Securing Clock Synchronization in Industrial Heterogeneous Networks

Sammanfattning: Today, wireless solutions for industrial networks are becoming more and more appealing since they increase flexibility and enable the use of additional wireless sensors, but also bring such advantages as mobility and weight reduction. Wired networks, on the other hand, are reliable and, more importantly, already existing in most distributed control loops. Heterogeneous networks consisting of wireless as well as wired sub-networks are gaining attention as such networks combine the advantages of both approaches. However, wireless communication links are more vulnerable to security breaches because of their broadcast nature. For this reason, industrial heterogeneous networks require a new type of security solutions, since they have different system assets and security objectives. This thesis aims to secure industrial heterogeneous networks. Such networks have real-time requirements due to interaction with some physical process, and thus have a schedule with one or more deadlines for data delivery in order to comply with the timing requirements of the application. The necessity to follow the schedule implies that all network participants should share the same notion of time and be synchronized. This fact makes clock synchronization a fundamental asset for industrial networks. The first step towards developing a security framework for industrial heterogeneous networks with real-time requirements is therefore to investigate ways of breaching clock synchronization. Once the vulnerabilities of this asset have been identified, the next step is to propose solutions to detect malicious attacks and mitigate their influence. The thesis provides a vulnerability analysis of the asset synchronization based on the widely deployed IEEE 1588 standard, and identifies a possibility to break clock synchronization through a combination of a man-in-the-middle attack and a delay attack. This attack is appealing to an adversary as it can target any network requiring synchronization. Next, several mitigation techniques, such as a relaxed synchronization condition mode, delay bounding and using knowledge of existing environmental conditions, are identified, making the network more resilient against these kinds of attacks. Finally, a network monitor aiming to detect anomalies introduced by the adversary performing attacks targeting clock synchronization is proposed as a mean to detect the delay attack.