Bitcoin Optech Newsletter #424

Bitcoin Optech Newsletter #424 introduces a significant proposal for enhancing the Lightning Network (LN) with post-quantum security, dubbed PQLN. This initiative, detailed by Ahmet Kurt on Delving Bitcoin, aims to upgrade LN's offchain protocols to withstand quantum computer attacks, building upon prior layer-by-layer analyses. A supporting paper and a functional implementation based on rust-lightning are available for testing. The proposal specifically targets offchain components, deliberately avoiding modifications to onchain operations, which would necessitate Bitcoin consensus changes. Key modifications include: Gossip (BOLT7) is updated to distribute post-quantum keys (ML-DSA and ML-KEM) directly through node_announcement messages, which also carry ML-DSA signatures. channel_update messages include only the signature, and keys are pinned to prevent fraudulent substitutions. The channel_announcement message remains unchanged due to its reliance on onchain funding keys. Transport (BOLT8) is modified to implement a hybrid Noise handshake, utilizing two ML-KEM encapsulations—one for the pinned static key and another for a new ephemeral key to ensure forward secrecy, without employing in-band negotiation.