Esfandiar Mohammadi

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The onion routing (OR) network Tor provides privacy to Internet users by facilitating anonymous web browsing. It achieves anonymity by routing encrypted traffic across a few routers, where the required encryption keys are established using a key exchange protocol. Goldberg, Stebila and Ustaoglu recently characterized the security and privacy properties(More)
Anonymous communication (AC) protocols such as the widely used Tor network have been designed to provide anonymity over the Internet to their participating users. While AC protocols have been the subject of several security and anonymity analyses in the last years, there still does not exist a framework for analyzing complex systems, such as Tor, and their(More)
In this paper we present MATor: a framework for rigorously assessing the degree of anonymity in the Tor network. The framework explicitly addresses how user anonymity is impacted by real-life characteristics of actually deployed Tor, such as its path selection algorithm, Tor consensus data, and the preferences and the connections of the user. The anonymity(More)
The onion routing network Tor is undoubtedly the most widely employed technology for anonymous web access. Although the underlying onion routing (OR) protocol appears satisfactory, a comprehensive analysis of its security guarantees is still lacking. This has also resulted in a significant gap between research work on OR protocols and existing OR anonymity(More)
We devise an abstraction of secure multi-party computations in the applied π-calculus. Based on this abstraction, we propose a methodology to mechanically analyze the security of cryptographic protocols employing secure multi-party computations. We exemplify the applicability of our framework by analyzing the SIMAP sugar-beet double auction protocol. We(More)
Dolev-Yao models of cryptographic operations constitute the foundation of many successful verification tools for security protocols, such as the protocol verifier ProVerif. Research over the past decade has shown that many of these symbolic abstractions are computationally sound, i.e., the absence of attacks against the abstraction entails the security of(More)
Protecting individuals' privacy in online communications has become a challenge of paramount importance. To this end, anonymous communication (AC) protocols such as the widely used Tor network have been designed to provide anonymity to their participating users. While AC protocols have been the subject of several security and anonymity analyses in the last(More)
Accountability of distributed systems aims to ensure that whenever a malicious behavior is observed, it can be irrefutably linked to a malicious node and that every honest node can disprove false accusations. Recent work, such as PeerReview and its extensions, shows how to achieve accountability in both deterministic and randomized systems. The basic idea(More)
The anonymous communication protocol Tor constitutes the most widely deployed technology for providing anonymity for user communication over the Internet. Several frameworks have been proposed that show strong anonymity guarantees for such protocols; none of these frameworks, however, are capable of modeling the class of traffic-related timing attacks(More)
Zero-knowledge (ZK) proofs have become a central building block for a variety of modern security protocols. Modern ZK constructions, such as the Groth-Sahai proof system, offer novel types of cryptographic flexibility: a participant is able to re-randomize existing ZK proofs, e.g., to achieve unlinkability in anonymity protocols; she can hide public parts(More)