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Communications technology

Secret- Key Extraction Technology based on Wireless Channel Characters

Wenbin Cai

Published Jan 1, 2014• 0 citations
OpenAlex

Abstract

Wireless channel enjoys the properties of reciprocity,temporal variations and spatial variations.These properties enable the legitimate partners to share secret key from the wireless channel. And effective secret- key extraction system could remarkably improve the key extraction rates. In the past three decades,the secret- key extraction technique has experienced the development process from theory study to practical experiments in real channel. From the aspects of channel- parameter choice,quantization,information negotiation and privacy enhancement techniques,this paper provides a comprehensive overview on current status,classified comparison and development trend of secret- key extraction techniques based on wireless channel characteristics.

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Wireless channel enjoys the properties of reciprocity,temporal variations and spatial variations.These properties enable the legitimate partners to share secret key from the wireless channel. And effective secret- key extraction system could remarkably improve the key extraction rates. In the past three decades,the secret- key extraction technique has experienced the development process from theory study to practical experiments in real channel. From the aspects of channel- parameter choice,quantization,information negotiation and privacy enhancement techniques,this paper provides a comprehensive overview on current status,classified comparison and development trend of secret- key extraction techniques based on wireless channel characteristics.
In this article, we give an overview of current research on shared secret-key agreement between two parties. This agree⁃ ment is based on radio wireless channel characteristics. We discuss the advantages of this approach over traditional cryp⁃ tographic mechanisms and present the theoretical background of this approach. We then give a detailed description of the key-agreement process and the threat model, and we summarize the typical performance metrics for shared se⁃ cret-key agreement. There are four processes in shared secret-key agreement: sampling, quantization, information recon⁃ ciliation, and privacy amplification. We classify prior and current research in this area according to innovation on these four processes. We conclude with a discussion of existing challenges and directions for future work.
Encryption of confidential data with a secret key has become a widespread technique for securing wireless transmissions. However, existing key distribution methods that either deliver the secret key with a key distribution center or exchange the secret key using public-key cryptosystems are unable to establish perfect secret keys necessary for symmetric encryption techniques. This research considers secret key establishment, under the broad research area of information theoretic security, using the reciprocal wireless channel as common randomness for the extraction of perfect secret keys in multiple-input multiple-output (MIMO)communication systems. The presentation discusses the fundamental characteristics of the time-variant MIMO wireless channel and establishes a realistic channel simulation model useful for assessing key establishment algorithms. Computational examples show the accuracy and applicability of the model. The discussion then turns to an investigation of the influence of the spatial and temporal correlation of the channel coefficients on the bound of the key size generated from the common channel, and it is found that a sampling approach exists that can generate a key using the minimum sampling time. A practical key generation protocol is then developed based on an enhancement of a published channel coefficient quantization method that incorporates flexible quantization levels, public transmission of the correlation eigenvector matrix and low-density parity-check (LDPC) coding to improve key agreement. This investigation leads to the development of improved channel quantization techniques that dynamically shift the quantization boundaries at one node based on the information provided by the other node. Analysis based on a closed-form bound for the key error rate (KER) and simulations based on the channel model and measurement data show that the enhanced algorithms are able to dramatically reduce key mismatch and asymptotically approach the KER bound. Finally, other secret key generation algorithms based on channel-encryption rather than quantization are discussed, leading to a new concept for secret key generation using the common wireless channel.
As an alternative and appealing approach to providing information security in wireless communication systems, secret key generation at physical layer has demonstrated its potential in terms of efficiency and reliability over traditional cryptographic methods. Without the necessity of a management centre for key distribution or reliance on computational complexity, physical layer key generation protocols enable two wireless entities to extract identical and dynamic keys from the randomness of the wireless channels associated with them.\nIn this thesis, the reliability of secret key generation at the physical layer is examined in practical wireless channels with imperfect channel state information (CSI). Theoretical analyses are provided to relate key match rate with channel's signal-to-noise ratio (SNR), degrees of channel reciprocity, and iterations of information reconciliation.\nIn order to increase key match rate of physical layer secret key generation, improved schemes in the steps of channel estimation and sample quantization are proposed respectively. In the channel estimation step, multiple observations of the wireless channels are integrated with a linear processor to provide a synthesized and more accurate estimation of the wireless channel. In the sample quantization step, a magnitude based quantization method with two thresholds is proposed to quantize partial samples, where specific quantization areas are selected to reduce cross-over errors. Significant improvements in key match rate are proven for both schemes in theoretical analysis and numerical simulations. Key match rate can even achieve 100% in both schemes with the assistance of information reconciliation process.\nIn the end, a practical application of physical layer secret key generation is presented, where dynamic keys extracted from the wireless channels are utilized for securing secret data transmission and providing efficient access control.
Exploiting the reciprocity and randomness of the wireless channel for secret key generation (SKG) is a promising technique, which attracts great interests recently toward physical layer security. Although various methods have been developed for efficient SKG, the key disagreement rate (KDR) performance is still difficult to be ensured when the transmission channel is with severe interference and noise. To alleviate this problem, this paper presents an efficient channel information extraction algorithm based on extracting effective channel paths to reduce the KDR. Simulation results demonstrate that the proposed algorithm provides significant improvement compared with the existing approaches.
We evaluate the effectiveness of secret key extraction, for private communication between two wireless devices, from the received signal strength (RSS) variations on the wireless channel between the two devices. We use real world measurements of RSS in a variety of environments and settings. The results from our experiments with 802.11-based laptops show that in certain environments, due to lack of variations in the wireless channel, the extracted bits have very low entropy making these bits unsuitable for a secret key, an adversary can cause predictable key generation in these static environments, and in dynamic scenarios where the two devices are mobile, and/or where there is a significant movement in the environment, high entropy bits are obtained fairly quickly. Building on the strengths of existing secret key extraction approaches, we develop an environment adaptive secret key generation scheme that uses an adaptive lossy quantizer in conjunction with Cascade-based information reconciliation and privacy amplification. Our measurements show that our scheme, in comparison to the existing ones that we evaluate, performs the best in terms of generating high entropy bits at a high bit rate. The secret key bit streams generated by our scheme also pass the randomness tests of the NIST test suite that we conduct. We also build and evaluate the performance of secret key extraction using small, low-power, hand-held devices-Google Nexus One phones-that are equipped 802.11 wireless network cards. Last, we evaluate secret key extraction in a multiple input multiple output (MIMO)-like sensor network testbed that we create using multiple TelosB sensor nodes. We find that our MIMO-like sensor environment produces prohibitively high bit mismatch, which we address using an iterative distillation stage that we add to the key extraction process. Ultimately, we show that the secret key generation rate is increased when multiple sensors are involved in the key extraction process.
We propose an improved method of secret key generation using the variations in wireless channel. We construct reciprocal channel profiles at a pair of transceivers and enhance it using the l 1 -norm minimization technique. Thereafter preliminary keys are obtained that are synchronized by a localized information reconciliation technique. The privacy of the synchronized keys is enhanced by generating secure hashes. We implement the proposed method on a testbed and validate its performance to show decreased rates of bit disagreement of preliminary keys, at an increased key generation rate.