LayerZero Research publishes two papers identifying structural weaknesses in the Poseidon hash function

Researchers at @LayerZero_Core have published two papers identifying structural weaknesses in Poseidon, a cryptographic hash function widely used inside zero-knowledge proof systems. The findings add to a growing body of scrutiny surrounding a primitive that underpins significant infrastructure across the blockchain industry.

What Poseidon Does and What the Research Found

Poseidon is a hash function built specifically to run cheaply inside zero-knowledge proofs. Its job is to convert data into a fixed digital fingerprint in a way that makes it computationally infeasible to engineer a specific output from a chosen input. It was first introduced in 2019 as a highly efficient cryptographic hash designed for zero-knowledge proof systems such as SNARKs, STARKs, and Bulletproofs, with its primary objective being to minimise circuit complexity and computational overhead.

@LayerZero_Core researcher Giuseppe Vitto showed that a hash output can be steered under certain conditions, a finding that points to structural limitations in how the function behaves in specific configurations. LayerZero has clarified that the results do not break Poseidon as it is currently deployed in any live system. Separately, a paper published on the IACR ePrint archive in August 2026 by Bhati, Tariq, and Ashur describes a related approach: a generalised S-box skipping gadget that absorbs initial rounds without increasing the polynomial degree of the Poseidon system, restricting the subspace of constraint solutions to map a computationally infeasible polynomial system into a bounded, low-degree form, and enabling a probability-one distinguisher over multiple rounds of Poseidon.

Ethereum Foundation Moves On

The LayerZero papers arrive in a climate of heightened scrutiny. The Ethereum Foundation (@ethereumfndn) has already changed course on Poseidon as a key piece of its post-quantum security strategy, with researcher Justin Drake naming SHA and BLAKE as potential replacements in an announcement on August 13.

The shift was not triggered by a practical break of deployed Poseidon parameters. Rather, advances in binary-field SNARK systems, including Binius and Flock, have made proving standard hashes efficient enough that Ethereum no longer needs a SNARK-friendly hash optimised for older proving constraints. The announcement concerns Ethereum's future layer 1 architecture rather than an immediate removal of Poseidon from existing applications. Rollups, virtual machines, and other projects that already use the function are not required to replace it because of the roadmap decision.

Sreeram Kannan, founder and CEO of Eigen Labs, noted that SHA and BLAKE offer a practical advantage over other post-quantum approaches because they have fewer known attack vectors, and years of public scrutiny should allow faster deployment compared with less-tested alternatives.

For now, the LayerZero findings stop short of a full practical break. But combined with the Ethereum Foundation's pivot and an active industry-wide cryptanalysis programme, the research reinforces a broader reassessment of whether Poseidon's design margins remain adequate for high-value applications.

Sources
IACR ePrint: From Round Skipping to S-Box Skipping, Attacking Poseidon's Partial Layer via Subspace Restriction
CoinMarketCap Academy: Ethereum Foundation Drops Poseidon Hash Function in Post-Quantum Shift
Crypto.news: Ethereum L1 drops Poseidon in post-quantum move