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
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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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Post-Quantum Public-Key Pseudorandom Correlation Functions for OT
Orateur : Mahshid Riahinia - ENS, CNRS
Public-Key Pseudorandom Correlation Functions (PK-PCF) are an exciting recent primitive introduced to enable fast secure computation. Despite significant advances in the group-based setting, success in the post-quantum regime has been much more limited. In this talk, I will introduce an efficient lattice-based PK-PCF for the string OT correlation. At the heart of our result lie several technical[…] -
Predicting Module-Lattice Reduction
Orateur : Paola de Perthuis - CWI
Is module-lattice reduction better than unstructured lattice reduction? This question was highlighted as `Q8' in the Kyber NIST standardization submission (Avanzi et al., 2021), as potentially affecting the concrete security of Kyber and other module-lattice-based schemes. Foundational works on module-lattice reduction (Lee, Pellet-Mary, Stehlé, and Wallet, ASIACRYPT 2019; Mukherjee and Stephens[…]-
Cryptography
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