What if I use a different key for each card?

I found the answer in the youtube comments:

Dan McNeill: What if I use a different key for each card?

MrBawn: In the physical version, you could absolutely identify each card by which of your keys unlocked your lock without unlocking your opponent's lock. In the crypto version, you can't tell which of your keys works on an encrypted card because your opponent's lock has turned it into gibberish. So an incorrect key would be indistinguishable from a correct key.