Transmission Systems

• Physical-layer Security: We are currently concentrating on the key generation for frequency-division duplexing systems, and are possibly the first group to realize that despite the use of different frequency ranges for both directions, still, there is a reciprocity in the channel properties. This is due to the fact that the paths between two users trying to communicate are essentially the same. We have shown that phase differences between received signals arriving at two antennas can directly be used to generate cryptographic keys. We are currently extending the work to key distribution for multiple users or devices. We have also used power-line connections that provide reciprocity to generate new keys. However, to generate new keys all the time, we showed that one would have to randomly change the channel, which is not possible for power lines as the channel is within cables laid out in walls, ceilings, and floors of buildings. Randomisation is however possible by, for example, changing one end randomly at unused wires of the three-wire power-line system. This leads to sufficient modifications and the required common randomness for physical-layer key generation. Such common randomness in physical-layer key generation can be harvested very cheaply compared to quantum key generation, which is essentially based on the same principle. 
• Channel coding: We incorporated other aspects of communications into the decoding of LDPC codes, one of the major modern coding schemes. This means integrating source coding, equalization, and the treatment of non-stationary impulse noise by dedicated adaptation or integrating into the underlying code graph. 
• DNA analysis: By regarding mutations as a communication channel and applying typical tools from information theory, coding, and machine learning, we were able to formally derive the very irregular mapping between base triplets (codons) and amino acids. Additionally, we directly related chemical relations between amino acids to the probability of mutations transferring one into the other. Furthermore, using parameters from information theory and probability theory, we determined which genes are essential for an organism’s survival. 
• TEMPEST: We also work to detect and understand compromising radiation that is emitted by, for example, circuitry. We are developing methods to make use of radio-frequency emissions of circuitry to first determine points of strong and usable egress and furthermore, determine the type of signal causing the emissions. We are also working to localize special function components, such as synchronization headers. In the end, we hope to possibly synchronize the signal and detect the underlying data. Furthermore, we are also working on countermeasures, like intentional jamming that could make it difficult or impossible to detect such signals.

• We have registered four patents in physical-layer key generation.
• Werner Henkel was invited to give one of the opening talks of an National Science Foundation workshop in the United States, which was set up to investigate joint projects between genetics and engineering in the US. 
• TEMPEST activities are part of a publicly funded project in cooperation with another university and a company. 
• Among other conferences, Werner Henkel is constantly invited as a TPC member of the security-related sessions of IEEE ICC and Globecom. After having assisted in organizing the ISTC coding conference, he has continuously served in the TPC.

In 2019-2022, the group comprised three to five PhD students and research associates, funded through four different DFG projects and a BMWifunded collaborative project.

• W. Henkel, A. Turjman, H. Y. Kim, and H. Qanadilo, “Common Randomness for Physical-Layer Key Generation in Power-Line Transmission,” IEEE ICC 2020 (CISS), Dublin, Ireland, 2020. 
• W. Henkel, H. Y. Kim, A. Turjman, and M. Bode, “A Simple Physical-Layer Key Generation Scheme for Power-Line Transmission,” IEEE ISPLC, Aachen (hybrid), Germany, October 26-27, 2021. 
• W. Henkel and M. Namachanja, “A Simple Physical-Layer Key Generation Scheme for FrequencyDivision Duplexing,” ICSPCS, online, December 13-15, 2021. 
• E. O. Torshizi, U. Uprety, and W. Henkel, “Highly Efficient FDD Secret Key Generation using ESPRIT and Jump Removal on Phase Differences,” IEEE CNS (CPS), Austin, TX, USA (hybrid), October 5, 2022. 
• E. O. Torshizi and W. Henkel, “Reciprocity and Secret Key Generation for FDD Systems using NonLinear Quantization,” IEEE Globecom, 7th IEEE Wireless-Sec workshop, Rio de Janeiro, Brazil (hybrid), December 4-8, 2022.