SHA3

SHA-3 refers to the Secure Hash Algorithm 3, a family of cryptographic hash functions standardized by NIST in 2015 under FIPS 202. It was derived from Keccak, the winner of NIST's SHA-3 competition, and designed as a complementary hash function to the SHA-2 family, rather than a replacement.

Construction and design principles: SHA-3 uses the sponge construction based on the Keccak-f[1600] permutation. The input is absorbed into a state with a rate and capacity, and the output is squeezed from the state. The capacity controls the security level; typically the capacity is twice the desired security level. The fixed-output variants produce digests of 224, 256, 384, or 512 bits, and the standard also defines extendable-output functions, SHAKE128 and SHAKE256, for arbitrary-length digests.

Variants and usage: The standard specifies four fixed-length digests: SHA3-224, SHA3-256, SHA3-384, and SHA3-512. Each variant employs padding and domain separation schemes designed to prevent interference with other sponge-based constructions and with the original Keccak proposal. The SHAKE family provides customizable output length, making it suitable for applications requiring variable-length hashes or keys derived from a hash function.

Security and properties: SHA3 is designed to resist length-extension attacks and to provide security roughly aligned with its output length against preimage and collision attacks, under conventional cryptographic assumptions. It offers the sponge-based versatility and can be used wherever a secure hash function is needed, alongside the SHA-2 family.

Implementation and adoption: SHA3 is widely implemented in software libraries and hardware, and can be used in digital signatures, message authentication, and data integrity checks. While SHA-2 remains widely deployed and often faster on some platforms, SHA3 provides an alternative design and future-proofing for cryptographic systems.