Neptune

Overview

Neptune is a variant of Poseidon developed by the Filecoin/Protocol Labs ecosystem. It adapts Poseidon for use in Filecoin's proof-of- replication and other storage proofs.

• Authors: Protocol Labs / Filecoin team
• Year: 2021
• S-box: $x^5$ (quintic)
• Structure: SPN, Poseidon-based with domain-specific parameter choices

Differences from Poseidon

Neptune uses Poseidon's core design but with:

• Specific parameter sets optimized for Filecoin's BLS12-381 deployment
• Particular choices of MDS matrices and round constants
• Arity-specific optimizations for Merkle tree hashing (2-to-1, 4-to-1, 8-to-1)

Security considerations

Neptune inherits Poseidon's security properties and is subject to the same cryptanalytic results. The main security questions are whether the specific parameter choices provide sufficient margin.

References

• Neptune specification (Filecoin documentation)
• Inherits from: Grassi et al. "Poseidon" (2021)