class Program
{
    static string encryptKey = "_uy=";    //定义密钥 --必为4个字节，得到的为64bit

    #region 加密字符串
    /// <summary> /// 加密字符串  
    /// </summary> 
    /// <param name="str">要加密的字符串</param> 
    /// <returns>加密后的字符串</returns> 
    static string Encrypt(string str)
    {
        DESCryptoServiceProvider descsp = new DESCryptoServiceProvider();   //实例化加/解密类对象  

        byte[] key = Encoding.Unicode.GetBytes(encryptKey); //定义字节数组，用来存储密钥   

        byte[] data = Encoding.Unicode.GetBytes(str);//定义字节数组，用来存储要加密的字符串 

        MemoryStream MStream = new MemoryStream(); //实例化内存流对象     

        //使用内存流实例化加密流对象  
        CryptoStream CStream = new CryptoStream(MStream, descsp.CreateEncryptor(key, key), CryptoStreamMode.Write);

        CStream.Write(data, 0, data.Length);  //向加密流中写入数据     

        CStream.FlushFinalBlock();              //释放加密流     

        return Convert.ToBase64String(MStream.ToArray());//返回加密后的字符串 
    }
    #endregion

    #region 解密字符串
    /// <summary> 
    /// 解密字符串  
    /// </summary> 
    /// <param name="str">要解密的字符串</param> 
    /// <returns>解密后的字符串</returns>   
    static string Decrypt(string str)
    {
        DESCryptoServiceProvider descsp = new DESCryptoServiceProvider();   //实例化加/解密类对象   

        byte[] key = Encoding.Unicode.GetBytes(encryptKey); //定义字节数组，用来存储密钥   

        byte[] data = Convert.FromBase64String(str);//定义字节数组，用来存储要解密的字符串 

        MemoryStream MStream = new MemoryStream(); //实例化内存流对象     

        //使用内存流实例化解密流对象      
        CryptoStream CStream = new CryptoStream(MStream, descsp.CreateDecryptor(key, key), CryptoStreamMode.Write);

        CStream.Write(data, 0, data.Length);      //向解密流中写入数据    

        CStream.FlushFinalBlock();               //释放解密流     

        return Encoding.Unicode.GetString(MStream.ToArray());       //返回解密后的字符串 
    }
    #endregion

    static void Main(string[] args)
    {
        Console.Write("请输入要加密的字符串：");   //提示输入字符串     
        Console.WriteLine();                  //换行输入  
        string str = Console.ReadLine();     //记录输入的字符串     
        string strNew = Encrypt(str);              //加密字符串     
        Console.WriteLine("加密后的字符串：" + strNew);  //输出加密后的字符串     
        Console.WriteLine("解密后的字符串：" + Decrypt(strNew)); //解密字符串并输出    
        Console.ReadLine();
    }
}