@lm @bobjonkman A zero-knowledge lets you prove that you know a certain secret. But here you're supposed to show that you _don't_ know the secret (because rigging your seed even for the first round can generate an advantage).

So maybe a two-way zero-knowledge proof in some fashion. I don't think it's hard to figure out if you can wait until the round is over (incentive to cheat is low if it's revealed once you win) - but having it in "real-time" (per-step, also initiated before any moves are made) is a bit weirder.

But then again, maybe if you prove that you had a secret and that this secret was properly hashed with whatever nonce was sent by the opponent... My brain is tying knots on itself.