private static string Encrypt(string s)
        {
            HashAlgorithm provider = null;

            try {
                provider = new SHA1Managed();
                byte[] bytes = Encoding.Unicode.GetBytes(s);

                provider.Initialize();
                bytes = provider.ComputeHash(bytes);
                return Convert.ToBase64String(bytes);
            }
            finally {
                if (provider != null)
                    provider.Clear();
            }
        }