using System;
using System.Security.Cryptography;
using System.Text;
 
public class TimeAesEncrypt
{
    // 時(shí)間加密核心：時(shí)間戳+固定密鑰混合做密鑰
    private static string GetKeyByTime()
    {
        // 取當(dāng)前時(shí)間戳（精確到分鐘，防止秒級(jí)變動(dòng)解密失?。?
        long timestamp = DateTime.Now.ToUniversalTime().Ticks / 10000000 / 60;
        return MD5.HashData(Encoding.UTF8.GetBytes("固定密鑰" + timestamp)).ToHexString().Substring(0, 16);
    }
 
    // 加密（帶時(shí)間因子）
    public static string Encrypt(string content)
    {
        using Aes aes = Aes.Create();
        aes.Key = Encoding.UTF8.GetBytes(GetKeyByTime());
        aes.IV = Encoding.UTF8.GetBytes("1234567812345678");//固定IV（可改）
        ICryptoTransform encryptor = aes.CreateEncryptor();
        byte[] bytes = Encoding.UTF8.GetBytes(content);
        return Convert.ToBase64String(encryptor.TransformFinalBlock(bytes, 0, bytes.Length));
    }
 
    // 解密（5分鐘內(nèi)有效，超時(shí)失效）
    public static string Decrypt(string cipherText)
    {
        // 校驗(yàn)5分鐘內(nèi)的時(shí)間戳，兼容時(shí)間誤差
        for (int i = 0; i <= 5; i++)
        {
            try
            {
                long timestamp = (DateTime.Now.ToUniversalTime().Ticks / 10000000 / 60) - i;
                string key = MD5.HashData(Encoding.UTF8.GetBytes("固定密鑰" + timestamp)).ToHexString().Substring(0, 16);
                using Aes aes = Aes.Create();
                aes.Key = Encoding.UTF8.GetBytes(key);
                aes.IV = Encoding.UTF8.GetBytes("1234567812345678");
                ICryptoTransform decryptor = aes.CreateDecryptor();
                byte[] bytes = Convert.FromBase64String(cipherText);
                return Encoding.UTF8.GetString(decryptor.TransformFinalBlock(bytes, 0, bytes.Length));
            }
            catch { continue; }
        }
        throw new Exception("加密超時(shí)或內(nèi)容無效");
    }
}

// 授權(quán)碼生成：比如生成7天有效期的授權(quán)碼
public static string CreateTimeAuthCode(string userId)
{
    DateTime expireTime = DateTime.Now.AddDays(7);
    string content = $"{userId}_{expireTime:yyyyMMddHHmmss}";
    // 加鹽MD5（不可逆，驗(yàn)證時(shí)重新計(jì)算比對(duì)）
    return MD5.HashData(Encoding.UTF8.GetBytes(content + "加鹽字符串")).ToHexString();
}
 
// 驗(yàn)證授權(quán)碼有效性
public static bool VerifyTimeAuthCode(string userId, string authCode)
{
    string content = $"{userId}_{DateTime.Now:yyyyMMddHHmmss}";
    string checkCode = MD5.HashData(Encoding.UTF8.GetBytes(content + "加鹽字符串")).ToHexString();
    if (checkCode == authCode) return true;
    // 補(bǔ)全有效期內(nèi)校驗(yàn)邏輯（略）
    return false;
}