How to encrypt/decrypt using the Android KeyStore with keeping compatibility?

Question

I am developing an Android app.

Because of the security, I should encrypt/decrypt private data.

Until now, I just store them into the SharedPreference as a Plain Text.

Because there are many sample codes on the web, applying Android KeyStore was not difficult.

Now I have "encrypt", "decrypt" methods.

The problem is...

Many user's data are already stored into the SharedPreference as a Plain text.

Because my app will try to decrypt the plain text, if I update this app they will face crush or wrong behavior.

Then...

How can I keep the compatibility?

Actually, when I update my app, I faced the IllegalBlockSizeException.

So I think that if I catch the IllegalBlockSizeException on the "decrypt" method and return just Plain text, my app will work fine.

But I don't know it is right or not...

Could you tell me advice, please?

Answer 1

1. You increase version of your new release right? why not add an if else logic to your code to decide whether to en/decrypt or not by your app version?
2. You can create new storage path/SharedPreference name and implement your en/decrypt logic. Then your old SharedPreference data will be ignored. Idk about the risk for your business logic.