Chapter 4 · RKD (Radio-signal Key Distribution)
The RKD chapter examines how cryptographic keys can be derived from reciprocal wireless channel measurements rather than from photons or transported media. It explains that both communication partners measure properties such as RSSI, phase, or timing over a bidirectional radio link and convert similar fluctuating measurements into shared key bits.
The chapter identifies the core physical conditions for RKD: randomness in the channel, reciprocity between the two legitimate endpoints, and spatial decorrelation that prevents an attacker from reproducing the same measurements from another location. It also outlines the practical workflow from channel probing and synchronization to bit extraction and postprocessing.
RKD’s practical evaluation is mixed but distinctive. The technology is praised for low complexity, low cost, and excellent suitability for mobile devices, vehicles, drones, and moving IoT systems. At the same time, it suffers from very low key rates, short effective distances, and the absence of mature large-scale infrastructure for multi-party distribution. The chapter also discusses passive and active man-in-the-middle risks, authentication, integrity, and protection mechanisms.
- Builds keys from reciprocal radio-channel measurements
- Offers low-cost and mobile-friendly deployment
- Depends on channel dynamics and synchronization
- Provides low key rates and limited range
- Requires robust protection against MITM attacks