PublicProfile.save encryption/decryption tool for Bloons TD Battles 2 1.0.4

btdb2savecrypt.py

import binascii
import sys
import string
import os

# the checksum algorithm operates on signed integers
def arsh32(n, b):
    n = n & 0xFFFFFFFFF
    n = (n ^ 0x80000000) - 0x80000000
    return (n >> b) & 0xFFFFFFFF

def checksum(data):
    ret = 0
    for i in range(len(data)):
        temp = (ret ^ data[i]) & 0xFF
        if (temp & 1) != 0:
            temp = arsh32(temp ^ 0xDB710641, 1)
        else:
            temp = arsh32(temp, 1)
        for j in range(7):
            if j != 0:
                temp = arsh32(temp, 1)
            if (temp & 1) != 0:
                temp ^= 0xDB710641
        ret = arsh32(temp, 1) ^ arsh32(ret, 8) & 0xFFFFFF
    return ret

# no scanf in python
def scan_hex(file):
    out = ""
    while True:
        try:
            char = file.read(1).decode("utf-8")
            if char in string.hexdigits:
                out += char
            else:
                break
        except UnicodeDecodeError:
            break
    file.seek(-1, os.SEEK_CUR)
    return int(out, 16)

def stephen_encrypt(data):
    for i in range(len(data)):
        data[i] += i % 6 + 21

def stephen_decrypt(data):
    for i in range(len(data)):
        data[i] += 6 * (i // 6) - i - 21

def decrypt_save(in_file, out_file):
    with open(in_file, "rb") as save:
        magic = save.read(6)
        if magic != b"DGDATA":
            print("wrong magic")
            return
        stored_crc = scan_hex(save)
        print(f"stored checksum: {hex(stored_crc)}")
        data = bytearray(save.read())
        stephen_decrypt(data)
        calced_crc = checksum(data)
        if stored_crc == calced_crc:
            print(f"checksum OK")
        else:
            print(f"checksum mismatch! (calculated: {hex(calced_crc)})")
        with open(out_file, "wb") as dec:
            dec.write(data)

def encrypt_save(in_file, out_file):
    with open(in_file, "rb") as dec:
        data = bytearray(dec.read())
        calced_crc = checksum(data)
        stephen_encrypt(data)
        data = bytearray(f"DGDATA{calced_crc:08x}", encoding="utf8") + data
        with open(out_file, "wb") as save:
            save.write(data)

if __name__ == "__main__":
    if len(sys.argv) != 4:
        print(f"usage: {sys.argv[0]} [decrypt/encrypt] [in] [out]")
        sys.exit(1)
    if sys.argv[1] == "decrypt":
        decrypt_save(sys.argv[2], sys.argv[3])
    elif sys.argv[1] == "encrypt":
        encrypt_save(sys.argv[2], sys.argv[3])
    else:
        print("invalid mode!")

Ok