A Generalized Notion of Non-interference for Flow Security of Sequential and Concurrent Programs

Abstract

For the last two decades, a wide spectrum of interpretations of non-interference11The notion of non-interference discussed in this paper enforces flow security in a program and is different from the concept of non-interference used for establishing functional correctness of parallel programs [1] have been used in the security analysis of programs, starting with the notion proposed by Goguen & Meseguer along with arguments of its impact on security practice. While the majority of works deal with sequential programs, several researchers have extended the notion of non-interference to enforce information flow-security in non-deterministic and concurrent programs. Major efforts of generalizations are based on (i) considering input sequences as a basic unit for input/output with semantic interpretation on a two-point information flow lattice, or (ii) typing of expressions as values for reading and writing, or (iii) typing of expressions along with its limited effects. Such approaches have limited compositionality and, thus, pose issues while extending these notions for concurrent programs. Further, in a general multi-point lattice, the notion of a public observer (or attacker) is not unique as it depends on the level of the attacker and the one attacked. In this paper, we first propose a compositional variant of non-interference for sequential systems that follow a general information flow lattice and place it in the context of earlier definitions of non-interference. We show that such an extension leads to the capturing of violations of information flow security in a concrete setting of a sequential language. Finally, we generalize non-interference for concurrent programs and illustrate its use for security analysis, particularly in the cases where information is transmitted through shared variables.