Options
Felber, Pascal
Nom
Felber, Pascal
Affiliation principale
Fonction
Professeur ordinaire
Email
pascal.felber@unine.ch
Identifiants
Résultat de la recherche
Voici les éléments 1 - 3 sur 3
- PublicationAccès libreDistributed systems and trusted execution environments : trade-offs and challenges(Neuchâtel : Université de Neuchâtel, Faculté des sciences, 2020)
; Security and privacy concerns in computer systems have grown in importance with the ubiquity of connected devices. Additionally, cloud computing boosts such distress as private data is stored and processed in multi-tenant infrastructure providers. In recent years, trusted execution environments (TEEs) have caught the attention of scientific and industry communities as they became largely available in user- and server-class machines. TEEs provide security guarantees based on cryptographic constructs built in hardware. Since silicon chips are difficult to probe or reverse engineer, they can offer stronger protection against remote or even physical attacks when compared to their software counterparts. Intel software guard extensions (SGX), in particular, implements powerful mechanisms that can shield sensitive data even from privileged users with full control of system software. Designing secure distributed systems is a notably daunting task, since they involve many coordinated processes running in geographically-distant nodes, therefore having numerous points of attack. In this work, we essentially explore some of these challenges by using Intel SGX as a crucial tool. We do so by designing and experimentally evaluating several elementary systems ranging from communication and processing middleware to a peer-to-peer privacy-preserving solution. We start with support systems that naturally fit cloud deployment scenarios, namely content-based routing, batching and stream processing frameworks. Our communication middleware protects the most critical stage of matching subscriptions against publications inside secure enclaves and achieves substantial performance gains in comparison to traditional software-based equivalents. The processing platforms, in turn, receive encrypted data and code to be executed within the trusted environment. Our prototypes are then used to analyse the manifested memory usage issues intrinsic to SGX. Next, we aim at protecting very sensitive data: cryptographic keys. By leveraging TEEs, we design protocols for group data sharing that have lower computational complexity than legacy methods. As a bonus,our proposals allow large savings on metadata volume and processing time of cryptographic operations, all with equivalent security guarantees. Finally, we focus our attention on privacy-preserving systems. After all, users cannot modify some existing systems like web-search engines, and the providers of these services may keep individual profiles containing sensitive private information about them. We aim at achieving indistinguishability and unlinkability properties by employing techniques like sensitivity analysis, query obfuscation and leveraging relay nodes. Our evaluation shows that we propose the most robust system in comparison to existing solutions with regard to user re-identification rates and results’ accuracy in a scalable way. All in all, this thesis proposes new mechanisms that take advantage of TEEs for distributed system architectures. We show through an empirical approach on top of Intel SGX what are the trade-offs of distinct designs applied to distributed communication and processing, cryptographic protocols and private web search. - PublicationAccès libreExploiting Concurrency and Heterogeneity for Energy-efficient Computing : An Actor-based ApproachTo accommodate energy efficiency, cloud providers started looking into radical ways of reducing the energy consumption. Energy-efficient optimizations should be addressed at both software and hardware levels of the datacenter. There have been numerous improvements in reducing the energy consumption on the hardware level. While they are efficient, however, their usage alone does not warrant significant decrease of energy dissipation. I argue that software-based methods for energy efficiency have not received as much attention as hardwarebased methods. As such, in this thesis, an important target is to provide a software framework that adapts itself in many different aspects in order to satisfy application performance and energy consumption requirements. For developing such a framework, I primarily concentrate on message passing models and, in particular, on the actor model. The actor model is arguably too conservative in its default concurrent settings. Specifically, I have identified a number of issues with the default concurrency settings of the actor model, which are: (1) message queuing delay during coordinated actions, (2) sequential message processing, (3) performance problems for concurrent message processing during high contention, and (4) the inability of the actor model to seamlessly exploit GPU resources. I use transactional memory for optimizing actor model’s message passing process, as well as propose DSL support for introducing GPU support. By addressing the identified problems I show that we can significantly improve performance, energy efficiency and programmability in the actor model.
- PublicationAccès librePractical Erasure Codes for Storage Systems : The Study of Entanglement Codes, an Approach that Propagates Redundancy to Increase Reliability and PerformanceThis dissertation deals with the design of practical erasure codes for storage systems. Hardware and logical disk failures are a common source of system failures that may lead to data loss. Nevertheless, it is predicted that spinning disks would remain the standard storage mediumin large datacenters. Cloud storage needs efficient codes to become reliable despite its low-cost components. As systems scale in size and complexity, their properties and requirements may change. When data ages, it is usuallymoved to dedicated archives. Yet the boundaries between storage systems and archives are getting diffuse as we move into applications that require low latency access such as mining data from large scientific archives. Moreover, the centralized approach of cloud backup services brings privacy and economics concerns. Some studies suggest that cooperative peer-to-peer networks aremore sustainable for the long term. But peer-to-peer nodes and spinning disks share an undesirable property: both are unreliable. The motivation for this study is to design flexible and practical codes that can provide high fault-tolerance to improve data durability and availability even in catastrophic scenarios. Survivability comes through the strength built with redundancy. It is difficult to devise a solution based on classic codes that considers all aspects of dependability: availability, reliability, safety, integrity and maintainability. Compromises are generally found through the complex combination ofmany techniques. This thesis argues that codes that are based exclusively on the use of parallel networks (such as replication) or mainly on the use of serial networks (as it is seen in the split and expand operations behind classic erasure codes) do not leverage all the resources available in a system. Entanglement codes create redundancy by tangling new data blocks with old ones, building entangled data chains that are woven into a growing mesh of interdependent content. We propose: 1) open and close entanglements as more reliable alternatives than mirroring, 2) alpha entanglements to achieve extremely high fault-tolerance with low storage overhead and low repair costs, and 3) spigot codes to reduce the space footprint from entangled data without significant loss of the entanglement’s properties. These codes can leverage storage and bandwidth resources efficiently by exploiting the combinatorial power of network reliability. Furthermore, their flexible design based on virtual chains of entangled data yields a scalable and suitable solution to accommodate future requirements. Finally, due to the combinatorial power of entangled data, all in all, dependability is boosted.