2,503 research outputs found
Transforming Password Protocols to Compose
International audienceFormal, symbolic techniques are extremely useful for modelling and analysing security protocols. They improved our understanding of security protocols, allowed to discover flaws, and also provide support for protocol design. However, such analyses usually consider that the protocol is executed in isolation or assume a bounded number of protocol sessions. Hence, no security guarantee is provided when the protocol is executed in a more complex environment. In this paper, we study whether password protocols can be safely composed, even when a same password is reused. More precisely, we present a transformation which maps a password protocol that is secure for a single protocol session (a decidable problem) to a protocol that is secure for an unbounded number of sessions. Our result provides an effective strategy to design secure password protocols: (i) design a protocol intended to be secure for one protocol session; (ii) apply our transformation and obtain a protocol which is secure for an unbounded number of sessions. Our technique also applies to compose different password protocols allowing us to obtain both inter-protocol and inter-session composition
Transforming Password Protocols to Compose
Formal, symbolic techniques are extremely useful for modelling and analysing security protocols. They improved our understanding of security protocols, allowed to discover flaws, and also provide support for protocol design. However, such analyses usually consider that the protocol is executed in isolation or assume a bounded number of protocol sessions. Hence, no security guarantee is provided when the protocol is executed in a more complex environment.
In this paper, we study whether password protocols can be safely composed, even when a same password is reused. More precisely, we present a transformation which maps a password protocol that is secure for a single protocol session (a decidable problem) to a protocol that is secure for an unbounded number of sessions. Our result provides an effective strategy to design secure password protocols: (i) design a protocol intended to be secure for one protocol session; (ii) apply our transformation and obtain a protocol which is secure for an unbounded number of sessions. Our technique also applies to compose different password protocols allowing us to obtain both inter-protocol and inter-session composition
Variable Bias Coin Tossing
Alice is a charismatic quantum cryptographer who believes her parties are
unmissable; Bob is a (relatively) glamorous string theorist who believes he is
an indispensable guest. To prevent possibly traumatic collisions of
self-perception and reality, their social code requires that decisions about
invitation or acceptance be made via a cryptographically secure variable bias
coin toss (VBCT). This generates a shared random bit by the toss of a coin
whose bias is secretly chosen, within a stipulated range, by one of the
parties; the other party learns only the random bit. Thus one party can
secretly influence the outcome, while both can save face by blaming any
negative decisions on bad luck.
We describe here some cryptographic VBCT protocols whose security is
guaranteed by quantum theory and the impossibility of superluminal signalling,
setting our results in the context of a general discussion of secure two-party
computation. We also briefly discuss other cryptographic applications of VBCT.Comment: 14 pages, minor correction
Expected loss analysis of thresholded authentication protocols in noisy conditions
A number of authentication protocols have been proposed recently, where at
least some part of the authentication is performed during a phase, lasting
rounds, with no error correction. This requires assigning an acceptable
threshold for the number of detected errors. This paper describes a framework
enabling an expected loss analysis for all the protocols in this family.
Furthermore, computationally simple methods to obtain nearly optimal value of
the threshold, as well as for the number of rounds is suggested. Finally, a
method to adaptively select both the number of rounds and the threshold is
proposed.Comment: 17 pages, 2 figures; draf
Asymptotic information leakage under one-try attacks
We study the asymptotic behaviour of (a) information leakage and (b) adversary’s error probability in information hiding systems modelled as noisy channels. Specifically, we assume the attacker can make a single guess after observing n independent executions of the system, throughout which the secret information is kept fixed. We show that the asymptotic behaviour of quantities (a) and (b) can be determined in a simple way from the channel matrix. Moreover, simple and tight bounds on them as functions of n show that the convergence is exponential. We also discuss feasible methods to evaluate the rate of convergence. Our results cover both the Bayesian case, where a prior probability distribution on the secrets is assumed known to the attacker, and the maximum-likelihood case, where the attacker does not know such distribution. In the Bayesian case, we identify the distributions that maximize the leakage. We consider both the min-entropy setting studied by Smith and the additive form recently proposed by Braun et al., and show the two forms do agree asymptotically. Next, we extend these results to a more sophisticated eavesdropping scenario, where the attacker can perform a (noisy) observation at each state of the computation and the systems are modelled as hidden Markov models
Timed Analysis of Security Protocols
We propose a method for engineering security protocols that are aware of
timing aspects. We study a simplified version of the well-known Needham
Schroeder protocol and the complete Yahalom protocol, where timing information
allows the study of different attack scenarios. We model check the protocols
using UPPAAL. Further, a taxonomy is obtained by studying and categorising
protocols from the well known Clark Jacob library and the Security Protocol
Open Repository (SPORE) library. Finally, we present some new challenges and
threats that arise when considering time in the analysis, by providing a novel
protocol that uses time challenges and exposing a timing attack over an
implementation of an existing security protocol
Composition of Password-based Protocols
International audienceFormal and symbolic techniques are extremely useful for modelling and analysing security protocols. They have helped to improve our understanding of such protocols, allowed us to discover aws, and they also provide support for protocol design. However, such analyses usually consider that the protocol is executed in isolation or assume a bounded number of protocol sessions. Hence, no security guarantee is provided when the protocol is executed in a more complex environment.\par In this paper, we study whether password protocols can be safely composed, even when a same password is reused. More precisely, we present a transformation which maps a password protocol that is secure for a single protocol session (a decidable problem) to a protocol that is secure for an unbounded number of sessions. Our result provides an effective strategy to design secure password protocols: (i) design a protocol intended to be secure for one protocol session; (ii) apply our transformation and obtain a protocol which is secure for an unbounded number of sessions. Our technique also applies to compose different password protocols allowing us to obtain both inter-protocol and inter-session composition
Data Minimisation in Communication Protocols: A Formal Analysis Framework and Application to Identity Management
With the growing amount of personal information exchanged over the Internet,
privacy is becoming more and more a concern for users. One of the key
principles in protecting privacy is data minimisation. This principle requires
that only the minimum amount of information necessary to accomplish a certain
goal is collected and processed. "Privacy-enhancing" communication protocols
have been proposed to guarantee data minimisation in a wide range of
applications. However, currently there is no satisfactory way to assess and
compare the privacy they offer in a precise way: existing analyses are either
too informal and high-level, or specific for one particular system. In this
work, we propose a general formal framework to analyse and compare
communication protocols with respect to privacy by data minimisation. Privacy
requirements are formalised independent of a particular protocol in terms of
the knowledge of (coalitions of) actors in a three-layer model of personal
information. These requirements are then verified automatically for particular
protocols by computing this knowledge from a description of their
communication. We validate our framework in an identity management (IdM) case
study. As IdM systems are used more and more to satisfy the increasing need for
reliable on-line identification and authentication, privacy is becoming an
increasingly critical issue. We use our framework to analyse and compare four
identity management systems. Finally, we discuss the completeness and
(re)usability of the proposed framework
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