Keccak is a cryptographic hash function designed by Guido Bertoni, Joan Daemen, Michaël Peeters, and Gilles Van Assche. In 2012, Keccak was selected as the basis for the SHA-3 standard. It offers multiple output lengths: 224-bit, 256-bit, 384-bit, and 512-bit. Using a sponge construction, it provides flexibility and security. Keccak-256 is widely used in blockchain technology, especially in Ethereum for generating addresses and signing transactions.