The bridge

How it works

The bridge is a BNB Chain contract that holds a vault for each coin. It never creates tokens. Moving to Bitcoin locks tokens in the vault, and moving back releases them. The contract cannot be upgraded, and its source is published and verified on BscScan; see Verify it on chain for every BRUNE address.

When the bridge opens

A coin's bridge opens by itself once its Rune is final on Bitcoin: 6 confirmations after the etching (about an hour), checked by two independent Rune indexers. Until then the coin trades on BNB Chain as usual and its page shows the Rune's progress.

Opening it is the only thing BRUNE's registrar key can do on the bridge, and it is bounded on chain:

• only for a coin created by the BRUNE launcher that passes every check the bridge makes on a Flap coin, and only once per coin;
• only with the default limits the admin set (the daily release cap and minimum), and only binding a Rune ID that no other coin uses;
• it cannot change limits, keys or fees; the guardian's pause stops it instantly, and the admin can revoke it.

Every other change to a coin's bridge, such as a higher cap, goes through the admin and its 48-hour timelock.

Custody: two keys, never one

Each coin's Runes sit at its own 2-of-2 Bitcoin address. A payout needs a signature from BRUNE and from an independent co-signer on the Internet Computer, which reads the bridge contract on BNB Chain itself and signs only real, finalized Bridge-to-Bitcoin requests: the right address, the exact amount, nothing else. See Verify custody, or press Verify custody under any coin's bridge to check it yourself.

Burned tokens

Anyone can burn their own tokens on BNB Chain (send them to the dead address). A burn never stops the bridge and never changes the backing:

• The burned tokens are gone from circulation for good.
• The same amount of Rune is locked in custody forever. No token can redeem it, so it is never sent to anyone.
• Every token still on BNB Chain stays backed 1:1, and bridging works as before.

The coin page shows it under the bridge: how much Rune backs the tokens on BNB Chain, and how much is locked for burned tokens.

BNB Chain → Bitcoin

1. On the coin page, open Bridge → To Bitcoin, choose an amount and connect your Bitcoin wallet (Xverse, UniSat or OKX) next to your BNB Chain one. The Rune goes to that wallet's own Taproot address (bc1p…; in Xverse, its Ordinals address), so it can never go to a mistyped or wrong address. Taproot is the only address type that can safely hold Runes. (No Bitcoin wallet in this browser? You can still type your own Taproot address.)
2. You sign a free permit, then send one BNB Chain transaction that locks the tokens in the vault, pays a small BNB fee that covers the Bitcoin network fee (never more than 0.05 BNB), and records the request on chain.
3. BRUNE and the co-signer send the Rune from the coin's 2-of-2 custody to your address, usually within a minute of the request being final on BNB Chain. After 3 Bitcoin confirmations (about 30 minutes) BRUNE records the Bitcoin transaction on the request.

If Bitcoin is busy and the payout is slow to confirm, BRUNE re-sends it with a higher fee (replace-by-fee). Each version pays the same Rune to the same address and is co-signed under the same rules, and only one version can ever confirm. Your bridge history marks it fee bumped and links the latest version.

If the send is impossible, the tokens are refunded to your own wallet. A refund needs the co-signer's signature too, and the co-signer gives it only for a request it never paid, so a request ends exactly one way: Sent or Refunded, never both.

Bitcoin → BNB Chain

1. On the coin page, open Bridge → To BNB Chain, connect your Bitcoin wallet (Xverse, UniSat or OKX) and choose how much to bridge.
2. Confirm in your wallet. One Bitcoin transaction sends exactly that amount of the Rune to your own deposit address for that coin; the rest stays in your wallet. (No Bitcoin wallet in this browser? Show the deposit address and send only that coin's Rune, without inscriptions, from any wallet.)
3. After 6 Bitcoin confirmations (about an hour), once two independent Rune indexers agree on the deposit, the same amount is released from the vault to your BNB Chain wallet.

Large releases wait. A release above the bridge's threshold is queued on BNB Chain for 30 minutes before it can be paid; your bridge history shows Release queued with the time left, and BRUNE completes it as soon as the wait is over. During the wait BRUNE's guardian can cancel a release that looks wrong. A cancelled release shows Release cancelled: the Runes you sent stay in your deposit address's 2-of-2 custody, and BRUNE sorts it out with you (email support@brune.fun with the Bitcoin transaction).

Your deposit address is yours for that coin and is a 2-of-2 address too: BRUNE and the co-signer must both sign to move what you deposit. The verify page lists every custody output.

Each Bitcoin output can be used for a release only once; the contract makes a second release impossible. A deposit that carries another Rune or an inscription is not released automatically; BRUNE checks it by hand.

Safety rules on chain

• A coin can be bridged only after its Rune is final and linked, and only coins created by the BRUNE launcher can be registered. The registrar key that opens new coins can do nothing else (see When the bridge opens).
• Releases are capped per coin over any rolling 24 hours (at first 1% of the supply), and the number of releases per day is capped for the whole bridge, limiting the damage if a key is ever compromised. Large releases wait 30 minutes before they can be executed, and the guardian can cancel them during the wait.
• A guardian can pause the bridge instantly; only the admin can resume it.
• The admin is a 2-of-3 Safe behind a 48-hour timelock: every change of keys, caps or co-signer is public two days before it can run. The admin can never move tokens.
• Refunds go only to the requester's wallet, releases only to the recipient the deposit was made for.