An example factory interface for creating a decryptor

ICryptoFactory.cs

    public interface ICryptoFactory
    {
        ICryptoAlgorithm Create<T>(string password, string salt) where T : SymmetricAlgorithm, new();
        ICryptoAlgorithm Create(Type type, string password, string salt);
    }

    public interface ICryptoAlgorithm
    {
        string Decrypt(string text);
        string Encrypt(string text);
        string HashKey(string text);
    }