linux编写限制软件试用期代码 ,对生成的配置文件进行openssl加密以及锁定，无法对其删除，提示剩余使用时间 C++示例

好的，针对你的问题，我提供以下代码作为参考：

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <ctime>
#include <string>
#include <cstring>
#include <openssl/evp.h>
#include <openssl/rand.h>

using namespace std;

// 加密函数
string encrypt(string str, string key) {
    unsigned char iv[EVP_MAX_IV_LENGTH];
    memset(iv, 0, EVP_MAX_IV_LENGTH);
    unsigned char *keyData = (unsigned char *)key.c_str();
    unsigned char *data = (unsigned char *)str.c_str();
    int dataLength = str.length();

    int cipherLength = dataLength + EVP_MAX_BLOCK_LENGTH;
    unsigned char *cipherData = new unsigned char[cipherLength];
    memset(cipherData, 0, cipherLength);

    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    EVP_EncryptInit_ex(ctx, EVP_aes_128_cbc(), NULL, keyData, iv);
    int length = 0;
    EVP_EncryptUpdate(ctx, cipherData, &length, data, dataLength);
    cipherLength = length;
    EVP_EncryptFinal_ex(ctx, cipherData + length, &length);
    cipherLength += length;
    EVP_CIPHER_CTX_free(ctx);

    string result((char *)cipherData, cipherLength);
    delete[] cipherData;
    return result;
}

// 解密函数
string decrypt(string str, string key) {
    unsigned char iv[EVP_MAX_IV_LENGTH];
    memset(iv, 0, EVP_MAX_IV_LENGTH);
    unsigned char *keyData = (unsigned char *)key.c_str();
    unsigned char *data = (unsigned char *)str.c_str();
    int dataLength = str.length();

    int plainLength = dataLength + EVP_MAX_BLOCK_LENGTH;
    unsigned char *plainData = new unsigned char[plainLength];
    memset(plainData, 0, plainLength);

    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    EVP_DecryptInit_ex(ctx, EVP_aes_128_cbc(), NULL, keyData, iv);
    int length = 0;
    EVP_DecryptUpdate(ctx, plainData, &length, data, dataLength);
    plainLength = length;
    EVP_DecryptFinal_ex(ctx, plainData + length, &length);
    plainLength += length;
    EVP_CIPHER_CTX_free(ctx);

    string result((char *)plainData, plainLength);
    delete[] plainData;
    return result;
}

// 生成配置文件
void generateConfigFile(string filename) {
    // 随机生成一个使用期限
    srand((unsigned)time(NULL));
    int days = rand() % 31 + 30;

    // 将使用期限写入配置文件并加密
    string content = to_string(days);
    unsigned char key[EVP_MAX_KEY_LENGTH];
    RAND_bytes(key, EVP_MAX_KEY_LENGTH);
    string encryptedContent = encrypt(content, (char *)key);
    ofstream fout(filename.c_str(), ios::binary);
    fout.write((char *)key, EVP_MAX_KEY_LENGTH);
    fout.write(encryptedContent.c_str(), encryptedContent.length());
    fout.close();

    // 锁定配置文件
    int result = chmod(filename.c_str(), 0444);
    if (result != 0) {
        cerr << "Error: Failed to lock config file!" << endl;
        exit(1);
    }
}

// 检查配置文件并返回剩余使用天数
int checkConfigFile(string filename) {
    // 尝试打开配置文件
    ifstream fin(filename.c_str(), ios::binary);
    if (!fin) {
        cerr << "Error: Config file not found!" << endl;
        exit(1);
    }

    // 读取配置文件内容并解密
    unsigned char key[EVP_MAX_KEY_LENGTH];
    fin.read((char *)key, EVP_MAX_KEY_LENGTH);
    string encryptedContent;
    getline(fin, encryptedContent);
    fin.close();
    string content = decrypt(encryptedContent, (char *)key);

    // 将读取的内容转换为整数
    int days = stoi(content);

    // 计算剩余使用天数
    time_t currentTime = time(NULL);
    struct tm *currentDate = localtime(&currentTime);
    int remainingDays = days - currentDate->tm_mday;

    // 返回剩余使用天数
    return remainingDays;
}

int main() {
    // 生成或检查配置文件
    string filename = "config.dat";
    if (access(filename.c_str(), F_OK) != 0) {
        generateConfigFile(filename);
    }
    int remainingDays = checkConfigFile(filename);

    // 显示剩余使用天数
    if (remainingDays > 0) {
        cout << "Remaining days: " << remainingDays << endl;
    } else {
        cout << "The trial period has expired!" << endl;
    }

    return 0;
}

这段代码使用了 OpenSSL 库中的加密和解密函数来保护配置文件中的使用期限，同时还使用了系统时间来计算剩余使用天数。你可以根据自己的需要进行修改和调整。