What is Keccak-256 and how is it different from SHA3-256?

Keccak-256 is the original Keccak algorithm submitted to NIST's SHA-3 competition. SHA3-256 is the NIST-standardized version with a modified padding scheme. This means Keccak-256('abc') and SHA3-256('abc') produce different hashes. Ethereum specifically uses the original Keccak-256, not SHA3-256.

How does Ethereum use Keccak-256?

Ethereum uses Keccak-256 (often mistakenly called 'SHA3' in Solidity) for: (1) computing function selectors from method signatures, (2) hashing in smart contract storage, (3) EIP-191 message signing, and (4) Merkle Patricia tree nodes. Every Ethereum transaction involves Keccak-256.

Why doesn't Ethereum use standard SHA3-256?

Ethereum was designed in 2014, before NIST finalized the SHA-3 standard in 2015. The Ethereum community adopted the original Keccak submission and chose not to break backward compatibility by switching to SHA3-256.

Is Keccak-256 secure despite not being standard SHA3?

Yes. The only difference between Keccak-256 and SHA3-256 is the padding rule — the core Keccak-f permutation is identical. The original Keccak padding is actually simpler and there are no known attacks exploiting this difference.

When should I use Keccak-256 vs SHA3-256?

Use Keccak-256 when working with Ethereum smart contracts, web3 development, or any system that explicitly requires the pre-NIST Keccak variant. Use SHA3-256 for all other purposes, especially when NIST compliance is needed.

Tools

Keccak-256|64 hex chars

Input

Output

Hash result will appear here...

0 chars|0 bytes

Keccak-256 Hash Tool — Ethereum Smart Contract Hashing

The hashing engine of Ethereum — powers every smart contract transaction and message signature (EIP-191). Uses original Keccak padding, producing different output than SHA3-256.

Features

✓Compute Keccak-256 hashes online — Ethereum's native hashing engine for smart contracts
✓Real-time 256-bit hash computation with 64 hex character output
✓One-click copy, download as .txt, and uppercase/lowercase toggle
✓Produces different output than SHA3-256 due to pre-NIST padding scheme
✓Hash verification against known Keccak-256 checksums
✓100% browser-based — essential for Ethereum developers and web3 builders

How to Use

1Type or paste your text into the input box above.
2Your hash digest appears instantly — no page reload needed.
3Toggle UPPERCASE / lowercase to change the hex output format.
4Click the copy icon to copy the hash to clipboard, or use Download to save as .txt.
5Paste an expected hash into the Verify field to check for a match.

Frequently Asked Questions

Related Tools

Keccak-512 Hash Generator — Full Original Keccak Output

The full 512-bit output of the original Keccak algorithm. Used in blockchain projects and cryptographic applications requiring high-security hashing with pre-NIST padding.

SHA3-256 Hash Calculator — NIST 3rd Gen Keccak Standard

NIST third-generation hash standard with 256-bit output. Built on the Keccak sponge — shares zero code with SHA-2, providing cryptographic diversity for critical systems.

SHA-256 Hash Calculator — Bitcoin & HTTPS Standard

The global industry standard — powers Bitcoin, HTTPS certificates, and digital signatures worldwide. 256-bit output, 128-bit security. The most trusted SHA-2 variant by far.