main.py

import itertools
import json
import math
import string

############################

encrypted_hex = """
put the encrypted response here
"""
key_len = 16
key_charset = string.ascii_lowercase[:14]
decrypted_charset = string.printable

###########################

key_charset_bytes = [ord(c) for c in key_charset]
decrypted_charset_bytes = [ord(c) for c in decrypted_charset]


def decrypt(key_bytes, encrypted_bytes):
    key_len = len(key_bytes)
    decrypted = []
    for (i, b) in enumerate(encrypted_bytes):
        decrypted.append(b ^ key_bytes[i % key_len])
    return bytes(decrypted)


def find_candidates_key_bytes(encrypted_bytes, key_offset):
    bytes_to_check = encrypted_bytes[key_offset::key_len]
    for k in key_charset_bytes:
        if all(k ^ b in decrypted_charset_bytes for b in bytes_to_check):
            yield k


def is_valid_json(decrypted):
    try:
        json.loads(decrypted)
    except json.JSONDecodeError:
        return False
    return True


def find_key(encrypted_bytes):
    candidates_key_bytes = [
        list(find_candidates_key_bytes(encrypted_bytes, i)) for i in range(16)
    ]

    number_of_keys = math.prod(len(l) for l in candidates_key_bytes)
    print(f"{number_of_keys} keys to test")

    for key in itertools.product(*candidates_key_bytes):
        decrypted = decrypt(key, encrypted_bytes)
        if is_valid_json(decrypted):
            key_ascii = "".join(chr(c) for c in key)
            print(f"potential key found: {key_ascii}")


if __name__ == "__main__":
    find_key(bytes.fromhex(encrypted_hex))