using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    private static string STX = @"3032";

    public static void Main()

    {

        var hex = "303235312e303130313033";

        var lrc = LRC(hex);

        var msg = hex + lrc;

        Console.WriteLine(msg);

    }

​

    private static string LRC(string dataAsHex)

    {

        var checksum = 0;

        foreach (var c in SplitToChars(dataAsHex.Replace(STX,"")))

        {

            checksum ^= Convert.ToByte(c);

        }

​

        return checksum.ToString("X2");

    }

    static IEnumerable<char> SplitToChars(string str)

    {

        return Enumerable.Range(0, str.Length / 2).Select(i => Convert.ToChar(int.Parse(str.Substring(i * 2, 2), System.Globalization.NumberStyles.HexNumber)));

    }

}