In this paper, experimental results are presented for an encrypted wireless link between two body-worn sensor nodes fully integrated onto textile antenna platforms. Wireless communication between two persons walking in an indoor environment occurs over a unique physical propagation channel. For the purpose of data encryption, channel measurements are performed at both sides of the link, providing highly correlated pseudo random number sequences, with envelope correlation coefficients always above 0.7. Signals captured by an eavesdropper are substantially decorrelated, with correlation coefficients always below 0.15, and are therefore not suitable for key extraction. The mutual information is also determined, providing extra insight into the key generating potential of the pseudo random sequences. Practical error free secret key generation on both sides of the link, with reconciliation by means of Hamming check bits, is performed successfully in all cases between legitimate parties. At the same time, an eavesdropper is unable to extract the secret key from measured signals, as confirmed by the key error rates, which are calculated for all possible signal combinations, resulting in a key error rate after reconciliation around 0.5 for most eavesdropper channels and remaining at least 0.3 in the worst-case scenario.
In this paper, experimental results are presented for an encrypted wireless link between two body-worn sensor nodes fully integrated onto textile antenna platforms. Wireless communication between two persons walking in an indoor environment occurs over a unique physical propagation channel. For the purpose of data encryption, channel measurements are performed at both sides of the link, providing highly correlated pseudo random number sequences, with envelope correlation coefficients always above 0.7. Signals captured by an eavesdropper are substantially decorrelated, with correlation coefficients always below 0.15, and are therefore not suitable for key extraction. The mutual information is also determined, providing extra insight into the key generating potential of the pseudo random sequences. Practical error free secret key generation on both sides of the link, with reconciliation by means of Hamming check bits, is performed successfully in all cases between legitimate parties. At the same time, an eavesdropper is unable to extract the secret key from measured signals, as confirmed by the key error rates, which are calculated for all possible signal combinations, resulting in a key error rate after reconciliation around 0.5 for most eavesdropper channels and remaining at least 0.3 in the worst-case scenario.
Medical data collected by wearable wireless sensor devices must be adequately secured. A prerequisite for mass deployment of these secure systems is the ability to periodically renew cryptographic keys without user involvement. Recent work has shown that two communicating devices can generate secret keys directly from measurements of their common wireless channel, which is symmetric but cannot be inferred in detail by an eavesdropper. These schemes may, however, yield mismatching keys at the two ends, requiring reconciliation mechanisms with high implementation and energy costs, unsuitable for resource-poor body-worn devices. In this work, we demonstrate a scheme for secret-key generation able to construct shared keys with near-perfect agreement, thereby avoiding reconciliation costs. Our specific contributions are: (1) we identify non-simultaneous probing of the channel by the link end-points as the dominant cause of channel measurement disagreement; (2) we develop a practical filtering scheme to reduce this disagreement, dramatically improving signal correlation between the two ends without affecting key entropy; and (3) we show that by restricting key generation to periods of significant channel fluctuation, we achieve near-perfect key agreement. We demonstrate in several representative body-worn settings that our scheme can generate secret bits with 99.8% agreement, and so yield near-perfect matching 128-bit keys approximately every half hour.
Reliable communication over Wireless Body Area Networks (WBANs) is an essential aspect of Wireless Body Area Networks (WBANs) because the physiological data flows between wearable sensor nodes is sensitive data. The convectional cryptography methods usually apply a lot of computational complexity as well as energy overhead besides which they are not going to fit in the ultra-low-power WBANs. In the current paper a light-weight, energy-efficient Physical Layer Key Generation (PLKG) scheme the possibilities of which based on the native randomness and reciprocity of the wireless channel is used to generate secure symmetric keys is presented. With WBANs, there is a lot of temporal and spatial dynamics in the human body and its surrounding environment, which causes great variability in channel characteristics, in terms of Received Signal Strength Indicator (RSSI) and Channel State Information (CSI). Such physical layer parameters can be used as perfect entropy sources in generation of unique, unpredictable secret keys with whose knowledge, communication between nodes is possible and mutually exclusive only. The channel probing in the proposed framework is also robust, multi-bit quantization is performed adaptively, information reconciliation is performed through error correction codes, and privacy amplification is made through cryptographic hashing. We have developed a resilient system against bit mismatch and efficiently against passively eavesdropping, we guarantee the secrecy of the generated keys under adversary situation. With realistic WBAN models simulation and experiment validation shows that the proposed approach is capable of generating keystokes with very high key generation rate (50 bps) and a bit mismatch rate of lower than 3 percent as compared to existing schemes that solely relied on RSSI, making this protocol more secure and reliable to use. In addition, the framework meets the statistical randomness requirements specified by NIST and it does not leak mutual information to eavesdroppers. The scheme allows real-time use on resource-constrained devices, e.g., wearable medical devices and health-monitoring sensor, as it has low computational and memory overhead. The findings establish the feasibility of employing physical layer properties to achieve secure WBANs communication without any pre-shared keys or a centralized trust paradigm, thus, opening the way to scalable and privacy-preserving healthcare systems.
Two legitimate parties, referred to as Alice and Bob, wish to generate secret keys from the wireless channel in the presence of an eavesdropper, referred to as Eve, in order to use such keys for encryption and decryption. In general, the secret key rate highly depends on the coherence time of the channel. In particular, a straightforward method of generating secret keys in static environments results in ultra-low rates. In order to resolve this problem, we introduce a low-complexity method called induced randomness. In this method, Alice and Bob independently generate local randomness to be used together with the uniqueness of the wireless channel coefficients in order to enable high-rate secret key generation. In this work, two scenarios are considered: first, when Alice and Bob share a direct communication channel, and second, when Alice and Bob do not have a direct link and communicate through an untrusted relay. After exchanging the induced randomness, post-processing is done by Alice and Bob to generate highly-correlated samples that are used for the key generation. Such samples are then converted into bits, disparities between the sequences generated by Alice and Bob are mitigated, and the resulting sequences are then hashed to compensate for the information leakage to the eavesdropper and to allow consistency checking of the generated key bit sequences. We utilize semantic security measures and information-theoretic inequalities to upper bound the probability of successful eavesdropping attack in terms of the mutual information measures that can be numerically computed. Given certain reasonable system parameters this bound is numerically evaluated to be 2-31and 2-10.57in the first and the second scenario, respectively.
Physical layer encryption is a promising solution to provide transmission security for Internet-of-Things (IoT). To realize physical layer encryption, channel state information (CSI) as a random source to generate secret keys should be exploited. The reciprocity of wireless channel between legitimate communication nodes which is typically assumed for time division duplex (TDD) systems, is of critical importance to ensure the consistency in generated keys at two nodes. However, in practical TDD systems, due to the asynchronous measurement of CSI, the receiver noise and the the difference in hardware, etc., the reciprocity of channel measurements between legitimate parties is hard to be guaranteed, which makes physical layer key generation approach infeasible. To address this issue, we propose a wireless key generation scheme based on deep learning techniques. Firstly, a feature extraction network, which consists of two auto-encoders trained jointly, is developed to extract the common feature from the different yet correlated channel observations at two legitimate nodes, which will be used as the source to generate keys. Then a quantizer with an adaptive guard band width is devised to output a binary secret-key sequence from the feature vector. Numerical results show that the proposed scheme achieves remarkable improvement in terms of key disagreement rate (KDR) and key generation rate (KGR) compared existing counterparts in the literature.
Due to the unavoidable shared nature of the wireless radio spectrum, providing security for wireless communications presents unique challenges. Cryptographic keys have been used as a primary technique for securing wireless networks but are not completely secure. The symmetric keys used for cryptographic purposes are vulnerable to man-in-the-middle and brute force attacks. More recently, PHY-layer based techniques have gained significant attention, where the principle of channel reciprocity and the natural randomness of the measured wireless channel to generate secret keys is leveraged. Although, PHY-layer secret key generation has been investigated and presented in the literature before, there has been a lack of discussion in terms of obtaining symmetric keys on both ends of the link. In this work, we present a novel PHY-layer secret key generation technique that aims for symmetric encryption keys while limiting the information leaked to an eavesdropper to ensure complete secrecy and to prevent potential intelligent attacks. Our algorithm utilizes forward and backward channel state information in a given wireless link and combats the minute differences observed in these pairs by generating channel trend information. We demonstrate our technique using experimental results from a realtime SDR testbed connected to a wireless channel emulator. Our results indicate that the algorithm is successful in generating symmetric keys under various wireless environments without revealing any information pertaining to the key via the open wireless channel. Our secret key extraction rate can reach values in excess of 17.3 Kbps.
There is growing interest in physical-layer key generation schemes that provide very strong or even perfect security in wireless communication systems. One such scheme is reciprocal channel key generation, where two nodes quantize reciprocal channel state information to generate keys. Although the use of multiple-input multiple-output (MIMO) techniques is interesting in this case since the number of random parameters available for rapid key generation is increased, MIMO techniques may also provide more information to an eavesdropper. This work presents a new MIMO measurement campaign performed in LOS and NLOS indoor environments that studies the correlation of the channel between legitimate users with the eavesdropper channel, revealing what key generation rates can be attained in practice and what fraction of generated key bits are safe from eavesdroppers. The effect of eavesdropper separation, number of antennas, eavesdropper advantage, and covariance separability are studied.