Downloads a file into a string via GET - Cached

CacheDlString.cs

public static string md5(string input, hashFlag flag = 0)
        {
            StringBuilder sb = new StringBuilder();
            Stream fs;
            if (flag == hashFlag.hashFile)
                if (File.Exists(input))
                    fs = File.OpenRead(input);
                else
                    throw new Exception("File does not exist");
            else
                fs = new MemoryStream(Encoding.ASCII.GetBytes(input));

            foreach (var item in MD5.Create().ComputeHash(fs)) sb.Append(item.ToString("X2"));
            return sb.ToString();
        }
        public static string dlString(string url, bool cache = true)
        {
            string urlSum = md5(url);

            if (!Directory.Exists(cachePath))
                Directory.CreateDirectory(cachePath);
            if (File.Exists(cachePath + "\\" + urlSum) && cache)
                return File.ReadAllText(cachePath + "\\" + urlSum);
            else
            {
                WebClient wc = new WebClient();
                wc.Encoding = UTF8Encoding.UTF8;
                wc.Proxy = null;
                wc.Headers["Cache-Control"] = "max-age=0";
                wc.Headers["Accept"] = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
                wc.Headers["User-agent"] = "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Firefox/45.0";
                wc.Headers["Accept-Language"] = "en-US,en;q=0.8";
                string webSite = wc.DownloadString(url);
                File.WriteAllText(cachePath + "\\" + urlSum, webSite);
                return webSite;
            }
        }