Confidentiality enforcement using dynamic information flow analyses

Abstract

With the intensification of communication in information systems, interest in security has increased. The notion of noninterference is typically used as a baseline security policy to formalize confidentiality of secret information manipulated by a program. This notion, based on ideas from classical information theory, has first been introduced by Goguen and Meseguer (1982) as the absence of strong dependency (Cohen, 1977). "information is transmitted from a source to a destination only when variety in the source can be conveyed to the destination" Cohen (1977) Building on the notion proposed by Goguen and Meseguer, a program is typically said to be noninterfering if the values of its public outputs do not depend on the values of its secret inputs. If that is not the case then there exist illegal information flows that allow an attacker, having knowledge about the source code of the program, to deduce information about the secret inputs from the public outputs of the execution. In contrast to the vast majority of previous work on noninterference which are based on static analyses (especially type systems), this PhD thesis report considers dynamic monitoring of noninterference. A monitor enforcing noninterference is more complex than standard execution monitors. "the information carried by a particular message depends on the set it comes from. The information conveyed is not an intrinsic property of the individual message." Ashby (1956). The work presented in this report is based on the combination of dynamic and static information flow analyses. The practicality of such an approach is demonstrated by the development of a monitor for concurrent programs including synchronization commands. This report also elaborates on the soundness with regard to noninterference and precision of such approaches.