Most secret key generation (SKG) methods need channel estimation and provide insufficient performance especially in time division duplex single input single output (TDD-SISO) system and quasi-static channel scenario. This paper proposed a two-way SKG method which can completely avoid channel estimation and achieve higher SKG rate (SKGR). Firstly, the legitimate users mutually send their own random signal via the reciprocal channel. Then, the multiplication of local random signal and the received signal can be used as common randomness to generate keys. The theoretical and practical SKGRs of the three methods, namely wireless channel based, one-way randomness and two-way randomness, are derived and compared. Simulation and estimation results show that the proposed TW method acquires a better performance not only in theory but also in practice, and the practical SKGR of TW method is time-linear which provides a feasible scheme to significantly improve the SKGR for quasi-static channel scenario.
Most secret key generation (SKG) methods need channel estimation and provide insufficient performance especially in time division duplex single input single output (TDD-SISO) system and quasi-static channel scenario. This paper proposed a two-way SKG method which can completely avoid channel estimation and achieve higher SKG rate (SKGR). Firstly, the legitimate users mutually send their own random signal via the reciprocal channel. Then, the multiplication of local random signal and the received signal can be used as common randomness to generate keys. The theoretical and practical SKGRs of the three methods, namely wireless channel based, one-way randomness and two-way randomness, are derived and compared. Simulation and estimation results show that the proposed TW method acquires a better performance not only in theory but also in practice, and the practical SKGR of TW method is time-linear which provides a feasible scheme to significantly improve the SKGR for quasi-static channel scenario.
A novel secret key generation (SKG) method based on two-way randomness is proposed for TDD-SISO system. The legitimate transceivers mutually transmit their own random signal via reciprocal wireless channel, then the multiplication of transmitted and received signal is used as common randomness to generate secret keys. In quasi-static channel, the theoretical SKG rates (SKGRs) of the three SKG methods, namely wireless channel based, one-way randomness and two-way randomness, are derived and compared. Further, two practical SKG schemes based on two-way randomness, Scheme-1bit and Scheme-3bit, are completely designed and simulated. Generally, Scheme-1bit applies to low signal to noise ratio (SNR) scenarios and achieves 0.13~0.86bit/TsSKGR and 10-2~10-5level secret key outage probability (SKOP), while Scheme-3bit fits high SNR situation and obtains 0.93~1.35bit/TsSKGR and 10-3~10-4level SKOP. At last, the national institute of standards and technology (NIST) test is conducted to evaluate the secret key randomness (SKRD) and the test results show that both of the proposed schemes have passed the test.
The secret key generation rate (SKGR) of current physical layer security methods is not high enough for practical requirements. A novel SKG method based on the cross multiplication (XM) of two-way random signals is proposed for TDD-MIMO system. The principle concealed beneath the XM method is found that the XM operation not only derives the common random source for both legitimate partners, but also employs new generated cross-terms due to bilinear operation to provide more measurements of the random source and more secret keys accordingly, which is essentially superior to the existing paired multiplication (PM) method. Then, the theoretical SKGR of two-way random signals is analyzed and it is validated that SKGR is determined by the randomness of the reciprocal channel and the two-way secure transmission rates collectively. Furthermore, SKGR of XM and PM methods are derived in closed-form respectively under infinite antenna condition and the former shows a linear increase with the channel coherence interval, which are also approximately valid for finite antenna. The innovative conclusion means the slow-changing property of some channel environments can be further exploited and the proposed XM method can be applied to solve the low SKGR problem in static or quasi-static channel environment such as IoT. Finally, the simulations verify the theoretical results and show that the XM method achieves several orders of magnitude higher SKGR than the PM method.
Secret key generation (SKG) is a promising solution to the problem of wireless communications security. As the first step of SKG, channel probing affects it significantly. Although there have been some probing schemes, there is a lack of research on the optimization of the probing process. This study investigates how to optimize correlated parameters to maximize the SKG rate (SKGR) in the time-division duplex (TDD) mode. First, we build a probing model which includes the effects of transmitting power, the probing period, and the dimension of sample vectors. Based on the model, the analytical expression of the SKGR is given. Next, we formulate an optimization problem for maximizing the SKGR and give an algorithm to solve it. We conclude the SKGR monotonically increases as the transmitting power increases. Relevant mathematical proofs are given in this study. From the simulation results, increasing appropriately the probing period and the dimension of the sample vector could increase the SKGR dramatically compared to a yardstick, which indicates the importance of optimizing the parameters related to the channel probing phase.
Physical layer secret key generation exploits the reciprocal channel randomness for key generation and has proven to be an effective addition security layer in wireless communications. However, static or scarcely random channels require artificially induced dynamics to improve the secrecy performance, e.g., using intelligent reflecting surface (IRS). One key challenge is that the induced random phase from IRS is also reflected in the direction to eavesdroppers (Eve). This leakage enables Eve nodes to estimate the legitimate channels and secret key via a globally known pilot sequence. To mitigate the secret key leakage issue, we propose to exploit random matrix theory to inform the design of a new physical layer secret key generation (PL-SKG) algorithm. We prove that, when sending appropriate random Gaussian matrices, the singular values of Alice's and Bob's received signals follow a similar probability distribution. Leveraging these common singular values, we propose a random Gaussian matrix based PL-SKG (RGM PL-SKG), which avoids the usages of the globally known pilot and thereby prevents the aforementioned leakage issue. Our results show the following: (i) high noise resistance which leads to superior secret key rate (SKR) improvement (up to 300%) in low SNR regime, and (ii) general improved SKR performance against multiple colluded Eves. We believe our combination of random matrix theory and PL-SKG shows a new paradigm to secure the wireless communication channels.
Over the last decade, physical layer secret key generation (PHY-SKG) techniques that exploit reciprocity of wireless channels have attracted considerable interest among researchers in the field of wireless communication. Compared to traditional cryptographic methods, PHY-SKG techniques offer the following advantages: a computationally bounded adversary does not need to be assumed; PHY-SKG avoids the requirement of key management, and secret keys can be dynamically replenished. Additionally, PHY-SKG can enhance existing security schemes because it operates independently of higher layer security schemes. However, a key drawback of PHY-SKG is low secret key generation rate (SKGR), a critical performance metric. Therefore, the role of advanced network technologies (e.g., multiple input multiple output (MIMO) and cooperative MIMO) must be explored to enhance SKGR. This paper describes how MIMO and cooperative MIMO techniques can enhance SKGR.
One of the fundamental problems in cryptography is the generation of a common secret key between two legitimate parties to prevent eavesdropping. In this paper, we propose an information-theoretic secret key generation (SKG) method for time division duplexing (TDD)-based orthogonal frequency-division multiplexing (OFDM) systems over multipath fading channels. By exploring physical layer properties of the wireless medium, i.e., the reciprocity, randomness, and privacy features of the radio channel, an SKG method is proposed to maximize the number of secret bits given a target secret key disagreement ratio (SKDR). In the proposed SKG method, the phase information of the estimated channel state information (CSI) is distilled for SKG, and a special guard band (GB) scheme is designed to achieve the target SKDR with a small phase information loss. The proposed GB consists of both the amplitude GB (AGB) and phase GB (PGB), where the AGB is determined by the average signal-to-interference plus noise ratio (SINR), whereas the PGB adapts itself to the instantaneous SINR and thus incurs a smaller phase information loss in the higher SINR region. Analyses show that this GB scheme trades off a small loss of channel phase information for a better SKDR performance, and achieves a much larger number of quantization levels for a given SKDR due to the fact that the PGB decreases quickly as the SINR increases. Based on the performance analysis on the SKDR, the average secret key length, the phase information loss percentage (PILP), and the optimal GB and quantization level of the adaptive quantizor are derived for a given target SKDR. Both analytical and simulation results are presented to demonstrate the superiority of the proposed scheme for TDD-OFDM systems over frequency-selective fading channels.