Controlled declassification based on intransitive noninterference

Abstract

Traditional noninterference cannot cope with common features of secure systems like channel control, information filtering, or explicit downgrading. Recent research has addressed the derivation and use of weaker security conditions that could support such features in a language-based setting. However, a fully satisfactory solution to the problem has yet to be found. A key problem is to permit exceptions to a given security policy without permitting too much. In this article, we propose an approach that draws its underlying ideas from intransitive noninterference, a concept usually used on a more abstract specification level. Our results include a new bisimulation-based security condition that controls tightly where downgrading can occur and a sound security type system for checking this condition.