ED Mathématiques et Informatique
Practical Analysis of Symmetric and Asymmetric Standards in the White-Box Context
by Agathe HOUZELOT (LaBRI - Laboratoire Bordelais de Recherche en Informatique)
The defense will take place at 15h00 - Amphithéâtre du LaBRI LaBRI, 351 cours de la Libération, 33400 Talence
in front of the jury composed of
- Arnaud CASTEIGTS - Professeur des universités - University of Geneva - Directeur de these
- Louis GOUBIN - Professeur des universités - University of Versailles-St-Quentin-en-Yvelines - Rapporteur
- Matthieu RIVAIN - Ingénieur - CryptoExperts - Rapporteur
- Alice PELLET-MARY - Chargée de recherche - Université de Bordeaux - Examinateur
- Pascal DESBARATS - Professeur des universités - Université de Bordeaux - Examinateur
- Marine MINIER - Professeure des universités - Université de Lorraine - Examinateur
White-box cryptography aims to secure implementations of cryptographic algorithms in hostile environments where the adversary may potentially gain full access to the implementation and its execution environment. Against this nearly omnipotent attacker, all solutions proposed to date in the literature for standard cryptosystems are considered vulnerable. However, in practice, the adversary may encounter obstacles that complicate the application of theoretically effective attacks, such as a limit on the number of executions with a given key or obfuscation layers forcing him to undertake a costly reverse-engineering phase. Therefore, the white-box model seems to define an attacker who is excessively powerful for several use-cases. In this context, companies develop proprietary solutions whose designs remain secret and are specifically tailored to their needs. It is thus crucial to study the attacks and countermeasures that can be practically applied to these implementations. In this thesis, we focus on two widely used standard cryptosystems in both symmetric and asymmetric cryptography, namely AES and ECDSA. While the literature on AES is abundant, very few publications address white-box implementations of ECDSA, despite their high relevance for the industry. For both cryptosystems, we present real-life attacks, focusing on features such as the possibility of automation, a reduced number of white-box executions and no requirement for chosen inputs. Specifically, we examine the various potential vulnerabilities of ECDSA white-boxes and show that most of them stem from the lack of reliable sources of randomness in the white-box context. We detail the attacks that we carried out to break the 97 candidate implementations of the 2021 WhibOx contest. We also demonstrate how fault injections can break the very first white-box implementation of ECDSA published in 2020 by Zhou et al., and we propose a countermeasure that does not increase the size of the code. Given that there is no other public ECDSA implementation, we also review various patents to gain insights into countermeasures used in practice in products. Regarding AES white-boxes, we propose a new and highly efficient attack that requires very few executions on random plaintexts. We also investigate the protection provided by internal encodings against side-channel attacks. This common countermeasure is used on table-based implementations and consists in applying random permutations on sensitive variables to obfuscate them. Although it is widely known that random encodings are broken with high probability, the question of whether a particular class of encodings could prevent side-channel attacks remained open. In this thesis, we answer it negatively and show that carefully crafting encodings with a specific property is not a viable solution.
ED Entreprise Economie Société
The weight of Confucianism in the financing decision of Chinese family listed firms
by Yuan FENG (IRGO - Institut de Recherche en Gestion des Organisations)
The defense will take place at 9h00 - C107 Bâtiment C, Pôle universitaire des sciences de gestion, 35 avenue Abadie, 33072, Bordeaux
in front of the jury composed of
- Pascal BARNETO - Professeur des universités - Université de Bordeaux - Directeur de these
- Thierry POULAIN-REHM - Professeur des universités - Université de La Rochelle - Rapporteur
- Philippe GILLET - Maître de conférences - Université Paris-Saclay - Rapporteur
- Gérard HIRIGOYEN - Professeur émérite - Université de Bordeaux - CoDirecteur de these
- Jessica FOUILLOUX-THOMASSET - Professeure des universités - Université de Bordeaux - Examinateur
- Jean-Pierre MATHIEU - Professeur émérite - ISPI - Examinateur
The objective of this thesis is to examine how traditional Confucian culture influences the financing choices of publicly listed family businesses in China. In this perspective, the issue and the interests of the study are first presented. Subsequently, the research objectives are developed. The works of Redding, Fukuyama, and Wong on the spirit of Chinese capitalism, the dominant role of Confucianism in traditional Chinese culture, and the aspects of governance, financing, and performance of publicly listed family businesses in China are then discussed in the first part. In the following section, the epistemological positioning, the reasoning approach, and the methodology used are explained. Thirdly, the data collection and processing, the statistical techniques employed in this study, and the results obtained are discussed. Finally, the contributions and limitations of this study are presented, along with suggestions for future research in the field.
ED Sciences Physiques et de l'Ingénieur
Study of the solid-to-plasma transition of polystyrene and its influence on direct drive inertial confinement fusion simulations
by Romain LIOTARD (Centre Lasers Intenses et Applications)
The defense will take place at 13h30 - Amphi B 351 cours de la Libération, Bâtiment A29, 33405 TALENCE Cedex
in front of the jury composed of
- Hervé JOUIN - Professeur - Université de Bordeaux, CELIA - Directeur de these
- Stefan HüLLER - Directeur de recherche - Institut Polytechnique de Paris - Rapporteur
- Jean-Philippe COLOMBIER - Professeur - Université Jean Monnet Saint-Etienne, Laboratoire Hubert Curien - Rapporteur
- Olivier PEYRUSSE - Professeur - Aix-Marseille Université, Laboratoire Lasers Plasmas Procédés Photoniques - Examinateur
- Guillaume DUCHATEAU - Directeur de recherche - CEA - CESTA - CoDirecteur de these
Direct drive inertial confinement fusion (ICF) is a method considered for achieving nuclear fusion reactions by irradiating a target with multiple high-intensity laser pulses. This target is a sphere made of a solid material called an ablator (usually polystyrene), which surrounds a fusion fuel (usually cryogenic deuterium-tritium (DT)). The energy delivered by the laser irradiation causes the ejection of the ablator and the implosion of the target due to the rocket effect. The mechanical work exerted on the hotspot (the center of the target) during the implosion is expected to trigger fusion reactions. Currently, the radiative hydrodynamic codes used to simulate ICF implosions generally assume that the ablator is initially in a plasma state, although it is actually in a solid state. This solid state could play a role during the initial interaction between the lasers and the target. Due to the initial transparency of the ablator, the laser can penetrate the target, leading to the "shine-through" effect, which can modify the laser energy deposition and potentially alter the dynamics of the shocks propagating within the target. Additionally, changes in the laser imprint can influence the evolution of hydrodynamic instabilities during the implosion. The objective of this thesis is to develop a solid-to-plasma transition model for polystyrene based on existing models, that can be integrated into hydrodynamic simulation codes for ICF. To achieve this, the model needed to be adapted to the specific constraints of these codes, taking into account the dependencies of the model on the evolution of all hydrodynamic quantities, and optimizing the numerical costs to avoid an excessive increase in simulation time. The integration of these modifications required experimental validation of the model, which was carried out through an experiment on the GCLT laser at CEA-DIF, measuring the evolution of the transmittance of a polystyrene sheet irradiated by a laser pulse. The results showed a good correlation between simulations and experimental measurements, confirming the validity of the new coupled model. This model was then used to study the potential effects of the initial solid state on direct drive ICF simulations. The results revealed that accounting for the solid-to-plasma transition influences the growth of hydrodynamic instabilities. Specifically, we observed a reduction in low spatial frequency instabilities for targets with a thick ablator, and a general increase in high spatial frequency instabilities due to the non-linearity of the solid-to-plasma transition phenomenon.