using System.Security.Cryptography;

  //MD5 md5 = MD5.Create();

            MD5 md5 = new MD5CryptoServiceProvider();

            byte[] buffer = Encoding.Default.GetBytes(str);

            byte[] bufferStr = md5.ComputeHash(buffer);

            string md5Str = "";

            foreach (byte item in bufferStr)

            {

                md5Str += item.ToString("x2");

            }

            return md5Str;

加密的还有des可逆对称加密，RSA非对称加密  数字整数ssl