Description
In November 2004, the European Network of Excellence for Cryptology (ECRYPT) launched a call for new stream cipher primitives. Authors from academia as well as industry submitted 34 designs, and in May 2008, 8 ciphers were chosen for the eSTREAM final portfolio. In this talk, we look back at the history of stream ciphers to understand the design choices made by cryptographers today. We start by reviewing "historical" designs based on linear feedback shift registers, such as the GSM A5/1 cipher. We explain basic cryptanalytic techniques - such as guess-and-determine attacks and correlation attacks - used to break LFSR-based ciphers. We also stop briefly to examine the importance of state size and key/IV length w.r.t. time-memory trade-offs. We then move on to the beginning of 2000s, which brought us new designs from the NESSIE research project, including SNOW 2.0, later to become the 3G mobile standard SNOW 3G. We discuss how new cryptanalytic tools, most notably algebraic cryptanalysis, reshaped design principles in modern ciphers, and review some of the eSTREAM submissions.<br/> In the second part of this talk, we focus on the cryptanalysis of one of the eSTREAM finalists, Moustique. We give a step-by-step overview of our attack that allows to recover the full 96-bit key in 2^{38} steps, using related keys, and allows to speed up exhaustive search in the standard case (without related keys) by a factor 28. Here, we invite the audience to interact, identify weaknesses that lead to the break and propose tweaks to thwart the attack. Cryptanalysis of Moustique is joint work with Vincent Rijmen, Tor E. Bjorstad, Christian Rechberger, Matt Robshaw and Gautham Sekar.
Prochains exposés
-
On the average hardness of SIVP for module lattices of fixed rank
Orateur : Radu Toma - Sorbonne Université
In joint work with Koen de Boer, Aurel Page, and Benjamin Wesolowski, we study the hardness of the approximate Shortest Independent Vectors Problem (SIVP) for random module lattices. We use here a natural notion of randomness as defined originally by Siegel through Haar measures. By proving a reduction, we show it is essentially as hard as the problem for arbitrary instances. While this was[…] -
Attacks and Remedies for Randomness in AI: Cryptanalysis of PHILOX and THREEFRY
Orateur : Yevhen Perehuda - Ruhr-University Bochum
In this work, we address the critical yet understudied question of the security of the most widely deployed pseudorandom number generators (PRNGs) in AI applications. We show that these generators are vulnerable to practical and low-cost attacks. With this in mind, we conduct an extensive survey of randomness usage in current applications to understand the efficiency requirements imposed in[…]-
Cryptography
-
-
Lightweight (AND, XOR) Implementations of Large-Degree S-boxes
Orateur : Marie Bolzer - LORIA
The problem of finding a minimal circuit to implement a given function is one of the oldest in electronics. In cryptography, the focus is on small functions, especially on S-boxes which are classically the only non-linear functions in iterated block ciphers. In this work, we propose new ad-hoc automatic tools to look for lightweight implementations of non-linear functions on up to 5 variables for[…]-
Cryptography
-
Symmetrical primitive
-
Implementation of cryptographic algorithm
-
-
Algorithms for post-quantum commutative group actions
Orateur : Marc Houben - Inria Bordeaux
At the historical foundation of isogeny-based cryptography lies a scheme known as CRS; a key exchange protocol based on class group actions on elliptic curves. Along with more efficient variants, such as CSIDH, this framework has emerged as a powerful building block for the construction of advanced post-quantum cryptographic primitives. Unfortunately, all protocols in this line of work are[…] -
Endomorphisms via Splittings
Orateur : Min-Yi Shen - No Affiliation
One of the fundamental hardness assumptions underlying isogeny-based cryptography is the problem of finding a non-trivial endomorphism of a given supersingular elliptic curve. In this talk, we show that the problem is related to the problem of finding a splitting of a principally polarised superspecial abelian surface. In particular, we provide formal security reductions and a proof-of-concept[…]-
Cryptography
-