  This paper investigates the security issue of the data replay attacks on the
control systems. The attacker is assumed to interfere with the control system
process in a steady-state case. The problem is presented as the standard way to
attack, which is storing measurements and replay ing them in further times to
the system. The controller is assumed to be the LQG controller. The main
novelty in this paper can be stated as proposing a different attack detection
criterion by using the K-L divergence method to cover more general control
system problems with these attacks and with higher-order dynamics. Also, there
exists a packet-dropout feature in transmitting the data as another
contribution of the paper. Formulations and numerical simulations prove the
effectiveness of the newly proposed attack detection procedure by having a
quick response to occurred attacks. Although, in previous approaches, the
trade-off between attack detection delay or LQG performance was significant, in
this approach it is proved that the difference in this trade-off is not
considered in early moments when the attack happens since the attack detection
rate is rapid and thus, these attacks can be stopped with defense strategies in
the first moments with the proposed attack detection criterion.
