Throw exception when IV is used with ECB or CTR

The IV parameter is currently ignored when initializing
a cipher in ECB or CTR mode.

For CTR mode, it is confusing: it takes some time to see
that a different parameter is needed (the counter).

For ECB mode, it is outright dangerous.

This patch forces an exception to be raised.

1 files changed, 23 insertions, 8 deletions

diff --git a/lib/Crypto/SelfTest/Cipher/common.py b/lib/Crypto/SelfTest/Cipher/common.py
index 420b6ff..a5f8a88 100644
--- a/lib/Crypto/SelfTest/Cipher/common.py
+++ b/lib/Crypto/SelfTest/Cipher/common.py
@@ -605,19 +605,34 @@ class RoundtripTest(unittest.TestCase):
         return """%s .decrypt() output of .encrypt() should not be garbled""" % (self.module_name,)
 
     def runTest(self):
-        for mode in (self.module.MODE_ECB, self.module.MODE_CBC, self.module.MODE_CFB, self.module.MODE_OFB, self.module.MODE_OPENPGP):
+
+        ## ECB mode
+        mode = self.module.MODE_ECB
+        encryption_cipher = self.module.new(a2b_hex(self.key), mode)
+        ciphertext = encryption_cipher.encrypt(self.plaintext)
+        decryption_cipher = self.module.new(a2b_hex(self.key), mode)
+        decrypted_plaintext = decryption_cipher.decrypt(ciphertext)
+        self.assertEqual(self.plaintext, decrypted_plaintext)
+
+        ## OPENPGP mode
+        mode = self.module.MODE_OPENPGP
+        encryption_cipher = self.module.new(a2b_hex(self.key), mode, self.iv)
+        eiv_ciphertext = encryption_cipher.encrypt(self.plaintext)
+        eiv = eiv_ciphertext[:self.module.block_size+2]
+        ciphertext = eiv_ciphertext[self.module.block_size+2:]
+        decryption_cipher = self.module.new(a2b_hex(self.key), mode, eiv)
+        decrypted_plaintext = decryption_cipher.decrypt(ciphertext)
+        self.assertEqual(self.plaintext, decrypted_plaintext)
+
+        ## All other non-AEAD modes (but CTR)
+        for mode in (self.module.MODE_CBC, self.module.MODE_CFB, self.module.MODE_OFB):
             encryption_cipher = self.module.new(a2b_hex(self.key), mode, self.iv)
             ciphertext = encryption_cipher.encrypt(self.plaintext)
-
-            if mode != self.module.MODE_OPENPGP:
-                decryption_cipher = self.module.new(a2b_hex(self.key), mode, self.iv)
-            else:
-                eiv = ciphertext[:self.module.block_size+2]
-                ciphertext = ciphertext[self.module.block_size+2:]
-                decryption_cipher = self.module.new(a2b_hex(self.key), mode, eiv)
+            decryption_cipher = self.module.new(a2b_hex(self.key), mode, self.iv)
             decrypted_plaintext = decryption_cipher.decrypt(ciphertext)
             self.assertEqual(self.plaintext, decrypted_plaintext)
 
+
 class PGPTest(unittest.TestCase):
     def __init__(self, module, params):
         unittest.TestCase.__init__(self)