MCQUIC: Multicast and unicast in a single transport protocol

Multicast enables efficient one-to-many communications. Several applications benefit from its scalability properties, e.g., live-streaming and large-scale software updates. Historically, multicast applications have used specialized transport protocols. The flexibility of the recently standardized QUIC protocol opens the possibility of providing both unicast and multicast services to applications with a single transport protocol. We present MCQUIC, an extended version of the QUIC protocol that supports multicast communications. We show how QUIC features and built-in security can be leveraged for multicast transport. We present the design of MCQUIC and implement it in Cloudflare quiche. We assess its performance through benchmarks and in emulated networks under realistic scenarios. We also demonstrate MCQUIC in a campus network. By coupling QUIC with our multicast extension, applications can rely on multicast for efficiency with the possibility to fall back on unicast in case of incompatible network conditions.Comment: 13 page

Stability comparison of two absolute gravimeters: optical versus atomic interferometers

We report the direct comparison between the stabilities of two mobile absolute gravimeters of different technology: the LNE-SYRTE Cold Atom Gravimeter and FG5X\#216 of the Universit\'e du Luxembourg. These instruments rely on two different principles of operation: atomic and optical interferometry. The comparison took place in the Walferdange Underground Laboratory for Geodynamics in Luxembourg, at the beginning of the last International Comparison of Absolute Gravimeters, ICAG-2013. We analyse a 2h10 duration common measurement, and find that the CAG shows better immunity with respect to changes in the level of vibration noise, as well as a slightly better short term stability.Comment: 6 page

Les dimensions des crises: analyse de deux études de cas sous les approches processuelle et événementielle

Due to their protean character, crises are unique and they demand specific actions. In order to offer managers a referential framework to better deal with crises, many authors have tried to identify and to classify them. Thus, two main approaches can be located: those qualified as event-driven (mainly based on the elements that trigged out the crisis and its consequences) and those qualified as a process-driven (which places the crisis in a context full of meanings, actors and victims). The aim of this work is to analyze an organizational crisis within two organizations (a French one and a Brazilian one) by using these two approaches. The results show, among other aspects, that the event-driven approach allows a more complete visualization of these critical situations regarding the event-driven approach. Besides, the analysis of the crisis dimensions shows that a systemic approach of crisis events, the capitalization over experiences and an optimistic and proactive posture performed by the managers are the key elements in this study of crisis management.En raison de leur caractère protéiforme, les cas de crise sont uniques et ils exigent des actions spécifiques. Afin d'offrir aux gestionnaires un cadre de référence pour mieux les affronter, de nombreux auteurs ont tenté d'identifier et de classifier les crises. Ainsi, deux approches principales peuvent être repérées : celle qualifiée d'événementielle (plutôt centrée sur les éléments déclencheurs des crises et ses conséquences) et celle caractérisée de processuelle (qui situe la crise dans un contexte plein de significations, acteurs et victimes). L'objectif de ce travail sera d'analyser une crise organisationnelle dans deux entreprises (française et brésilienne) en faisant cohabiter ces deux approches. Les résultats indiquent, parmi d'autres aspects, que l'approche processuelle permet une visualisation beaucoup plus complète des situations critiques par rapport à l'approche événementielle. En plus, l'analyse des dimensions de crise montre que une approche systémique des événements de crise, la capitalisation sur les expériences vécues et une posture optimiste et proactive des gestionnaires ressortent de cette étude comme éléments clé de la gestion des crises

Individual Verifiability and Revoting in the Estonian Internet Voting System

Individual verifiability remains one of the main practical challenges in e-voting systems and, despite the central importance of this property, countries that sought to implement it faced repeated security problems. In this note, we revisit this property in the context of the IVXV version of the Estonian voting system, which has been in used for the Estonian municipal elections of 2017 and for the Estonian and European parliamentary elections of 2019. We show that a compromised voter device can defeat the individual verifiability mechanism of the current Estonian voting system. Our attack takes advantage of the revoting option that is available in the Estonian voting system, and only requires compromise of the voting client application: it does not require compromising the mobile device verification app, or any server side component

Modeling Computational Security in Long-Lived Systems, Version 2

For many cryptographic protocols, security relies on the assumption that adversarial entities have limited computational power. This type of security degrades progressively over the lifetime of a protocol. However, some cryptographic services, such as timestamping services or digital archives, are long-lived in nature; they are expected to be secure and operational for a very long time (i.e., super-polynomial). In such cases, security cannot be guaranteed in the traditional sense: a computationally secure protocol may become insecure if the attacker has a super-polynomial number of interactions with the protocol. This paper proposes a new paradigm for the analysis of long-lived security protocols. We allow entities to be active for a potentially unbounded amount of real time, provided they perform only a polynomial amount of work per unit of real time. Moreover, the space used by these entities is allocated dynamically and must be polynomially bounded. We propose a new notion of long-term implementation, which is an adaptation of computational indistinguishability to the long-lived setting. We show that long-term implementation is preserved under polynomial parallel composition and exponential sequential composition. We illustrate the use of this new paradigm by analyzing some security properties of the long-lived timestamping protocol of Haber and Kamat