function GetMd5(AValue : string) : string;

var

   md5 : TIdHashMessageDigest5;

     bytes,byte1 : TBytes;

begin

        md5 := TIdHashMessageDigest5.Create;

       try

          Result := LowerCase( md5.HashStringAsHex(AValue));

       finally

          md5.Free;

       end;

end;

//一轮:

Result :=GetMd5('test');

//二轮

Result :=  GetMd5(GetMd5(vValue));