private static string GetContextId(HttpRequestBase request, CapttiaSection config, Encryption encryption)
        {
            var contextId = AnonymousIdentifier.GetContextId(request.RequestContext.HttpContext);

            // Check for existing cookie
            var existingCookie = request.Cookies[config.CookieName];
            if (existingCookie != null)
            {
                var cookieId = existingCookie.Value;
                if (!string.IsNullOrWhiteSpace(cookieId))
                {
                    try
                    {
                        var decryptedCookieId = encryption.Decrypt(cookieId, config.PassPhraseB);
                        var cookieBrowserId = AnonymousIdentifier.GetBrowserStampFromId(decryptedCookieId);
                        var contextBrowserId = AnonymousIdentifier.GetBrowserStampFromId(contextId);
                        if (cookieBrowserId.Equals(contextBrowserId))
                        {
                            contextId = decryptedCookieId;
                        }
                    }
                    catch (CryptographicException)
                    {
                        request.Cookies[config.CookieName].Expires = DateTime.Today.AddDays(-1);
                    }
                }
            }

            return contextId;
        }
        /// <summary>
        /// Writes a CAPTTIA element to the form.
        /// </summary>
        /// <param name="html"></param>
        /// <param name="request"></param>
        /// <returns></returns>
        public static MvcHtmlString Capttia(this HtmlHelper html, HttpRequestBase request)
        {
            var config = ConfigurationManager.GetSection("capttia") as CapttiaSection;
            var encryption = new Encryption();
            var ids = new ScriptIds(config.ModuleName);

            string contextId = GetContextId(request, config, encryption);

            // Place it in a cookie
            var cookieContextId = encryption.Encrypt(contextId, config.PassPhraseB);
            request.RequestContext.HttpContext.Response.SetCookie(new HttpCookie(config.CookieName, cookieContextId) { HttpOnly = true });

            // Place it on the form
            var formId = encryption.Encrypt(contextId, config.PassPhrase);
            var token = JavaScript.EncodeForSingleQuotes(formId);

            return MvcHtmlString.Create(GetHoneyPot(ids) + GetScriptElement(ids, token));
        }