Encrypt backup using master password

[andotp]

Encrypt backup using master password

[flocke]

I don't mind adding an option to have encrypted backups with a password, but this will need some additional research since this is my first Android app.

But I won't add a master password for opening the app itself, there already is a fork of OTP Authenticator that encrypts the stored internal data with a master password out there: https://github.com/kckrinke/onetimepad

Also the current method of locking the app has nothing to do with the encryption, it's just an additional check that closes the app again if the authentication fails. The encryption of the data is not coupled to the authentication in any way.