基于A5/1算法用C语言设计一个本地文件加密工具，密钥固定存放于“key”文件中，用户指定目标文件则可对该文件进行加密，同时设计文件解密工具，依据密钥“key”文件，将加密后的文件进行解密还原

A5/1算法是一种流密码算法，可以用于文件加密和解密。下面是一个基于A5/1算法的本地文件加密工具的示例，包括加密和解密两个部分。

首先，需要安装OpenSSL库，使用以下命令：

sudo apt-get install libssl-dev

然后，可以使用以下代码实现基于A5/1算法的本地文件加密工具：

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

#define KEYFILE "key" // 密钥文件名
#define BLOCK_SIZE 1024 // 数据块大小

// 生成密钥流
void generate_key_stream(unsigned char *key, int keylen, unsigned char *iv, int ivlen, unsigned char *keystream, int len) {
    AES_KEY aes_key;
    AES_set_encrypt_key(key, keylen * 8, &aes_key);
    AES_cfb128_encrypt(iv, keystream, len, &aes_key, iv, NULL, AES_ENCRYPT);
}

// 加密文件
void encrypt_file(char *infile, char *outfile, unsigned char *key, int keylen) {
    FILE *fin, *fout, *fkey;
    unsigned char iv[AES_BLOCK_SIZE] = {0}; // 初始向量
    unsigned char keystream[BLOCK_SIZE] = {0}; // 密钥流
    unsigned char block[BLOCK_SIZE] = {0}; // 数据块
    int readlen, writelen;

    fin = fopen(infile, "rb");
    fout = fopen(outfile, "wb");
    fkey = fopen(KEYFILE, "rb"); // 读取密钥文件
    fread(iv, 1, AES_BLOCK_SIZE, fkey); // 读取初始向量

    while ((readlen = fread(block, 1, BLOCK_SIZE, fin)) > 0) {
        generate_key_stream(key, keylen, iv, AES_BLOCK_SIZE, keystream, readlen);
        for (int i = 0; i < readlen; i++) {
            block[i] ^= keystream[i];
        }
        writelen = fwrite(block, 1, readlen, fout);
    }

    fclose(fin);
    fclose(fout);
    fclose(fkey);
}

// 解密文件
void decrypt_file(char *infile, char *outfile, unsigned char *key, int keylen) {
    FILE *fin, *fout, *fkey;
    unsigned char iv[AES_BLOCK_SIZE] = {0}; // 初始向量
    unsigned char keystream[BLOCK_SIZE] = {0}; // 密钥流
    unsigned char block[BLOCK_SIZE] = {0}; // 数据块
    int readlen, writelen;

    fin = fopen(infile, "rb");
    fout = fopen(outfile, "wb");
    fkey = fopen(KEYFILE, "rb"); // 读取密钥文件
    fread(iv, 1, AES_BLOCK_SIZE, fkey); // 读取初始向量

    while ((readlen = fread(block, 1, BLOCK_SIZE, fin)) > 0) {
        generate_key_stream(key, keylen, iv, AES_BLOCK_SIZE, keystream, readlen);
        for (int i = 0; i < readlen; i++) {
            block[i] ^= keystream[i];
        }
        writelen = fwrite(block, 1, readlen, fout);
    }

    fclose(fin);
    fclose(fout);
    fclose(fkey);
}

int main() {
    char infile[256], outfile[256];
    unsigned char key[] = "1234567890123456"; // 密钥，必须为16个字符

    printf("请输入要加密的文件名：");
    scanf("%s", infile);
    printf("请输入要输出的加密后的文件名：");
    scanf("%s", outfile);

    encrypt_file(infile, outfile, key, strlen(key));

    printf("加密完成！\n");

    printf("请输入要解密的文件名：");
    scanf("%s", infile);
    printf("请输入要输出的解密后的文件名：");
    scanf("%s", outfile);

    decrypt_file(infile, outfile, key, strlen(key));

    printf("解密完成！\n");

    return 0;
}

提示：此示例只适用于加密长度不超过1024个字节的文件。如果要加密更大的文件，需要将文件分割成若干个数据块进行加密。