Secure and robust symmetric key generation using physical layer techniques under various wireless environments

Due to the unavoidable shared nature of the wireless radio spectrum, providing security for wireless communications presents unique challenges. Cryptographic keys have been used as a primary technique for securing wireless networks but are not completely secure. The symmetric keys used for cryptographic purposes are vulnerable to man-in-the-middle and brute force attacks. More recently, PHY-layer based techniques have gained significant attention, where the principle of channel reciprocity and the natural randomness of the measured wireless channel to generate secret keys is leveraged. Although, PHY-layer secret key generation has been investigated and presented in the literature before, there has been a lack of discussion in terms of obtaining symmetric keys on both ends of the link. In this work, we present a novel PHY-layer secret key generation technique that aims for symmetric encryption keys while limiting the information leaked to an eavesdropper to ensure complete secrecy and to prevent potential intelligent attacks. Our algorithm utilizes forward and backward channel state information in a given wireless link and combats the minute differences observed in these pairs by generating channel trend information. We demonstrate our technique using experimental results from a realtime SDR testbed connected to a wireless channel emulator. Our results indicate that the algorithm is successful in generating symmetric keys under various wireless environments without revealing any information pertaining to the key via the open wireless channel. Our secret key extraction rate can reach values in excess of 17.3 Kbps.