A more perfect vacuum

I was unlocking the door to the bike shed at my apartment perhaps two years ago when a thought occurred to me. There are actually only two kinds of locks -- those which require secret knowledge, i.e., combination locks, and mechanical ward locks, for instance a key and tumbler lock. On the computer, however, the only sort of lock one can find is the secret knowledge type, (at least implemented as software). I wondered if it would be possible to conceive of a key lock that was entirely implemented in software? I thought and thought but couldn't come up with anything that didn't involve translating some physical quantity into a number, "secret knowledge," and then employing that in the software. If one captured the "secret knowledge" in some way, one could in principle access the locked data, whether or not one had the locking device. I know my thinking isn't sufficient to prove the matter absolutely impossible, but I began to suspect it was showing me a fundamental philosophical problem, something which simply couldn't be solved.