tBTC & nBTC

tBTC

tBTC is a decentralized bridge between Bitcoin and Ethereum, enabling Bitcoin holders to access DeFi and the expanding Web3 universe without relying on intermediaries. It allows users to bridge their Bitcoin assets securely and without the need for trust in third parties.

Components

Bridge

• Deployed as smart-contract on the ETH chain
• Handles deposits to the vault
• Issues withdrawal, sweeping and move requests to the Wallet Coordinator
• Issues balance updates to the Bank
• Issues create/close vault wallets requests to the Wallet Registry

Wallet Coordinator

• Deployed as smart-contract on the ETH chain
• Handles withdrawal, sweeping and move requests for the BTC chain

Wallet Registry

• Deployed as smart-contract on the ETH chain
• Handles creating and closing vault wallet on the BTC chain

Bank

• Deployed as smart-contract on the ETH chain
• Keeps track of tBTC balances and allowances
• DOES NOT issue ERC-20 tokens

tBTC Vault

• Deployed as smart-contract on the ETH chain
• Mints/burns tBTC tokens
• Handles tBTC tokens on user's behalf

Random Beacon

• Deployed as smart-contract on the ETH chain
• Provides randomness to the validation group selection and key generation process

Threshold Node

• Deployed off-chain
• Handles key generation for the DKG process
• Handles signing transactions

TSS

• Multi-party threshold ECDSA algorithm
• Randomly selected 51-of-100 wallet signers to produce signature

Nomic BTC

Nomic BTC is a Bitcoin sidechain based on the Tendermint consensus protocol, enabling the development of decentralized networks which coordinate to manage reserves of Bitcoin, allowing for custom application code and smart contracts which use Bitcoin as the native currency.

Components

Nomic Node

• Handles processing inbound/outbound transfers
• Stores transactions waiting to be signed
• Stores public key shares from signers

Relayer

• Observes BTC chain
• Broadcasts new BTC block info to the Nomic chain
• Broadcasts deposits to the Nomic chain
• Broadcasts transactions from the Nomic chain to BTC

Signer

• Generates new key shares
• Submits key shares to the Nomic chain

Reserve Wallet (Vault)

• A Taproot script - "reserve script"

Signing

Checkpoints

Transaction on the BTC chain which spends from the current "reserve script" incorporates:

• Collecting latest deposits
• Updating the "reserve script" (vault) to reflect changes in signatory set
• Executing pending withdrawals

Flow

1. Collect smallest set of signers with >2/3 voting power - Musig2 N-of-N
2. Create aggregated pub key for this set
3. Create a "fallback script" - a large weighted multisig script for all signers
   • Allows correct funds unlock in case Musig2 aggregation fails
4. Relayers broadcast signed checkpoint txs to the BTC chain

iBTC

iBTC facilitates cross-chain asset transfers between Int3face and various external chains to enable decentralized cross-chain asset transfers, seamlessly connecting Int3face with other blockchain ecosystems.

Components

Bridge

• Deployed as part of the Int3face node
• Handles processing inbound/outbound transactions
• Issues mint/burn requests to the Token Factory

Token Factory

• Deployed as part of the Int3face node
• Handles minting/burning tokens to/from user's wallet

Bank

• Deployed as part of the Int3face node
• Keeps track of user's balances on the Int3face chain

UTXO Chain Observer

• Deployed off-chain
• Observes target chain for inbound transactions
• Notifies Observer about inbound transactions

UTXO Chain Client

• Deployed off-chain
• Handles communication (signing, broadcasting, queries) with the target chains

Int3face Chain Observer

• Deployed off-chain
• Observes Int3face chain for outbound transactions
• Notifies Observer about outbound transactions

Int3face Chain Client

• Deployed off-chain
• Handles communication (signing, broadcasting, queries) with the Int3face chain

Observer

• Deployed off-chain
• Handles routing inbound/outbound transactions between chains

TSS

• Multi-party 2/3+1 threshold ECDSA algorithm

Comparison

Asset	tBTC	iBTC	Nomic BTC
Blockchain	Ethereum	Int3face (Cosmos)	Nomic (Cosmos)
Token	ERC-20	Custom Token Factory token (IBC compatible)	nBTC (IBC compatible)
Finality	Settles on ETH	Settles on Int3face	Settles on Nomic
Deployment	On-chain smart contracts and off-chain	Part of the chain and off-chain	Sidechain network
TSS	Multi-party 51-of-100 threshold ECDSA	Multi-party 2/3+1 threshold ECDSA	Musig2 N-of-N for 2/3 of voting power + "fallback" script
Deposit flow	Manually triggered by user after transfer to vault	Automatically triggered by observer	Manually triggered by user after transfer to vault
Deposit script	P2SH/P2WSH with custom sig script format	P2PK, P2PKH, P2WPKH, P2SH, P2WSH with additional OP_RETURN tx	P2TR with OP_RETURN tx and optional timelock
Withdrawal flow	Triggered by user with transaction to bridge	Triggered by user with transaction to bridge	Triggered by user with transaction to bridge
Withdrawal script	P2PKH, P2WPKH, P2SH, P2WSH	P2PK, P2PKH, P2WPKH, P2SH, P2WSH	P2PK, P2PKH, P2WSH
Ownership	Vault handles tokens on user's behalf	Tokens reside on user's wallet	Tokens reside on user's wallet
Vaults	Multiple active vaults	Single vault	Single vault
Vault rotation	Triggered on timeout, reaching an amount of funds or failing to heartbeat	TBD	On timeout, ideally - each block
Fees	Mint 0%, Withdraw 0.2%	TBD	Deposit 1%, Withdrawal 0%
Sweeping	Each 8 hours	TBD	On the vault rotation
Validator selection	Token-weighted selection	TBD	Token-weighted selection
Refunds	Embedded into tx script	TBD	Timelock embedded into the tx script
Valset entry	Stake of 40,000T	TBD	No info
Unstake period	45 days	TBD	14 days