A new research preprint dated Sept. 12 proposes a hybrid post-quantum extension for the Lightning Network, showing that off-chain Bitcoin payments could adopt quantum-resistant cryptography even if Bitcoin’s on-chain outputs remain unresolved. The paper introduces PQLN, implemented as a rust-lightning research prototype, and targets five Lightning components: gossip that distributes node and channel information, encrypted peer connections, signed invoices and reusable payment offers, and onion packets that conceal payment-routing details.
Lightning currently uses secp256k1-based ECDSA, Schnorr signatures or ECDH across those functions. PQLN keeps the classical mechanisms while adding ML-DSA signatures to gossip, invoices and offers, and adds hybrid ML-KEM key exchange to transport, payment onions and BOLT 12 privacy paths. The authors built a feature-gated rust-lightning fork and a modified ldk-sample node. Their 12-scenario matrix found that post-quantum and vanilla binaries built from the same rust-lightning base could coexist, though mixed setups either used classical protection or failed closed depending on route and settings. The study notes that compatibility does not establish network-wide readiness and the repositories are described as research artifacts, with tests against other Lightning implementations deferred.
Communication, rather than raw cryptographic computation, dominated the results. During static synchronization of a full network graph, the default ML-DSA-44 and ML-KEM-768 design increased gossip downloads 10.2 times and stored graph data 8.8 times compared with vanilla Lightning. A smaller Falcon-derived FN-DSA configuration reduced the download multiple to 4.2 times, but NIST still lists that scheme as under development rather than a final standard. Private payment routing carried another bandwidth penalty: a fixed 21.8-kilobyte post-quantum ciphertext list added 19 to 53 milliseconds per hop on an emulated 10 Mbit/s link and 160 to 187 milliseconds per hop at 1 Mbit/s. By contrast, ML-DSA-44 signing averaged 327 microseconds on the authors’ 16-core AMD Ryzen Threadripper PRO 3955WX workstation with 64 GB of RAM, a hardware-specific primitive measurement that should not be read as end-to-end payment latency.
PQLN also leaves Bitcoin-rooted risks untouched. It does not secure the on-chain keys protecting funding, commitment and HTLC outputs or penalty transactions, so safeguarding channel funds still requires Bitcoin-layer post-quantum changes. The preprint assumes a future cryptographically relevant quantum adversary and does not report a present-day quantum compromise of Bitcoin or Lightning. Its prototype suggests Lightning’s off-chain defenses can be tested independently of a Bitcoin upgrade, but not that the network is ready to migrate. The hard operational question is how much extra gossip, storage and payment traffic node operators can absorb.
