To Counter Quantum Threat, Ethereum Abandons Poseidon and Switches to Traditional Hashes
On August 13th, Ethereum researcher Justin Drake announced a strategic pivot in the face of the quantum computing threat: the Ethereum Foundation will abandon the SNARK-friendly hash function Poseidon at the L1 level in favor of traditional hash functions like SHA2 or BLAKE2. This decision, informed by eight years of research, represents a major shift in Ethereum's post-quantum cryptography roadmap.
Poseidon, introduced in 2019, has been favored for zkRollups and zkVMs due to its efficiency within SNARK circuits. However, its shorter cryptographic history and analysis timeline became liabilities when post-quantum security became a critical requirement.
The change is enabled by breakthroughs in SNARK design, particularly the adoption of "binary field" arithmetic. This allows traditional hash functions (which rely heavily on bitwise operations) to be verified efficiently in SNARKs, with recent benchmarks achieving millions of hashes per second on a laptop.
Another key driver is the accelerating timeline of the quantum threat. Reports warn that "Cryptographically Relevant Quantum Computers" (CRQCs) could break current public-key cryptography (like ECDSA) as early as the 2030s, risking trillions in on-chain assets. The enhanced cryptanalysis capabilities of AI have also weakened some post-quantum candidates, pushing Ethereum towards hash-based schemes, deemed more quantum-resistant.
Ethereum's post-quantum deployment plan aims for a production-ready leanVM by 2027, followed by full deployment across the consensus, execution, and data availability layers by 2028. This leanVM will aggregate numerous large post-quantum signatures into a single compact proof per block.
Other major blockchains are also preparing. Solana's core developers have independently chosen the NIST-standardized Falcon signature scheme for their post-quantum roadmap. Starknet has outlined a multi-phase plan, starting with replacing its Pedersen hash with BLAKE2.
By moving from the specialized Poseidon to the battle-tested SHA2/BLAKE2, Ethereum is opting for mature, widely analyzed cryptographic primitives, prioritizing long-term security assurance in the quantum era.
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