How to Encoding & Decoding the string in asp.net

string  message ="adi";

string str=obj.encode(str);

str=obj.decode(str);

public string encode(string message)

    {

        return Convert.ToBase64String(Encoding.UTF8.GetBytes(message));

    }

    public string decode(string message)

    {

        return Encoding.UTF8.GetString(Convert.FromBase64String(message));

    }