How can I update a Java Card applet that contains data that need to be preserved across versions? As best as I can tell updating an applet is done by deleting it and then installing the new version, which seems like it would also delete any persistent data associated with the app.
As a concrete example, suppose I was writing an authentication and encryption applet. Version 1 of the applet would generate a key protected by the hardware on installation, and support signing messages, but not encrypting them. Suppose I then wanted to release a version 2 that also supported encryption, and could use the keys created by version 1. What would I need to do in version 1 and 2 in order to make that possible?
I'm open to solutions that use GlobalPlatform mechanics in addition to pure Java Card.
You need a second applet which owns all objects you want to preserve across re-installation of first applet. Let's call them Storage applet and Worker applet.
This means that every time a Worker applet needs to use resources from Storage applet it has to invoke Shareable interface. There is a penalty in code size, code maintainability and a penalty in speed. I can not think of another way to do this in Java Card or Global Platform.