C# MD5加密

public string md5(string str, int code)
{
  　　if (code == 16) //16位MD5加密（取32位加密的9~25字符）   
     {
          return System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(str, "MD5").ToLower().Substring(8, 16);
     }
     else//32位加密   
     {
          return System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(str, "MD5").ToLower();
     }
}