using System;

using System.Text;

using System.Security.Cryptography;

public class Program

{

    public static void Main()

    {

        var identifierBytes = Convert.FromBase64String("rplx5ydcRpGFWHBIcneo+g==");

        var opaqueHex = Convert.FromHexString("53547E14B435DDCBE06ED2BF986F4F5B");

        var bundleIdHex = Convert.FromHexString("0C0F63682E6371642E5469636BC57473");

        var payloadLength = opaqueHex.Length + bundleIdHex.Length + identifierBytes.Length;

        byte[] payload = new byte[payloadLength];

        var destOffset = 0;

        Buffer.BlockCopy(identifierBytes, 0, payload, destOffset, identifierBytes.Length);

        destOffset += identifierBytes.Length;

        Buffer.BlockCopy(opaqueHex, 0, payload, destOffset, opaqueHex.Length);

        destOffset += opaqueHex.Length;     

        Buffer.BlockCopy(bundleIdHex, 0, payload, destOffset, bundleIdHex.Length);

        using (var sha1 = new SHA1Managed())

        {

            var hash = sha1.ComputeHash(payload);

            Console.WriteLine(Convert.ToHexString(hash));

        }

    }

}