Sébastien Vaucher

Franz Gregor, Wojciech Ozga, Sébastien Vaucher et al.

Trust is arguably the most important challenge for critical services both deployed as well as accessed remotely over the network. These systems are exposed to a wide diversity of threats, ranging from bugs to exploits, active attacks, rogue operators, or simply careless administrators. To protect such applications, one needs to guarantee that they are properly configured and securely provisioned with the "secrets" (e.g., encryption keys) necessary to preserve not only the confidentiality, integrity and freshness of their data but also their code. Furthermore, these secrets should not be kept under the control of a single stakeholder - which might be compromised and would represent a single point of failure - and they must be protected across software versions in the sense that attackers cannot get access to them via malicious updates. Traditional approaches for solving these challenges often use ad hoc techniques and ultimately rely on a hardware security module (HSM) as root of trust. We propose a more powerful and generic approach to trust management that instead relies on trusted execution environments (TEEs) and a set of stakeholders as root of trust. Our system, PALAEMON, can operate as a managed service deployed in an untrusted environment, i.e., one can delegate its operations to an untrusted cloud provider with the guarantee that data will remain confidential despite not trusting any individual human (even with root access) nor system software. PALAEMON addresses in a secure, efficient and cost-effective way five main challenges faced when developing trusted networked applications and services. Our evaluation on a range of benchmarks and real applications shows that PALAEMON performs efficiently and can protect secrets of services without any change to their source code.

Stefan Contiu, Sébastien Vaucher, Rafael Pires et al.

Using public cloud services for storing and sharing confidential data requires end users to cryptographically protect both the data and the access to the data. In some cases, the identity of end users needs to remain confidential against the cloud provider and fellow users accessing the data. As such, the underlying cryptographic access control mechanism needs to ensure the anonymity of both data producers and consumers. We introduce A-SKY, a cryptographic access control extension capable of providing confidentiality and anonymity guarantees, all while efficiently scaling to large organizations. A-SKY leverages trusted execution environments (TEEs) to address the impracticality of anonymous broadcast encryption (ANOBE) schemes, achieving faster execution times and shorter ciphertexts. The innovative design of A-SKY limits the usage of the TEE to the narrow set of data producing operations, and thus optimizes the dominant data consumption actions by not requiring a TEE. Furthermore, we propose a scalable implementation for A-SKY leveraging micro-services that preserves strong security guarantees while being able to efficiently manage realistic large user bases. Results highlight that the A-SKY cryptographic scheme is 3 orders of magnitude better than state of the art ANOBE, and an end-to-end system encapsulating A-SKY can elastically scale to support groups of 10 000 users while maintaining processing costs below 1 second.

Stefan Contiu, Rafael Pires, Sébastien Vaucher et al.

While many cloud storage systems allow users to protect their data by making use of encryption, only few support collaborative editing on that data. A major challenge for enabling such collaboration is the need to enforce cryptographic access control policies in a secure and efficient manner. In this paper, we introduce IBBE-SGX, a new cryptographic access control extension that is efficient both in terms of computation and storage even when processing large and dynamic workloads of membership operations, while at the same time offering zero knowledge guarantees. IBBE-SGX builds upon Identity-Based Broadcasting Encryption (IBBE). We address IBBE's impracticality for cloud deployments by exploiting Intel Software Guard Extensions (SGX) to derive cuts in the computational complexity. Moreover, we propose a group partitioning mechanism such that the computational cost of membership update is bound to a fixed constant partition size rather than the size of the whole group. We have implemented and evaluated our new access control extension. Results highlight that IBBE-SGX performs membership changes 1.2 orders of magnitude faster than the traditional approach of Hybrid Encryption (HE), producing group metadata that are 6 orders of magnitude smaller than HE, while at the same time offering zero knowledge guarantees.