My Own Easy Encrypt & Decrypt in C#

using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.IO;
using System.Text;
///

/// Summary description for EnD
///

public class EnD
{
    public static string[] data = { "A", "B", "C", "D", "E", "F", "G", "H",
                                          "I", "J", "K", "L", "M", "N","O","P",
                                      "Q", "R", "S", "T", "U", "V","W","X",
                                      "Y", "Z", "0", "1", "2", "3","4","5","6","7","8","9"};
    public string imranEncrypt(string input, int key)
    {
        input = input.ToUpper();
        string output = "";
        int shift = 0;
        for (int i = 0; i < input.Length; i++)
        {
            if ((Array.IndexOf(data, input.Substring(i, 1)) + key + shift) > 35)
                output = output + data[(Array.IndexOf(data, input.Substring(i, 1)) + key + shift) % 36];
            else
                output = output + data[Array.IndexOf(data, input.Substring(i, 1)) + key + shift];
            shift++;
        }
        return output;
    }
    public string imranDecrypt(string input, int key)
    {
        int shift = 0;
        input = input.ToUpper();
        string output = "";
        int indexLen = 0;

        for (int i = 0; i < input.Length; i++)
        {
            indexLen = (Array.IndexOf(data, input.Substring(i, 1))) - key - shift;
            if (indexLen < 0)
            {
                do
                {
                    indexLen += 36;
                } while (indexLen < 0);
                output = output + data[indexLen];
            }
            else
                output = output + data[indexLen];
            shift++;
        }
        return output;
    }
    public EnD()
    {

    }
}