Does Short Deck Have the Three Security Bounty Holes? Our Audit

People often ask: do the three security bounty challenges apply to Short Deck Hold’em too? The bounty lists three targets: predict the community cards early, obtain another player’s hidden hole cards, or change your own hand so the server settles on it. Each reproduced and confirmed challenge pays RMB 10,000, and the campaign runs until December 31, 2026. Our late-October audit covered Texas Hold’em. Short Deck has its own rules code (36 cards, antes plus a button blind, flush over full house) plugged into the card table that our card games share, so the Hold’em verdicts do not carry over automatically. We therefore ran a separate source review along the Short Deck code path. The result: no exploitable path for any of the three.

First, where the cards come from. Each deck is built from a 32-byte secret the server takes from the operating system’s random source: the 36 cards are encrypted and secretly shuffled, and a commitment to that locked deck is published before the hand. Each connected human player’s client then commits to a random value and reveals it, and the final deal order rearranges the locked deck using those player values. Bots contribute no value; if a player does not commit or reveal in time, their value is left out, the hand is dealt anyway, and verification afterwards reports that the deal cannot be fully verified. The secret is never sent out and is not published after the hand. To be clear, this does not mean the server cannot see the cards: the dealing process still knows them. What it guarantees is that the deck was locked before you contributed your random value, and that after the hand you can check the cards you saw from Verify dealing in the table menu.

Predicting the board: no path. All five community cards are fixed on the server when the hand starts, but the table data sent to anyone contains only the cards already turned, and each deal entry in the action log carries only that street’s cards. Neither the commitment nor the players’ random values reveal which position holds which card, because that mapping sits inside the secret shuffle only the server holds. Each random value is locked by its commitment before it is revealed, so the last player to reveal can only choose whether to reveal, and cannot see which order either choice produces. There is no way to steer a chosen card onto the river.

Seeing other players’ hole cards: no path. Every connection receives table data built for that viewer. During a hand only the seat’s owner sees its two hole cards, and the check is against the account that held the seat when the hand began, so someone who sits down mid-hand does not inherit the previous player’s cards. During a hand, spectators see no hole cards. Cards shown down are visible to everyone; folded cards stay private unless their owner chooses to show them after the hand, and room records and personal hand history apply the same masking. The post-hand deal proof opens only the board, cards already shown and your own two cards, and contains no secret that could rebuild anyone else’s folded hand. Early Hold’em commit-reveal dealing handed out its seed after each hand, which let participants rebuild unshown folded cards, as disclosed in Three Poker Security Challenges; the method Short Deck uses now has no such gap.

Changing your hand to affect settlement: no path. The only client messages that act on the hand are fold, check, call, raise, all-in, show cards and the dealing random value; none of them carries a card. At showdown the server evaluates hands and splits pots from the hole cards and board it holds itself, and every betting action is checked for turn order and a legal amount. Editing your cards into a straight flush in the browser changes only what your own screen shows.

Some limits. This was a source review, not a penetration test of production, and we did not separately confirm that the running build matches the source exactly. The verdicts cover Short Deck hands only, not other games or tournaments. Default dealing still asks you to trust the operator: a leaked secret, a compromised server or an undiscovered bug would change the conclusions above, so we will not call it absolutely secure. Short Deck uses only practice chips and Beans, never real money. The bounty is still open, with rules and the deadline on the bounty page; if you find a counterexample, contact the administrator as the bounty page describes, with reproduction steps and the hand ID.