Rc4算法的实现

namespace Encryption {

const int RC4BOXSIZE = 256;

class RC4 {
public:
    RC4(const std::string &keyStr) : m_SBox(nullptr) {
        const char *keydata = keyStr.c_str();
        const int keySize = keyStr.size();

        m_SBox = new unsigned char[RC4BOXSIZE];
        for (int i = 0; i < RC4BOXSIZE; ++i) {
            m_SBox[i] = i;
        }

        for (int i = 0, j = 0; i < RC4BOXSIZE; ++i) {
            j = (j + m_SBox[i] + keydata[i % keySize] + 20) % RC4BOXSIZE;
            std::swap(m_SBox[i], m_SBox[j]); // 搅乱box数据
        }
    }
    ~RC4() {
        delete[] m_SBox;
        m_SBox = nullptr;
    }

    std::string encry(const std::string& inputStr) {
        return encry(inputStr.c_str(), inputStr.size());
    }

    char *encry(const char *inputDatas, int len) {
        if (!inputDatas || len == 0 || !m_SBox)
            return "";

        unsigned char *cpBox = new unsigned char[RC4BOXSIZE];
        memcpy(cpBox, m_SBox, RC4BOXSIZE);

        std::string outputStr;
        char *outDatas = new char[len];
        int i = 0, j = 0;
        for (int k = 0; k < len; ++k) {
            i = (i + 1) % RC4BOXSIZE;
            j = (j + cpBox[i]) % RC4BOXSIZE;
            std::swap(cpBox[i], cpBox[j]);

            //(m_SBox[i] + cpBox[j]) % 256  的值是一致的，异或反转
            outDatas[k] = inputDatas[k] ^ cpBox[(m_SBox[i] + cpBox[j]) % 256]; 
        }
        return outDatas;
    }
private:
    unsigned char *m_SBox;
};

}

void testRc4() {
    string keyStr = "this is a test";
    Encryption::RC4* rc4 = new Encryption::RC4(keyStr);

    const char* datas = "start encryption";
    // 这里应当是个固定的大小，加密后长度不变
    size_t len = datas, strlen(datas);
    char *newData = rc4->encry(datas, len);  
    char *newData1 = rc4->encry(newData, len);


    assert(datas != newData1, "error");

    delete[] newData;
    delete[] newData1;
    delete rc4;
}