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test.py
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test.py
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#! /usr/bin/python
"""
Padding Oracle Attack implementation without remote server
Check the readme for a full cryptographic explanation
Author: mpgn <martial.puygrenier@gmail.com>
Date: 2016
"""
import argparse
import re
import sys
import time
from itertools import cycle
from Cryptodome.Cipher import AES
"""
AES-CBC
function encrypt, decrypt, pad, unpad)
"""
def pad(s):
pad_byte = 16 - len(s) % 16
for i in range(pad_byte):
s.append(pad_byte)
return s
def unpad(s):
exe = re.findall("..", s.hex())
padding = int(exe[-1], 16)
exe = exe[::-1]
if padding == 0 or padding > 16:
return 0
for i in range(padding):
if int(exe[i], 16) != padding:
return 0
return s[: -ord(s[len(s) - 1 :])]
def encrypt(msg, iv):
raw = pad(msg)
cipher = AES.new(b"V38lKILOJmtpQMHp", AES.MODE_CBC, iv)
return cipher.encrypt(raw), iv
def decrypt(enc, iv):
decipher = AES.new(b"V38lKILOJmtpQMHp", AES.MODE_CBC, iv)
return unpad(decipher.decrypt(enc))
""" The function you want change to adapt the result to your problem """
def test_validity(error):
if error != 404:
return 1
return 0
def call_oracle(up_cipher, iv):
if decrypt(bytes.fromhex(up_cipher), iv) == 0:
return 404
return 200
""" Create custom block for the byte we search"""
def block_search_byte(size_block, i, pos, l):
hex_char = hex(pos).split("0x")[1]
return (
"00" * (size_block - (i + 1))
+ ("0" if len(hex_char) % 2 != 0 else "")
+ hex_char
+ "".join(l)
)
""" Create custom block for the padding"""
def block_padding(size_block, i):
l = []
for t in range(0, i + 1):
l.append(
("0" if len(hex(i + 1).split("0x")[1]) % 2 != 0 else "")
+ (hex(i + 1).split("0x")[1])
)
return "00" * (size_block - (i + 1)) + "".join(l)
def split_len(seq, length):
return [seq[i : i + length] for i in range(0, len(seq), length)]
def hex_xor(s1, s2):
b = bytearray()
for c1, c2 in zip(bytes.fromhex(s1), cycle(bytes.fromhex(s2))):
b.append(c1 ^ c2)
return b.hex()
def run(cipher, size_block):
cipher = cipher.upper()
found = False
valide_value = []
result = []
len_block = size_block * 2
cipher_block = split_len(cipher, len_block)
if len(cipher_block) == 1:
print(
"[-] Abort there is only one block. I can't influence the IV. Try a longer message."
)
sys.exit()
# for each cipher_block
for block in reversed(range(1, len(cipher_block))):
if len(cipher_block[block]) != len_block:
print("[-] Abort length block doesn't match the size_block")
break
print("[+] Search value block : ", block, "\n")
# for each byte of the block
for i in range(0, size_block):
# test each byte max 255
for ct_pos in range(0, 256):
# 1 xor 1 = 0 or valide padding need to be checked
if ct_pos != i + 1 or (
len(valide_value) > 0 and int(valide_value[-1], 16) == ct_pos
):
bk = block_search_byte(size_block, i, ct_pos, valide_value)
bp = cipher_block[block - 1]
bc = block_padding(size_block, i)
tmp = hex_xor(bk, bp)
cb = hex_xor(tmp, bc).upper()
up_cipher = cb + cipher_block[block]
# time.sleep(0.5)
# we call the oracle, our god
error = call_oracle(up_cipher, iv)
if args.verbose == True:
exe = re.findall("..", cb)
discover = ("").join(exe[size_block - i : size_block])
current = ("").join(exe[size_block - i - 1 : size_block - i])
find_me = ("").join(exe[: -i - 1])
sys.stdout.write(
"\r[+] Test [Byte %03i/256 - Block %d ]: \033[31m%s\033[33m%s\033[36m%s\033[0m"
% (ct_pos, block, find_me, current, discover)
)
sys.stdout.flush()
if test_validity(error):
found = True
# data analyse and insert in rigth order
value = re.findall("..", bk)
valide_value.insert(0, value[size_block - (i + 1)])
if args.verbose == True:
print("")
print("[+] Block M_Byte : %s" % bk)
print("[+] Block C_{i-1}: %s" % bp)
print("[+] Block Padding: %s" % bc)
print("")
bytes_found = "".join(valide_value)
if (
i == 0
and int(bytes_found, 16) > size_block
and block == len(cipher_block) - 1
):
print(
"[-] Error decryption failed the padding is > "
+ str(size_block)
)
sys.exit()
print(
"\033[36m" + "\033[1m" + "[+]" + "\033[0m" + " Found",
i + 1,
"bytes :",
bytes_found,
)
print("")
break
if found == False:
# lets say padding is 01 for the last block (the padding block)
if len(cipher_block) - 1 == block and i == 0:
value = re.findall("..", bk)
valide_value.insert(0, "01")
if args.verbose == True:
print("")
print(
"[-] No padding found, but maybe the padding is length 01 :)"
)
print("[+] Block M_Byte : %s" % bk)
print("[+] Block C_{i-1}: %s" % bp)
print("[+] Block Padding: %s" % bc)
print("")
bytes_found = "".join(valide_value)
else:
print("\n[-] Error decryption failed")
result.insert(0, "".join(valide_value))
hex_r = "".join(result)
if len(hex_r) > 0:
print("[+] Partial Decrypted value (HEX):", hex_r.upper())
padding = int(hex_r[len(hex_r) - 2 : len(hex_r)], 16)
print(
"[+] Partial Decrypted value (ASCII):",
bytes.fromhex(hex_r[0 : -(padding * 2)]).decode(),
)
sys.exit()
found = False
result.insert(0, "".join(valide_value))
valide_value = []
print("")
hex_r = "".join(result)
print("[+] Decrypted value (HEX):", hex_r.upper())
padding = int(hex_r[len(hex_r) - 2 : len(hex_r)], 16)
decoded = bytes.fromhex(hex_r[0 : -(padding * 2)]).decode()
print("[+] Decrypted value (ASCII):", decoded)
return decoded
if __name__ == "__main__":
parser = argparse.ArgumentParser(description="Exploit of Padding Oracle Attack")
parser.add_argument("-m", "--message", required=True, help="message to pown")
parser.add_argument(
"-v",
"--verbose",
help="debug mode, you need a large screen",
action="store_true",
)
args = parser.parse_args()
print("[+] Encrypt", args.message)
cipher, iv = encrypt(bytearray(args.message, "UTF-8"), b"1234567812345678")
print("[+] %s ---> %s" % (args.message, cipher.hex()))
plaintext = decrypt(cipher, iv)
run(cipher.hex(), 16)