Five core functions of the Lightning Network would still require independent cryptographic upgrades even if Bitcoin itself adopted post-quantum protections, according to a research preprint released Sept. 12.
The study, which tested a hybrid extension called PQLN (post-quantum Lightning Network), found that off-chain payment routing, node communication, and invoice signing cannot rely solely on Bitcoin’s on-chain key updates. Instead, each of the five targeted functions requires its own post-quantum implementation.
Functions Tested
Researchers focused PQLN on gossip (node and channel information distribution), encrypted peer connections, signed invoices and reusable payment offers, and onion packets that conceal routing details. Lightning currently uses secp256k1-based ECDSA, Schnorr signatures, or ECDH for these functions.
PQLN adds ML-DSA signatures to gossip, invoices and offers, while introducing hybrid ML-KEM key exchange to transport, payment onions and BOLT 12 privacy paths. The hybrid design preserves classical mechanisms alongside post-quantum alternatives, allowing post-quantum and standard binaries built from the same rust-lightning codebase to operate in mixed network setups.
Bandwidth and Performance Trade-offs
Testing revealed significant overhead. Default ML-DSA and ML-KEM settings increased gossip downloads by a factor of 10.2, while post-quantum design increased stored graph data by 8.8 times compared to standard Lightning. A FN-DSA configuration reduced the download multiple to 4.2 times, with post-quantum ciphertext lists reaching 21.8 kilobytes.
Latency per hop ranged from 19 to 53 milliseconds on a 10 Mbit/s emulated link and 160 to 187 milliseconds on a 1 Mbit/s link. ML-DSA-44 signing averaged 327 microseconds on the test hardware, a 16-core AMD Ryzen Threadripper PRO 3955WX workstation with 64 GB of RAM. Communication bandwidth dominated the performance results over raw cryptographic computation.
On-Chain Keys Remain Unprotected
A critical limitation: PQLN does not secure on-chain keys protecting funding, commitment and HTLC outputs or penalty transactions. Bitcoin-layer post-quantum changes are still required to safeguard channel funds. This separation means that even with PQLN deployed across the Lightning Network, quantum threats to Bitcoin’s base layer would persist until Bitcoin itself implements post-quantum key protections.
The researchers used modified versions of rust-lightning and ldk-sample node implementations for testing. The study deferred comparative tests against other Lightning implementations, leaving questions about interoperability with alternative clients unresolved.
