祖冲之序列密码算法c语言实现 使用s盒

祖冲之序列密码算法是一种基于伪随机序列的加密算法，它的核心是使用祖冲之序列作为密钥流，对明文进行异或运算来实现加密。S盒是一种用于替换明文中的每个字节的表格，它可以增强密码算法的安全性。

以下是祖冲之序列密码算法的C语言实现，使用了S盒：

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

#define S_BOX_SIZE 256

unsigned char s_box[S_BOX_SIZE];

void init_s_box(unsigned char *key, int key_len) {
    int i, j;
    unsigned char tmp;
    for (i = 0; i < S_BOX_SIZE; i++) {
        s_box[i] = i;
    }
    j = 0;
    for (i = 0; i < S_BOX_SIZE; i++) {
        j = (j + s_box[i] + key[i % key_len]) % S_BOX_SIZE;
        tmp = s_box[i];
        s_box[i] = s_box[j];
        s_box[j] = tmp;
    }
}

void generate_key_stream(unsigned char *key_stream, int key_stream_len) {
    int i, j, k;
    unsigned char tmp;
    i = j = 0;
    for (k = 0; k < key_stream_len; k++) {
        i = (i + 1) % S_BOX_SIZE;
        j = (j + s_box[i]) % S_BOX_SIZE;
        tmp = s_box[i];
        s_box[i] = s_box[j];
        s_box[j] = tmp;
        key_stream[k] = s_box[(s_box[i] + s_box[j]) % S_BOX_SIZE];
    }
}

void encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key, int key_len, unsigned char *ciphertext) {
    int i;
    unsigned char *key_stream = (unsigned char *)malloc(plaintext_len);
    init_s_box(key, key_len);
    generate_key_stream(key_stream, plaintext_len);
    for (i = 0; i < plaintext_len; i++) {
        ciphertext[i] = plaintext[i] ^ key_stream[i];
    }
    free(key_stream);
}

void decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key, int key_len, unsigned char *plaintext) {
    int i;
    unsigned char *key_stream = (unsigned char *)malloc(ciphertext_len);
    init_s_box(key, key_len);
    generate_key_stream(key_stream, ciphertext_len);
    for (i = 0; i < ciphertext_len; i++) {
        plaintext[i] = ciphertext[i] ^ key_stream[i];
    }
    free(key_stream);
}

int main() {
    unsigned char plaintext[] = "Hello World!";
    int plaintext_len = strlen((char *)plaintext);
    unsigned char key[] = "secret";
    int key_len = strlen((char *)key);
    unsigned char ciphertext[plaintext_len];
    encrypt(plaintext, plaintext_len, key, key_len, ciphertext);
    printf("Ciphertext: %s\n", ciphertext);
    unsigned char decrypted_plaintext[plaintext_len];
    decrypt(ciphertext, plaintext_len, key, key_len, decrypted_plaintext);
    printf("Decrypted plaintext: %s\n", decrypted_plaintext);
    return 0;
}