cryptopals

commit 9fa8aaf36b97dd89bc739755278581048f2f1ed7
parent 9782852d4d776f5896414b4cefbd789ac37384eb
Author: mpizzzle <michael.770211@gmail.com>
Date:   Thu, 26 Oct 2017 20:16:30 +0100

set 2 challenge 15 complete

Diffstat:
A
set2/pkcs7_padding_validation.py
 | 
18
++++++++++++++++++

1 file changed, 18 insertions(+), 0 deletions(-)
diff --git a/set2/pkcs7_padding_validation.py b/set2/pkcs7_padding_validation.py
@@ -0,0 +1,18 @@
+from Crypto.Cipher import AES
+
+def pkcs7_padding(msg):
+    pad_len = AES.block_size - (len(msg) % AES.block_size)
+    return msg + ''.join([chr(pad_len) for x in range(pad_len)])
+
+def pkcs7_padding_stripper(msg):
+    for char in msg[:len(msg) - ord(msg[len(msg) - 1]) : -1]:
+        if char != msg[len(msg) - 1]:
+            raise Exception("invalid pkcs7 padding")
+
+    return msg[:len(msg) - ord(msg[len(msg) - 1])]
+
+plaintext = "YELLOW SUBMARINE"
+
+pad = pkcs7_padding(plaintext)
+print pad.encode("hex")
+print pkcs7_padding_stripper(pad).encode("hex")