// s = '1234'
        private static string Encrypt(string s)
        {
            HashAlgorithm provider = null;

            try {
                provider = new SHA1Managed();
                byte[] bytes = Encoding.Unicode.GetBytes(s);
                // bytes = 49, 0, 50, 0, 51, 0, 52, 0

                provider.Initialize();
                bytes = provider.ComputeHash(bytes);
               // bytes = 19, 519, 105, 201, 60, 4, 36, 150, 168, 233, 88, 236, 89, 48, 102, 44, 108, 204, 175, 191
                return Convert.ToBase64String(bytes);
                // bytes = E59pyTwEJJao6VjsWTBmLGzMr78=
            }
            finally {
                if (provider != null)
                    provider.Clear();
            }
        }