  We study the problem of remote state estimation in the presence of a passive
eavesdropper, under the challenging network environment of no packet receipt
acknowledgments. A remote legitimate user estimates the state of a linear plant
from the state information received from a sensor via an insecure and
unreliable network. The transmission from the sensor may be intercepted by the
eavesdropper. To maintain state confidentiality, we propose an encoding scheme.
Our scheme transmits noise based on a pseudo-random indicator, pre-arranged at
the legitimate user and sensor. The transmission of noise harms the
eavesdropper's performance, more than that of the legitimate user. Using the
proposed encoding scheme, we impair the eavesdropper's expected estimation
performance, whilst minimising expected performance degradation at the
legitimate user. We explore the trade-off between state confidentiality and
legitimate user performance degradation.
