cryptopals

commit 82e6fb6b919162dcc0b801d7a8094fa18bde5228
parent 2c14f2e2a1a97bba3f48503feb90661ec9a5876e
Author: mpizzzle <michael.770211@gmail.com>
Date:   Mon, 30 Oct 2017 17:56:26 +0000

temp commit for challenge 17

Diffstat:
A
set3/cbc_padding_oracle.py
 | 
68
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A
set3/files/17.txt
 | 
10
++++++++++

2 files changed, 78 insertions(+), 0 deletions(-)
diff --git a/set3/cbc_padding_oracle.py b/set3/cbc_padding_oracle.py
@@ -0,0 +1,68 @@
+from Crypto.Cipher import AES
+from Crypto import Random
+from Crypto.Random import random
+
+key = Random.new().read(AES.block_size)
+iv  = Random.new().read(AES.block_size)
+
+with open('files/17.txt') as f:
+    split_file = f.read().splitlines()
+
+def pkcs7_padding_validator(msg):
+    if ord(msg[len(msg) - 1]) > AES.block_size or ord(msg[len(msg) - 1]) == 0:
+        return False
+    for c in msg[:len(msg) - ord(msg[len(msg) - 1]) - 1 : -1]:
+        if c != msg[len(msg) - 1]:
+            return False
+    return True
+
+qwer = random.randint(0, 9)
+def encryption_oracle():
+    plaintext = split_file[3]
+    pad_len = AES.block_size - (len(plaintext) % AES.block_size)
+    return AES.new(key, AES.MODE_CBC, iv).encrypt(plaintext + ''.join([chr(pad_len) for i in range(pad_len)]))
+
+def decrypt_and_validate_padding(ciphertext):
+    return pkcs7_padding_validator(AES.new(key, AES.MODE_CBC, iv).decrypt(ciphertext))
+
+ct1 = iv + encryption_oracle()
+blocks = [ct1[i:i + AES.block_size] for i in range(0, len(ct1), AES.block_size)]
+pt = ""
+
+for block in blocks[::-1][:len(blocks) - 1]:
+
+    b = list(block)#list(blocks[len(blocks) - 2])
+    blep = []
+
+    for i in range(AES.block_size):
+        ignore = b[AES.block_size - (i + 1)]
+        br = False
+
+        for j in range(0xff):
+            if chr(j) != ignore:
+                b[AES.block_size - (i + 1)] = chr(j)
+
+            blocks[len(blocks) - 2] = ''.join(b)
+
+            if decrypt_and_validate_padding(''.join(blocks)):
+                pt += chr(j ^ ord(ignore) ^ (i + 1))
+                print list(chr(j ^ ord(ignore) ^ (i + 1)))
+                blep.append(j)
+
+                for k in range(i + 1):
+                    b[AES.block_size - (k + 1)] = chr(blep[k] ^ (k + 1) ^ (i + 2))
+
+                br = True
+                break
+
+        if not br:
+            blep.append(ord(ignore))
+
+            for k in range(i + 1):
+                b[AES.block_size - (k + 1)] = chr(blep[k] ^ (k + 1) ^ (i + 2))
+            print list("br" + chr(i + 1))
+            pt += chr(i + 1)
+
+print pt[::-1]
+print split_file[3]
+print pt[::-1].decode("base64")
diff --git a/set3/files/17.txt b/set3/files/17.txt
@@ -0,0 +1,10 @@
+MDAwMDAwTm93IHRoYXQgdGhlIHBhcnR5IGlzIGp1bXBpbmc=
+MDAwMDAxV2l0aCB0aGUgYmFzcyBraWNrZWQgaW4gYW5kIHRoZSBWZWdhJ3MgYXJlIHB1bXBpbic=
+MDAwMDAyUXVpY2sgdG8gdGhlIHBvaW50LCB0byB0aGUgcG9pbnQsIG5vIGZha2luZw==
+MDAwMDAzQ29va2luZyBNQydzIGxpa2UgYSBwb3VuZCBvZiBiYWNvbg==
+MDAwMDA0QnVybmluZyAnZW0sIGlmIHlvdSBhaW4ndCBxdWljayBhbmQgbmltYmxl
+MDAwMDA1SSBnbyBjcmF6eSB3aGVuIEkgaGVhciBhIGN5bWJhbA==
+MDAwMDA2QW5kIGEgaGlnaCBoYXQgd2l0aCBhIHNvdXBlZCB1cCB0ZW1wbw==
+MDAwMDA3SSdtIG9uIGEgcm9sbCwgaXQncyB0aW1lIHRvIGdvIHNvbG8=
+MDAwMDA4b2xsaW4nIGluIG15IGZpdmUgcG9pbnQgb2g=
+MDAwMDA5aXRoIG15IHJhZy10b3AgZG93biBzbyBteSBoYWlyIGNhbiBibG93