SHA-3 Hasher
Compute SHA3-256, SHA3-384 and SHA3-512 hashes.
Overview
The SHA-3 hasher computes SHA3-256, SHA3-384, and SHA3-512 digests of any text or byte input. Paste a message and the tool returns the chosen-size digest in hex, ready for signature verification, integrity checks, or matching against a NIST test vector.
It is the right tool when you need the NIST standard alternative to SHA-2 — increasingly common in post-quantum-curious designs, government applications, and Ethereum-related work (which uses Keccak-256, a close cousin). A SHA-3 hash generator online lets you cross-check an implementation without spinning up openssl dgst -sha3-256.
How it works
SHA-3, standardised in FIPS 202 (2015), is built on the Keccak sponge construction — fundamentally different from SHA-2's Merkle–Damgård design. The state is a 1600-bit 5×5×64 matrix transformed by 24 rounds of the Keccak-f[1600] permutation, which mixes the state via the θ, ρ, π, χ, ι sub-permutations. Input is XOR'd into the "rate" portion of the state one block at a time (the "absorb" phase); output is read from the rate after each application of the permutation (the "squeeze" phase). The capacity portion (2 × output_bits wide) is never directly touched, providing the security margin.
SHA3-256 has 256-bit output, 1088-bit rate, 512-bit capacity. SHA3-384 has 384-bit output. SHA3-512 has 512-bit output. SHAKE128 and SHAKE256 are the related XOFs (extendable-output functions) producing any number of bits.
Examples
Input: "" (empty)
SHA3-256: a7ffc6f8bf1ed76651c14756a061d662f580ff4de43b49fa82d80a4b80f8434a
SHA3-512: a69f73cca23a9ac5c8b567dc185a756e97c982164fe25859e0d1dcc1475c80a615b2123af1f5f94c11e3e9402c3ac558f500199d95b6d3e301758586281dcd26
Input: "abc"
SHA3-256: 3a985da74fe225b2045c172d6bd390bd855f086e3e9d525b46bfe24511431532
Input: "The quick brown fox jumps over the lazy dog"
SHA3-256: 69070dda01975c8c120c3aada1b282394e7f032fa9cf32f4cb2259a0897dfc04
FAQ
SHA-3 or SHA-256 — which should I pick?
For new designs without specific compliance needs, SHA-256 is faster on most CPUs and equally secure. SHA-3 is the right choice for FIPS-compliant designs, for diversification against an unknown future SHA-2 break, and for use with constructions like KMAC.
Is SHA-3 the same as Keccak-256?
Almost. SHA-3 uses a different domain-separation byte (0x06 for SHA-3, 0x01 for Keccak as originally submitted). Ethereum's "Keccak-256" is the pre-FIPS version with the original padding rule, so its hashes differ from SHA3-256 even for the same input.
Is SHA-3 immune to length-extension?
Yes. The sponge construction zeroises capacity bits, so an attacker cannot resume the state from the digest. This is one of SHA-3's structural advantages over SHA-2.
What about SHAKE?
SHAKE128 and SHAKE256 are XOF (extendable-output) modes of the same sponge, producing any number of output bits. Useful for stream-key derivation, but not surfaced in this tool.