Atomic swaps

An atomic swap trades your Bitcoin for Monero directly with a market maker, using the protocol created by the eigenwallet project. Nobody holds your coins in between: either the swap completes, or your Bitcoin comes back to you. Atomic swaps are in beta.

Step by step

  1. Your Bitcoin wallet must be set up and synchronized: the swap pays from it.
  2. On Swap, choose Atomic swap, then Find makers. Biscuit asks public rendezvous servers for makers and lists their offers: price, minimum and maximum, how each compares to the market, and what they keep if a swap is refunded.
  3. Pick an offer and enter how much Bitcoin to swap. Biscuit shows about how much Monero you get. The Bitcoin network fee is paid on top.
  4. Start swap. Keep Biscuit open until it’s done: about an hour, mostly waiting for Bitcoin confirmations. The Monero arrives on a new subaddress of your wallet.

One atomic swap at a time. If Biscuit closes during a swap, the swap continues the next time you open this wallet.

How your Bitcoin stays safe

  1. Your Bitcoin is locked in a shared address that neither side can spend alone.
  2. The maker locks the Monero the same way.
  3. Biscuit gives the maker what they need to take the Bitcoin, and taking it reveals to Biscuit the key to the Monero. Biscuit sweeps the Monero to your wallet.

If the maker never locks the Monero, the swap is cancelled after 24 Bitcoin blocks, about 4 hours, and your Bitcoin comes back automatically. Biscuit must be running to get it back: after the cancel, you have about a day (144 blocks) to open it. After that, the maker may take the Bitcoin. Open Biscuit at least once a day while a swap isn’t finished.

Some makers keep a small share of the Bitcoin when a swap is refunded, to discourage people from starting swaps they don’t finish. It shows in the Kept if refunded column; pick a maker with “none” if you prefer.

Privacy

Without Tor, the rendezvous servers and the makers you connect to see your IP address. Tick Connect through Tor to hide it; finding makers then takes longer. In Tor mode, and on Tails and Whonix, atomic swaps always use Tor.

The swap helper

Atomic swaps run in a separate program, biscuit-swapd, built from eigenwallet’s code and shipped with Biscuit. In the portable and tar.gz versions, keep it next to Biscuit. It’s free software under the GPL-3.0, and its source is published with every release. Your atomic swap data is in the atomicswaps folder of Biscuit’s settings folder: never delete it while a swap is running.