# Time Synchronization Attack and Countermeasure for Multi-System Scheduling in Remote Estimation

## TL;DR

This paper investigates time synchronization attacks on multi-system remote estimation, demonstrating how attackers can cause divergence in estimation error and proposing countermeasures to maintain system stability.

## Contribution

It introduces a novel attack strategy that exploits time offsets and develops shift-invariant policies as effective countermeasures.

## Key findings

- Attack can cause unbounded estimation error without system knowledge.
- Optimal attack minimizes sensor spoofing while maximizing error.
- Countermeasures improve system robustness against synchronization attacks.

## Abstract

We consider time synchronization attack against multi-system scheduling in a remote state estimation scenario where a number of sensors monitor different linear dynamical processes and schedule their transmissions through a shared collision channel. We show that by randomly injecting relative time offsets on the sensors, the malicious attacker is able to make the expected estimation error covariance of the overall system diverge without any system knowledge. For the case that the attacker has full system information, we propose an efficient algorithm to calculate the optimal attack, which spoofs the least number of sensors and leads to unbounded average estimation error covariance. To mitigate the attack consequence, we further propose a countermeasure by constructing shift invariant transmission policies and characterize the lower and upper bounds for system estimation performance. Simulation examples are provided to illustrate the obtained results.