27 April 2010 Breaking on/off phase-shift keying in optical chaos-based cryptosystems
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Optical chaos-based cryptosystems hide an information-bearing message within the chaotic dynamics of a laser system. On-off phase-shift keying (OOPSK) is considered to be a particularly efficient encryption technique. It is based on the modulation of the feedback phase of a chaotic external-cavity emitter laser at the rhythm of a digital message. At the receiving end, message values are decrypted by observing the synchronization and de-synchronization of an external-cavity receiver which has a constant feedback phase. This cryptosystem is popular because so far it has been thought to be impossible to find the message by analyzing the chaotic optical field transmitted from the emitter to the receiver laser, thus, it is hitherto thought, providing high security. We demonstrate that the phase modulation produces a displacement of the chaotic attractor which is detectable by analyzing low-dimensional projections or sections of the high-dimensional attractor. This leads to the successful decryption of the message value based on an analysis of the chaotic optical field sent to the receiver only. We show that the bit-error-rate (BER) of the decrypted message varies with the modulation depth and speed. Though small depths and large bit rates lead to an increase of the BER, we find it possible to extract the message for most operating conditions of an on/off phase- shift keying-based cryptosystem.
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J. Winebarger, J. Winebarger, A. Locquet, A. Locquet, D. S. Citrin, D. S. Citrin, } "Breaking on/off phase-shift keying in optical chaos-based cryptosystems", Proc. SPIE 7720, Semiconductor Lasers and Laser Dynamics IV, 772025 (27 April 2010); doi: 10.1117/12.854533; https://doi.org/10.1117/12.854533

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