【Python】RC4の実装

def KSA(key):
	S = list(range(256))
	j = 0
	for i in range(256):
		j = (j + S[i] + ord(key[i % len(key)])) % 256
		S[i], S[j] = S[j], S[i]
	return S

def PRGA(S):
	i,j = 0, 0
	while True:
		i = (i + 1) % 256
		j = (j + S[i]) % 256
		S[i], S[j] = S[j], S[i]
		K = S[(S[i] + S[j]) % 256]
		yield K

def RC4(data, key):
	S = KSA(key)
	gen = PRGA(S)
	data = bytearray(data, encoding='utf-8')
	result = bytearray(c ^ n for c, n in zip(data, gen))
	return str(result)

key = 'this_is_a_key'
message = 'this_is_a_message'

chiphertext = RC4(message, key)
print(chiphertext)

これでもいける

from Crypto.Cipher import ARC4
key = b'Very long and confidential key'
cipher = ARC4.new(key)
msg = cipher.encrypt(b'Open the pod bay doors, HAL')
print(msg)