加密与解密

public static string MD5Encrypt(string pToEncrypt, string sKey)
        {
            //8位密钥，16位加密结果
            //try
            //{
            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            byte[] inputByteArray = System.Text.Encoding.Default.GetBytes(pToEncrypt);
            des.Key = System.Text.ASCIIEncoding.ASCII.GetBytes(sKey);
            des.IV = System.Text.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();
            System.Text.StringBuilder ret = new System.Text.StringBuilder();
            foreach (byte b in ms.ToArray())
            {
                ret.AppendFormat("{0:X2}", b);
            }
            ret.ToString();
            return ret.ToString();
            //}
            //catch
            //{
            //    throw new Exception("Card Num is unvaildate!");
            //}
        }
        /**/
        ///MD5解密 
        public static string MD5Decrypt(string pToDecrypt, string sKey)
        {
            try
            {
                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 = System.Text.ASCIIEncoding.ASCII.GetBytes(sKey);
                des.IV = System.Text.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();
                System.Text.StringBuilder ret = new System.Text.StringBuilder();
                return System.Text.Encoding.Default.GetString(ms.ToArray());
            }
            catch
            {
                return pToDecrypt;
            }
        }