Static Security Optimization for Real-Time Systems

An increasing number of real-time applications like railway signaling control systems and medical electronics systems require high quality of security to assure confidentiality and integrity of information. Therefore, it is desirable and essential to fulfill security requirements in security-critical real-time systems. This paper addresses the issue of optimizing quality of security in real-time systems. To meet the needs of a wide variety of security requirements imposed by real-time systems, a group-based security service model is used in which the security services are partitioned into several groups depending on security types. While services within the same security group provide the identical type of security service, the services in the group can achieve different quality of security. Security services from a number of groups can be combined to deliver better quality of security. In this study, we seamlessly integrate the group-based security model with a traditional real-time scheduling algorithm, namely earliest deadline first (EDF). Moreover, we design and develop a security-aware EDF schedulability test. Given a set of real-time tasks with chosen security services, our scheduling scheme aims at optimizing the combined security value of the selected services while guaranteeing the schedulability of the real-time tasks. We study two approaches to solve the security-aware optimization problem. Experimental results show that the combined security values are substantially higher than those achieved by alternatives for real-time tasks without violating real-time constraints.

I. Introduction

Recently there have been some efforts devoted to the development of real-time applications with security requirements. Security requirements in many real-time applications (see, for example, [25] and [27]) must be met in addition to satisfying timing constraints of the real-time applications. Examples of security sensitive real-time applications include online transaction processing systems [18], medical electronics [30], radar for tracking missiles [17], and aircraft control [9]. Sensitive data and processing in a variety of real-time systems must be protected against unauthorized accesses. For example, a radar tracking and processing system needs to read the images from the tracking subsystem periodically and send the tracking commands and directions to the tracking subsystem. In a railway signaling system, a train needs to communicate with the control center about its position, speed and the control center sends commands to the train of which track to follow and sets the train's speed if necessary. Such real-time applications require high quality of security to guarantee the messages between the subsystems not being read or altered by malicious users, and to guarantee the user really be whom he or she claims to be.