Bitcoin Optech: Newsletter #404 Recap

— Node fingerprinting via dual-homed networks: Researchers can correlate Bitcoin node identities across different networks (Tor/IPv4) by analyzing address gossip responses and their timestamps. Five potential mitigation approaches are being evaluated, including fuzzing timestamps, network-specific timestamp handling, and making older addresses appear older.

— Just-in-time (JIT) Lightning channels and trust model: Current JIT channels require either client or server trust, creating centralization pressure. Thomas Voegtlin proposes using blockchain-published preimages as fraud proofs to reduce trust requirements and enable decentralized Lightning Service Providers.

— Public fraud proofs for JIT channels: A three-part fraud proof consists of LSP commitment to channel funding with specific UTXOs, client publishing the HTLC preimage on-chain before a deadline, and proof of UTXO double-spending. Fraud detection infrastructure via Nostr is proposed.

— PSBT version 2 support in Bitcoin Core: After five years in development, Bitcoin Core now defaults to creating PSBT v2 (BIP-370) while maintaining backward compatibility. PSBT v2 improves modularity for multiparty transactions by eliminating redundant transaction duplication.

— Multiple Lightning protocol upgrades: Eclair and other implementations now support simple Taproot channels and official splicing protocol from Bolt specifications. LDK adds reserve checks for zero-fee commitment channels to prevent issues during simultaneous force closes.

— Dust UTXO disposal standard (BIP-451): A new specification enables safe disposal of unwanted dust UTXOs by spending them to zero-value OP_RETURN outputs, with sighash ANYONECANPAY allowing batching of multiple dust disposal transactions.

— Evaluate node privacy practices: If running dual-homed Bitcoin nodes (clearnet + Tor), monitor ongoing research on timestamp fuzzing mitigations. Once solutions are implemented in Bitcoin Core, prioritize upgrading to reduce fingerprinting risk.

— Test PSBT v2 compatibility: Developers building multisig or collaborative transaction workflows should begin testing PSBT v2 implementations, as ecosystem adoption is accelerating and it offers superior modularity compared to v0.

— Monitor JIT channel developments: Users relying on Lightning wallets with JIT channels should watch for LSP implementations adopting fraud-proof mechanisms, as this could improve non-custodial trust assumptions and reduce Lightning Network centralization.