title: Code extraction from encoded signal in time-spreading optical code division multiple access.
abstract: 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.
authors.affiliation: State Key Laboratory on Integrated Optoelectronics, Tsinghua National Laboratory for Information,Science and Technology (TNList), Department of Electronic Engineering, Tsinghua University, Beijing 100084, China.
authors.forename: Zhijian
authors.initials: Z
authors.lastname: Si
authors.forename: Feifei
authors.initials: F
authors.lastname: Yin
authors.forename: Ming
authors.initials: M
authors.lastname: Xin
authors.forename: Hongwei
authors.initials: H
authors.lastname: Chen
authors.forename: Minghua
authors.initials: M
authors.lastname: Chen
authors.forename: Shizhong
authors.initials: S
authors.lastname: Xie