptography/primitives/block/modes.py
@@ -28,4 +28,13 @@ class ECB(object):
     name = "ECB"
 
 
+class OFB(object):
+    name = "OFB"
+
+    def __init__(self, initialization_vector):
+        super(OFB, self).__init__()
+        self.initialization_vector = initialization_vector
+
+
 interfaces.ModeWithInitializationVector.register(CBC)
+interfaces.ModeWithInitializationVector.register(OFB)
diff --git a/docs/primitives/symmetric-encryption.rst b/docs/primitives/symmetric-encryption.rst
index d0429d4b..7ec42a30 100644
--- a/docs/primitives/symmetric-encryption.rst
+++ b/docs/primitives/symmetric-encryption.rst
@@ -68,6 +68,19 @@ Modes
                                         reuse an ``initialization_vector`` with
                                         a given ``key``.
 
+.. class:: cryptography.primitives.block.modes.OFB(initialization_vector)
+
+    OFB (Output Feedback) is a mode of operation for block ciphers. It
+    transforms a block cipher into a stream cipher.
+
+    :param bytes initialization_vector: Must be random bytes. They do not need
+                                        to be kept secret (they can be included
+                                        in a transmitted message). Must be the
+                                        same number of bytes as the
+                                        ``block_size`` of the cipher. Do not
+                                        reuse an ``initialization_vector`` with
+                                        a given ``key``.
+
 
 Insecure Modes
 --------------
diff --git a/tests/primitives/test_nist.py b/tests/primitives/test_nist.py
index 3dc8277a..0e16cc9c 100644
--- a/tests/primitives/test_nist.py
+++ b/tests/primitives/test_nist.py
@@ -133,3 +133,50 @@ class TestAES_ECB(object):
         actual_ciphertext = cipher.encrypt(binascii.unhexlify(plaintext))
         actual_ciphertext += cipher.finalize()
         assert binascii.hexlify(actual_ciphertext) == ciphertext
+
+
+class TestAES_OFB(object):
+    @parameterize_encrypt_test(
+        "AES", "KAT",
+        ("key", "iv", "plaintext", "ciphertext"),
+        [
+            "OFBGFSbox128.rsp",
+            "OFBGFSbox192.rsp",
+            "OFBGFSbox256.rsp",
+            "OFBKeySbox128.rsp",
+            "OFBKeySbox192.rsp",
+            "OFBKeySbox256.rsp",
+            "OFBVarKey128.rsp",
+            "OFBVarKey192.rsp",
+            "OFBVarKey256.rsp",
+            "OFBVarTxt128.rsp",
+            "OFBVarTxt192.rsp",
+            "OFBVarTxt256.rsp",
+        ]
+    )
+    def test_KAT(self, key, iv, plaintext, ciphertext):
+        cipher = BlockCipher(
+            ciphers.AES(binascii.unhexlify(key)),
+            modes.OFB(binascii.unhexlify(iv))
+        )
+        actual_ciphertext = cipher.encrypt(binascii.unhexlify(plaintext))
+        actual_ciphertext += cipher.finalize()
+        assert binascii.hexlify(actual_ciphertext) == ciphertext
+
+    @parameterize_encrypt_test(
+        "AES", "MMT",
+        ("key", "iv", "plaintext", "ciphertext"),
+        [
+            "OFBMMT128.rsp",
+            "OFBMMT192.rsp",
+            "OFBMMT256.rsp",
+        ]
+    )
+    def test_MMT(self, key, iv, plaintext, ciphertext):
+        cipher = BlockCipher(
+            ciphers.AES(binascii.unhexlify(key)),
+            modes.OFB(binascii.unhexlify(iv))
+        )
+        actual_ciphertext = cipher.encrypt(binascii.unhexlify(plaintext))
+        actual_ciphertext += cipher.finalize()
+        assert binascii.hexlify(actual_ciphertext) == ciphertext