Quick hack to decrypt the URL for Zone 4 http://snowmiser.counterhack.com/zone-3-EAB6B031-4EFA-49F1-B542-30EBE9EB3962/

Output

The key is: 5ab678a3efaac87a07dc29c8827a245f273a8f5cb4bb1485fd36b42b0fdd4f5e05709e0c8a2ebbe851ab7a
Plain Text: zone-4-9D469367-B60E-4E08-BDF1-FED7CC74AF33

Program.cs

using System;

namespace xorStrings
{
    class Program
    {
        static void Main(string[] args)
        {
            string cipherText       = "20d916c6c29ee53c30ea1effc63b1c72147eb86b998a25c0cf1bf66939e8621b3132d83abb1683df619238";
            string plainText        = "zone-4-F7677DA8-3D77-11E2-BB65-E4BF6188709B";
            string unknownKey       = "";

            string newCipherText    = "20d916c6c29ee54343e81ff1b14c1372650cbf19998f51b5c51bf66f49ec62184034a94fc9198fa9179849";
            string unknownPlainText = "";


            for (int i = 0; i < cipherText.Length/2; i++)
            {
                int ct = Convert.ToInt32(cipherText.Substring(i * 2, 2), 16);
                int pt = char.Parse(plainText.Substring(i, 1));
                
                unknownKey += (ct ^ pt).ToString("X2");
            }
            Console.WriteLine("The key is: {0}", unknownKey.ToLower());


            for (int i = 0; i < newCipherText.Length / 2; i++)
            {
                int ct = Convert.ToInt32(newCipherText.Substring(i * 2, 2), 16);
                int ky = Convert.ToInt32(unknownKey.Substring(i * 2, 2), 16);

                unknownPlainText += (char)(ct ^ ky);
            }
            Console.WriteLine("Plain Text: {0}", unknownPlainText);
        }

    }
}