对称加密算法实现（通常是加密web.config)

    /// <summary>
    /// 加密解密类
    /// </summary>
    public class EncryptAndDescrypt
    {
        private SymmetricAlgorithm myjl;//表示所有对称算法的实现都必须从中继承的抽象基类。
        private const string CIV = "abceftjp152=";//密钥
        private const string CKEY = "Acefslqbqjs=";//初始化向量
      

       /// <summary>
       /// 生成加密解密类
       /// </summary>
        public EncryptAndDescrypt()
        {
            myjl = new DESCryptoServiceProvider();//定义访问数据加密标准 (DES) 算法的加密服务提供程序 (CSP) 版本的包装对象。 此类不能被继承
        }

        /// <summary>
        /// 通过对称算法进行加密
        /// </summary>
        /// <param name="value">要加密的字符串</param>
        /// <returns></returns>
        public string EncryptString(string value)
        {
             ICryptoTransform ct;//定义基本的加密运算符
            MemoryStream ms;
            CryptoStream cs;//定义将数据流转链接到加密转换的流
            byte[] byt;
            //CreateEncryptor创建加密对象
            ct = myjl.CreateEncryptor(Convert.FromBase64String(CKEY), Convert.FromBase64String(CIV));

            byt = Encoding.UTF8.GetBytes(value);

            ms = new MemoryStream();
            cs = new CryptoStream(ms, ct, CryptoStreamMode.Write);
            cs.Write(byt, 0, byt.Length);
            cs.FlushFinalBlock();

            cs.Close();

            return Convert.ToBase64String(ms.ToArray());
           
        }

        /// <summary>
        /// 解密算法
        /// </summary>
        /// <param name="value">输入要解密的字符</param>
        /// <returns></returns>
        public String DescrptyString(string value)
        {
            //定义基本的加密转换运算
            ICryptoTransform ct;
            MemoryStream ms;
            CryptoStream cs;
            byte[] byt;

            ct = myjl.CreateDecryptor(Convert.FromBase64String(CKEY), Convert.FromBase64String(CIV));

            byt = Convert.FromBase64String(value);

            ms = new MemoryStream();
            cs = new CryptoStream(ms, ct, CryptoStreamMode.Write);
            cs.Write(byt, 0, byt.Length);
            cs.FlushFinalBlock();

            cs.Close();

            return Encoding.UTF8.GetString(ms.ToArray());
       
        }

 

    }