Xor a value with a key.

def xor_app(parser, cmd, args):  # pragma: no cover
    """
    Xor a value with a key.
    """

    parser.add_argument(
        '-d', '--dec',
        help='interpret the key as a decimal integer',
        dest='type',
        action='store_const',
        const=int
    )
    parser.add_argument(
        '-x', '--hex',
        help='interpret the key as an hexadecimal integer',
        dest='type',
        action='store_const',
        const=lambda v: int(v, 16)
    )
    parser.add_argument('key', help='the key to xor the value with')
    parser.add_argument('value', help='the value to xor, read from stdin if omitted', nargs='?')

    args = parser.parse_args(args)
    if args.type is not None:
        args.key = args.type(args.key)

    return xor(args.key, pwnypack.main.binary_value_or_stdin(args.value))