using System;

using System.Collections.Generic;

using System.Linq;

using System.Xml.Linq;

using System.Xml;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Read Xml");

        var xml=@"

        <HelperKey>

 <HardwareType Module=""1234"">

  <m2MainHelperKey>F1DF15D4D1F5D3</m2MainHelperKey>

  <m2LowerHelperKey>ER66T4T4R5T4R</m2LowerHelperKey>

  <m2UpperHelperKey>4VXC4V5C54VC5</m2UpperHelperKey>

 </HardwareType>

 <HardwareType Module=""AB45"">

  <m2MainHelperKey>F1DF15FGFD4D1F5D3</m2MainHelperKey>

  <m2LowerHelperKey>ERTRTRR66T4T4R5T4R</m2LowerHelperKey>

  <m2UpperHelperKey>4VXC4FDFDFDV5C54VC5</m2UpperHelperKey>

 </HardwareType>

</HelperKey>

";

         XDocument doc = XDocument.Parse(xml);

            //get all elements for certain attribute

            var q = doc.Descendants("HardwareType").Where(c => (string) c.Attribute("Module") == "1234");

            foreach (var x in q.Elements())

            {

                Console.WriteLine("Name: {0}    value: {1}",x.Name , x.Value);

            }

​

            //get one element by name

            var el = q.Elements("m2LowerHelperKey").FirstOrDefault().Value;

            Console.WriteLine(el);

    }

}