Limit access to unlocked OpenPGP SmartCard?

[Felix E. Klee]

Well, I think I could extend my SPR332 [mod][1]:

  * Add a push-button that one has to press to close the C7 circuit for
    I/O.  Without that button pressed, the smart card cannot communicate
    with the reader.  That means, for every operation, one would need to
    hold that button, kind of – but not as elegantly – as with a
    YubiKey.

  * Using some electronics detect when the green PIN pad ✓-button is
    pressed to confirm PIN entry on the reader.  Let it trigger a timer
    that cuts I/O for good after a few minutes.

Very likely there are some issues that I don’t see at the moment.

[1]: https://github.com/feklee/0.332