def crypt(data, key):
    """RC4 algorithm"""

    key = [ord(c) for c in key]  # or `key = key.encode()` for python3

    x = 0
    box = list(range(256))
    for i in range(256):
        x = (x + int(box[i]) + int(key[i % len(key)])) % 256
        box[i], box[x] = box[x], box[i]
    x = y = 0
    out = []
    for char in data:
        x = (x + 1) % 256
        y = (y + box[x]) % 256
        box[x], box[y] = box[y], box[x]
        out.append(chr(ord(char) ^ box[(box[x] + box[y]) % 256]))

    return ''.join(out)


key = 'mysecret'
a = crypt("hello world!", key)
print(a)
b = crypt(a, key)
print(b)