CRIME-cbc-poc.py

"""
    CRIME attack - PoC
    Implementation of the compression oracle attack behind CRIME
    Algo: AES-CBC
    Author: mpgn <martial.puygrenier@gmail.com> - 2018
    @mpgn_x64
"""

import sys
import random
import string
import zlib
from Crypto.Cipher import AES
from Crypto import Random

"""
    Implementation of AES-256 with CBC cipher mode
    cipher = plaintext + padding
    IV and KEY are random
    there is no handshake (no need)
"""

# padding for the CBC cipher block
def pad(s):
    return (16 - len(s) % 16) * chr((16 - len(s) - 1) % 16)


# cipher a message
def encrypt(msg):
    data = msg.encode()
    compress = zlib.compress(data)
    padding = pad(compress)
    raw = compress + padding.encode()
    cipher = AES.new(KEY, AES.MODE_CBC, IV)
    return cipher.encrypt(raw)


def two_true_recursive(found, p):
    tmp = []
    for i in range(33, 127):
        enc1 = encrypt(
            GARB + IKNOW + "".join(found) + chr(i) + "~#:/[|/ç" + " " + SECRET
        )
        enc2 = encrypt(
            GARB + IKNOW + "~#:/[|/ç" + "".join(found) + chr(i) + " " + SECRET
        )
        if len(enc1) < len(enc2):
            tmp.append(chr(i))
    for i in range(0, len(tmp)):
        t = "temp" + str(i)
        t = list(found)
        t.append(tmp[i])
        sys.stdout.write("\r[+] flag=%s" % "".join(t))
        p = two_true_recursive(t, p)

    if len(tmp) == 0:
        p += 1
        print("")
    return p


def adjust_padding():
    garb = ""
    found = []
    l = 0
    origin = encrypt(garb + IKNOW + "".join(found) + "~#:/[|/ç" + " " + SECRET)
    while True:
        enc = encrypt(garb + IKNOW + "".join(found) + "~#:/[|/ç" + " " + SECRET)
        if len(enc) > len(origin):
            break
        else:
            l += 1
            garb = "".join(random.sample(string.ascii_lowercase + string.digits, k=l))
    return garb[:-1]


def run():
    found = []
    p = two_true_recursive(found, 0)
    print("\nFound", str(p), "possibilities of secret flag")
    return


if __name__ == "__main__":
    print("{-} CRIME Proof of Concept by @mpgn_x64\n")
    IV = Random.new().read(AES.block_size)
    KEY = Random.new().read(AES.block_size)
    SECRET = "flag={quokkalight_1s_th3_b3st_t34m}"
    IKNOW = "flag="
    print("[+] Secret TOKEN :", SECRET)
    print("[+] Encrypted with \033[33mAES-256-CBC\033[0m")
    print(
        "[+] Trying to decrypt with a compression oracle attacks using a \033[33mrecursive two_tries\033[0m method"
    )
    print("")
    print("[+] Adjusting the padding to 1")
    GARB = adjust_padding()
    print("")
    run()
    print("")