XOR a message with a key: TypeError: 'int' object is not callable

Trying to XOR a message byte by byte with a given key b"ICE". To do this I have to enumerate through the key indices and message whilst making sure to use the modulo of the key to loop through it.

However, I'm getting the TypeError: 'int' object is not callable.

I'm not sure how to fix this. Any advice is much appreciated. All code is below.

def repeating_key_xor(message_bytes, key):
    output_bytes = b''
    for i, bytes in enumerate(message_bytes):
        output_bytes += bytes([key[i % len(key)] ^ bytes])
    return output_bytes


def main():
    key = b"ICE"
    message = b"Burning 'em, if you ain't quick and nimble\nI go crazy when I hear a cymbal"
    ciphertext = repeating_key_xor(message, key)
    print(ciphertext)


if __name__ == '__main__':
    main()

bytes is a built-in which you are overriding.

You probably meant:

def repeating_key_xor(message_bytes, key):
    output_bytes = b''
    for i, byte in enumerate(message_bytes):
        output_bytes += bytes([key[i % len(key)] ^ byte])
    return output_bytes

As said in the previous answer, you are overriding bytes creating a variable with the same name.

I would suggest to exploit python's elegant features and libraries, avoid indexing and optimise the code

import itertools as it

def repeating_key_xor(message_bytes, key):
    for byte, k in zip(message_bytes, it.cycle(key)):
        yield k ^ byte

def main():
    key = b"ICE"
    message = b"Burning 'em, if you ain't quick and nimble\nI go crazy when I hear a cymbal"
    ciphertext = bytes(repeating_key_xor(message, key))
    print(ciphertext)

if __name__ == '__main__':
    main()

Which produces

b'\x0b67\'*+.cb,.ii*#i:*<c$ -b=c4<*&"c$\'\'e\'*(+/ C\ne.,e*1$3:e>+ \'c\x0ci+ (1e(c&0.\'(/'