Support loading cached key about go-tpm-tools HOT 2 CLOSED

That would be useful. We probably won't get to it for some time, but I'd be happy to review this PR.

from go-tpm-tools.

There are currently some things that prevent a clean implementation on my part.
This is mainly due to the session parameter of the Key struct, which is currently private.

In my fork, I simply set it to nullSession, which looks like this:

func LoadCachedKey(rw io.ReadWriter, cachedHandle tpmutil.Handle) (k *Key, err error) {
	cachedPub, _, _, err := tpm2.ReadPublic(rw, cachedHandle)
	if err != nil {
		return nil, fmt.Errorf("failed to read public area of cached key: %w", err)
	}

	k = &Key{
		rw: rw,
		handle: cachedHandle,
		pubArea: cachedPub,
		session: nullSession{}, // <- use nullSession for authentication
	}
	return k, k.finish()
}

Ideally we could just provide sessions as a parameter to the function.
However, for this to be usable this would also require making (at least some) session implementations, e.g. nullSession, and the interface public as well.

from go-tpm-tools.