Physical-Layer Authentication

Authentication is the process where claims of identity are verified. Most mechanisms of authentication (e.g., digital signatures and certificates) exist above the physical layer, though some (e.g., spread-spectrum communications) exist at the physical layer often with an additional cost in bandwidth. This paper introduces a general analysis and design framework for authentication at the physical layer where the authentication information is transmitted concurrently with the data. By superimposing a carefully designed secret modulation on the waveforms, authentication is added to the signal without requiring additional bandwidth, as do spread-spectrum methods. The authentication is designed to be stealthy to the uninformed user, robust to interference, and secure for identity verification. The tradeoffs between these three goals are identified and analyzed in block fading channels. The use of the authentication for channel estimation is also considered, and an improved bit-error rate is demonstrated for time-varying channels. Finally, simulation results are given that demonstrate the potential application of this authentication technique.

I. Introduction

The concept of security encapsulates a set of ideas that includes authentication, integrity, and secrecy. This paper focuses on the authentication aspect of security; namely, can a node be identified solely by its transmission characteristics? We show that the answer is yes, subject to specifically identified tradeoffs in the stealth, robustness, and security of the system. For an authentication system, the uniqueness and nonreproducibility of the identification signal are of the utmost importance.