XOR

xor.py

#!/usr/bin/env python3

import os
import numpy
from zlib import crc32
from shutil import copy
from argparse import ArgumentParser


def xor(data, key):
    buff = numpy.frombuffer(data, dtype=numpy.dtype('B'))
    return numpy.bitwise_xor(buff, key)


def crc(filename):
    MAX_FILE_SIZE = 1024 * 1024 * 1024 * 2  # 2 GiB
    if os.path.getsize(filename) > MAX_FILE_SIZE:
        return NotImplemented
    data = open(filename, 'rb').read()
    c = crc32(data)
    return '{:08X}'.format(c)


def main():
    a, b = args.filename, args.output
    copy(a, b)
    aa = open(a, 'rb')
    bb = open(b, 'r+b')

    chunk = aa.read(args.offset)
    print('Doing XOR, key = {} ...'.format(hex(args.key)))
    bb.write(xor(chunk, args.key))
    print('Caculating CRC32 for {} and {} ...'.format(a, b))
    crc_a, crc_b = crc(a), crc(b)
    print('{} -> {}'.format(crc_a, crc_b))

    aa.close()
    bb.close()


if __name__ == '__main__':
    argparser = ArgumentParser()
    argparser.add_argument('filename')
    argparser.add_argument('-O', '--output')
    argparser.add_argument('-o', '--offset', default=-1, type=int)
    argparser.add_argument('-k', '--key', default=0x18, type=int)
    args = argparser.parse_args()
    if not args.output:
        args.output = '{}.xor'.format(args.filename)
    main()