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 pad10*1 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.