  Stealthy sensor injection attacks are serious threats for industrial plants
as they can compromise the plant's integrity without being detected by
traditional fault detectors. In this manuscript, we study the possibility of
revealing the presence of such attacks by monitoring only the control input.
This approach consists in computing an ellipsoidal bound of the input reachable
set. When the control input does not belong to this set, this means that a
stealthy sensor injection attack is driving the plant to critical states. The
problem of finding this ellipsoidal bound is posed as a convex optimization
problem (convex cost with Linear Matrix Inequalities constraints). Our
monitoring approach is tested in simulation.
