How is SHA-3 different from SHA-2?

SHA-3, standardised in FIPS 202, uses the Keccak sponge construction with the Keccak-f[1600] permutation, a completely different internal design from the Merkle-Damgard structure of SHA-2. It is immune to length-extension attacks.

Is SHA3-256 the same as Keccak-256?

No. SHA3-256 uses the NIST-standardised domain-separation suffix 0x06 during padding, while the original Keccak-256 used by Ethereum uses 0x01. The two produce different digests for the same input.

Is my text uploaded anywhere?

No. The Web Crypto API does not implement SHA-3, so this tool runs a pure-JavaScript Keccak engine locally. Your text never leaves the browser.

What is the output size?

SHA3-256 always outputs 256 bits, shown as 64 hexadecimal characters, regardless of how long or short the input is.

SHA-3 (256-bit) Hash Generator

What this SHA3-256 generator does

This tool computes the SHA3-256 hash of any text, returning a 256-bit value as 64 hexadecimal characters. SHA-3 is the most recent NIST-standardised hash family and offers a structurally different alternative to the SHA-2 functions for protocols that want defence-in-depth or length-extension immunity.

How it works

SHA-3 (FIPS 202) is built on the sponge construction over the Keccak-f[1600] permutation. The state is 1600 bits arranged as twenty-five 64-bit lanes. For SHA3-256 the rate is 1088 bits (136 bytes) and the capacity is 512 bits. The message is padded with the multi-rate rule — appending the byte 0x06, zero or more zero bytes, then setting the high bit 0x80 of the last block — then absorbed block-by-block into the state, applying 24 rounds of the theta, rho, pi, chi, and iota steps each time. Finally the first 256 bits are squeezed out as the digest. All of this runs in pure JavaScript using BigInt lane arithmetic, because browsers do not provide SHA-3 natively.

Tips and notes

The 0x06 padding suffix is what distinguishes SHA3-256 from Ethereum’s Keccak-256.
SHA-3 cannot be length-extended, unlike plain SHA-256 or SHA-512.
Example: the empty string hashes to a7ffc6f8bf1ed76651c14756a061d662f580ff4de43b49fa82d80a4b80f8434a.
A single changed byte completely changes the digest (avalanche effect).