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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Lie algebras and the security of cryptosystems based on classical varieties in disguise
Orateur : Mingjie Chen - KU Leuven
In 2006, de Graaf et al. proposed a strategy based on Lie algebras for finding a linear transformation in the projective linear group that connects two linearly equivalent projective varieties defined over the rational numbers. Their method succeeds for several families of “classical” varieties, such as Veronese varieties, which are known to have large automorphism groups. In this talk, we[…]-
Cryptography
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Some applications of linear programming to Dilithium
Orateur : Paco AZEVEDO OLIVEIRA - Thales & UVSQ
Dilithium is a signature algorithm, considered post-quantum, and recently standardized under the name ML-DSA by NIST. Due to its security and performance, it is recommended in most use cases. During this presentation, I will outline the main ideas behind two studies, conducted in collaboration with Andersson Calle-Vierra, Benoît Cogliati, and Louis Goubin, which provide a better understanding of[…] -
Wagner’s Algorithm Provably Runs in Subexponential Time for SIS^∞
Orateur : Johanna Loyer - Inria Saclay
At CRYPTO 2015, Kirchner and Fouque claimed that a carefully tuned variant of the Blum-Kalai-Wasserman (BKW) algorithm (JACM 2003) should solve the Learning with Errors problem (LWE) in slightly subexponential time for modulus q = poly(n) and narrow error distribution, when given enough LWE samples. Taking a modular view, one may regard BKW as a combination of Wagner’s algorithm (CRYPTO 2002), run[…]-
Cryptography
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CryptoVerif: a computationally-sound security protocol verifier
Orateur : Bruno Blanchet - Inria
CryptoVerif is a security protocol verifier sound in the computational model of cryptography. It produces proofs by sequences of games, like those done manually by cryptographers. It has an automatic proof strategy and can also be guided by the user. It provides a generic method for specifying security assumptions on many cryptographic primitives, and can prove secrecy, authentication, and[…]-
Cryptography
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Structured-Seed Local Pseudorandom Generators and their Applications
Orateur : Nikolas Melissaris - IRIF
We introduce structured‑seed local pseudorandom generators (SSL-PRGs), pseudorandom generators whose seed is drawn from an efficiently sampleable, structured distribution rather than uniformly. This seemingly modest relaxation turns out to capture many known applications of local PRGs, yet it can be realized from a broader family of hardness assumptions. Our main technical contribution is a[…]-
Cryptography
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