Serge Vaudenay | EPFL Graph Search

Serge Vaudenay, né le à Saint-Maur-des-Fossés, est un cryptologue français, directeur de la section des systèmes de communication au sein de l'École polytechnique fédérale de Lausanne. Biographie Serge Vaudenay est un ancien élève du professeur Robillard (lycée Champlain de Chennevières-sur-Marne) et de l'École normale supérieure de la rue d'Ulm (promotion 1989) et agrégé de mathématiques. Il a commencé sa thèse en 1991, sous la direction de Jacques Stern, et sur le thème de la sécurité des primitives cryptographiques (dans un contexte symétrique). Il obtient son doctorat en informatique à l'Université Paris 7 en 1995. Chercheur au CNRS jusqu'en 1999, année où il obtient son habilitation à diriger des recherches, il devient le directeur du Laboratoire de sécurité et de cryptographique (LASEC) à l'École polytechnique fédérale de Lausanne. Auteur de nombreux articles de cryptanalyse et concepteur d'algorithmes de chiffrement dont FOX, il est plus connu pour son attaque sur

Le Traçage Anonyme, Dangereux Oxymore

Anne Canteaut, Stéphanie Lacour, Serge Vaudenay

Nicolas Anciaux, Xavier Bonnetain, Anne Canteaut, Véronique Cortier, Pierrick Gaudry, Lucca Hirschi, Steve Kremer, Stéphanie Lacour, Gaëtan Leurent, Matthieu Lequesne, Léo Perrin, André Schrottenloher, Emmanuel Thomé, Serge Vaudenay, Christophe Vuillot Dans le but affiché de ralentir la progression de l'épidémie COVID-19, la France envisage de mettre en place un système de traçage des contacts des malades à l'aide d'une application mobile. Les concepteurs de ce type d'applications assurent qu'elles sont respectueuses de la vie privée. Cependant cette notion reste vague. Nous souhaitons donc contribuer au débat public en apportant un éclairage sur ce que pourrait et ne pourrait pas garantir une application de traçage, afin que chacun puisse se forger une opinion sur l'opportunité de son déploiement.

2020

Resistance Against Iterated Attacks by Decorrelation Revisited

Asli Bay, Atefeh Mashatan, Serge Vaudenay

Iterated attacks are comprised of iterating adversaries who can make

d

plaintext queries, in each iteration to compute a bit, and are trying to distinguish between a random cipher

C

and the ideal random cipher

C^*

based on all bits. In EUROCRYPT '99, Vaudenay showed that a

2d

-decorrelated cipher resists to iterated attacks of order

d

when iterations make almost no common queries. Then, he first asked what the necessary conditions are for a cipher to resist a non-adaptive iterated attack of order

d

. Secondly, he speculated that repeating a plaintext query in different iterations does not provide any advantage to a non-adaptive distinguisher. We close here these two long-standing open problems. We show that, in order to resist non-adaptive iterated attacks of order

d

, decorrelation of order

2d-1

is not sufficient. We do this by providing a counterexample consisting of a cipher decorrelated to the order

2d-1

and a successful non-adaptive iterated attack of order

d

against it. Moreover, we prove that the aforementioned claim is wrong by showing that a higher probability of having a common query between different iterations can translate to a high advantage of the adversary in distinguishing

C

from

C^*

. We provide a counterintuitive example consisting of a cipher decorrelated to the order

2d

which can be broken by an iterated attack of order 1 having a high probability of common queries.

Springer2012

Revisiting Iterated Attacks in the Context of Decorrelation Theory

Asli Bay, Atefeh Mashatan, Serge Vaudenay

Iterated attacks are comprised of iterating adversaries who can make d plaintext queries, in each iteration to compute a bit, and are trying to distinguish between a random cipher C and the perfect cipher C* based on all bits. Vaudenay showed that a 2d-decorrelated cipher resists to iterated attacks of order d. when iterations have almost no common queries. Then, he first asked what the necessary conditions are for a cipher to resist a non-adaptive iterated attack of order d. I.e., whether decorrelation of order 2d-1 could be sufficient. Secondly, he speculated that repeating a plaintext query in different iterations does not provide any advantage to a non-adaptive distinguisher. We close here these two long-standing open problems negatively. For those questions, we provide two counter-intuitive examples. We also deal with adaptive iterated adversaries who can make both plaintext and ciphertext queries in which the future queries are dependent on the past queries. We show that decorrelation of order 2d protects against these attacks of order d. We also study the generalization of these distinguishers for iterations making non-binary outcomes. Finally, we measure the resistance against two well-known statistical distinguishers, namely, differential-linear and boomerang distinguishers and show that 4-decorrelation degree protects against these attacks.

2014

Resistance Against Iterated Attacks by Decorrelation Revisited

Asli Bay, Atefeh Mashatan, Serge Vaudenay

Iterated attacks are comprised of iterating adversaries who can make

d

plaintext queries, in each iteration to compute a bit, and are trying to distinguish between a random cipher

C

and the ideal random cipher

C^*

based on all bits. In EUROCRYPT '99, Vaudenay showed that a

2d

-decorrelated cipher resists to iterated attacks of order

d

when iterations make almost no common queries. Then, he first asked what the necessary conditions are for a cipher to resist a non-adaptive iterated attack of order

d

d

, decorrelation of order

2d-1

is not sufficient. We do this by providing a counterexample consisting of a cipher decorrelated to the order

2d-1

and a successful non-adaptive iterated attack of order

d

C

from

C^*

. We provide a counterintuitive example consisting of a cipher decorrelated to the order

2d

which can be broken by an iterated attack of order 1 having a high probability of common queries.

Springer2012