Bert Lagaisse

Serverless computing has emerged as a popular paradigm in modern cloud environments, offering flexibility and scalability to tenants. A serverless function might handle sensitive tenant data. Employing Trusted Execution Environment (TEE) techniques to protect such a function from untrusted cloud service providers is attractive for tenant privacy. However, this introduces response latency, thereby impacting the performance of function execution. This paper introduces Fundue, a serverless architecture with bidirectional isolation between tenant and cloud provider that achieves light-weight isolation of functions and reduces cold start latency by fusing functions. Fundue enables multiple functions uploaded by the same tenant to share a single execution environment embedded into the enclave. Fundue allocates separate memory for each serverless function within the execution environment and establishes robust isolation between functions through bounds checking mechanisms. We extensively evaluate Fundue with diverse workloads and representative serverless functions. Our results demonstrate a significant reduction in response latency of serverless function execution, ranging from 17.8% to 88.7% compared to AccTEE, an open-source two-way sandbox serverless framework. Additionally, Fundue mitigates vulnerabilities in existing execution environments, such as stack-based buffer overflows.

In this paper, we introduce a new decentralized access control framework with transitive delegation capabilities that tackles the performance and scalability limitations of the existing state-of-the-art solutions. In order to accomplish this, the proposed solution is anchored in the self-sovereign identity (SSI) paradigm, which embodies a distributed identity management system. By adopting this paradigm, we obviate slow cryptographic premises such as identity-based encryption (IBE) that were used in prior work. Furthermore, we enhance the existing verifiable credentials (VCs) from this paradigm by introducing our own decentralized permission objects to support the concept of transitive delegations. This concept allows delegates to further delegate their access to resources with the same or fewer privileges to other entities within the framework. This renders our solution suitable for diverse scenarios, including applications in decentralized building access management. To the best of our knowledge, we are the first to introduce the concept of transitive delegations in this paradigm. Finally, our performance experiments show a performance enhancement of three orders of magnitude compared to the prevailing state-of-the-art solutions.

Many service providers rely on location data or streams to offer personalized services. However, reckless release of location streams can have serious privacy implications, especially with respect to sensitive zones, paths and time intervals. Unfortunately, current approaches by mobile platform providers to enhance privacy expose major shortcomings, especially with respect to releasing location information of frequently visited areas and in the presence of colluding service providers that are willing to combine local knowledge to retrieve more accurate information.This paper presents a practical approach to obfuscate location streams in the presence of the aforementioned challenges. Our solution combines multiple technologies and is validated through the development of a novel privacy-friendly location service in Android. It aims to realize a reasonable trade-off between privacy and utility concerns respectively raised by end-users and service providers. Thereby, sensitive locations, zones, paths, timestamps, and time intervals are highly configurable.

Distributed Ledger Technology (DLTs) or blockchains have been steadily emerging and providing innovation in the past decade for several use cases, ranging from financial networks, to notarization, or trustworthy execution via smart contracts. DLTs are enticing due to their properties of decentralization, non-repudiation, and auditability (transparency). These properties are of high potential to access control systems that can be implemented on-chain, and are executed without infringement and full transparency. While it remains uncertain which use cases will truly turn out to be viable, many use cases such as financial transactions can benefit from integrating certain restrictions via access control on the blockchain. In addition, smart contracts may in the future present security risks that are currently yet unknown. As a solution, access control policies can provide flexibility in the execution flow when adopted by smart contracts. In this paper, we present our DEDACS architecture which provides decentralized and dynamic access control for smart contracts in a policy-based manner. Our access control is expressive as it features policies, and dynamic as the environment or users can be changed, or alternative policies can be assigned to smart contracts. DEDACS ensures that our access control preserves the desired properties of decentralization and transparency, while aiming to keep the costs involved as minimal as possible. We have evaluated DEDACS in the context of a Uniswap token-exchange platform, in which we evaluated the costs related to (i) the introduced overhead at deployment time and (ii) the operational overhead cost. DEDACS introduces a relative overhead of on average 52% at deployment time, and an operational overhead between 52% and 80% depending on the chosen policy and its complexity.

In recent years, part of the web is shifting to a client-centric, decentralized model where web clients become the leading execution environment for application logic and data storage. However, current solutions to build decentralized web applications with multiple distrusting parties often involve a decentralized backend of servers running a BFT protocol between them. Existing consensus protocols using either all-to-all communication, or leader-based gossip suffer from performance degradation in unstable network conditions. In this paper, we present BeauForT, a purely browser-based platform for decentralized BFT consensus in client-centric, community-driven applications. We propose a novel, optimistic, leaderless, gossip-based consensus protocol, tolerating Byzantine replicas, combined with a robust and efficient state-based synchronization protocol. This protocol makes BeauForT well suited for the decentralized client-centric web and its dynamic nature with many network disruptions or node failures.

Many enterprise software services are adopting a fully web-based architecture for both internal line-of-business applications and for online customer-facing applications. Although wireless connections are becoming more ubiquitous and faster, mobile employees and customers are often offline due to expected or unexpected network disruptions. Nevertheless, continuous operation of the software is expected. This paper presents OWebSync: a web-based middleware for data synchronization in interactive groupware with fast resynchronization of offline clients and continuous, interactive synchronization of online clients. To automatically resolve conflicts, OWebSync implements a fine-grained data synchronization model and leverages state-based Conflict-free Replicated Data Types. This middleware uses Merkle-trees embedded in the tree-structured data and virtual Merkle-tree levels to achieve the required interactive performance. Our comparative evaluation with available operation-based and delta-state-based middleware solutions shows that OWebSync is especially better in operating in and recovering from offline settings and network disruptions. In addition, OWebSync scales more efficiently over time, as it does not store version vectors or other meta-data for all past clients.

(1) Background: Container orchestration frameworks provide support for management of complex distributed applications. Different frameworks have emerged only recently, and they have been in constant evolution as new features are being introduced. This reality makes it difficult for practitioners and researchers to maintain a clear view of the technology space. (2) Methods: we present a descriptive feature comparison study of the three most prominent orchestration frameworks: Docker Swarm, Kubernetes, and Mesos, which can be combined with Marathon, Aurora or DC/OS. This study aims at (i) identifying the common and unique features of all frameworks, (ii) comparing these frameworks qualitatively and quantitatively with respect to genericity in terms of supported features, and (iii) investigating the maturity and stability of the frameworks as well as the pioneering nature of each framework by studying the historical evolution of the frameworks on GitHub. (3) Results: (i) we have identified 124 common features and 54 unique features that we divided into a taxonomy of 9 functional aspects and 27 functional sub-aspects. (ii) Kubernetes supports the highest number of accumulated common and unique features for all 9 functional aspects; however, no evidence has been found for significant differences in genericity with Docker Swarm and DC/OS. (iii) Very little feature deprecations have been found and 15 out of 27 sub-aspects have been identified as mature and stable. These are pioneered in descending order by Kubernetes, Mesos, and Marathon. (4) Conclusion: there is a broad and mature foundation that underpins all container orchestration frameworks. Likely areas for further evolution and innovation include system support for improved cluster security and container security, performance isolation of GPU, disk and network resources, and network plugin architectures.