c语言实验des的cbc工作模式代码

以下是使用C语言实现DES算法的CBC工作模式的代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/des.h>

#define BUFFER_SIZE 1024
#define IV "12345678" // 初始化向量

// DES加密函数
void des_encrypt(const unsigned char *input, unsigned char *output, const unsigned char *key) {
    DES_cblock des_key;
    DES_key_schedule key_schedule;
    DES_string_to_key(key, &des_key);
    DES_set_key_checked(&des_key, &key_schedule);

    DES_cblock iv;
    memcpy(iv, IV, 8);

    DES_ncbc_encrypt(input, output, strlen((char *)input), &key_schedule, &iv, DES_ENCRYPT);
}

// DES解密函数
void des_decrypt(const unsigned char *input, unsigned char *output, const unsigned char *key) {
    DES_cblock des_key;
    DES_key_schedule key_schedule;
    DES_string_to_key(key, &des_key);
    DES_set_key_checked(&des_key, &key_schedule);

    DES_cblock iv;
    memcpy(iv, IV, 8);

    DES_ncbc_encrypt(input, output, strlen((char *)input), &key_schedule, &iv, DES_DECRYPT);
}

int main(int argc, char *argv[]) {
    // 明文和密钥
    unsigned char plain[BUFFER_SIZE] = "Hello, world!";
    unsigned char key[] = "12345678";

    // CBC模式加密
    int plain_len = strlen((char *)plain);
    int padding_len = 8 - plain_len % 8;
    unsigned char *padded_plain = (unsigned char *)malloc(plain_len + padding_len + 1);
    memset(padded_plain, padding_len, padding_len);
    memcpy(padded_plain, plain, plain_len);

    int cipher_len = plain_len + padding_len;
    unsigned char *cipher = (unsigned char *)malloc(cipher_len + 1);
    memset(cipher, 0, cipher_len + 1);

    unsigned char *prev_cipher = (unsigned char *)malloc(8);
    memset(prev_cipher, 0, 8);
    for (int i = 0; i < cipher_len; i += 8) {
        unsigned char block[8];
        memcpy(block, padded_plain + i, 8);

        for (int j = 0; j < 8; j++) {
            block[j] ^= prev_cipher[j];
        }

        des_encrypt(block, cipher + i, key);
        memcpy(prev_cipher, cipher + i, 8);
    }

    // CBC模式解密
    unsigned char *decrypted = (unsigned char *)malloc(cipher_len + 1);
    memset(decrypted, 0, cipher_len + 1);

    memset(prev_cipher, 0, 8);
    for (int i = 0; i < cipher_len; i += 8) {
        unsigned char block[8];
        memcpy(block, cipher + i, 8);

        unsigned char temp[8];
        des_decrypt(block, temp, key);

        for (int j = 0; j < 8; j++) {
            temp[j] ^= prev_cipher[j];
        }

        memcpy(decrypted + i, temp, 8);
        memcpy(prev_cipher, block, 8);
    }

    printf("Plaintext: %s\n", plain);
    printf("Cipher: %s\n", cipher);
    printf("Decrypted: %s\n", decrypted);

    free(padded_plain);
    free(cipher);
    free(prev_cipher);
    free(decrypted);

    return 0;
}

在上面的代码中，我们使用了OpenSSL库中提供的DES加密和解密函数，分别是`DES_ncbc_encrypt`和`DES_string_to_key`。在CBC模式中，我们需要维护一个8字节的初始化向量IV，并在加密和解密过程中使用它。在加密过程中，我们将明文分块并与前一个密文块进行异或操作，然后再进行加密。在解密过程中，我们将密文分块并进行解密，然后再与前一个密文块进行异或操作，最后得到明文。