Introducing EarthBucks Swap: Cross-Chain Atomic Swaps with Bitcoin Cash

Today we launch EarthBucks Swap. Swap is a market where you trade EBX for Bitcoin Cash (BCH) with other users, directly from your wallet to their wallet.

Swap is:

• Self-custodial. Your coins stay in your wallet until the contract pays them. EarthBucks never holds your coins, and it never has your private keys. Your browser holds your keys and signs each step.
• Cross-chain. EBX and BCH are two different blockchains. Each side of a trade is locked on its own chain.
• Atomic. Either both users get the agreed coins, or both users get their own coins back. No step can leave one user with both sides.

We wrote three posts with the details. This post is a summary of all three.

How it works

A swap uses a hash time lock contract (HTLC) on each chain. Each lock pays the other user if they show a secret, and it pays back its owner after a refund time.

The seller (who gives EBX) makes a random secret in their browser and gives only its SHA-256 hash. Both locks use that hash. Then the wallets do these steps:

1. The seller locks EBX. The buyer’s wallet waits until the lock is final.
2. The buyer locks BCH. The seller’s wallet checks the BCH lock for a double-spend, which takes a few seconds. For a large trade, the maker can choose to wait for BCH confirmations.
3. The seller claims the BCH. The claim shows the secret on the BCH blockchain.
4. The buyer’s wallet reads the secret from that claim and claims the EBX.

The buyer’s BCH refund comes first, and the seller’s EBX refund comes hours later. Thus the seller can never take back their EBX and also claim the BCH, and the buyer has hours to claim the EBX after the secret is public.

Some of the details:

• Every EBX output has recovery and expiry, and the swap lock does too. Its swap branch is inside the standard EBX wallet script.
• The fee is in the script. The taker’s lock pays the 1% fee only when it is claimed. A refund pays no Swap fee. For this, we added three introspection opcodes to EBX, the same as on BCH.
• Each trade has new keys from your master key, and the state of each trade is encrypted by your wallet.
• The wallets handle the edge cases: a user who stops, a late lock, a lost message to the network, and a BCH reorganization.

The one thing that your wallet cannot do without you is be online. Keep an EarthBucks tab open until your trade is done.

Read more: How EarthBucks Swap Works: The Contracts.

How to use it

Open Swap. The room shows the best price to buy EBX and the best price to sell EBX, a feed of messages and trade cards, and the users who are online.

• Take a card to trade at its price. The trade starts at once.
• Post a card with Sell EBX or Buy EBX. Select the amount, the price and an expiry from 5 minutes to 4 hours.
• Your first post or take joins the room. You can be in the room in one tab only. When you leave, your open cards are cancelled.

The main rules for the launch:

Rule	Value
Taker’s fee	1% of the coin that you pay
Maker’s fee	None
BCH network fee of each BCH transaction	1,000 satoshis
Size of one trade	$1.00 to $100.00 of BCH
Trades of one account in 24 hours	$1,000.00
Lowest EBX price on a card	$0.10
Open cards and trades in progress	5 together
Users in the room	100 verified, 100 unverified

Every user can trade and post messages. An unverified user can send 5 messages in each 10 seconds, and a verified user can send 10. Only trades between two verified users count in the EBX price index: the median price of the last 24 hours, weighted by value, with a cap for each account.

Read more: How to Use EarthBucks Swap.

Where it came from, and what comes next

The first trade of EBX was for BCH, in December 2024, and BCH has been part of the plan for EarthBucks since then. In the last seven weeks, we built a BCH library, added SHA-256 to EBX, tested an offline swap prototype, ran our own BCH node, gave every account a BCH wallet, added BCH to EarthBucks Pay, and then built Swap.

Next, we will publish open-source wallet node software. Anybody will be able to run a wallet node for EBX, BCH and other UTXO blockchains on their own domain. Wallet nodes will form a federated network, like email, so that alice@earthbucks.com can send payments, messages and swaps to bob@example.com. All of this is part of EarthBucks 2.0.

Read more: Bitcoin Cash in EarthBucks: The History and What Comes Next.

Try it

1. Deposit some BCH on the Bitcoin Cash page of your wallet, or get some EBX.
2. Open Swap, and select the Swap title for a short summary.
3. Take a card, or post one.
4. Keep the tab open until your trade settles.