Physical Layer Cryptographic Key Generation by Exploiting PMD of an Optical Fiber Link

We present a symmetric physical layer based secret key generation scheme for Point-to-Point Optical Link (PPOL) communication by exploiting Polarization Mode Dispersion (PMD) as a random and inimitable channel characteristic. The randomness and security strength of generated cryptographic keys based on PMD is significantly high. In this paper, we present that random modulation of a probe signal caused by PMD in a high-speed data communication network (40 Gb/s and 60 Gb/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. We have shown through simulations with a 50 km 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, we considered an attack model of a noninvasive adversary intercepting at 10 km into the link and found that the generated keys have high average key bit mismatch rates (>40%).