The wireless radio communications channel between two legitimate user terminals has long been considered as a renewable source of shared secrecy. As characterization of the channel, the time-varying channel impulse response (CIR) is commonly used for this purpose due to its reciprocity and inherent difficulty in being captured by an adversary. While each terminal generates a secret key at its side, based on its own channel measurements combined with an independent noise component, mismatches may occur in the extracted information or in the obtained bit sequences after a sampling and quantization process. To mitigate such bit mismatches, we propose a method that utilizes the properties of the Golay code to correct or detect the bit mismatches for CIR-based secret key agreement. In our approach, the reconciliation information in the transmission is deliberately designed to hide the original shared information (perfect or imperfect). The correctness of our bit mismatch mitigation algorithm is thoroughly analyzed for all possible scenarios. In addition, the effectiveness of our algorithm is validated through simulations using MATLAB for generated CIR data, the results of which match our theoretical analysis. Our design is shown to be secure and optimal by security analysis and comparisons between our proposed algorithm and its variants. The comparisons with related techniques and the scenarios in which our design can benefit are also discussed.
The wireless radio communications channel between two legitimate user terminals has long been considered as a renewable source of shared secrecy. As characterization of the channel, the time-varying channel impulse response (CIR) is commonly used for this purpose due to its reciprocity and inherent difficulty in being captured by an adversary. While each terminal generates a secret key at its side, based on its own channel measurements combined with an independent noise component, mismatches may occur in the extracted information or in the obtained bit sequences after a sampling and quantization process. To mitigate such bit mismatches, we propose a method that utilizes the properties of the Golay code to correct or detect the bit mismatches for CIR-based secret key agreement. In our approach, the reconciliation information in the transmission is deliberately designed to hide the original shared information (perfect or imperfect). The correctness of our bit mismatch mitigation algorithm is thoroughly analyzed for all possible scenarios. In addition, the effectiveness of our algorithm is validated through simulations using MATLAB for generated CIR data, the results of which match our theoretical analysis. Our design is shown to be secure and optimal by security analysis and comparisons between our proposed algorithm and its variants. The comparisons with related techniques and the scenarios in which our design can benefit are also discussed.
The physical characteristics of wireless channels, in particular the channel impulse response (CIR), have become an attractive source of shared secrecy between two communicating parties for many wireless applications. However, ensuring high-entropy secret bits from the CIR may not be always feasible, including in IoT and/or indoor environments, where the coherence time may not be easy to obtain, or mobility is limited. Many techniques have been developed to resolve the above problems, including privacy amplification for higher entropy output, and pre-processing for data distillation. In this paper, we develop a framework for extracting entropy from sequentially arriving channel impulse response observation samples, and propose algorithms for both online and offline versions of the problem. We fully characterize the optimal solutions to these problems through a series of analytic results, and establish the optimality of our proposed online and offline algorithms, namely A_EMSON and A_EMSOFF to solve the problem. We also verify the performance of the algorithms through comparisons with the existing related techniques, and evaluate their capability to ensure high-entropy under different channel models using MATLAB simulations.
It has been shown that the radio channel impulse response for a pair of legitimate Ultra-wide band (UWB) transceivers can be used to generate secret keys for secure communications. Past proposed secret key generation algorithms under-exploited the available number of secret key bits from the radio channel. This paper proposes a new efficient method for generation of the shared key where the transceivers use LDPC decoders to resolve the differences in their channel impulse response measurements caused by measurement noise. To ensure secret key agreement, a method of public discussion between the two users is performed using the syndrome from Hamming (7,3) binary codes. An algorithm is proposed to check the equality of generated keys for both legitimate users, and ensure error-free secure communication. The security of this algorithm has been verified by AVISPA. Comparisons are performed with previous work on secret key generation and it has been shown that this algorithm reliably generates longer secret keys in standard UWB radio channels.
In the recent years, a set of works have addressed inherent characteristics of the fading propagation channel in an information-theoretic framework oriented towards security. In particular, for cryptographic purposes, secure key bits can be extracted from reciprocal radio channels, seen as a shared source of randomness between any two entities. In this paper we intend to assess the impact of true radio channel features on the security performance, by quantizing the complex channel coefficients into discrete key bits. To this end, indoor channel measurements were performed and investigated in different scenarios, e.g. LOS/NLOS condition, narrowband (NB) as well as wide band (WB) targeting OFDM systems. Secret key robustness is firstly studied for the legitimate terminals in terms of key bit disagreement ratio and key randomness, and secondly by considering an eavesdropper in a wide set of positions around these terminals and by evaluating the difference between the generated keys. A simplified channel model is also analyzed in comparison with the measured channels, as regards the characteristics of generated key bits.
Providing extra security in wireless communication networks using channel impulse response as a source of common randomness is an appealing direction in prospective systems. While some theoretical and experimental work has demonstrated its potential, a number of issues remain unexplored. This paper is concerned with the reliability of secret key generation under practical estimation requirements. We provide an analytical expression which relates the channel SNRs and degree of reciprocity to probability of key mismatch. In the next step we show how this affects key reconciliation and secrecy leaking. Finally, we consider how quantization with a protective band can help to trade the secret key rate for increased reliability and security of the scheme.
Wireless networks are vulnerable to various attacks due to their open nature, making them susceptible to eavesdropping and other security threats. Eavesdropping attack takes place at the physical layer. Traditional wireless network security relies on cryptographic techniques to secure data transmissions. However, these techniques may not be suitable for all scenarios, especially in resource-constrained environments such as wireless sensor networks and adhoc networks. In these networks having limited power resources, generating cryptographic keys between mobile entities can be challenging. Also, the cryptographic keys are computationally complex and require key management infrastructure. Physical Layer Key Generation (PLKG) is an emerging solution to address these challenges. It establishes secure communication between two users by taking advantage of the wireless channel's inherent features. PLKG process involves channel probing, quantization, information reconciliation (IR) and privacy amplification to generate symmetric secret key. The researchers have used various PLKG techniques to get the secret key, sTop of Form till they face problems in the IR scheme to obtain symmetric keys between the users who share the same channel for communication. Both the code based and protocol based methods proposed in the literature have advantages and limitations related to their performance parameters such as information leakage, interaction delay and computation complexity. This research work proposes a novel IR mechanism that combines the protocol and code-based error correction methods to obtain reduced Bit Mismatch Rate (BMR), reduced information leakage, reduced interaction delay, and reduced computational time to enhance physical layer secret key's quality. In the proposed research work, the channel samples are generated using the Received Signal Strength (RSS) and Channel Impulse Response (CIR) parameters. These samples are quantized using Vector Quantization with Affinity Propagation Clustering (VQAPC) method to generate the preliminary key. The samples collected by the two users who wish to communicate, (for example Alice and Bob) will be different due to noise in the channel and hardware limitations. Hence their preliminary keys will be different. Removing this discrepancy between Bob's and Alice's initial keys, using novel Hybrid Protocol and Code related Information Reconciliation (HPC-IR) scheme to generate error corrected key, is the most important contribution of this research work. This key is further encoded by the MD5 hash function to generate a final secret key for exchanging information between two users over the wireless channel. It is observed that the proposed HPC-IR scheme achieves BMR of 19.4%, information leakage is 0.002, interaction delay is 0.001 seconds and computation time is 0.02 seconds.
Secure communication in a wireless environment is very vital, and cryptographic schemes are usually used to ensure it. Secret keys that are unknown to the tappers are needed by cryptographic schemes to secure communication between two legitimate users. In recent years the secret key generation scheme that utilizes a wireless channel as a secret key generation source has become a very interesting and promising topic. The main problem of this scheme is the high wireless channel mismatch between two users due to nonsimultaneous measurements and noise from the device. In this paper, we proposed a secret key generation scheme that uses the Savitzky-Golay filter method to reduce the high mismatch wireless channel. The scheme that was built was also equipped with a multibit quantization method to increase the speed of generation of secret keys. The results of our tests show a decrease in wireless channel mismatch between two users and an increase in the speed of generation of secret keys.