对称加密

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

/// <summary>
/// jm 的摘要说明
/// </summary>
public class jm
{
public jm()
{
//
// TODO: 在此处添加构造函数逻辑
//
}
    public class SymmetricMethod
    {

        private SymmetricAlgorithm mobjCryptoService;
        private string Key;
        /**/
        /// <summary>
        /// 对称加密类的构造函数
        /// </summary>
        public SymmetricMethod()
        {
            mobjCryptoService = new RijndaelManaged();
            Key = "lijianfufaicaixiaoke";
        }
        /**/
        /// <summary>
        /// 获得密钥
        /// </summary>
        /// <returns>密钥</returns>
        private byte[] GetLegalKey()
        {
            string sTemp = Key;
            mobjCryptoService.GenerateKey();
            byte[] bytTemp = mobjCryptoService.Key;
            int KeyLength = bytTemp.Length;
            if (sTemp.Length > KeyLength)
                sTemp = sTemp.Substring(0, KeyLength);
            else if (sTemp.Length < KeyLength)
                sTemp = sTemp.PadRight(KeyLength, ' ');
            return ASCIIEncoding.ASCII.GetBytes(sTemp);
        }
        /**/
        /// <summary>
        /// 获得初始向量IV
        /// </summary>
        /// <returns>初试向量IV</returns>
        private byte[] GetLegalIV()
        {
            string sTemp = "caoxiaokeailijianfu";
            mobjCryptoService.GenerateIV();
            byte[] bytTemp = mobjCryptoService.IV;
            int IVLength = bytTemp.Length;
            if (sTemp.Length > IVLength)
                sTemp = sTemp.Substring(0, IVLength);
            else if (sTemp.Length < IVLength)
                sTemp = sTemp.PadRight(IVLength, ' ');
            return ASCIIEncoding.ASCII.GetBytes(sTemp);
        }
        /**/
        /// <summary>
        /// 加密方法
        /// </summary>
        /// <param name="Source">待加密的串</param>
        /// <returns>经过加密的串</returns>
        public string Encrypto(string Source)
        {
            byte[] bytIn = UTF8Encoding.UTF8.GetBytes(Source);
            MemoryStream ms = new MemoryStream();
            mobjCryptoService.Key = GetLegalKey();
            mobjCryptoService.IV = GetLegalIV();
            ICryptoTransform encrypto = mobjCryptoService.CreateEncryptor();
            CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Write);
            cs.Write(bytIn, 0, bytIn.Length);
            cs.FlushFinalBlock();
            ms.Close();
            byte[] bytOut = ms.ToArray();
            return Convert.ToBase64String(bytOut);
        }
        /**/
        /// <summary>
        /// 解密方法
        /// </summary>
        /// <param name="Source">待解密的串</param>
        /// <returns>经过解密的串</returns>
        public string Decrypto(string Source)
        {
            byte[] bytIn = Convert.FromBase64String(Source);
            MemoryStream ms = new MemoryStream(bytIn, 0, bytIn.Length);
            mobjCryptoService.Key = GetLegalKey();
            mobjCryptoService.IV = GetLegalIV();
            ICryptoTransform encrypto = mobjCryptoService.CreateDecryptor();
            CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Read);
            StreamReader sr = new StreamReader(cs);
            return sr.ReadToEnd();
        }
    }
}

APSX页面调用
    <form id="form1" runat="server">

        <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label><br />
        <asp:Label ID="Label2" runat="server" Text="Label"></asp:Label><br />

    </form>
APSX CS代码
jm.SymmetricMethod sm = new jm.SymmetricMethod();
Label1.Text = sm.Encrypto("123");
Label2.Text = sm.Decrypto("CmpMHPLcNTjE6O6pV2gi3g==");