Author: r2Jamong (Researcher at Four Pillars)
Compiled by Deep潮 TechFlow
Shenchao Overview: As quantum computing hardware advances rapidly and the U.S. National Institute of Standards and Technology (NIST) post-quantum cryptography standards are gradually implemented, blockchain public chains' defense against quantum attacks has evolved from an academic hypothesis into an urgent, fundamental survival challenge. However, the common assumption that one can simply replace existing signatures with quantum-resistant algorithms faces a catastrophic physical bottleneck when confronted with the demands of high-performance consensus throughput.
Researcher r2Jamong from Four Pillars provides a detailed technical analysis comparing the fundamental differences between Monad’s newly released post-quantum consensus protocol, Quantum Cadence, and Ethereum’s quantum-resistant evolution path. Ethereum, with its 860,000 active validator nodes, is constrained by the communication overhead of its highly decentralized network, relying on leanXMSS signatures and time-intensive SNARK proofs for compression within its 12-second slot intervals to steadfastly uphold decentralization. In contrast, Monad, determined to maintain its 100-millisecond slot limit, cannot tolerate the computational latency of SNARK aggregation and has decisively eliminated the heavy signature bundling from its consensus critical path entirely.
By switching to a lightweight mutual authentication channel, using hash-based peer-to-peer ticket verification, and strictly limiting the massive post-quantum signatures to the post-facto slashing phase, Monad achieves near-instant finality of 231 milliseconds in a high-concurrency network of 200 nodes while dramatically reducing upstream bandwidth consumption by 27%. This paper reveals a fundamental insight to the industry: security in the post-quantum era for public blockchains is not a one-size-fits-all standard, but a systemic engineering challenge that each blockchain must independently solve through its own architectural trade-offs.
On October 27, Monad’s development team, Category Labs, officially unveiled Quantum Cadence, a post-quantum upgrade to Cadence—the multi-proposer consensus protocol launched by Monad in July of this year.
Cadence itself has not yet been officially launched on mainnet. Therefore, Quantum Cadence should be understood as a forward-looking preview of Monad’s high-performance Layer 1 blockchain’s strategic technological preparation for the post-quantum era.
Monad’s Quantum Cadence takes a completely different technical path from Ethereum’s post-quantum design. While Ethereum aims to refactor its vulnerable signature bundles into new quantum-resistant forms, Monad achieves quantum resistance by entirely eliminating signature bundles altogether.
Both are blockchain networks running the same execution environment, the EVM. So why do they differ so significantly in their technological approaches to the post-quantum era?
Decrypting Monad's Quantum-Resistant Consensus Architecture
Diagram: Monad's Quantum-Resistant Cadence Consensus Architecture Compared to Traditional Certificate Exchange
Most high-performance blockchains today rely heavily on quorum certificates (QCs) for consensus. A QC is essentially an aggregated bundle of signatures that proves at least two-thirds of validators have voted in favor of the same block, with validators exchanging these certificates 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 miniature signature of just 96 bytes. However, the critical issue is that quantum computers can easily break the BLS signature algorithm.
Quantum-resistant digital signatures are typically extremely large in size and inherently difficult to aggregate efficiently.
For example, the ML-DSA-44 algorithm standardized by the National Institute of Standards and Technology (NIST) produces a single signature as large as 2,420 bytes. Currently, no post-quantum signature scheme can achieve the same level of compactness and speed in aggregation as BLS signatures.
Without an efficient aggregation mechanism, a consensus certificate would rapidly swell into a heavy list containing hundreds of large signatures. Monad’s Cadence consensus aims to achieve an ultra-short slot interval of 100 milliseconds and allows multiple block proposers to submit blocks in parallel simultaneously. It simply cannot withstand the network burden of having every validator broadcast such a massive certificate to the entire network in every slot.
Therefore, rather than passively waiting for smaller post-quantum aggregation algorithms to emerge, Monad has chosen to completely remove the heavy signature bundles from the consensus main process.
Under the new mechanism, each validator independently counts and verifies the quorum locally upon receiving votes. The network’s safety and liveness are based on authenticated secure communication channels and hash verification, rather than relying on nested layers of signature proofs.
The large post-quantum signatures are streamlined and retained solely for identifying and penalizing malicious validators after the fact. Under normal circumstances, each validator needs to sign at most two votes per slot.
In the technical paper released on October 23, the research team conducted extensive simulations under stringent assumptions: a 1 Gbps network connection, 200 validators, a fault-free execution path, and a single signature of 5,000 bytes.
In the extreme scenario with 100 proposers producing blocks in parallel, each validator’s network upload bandwidth consumption decreases by an astonishing 27%, dropping from 772 Mbps to 561 Mbps, compared to the original Cadence protocol. Meanwhile, transaction finality time remains virtually unchanged at 231 milliseconds, compared to 229 milliseconds in the original version.
Ethereum's core tension is decentralization; Monad's core tension is extreme speed.
Figure: Overview of the performance trade-offs between Ethereum SNARK signature aggregation and Monad authenticated hash channels
As of early October, the Ethereum network had approximately 860,000 active independent validators. It is entirely impractical for Ethereum to allow anyone to join without barriers and yet have such a large, highly decentralized group of participants directly count each other’s votes.
Therefore, Ethereum has no choice but to restructure its signature bundles. It plans to fully replace the vulnerable BLS signatures with the hash-based leanXMSS signature scheme and compress these large signatures— which cannot otherwise be directly aggregated—using SNARK zero-knowledge proofs.
Generating zero-knowledge proofs requires considerable time, but Ethereum's relatively long slot time (currently 12 seconds) provides ample buffer to absorb this computational overhead.
Monad’s technical requirements are precisely the opposite. Cadence targets a maximum slot interval of 100 milliseconds, leaving it no time to wait for lengthy SNARK proof aggregation computations.
On the other hand, Monad’s relatively compact network of 200 validator nodes makes it entirely feasible for each validator to count and verify all other validators’ votes locally.
Faced with the monumental challenge of quantum threats, Ethereum has chosen an architectural design that fully safeguards its extreme decentralization, while Monad has committed to a technical path that fiercely protects maximum throughput and response speed.
Quantum-resistant signature algorithms cannot solve everything: Deep restructuring at the consensus architecture level
Although NIST has standardized advanced signature algorithms capable of resisting quantum computer attacks, these industry-wide standards cannot be directly and seamlessly applied to networks operating in different environments.
In the field of blockchain consensus, simply switching to post-quantum signature algorithms cannot solve all engineering challenges. Each network must proactively address its unique performance and topology bottlenecks rather than passively waiting for external, ready-made solutions.
For Monad, achieving quantum resistance has never been about simply choosing a specific signature algorithm; it requires a fundamental restructuring of the underlying consensus mechanism that relies on certificate exchange.
Other blockchain networks face the same ultimate choice. EVM-compatible chains may draw inspiration from Ethereum’s advancements in account abstraction and quantum-resistant signatures when migrating conventional account signatures; however, at the level of underlying consensus architecture, this is entirely a unique challenge for each public chain, and no one can step in to solve it on their behalf.
Quantum computers powerful enough to genuinely threaten the security of mainstream blockchains have not yet been developed; industry consensus predicts their emergence will occur in the early to mid-2030s. Nevertheless, the window of time available for public blockchain teams to transition technologically is far from ample.
Even Ethereum itself is expected to take at least until 2029 to complete its Layer 1 quantum-resistant upgrade; transitioning a brand-new consensus mechanism from academic research to final deployment on the mainnet typically requires years of rigorous development and real-world testing.
This is precisely why the Monad team rushed to release its quantum-resistant version before the Cadence protocol had even officially launched on mainnet.
The defense against post-quantum cryptography will not automatically be settled merely because one institution establishes a universal standard. It is a rigorous, essential question that each blockchain network must independently solve, within the context of its own unique system architecture and trade-offs.
