# A New Cyber-Secure Countermeasure for LTI systems under DoS attacks

## TL;DR

This paper introduces a cyber-secure control strategy for LTI systems under DoS attacks, combining sparse LQR design, message rerouting, and structured H2 control to maintain system stability and performance.

## Contribution

It proposes a novel countermeasure integrating message rerouting and structured H2 control to enhance cyber-security in LTI systems against DoS attacks.

## Key findings

- The rerouting strategy effectively mitigates the impact of link attacks.
- Structured H2 control maintains optimal feedback gains post-attack.
- Simulations demonstrate improved system resilience under cyber-attacks.

## Abstract

This paper presents a new counter-measure to mitigate denial-of-service cyber-attacks in linear time-invariant (LTI) systems. We first design a sparse linear quadratic regulator (LQR) optimal controller for a given LTI plant and evaluate the priority of the feedback communication links in terms of the loss of closed-loop performance when the corresponding block of the feedback gain matrix is removed. An attacker may know about this priority ordering, and thereby attack the links with the highest priority. To prevent this, we present a message rerouting strategy by which the states that are scheduled to be transmitted through the high priority links can be rerouted through lower priority ones in case the former get attacked. Since the attacked link is not available for service, and the states of the low priority links can no longer be accommodated either, we run a structured $\mathcal{H}_2$ control algorithm to determine the post-attack optimal feedback gains. We illustrate various aspects of the proposed algorithms by simulations.