Researchers at East Texas A&M University have developed what they describe as the first implemented and experimentally evaluated post-quantum design for Bitcoin's Lightning Network. Lightning, Bitcoin's off-chain payments layer, routes transactions across a network of nodes whose identities, invoices and messaging currently rely on classical cryptography. The system, known as PQLN, protects the network's off-chain communication and payment functions without requiring any changes to Bitcoin's consensus rules.

The PQLN research, published by Ahmet Kurt, Abdul-Salem Beibitkhan, Yacoub Hanna and Abdullah Aydeger, covers five core Lightning surfaces: gossip, peer transport, invoices, payment onions and BOLT 12 offers. The team implemented the design in rust-lightning and validated it against real Lightning nodes.

PQLN combines ML-DSA digital signatures and ML-KEM key exchange with Lightning's existing cryptography. Both algorithms were standardized by the U.S. National Institute of Standards and Technology (NIST) in 2024 under FIPS 204 and FIPS 203, respectively.

PQLN Protects Five Lightning Surfaces

Lightning currently depends heavily on secp256k1 elliptic-curve cryptography. A sufficiently capable quantum computer running Shor's algorithm could derive secret keys from exposed public keys, opening the door to node impersonation, forged invoices, transport decryption and payment-route deanonymization.

The new system addresses this existing quantum exposure on Lightning without attempting to replace Bitcoin's on-chain cryptography. PQLN distributes post-quantum node identities through BOLT 7 gossip, adds ML-KEM to the BOLT 8 transport handshake, signs BOLT 11 invoices with ML-DSA and extends post-quantum protections to BOLT 12 offers. Payment onions under BOLT 4 retain their existing format, with hybrid ML-KEM secrets carried alongside them.

Funding, commitment and penalty transactions remain outside the system's scope. Their keys are rooted in Bitcoin transactions and would require changes at the Bitcoin protocol level to receive equivalent protection.

Separately, Bitcoin developers are discussing protocol-level approaches such as BIP 360, while StarkWare demonstrated a quantum-safe transaction on Bitcoin mainnet in August without altering consensus rules. PQLN addresses the Lightning application layer of that same problem, where identities, invoices and routing data are exchanged.

Cryptographic Overhead Stays Below One Millisecond

Testing found that post-quantum computation added relatively little processing time. The slowest cryptographic operation measured by the researchers, ML-DSA signing, took 0.33 milliseconds.

Payments over an emulated 50-millisecond internet connection took an additional 19 to 53 milliseconds per hop, with most of that delay stemming from the transmission of larger post-quantum data rather than the cryptographic calculations themselves.

Bandwidth and storage produced a substantially larger cost. Using ML-DSA, a PQLN node downloaded roughly 10 times as much gossip data and stored about nine times as much as unmodified node. Applied to a network with roughly 33,000 public channels, the measurements imply that an initial gossip download would grow from about 26 MB to approximately 270 MB. Choosing the smaller FN-DSA-512 signature scheme reduced gossip growth to roughly four times the existing level. Taken together, the figures indicate that for node operators, the heavier cost of a post-quantum transition would come from data volume rather than computation.

Existing Lightning Nodes Remain Compatible

The researchers tested 12 configurations combining PQLN and standard Lightning nodes. Payments completed when upgraded and unmodified nodes shared a route, with connections falling back to classical cryptography when post-quantum protection was unavailable. Operators seeking stricter guarantees can instead enable a mode that rejects such downgrades and stops the payment before an HTLC is sent.

The open-source implementation adds roughly 11,000 lines to a research fork of rust-lightning. Its developers describe the code as a research artifact rather than a production release, and additional interoperability testing against Core Lightning, LND and Eclair is still required. Those tests are the next step in determining whether the design can move beyond a research artifact.

NIST has already standardized ML-KEM and ML-DSA and says organizations should begin migrating away from quantum-vulnerable public-key cryptography now. Under its current transition plan, vulnerable algorithms are to be deprecated and ultimately removed by 2035, with higher-risk systems expected to transition earlier. Because PQLN operates without consensus changes, it gives Lightning a way to align node-level communications with that timeline independently of Bitcoin's base-protocol decisions.

Source: Crypto Adventure