Keccak-256
Keccak-256 is the 256-bit cryptographic hash function Ethereum uses everywhere — transaction hashes, addresses, event topics, and function selectors are all Keccak-256 digests.
Keccak vs SHA-3
Keccak is the algorithm family that won the SHA-3 competition, but Ethereum standardized on Keccak before NIST finalized the SHA-3 padding change — so Ethereum’s Keccak-256 and the standardized SHA3-256 produce different outputs for the same input. Interoperating tools must know which variant they are computing; a SHA3-256 hash of calldata will not match an Ethereum function selector.
In Ethereum the hash shows up in three places developers touch daily: addresses (last 20 bytes of the public key’s Keccak-256), transaction and block hashes, and function selectors (first 4 bytes of the selector signature’s Keccak-256, e.g. transfer(address,uint256)).
Properties
Like all cryptographic hashes it is one-way, deterministic, and collision-resistant — suitable for fingerprints and commitments, not for encryption. Our hash generator computes both the SHA-2 family and Keccak variants side by side, and the dedicated Keccak256 page targets the Ethereum use case directly.
Related Standards
- •Keccak — pre-standard SHA-3 variant used by Ethereum
- •FIPS 202 — SHA-3 (different padding)
Free Tools & Resources
Further Reading
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