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  The number of security incidents in recent years shows a considerable increase in cyber attacks. The targets of these attacks are diverse, but also increasingly safety-critical systems like airplanes or power plants fall victim to attackers. These attacks show that even embedded systems cannot be considered inaccessible to malevolent actors anymore. As a consequence, security has become a primary concern for embedded systems and thus also for real-time systems which are often deployed as embedded systems in a safety-critical environment. Real-time systems are not only constrained by limitations typical for embedded systems, like power or memory, but they must also fulfill timing constraints. Thus, any security measure employed on a real-time system must adhere to timing constraints. However, these constraints allow for new attack vectors targeting the timing of the system. For example, a single deadline miss in a hard real-time system can already threaten system safety and have catastrophic consequences for the system or its environment. This inherent vulnerability of real-time systems to attacks in the time domain poses new and real-time specific challenges to security. This thesis analyses threats to and vulnerabilities of real-time systems with a focus on time-triggered real-time systems. It shows how attackers may threaten fundamental system assumptions. The fault model of a system usually considers failures to be independent from each other, but an attacker violates this independence assumption when provoking failures. Moreover, an attacker may cause the system to reach a state that was not considered when worst case execution times were derived. As a consequence, these worst case execution time bounds may prove to be unsafe in a system under attack. Another vulnerability this thesis presents lies within a desirable system property itself. Time-triggered real-time systems provide deterministic scheduling behaviour. Deterministic behaviour is desirable for safety-critical systems as it allows for easy derivation of safe bounds on worst case execution time and simplifies system certification. However, the predictable schedules of time-triggered systems also ease attacks which exploit timing information for precisely timed attacks. In this thesis, we detail these threats, present attack vectors for single core as well as multicore time-triggered real-time systems and introduce mitigation strategies tailored to these systems. The mitigation strategies employ randomization to prevent precisely timed attacks while also guaranteeing that all tasks meet their deadlines. We implement our mitigation strategies on FreeRTOS and demonstrate their low runtime overheads and small memory requirements.

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