Secrecy Logic: Protoalgebraic S-Secrecy Logics

In recent work the notion of a secrecy logic S over a given deductive system S was introduced. Secrecy logics capture the essential features of structures that are used in performing secrecy-preserving reasoning in practical applications. More precisely, they model knowledge bases that consist of information, part of which is considered known to the user and part of which is to remain secret from the user. S-secrecy structures serve as the models of secrecy logics. Several of the universal algebraic and model theoretic properties of the class of S-secrecy structures of a given S-secrecy logic have already been studied. In this paper, our goal is to show how techniques from the theory of abstract alge-braic logic may be used to analyze the structure of a secrecy logic and draw conclusions about its algebraic character. In particular, the notion of a protoalgebraic S-secrecy logic is introduced and several characterizing properties are provided. The relationship between protoalgebraic S-secrecy logics and the protoalgebraicity of their underlying deductive systems is also investigated