#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void RC4_Init(unsigned char* key, size_t keyLength, unsigned char* S) {
    int i, j = 0;
    unsigned char temp;

    for (i = 0; i < 256; i++) {
        S[i] = i;
    }

    for (i = 0; i < 256; i++) {
        j = (j + S[i] + key[i % keyLength]) % 256;
        temp = S[i];
        S[i] = S[j];
        S[j] = temp;
    }
}

void RC4_Crypt(unsigned char* message, size_t messageLength, unsigned char* S) {
    int i = 0, j = 0, k;
    unsigned char temp, t;
    for (k = 0; k < messageLength; k++) {
        i = (i + 1) % 256;
        j = (j + S[i]) % 256;
        temp = S[i];
        S[i] = S[j];
        S[j] = temp;
        t = (S[i] + S[j]) % 256;
        message[k] ^= S[t];
    }
}

int main() {
    unsigned char key[] = "MySecretKey";
    unsigned char message[] = "Hello, RC4!";

    size_t keyLength = strlen((char*)key);
    size_t messageLength = strlen((char*)message);

    unsigned char S[256];
    RC4_Init(key, keyLength, S);

    RC4_Crypt(message, messageLength, S);

    printf("暗号化されたメッセージ: ");
    for (size_t i = 0; i < messageLength; i++) {
        printf("%02X ", message[i]);
    }
    printf("\n");

    RC4_Crypt(message, messageLength, S);

    printf("復号化されたメッセージ: %s\n", message);

    return 0;
}