XOR decoder

xor_decoder.py

#!/usr/bin/python

import sys, argparse
import re

def get_bytes(buf):
    if not buf:
        return None
    t = re.findall ('[0-9a-fA-F]{2}', buf)
    byte_buf = []
    for chunk in t:
        num = int (chunk, 16)
        byte_buf.append(num)
    return byte_buf

def decode(data, key):
    maxlen = len(data)
    keylen = len(key)
    j = 0 #key index
    decoded = bytearray()
    for i in range(0, maxlen):
        dec = data[i] ^ key[j % keylen]
        j += 1
        decoded.append(dec) 
    return decoded

def main():
    parser = argparse.ArgumentParser(description="XOR decoder")
    parser.add_argument('--infile', dest="infile", default=None, help="Input file", required=True)
    parser.add_argument('--keyfile', dest="keyfile", default=None, help="Key file")
    parser.add_argument('--outfile', dest="outfile", default=None, help="Output file")
    args = parser.parse_args()

    infile = args.infile
    outfile = args.outfile

    data = open(infile, 'rb').read()
    bytes = bytearray(data)

    if args.keyfile is not None:
        kdata = open(keyfile, 'rb').read()
        key = bytearray(get_bytes(kdata))
    else:
        key = bytearray([0xE9, 0x03, 0, 0]) #test

    out = decode(bytes, key)
    sys.stdout.write(out)

if __name__ == "__main__":
    main()