cryptopals

commit eaff2c4988b536dd0175bfd1e426e849f378fed5
parent 814fdcda46c0c9f20c1da3a6951b1e4a9794fba9
Author: mpizzzle <michael.770211@gmail.com>
Date:   Sun, 17 Feb 2019 00:11:44 +0000

challenge 27 complete

Diffstat:
A
set4/cbc_recover_key_from_iv.py
 | 
37
+++++++++++++++++++++++++++++++++++++

1 file changed, 37 insertions(+), 0 deletions(-)
diff --git a/set4/cbc_recover_key_from_iv.py b/set4/cbc_recover_key_from_iv.py
@@ -0,0 +1,37 @@
+import re
+from Crypto.Cipher import AES
+from Crypto import Random
+
+key = Random.new().read(AES.block_size)
+
+def encrypt(msg):
+    pad_len = AES.block_size - (len(msg) % AES.block_size)
+    return AES.new(key, AES.MODE_CBC, key).encrypt(msg + ''.join([chr(pad_len) for x in range(pad_len)]))
+
+def decrypt(cipher):
+    plaintext = AES.new(key, AES.MODE_CBC, key).decrypt(cipher)
+    
+    for c in plaintext:
+        if ord(c) >= 128:
+            print "invalid character found: " + plaintext
+            break
+
+    return plaintext
+
+def xor(a, b):
+    return "".join([chr(ord(x) ^ ord(y)) for (x, y) in zip(a, b)])
+
+def encryption_oracle(m):
+    return encrypt("comment1=cooking%20MCs;userdata=" + re.sub("[;|=]", '', m) + ";comment2=%20like%20a%20pound%20of%20bacon")
+
+plaintext = "hello-admin-truehello-admin-truehello-admin-true"
+ciphertext = list(encryption_oracle(plaintext))
+
+for i in range(AES.block_size):
+    ciphertext[i + AES.block_size] = '\x00'
+    ciphertext[i + AES.block_size + AES.block_size] = ciphertext[i]
+
+corrupted = decrypt(''.join(ciphertext))
+recovered_key = xor(corrupted[:AES.block_size], corrupted[2 * AES.block_size : 3 * AES.block_size])
+
+print recovered_key == key