Description
In October 2012, the American National Institute of Standards and Technology (NIST) announced the selection of Keccak as the winner of the SHA-3 Cryptographic Hash Algorithm Competition. This concluded an open competition that was remarkable both for its magnitude and the involvement of the cryptographic community. Public review is of paramount importance to increase the confidence in the new standard and to favor its quick adoption. The SHA-3 competition explicitly took this into account by giving open access to the candidate algorithms and everyone in the cryptographic community could try to break them, compare their performance, or simply give comments.<br/> While preparing for the SHA-3 competition, we developed and presented the sponge construction. Our initial goal of this effort was to solve the problem of compactly expressing a comprehensive security claim. It turned out to be a powerful tool for building a hash function and we adopted it for our SHA-3 candidate Keccak. Additionally, with its variable output length it can be used as a mask generating function, a stream cipher or a MAC computation function. To support more sophisticated modes such as single-pass authenticated encryption and reseedable pseudorandom sequence generation, we additionally introduced the duplex construction. We have proven both sponge and duplex constructions sound in the indifferentiability framework. Our permutation-based modes can be seen as an alternative to the block-cipher based modes that have dominated mainstream symmetric cryptography in the last decades. They are simpler than the traditional block cipher modes and offer at the same time more flexibility by allowing to trade in security strength level for speed and vice versa. At the core of Keccak is a set of seven permutations called Keccak-f[b], with width b chosen between 25 and 1600 by multiplicative steps of 2. Depending on b, the resulting function ranges from a toy cipher to a wide function. The instances proposed for SHA-3 use exclusively Keccak-f[1600] for all security levels, whereas lightweight alternatives can use for instance Keccak-f[200] or Keccak-f[400], leaving Keccak-f[800] as an intermediate choice. Inside Keccak-f, the state to process is organized in 5 × 5 lanes of b/25 bits each, or alternatively as b/25 slices of 25 bits each. The round function processes the state using a non-linear layer of algebraic degree two, a linear mixing layer, inter- and intra-slice dispersion steps and the addition of round constants. The choice of operations in Keccak-f makes it very different from the SHA-2 family or even Rijndael (AES). On the implementation side, these operations are efficiently translated into bitwise Boolean operations and circular shifts, they lead to short critical paths in hardware implementations and they are well suited for protections against side-channel attacks.
Prochains exposés
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Key Attack on the ACDGV Matrix Encryption Scheme
Orateur : Anmoal Porwal - Technical University of Munich
I will present our key-recovery attack on the ACDGV public-key encryption scheme proposed at ASIACRYPT 2024 by Aragon, Couvreur, Dyseryn, Gaborit, and Vinçotte. The secret key is a Gabidulin code hidden by appending random rows and columns and by left- and right-multiplication with invertible matrices. Our attack exploits the resulting algebraic structure to recover an equivalent secret key. It[…]-
Cryptography
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Asymmetric primitive
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Module Learning With Errors and Structured Extrapolated Dihedral Cosets
Orateur : Jinwei Zheng - Télécom Paris
The Module Learning With Errors (MLWE) problem is the fundamental hardness assumption underlying the key encapsulation and signature schemes ML-KEM and ML-DSA, which have been selected by NIST for post-quantum cryptography standardization. Understanding its quantum hardness is crucial for assessing the security of these standardized schemes. Inspired by the equivalence between LWE and[…]-
Cryptography
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European Cyber Week: atelier cryptographie post-quantique
Dans la continuité des éditions 2021, 2022 et 2024, la DGA — en partenariat avec CREACH LABS et avec le soutien de l'ANSSI, de l'IRISA, de l'IRMAR et du Pôle d'Excellence Cyber — organise la 4e édition de l'atelier consacré à la cryptographie post-quantique dans le cadre de l'European Cyber Week 2026. Attention, il faut s'inscrire (gratuitement) au préalable — s'inscrire à la conférence Les[…] -
Journée post-quantique du séminaire crypto
Journée scientifique sur la cryptographie post-quantique dans la foulée de l'European Cyber Week avec des exposés plus techniques que ceux de l'ECW.