challenge 15 set 2

src/padding.py

@@ -20,3 +20,14 @@ def strip_pkcs7_pad(block, block_size=16):
         if last_byte > 0 and last_byte < block_size:
             return block[0:(-1*last_byte)]
     return block
+
+def throw_bad_padding(block, block_size=16):
+    block_len = len(block)
+    if block_len % block_size == 0:
+        # check last byte
+        last_byte = block[-1]
+        pad_bytes = block[(-1*last_byte):]
+        for pad_byte in pad_bytes:
+            if pad_byte != last_byte:
+                raise Exception("Bad padding")
+

tests/test_set2.py

@@ -148,9 +148,18 @@ def test_set2_challenge14(self):
         plaintext = b''.join([i.to_bytes() for i in plaintext_bytes])
         self.assertEqual(expected, plaintext) # cool af
 
-        return
     def test_set2_challenge15(self):
-        return
+        cases = [
+            b'ICE ICE BABY\x04\x04\x04\x04',
+            b'ICE ICE BABY\x05\x05\x05\x05',
+            b'ICE ICE BABY\x01\x02\x03\x04'
+        ]
+        for c in cases:
+            try:
+                padding.throw_bad_padding(c)
+            except Exception as e:
+                self.assertRaises(Exception, e)
+
     def test_set2_challenge16(self):
         return