1,720,968 research outputs found
Relating Strand Spaces and Distributed Temporal Logic for Security Protocol Analysis
No full textIn previous work, we introduced a version of distributed temporal logic that is well-suited both for verifying security protocols and as a metalogic for reasoning about, and relating, different security protocol models. In this paper, we formally investigate the relationship between our approach and strand spaces, which is one of the most successful and widespread formalisms for analyzing security protocols. We define translations between models in our logic and strand-space models of security protocols, and we compare the results obtained with respect to the level of abstraction that is inherent in each of the formalisms. This allows us to clarify different aspects of strand spaces that are often left implicit, as well as pave the way to transfer results, techniques and tools across the two approaches
On the negative impact of social influence in recommender systems: A study of bribery in collaborative hybrid algorithms
Full text linkRecommender systems are based on inherent forms of social influence. Indeed, suggestions are provided to the users based on the opinions of peers. Given the relevance that ratings have nowadays to push the sales of an item, sellers might decide to bribe users so that they rate or change the ratings given to items, thus increasing the sellers’ reputation. Hence, by exploiting the fact that influential users can lead an item to get recommended, bribing can become an effective way to negatively exploit social influence and introduce a bias in the recommendations. Given that bribing is forbidden but still employed by sellers, we propose a novel matrix completion algorithm that performs hybrid memory-based collaborative filtering using an approximation of Kolmogorov complexity. We also propose a framework to study the bribery effect and the bribery resistance of our approach. Our theoretical analysis, validated through experiments on real-world datasets, shows that our approach is an effective way to counter bribing while, with state-of-the-art algorithms, sellers can bribe a large part of the users
Metareasoning about Security Protocols using Distributed Temporal Logic
No full textWe introduce a version of distributed temporal logic for rigorously formalizing and proving metalevel properties of different protocol models, and establishing relationships between models. The resulting logic is quite expressive and provides a natural, intuitive language for formalizing both local (agent specific) and global properties of distributed communicating processes. Through a sequence of examples, we show how this logic may be applied to formalize and establish the correctness of different modeling and simplification techniques, which play a role in building effective protocol tools
On the semantics of Alice&Bob specifications of security protocols
No full textIn the context of security protocols, the so-called Alice&Bob notation is often used to describe the messages exchanged between honest principals in successful protocol runs. While intuitive, this notation is ambiguous in its description of the actions taken by principals, in particular with respect to the conditions they must check when executing their roles and the actions they must take when the checks fail.
In this paper, we investigate the semantics of protocol specifications in Alice&Bob notation. We provide both a denotational and an operational semantics for such specifications, rigorously accounting for these conditions and actions. Our denotational semantics is based on a notion of incremental symbolic runs, which reflect the data possessed by principals and how this data increases monotonically during protocol execution. We contrast this with a standard formalization of the behavior of principals, which directly interprets message exchanges as sequences of atomic actions. In particular, we provide a complete characterization of the situations where this simpler, direct approach is adequate and prove that incremental symbolic runs are more expressive in general. Our operational semantics, which is guided by the denotational semantics, implements each role of the specified protocol as a sequential process of the pattern-matching spi calculus
Deconstructing Alice and Bob
No full textAlice&Bob–notation is a simple notation for describing security protocols as sequences of message exchanges. We show that, despite the fact that Alice&Bob–notation does not include explicit control flow constructs, it is possible to make some of these aspects explicit when producing formal protocol models without having to resort to more expressive protocol description languages. We introduce a notion of incremental symbolic run to formally handle message forwarding and conditional abortion. In incremental symbolic runs, we use variables to represent messages that the principals cannot read, and we characterize each of the execution steps in order to build a collection of symbolic subruns of increasing lengths, reflecting the data possessed by the principals up to that point in the execution. We contrast this with the simpler (more standard) approach based on formalizing the behavior of principals by directly interpreting message exchanges as sequences of atomic actions. In particular, we provide a complete characterization of the situations where this simpler approach is adequate and prove that incremental symbolic runs are more expressive in general
Labelled Tableaux for Distributed Temporal Logic
No full textThe distributed temporal logic DTL is a logic for reasoning about temporal properties of discrete distributed systems from the local point of view of the system’s agents, which are assumed to execute sequentially and to interact by means of synchronous event sharing. We present a sound and complete labelled tableaux system for full DTL. To achieve this, we first formalize a labelled tableaux system for reasoning locally at each agent and afterwards we combine the local systems into a global one by adding rules that capture the distributed nature of DTL. We also provide examples illustrating the use of DTL and our tableaux system
A labeled tableaux system for the Distributed Temporal Logic DTL
No full textDTL is a distributed temporal logic for reasoning about temporal properties of distributed systems from the local point of view of the system's agents, which are assumed to execute sequentially and to interact by means of synchronous event sharing. We present a sound and complete labeled tableaux system for future-time DTL. To achieve this, we first formalize a labeled tableaux system for reasoning locally at each agent, which provides a system for full future-time LTL, and afterwards we combine the local systems into a global one by adding rules that capture the distributed nature of DTL
A Robust Reputation-Based Group Ranking System and Its Resistance to Bribery
Full text linkThe spread of online reviews and opinions and its growing influence on people's behavior and decisions boosted the interest to extract meaningful information from this data deluge. Hence, crowdsourced ratings of products and services gained a critical role in business and governments. Current state-of-the-art solutions rank the items with an average of the ratings expressed for an item, with a consequent lack of personalization for the users, and the exposure to attacks and spamming/spurious users. Using these ratings to group users with similar preferences might be useful to present users with items that reflect their preferences and overcome those vulnerabilities. In this article, we propose a new reputation-based ranking system, utilizing multipartite rating subnetworks, which clusters users by their similarities using three measures, two of them based on Kolmogorov complexity. We also study its resistance to bribery and how to design optimal bribing strategies. Our system is novel in that it reflects the diversity of preferences by (possibly) assigning distinct rankings to the same item, for different groups of users. We prove the convergence and efficiency of the system. By testing it on synthetic and real data, we see that it copes better with spamming/spurious users, being more robust to attacks than state-of-the-art approaches. Also, by clustering users, the effect of bribery in the proposed multipartite ranking system is dimmed, comparing to the bipartite case
Towards a Metalogic for Security Protocol Analysis
No full textTowards a Metalogic for Security Protocol Analysi
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