Profiling the Strength of Physical-Layer Security: A Study in Orthogonal Blinding

Yao Zheng, Matthias Schulz, Wenjing Lou, Y. Thomas Hou, Matthias Hollick

Physical layer security for wireless communication is broadly considered as a promising approach to protect data confidentiality against eavesdroppers. However, despite its ample theoretical foundation, the transition to practical implementations of physical-layer security still lacks success. A close inspection of proven vulnerable physical-layer security designs reveals that the flaws are usually overlooked when the scheme is only evaluated against an inferior, single-antenna eavesdropper. Meanwhile, the attacks exposing vulnerabilities often lack theoretical justification. To reduce the gap between theory and practice, we posit that a physical-layer security scheme must be studied under multiple adversarial models to fully grasp its security strength. In this regard, we evaluate a specific physical-layer security scheme, i.e. orthogonal blinding, under multiple eavesdropper settings. We further propose a practical “ciphertext-only attack” that allows eavesdroppers to recover the original message by exploiting the low entropy fields in wireless packets. By means of simulation, we are able to reduce the symbol error rate (SER) at an eavesdropper below 1% using only the eavesdropper’s receiving data and a general knowledge about the format of the wireless packets.

This paper looks at the orthogonal blinding technique: a physical layer security approach in which the transmitter sends information directed to the receiver (using beamforming) and sends noise toward the eavesdropper (in the case of known CSI) or in the null space of the receiver (in the case of unknown CSI). Authors discuss the security of orthogonal blinding in a multi-antenna eavesdropper scenario with security evaluations based on the number of the antennas. The paper categorizes the security based on the availability of the eavesdropper CSI (i.e., Honest/Dishonest Eve) and the number of antennas (i.e., Inferior/Superior Eve). Next, the paper focuses on the ciphertext-only attacks and proposes an algorithm, which uses the low-entropy parts of the packets to attack the aforementioned method. The algorithm is implemented in MATLAB.

The reviewers appreciated the topic, noting the importance of making physical layer approaches practical. They also found the paper well-structured and interesting to read, making use of intuitive discussions in many parts. Furthermore, the reveiwers appreciated the MATLAB implementation of the attack algorithm. However, the reviewers felt that the technical contribution of the paper could be strengthened. For example, the security level categorization uses known techniques and the success of the proposed attack algorithm does not have a proof.