字符串MD5加密运算

 public static string GetMd5String(string str)
       {
           MD5 md5 = MD5.Create();
           byte[]buffer=System.Text.Encoding.UTF8.GetBytes(str);
           byte[]md5Buffer=md5.ComputeHash(buffer);
           StringBuilder sb = new StringBuilder();
           foreach (byte b in md5Buffer)
           {
               sb.Append(b.ToString("x2"));
           }
           return sb.ToString();
       }