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IEEE Transactions on Communications

Secret-Key Generation: Full-Duplex Versus Half-Duplex Probing

Hendrik Vogt, Zohaib Hassan Awan, Aydin Sezgin

Published Sep 5, 2018• 19 citations
Publisher

Abstract

A secret-key agreement for in-band full-duplex (FD) technology can be regarded as a valuable method for establishing security at the physical layer level. In this paper, we study an FD system model in conjunction with a secret-key agreement. The legitimate users interact through two-way channel probing and one-way reconciliation. We first introduce two complementary key generation models for FD and half-duplex (HD) settings, and compare their performances by introducing the key-reconciliation function. Furthermore, we study the impact of probing-reconciliation tradeoff and the role of a strong eavesdropper, and analyze the system performance in the high-signal-to-noise ratio regime. We show that under certain conditions, the FD mode negatively affects the capabilities of the eavesdropper and offers several advantages in terms of secret-key rate over the conventional HD setups. Our analysis reveals that the perfect self-interference cancellation is not necessary to obtain performance gains over the HD mode.

DOI
10.1109/tcomm.2018.2868714

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A secret-key agreement for in-band full-duplex (FD) technology can be regarded as a valuable method for establishing security at the physical layer level. In this paper, we study an FD system model in conjunction with a secret-key agreement. The legitimate users interact through two-way channel probing and one-way reconciliation. We first introduce two complementary key generation models for FD and half-duplex (HD) settings, and compare their performances by introducing the key-reconciliation function. Furthermore, we study the impact of probing-reconciliation tradeoff and the role of a strong eavesdropper, and analyze the system performance in the high-signal-to-noise ratio regime. We show that under certain conditions, the FD mode negatively affects the capabilities of the eavesdropper and offers several advantages in terms of secret-key rate over the conventional HD setups. Our analysis reveals that the perfect self-interference cancellation is not necessary to obtain performance gains over the HD mode.
Secret-key agreement from reciprocal wireless channels has been considered a valuable supplement for security at the physical-layer. On the one hand, full-duplex (FD) communication is regarded as one of the key technologies in future 5G systems. On the other hand, the success of 5G depends, among other things, on the ability to allow for secure communication. However, most key agreement models are based on half-duplex (HD) setups. Therefore, in this work, we propose representations of key generation models in both HD and FD modes. We analyze the performance of FD vs. HD modes by utilizing the key-communication function of secret-key agreement. It turns out that, for the application of key agreement, the FD approach enables advantages over the conventional HD setups. In particular, we derive a condition that guarantees improved performance of FD over HD mode in the high SNR regime.
In this paper, the impact of in-band full-duplex (IBFD) wireless communications on secret key generation via physical layer channel state information is investigated. A key generation strategy for IBFD wireless devices to increase the rate of generated secret keys over multipath fading channels is proposed. Conventionally, due to the half-duplex (HD) constraint on wireless transmissions, sensing simultaneous reciprocal channel measurements is not possible, which leads to a degraded key generation rate. However, with the advent of IBFD wireless devices, the legitimate nodes can sense the shared wireless link simultaneously at the possible cost of a self-interference (SI) channel estimation and some residual self-interference (RSI). As we demonstrate, with HD correlated observations the key rate is upper bounded by a constant, while with IBFD the key rate is only limited by the SI cancellation performance and is in general greater than that of its HD counterpart. Our analysis shows that with reasonable levels of SI cancellation, in the high SNR regime the key rate of IBFD is much higher, while in low SNRs, the HD system performs better. Finally, the key rate loss due to the overhead imposed by the SI channel estimation phase is discussed.
In the upcoming Internet of Things (IoT), encryption of confidential data by secret keys is vital. Secret-key generation from reciprocal wireless channels has received much attention in the research community in recent time. However, most implementations were restricted to half-duplex channel probing only. Communication setups with full-duplex (FD) capability enable new prospects for secret-key generation, since the inherent superposition of FD signals renders the acquisition of secret information more difficult for an eavesdropper. In this work, we demonstrate a practical testbed with FD capability in order to evaluate its advantages for secret-key agreement. We quantify the performance by computing correlation coefficients and mutual information of all channel estimates. Our work provides new insights into the opportunity of downgrading the capabilities of eavesdroppers by using full-duplex nodes.
This paper presents a random pilot full-duplex (FD) secret key generation scheme designed to enhance security in static wireless environments. In these environments, where inherent channel randomness is limited, efficiently extracting secret keys poses a significant challenge. The proposed scheme leverages the benefits of both FD operation and random pilot transmission to overcome this limitation and enhance the physical layer security. In this scheme, one of the FD nodes transmits random pilot signals, unknown to the eavesdropper, during the channel probing phase to artificially increase the shared randomness between the legitimate communicating nodes. By considering correlated eavesdropping, we derive the lower and upper bounds for the achievable secret key rate (SKR). The results reveal that the proposed FD scheme outperforms the HD scheme even in the presence of residual SI. Furthermore, the secret key rate can be improved by better SIC channel estimation and lower eavesdropper channel correlation.
Full duplex (FD) communication promises significant performance gains under ideal network settings. Generally, it has been shown that the throughput and delay gains of FD communication are somewhat limited in realistic conditions, leading researchers to study other possible applications where significantly higher gains over half duplex communication can be availed. The potential of FD nodes in improving the physical layer security of a communication link is investigated in this contribution. Specifically, we present a thorough analysis of the achievable secrecy rate for a transceiver pair in FD mode in the presence of a passive eavesdropper assuming a generic system model. The ergodic secrecy rate with FD communication is found to grow linearly with the log of the direct channel signal to noise ratio as opposed to the flattened out secrecy rate with conventional half duplex communication and irrespective of the eavesdropper channel strengths.
Physical layer-based secret key generation (PHY-SKG) schemes have attracted significant attention in recent years due to their lightweight implementation and ability to achieve information-theoretical security. In this paper, we study a channel frequency response (CFR)-based SKG scheme for in-band full-duplex (IBFD)-multi-input and multi-output (MIMO) systems. We formulate the intrinsic practical imperfections and derive their effects on the probing errors. Then we derive closed-form expressions for the secret key capacity (SKC) in the presence of a passive eavesdropper accordingly. We analyze the asymptotic behavior of the SKC in the high-SNR regime and reveal the fundamental limits for IBFD and HD probing. Based on the asymptotic SKC, we investigate the conditions under which IBFD can outperform HD. Numerical results illustrate that effective analog self-interference cancellation (ASIC) depth is the basis for IBFD probing to gain benefits over HD. Finally, we analyze the properties of the collected samples of the CFR-based SKG scheme and propose an averaging pre-processing and a segmental quantization, which reduce the key disagreement rate and remove the effects of large-scale fading to guarantee randomness. 3GPP specification-based simulations and the National Institute of Standards and Technology (NIST) test suite verify the theoretical analysis and the effectiveness of the proposed SKG scheme.