Tic-tac-toe with stakes
Take the simplest game that can carry money, and put money on it: tic-tac-toe, for stakes.
Two strangers lock funds into a pot on the Kaspa network and play a multi-round match. When the match ends, the winner takes the pot; a draw splits it. There is no casino and no escrow agent. The loser cannot refuse to pay, and the winner cannot claim more than they earned. The operator cannot rewrite the scoreboard either, because the scoreboard is a proof, not a statement by anyone.
This is vprog-tictactoe (we’ll call it tt), a working example built on vprogs, a framework for based computation on Kaspa (Based rollup on Kaspa explains the word). The game is chosen for size: tic-tac-toe is small enough to hold in your head and still exercises every part of the framework, a proof of concept, not a claim that this game needs a rollup. In tt, the game’s own actions, accounts, and rules are the only application-specific code; everything else is reused machinery: executing, proving, settling, exiting. The moves you make in a browser are signed user actions; the match state lives in a verifiable program; the payout lands on the real Kaspa chain.
The rest of this short book explains the machine:
- what a based rollup is, and what it demonstrates Kaspa can do,
- the small set of transaction types the whole machine is built from,
- how proofs chain user actions, deposits, and settlements across many blocks of the Kaspa chain (its L1),
- what a zkVM has to do with it,
- how this compares to a smart-contract platform like Solana,
- and what you can build on it today.
A live demo of tt runs alongside this material.
Two things to state up front. First, everything the machine needs is live on Kaspa mainnet; the demo itself runs on the public testnet, a demonstration network with looser security assumptions (Based rollup on Kaspa gives the details). Second, safety and liveness are different guarantees. The chain guarantees that no one can falsify state or steal funds, but moving money requires the machine to keep running. Who runs it, what can stall it, and what happens when nobody does are covered in The machinery and Building an app on it.