[시스템 보안] RC4 알고리즘 구현(C++)

#include <iostream>
#include <cstring>
#include <vector>
using namespace std;

int main()
{
    char S[256];  
    char K[256];  

    int i, t;
    char key[] = "key";  
    char plainText[] = "killhitler";
    vector<char> KeyStream(strlen(plainText));

    cout << "키 값: " << key << endl;
    cout << "평문 : " << plainText << endl;

    //초기화
    for (i = 0; i < 256; i++){ 
        S[i] = i;
        K[i] = key[i % strlen(key)];
    }

    int j = 0;

    // S의 배열을 섞는다.
    for (i = 0; i < 256; i++) {
        j = (j + S[i] + K[i]) % 256;
        swap(S[i], S[j]);
    }

    i = j = 0;

   //암호화 과정
    for (int k = 0; k < strlen(plainText); k++)
    {
        i = (i + 1) % 256;
        j = (j + S[i]) % 256;
        swap(S[i], S[j]);

        t = (S[i] + S[j]) % 256;
        KeyStream[k] = S[t];
        plainText[k] ^= S[KeyStream[k]];  //  암호화

        cout << (k + 1) << "'s 키스트림 :  " << (unsigned int)KeyStream[k] << endl; 
    }

    cout << endl << "암호화된 평문  :  " << plainText << endl;

    //복호화 과정
    for (int k = 0; k < strlen(plainText); k++){
        plainText[k] ^= S[KeyStream[k]];  //  복호화
    }

    cout << endl << "복호화된 평문  :  " << plainText << endl;

    exit(0);
}