A Hybrid Information Reconciliation Method for Physical Layer Key Generation

Abstract

Physical layer key generation (PKG) has become a research focus as it solves the key distribution problem, which is difficult in traditional cryptographic mechanisms. Information reconciliation is a critical process in PKG to obtain symmetric keys. Various reconciliation schemes have been proposed, including the error detection protocol-based approach (EDPA) and error correction code-based approach (ECCA). Both EDPA and ECCA have advantages and drawbacks, regarding information leakage, interaction delay, and computation complexity. In this paper, we choose the BBBSS protocol from EDPA and BCH code from ECCA as a case study, analyzing their comprehensive efficiency performance versus pass number and bit disagreement ratio (BDR), respectively. Next, we integrate the strength of the two to design a new hybrid information reconciliation protocol (HIRP). The design of HIRP consists of three main phases, i.e., training, table lookup, and testing. To comprehensively evaluate the reconciliation schemes, we propose a novel efficiency metric to achieve a balance of corrected bits, information leakage, time delay, and computation time, which represents the effectively corrected bits per unit time. The simulation results show that our proposed method outperforms other reconciliation schemes to improve the comprehensive reconciliation efficiency. The average improvement in efficiency is 2.48 and 22.36 times over the BBBSS and BCH code, respectively, when the range of the BDR is from 0.5% to 11.5%. Compared to the BBBSS protocol and the BCH code, HIRP lies at a mid-level in terms of information leakage and computation time cost. Besides, with the lowest time delay cost, HIRP reaches the highest reconciliation efficiency. Entropy 2019, 21, 688 2 of 17Recently, physical layer key generation (PKG) has been emerging as a supplement to the upper layer key distribution method [2]. The underlying idea of it lies in the use of channel reciprocity and the uncertainty of multipath characteristics to encrypt the transmitted information in order to solve the problem of symmetric secret key distribution [3,4]. Besides, the spatial variation prevents eavesdroppers from observing the same randomness as legitimate users, for a sufficiently large distance between them.Although the uplink and downlink channels are reciprocal, measurements of radio channels are not the same, due to the differences originating from additive noise, transceiver hardware, and time delay in time division duplex (TDD) systems [5]. However, the objective of PKG is to generate a pair of strict identical symmetric keys. Even one bit of difference would lead to decryption failure due to the avalanche effect. To address this issue, information reconciliation is exploited to detect and correct errors in the preliminary key material between the two communicating parties [6].Several information reconciliation approaches have been proposed in previous work. Generally, these approaches can be classified into two categories, i.e., error detection protocol-based approaches (EDPAs...

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