Non-interference is typically used as a baseline security policy to formalize confidentiality of secret information manipulated by a program. In contrast to static checking of non-interference, this paper considers dynamic, automaton-based, monitoring of information flow for a single execution of a sequential program. The monitoring mechanism is based on a combination of dynamic and static analyses. During program execution, abstractions of program events are sent to the automaton, which uses the abstractions to track information flows and to control the execution by forbidding or editing dangerous actions. The mechanism proposed is proved to be sound, to preserve executions of well-typed programs (in the security type system of Volpano, Smith and Irvine), and to preserve some safe executions of ill-typed programs.

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Temporal epistemic logic is a well-established framework for expressing agents knowledge and how it evolves over time. Within language-based security these are central issues, for instance in the context of declassification. We propose to bring these two areas together. The paper presents a computational model and an epistemic temporal logic used to reason about knowledge acquired by observing program outputs. This approach is shown to elegantly capture standard notions of noninterference and declassification in the literature as well as information flow properties where sensitive and public data intermingle in delicate ways.

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