linux,限制软件试用期的C++函数 ,对配置文件进行加密，配置文件无法删除，防止删除与修改配置文件，提示剩余时间 ,超过时间返回0

实现这个功能的关键在于如何保护配置文件并控制试用期。以下是一个简单的C++函数示例，演示了如何实现软件试用期限制和配置文件加密：

#include <iostream>
#include <fstream>
#include <string>
#include <ctime>
#include <chrono>
#include <ratio>
#include <openssl/aes.h>

using namespace std;

// AES加密函数
void aes_encrypt(const unsigned char *in, unsigned char *out, const unsigned char *key) {
    AES_KEY aes_key;
    AES_set_encrypt_key(key, 128, &aes_key);
    AES_encrypt(in, out, &aes_key);
}

// AES解密函数
void aes_decrypt(const unsigned char *in, unsigned char *out, const unsigned char *key) {
    AES_KEY aes_key;
    AES_set_decrypt_key(key, 128, &aes_key);
    AES_decrypt(in, out, &aes_key);
}

// 获取当前时间戳
time_t get_timestamp() {
    return chrono::system_clock::to_time_t(chrono::system_clock::now());
}

// 读取配置文件
string read_config(const char *filename) {
    ifstream ifs(filename);
    if (!ifs) {
        throw runtime_error("failed to open config file");
    }
    string content((istreambuf_iterator<char>(ifs)), (istreambuf_iterator<char>()));
    return content;
}

// 加密并保存配置文件
void save_config(const char *filename, const string &content, const unsigned char *key) {
    unsigned char iv[AES_BLOCK_SIZE] = {0};
    unsigned char ciphertext[content.size() + AES_BLOCK_SIZE] = {0};
    aes_encrypt(reinterpret_cast<const unsigned char *>(content.c_str()), ciphertext, key);
    ofstream ofs(filename, ios::binary | ios::trunc);
    if (!ofs) {
        throw runtime_error("failed to open config file for writing");
    }
    ofs.write(reinterpret_cast<const char *>(iv), sizeof(iv));
    ofs.write(reinterpret_cast<const char *>(ciphertext), content.size() + AES_BLOCK_SIZE);
}

// 解密配置文件
string decrypt_config(const char *filename, const unsigned char *key) {
    ifstream ifs(filename, ios::binary);
    if (!ifs) {
        throw runtime_error("failed to open config file");
    }
    unsigned char iv[AES_BLOCK_SIZE] = {0};
    ifs.read(reinterpret_cast<char *>(iv), sizeof(iv));
    string content((istreambuf_iterator<char>(ifs)), (istreambuf_iterator<char>()));
    unsigned char *ciphertext = reinterpret_cast<unsigned char *>(&content[0]);
    unsigned char plaintext[content.size()] = {0};
    aes_decrypt(ciphertext, plaintext, key);
    return reinterpret_cast<const char *>(plaintext);
}

// 获取剩余时间
int get_remaining_days(const time_t &start_time, const int &days) {
    time_t now = get_timestamp();
    int elapsed_days = (now - start_time) / (24 * 60 * 60);
    int remaining_days = days - elapsed_days;
    return remaining_days > 0 ? remaining_days : 0;
}

// 检查软件试用期限制
bool check_trial_period(const char *config_file, const unsigned char *key, const int &days) {
    try {
        string content = decrypt_config(config_file, key);
        int remaining_days = get_remaining_days(stoi(content), days);
        if (remaining_days == 0) {
            return false;
        }
        save_config(config_file, to_string(get_timestamp()), key);
        return true;
    } catch (const exception &e) {
        save_config(config_file, to_string(get_timestamp()), key);
        return true;
    }
}

// 主函数
int main(int argc, char **argv) {
    const char *config_file = "config.bin";
    const unsigned char key[] = "my secret key";
    const int trial_days = 30;
    if (!check_trial_period(config_file, key, trial_days)) {
        cout << "trial period has expired" << endl;
        return 0;
    }
    // do something
    return 0;
}

该函数使用AES加密算法加密配置文件，并将加密后的内容保存到二进制文件中。它还使用时间戳来记录软件的试用期，并在每次运行时检查剩余时间。如果试用期已过期，则程序将退出。