Keccak

Keccak is a family of cryptographic hash functions designed by Guido Bertoni, Joan Daemen, Michaël Peeters, and Gilles Van Assche. It is built around the sponge construction and uses the Keccak-f[1600] permutation on a 1600-bit state. In operation, data are absorbed into the state in rate blocks, the permutation is applied, and the output is squeezed from the state. Keccak uses pad101 as its padding rule and is designed to be secure with inputs of variable length.

It was selected as the winner of the NIST SHA-3 cryptographic hash function competition in 2010. The algorithm was later standardized under the SHA-3 umbrella (FIPS 202) with additional variants and naming; the Keccak design remains the basis. The standard defines fixed-length hash functions SHA3-224, SHA3-256, SHA3-384, SHA3-512, and extendable-output functions SHAKE128 and SHAKE256, among others. The original Keccak family and the SHA-3 variants share the same core; however, the standardized versions use a specific padding rule and domain separation for differentiating between hash outputs and XOFs.

Security and performance: Keccak’s security level is set by the sponge’s capacity; higher capacity yields stronger resistance to preimage and collision attacks and supports longer outputs. The algorithm is noted for efficient hardware implementation and competitive software performance. Since the SHA-3 standardization, Keccak-based primitives have been widely adopted in various protocols and security libraries.