Deconstructing Monad's quantum-resistant Cadence: why is its technical path diametrically opposed to Ethereum's?

Author: r2Jamong (Research Fellow at Four Pillars)

Compiled by: TechFlow

TechFlow Summary: With the accelerated evolution of quantum computing hardware and the gradual implementation of post-quantum cryptography standards by the National Institute of Standards and Technology (NIST), the ability of blockchain public chains to resist quantum attacks has evolved from an academic hypothesis into an urgent underlying survival battle. However, the vast majority's assumption of "simply replacing existing signatures with post-quantum algorithms" has encountered a devastating physical wall when faced with high-performance consensus throughput.

In this in-depth technical research report, Four Pillars researcher r2Jamong systematically compares and analyzes the fundamental divergence between Monad's newly released post-quantum consensus protocol, Quantum Cadence, and Ethereum's post-quantum evolution roadmap. Ethereum boasts 860,000 active validator nodes, but constrained by the communication overhead of a highly distributed network, it can only rely on leanXMSS signatures within its 12-second long slots and use time-consuming SNARK proofs for compression, firmly defending its decentralization baseline. In contrast, Monad, aiming to uphold its 100-millisecond ultra-short slot limit, cannot bear the computational latency of SNARK aggregation, and decisively chooses to completely excise heavy signature bundles from the consensus critical path.

By switching to lightweight bidirectional authenticated channels, hash-based peer-to-peer vote verification, and strictly confining massive post-quantum signatures to the post-event punishment (Slashing) phase, Monad not only achieves 231-millisecond near-instant finality in a high-concurrency network of 200 nodes, but also dramatically reduces network upload bandwidth consumption by 27%. This article profoundly reveals a core industry insight: public chain security in the post-quantum era is by no means a one-size-fits-all off-the-shelf standard, but rather a systems engineering challenge that each public chain must independently solve within the trade-offs of its own architecture.

On October 27, Monad's development team, Category Labs, officially unveiled the post-quantum consensus protocol, Quantum Cadence. Quantum Cadence is the post-quantum upgraded version of Cadence, which is Monad's multi-proposer consensus protocol launched this July.

Cadence itself has not yet been officially deployed to mainnet. Therefore, Quantum Cadence should be understood as a forward-looking unveiling of the strategic technical reserves that the high-performance Layer 1 public chain Monad has made in advance for the post-quantum era.

Monad's Quantum Cadence takes a completely different technical direction compared to Ethereum's post-quantum design. Ethereum is committed to reconstructing its quantum-vulnerable signature bundles into entirely new post-quantum forms; whereas Monad, to achieve post-quantum security, simply and completely abandons signature bundles altogether.

Both are blockchain networks running the same execution environment, the EVM. So why do they diverge so drastically in their technical pathways for addressing the post-quantum era?

Decoding Monad's Post-Quantum Consensus Architecture

Figure: Comparison between Monad's Quantum-Resistant Cadence Consensus Architecture and Traditional Certificate Exchange

The consensus mechanisms of most high-performance blockchains today heavily rely on Quorum Certificates (QCs). QCs are essentially aggregated signature bundles used to prove that at least two-thirds of validators have cast an affirmative vote for the same block, with these certificates being passed among validators through mutual broadcasting.

BLS signatures make this process extremely cheap, as hundreds or thousands of signatures can be losslessly compressed and aggregated into a single micro-signature of just 96 bytes. However, the fatal flaw is that quantum computers can easily break the BLS signature algorithm.

Secure signatures capable of resisting quantum computer attacks are typically extremely large, and they are inherently very difficult to aggregate effectively.

For example, the NIST-standardized ML-DSA-44 algorithm produces individual signatures that are as large as 2,420 bytes. Currently, no post-quantum signature can achieve such compactness and rapid aggregation as BLS signatures.

Without efficient aggregation mechanisms, a single consensus certificate quickly swells into a burdensome list containing hundreds of large-volume signatures. Monad's Cadence consensus aims for an ultra-short slot interval of 100 milliseconds and allows multiple block proposers to submit blocks concurrently. It simply cannot bear the network burden of requiring every validator to broadcast such massive certificates across the entire network in every slot.

Therefore, instead of passively waiting for smaller post-quantum aggregation algorithms to emerge, Monad chose to directly and completely remove heavy signature bundles from the main consensus workflow.

Under the new mechanism, each validator independently counts votes locally upon receipt and verifies whether a quorum has been reached. Network safety and liveness are built upon authenticated secure communication channels and hash verification, rather than relying on nested signature proofs.

Massive post-quantum signatures are streamlined and retained only for post-event identification and punishment of malicious misbehaving validators. Under normal circumstances, each validator needs to sign at most two votes per slot.

In the technical paper published on October 23, the research team conducted an in-depth simulation under strict assumptions of a 1Gbps network connection, 200 validators, fault-free operational paths, and a single signature size of 5,000 bytes.

In the extreme scenario of 100 proposers mining blocks concurrently, the network upload bandwidth consumption per validator decreased surprisingly by 27% compared to the original Cadence protocol, plummeting from 772 Mbps to 561 Mbps. Meanwhile, the time for transactions to reach final confirmation was 231 milliseconds, nearly identical to the original 229 milliseconds.

Ethereum's Core Dilemma Is Decentralization, Monad's Is Ultimate Speed

Figure: Panoramic Overview of Ethereum's SNARK Signature Aggregation vs. Monad's Authenticated Hash Channel Performance Trade-offs

As of early October, the Ethereum network boasts approximately 860,000 active independent validators. Ethereum allows anyone to join without barriers, making it completely unrealistic for such a vast and highly decentralized distribution of participants to directly verify each other's votes.

Therefore, Ethereum has no choice but to reconstruct its signature bundles. It plans to adopt the hash-based signature scheme leanXMSS to fully replace the vulnerable BLS signatures, and uses SNARK zero-knowledge proofs to compress these numerous signatures that cannot be directly merged.

Generating zero-knowledge proofs requires considerable time, but Ethereum's relatively long slot time (currently 12 seconds) provides ample buffer space to absorb these computational overheads.

Monad's technical requirements are diametrically opposed. Cadence targets an ultra-short slot interval of 100 milliseconds, meaning it simply has no leisure time to wait for prolonged SNARK proof aggregation computations.

On the other hand, Monad's relatively compact scale of 200 validator nodes makes it entirely practical for each validator to count votes locally and verify everyone else's votes directly.

Faced with the grand challenge of quantum threats, Ethereum chose an architectural design that fully protects its extreme decentralization characteristics, while Monad chose a technical route dedicated to safeguarding ultimate throughput and response speed.

Post-Quantum Signature Algorithms Are Not a Panacea: Deep Reconstruction at the Consensus Architecture Level

Although NIST has standardized advanced signature algorithms capable of resisting quantum computer decryption, these industry-wide generic standards cannot be seamlessly applied directly to any networks operating in different scenarios.

In the realm of blockchain consensus, merely swapping in post-quantum signature algorithms cannot possibly solve all engineering challenges. Every network must proactively address its unique performance and topological bottlenecks as early as possible, rather than passively waiting for external off-the-shelf solutions to save it.

For Monad, the key to achieving post-quantum security has never been about simply selecting a specific signature algorithm, but rather requires sweeping reconstruction at the level of the underlying consensus mechanism structure that relies on certificate exchange.

Other blockchain networks face this ultimate dilemma as well. EVM-compatible chains may draw upon Ethereum's exploratory achievements in account abstraction and post-quantum signatures when migrating regular account signatures; however, at the foundational consensus architecture level, this is entirely a proprietary challenge for each public chain, with no one able to take matters into their hands and solve it for them.

Powerful quantum computers capable of truly threatening mainstream blockchain security have not yet emerged, with industry predictions generally placing their arrival in the early to mid-2030s. Nevertheless, the time window left for public chain teams to undergo technological transformation is by no means generous or relaxed.

Even Ethereum itself is expected to require its Layer 1 post-quantum transition upgrade to last at least until 2029; and taking an entirely new consensus mechanism from cutting-edge academic exploration to final mainnet deployment often demands years of rigorous research and real-world testing.

This is precisely why the Monad team impatiently rushed to release its post-quantum version even before the Cadence protocol officially hit mainnet.

The defensive war in post-quantum cryptography will never naturally conclude simply because an institution establishes a universal standard. It is a hardcore mandatory question that each blockchain network must independently solve through the trade-offs of its own unique system architecture.