We numerically show that chaos shift keying (CSK) encryption can be
achieved by using a single receiver, thus providing a better
performance when comparing with the traditional CSK scheme based on
two receivers. We analyze the rate equation model for two
unidirectionally coupled single-mode external-cavity semiconductor
lasers operating in a chaotic regime. The message is encoded in the
emitter by slightly varying its injection current. We find that under
appropriate conditions, the receiver laser synchronizes to the
chaotic emitter, filtering the encoded message and allowing message
extraction.