Changeset 36 for trunk

Timestamp:

02/12/13 15:47:25 (11 years ago)

Author:

tmorgan

Message:

added option for logging PKCS7 stripping/sanity checking

Location:

trunk/lib/bletchley

Files:

• CBC/__init__.py (modified) (1 diff)
• buffertools.py (modified) (2 diffs)

trunk/lib/bletchley/CBC/__init__.py

@@ -284 +284 @@
             decrypted = self.decrypt_block(self._iv, blocks[0]) + decrypted
             
-        return buffertools.stripPKCS7Pad(decrypted, self.block_size)
+        return buffertools.stripPKCS7Pad(decrypted, self.block_size, self.log_fh)
 
 

trunk/lib/bletchley/buffertools.py

@@ -122 +122 @@
         return chr(length) * length
 
-def stripPKCS7Pad(decrypted, block_size=16):
+def stripPKCS7Pad(decrypted, block_size=16, log_file=None):
     '''
     Validates a plaintext containing a PKCS5/7 pad, then returns the plaintext 
@@ -128 +128 @@
     '''
     if len(decrypted) % block_size != 0:
+        if log_file:
+            log_file.write("Can't strip PKCS7 pad.  Plaintext not correct length\n")
         return None
 
     length = ord(decrypted[-1])
     if length > block_size:
+        if log_file:
+            log_file.write("Can't strip PKCS7 pad.  Final byte length (%d) too large.\n" % length)
         return None
 
-    if decrypted[0-length:] != pkcs7Pad(length):
+    pad = decrypted[0-length:]
+    if pad != pkcs7Pad(length):
+        if log_file:
+            log_file.write("Can't strip PKCS7 pad.  Pads don't match. (%s != %s)\n" % (repr(pad), repr(pkcs7Pad(length))))
         return None