  Secrecy encoding for remote state estimation in the presence of adversarial
eavesdroppers is a well studied problem. Typical existing secrecy encoding
schemes rely on the transmitter's knowledge of the remote estimator's current
performance. This performance measure is often shared via packet receipt
acknowledgments. However, in practical situations the acknowledgment channel
may be susceptible to interference from an active adversary, resulting in the
secrecy encoding scheme failing. Aiming to achieve a reliable state estimate
for a legitimate estimator while ensuring secrecy, we propose a secrecy
encoding scheme without the need for packet receipt acknowledgments. Our
encoding scheme uses a pre-arranged scheduling sequence established at the
transmitter and legitimate receiver. We transmit a packet containing either the
state measurement or encoded information for the legitimate user. The encoding
makes the packet appear to be the state but is designed to damage an
eavesdropper's estimate. The pre-arranged scheduling sequence and encoding is
chosen psuedo-random. We analyze the performance of our encoding scheme against
a class of eavesdropper, and show conditions to force the eavesdropper to have
an unbounded estimation performance. Further, we provide a numerical
illustration and apply our encoding scheme to an application in power systems.
