Andriod Encryption Decryption

It make no sense until you describe your scenario and purpose. Decryption can be different first of all, open-key or symmetric. If you don't know the encryption algorithm, you need to explain your purpose and detail of your scenario even on greater detail. No one encrypts just for encryption. This is done to provide access to one person or party and prevent to others. You will need to describe those roles and all the scenarios: creation, distribution of keys, getting access, preventing access, all of that.
—SA