The Ethereum Foundation is dropping the Poseidon hash function from its post-quantum security plan, a pivot driven by recent advances in compact proofs that have wiped out Poseidon's performance advantage. The change, attributed to researcher Justin Drake, marks a notable shift in how Ethereum intends to defend against quantum computers.
Why Poseidon is out
Poseidon was designed as a zero-knowledge-friendly hash function, optimized to work efficiently inside SNARKs and STARKs. For years, it was seen as a cornerstone of Ethereum's post-quantum strategy because it could keep proof generation fast and cheap. But that edge has evaporated. According to Drake, improvements in compact proofs have made Poseidon's specialized design unnecessary. The hash function's complexity no longer buys the performance it once did.
What changed
The breakthrough is in the proof systems themselves. Researchers have found ways to compress proofs further and verify them faster, reducing the need for a hash function that's tailor-made for ZK circuits. As these compact proof techniques mature, the trade-off that made Poseidon attractive — a bit of extra hashing overhead in exchange for faster proving — has flipped. Now, standard hash functions can do the job without the added complexity.
The pivot doesn't mean Ethereum is giving up on quantum resistance. It means the foundation is rethinking the tools it will use. Poseidon was one option; there are others, including newer constructions that might be simpler or more auditable. The decision also signals that the foundation is willing to change course as the cryptography evolves. That's a healthy sign for a project that has to stay ahead of a threat that's still years away but could be existential.
The shift comes as the foundation continues to work on its post-quantum roadmap. The foundation hasn't yet named a replacement for Poseidon. That decision will likely come as part of a revised plan, and the community will be watching closely for what comes next.
