Cryptographic

SHA3-256

A 256-bit hash function based on the Keccak sponge construction, designed by Bertoni, Daemen, Peeters, and Van Assche; selected as the SHA-3 standard by NIST in 2015 (FIPS 202). A drop-in alternative to SHA-256 with a fundamentally different internal design , chosen precisely so a future attack on SHA-2 would not also break SHA-3.

At a glance

Sponge construction, in two paragraphs

SHA3-256 maintains a 1600-bit state, partitioned into a 1088-bit “rate” and a 512-bit “capacity”. To absorb a message, XOR rate-sized blocks into the state and apply the Keccak-f[1600] permutation between blocks. To squeeze output, take rate-sized chunks of the state (possibly applying the permutation again between chunks). For SHA3-256 only one squeeze block is needed because the digest is 256 bits.

The capacity is never directly exposed to the attacker: input mixes with the rate, and only after the permutation can the capacity affect the output. That construction (with capacity at least 2× the security level) gives SHA-3 its main differentiators over SHA-2: a clean security proof in the random-permutation model, and immunity to length-extension.

Where it is used

• NIST hash-based signatures , SLH-DSA / SPHINCS+ uses SHA-3 / SHAKE variants.
• Post-quantum protocols , CRYSTALS-Kyber and CRYSTALS-Dilithium use SHAKE-128 / SHAKE-256 (Keccak family) for randomness extraction.
• Some TLS suites and libsodium primitives when authors want length-extension immunity.
• Note: Ethereum’s “keccak256” is the original Keccak submission’s padding scheme, not NIST SHA-3-256. They produce different digests for the same input.

Security status

No collision or preimage attack better than the generic bound is known on full SHA-3. The most progress has come on reduced-round Keccak variants and on related-key / structural distinguishers that do not translate to real attacks on the standard.

SHA-3 family relationships

• SHA3-224 / 256 / 384 / 512 , fixed-output cousins, differ only in rate / capacity and output truncation.
• SHAKE128 / SHAKE256 , extendable-output functions (XOFs) based on the same permutation; produce any number of output bits.
• cSHAKE / KMAC / TupleHash / ParallelHash , domain-separated building blocks defined in NIST SP 800-185.
• KangarooTwelve / TurboSHAKE , faster, reduced-round Keccak-family hashes proposed by the original Keccak team.

Try it

The multi-algorithm hasher includes SHA3-256 alongside SHA-256, BLAKE2b, and BLAKE3, so the lengths and family differences are visible at a glance.

References

• NIST FIPS 202 , SHA-3 Standard
• The Keccak reference (Bertoni, Daemen, Peeters, Van Assche)
• NIST SP 800-185 , cSHAKE, KMAC, TupleHash, ParallelHash
• KangarooTwelve / TurboSHAKE