Quantum Cadence achieves signature-free post-quantum consensus with comparable latency
The claim
Quantum Cadence provides safety and liveness without signatures while matching the fast-path latency of existing protocols
Published as: “Quantum Cadence: Post-Quantum Consensus with Multiple Concurrent Proposers”
So what
Enables blockchain consensus that remains secure against quantum adversaries without incurring the bandwidth and computation costs of large post-quantum certificate aggregation.
The five-minute version
Quantum Cadence achieves post-quantum consensus without quorum certificates, keeping the same three-round fast-path latency as Chorus while using far fewer signatures per validator. In simulation with 200 validators on 1 Gbps links, a validator finalizes a slot in about 200 ms after a proposal broadcast and reaches speculative finality roughly 50 ms earlier. The protocol’s latency is comparable to Chorus and scales better as the number of proposers grows, but the evaluation is limited to simulation and the Conductor’s full design is left for future work.
What they found 3
- Latency comparable to Chorus and better scalability with more proposers
“its latency is comparable to that of Chorus, and it scales better with the number of proposers.”
- Fast-path finalization time in simulation
“With 20 proposers, a validator finalizes a slot on average about 200 ms after a proposer’s broadcast, and reaches speculative finality about 50 ms earlier.”
- Fast path retains optimal three-round latency
“The fast path of Quantum Chorus keeps the optimal latency of Chorus [4]: correct validators finalize in three communication rounds, dissemination included, and reach speculative finality one round earlier, even when some proposers are offline.”
Stated limits 3
- We outline how the Conductor can work without certificates and with a signature-free agreement, and leave its full specification and analysis to a later version.
- Proofs of finality for parties outside consensus, such as light clients and bridges, are outside the scope of this paper; certificates of ordinary post-quantum signatures can serve them, since such a certificate need not be broadcast by every validator.
- We evaluate Quantum Chorus against Chorus in simulation, for 200 validators with 1 Gbps links: its latency is comparable to that of Chorus, and it scales better with the number of proposers.
What’s new here 4
- Removes quorum certificates entirely, relying only on authenticated channels and hash functions for safety and liveness.
- Introduces Quantum Chorus fast path with a single signature per vote vector, drastically reducing signature count per validator.
- Adds a signature-free fallback Byzantine agreement (Coda) to replace the certified fallback in Chorus.
- Provides a post-quantum accountable design where validators sign only for misbehavior proof, not for protocol progress.
Artifacts & methods 5
- Quantum Chorussystem
- Codasystem
- Conductor (slot scheduler)system
- post-quantum signature scheme (accountability)primitive
- simulation evaluationevaluation