CFB support

This requires a bit of explanation. OpenSSL has methods that implement
standard CFB, 1-bit CFB (cfb1), and 8-bit CFB (cfb8). Unfortunately,
while old (read: 0.9.7) versions of OpenSSL appear to test these
variants, newer versions have a comment stating that cfb{1,8} are
unsupported. Accordingly, I've backed out any support for the variants
for now. We can add it back into the CFB class if and when we gain a
backend that supports arbitrary s for 1 <= s <= block_size

2 files changed, 56 insertions, 0 deletions

diff --git a/cryptography/primitives/block/modes.py b/cryptography/primitives/block/modes.py
index 62a1c2c9..0f17a1a5 100644
--- a/cryptography/primitives/block/modes.py
+++ b/cryptography/primitives/block/modes.py
@@ -36,5 +36,14 @@ class OFB(object):
         self.nonce = nonce
 
 
+class CFB(object):
+    name = "CFB"
+
+    def __init__(self, initialization_vector):
+        super(CFB, self).__init__()
+        self.initialization_vector = initialization_vector
+
+
 interfaces.ModeWithInitializationVector.register(CBC)
 interfaces.ModeWithNonce.register(OFB)
+interfaces.ModeWithInitializationVector.register(CFB)
diff --git a/tests/primitives/test_nist.py b/tests/primitives/test_nist.py
index 0e16cc9c..1e5d2396 100644
--- a/tests/primitives/test_nist.py
+++ b/tests/primitives/test_nist.py
@@ -180,3 +180,50 @@ class TestAES_OFB(object):
         actual_ciphertext = cipher.encrypt(binascii.unhexlify(plaintext))
         actual_ciphertext += cipher.finalize()
         assert binascii.hexlify(actual_ciphertext) == ciphertext
+
+
+class TestAES_CFB(object):
+    @parameterize_encrypt_test(
+        "AES", "KAT",
+        ("key", "iv", "plaintext", "ciphertext"),
+        [
+            "CFB128GFSbox128.rsp",
+            "CFB128GFSbox192.rsp",
+            "CFB128GFSbox256.rsp",
+            "CFB128KeySbox128.rsp",
+            "CFB128KeySbox192.rsp",
+            "CFB128KeySbox256.rsp",
+            "CFB128VarKey128.rsp",
+            "CFB128VarKey192.rsp",
+            "CFB128VarKey256.rsp",
+            "CFB128VarTxt128.rsp",
+            "CFB128VarTxt192.rsp",
+            "CFB128VarTxt256.rsp",
+        ]
+    )
+    def test_KAT(self, key, iv, plaintext, ciphertext):
+        cipher = BlockCipher(
+            ciphers.AES(binascii.unhexlify(key)),
+            modes.CFB(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"),
+        [
+            "CFB128MMT128.rsp",
+            "CFB128MMT192.rsp",
+            "CFB128MMT256.rsp",
+        ]
+    )
+    def test_MMT(self, key, iv, plaintext, ciphertext):
+        cipher = BlockCipher(
+            ciphers.AES(binascii.unhexlify(key)),
+            modes.CFB(binascii.unhexlify(iv))
+        )
+        actual_ciphertext = cipher.encrypt(binascii.unhexlify(plaintext))
+        actual_ciphertext += cipher.finalize()
+        assert binascii.hexlify(actual_ciphertext) == ciphertext