A Novel Secret Key Generation Scheme in the Presence of an Untrusted Relay

Document Type : Original Article

Authors

1 Assistant Professor at Department of Communication and Electrical Engineering, Qom University of Technology.

2 Assistant Professor, Communication and Information Technology Research Institute, Tehran, Iran

Abstract

Compared to conventional cryptography methods, physical layer secret key generation (SKG) is more efficient and suitable for sixth-generation (6G) networks due to features such as lightweight and scalability. In the field of SKG, schemes based on local random generators are used for high-rate key generation. One of these schemes is random phase injection, where the channel probing signals with random phase are exchanged between communication parties (Alice and Bob). In this research work, an SKG scheme is presented in the presence of an untrusted relay, where the relay cannot obtain the key. In order to make the scheme practical, for the first time, the channel probing signals are considered discrete random phase, and a single-bit quantizer is used in reception. In addition, in order to reduce the key error rate, quantization with guard bands (GB) is used for key extraction. For such a scenario, we provide expressions for the key matching rate, key mismatch rate (KMR), and key discarding rate (KDR) per channel probe. Although increasing the GB range decreases the KMR metric, the key length also shortens. In order to evaluate the effect of GB on the efficiency of the proposed key generation scheme, the raw key generation rate is defined and calculated. In the simulation section, we provide useful engineering insights into determining the probing signal power, the GB size as well as the required coding correction capability. We also discuss the security evaluation of the proposed scheme in this article. While calculating the secret key capacity, we will see that the untrusted relay and external eavesdropper cannot discover the key by intercepting the channel probing steps.

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History

  • Receive Date: 28 July 2024
  • Revise Date: 14 September 2024
  • Accept Date: 14 October 2024
  • Publish Date: 22 October 2024

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