Cybersecurity Breakfast - May 28th

We are excited to announce the next edition of Les Petits-Déjeuners de la Cybersécurité, taking place on Wednesday, May 28th, at 09:30 AM. The event will be held in the IMAG Auditorium located at 155 place du torrent, 38400 Saint-Martin-d'Hères.

This morning session will feature two presentations, each lasting approximately 20 minutes, followed by a Q&A session and informal discussions over coffee and croissants.

Program Highlights

1. Cybersecurity and the "Capitalism of Vulnerabilities", by Guillaume Vallet
This presentation aims to connect cybersecurity issues with my research work. Lately, my research has shifted toward analyzing the contemporary form of a phase of capitalism, which I refer to as “the capitalism of vulnerabilities.” Within this framework, cybersecurity issues emerge along two main lines of inquiry:

• Securing payment systems by central banks: The rise of cryptocurrencies — some of which position themselves as “anti-system” — calls for a redefinition of how payment networks are secured, and more broadly, of the central banks’ role and mission.

• In the “capitalism of vulnerabilities,” large multinational corporations — particularly the GAFAM — hold not only market power within their sectors, but also control over the networks through which information flows. As a result, major cybersecurity challenges arise around these infrastructures, reshaping the balance of power between public and private actors in the field of regulation.

2. Optimal communication unbalanced private set union by Alexis Galan
We propose a new protocol for Unbalanced Private Set Union (UPSU) between two parties. In this setting, the sender and the receiver each hold a dataset, with the receiver potentially holding a significantly larger set. The goal is for the receiver to learn the union of both sets and nothing more; in particular, the elements in the intersection of the two original sets must remain unknown. Moreover, we aim to minimize the cost for the “small” sender; specifically, we seek an asymptotic computation and communication cost proportional to the size of the sender’s set.

The UPSU problem has numerous practical applications and has recently attracted significant attention in the literature. However, to the best of our knowledge, our protocols are the first to achieve both arithmetic cost and communication volume that are linear in the size of the sender’s set and independent of the receiver’s set size.

Our constructions combine linearly homomorphic encryption (LHE) and fully homomorphic encryption (FHE). The core idea is to represent the receiver’s set as the roots of a polynomial, and to evaluate this polynomial at all points of the sender’s set—i.e., to perform an efficient and homomorphic multipoint polynomial evaluation.

Our first protocol relies on a parallelizable algorithm that makes effective use of the SIMD structure in FHE. This approach has the advantage of a low multiplicative depth, but results in a quadratic arithmetic cost for the receiver. A trade-off can be made to further reduce the multiplicative depth at the expense of a constant increase in communication volume, using results from number theory—specifically, the postage stamp problem.

The second protocol builds on an efficient multipoint evaluation algorithm from computer algebra, based on fast Euclidean division. This method yields a quasi-linear cost for the receiver, slightly increases the sender's cost, but doubles the multiplicative depth, which has a significant practical impact.

Our preliminary experimental results using the HElib homomorphic encryption library show that a sender holding 1,000 elements of 384 bits each can complete our protocol with a computation time of approximately 2 seconds, and a communication volume around 9 MB, regardless of the receiver’s set size.