I dunno if that works or is any less confusing, to be honest.

I don’t think there’s any process or entity in the physical world that is reasonably familiar to most people that is even remotely suitable as an analogy to public key cryptography.

I think this is worth highlighting. Public Key Cryptography is a surprising idea. Like Computation, if you'd told a 19th century mathematician about this, they might buy it as a concept but deem it unlikely to ever happen in practice or be of any significance, in the 20th century these were both realised and caused a massive change to our society.

These are not analogs to things ordinary people had already seen. For Computation we just got used to it being everywhere and so we don't need to explain it so much.