Physical layer security (PLS) is seen as the means to enhance physical layer trustworthiness in 6G. This work provides a proof-of-concept for one of the most mature PLS technologies, i.e., secret key generation (SKG) from wireless fading coefficients during the channel’s coherence time. As opposed to other works, where only specific parts of the protocol are typically investigated, here, we implement the full SKG chain in four indoor experimental campaigns. In detail, we consider two legitimate nodes, who use the wireless channel to extract secret keys and a malicious node placed in the immediate vicinity of one of them, who acts as a passive eavesdropper. To estimate the final SKG rate we evaluate the conditional min-entropy by taking into account all information available at the eavesdropper. Finally, we use this paper to announce the first ever physical layer security challenge, mirroring practices in cryptography. We call the community to scrutinize the presented results and try to “break” our SKG implementation. To this end, we provide, i) the full dataset observed by the  eavesdroppers, ii) 20 blocks of 16−byte long ciphertexts, encrypted using one-time pad with 20 distilled secret keys, and, iii) all codes and software used in our SKG implementation. An attack will be considered successful if any part(s) of the plaintext are successfully retrieved.

The massive deployment of low-end wireless Internet of things (IoT) devices opens the challenge of finding de-centralized and lightweight alternatives for secret key distribution. A possible solution, coming from the physical layer, is the secret key generation (SKG) from channel state information (CSI) during the channel’s coherence time. This work acknowledges the fact that the CSI consists of  deterministic (predictable) and stochastic (unpredictable) components, loosely captured through the terms large-scale and small-scale fading, espectively. Hence, keys must be generated using only the random and unpredictable part. To detrend CSI measurements from deterministic components, a simple and lightweight approach based on Kalman filters is proposed and is evaluated using an implementation of the complete SKG protocol (including privacy amplification that is typically missing in many published works). In our study we use a massive multiple input multiple output (mMIMO) orthogonal frequency division multiplexing outdoor measured CSI dataset. The threat model assumes a passive eavesdropper in the vicinity (at 1 meter distance or less) from one of the legitimate nodes and the Kalman filter is parameterized to maximize the achievable key rate.

A large spectrum of technologies are collectively dubbed as physical layer security (PLS), ranging from wiretap coding, secret key generation (SKG), authentication using physical unclonable functions (PUFs), localization / RF fingerprinting, anomaly detection monitoring the physical layer (PHY) and hardware. Despite the fact that the fundamental limits of PLS have long been characterized, incorporating PLS in future wireless security standards requires further steps in terms of channel engineering and pre-processing. Reflecting upon the growing discussion in our community, in this critical review paper, we ask some important questions with respect to the key hurdles in the practical deployment of PLS in 6G, but also present some research directions and possible solutions, in particular our vision for context-aware 6G security that incorporates PLS.