The structure of SHA-3 is very different from that of SHA-1 and SHA-2. The key idea behind SHA-3 is based on unkeyed permutations, as opposed to other typical hash function constructions that used keyed permutations. Keccak also does not make use of the Merkle-Damgard transformation that is commonly used to handle arbitrary-length input messages in hash functions. A newer approach called sponge and squeeze construction is used in Keccak. It is a random permutation model. Different variants of SHA-3 have been standardized, such as SHA-3-224, SHA-3-256, SHA-3-384, SHA-3-512, SHAKE-128, and SHAKE-256. SHAKE-128 and SHAKE-256 are Extendable Output Functions (XOFs), which are also standardized by NIST. XOFs allow the output ...
Design of SHA-3 (Keccak)
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