The Avalanche Bridge (AB) can be used to transfer BTC from Bitcoin to Avalanche's C-Chain and vice versa. This document answers common questions about the bridge. If there are additional questions, please contact the Ava Labs team on Avalanche's support website, Discord, or Telegram.
Where can I actually bridge my BTC to Avalanche?
Users can download the Core Wallet Extension to access BTC bridging. Note that BTC bridging is ONLY currently available through the Core Wallet Extension. BTC bridging with Avalanche Bridge is not supported with Metamask or any other wallet. This is because the Core Wallet Extension was custom-built to support Bitcoin and the Avalanche Bridge and to handle the technical problems of linking Bitcoin and EVM chains within a wallet. See here for more details on how to bridge BTC. Do not attempt to use any wallet other than the Core Wallet Extension for BTC bridging – you may lose all your funds.
What is the Core Wallet Extension?
Core Wallet Extension is a new alternative to other crypto wallet extensions, such as the Metamask Wallet Extension. Users can use the Core Wallet Extension to bridge BTC to Avalanche C-Chain or ERC20 tokens to Avalanche C-Chain and back. Note: While users are able to bridge between Ethereum and the Avalanche C-chain, users won’t be able to use the Core Wallet Extension to interact with their Ethereum assets on the Ethereum blockchain. Core Wallet Extension support to interact with the Ethereum blockchain is coming soon.
Can I use Core.app/bridge for BTC bridging?
Core.app/bridge does not currently support Core Wallet Extension or BTC bridging, but full support is coming soon. For now, please use the Core Wallet Extension only for BTC bridging with Avalanche Bridge.
What are some of the key differences between the Ethereum Bridge and the Bitcoin Bridge?
BTC bridging support on the Avalanche Bridge leverages much of the same technology and design of the original Avalanche bridge architecture overviewed.
How does the bridge work?
To initiate bridging from Bitcoin to Avalanche, a transaction is sent on Bitcoin from the new Core Wallet that transfers BTC to the bridge address controlled only by the SGX enclave. The bridge is designed to only support Pay-To-Witness-Public-Key-Hash output types on Bitcoin. In order to ensure that the BTC transfer has this output type and meets all of the bridging requirements, users should always use the bridge UI in the Core Wallet extension that is built to provide a quick and easy bridging experience. Once this transaction is accepted into a block on Bitcoin and receives the necessary number of confirmations, it will be indexed by the Bridge Nodes and reported to the Intel SGX application for processing. The SGX enclave only processes transfers when it receives approvals from at least 6 of the 8 Bridge Nodes, At this point, the SGX application mints (creates) the equivalent amount of BTC.b to the user wallet that sent the initiating Bitcoin transaction.
Similarly, when moving BTC.b from Avalanche back to Bitcoin, the user sends a transaction on Avalanche that calls the “unwrap” method of the BTC.b contract, which burns (destroys) the BTC.b tokens. The Bridge Nodes will index this transaction, and it will be processed by the SGX enclave by sending the equivalent amount of native BTC back to the user’s wallet on Bitcoin
How does the Bridge derive the Bitcoin address?
Bitcoin uses an entirely different address scheme than Ethereum Network. In order to determine the Avalanche address that corresponds to a Bitcoin address that provided collateral to the bridge, the Bridge Nodes recover the public key of the user wallet from the signed transaction on the Bitcoin network and use it to derive the Avalanche C-chain address. This way, the funds on both networks are controlled by the same private key or mnemonic phrase, and that secret never leaves the sole possession of the user’s wallet.
Is there an airdrop provided for users when they bridge from the BTC Network to the Avalanche Network?
Like the Ethereum Bridge, when users bridge $75 or more of assets from the BTC Network to the Avalanche Network, a portion of AVAX will be airdropped to help pay for initial transactions. AVAX is used to pay for gas on the Avalanche C-Chain and is needed to perform on-chain actions. The amount airdropped should help users get started.
What if the transaction fees are more than the amount I am transferring?
When moving assets from Avalanche back to Bitcoin, the bridge charges an in-kind transfer fee. The user interface does not allow transfers of less than the fee amount. If a user manually generates and issues such a transaction, the bridge will mark the transfer as invalid and not process it.
What does the .b suffix in the token name mean?
When Bitcoin is bridged to Avalanche, it is represented by an ERC20 token on the Avalanche C-chain with the symbol BTC.b. The “.b” indicates that the token was bridged from the Bitcoin network, just as Avalanche Bridge tokens bridged from Ethereum end in “.e”. Each BTC.b token is fully backed by a Bitcoin locked by the bridge enclave application. The BTC.b token contract can be found on Snowtrace here, and the bridge enclave application Bitcoin address can be viewed here.
How long does a bridge transfer take?
The Bitcoin Network transaction will typically take 1 hour. The Bitcoin network will need to achieve 6 confirmations to complete.
The Avalanche Network transaction takes a few seconds.
Can I speed up the Bitcoin Network transaction?
No, increasing the Bitcoin Network fee will not speed up the transaction. Once it's included in a block there is no way to speed up the next 5 blocks getting created. Therefore, this will still typically take approximately 1 hour for all 6 confirmations.
Why is the Avalanche transaction part of the bridge taking so long?
This transaction only takes a few seconds, and if the Avalanche Bridge interface shows it taking longer, then check the transaction in the Explorer to see if it was successful. Users may need to add the token to the wallet on the Avalanche Network for it to appear.
Can I send tokens created on Avalanche to Bitcoin?
No. The bridge only supports the transfer of BTC and ERC20 tokens created on Bitcoin and Ethereum, respectively, to Avalanche and back.
What types of BTC withdrawal addresses are supported?
At this time, the Core Wallet supports "Native Segwit" addresses for BTC withdrawals, and these start with - bc1q. For more information on the types of BTC addresses please visit this link.
What if my transaction is not visible in the explorer?
The transactions that correspond to bridge transfers will appear on explorers for the Avalanche and Bitcoin networks. It may take a few minutes for the transactions to appear. To search for your transaction in the Explorer, copy and paste your address into Avalanche's C-Chain Explorer or Blockchain.com. To view the transactions sent by the bridge itself, you can look here for Avalanche and here for Bitcoin. If you still don't see your transaction, reach out on Telegram or Discord. Please be wary of anyone you are not familiar with offering to help, as they may be scammers attempting to obtain your Recovery Phrase or private keys.
Are there tutorials on how to use the bridge?
Yes, you can view video tutorials for bridge functionality here.
Is there an airdrop for BTC bridge transactions?
On Avalanche, transaction fees are paid in the native asset, AVAX. In order to send transactions on the Avalanche C-Chain, you must have sufficient AVAX in your wallet to cover the cost of the gas for the transaction. To help you get started on Avalanche, the bridge will airdrop you a small amount of AVAX if you move more than $75 (subject to change) worth of tokens over from Bitcoin. In order to avoid running out of AVAX to cover your transaction fees, we recommend first obtaining an adequate amount of AVAX. You can acquire AVAX on Pangolin or any other exchange.
How is my BTC address linked to my Avalanche C-Chain address?
In order to determine the Avalanche address that corresponds to a Bitcoin address that provided collateral to the bridge, the Bridge Nodes will identify the public key of the user wallet from the signed transaction on the Bitcoin network, and use it to derive the Avalanche C-chain address. This way, the funds on both networks are controlled by the same private key or Recovery Phrase, and that secret never leaves the sole possession of the user’s wallet. Similarly, when a user goes to transfer funds from Avalanche back to Bitcoin, the user's Bitcoin address is derived from the public key identified from the Avalanche transaction that burns the wrapped asset.
Can I send assets to a different address on the other network?
The bridge only allows transfers to the same address on the other network. After the asset is transferred to the other network, it can be sent to any address or contract in a typical send transaction.
Do Bridge Nodes rotate their secrets and does this affect the Bridge addresses?
Yes, the Bridge Nodes perform periodic key rollovers as a routine proactive security measure, including whenever new Bridge Nodes are added or removed. When this key rollover occurs, the Bridge Nodes rotate their key shards and the bridge collateral is moved to the new corresponding address.
As noted here, anyone attempting to use the EVM Bridge without going through the UI could potentially lose their funds if they send tokens to an old address no longer used by the bridge. To ensure the safety of users and the protection of their funds, the EVM Bridge should only be accessed and used through the UI, located here.
As noted here, the BTC Bridge is ONLY currently available through the Core Wallet Extension. Do not attempt to use any wallet other than the Core Wallet Extension for BTC bridging – you may lose all your funds.
What is the Bridge's address on Bitcoin and Avalanche?
Note: Never directly transfer tokens to these addresses. You should use the Bridge's user interface, which checks for malformed transactions.
What is the BTC.B token contract address?
BTC.b Contract Address: 0x152b9d0fdc40c096757f570a51e494bd4b943e50
To ensure the safety of users and the protection of their funds, the Avalanche Bridge should only be accessed and used through the UI, located here. Any other use of the Avalanche Bridge could result in the permanent loss of funds. The non-exhaustive list below enumerates possible ways to permanently lose funds by attempting to use the Avalanche Bridge through sources that are not recommended. Funds lost in the examples listed below will be permanently lost, and are not recoverable by Ava Labs, the Bridge Nodes, or the bridge.
USERS MUST NOT SEND FUNDS DIRECTLY TO ANY OF THE AVALANCHE BRIDGE CONTRACT ADDRESSES. The Avalanche Bridge should only be accessed through the Avalanche Bridge UI, located here. Any funds sent directly to the Avalanche Bridge contract addresses will be permanently lost, and are not recoverable.
USERS MUST NOT SEND FUNDS DIRECTLY TO ANY OF THE AVALANCHE BRIDGE WALLET ADDRESSES. The Avalanche Bridge should only be accessed through the Avalanche Bridge UI, located here. Any funds sent directly to the Avalanche Bridge wallet addresses will be permanently lost and not recoverable.
DO NOT ATTEMPT TO USE ANY SMART-CONTRACT WALLET WITH THE AVALANCHE BRIDGE. The Avalanche Bridge is currently not compatible with smart contract wallets because smart contracts are currently not supported by the Avalanche Bridge. Using the Avalanche Bridge with a smart contract wallet or smart contract will result in the permanent loss of funds. Users should not use smart contracts with the Avalanche Bridge at this time because no one can retrieve tokens lost when smart contract wallets try to use the Avalanche Bridge. This is not a statement against smart contract wallets or the below list of smart contract wallet projects, which is not an exhaustive list. This is to make users aware of the current technical architecture. WE CAN NOT RETRIEVE YOUR TOKENS.
There is a bug in the Metamask Mobile app that affects bridge transactions (only on mobile). Until this is resolved, don't use the Metamask mobile app for bridge transfers. We suggest using the Metamask desktop app, or, if on mobile, Coinbase Wallet.
You need AVAX to pay transaction fees on Avalanche network. You should use the AVAX you receive in the airdrop to do a swap for more AVAX on an AMM so that you can pay transaction fees. If you run out of AVAX, you will not be able to do transactions on Avalanche network.
For a more in-depth read on how the Avalanche Bridge works, please read the following articles.