基于DES的文件加/解密系统（CFB模式）C语言

好的，我可以为您提供一个基于DES的文件加/解密系统（CFB模式）的C语言实现。首先需要注意的是，DES算法已经被证明不够安全，因此不建议在实际应用中使用。下面是代码实现：

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

#define BUFSIZE 1024

void des_encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key, unsigned char *iv, unsigned char *ciphertext) {

    DES_cblock des_key = {0};
    DES_cblock des_iv = {0};
    DES_key_schedule schedule;

    memcpy(des_key, key, sizeof(DES_cblock));
    memcpy(des_iv, iv, sizeof(DES_cblock));

    DES_set_key_checked(&des_key, &schedule);

    DES_cfb64_encrypt(plaintext, ciphertext, plaintext_len, &schedule, &des_iv, DES_ENCRYPT);
}

void des_decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key, unsigned char *iv, unsigned char *plaintext) {

    DES_cblock des_key = {0};
    DES_cblock des_iv = {0};
    DES_key_schedule schedule;

    memcpy(des_key, key, sizeof(DES_cblock));
    memcpy(des_iv, iv, sizeof(DES_cblock));

    DES_set_key_checked(&des_key, &schedule);

    DES_cfb64_encrypt(ciphertext, plaintext, ciphertext_len, &schedule, &des_iv, DES_DECRYPT);
}

void print_hex(unsigned char *buf, int len) {
    int i;
    for (i = 0; i < len; i++) {
        printf("%02x", buf[i]);
    }
    printf("\n");
}

int main(int argc, char *argv[]) {

    unsigned char key[DES_KEY_SZ] = {0};
    unsigned char iv[DES_KEY_SZ] = {0};
    unsigned char buf[BUFSIZE] = {0};
    unsigned char ciphertext[BUFSIZE] = {0};
    unsigned char decrypted[BUFSIZE] = {0};

    int nread, ciphertext_len, decrypted_len;

    FILE *fp = fopen(argv[1], "rb");
    FILE *out = fopen(argv[2], "wb");

    if (argc != 3) {
        printf("Usage: %s <plaintext file> <ciphertext file>\n", argv[0]);
        return 1;
    }

    if (fp == NULL) {
        perror("Error opening plaintext file");
        return 1;
    }

    // Generate a random key and iv
    srand(time(NULL));
    rand_bytes(key, sizeof(key));
    rand_bytes(iv, sizeof(iv));

    fwrite(key, 1, sizeof(key), out);
    fwrite(iv, 1, sizeof(iv), out);

    while ((nread = fread(buf, 1, BUFSIZE, fp)) > 0) {
        des_encrypt(buf, nread, key, iv, ciphertext);
        fwrite(ciphertext, 1, nread, out);
    }

    fclose(fp);
    fclose(out);

    fp = fopen(argv[2], "rb");

    if (fp == NULL) {
        perror("Error opening ciphertext file");
        return 1;
    }

    fread(key, 1, sizeof(key), fp);
    fread(iv, 1, sizeof(iv), fp);

    while ((nread = fread(buf, 1, BUFSIZE, fp)) > 0) {
        des_decrypt(buf, nread, key, iv, decrypted);
        fwrite(decrypted, 1, nread, stdout);
    }

    fclose(fp);

    return 0;
}

在使用之前，需要安装OpenSSL库。可以使用以下命令进行安装：

sudo apt-get install libssl-dev

使用方法：

1. 编译代码：`gcc -o des des.c -lcrypto`
2. 加密文件：`./des plaintext.txt ciphertext.txt`
3. 解密文件：`./des ciphertext.txt plaintext.txt`

其中，`plaintext.txt`是明文文件，`ciphertext.txt`是密文文件。程序会自动生成一个随机的密钥和初始向量，并将它们保存在密文文件的开头。