Even if Bitcoin eventually adopts post-quantum protections for on-chain outputs, five parts of the Lightning Network’s off-chain payment system would still need separate upgrades, according to a Sept. 12 research preprint .

The paper proposes PQLN, a hybrid post-quantum extension implemented as a rust-lightning research prototype. It targets gossip, which 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. It 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. Depending on the route and settings, mixed setups used classical protection or failed closed.

That compatibility does not establish network-wide readiness. The repositories describe the software as a research artifact, and the study deferred tests against other Lightning implementations.

Communication, rather than raw cryptographic computation, dominated the authors’ 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.