Fix LP#1132550: Expect uppercase 'IV' kwarg instead of lowercase 'iv' for MODE_OPENPGP

For most modes, the IV is passed as a kward named 'IV' (uppercase), but
for MODE_OPENPGP, it needed to be 'iv' (lowercase).

This change does not affect the use of positional arguments with
MODE_OPENPGP, and it does not affect the other modes.

Bug report: https://bugs.launchpad.net/pycrypto/+bug/1132550

2 files changed, 19 insertions, 3 deletions

diff --git a/lib/Crypto/Cipher/blockalgo.py b/lib/Crypto/Cipher/blockalgo.py
index dd183dc..8f78cc8 100644
--- a/lib/Crypto/Cipher/blockalgo.py
+++ b/lib/Crypto/Cipher/blockalgo.py
@@ -26,6 +26,9 @@ if sys.version_info[0] == 2 and sys.version_info[1] == 1:
     from Crypto.Util.py21compat import *
 from Crypto.Util.py3compat import *
 
+import warnings
+from Crypto.pct_warnings import LowercaseIV_DeprecationWarning
+
 #: *Electronic Code Book (ECB)*.
 #: This is the simplest encryption mode. Each of the plaintext blocks
 #: is directly encrypted into a ciphertext block, independently of
@@ -150,10 +153,20 @@ class BlockAlgo:
             
             self._done_first_block = False
             self._done_last_block = False
-            self.IV = _getParameter('iv', 1, args, kwargs)
+            self.IV = _getParameter('IV', 1, args, kwargs)
             if not self.IV:
-                raise ValueError("MODE_OPENPGP requires an IV")
-            
+                # XXX - When MODE_OPENPGP was introduced in PyCrypto 2.6, it
+                # expected a lowercase 'iv' kwarg, but every other block cipher
+                # module expected uppercase 'IV'.  For backward-compatibility,
+                # we'll support the old form for a release or two, then remove
+                # it.
+                self.IV = _getParameter('iv', 1, args, kwargs)
+                if self.IV:
+                    warnings.warn("lowercase 'iv' kwarg will be removed in a future version of PyCrypto",
+                                  LowercaseIV_DeprecationWarning, 4)
+                else:
+                    raise ValueError("MODE_OPENPGP requires an IV")
+
             # Instantiate a temporary cipher to process the IV
             IV_cipher = factory.new(key, MODE_CFB,
                     b('\x00')*self.block_size,      # IV for CFB
diff --git a/lib/Crypto/pct_warnings.py b/lib/Crypto/pct_warnings.py
index 9b4361e..10cf33a 100644
--- a/lib/Crypto/pct_warnings.py
+++ b/lib/Crypto/pct_warnings.py
@@ -52,6 +52,9 @@ class GetRandomNumber_DeprecationWarning(CryptoDeprecationWarning):
 class PowmInsecureWarning(CryptoRuntimeWarning):
     """Warning for when _fastmath is built without mpz_powm_sec"""
 
+class LowercaseIV_DeprecationWarning(CryptoDeprecationWarning):
+    """Issued when lowercase 'iv' kwarg is passed to a block cipher"""
+
 # By default, we want this warning to be shown every time we compensate for
 # clock rewinding.
 import warnings as _warnings