  The idea of secure communication of digital signals via chaos synchronization
has been plagued by the possibility of attractor reconstruction by
eavesdroppers as pointed out by Perez and Cerdeira. In this Letter, we wish to
present a very simple mechanism by which this problem can be overcome, wherein
the signal is transmitted via a multistep parameter modulation combined with
alternative driving of different transmitter variables, which makes the
attractor reconstruction impossible. The method is illustrated by means of the
Lorenz system and Chua's circuit as examples.

Chaotic Dynamics