Masked signal communication between two chaotic lasers, described by rate equations, was implemented using analog circuits. Digital modulation of the gain parameter in the master circuit generated the messages. It is shown that there is a level of modulation for which the receiver circuit decodes the signal by on-off synchronization while the Poincare´ sections, the first return maps and the time of return maps recovered directly from the master signal could not distinguish the bits. The circuits simulate the dynamics of two optically coupledCO2lasers with intracavity saturable absorber. The signal appears to be unbreakable in such low dimensional systems because they operate at homoclinic chaos which corresponds to multibranched one-dimensional return maps. ©1997 American Institute of Physics.