crypt@b-it 2013

Joan Daemen

Sponge functions and Keccak

Abstract

This mini-course treats the subject of permutation-based symmetric cryptography in general and the NIST SHA-3 contest winner Keccak in particular and the SHA-3 competition.

Cryptographic services such as hashing, encryption, MAC computation, authenticated encryption and pseudorandom sequence generation can be realized efficiently with fixed-length permutations. Two constructions play a central role in this realization: the sponge and the duplex construction. We will discuss their security properties and modes of use.

Keccak is a family of sponge functions based on a set of 7 permutations called Keccak-f, with widths 25, 50, 100 ... up to 1600 bits. These permutations are constructed by iterating a relatively simple round functions. This is similar to a block cipher without a key schedule (but with round constants). We will discuss the design of the round function and the criteria that played a role in it such as differential and linear cryptanalysis, algebraic and symmetry properties and implementation efficiency.

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