C和C++ 编程实现RC4算法

以下是C++实现的RC4算法代码：

#include <iostream>
#include <string>
#include <vector>

using namespace std;

vector<int> KSA(string key) {
    int key_length = key.length();
    vector<int> S(256);
    for (int i = 0; i < 256; i++) {
        S[i] = i;
    }
    int j = 0;
    for (int i = 0; i < 256; i++) {
        j = (j + S[i] + key[i % key_length]) % 256;
        swap(S[i], S[j]);
    }
    return S;
}

vector<int> PRGA(vector<int> S) {
    int i = 0;
    int j = 0;
    vector<int> K;
    while (true) {
        i = (i + 1) % 256;
        j = (j + S[i]) % 256;
        swap(S[i], S[j]);
        int K_value = S[(S[i] + S[j]) % 256];
        K.push_back(K_value);
        if (K.size() == 256) {
            break;
        }
    }
    return K;
}

string RC4(string key, string plaintext) {
    vector<int> S = KSA(key);
    vector<int> K = PRGA(S);
    int plaintext_length = plaintext.length();
    string ciphertext(plaintext_length, '\0');
    for (int i = 0; i < plaintext_length; i++) {
        ciphertext[i] = plaintext[i] ^ K[i];
    }
    return ciphertext;
}

int main() {
    string key = "Key";
    string plaintext = "Hello, world!";
    string ciphertext = RC4(key, plaintext);
    cout << ciphertext << endl;
    return 0;
}

其中，KSA函数用于初始化S盒，PRGA函数用于生成密钥流，RC4函数则是调用KSA和PRGA函数的组合。在加密过程中，将明文和密钥流按位进行异或运算即可得到密文。