Changeset 119 for trunk

Timestamp:

10/25/16 18:31:57 (8 years ago)

Author:

tim

Message:

comments

File:

• trunk/lib/bletchley/CBC/__init__.py (modified) (3 diffs)

trunk/lib/bletchley/CBC/__init__.py

@@ -151 +151 @@
         if pad_length > 1:
             # XXX: If this test case fails, we should try instead
-            # lengthing the pad by one byte with all 256 values (as is
+            # lengthening the pad by one byte with all 256 values (as is
             # done in the 1-byte pad case).
             #
@@ -208 +208 @@
         """
 
+        # XXX: If the second-to-last byte of a block happens to be 0x02
+        #      then changing the final byte to either 0x01 or 0x02 would
+        #      cause no error to be generated by the oracle.  Need to
+        #      handle that corner case.  This doesn't occur on any other
+        #      offset, since we'll have already set the previously
+        #      decrypted bytes to a specific pad value, eliminating the
+        #      ambiguity.
+
         if(len(block)!=self.block_size):
             raise InvalidBlockError
@@ -224 +232 @@
 
         # XXX: catch any signal exceptions, such as ^C, and communicate
-        #      this back to the rest of the script so it can end immediately 
+        #      this back to the rest of the script so it can end immediately
         for x in range(0, 1+self.retries):
             # Each thread spawned searches a subset of the next byte's