simple LCG-based stream cipher

simple_cipher.py

import sys

# def xor(b, s): return "".join(map(lambda x: chr(x^b), map(lambda x: ord(x), s)))
def xor(b, s): return map(lambda x: x^b, map(lambda x: ord(x), s))

M = sys.maxsize
M = 128

def lcg(m, a, c, x): return (a*x + c) % m

def enc(msg, seed):
    res = []
    for ch in msg:
        res.extend(xor(lcg(M, 1664525, 1013904223, seed), ch))
        seed = lcg(M, 1664525, 1013904223, seed)
    return res

def dec(msg, seed):
    res = []
    for ch in msg:
        res.append(lcg(M, 1664525, 1013904223, seed)^ch)
        seed = lcg(M, 1664525, 1013904223, seed)
    return ''.join(map(chr, res))