public class MD5Helper    {        ///DES加密            ///sKey         public  string MD5Encrypt(string pToEncrypt, string sKey)        {            DESCryptoServiceProvider des = new DESCryptoServiceProvider();            byte[] inputByteArray = Encoding.Default.GetBytes(pToEncrypt);            des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);            des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);            MemoryStream ms = new MemoryStream();            CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);            cs.Write(inputByteArray, 0, inputByteArray.Length);            cs.FlushFinalBlock();            StringBuilder ret = new StringBuilder();            foreach (byte b in ms.ToArray())            {                ret.AppendFormat("{0:X2}", b);            }            ret.ToString();            return ret.ToString();        }        ///DES解密            public  string MD5Decrypt(string pToDecrypt, string sKey)        {            DESCryptoServiceProvider des = new DESCryptoServiceProvider();            byte[] inputByteArray = new byte[pToDecrypt.Length / 2];            for (int x = 0; x < pToDecrypt.Length / 2; x++)            {                int i = (Convert.ToInt32(pToDecrypt.Substring(x * 2, 2), 16));                inputByteArray[x] = (byte)i;            }            des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);            des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);            MemoryStream ms = new MemoryStream();            CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);            cs.Write(inputByteArray, 0, inputByteArray.Length);            cs.FlushFinalBlock();            StringBuilder ret = new StringBuilder();            return System.Text.Encoding.Default.GetString(ms.ToArray());        }        public  string MD5Encrypt(string pToEncrypt, string sKey, out string msg)        {            DESCryptoServiceProvider des = new DESCryptoServiceProvider();            StringBuilder ret = new StringBuilder();            try            {                byte[] inputByteArray = Encoding.Default.GetBytes(pToEncrypt);                msg = "SUCC:";                int length = sKey.Length;                if (length < 8)                { msg = "ERR:密钥长度不能小于8"; return ""; }                int _dif = length - 8;                int _sub_Index = _dif / 2 + _dif % 2;                _sub_Index = _sub_Index <= 0 ? 0 : _sub_Index;                sKey = sKey.Substring(_sub_Index, 8);                des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);                des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);                MemoryStream ms = new MemoryStream();                CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);                cs.Write(inputByteArray, 0, inputByteArray.Length);                cs.FlushFinalBlock();                foreach (byte b in ms.ToArray())                {                    ret.AppendFormat("{0:X2}", b);                }            }            catch (Exception ex)            {                msg = "ERR:" + ex.Message;            }            return ret.ToString();        }        ///DES解密            public  string MD5Decrypt(string pToDecrypt, string sKey, out string msg)        {            DESCryptoServiceProvider des = new DESCryptoServiceProvider();            string _value = http://www.mamicode.com/"";            try            {                msg = "SUCC:";                int length = sKey.Length;                if (length < 8)                { msg = "ERR:密钥长度不能小于8"; return ""; }                int _dif = length - 8;                int _sub_Index = _dif / 2 + _dif % 2;                _sub_Index = _sub_Index <= 0 ? 0 : _sub_Index;                sKey = sKey.Substring(_sub_Index, 8);                byte[] inputByteArray = new byte[pToDecrypt.Length / 2];                for (int x = 0; x < pToDecrypt.Length / 2; x++)                {                    int i = (Convert.ToInt32(pToDecrypt.Substring(x * 2, 2), 16));                    inputByteArray[x] = (byte)i;                }                des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);                des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);                MemoryStream ms = new MemoryStream();                CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);                cs.Write(inputByteArray, 0, inputByteArray.Length);                cs.FlushFinalBlock();                StringBuilder ret = new StringBuilder();                _value = Encoding.Default.GetString(ms.ToArray());            }            catch (Exception ex)            {                msg = "ERR:" + ex.Message;            }            return _value;        }    }

 MD5Helper md5 = new MD5Helper(); string key = ConfigurationManager.AppSettings["MD5Encrypt"]; loginPassword = md5.MD5Encrypt(loginPassword, key);