Bounds on entanglement distillation and secret key agreement for quantum broadcast channels

The squashed entanglement of a quantum channel is an additive function of quantum channels, which finds application as an upper bound on the rate at which secret key and entanglement can be generated when using a quantum channel a large number of times in addition to unlimited classical communication. This quantity has led to an upper bound of $\log((1+\eta)/(1-\eta))$ on the capacity of a pure-loss bosonic channel for such a task, where $\eta$ is the average fraction of photons that make it from the input to the output of the channel. The purpose of the present paper is to extend these results beyond the single-sender single-receiver setting to the more general case of a single sender and multiple receivers (a quantum broadcast channel). We employ multipartite generalizations of the squashed entanglement to constrain the rates at which secret key and entanglement can be generated between any subset of the users of such a channel, along the way developing several new properties of these measures. We apply our results to the case of a pure-loss broadcast channel with one sender and two receivers.Comment: 35 pages, 1 figure, accepted for publication in IEEE Transactions on Information Theor

Towards a Safe and Secure web semantic framework

This thesis describes the work I did during my internship at the INRIA research center in Sophia-Antipolis, within the INDES team and under the supervision of Ilaria Castellani and Tamara Rezk.The main objectives of the INDES team is to study models and develop languages for Diffuse computing, a computing paradigm in which it is necessary to manage and maintain computing structures distributed on several heterogeneous nodes that usually do not trust each other. INDES focuses on the study of the different concurrency models that underlie these systems and pays particular attention to Multitier programming, an emerging programming paradigm that aims to reduce complexity in the development of web applications by adopting a single language to program all their components. The role played by security issues (and particularly the protection of confidentiality and integrity of data) is crucial in these applications, and ensuring security of web applications is another important goal of the INDES team. My internship took place in the context of the ANR CISC project, whose objective is to provide semantics, languages and attack models for the Internet of Things (IoT), a term that refers to systems composed of a set of interconnected devices, which interact with the environment in which they are placed by means of different sensors and actuators. My individual research took place within Webi, a semantic framework that aims at a primitive simulation of the interactions that take place between servers and clients on the web, developed by Tamara Rezk and her colleagues. In particular, I concentrated on an extension of Webi called WebiLog, which allows one to represent authenticated sessions and to formalize attacks aimed at compromising their integrity