[pwlb]

It's gonna be hard if you really want security. Card developers put a lot of effort into securing operations against sidechannel pertuberation, sidechannel and many more attacks, that opensource developers will hardly be able to handle on theeir own.

[btchip]

This architecture allows you to move gradually from certified libraries (included in the proprietary HAL) to your own custom libraries when you're satisfied with the result.