How to create an entity which is like another entities But diffrent

I know the question is not understandable but I will make it more clear, thats a design question. Lets say I have a encryption/decryption program. Every encryption/decryption has two methods it has to have - encrypting method and decrypting method, So I have a interface which every encyption/decryption implemnts it. Now lets say I have an encryption/decryption method which uses the other encryption/decryption way. So its also should implemnts the encryption/decryption, But It also should use the other encryption/decryption ways. So the interface should look like this- Public String encryptData(String data,int key) Public String decryptData(String data,int key) <\code>

But the encryption/decryption thats uses other encryption/decryption ways should look like this-

Public String encryptData(String data,int key , interface method) Public String decryptData(String data,int key, interface method) <\code>

And ideas?