[python]自定义RC4算法

RC4算法的介绍

RC4算法是一种流加密算法。所谓流加密，即密文由明文与**逐比特异或所得。因此该算法仅包含初始化**生成算法（KSA算法）和伪随机**流生成算法（PRGA）。关于这两个算法的描述：

KSA算法

执行该算法需给定一个初始**key，key的长度可变（范围为1~256字节）。利用这个初始**，可以生成一个S盒（一般为256进256出）。

PRGA算法

执行该算法可以输出一个**流。假设明文长度为n，则该算法执行n次，将这n个**流与明文逐比特异或，即可得到密文。

语言：python
版本：3.7

#测试用例参考文件:'RC4 Encryption.pdf'
class RC4:

    def __init__(self):
        # 状态初始化
        self.i = 0
        self.n = 0
        self.state = []
        self.max_key_length = 256

    def set_key(self, userkey=""):
        for i in range(self.max_key_length):
            self.state.append(i)

        key_length = len(userkey)
        T = []
        userkey_bytes = userkey.encode()
        for i in range(self.max_key_length):
            elem = userkey_bytes[i % key_length]
            T.append(elem)

        j = 0
        for i in range(self.max_key_length):
            j = (j + T[i] + self.state[i]) % self.max_key_length
            # 交换下标i和下标j对应的值
            temp = self.state[i]
            self.state[i] = self.state[j]
            self.state[j] = temp

    def keystream(self):
        self.i = (self.i + 1) % self.max_key_length
        self.n = (self.n + self.state[self.i]) % self.max_key_length
        # 交换下标i和下标n的值
        temp = self.state[self.i]
        self.state[self.i] = self.state[self.n]
        self.state[self.n] = temp

        index = (self.state[self.i] + self.state[self.n]) % self.max_key_length
        return self.state[index]

    @staticmethod
    def list2hex(list=[]):
        result = ""
        for elem in list:
            result += str(hex(elem)[2:]).upper()
        return result

    @staticmethod
    def list2str(list=[]):
        result = ""
        for elem in list:
            result += str(chr(elem))
        return result

    def encrypt(self, message="", message2=[]):
        if message:
            msg_len = len(message)
            message_bytes = message.encode(encoding='UTF-8', errors='strict')
        elif message2:
            msg_len = len(message2)
            message_bytes = message2
        cipher = []
        for i in range(msg_len):
            c = self.keystream() ^ message_bytes[i]
            cipher.append(c)
        return cipher

    def decrypt(self, cipher=[]):
        return self.encrypt("", cipher)

if __name__ == '__main__':

    userkey = 'pwd12'
    print("userkey(0x):")
    print(userkey)
    #userkey = userkey.decode()

    rc4_enc = RC4()
    rc4_dec = RC4()

    rc4_enc.set_key(userkey)
    rc4_dec.set_key(userkey)
    # for i in range(16):
    # print(hex(rc4.keystream()))

    plain = "Math 310 Proves!"
    cipher = rc4_enc.encrypt(plain)
    print("\ncipher:")
    print(rc4_enc.list2hex(cipher))

    plain_new = rc4_dec.decrypt(cipher)
    print("\nplain_new:")
    print(rc4_dec.list2str(plain_new))