  We study timely status updates of a real-time system in an adversarial
setting. The system samples a physical process, and sends the samples from the
source (e.g., a sensor) to the destination (e.g, a control center) through a
channel. For real-time monitoring/control tasks, it is crucial for the system
to update the status of the physical process "timely". We measure the
timeliness of status updates by the time elapsed since the latest update at the
destination was generated at the source, and define the time elapsed as age of
information, or age in short. To sabotage the system, an attacker aims to
maximize the age by jamming the channel and hence causing delay in status
updates. The system aims to minimize the age by judiciously choosing when to
sample and send the updates. We model the ongoing repeated interaction between
the attacker and the system as a dynamic game. In each stage game, the attacker
chooses the jamming time according to the jamming time distribution, and the
system responds by delaying the sampling according to the sampling policy. We
prove that there exists a unique stationary equilibrium in the game, and
provide a complete analytical characterization of the equilibrium. Our results
shed lights on how the attacker sabotages the system and how the system should
defend against the attacker.
