Bitcoin: Lightning can already prepare its defense
A sufficiently powerful quantum computer could one day break some of the cryptographic mechanisms currently used by Bitcoin. The threat is not operational with today’s machines, but the shift to post-quantum cryptography has already become a concrete issue.
PQLN specifically targets Lightning’s “off-chain” surfaces. These include communications between nodes, the gossip protocol used to distribute information across the network, Lightning invoices, BOLT 12 offers and the famous “payment onions” that route payments through multiple nodes without revealing their entire path.
The researchers use a hybrid approach. PQLN keeps the current cryptographic mechanisms while adding algorithms designed to withstand quantum computers, notably ML-KEM for key exchange and ML-DSA for signatures.
Put simply, Lightning is not replacing its locks today. PQLN adds a second lock designed for a world in which some current cryptographic techniques could become vulnerable.
This is particularly important for the Lightning Network, Bitcoin’s fast payment layer. Transactions there mainly move outside the main blockchain, with final settlement on Bitcoin.
0.33 milliseconds, but far more data
The results published on September 12, 2026, in the PQLN scientific preprint provide an initial indication of the technical cost of this migration.
The team added nearly 11,000 lines of code to rust-lightning, one of the main Lightning implementations. The researchers then tested PQLN on real nodes.
The most reassuring result concerns performance. In their measurements, the additional cryptographic operations added no more than 0.33 milliseconds. Interoperability tests also covered twelve configurations combining PQLN nodes with standard Lightning nodes. No payment remained stuck.
The cost is instead found on the bandwidth side.
Post-quantum signatures are significantly larger than those currently in use. With ML-DSA, gossip data can increase by approximately tenfold. The researchers also tested Falcon, another signature approach, which brings the increase down to around fourfold.
This is far from a minor detail. Lightning has many nodes that must constantly exchange information about channels and the network’s topology. Additional security that massively increased communications could create problems for machines with limited bandwidth.
PQLN does not yet make Bitcoin “quantum-proof”
PQLN’s limitation is essential: it does not protect bitcoins locked in channel funding, commitment or penalty transactions on Lightning.
These elements depend directly on Bitcoin’s cryptographic rules. Changing them would require an evolution of the base protocol and therefore much broader consensus among developers, node operators and other network participants. PQLN does not bypass this difficulty.
Its value lies elsewhere.
The researchers notably highlight the risk known as “harvest now, decrypt later.” An attacker can record encrypted Lightning communications today and store them for years. If a sufficiently powerful quantum computer later emerges, it could attempt to decrypt them retroactively. PQLN is specifically intended to prevent this scenario for communications that can be upgraded now.
This is an important difference from Bitcoin itself. Part of Lightning can evolve through software updates without waiting for a change to the blockchain’s consensus rules.
For now, the project remains a research proposal and experimental implementation, not a general network upgrade. Lightning operators are therefore not suddenly protected against all quantum attacks.
The work nevertheless demonstrates something concrete: the transition can begin layer by layer. This is consistent with efforts already underway elsewhere in cybersecurity, as post-quantum cryptography begins to move beyond the laboratory.
Bitcoin will probably have to address the issue one day at its base layer. Lightning, meanwhile, has shown that it does not have to wait.
In brief
- PQLN adds post-quantum protection to Lightning’s off-chain communications and payments.
- The system notably uses ML-KEM and ML-DSA.
- The implementation adds nearly 11,000 lines of code to rust-lightning.
- The cryptographic operations tested add no more than 0.33 ms.
- PQLN nodes remain compatible with standard Lightning nodes.
- On-chain funds and certain channel transactions are not protected by PQLN.
