Every auction on a public blockchain leaks. Your bid is visible, so someone outbids you by one cent at the last second. Your wallet is visible, so whales get front run and buyers get tracked forever. The usual fix is a middleman who holds everyone's money and promises not to peek. For the Zecathon we built Tacit to make that middleman unnecessary @zksnarks_ Tacit is sealed bid auctions and shielded escrow on @Zcash The price is public. The participants are not. Here is a walk through of what actually happens when you use it. 1. You open a wallet in your browser Pick a 12 or 24 word phrase, set a passcode, done. The wallet is a full Zcash Ironwood light client compiled to WebAssembly. It syncs by decrypting blocks locally, so the server never learns which coins are yours, and every zero knowledge proof is made right there in your tab. On testnet there is a Faucet page that sends you free coins in one tap. It already works on NU7, while the public faucets are still waiting for wallet updates. 2. A seller lists something Item, reserve price, bond, how long bidding runs, and the price rule (first price or second price). The seller's browser, an operator and an arbiter then create a brand new 2 of 3 FROST vault together. Each one holds a single key share. The full key never exists anywhere, and moving money takes two of the three. Tacit also shows you who runs each agent, and warns you if two shares would sit with the same party. Anyone can run an agent with two commands. 3. You place a sealed bid Your browser encrypts the bid to a future round of the drand randomness beacon. The key for that round does not exist yet, so nobody can read your bid early. Not the seller, not the operator, not us. Every bidder deposits the same bond, so the chain shows nothing about how much anyone bid. Tacit starts proving the deposit the moment you click, so by the time you confirm, it sends instantly. You can bid from the Tacit wallet, from the Noir browser extension in one click, or from any mobile wallet by scanning a payment request. 4. The bids unseal When drand publishes the round, every bid opens at the same moment. Nobody can refuse to reveal. The agents recompute the result from the published rules, and each one refuses to sign anything else. One shielded payout goes out: the price to the seller, the rest of every bond back to a fresh address. 5. Anyone can audit it The vault's viewing key is public by design. Press "Run audit in this tab" and your browser finds every deposit, verifies the beacon, opens the bids and checks the vault paid exactly what the rules require. It shows amounts, never who sent them. The Proof page runs that audit for every auction, live. The same vaults power shielded escrow too. Buyer, seller and an arbiter each hold a share, the buyer pays in, then releases the money when the deal is done. Nobody on chain can tell it was an escrow at all. This is not a mockup. Our first auction with real ZEC has settled on mainnet and passed the public audit: 8d9f0e7040eda2052a8cde555e4c2595ae8decff9c17be47f080da7525bef49c Why this matters for Zcash: there are no smart contracts here, so fair markets and trustless escrow always needed someone you had to trust. Threshold vaults, timelocked bids and public audit keys change that. The same pieces work for OTC trades, tenders, domain sales and freelance work. Zcash can be the place where you trade without being watched. Try it: tacit-production-6a96.up.rai… Read the code: github.com/angelraph/tacit Open source, MIT or Apache 2.0. Feedback very welcome, especially the hard kind.