A fingerprint function designed to be cheap inside zero-knowledge proofs. Newer and less battle-tested than Keccak.
The idea: Inside a zero-knowledge proof, everything becomes arithmetic on large numbers, and hashes like Keccak, built from bit shuffling, cost a huge number of such operations. Poseidon is built from that arithmetic itself (additions, multiplications and small powers), so it costs a small fraction. The trade-off: algebraic structure gives attackers algebraic tools, and it has had far less scrutiny.
Why it matters: Used by privacy apps and many ZK rollups.
On the map: young algebraic hash used inside proofs. EF runs a cryptanalysis bounty program
Poseidon is a hash function designed to be cheap inside zero-knowledge proofs[1], where hashes like Keccak are very expensive. It is used in privacy apps, many ZK rollups and the leanSig prototype[2].
It is much younger than SHA-256 or Keccak and built on algebraic structure, which gives attackers new angles. The Ethereum Foundation runs a cryptanalysis initiative with bounties[3] to stress-test it, and some reduced-round variants have been attacked.
If any of these breaks, this breaks too.
If this breaks, these break with it.