c#字符串MD5加密GetMD5Hash

/// <summary>
        /// 把字符转换成MD5
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string GetMD5Hash(String str)
        {
                   //把字符串转换成字节数组
                   byte[] buffer = Encoding.Default.GetBytes(str);

                  MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
                   //md5加密
                   byte[] cryptBuffer = md5.ComputeHash(buffer);
                   string s = "";
                   //把每一个字节 0-255，转换成两位16进制数     
                   for (int i = 0; i < cryptBuffer.Length; i++)
                   {
                           //大X转黄的是大写字母，小X转换的是小写字母
                           s += cryptBuffer[i].ToString("x2");
                   }
              return s;
        }