Wireless One-time PAD : A Practical Method to Achieve Perfect Secrecy

In this thesis, a new practical method to realize one-time pad perfect secrecy for wireless communication is presented. Most commonly used security methods are based on cryp- tographic techniques employed at the upper layers of a wireless network. These methods basically rely on the computational hardness of some mathematical problems. This com- putational complexity is vulnerable in nature due to fast-growing computational power of hardware technology, yet not taking into account the revolution of Quantum computing in further future. Another core problematic issue exists in symmetric security systems; there is a deadlock between securing the channel and establishing the shared key. We need the key for securing the channel, on the other hand, for sharing the key we need a secure channel. To address such vulnerabilities, Physical Layer Security (PLS) has been widely studied in recent years. PLS schemes build on the idea of turning unpredictable and random wire- less channel characteristics into a source for information-theoretic security. Information- theoretic security itself, relies on Shannon’s pioneer work . Shannon, inspired by one-time pad, also known as Vernam cipher, theoretically showed that the only unconditional per- fect secrecy system is a one-time pad with a key at least as random as the plaintext, i.e., a system that uses a different random key to cipher any new plaintext. In PLS key genera- tion methods, legitimate parties alternately send probe signals and estimate Channel State Information (CSI) of common random channel and then convert enough amount of these estimates to secure shared keys. To achieve perfect secrecy, the key generation methods must meet the key randomness and Key Generation Rate (KGR) requirements of their specific cryptographic applications. In this research a new practical system for achieving unconditional perfect secrecy is presented. Our system uses channel phase as the probing parameter to fully benefit from its uniform distribution over [0, 2π]. It also uses an encryption method based on modulo- 2π addition of phase values which is the perfect counterpart of XOR addition in binary one-time pad. Moreover, by intentionally perturbing the wireless channel in vicinity of the transceiver antenna based on RF-mirrors structure, it produces different random phase values in each channel probing, much faster than the inherent channel variation would do, resulting in dramatically higher KGR than any wide-band PLS scheme presented so far and realizing true perfect secrecy. Most importantly, the focus of this research is a detailed practical algorithm for implementing the system as well as empirical results which makes our system the first channel-phase-based PLS scheme implementation, reported so far