Censure

Résumé

La censure est la limitation de la liberté d'expression par un pouvoir (étatique, religieux ou privé) sur des livres, médias ou diverses œuvres d'art, avant ou après leur diffusion (censure a priori et a posteriori) au public. Par extension, certains auteurs parlent de censure doctrinale mais aussi de censure indirecte, non officielle, sous forme de pression due notamment à la concentration des médias, et d'autocensure déclenchée par la crainte ou la menace de censure. Étymologie et évolution sémantique En latin, le sens primaire du verbe censere avait une valeur religieuse : « déclarer solennellement et selon les formes ». Son sens secondaire a été « jugé, évalué » avec les mots censor et censura, qui ont pris aussi le sens de « critique ». À l'origine, le poste de censeur, créé à Rome en -443, avait pour but de répartir les citoyens en cinq classes censitaires. Il évolue ensuite en garantissant aussi le contrôle de l'adjudication des travaux publics, et la sanction mo

Source officielle

https://fr.wikipedia.org/wiki/Censure

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Virtually every connection to an Internet service is preceded by a DNS lookup. Lookups are performed without any traffic-level protection, thus enabling manipulation, redirection, surveillance, and censorship. To address these issues, large organizations such as Google and Cloudflare are deploying standardized protocols that encrypt DNS traffic between end users and recursive resolvers: DNS-over-TLS (DoT) and DNS-over-HTTPS (DoH). In this paper, we examine whether encrypting DNS traffic can protect users from traffic analysis-based monitoring and censoring. We propose a novel feature set to perform traffic analysis attacks, as the features used to attack HTTPS or Tor traffic are not suitable for DNS' characteristics. We show that traffic analysis enables the identification of domains with high accuracy in closed and open world settings, using 124 times less data than attacks on HTTPS flows. We also show that DNS-based censorship is still possible on encrypted DNS traffic. We find that factors such as end-user location, recursive resolver, platform, or DNS client do negatively affect the attacks' performance, but they are far from completely stopping them. We demonstrate that the standardized padding schemes are not effective. Yet, Tor -which does not effectively mitigate traffic analysis attacks on web traffic- is a good defense against DoH traffic analysis.

INTERNET SOC2020

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The Cloud trend is an attempt to leverage economics of scale in the domain of computing resources. Unfortunately, this often means losing control of the lower levels of a computer system, and exposing users to new threat vectors. These threats may be significant enough to forbid the use of clouds, and force giving up on their economical advantages. Chapter 1 introduces some issues with current cloud storage systems, that should be fixed before a cloud storage system can be considered as safe as a self-managed system. Among these, we will focus on censorship resistance. We also explain the not immediately obvious way in which they relate to issues discussed in the two latter chapters. Chapter 2 formally defines censorship-resistance and describes the ST E P-archive, an abstract model for a generic class of censorship-resistant storage systems. Within this model, we expose an asymmetry in hardness between attack algorithms (trying to perform censorship) and defense algorithms (trying to repair censored files). We discuss ideal choices for the many parameters and derive useful mathematical bounds when possible. We also simulate the behaviour of an ideal storage system to obtain experimental evidence of the effect of these parameter choices. We show that this model exhibits several counter-intuitive properties. Chapter 3 deals with the issue of incorrect key generation. Cryptography being an essential component of our proposed secure storage system, we discuss common pitfalls in implemen- tations of popular asymmetric cryptographic algorithms, and evidence of their presence in real-world implementations. Chapter 4 discusses an operational aspect of storage systems, the choice of a block storage unit, and the consequences of lack thereof. In particular, it shows how the size of a ciphertext can act as a side channel and leak information about encrypted contents to an attacker, within the context of large media files distributed through public file sharing systems.

EPFL2016

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EPFL2016