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Journal of Computer Security

A secret key establishment protocol for wireless networks using noisy channels

Albert Guan, Wen-Guey Tzeng

Published Feb 24, 2017• 3 citations
Publisher

Abstract

An efficient protocol for establishing secret keys for neighboring nodes in a wireless network is presented in this paper. The security of the key generated by our protocol is based on the unpredictability of the noises in binary symmetric communication channels. The two nodes which try to establish a common secret key receive messages from a common source of random bit strings. Due to noises in the communication channel, the messages received by them, and most importantly the messages received by the eavesdropper, are not the same. We show that the two nodes can modify their messages in an efficient way to obtain a common string which contains enough uncertainty to the eavesdropper. Then, a secure universal hash function is applied to compute a secret key for extracting randomness from the common string. We prove that the probability for the eavesdropper to know the value of the key is negligible. One advantage of our proposed protocol is that the secret key rate is better than the known scheme in other models, such as the bounded storage model. Furthermore, our proposed protocol needs only to perform exclusive-or operations and compute hash values. Thus, it is a computationally light-weight protocol and suitable for devices with limited computing resources, such as sensors in sensor networks.

DOI
10.3233/jcs-15807

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An efficient protocol for establishing secret keys for neighboring nodes in a wireless network is presented in this paper. The security of the key generated by our protocol is based on the unpredictability of the noises in binary symmetric communication channels. The two nodes which try to establish a common secret key receive messages from a common source of random bit strings. Due to noises in the communication channel, the messages received by them, and most importantly the messages received by the eavesdropper, are not the same. We show that the two nodes can modify their messages in an efficient way to obtain a common string which contains enough uncertainty to the eavesdropper. Then, a secure universal hash function is applied to compute a secret key for extracting randomness from the common string. We prove that the probability for the eavesdropper to know the value of the key is negligible. One advantage of our proposed protocol is that the secret key rate is better than the known scheme in other models, such as the bounded storage model. Furthermore, our proposed protocol needs only to perform exclusive-or operations and compute hash values. Thus, it is a computationally light-weight protocol and suitable for devices with limited computing resources, such as sensors in sensor networks.
Symmetric cryptosystems are very important for secure communication. They are much more efficient then asymmetric cryptosystems. Secret keys are required for symmetric cryptosystems, such as AES. In 2017, Guan and Tzeng designed a secret key establishment protocol whose security depends on the unpredictability of noise in communication channel. They showed that these protocols are secure even if the eavesdropper has infinite computing power. Their protocol works most efficiently for channels with bit-flip rate around 0.01. For the case when bit-flip rate is much smaller than 0.01, their protocol needs a long random bit string to accumulate enough uncertainty to establish a secret key. In this article, an improved protocol for establishing secret key is proposed. The new method requires much less random bits for channels with small bit-flip rates, such as in the range [0.001, 0.010]. With the improvement of wireless communication technology, the bit-flip rate is reducing. Therefore, the new method is suitable for the current wireless networks technology.
Abstract. We study the problem of unconditionally secure Secret Key Establishment (SKE) when Alice and Bob are connected by two noisy channels in opposite directions, and the channels are eavesdropped by Eve. We consider the case that Alice and Bob do not have any sources of initial randomness at their disposal. We start by discussing special cases of interest where SKE is impossible, and then provide a simple SKE construction over a binary symmetric channel that achieves some rates of secret key. We next focus on the Secret Key (SK) capacity, i.e., the highest rate of secure and reliable key establishment (in bits per channel use) that the parties can achieve. Relying on the existence of capacity-achieving coding schemes, we propose a multi-round SKE protocol, called the main protocol, that proves a lower bound on the SK capacity. The main protocol consists of an initialization round, followed by repeated use of a two-round SKE protocol, called the basic protocol. We also provide an upper bound on the SK capacity and show that the two bounds coincide when channels do not leak information to the adversary. We apply the results to the case that communicants are connected by binary symmetric channels. 1
Wireless sensor networks with a large number of cheap low-power interconnected devices bring up challenging tasks when considering the security of their communications. Our paper addresses the issue how cryptographic link keys between communicating sensor nodes can be continuously re-secured even in presence of an attacker who can read the memory of captured nodes. Distributed sensor systems enable us to use two different approaches to link key (re-)establishment - secrecy amplification and key extraction from radio channel fading. A secrecy amplification protocol lets a group of neighboring nodes cooperate together to re-secure previously compromised link keys using the non-compromised paths, and previous research showed the ability of secrecy amplification protocols to improve the security of a network from 50% of compromised link keys to 90% of secure keys. Key extraction then exploits radio channel properties to generate secret bits shared between two radio-enabled devices. We propose to combine secrecy amplification and key extraction into a dynamic protocol, where every node will dynamically decide what approach provides a greater benefit, considering the probability of getting the link key re-secured and the resources available. In principle, the more standard traffic messages are exchanged on a given link, the more beneficiary is the usage of key extractions. And less busy links then rely on secrecy amplification.
Due to the broadcast nature of wireless channels, wireless communication is vulnerable to eavesdropping, message modification, and node impersonation. Securing the wireless communication requires the shared secret keys between the communicating entities. Traditional security schemes rely on public key infrastructures and cryptographic algorithms to manage secret keys. Recently, many physical-layer-based methods have been proposed as alternative solutions for key generation in wireless networks. These methods exploit the inherent randomness of the wireless fading channel to generate secret keys while providing information-theoretical security without intensive cryptographic computations. This article provides an overview of the existing PHY-based key generation schemes exploiting the randomness of the wireless channels. Specifically, we first introduce the fundamental and general framework of the PHY-based key generation schemes and then categorize them into two classes: received-signal-strength-based and channel- phase-based protocols. Finally, we present a performance comparison of them in terms of key disagreement probability, key generation rate, key bit randomness, scalability, and implementation issues.
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.
In MIMO wireless channels, channel estimation can provide a source of randomness common to sender and receiver that may be used to generate secret keys. These keys can provide information theoretically secure communication. Alternatively, a known MIMO channel allows transmitting artificial noise in the null space of the main channel to secure communication. In this paper, we show that both methods can be combined to further enhance secrecy. Symbols encrypted at the transmitter simultaneously act as message for the intended receiver and as noise for any potential eavesdroppers. We derive expressions for the minimum-guaranteeable secrecy rate as a function of number of symbols encrypted. Given at least one symbol can be encrypted, our proposed method outperforms the standard artificial noise scheme in terms of both secrecy rate and power expenditure. We first analyze the system assuming keys can be instantaneously extracted from channel measurements. We then derive bounds for rates assuming the overhead time required for key generation produces a Gaussian channel-estimation error.