Time delay identification in chaotic cryptosystems ruled by delay-differential equations

Feedback circuits ruled by time-delayed differential equations (DDE) call be used as the emitters in optical and electronic chaos-based secure communications. The degree of security of communications is limited by the possibility of recovering the parameters of the chaos-generating emitter. We analyze several methods for recovering the time delays ill modified DDE systems with two feedbacks. With increasing gain factor of the feedbacks it becomes difficult or even impossible to recover the time delay of the modified circuit. (c) 2005 Optical Society of America.