public static string GetMD5Hash(string fileName)
        {
            try
            {
                FileStream file = new FileStream(fileName, FileMode.Open);
                System.Security.Cryptography.MD5 md5 = new System.Security.Cryptography.MD5CryptoServiceProvider();
                byte[] retVal = md5.ComputeHash(file);
                file.Close();
 
                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < retVal.Length; i++)
                {
                    sb.Append(retVal[i].ToString("x2"));
                }
                return sb.ToString();
             }
             catch (Exception ex)
             {
                throw new Exception("GetMD5Hash() fail,error:" + ex.Message);
             }
         }

        public static string GetMD5Hash(byte[] bytedata)
        {
            try
            {                
                System.Security.Cryptography.MD5 md5 = new System.Security.Cryptography.MD5CryptoServiceProvider();
                byte[] retVal = md5.ComputeHash(bytedata);

                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < retVal.Length; i++)
                {
                    sb.Append(retVal[i].ToString("x2"));
                }
                return sb.ToString();
            }
            catch (Exception ex)
            {
                throw new Exception("GetMD5Hash() fail,error:" + ex.Message);
            }
        }