Abstract. In this paper, we propose a taxonomy of privacy-related information-hiding/disclosure properties in terms of the modal logic of knowledge for multiagent systems. The properties considered here are anonymity, privacy, onymity, and identity. Intuitively, anonymity means the property of hiding who performed a certain specific action, privacy involves hiding what was performed by a certain specific agent, onymity refers to disclosing who performed a certain specific action, and identity relates to disclosing what was performed by a certain specific agent. Building on Halpern and O'Neill's work, we provide formal definitions of these properties and study the logical structure underlying them. In particular, we show that some weak forms of anonymity and privacy are compatible with some weak forms of onymity and identity, respectively. We also discuss the relationships between our definitions and existing standard terminology, in particular Pfitzmann and Hansen's consolidated proposal.
In this paper, we present an epistemic logic approach to the compositionality of several privacy-related informationhiding/disclosure properties. The properties considered here are anonymity, privacy, onymity, and identity. Our initial observation reveals that anonymity and privacy are not necessarily sequentially compositional; this means that even though a system comprising several sequential phases satisfies a certain unlinkability property in each phase, the entire system does not always enjoy a desired unlinkability property. We show that the compositionality can be guaranteed provided that the phases of the system satisfy what we call the independence assumptions. More specifically, we develop a series of theoretical case studies of what assumptions are sufficient to guarantee the sequential compositionality of various degrees of anonymity, privacy, onymity, and/or identity properties. Similar results for parallel composition are also discussed.We briefly review epistemic logic for multiagent systems. Notions and terminologies are borrowed from [9,12].A multiagent system consists of n agents with their local states and develops over time. We assume that an agent's local state encapsulates all the information to which the agent has access. Let I = {i 1, . . . , in} be the set of n agents. A global state is defined as the tuple (s i 1 , . . . , si n ) with all local states from i 1 to in. A run is a function from time, ranging over the natural numbers, to global states. A point is a pair
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