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Analysing Unlinkability and Anonymity Using the Applied Pi Calculus
"... Abstract—An attacker that can identify messages as coming from the same source, can use this information to build up a picture of targets ’ behaviour, and so, threaten their privacy. In response to this danger, unlinkable protocols aim to make it impossible for a third party to identify two runs of ..."
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Abstract—An attacker that can identify messages as coming from the same source, can use this information to build up a picture of targets ’ behaviour, and so, threaten their privacy. In response to this danger, unlinkable protocols aim to make it impossible for a third party to identify two runs of a protocol as coming from the same device. We present a framework for analysing unlinkability and anonymity in the applied pi calculus. We show that unlinkability and anonymity are complementary properties; one does not imply the other. Using our framework we show that the French RFID epassport preserves anonymity but it is linkable therefore anyone carrying a French epassport can be physically traced. I.
Election verifiability in electronic voting protocols
, 2010
"... We present a symbolic definition of election verifiability for electronic voting protocols in the context of the applied pi calculus. Our definition is given in terms of boolean tests which can be performed on the data produced by an election. The definition distinguishes three aspects of verifiabil ..."
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Cited by 19 (8 self)
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We present a symbolic definition of election verifiability for electronic voting protocols in the context of the applied pi calculus. Our definition is given in terms of boolean tests which can be performed on the data produced by an election. The definition distinguishes three aspects of verifiability, which we call individual verifiability, universal verifiability, and eligibility verifiability. It also allows us to determine precisely which aspects of the system’s hardware and software must be trusted for the purpose of election verifiability. In contrast with earlier work our definition is compatible with a large class of electronic voting schemes, including those based on blind signatures, homomorphic encryption and mixnets. We demonstrate the applicability of our formalism by analysing two protocols which have been deployed; namely Helios 2.0, which is based on homomorphic encryption, and Civitas, which uses mixnets. In addition we consider the FOO protocol which is based on blind signatures.
Attacking and fixing helios: An analysis of ballot secrecy
, 2010
"... Helios 2.0 is an opensource webbased endtoend verifiable electronic voting system, suitable for use in lowcoercion environments. In this paper, we analyse ballot secrecy and discover a vulnerability which allows an adversary to compromise the privacy of voters. This vulnerability has been success ..."
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Cited by 17 (6 self)
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Helios 2.0 is an opensource webbased endtoend verifiable electronic voting system, suitable for use in lowcoercion environments. In this paper, we analyse ballot secrecy and discover a vulnerability which allows an adversary to compromise the privacy of voters. This vulnerability has been successfully exploited to break privacy in a mock election using the current Helios implementation. Moreover, the feasibility of an attack is considered in the context of French legislative elections and, based upon our findings, we believe it constitutes a real threat to ballot secrecy in such settings. Finally, we present a fix and show that our solution satisfies a formal definition of ballot secrecy using the applied pi calculus.
A method for proving observational equivalence
"... Abstract—Formal methods have proved their usefulness for analyzing the security of protocols. Most existing results focus on trace properties like secrecy (expressed as a reachability property) or authentication. There are however several security properties, which cannot be defined (or cannot be na ..."
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Cited by 15 (8 self)
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Abstract—Formal methods have proved their usefulness for analyzing the security of protocols. Most existing results focus on trace properties like secrecy (expressed as a reachability property) or authentication. There are however several security properties, which cannot be defined (or cannot be naturally defined) as trace properties and require the notion of observational equivalence. Typical examples are anonymity, privacy related properties or statements closer to security properties used in cryptography. In this paper, we consider the applied pi calculus and we show that for determinate processes, observational equivalence actually coincides with trace equivalence, a notion simpler to reason with. We exhibit a large class of determinate processes, called simple processes, that capture most existing protocols and cryptographic primitives. Then, for simple processes without replication nor else branch, we reduce the decidability of trace equivalence to deciding an equivalence relation introduced by M. Baudet. Altogether, this yields the first decidability result of observational equivalence for a general class of equational theories. I.
YAPA: A generic tool for computing intruder knowledge
, 2009
"... Reasoning about the knowledge of an attacker is a necessary step in many formal analyses of security protocols. In the framework of the applied pi calculus, as in similar languages based on equational logics, knowledge is typically expressed by two relations: deducibility and static equivalence. Sev ..."
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Cited by 13 (4 self)
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Reasoning about the knowledge of an attacker is a necessary step in many formal analyses of security protocols. In the framework of the applied pi calculus, as in similar languages based on equational logics, knowledge is typically expressed by two relations: deducibility and static equivalence. Several decision procedures have been proposed for these relations under a variety of equational theories. However, each theory has its particular algorithm, and none has been implemented so far. We provide a generic procedure for deducibility and static equivalence that takes as input any convergent rewrite system. We show that our algorithm covers all the existing decision procedures for convergent theories. We also provide an efficient implementation, and compare it briefly with the more general tool ProVerif.
Automating security analysis: symbolic equivalence of constraint systems
, 2010
"... Abstract. We consider security properties of cryptographic protocols, that are either trace properties (such as confidentiality or authenticity) or equivalence properties (such as anonymity or strong secrecy). Infinite sets of possible traces are symbolically represented using deducibility constrain ..."
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Abstract. We consider security properties of cryptographic protocols, that are either trace properties (such as confidentiality or authenticity) or equivalence properties (such as anonymity or strong secrecy). Infinite sets of possible traces are symbolically represented using deducibility constraints. We give a new algorithm that decides the trace equivalence for the traces that are represented using such constraints, in the case of signatures, symmetric and asymmetric encryptions. Our algorithm is implemented and performs well on typical benchmarks. This is the first implemented algorithm, deciding symbolic trace equivalence. 1
Trace equivalence decision: Negative tests and nondeterminism
 IN: CCS’11
, 2011
"... We consider security properties of cryptographic protocols that can be modeled using the notion of trace equivalence. The notion of equivalence is crucial when specifying privacytype properties, like anonymity, voteprivacy, and unlinkability. In this paper, we give a calculus that is close to the ..."
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Cited by 11 (5 self)
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We consider security properties of cryptographic protocols that can be modeled using the notion of trace equivalence. The notion of equivalence is crucial when specifying privacytype properties, like anonymity, voteprivacy, and unlinkability. In this paper, we give a calculus that is close to the applied pi calculus and that allows one to capture most existing protocols that rely on classical cryptographic primitives. First, we propose a symbolic semantics for our calculus relying on constraint systems to represent infinite sets of possible traces, and we reduce the decidability of trace equivalence to deciding a notion of symbolic equivalence between sets of constraint systems. Second, we develop an algorithm allowing us to decide whether two sets of constraint systems are in symbolic equivalence or not. Altogether, this yields the first decidability result of trace equivalence for a general class of processes that may involve else branches and/or private channels (for a bounded number of sessions).
Epistemic Logic for the Applied Pi Calculus ⋆
"... Abstract. We propose an epistemic logic for the applied pi calculus, which is a variant of the pi calculus with extensions for modeling cryptographic protocols. In such a calculus, the security guarantees are usually stated as equivalences. While process calculi provide a natural means to describe t ..."
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Abstract. We propose an epistemic logic for the applied pi calculus, which is a variant of the pi calculus with extensions for modeling cryptographic protocols. In such a calculus, the security guarantees are usually stated as equivalences. While process calculi provide a natural means to describe the protocols themselves, epistemic logics are often better suited for expressing certain security properties such as secrecy and anonymity. We intend to bridge the gap between these two approaches: using the set of traces generated by a process as models, we define a logic which has constructs for reasoning about both intruder’s epistemic knowledge and the set of messages in possession of the intruder. As an example we consider two formalizations of privacy in electronic voting and study the relationship between them. 1
Deducibility constraints
, 2009
"... Abstract. In their work on tractable deduction systems, D. McAllester and later D. Basin and H. Ganzinger have identified a property of inference systems (the locality property) that ensures the tractability of the Entscheidungsproblem. On the other hand, deducibility constraints are sequences of de ..."
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Cited by 10 (2 self)
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Abstract. In their work on tractable deduction systems, D. McAllester and later D. Basin and H. Ganzinger have identified a property of inference systems (the locality property) that ensures the tractability of the Entscheidungsproblem. On the other hand, deducibility constraints are sequences of deduction problems in which some parts (formulas) are unknown. The problem is to decide their satisfiability and to represent the set of all possible solutions. Such constraints have also been used for deciding some security properties of cryptographic protocols. In this paper we show that local inference systems (actually a slight modification of such systems) yield not only a tractable deduction problem, but also decidable deducibility constraints. Our algorithm not only allows to decide the existence of a solution, but also gives a representation of all solutions. 1