using System;

    using System.Security.Cryptography;

    using System.Text;

    using System.Web;

    public class Test

    {

        static readonly char[] padding = { '=' };

        public static void Main()

        {

            string siteSecret = "12345678";

            string jsonToken = "{'session_id':'abf52ca5-9d87-4061-b109-334abb7e637a','ts_ms':1445705791480}";

            string jsonTokenValid = "{\"session_id\":\"abf52ca5-9d87-4061-b109-334abb7e637a\",\"ts_ms\":1445705791480}";

            Console.WriteLine("Returned: \n" + EncryptText(jsonToken, siteSecret));

            Console.WriteLine("Valid returned: \n" + EncryptText(jsonTokenValid, siteSecret));

        }

        public static string EncryptText(string PlainText, string siteSecret)

        {

            using (RijndaelManaged aes = new RijndaelManaged())

            {

                aes.Mode = CipherMode.ECB;

                aes.Padding = PaddingMode.PKCS7;

                var bytes = Encoding.UTF8.GetBytes(siteSecret);

                SHA1 sha1 = SHA1.Create();

                var shaKey = sha1.ComputeHash(bytes);

                byte[] targetArray = new byte[16];

                Array.Copy(shaKey, targetArray, 16);

                aes.Key = targetArray;

                ICryptoTransform encrypto = aes.CreateEncryptor();

                byte[] plainTextByte = Encoding.UTF8.GetBytes(PlainText);

                byte[] CipherText = encrypto.TransformFinalBlock(plainTextByte, 0, plainTextByte.Length);

                string returnValue = System.Convert.ToBase64String(CipherText)

                    .TrimEnd(padding).Replace('+', '-').Replace('/', '_');

                Console.WriteLine("Proper: \n" + returnValue);

                return HttpServerUtility.UrlTokenEncode(CipherText);

            }

        }

    }