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Physical Layer Security Key Generation for Fiber Optic and Inter-Vehicular Optical Communication Link


Point to Point Optical Link (PPOL) and Inter Vehicular Visible Light Communications (IVVLC) as susceptible to many security threats including jamming, eavesdropping, interception and physical infrastructure attack. To address this problem, researchers have recently proposed to generate secret keys from the randomness of the physical environment such as wireless communication channel fading characteristics, phase fluctuation inside optical fiber and polarization mode dispersion in a long-haul network. In this thesis, I presented a novel symmetric physical layer based secret key generation schemes for both PPOL and IVVLC. Polarization Mode Dispersion (PMD) of long optical fiber links and intensity variations due to road surface roughness along with driving behavior are exploited as a random channel characteristic to generate cryptographic keys for PPOL and IVVLC, respectively. It has been demonstrated, modulation of a probe signal caused by PMD in a high speed PPOL (40Gb/s and 60Gb/s) is reciprocal with average Pearson correlation coefficient of 0.862, despite the presence of optical nonlinearities, dispersion, and noise in the system. 128-bit symmetric cryptographic key has been successfully generated using the proposed scheme. Moreover, PMD based encryption keys passed the National Institute of Standards and Technology (NIST) tests. It is proved through simulations of a 50km link that, with optimal key generation settings, symmetric keys can be generated with high randomness (high P-values for NIST randomness tests) and with sufficient generation rates (>50%). Furthermore, this key generation algorithm successfully generated, with extremely low error, high entropy, secret keys with lengths up to 128-bits using a 1kbps probe signal with the proposed scheme. It is also found that the vehicular visible light channels have high entropy (e.g., 12-14 bits for 5000 samples) and that separate channels are highly uncorrelated to one another (e.g., Pearson correlation coefficient of 0.32). These results prove that physical communication channel can be exploited to generate symmetric cryptographic keys.

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