A vulnerability that allows eavesdroppers to extract the code from the waveform of the noiselike encoded signal of an isolated user in a standard time-spreading optical code division multiple access communication system using bipolar phase code is experimentally demonstrated. The principle is based on fine structure in the encoded signal. Each dip in the waveform corresponds to a transition of the bipolar code. Eavesdroppers can get the code by analyzing the chip numbers between any two transitions; then a decoder identical to the legal user’s can be fabricated, and they can get the properly decoded signal.
© 2010 Optical Society of America
Fiber Optics and Optical Communications
Original Manuscript: September 15, 2009
Revised Manuscript: December 3, 2009
Manuscript Accepted: December 3, 2009
Published: January 15, 2010
Zhijian Si, Feifei Yin, Ming Xin, Hongwei Chen, Minghua Chen, and Shizhong Xie, "Code extraction from encoded signal in time-spreading optical code division multiple access," Opt. Lett. 35, 229-231 (2010)