public static string SHA1ForFile(this string filePath)
        {
            if (!File.Exists(filePath))
            {
                return(null);
            }
            var algo = new HashLib.Crypto.SHA1();
            var byts = File.ReadAllBytes(filePath);
            var hash = algo.ComputeBytes(byts);

            return(hash.ToString().ToLower());
        }