College of Computer

The development of medical sensor networks (MSNs) is imperative for e-healthcare, but security remains a formidable challenge yet to be resolved. Traditional cryptographic mechanisms do not suffice given the unique characteristics of MSNs, and the fact that MSNs are susceptible to a variety of node misbehaviors. In such situations, the security and performance of MSNs depend on the cooperative and trust nature of the distributed nodes, and it is important for each node to evaluate the trustworthiness of other nodes. In this paper, we identify the unique features of MSNs and introduce relevant node behaviors, such as transmission rate and leaving time, into trust evaluation to detect malicious nodes. We then propose an application-independent and distributed trust evaluation model for MSNs. The trust management is carried out through the use of simple cryptographic techniques. Simulation results demonstrate that the proposed model can be used to effectively identify malicious behaviors and thereby exclude malicious nodes. This paper also reports the experimental results of the Collection Tree Protocol with the addition of our proposed model in a network of TelosB motes, which show that the network performance can be significantly improved in practice. Further, some suggestions are given on how to employ such a trust evaluation model in some application scenarios.

Code dissemination in a wireless sensor network (WSN) is the process of propagating a new program image or relevant commands to sensor nodes. As a WSN is usually deployed in hostile environments, secure code dissemination is and will continue to be a major concern. Most code dissemination protocols are based on the centralized approach in which only the base station has the authority to initiate code dissemination. However, it is desirable and sometimes necessary to disseminate code images in a distributed manner which allows multiple authorized network users to simultaneously and directly update code images on different nodes without involving the base station. Motivated by this consideration, we develop a secure and distributed code dissemination protocol named DiCode. A salient feature of DiCode is its ability to resist denial-of-service attacks which have severe consequences on network availability. Further, the security properties of our protocol are demonstrated by theoretical analysis. To verify the efficiency of the proposed approach in practice, we also implement the proposed mechanism in a network of resource-constrained sensor nodes.

Wireless reprogramming in a wireless sensor network (WSN) is the process of propagating a new code image or relevant commands to sensor nodes. As a WSN is usually deployed in hostile environments, secure reprogramming is and will continue to be a major concern. While all existing insecure/secure reprogramming protocols are based on the centralized approach, it is important to support distributed reprogramming in which multiple authorized network users can simultaneously and directly reprogram sensor nodes without involving the base station. Very recently, a novel secure and distributed reprogramming protocol named SDRP was proposed, which is the first work of its kind. However, in this paper, we identify an inherent design weakness in the user pre-processing phase of SDRP, and demonstrate that it is vulnerable to an impersonation attack by which an adversary can easily impersonate any authorized user to carry out reprogramming. Subsequently, we propose a simple modification to fix the identified security problem without losing any features of SDRP. Our experimental results demonstrate that it is possible to eliminate the design weakness by adding a 1-byte redundant data, and that the execution time of the suggested solution in a 1.6-GHz Laptop PC is no more than one milli-second. Therefore, our solution is feasible and secure for real world applications. Moreover, we show that, in order to further improve the security and efficiency of SDRP, any better established identity-based signature algorithm can be directly employed in SDRP. Based on implementation results, we demonstrate efficiency improvement over the original SDRP.

A distributed access control module in wireless sensor networks (WSNs) allows the network to authorize and grant user access privileges for in-network data access. Prior research mainly focuses on designing such access control modules for WSNs, but little attention has been paid to protect user's identity privacy when a user is verified by the network for data accesses. Often, a user does not want the WSN to associate his identity to the data he requests. In this paper, we present the design, implementation, and evaluation of a novel approach, Priccess, to ensure distributed privacy-preserving access control. In Priccess, users who have similar access privileges are organized into the same group by the network owner. A network user signs a query command on behalf of his group and then sends the signed query to the sensor nodes of his interest. The signature can be verified by its recipient as coming from someone authorized without exposing the actual signer. In addition to the theoretical analysis that demonstrates the security properties of Priccess, this paper also reports the experimental results of Priccess in a network of Imote2 motes, which show the efficiency of Priccess in practice.

Seamless roaming over wireless network is highly desirable to mobile users, and security such as authentication of mobile users is challenging. Recently, due to tamper-resistance and convenience in managing a password file, some smart card based secure authentication schemes have been proposed. This paper shows some security weaknesses in those schemes. As the main contribution of this paper, a secure and light-weight authentication scheme with user anonymity is presented.

Abstract Wireless networking is becoming an increasingly important and popular way of providing global information access to users on the move. One of the main challenges for seamless mobility is the availability of simple and robust vertical handoff algorithms, which allow a mobile node to roam among heterogeneous wireless networks.

Abstract Seamless roaming in the global mobility network (GLOMONET) is highly desirable for mobile users, although their proper authentication is challenging. This is because not only are wireless networks susceptible to attacks, but also mobile terminals have limited computational power. Recently, some authentication schemes with anonymity for the GLOMONET have been proposed. This paper shows some security weaknesses in those schemes.

Abstract A handover authentication protocol in mobile networks enables mobile nodes to securely and seamlessly roam over multiple access points. Many such protocols have been proposed but shown to be either insecure or inefficient. Very recently, a novel handover authentication protocol named PairHand was proposed, which has been shown to outperform all other protocols in terms of security and efficiency.

SUMMARY When one considers the broad range of wirelessly connected mobile devices used today, it is clear that integrating such network-enabled devices into secure roaming over wireless networks is of essential importance. Over the years, many authentication protocols have been suggested to address this issue. Among these protocols, the recently proposed privacy-preserving universal authentication protocol, Priauth, exceeds the security and efficiency of other authentication techniques.

Abstract A body sensor network (BSN) is a wireless network of biosensors and a local processing unit, which is commonly referred to as the personal wireless hub (PWH). Personal health information (PHI) is collected by biosensors and delivered to the PWH before it is forwarded to the remote healthcare center for further processing. In a BSN, it is critical to only admit eligible biosensors and PWH into the network.

SUMMARY Password-authenticated group key exchange protocols enable communication parties to establish a common secret key (a session key) by only using short secret passwords. Such protocols have been receiving significant attention. This paper shows some security weaknesses in some recently proposed password-authenticated group key exchange protocols. Furthermore, a secure and efficient password-authenticated group key exchange protocol in mobile ad hoc networks is proposed.

Designing a user authentication protocol for wireless sensor networks is a difficult task because wireless networks are susceptible to attacks and sensor node has limited energy, processing and storage resources. Recently, several authentication schemes have been proposed. This short paper shows some security problems and design weaknesses in those schemes. Furthermore, an enhanced two-factor user authentication protocol is presented.

Abstract Seamless handover over multiple access points is highly desirable to mobile nodes, but ensuring security and efficiency of this process is challenging. This paper shows that prior handover authentication schemes incur high communication and computation costs, and are subject to a few security attacks. Further, a novel handover authentication protocol named PairHand is proposed. PairHand uses pairing-based cryptography to secure handover process and to achieve high efficiency.

Abstract Seamless roaming over wireless networks is highly desirable to mobile users, and security such as authentication of mobile users is challenging. In this paper, we propose a privacy-preserving universal authentication protocol, called Priauth, which provides strong user anonymity against both eavesdroppers and foreign servers, session key establishment, and achieves efficiency. Most importantly, Priauth provides an efficient approach to tackle the problem of user revocation while supporting strong user untraceability.

Objective. The high-dimensional neural recordings bring computational challenges to movement decoding in motor brain machine interfaces (mBMI), especially for portable applications. However, not all recorded neural activities relate to the execution of a certain movement task. This paper proposes to use a local-learning-based method to perform neuron selection for the gesture prediction in a reaching and grasping task. Approach. Nonlinear neural activities are decomposed into a set of linear ones in a weighted feature space. A margin is defined to measure the distance between inter-class and intra-class neural patterns. The weights, reflecting the importance of neurons, are obtained by minimizing a margin-based exponential error function. To find the most dominant neurons in the task, 1-norm regularization is introduced to the objective function for sparse weights, where near-zero weights indicate irrelevant neurons. Main results. The signals of only 10 neurons out of 70 selected by the proposed method could achieve over 95% of the full recording's decoding accuracy of gesture predictions, no matter which different decoding methods are used (support vector machine and K-nearest neighbor). The temporal activities of the selected neurons show visually distinguishable patterns associated with various hand states. Compared with other algorithms, the proposed method can better eliminate the irrelevant neurons with near-zero weights and provides the important neuron subset with the best decoding performance in statistics. The weights of important neurons converge usually within 10-20 iterations. In addition, we study the temporal and spatial variation of neuron importance along a period of one and a half months in the same task. A high decoding performance can be maintained by updating the neuron subset. Significance. The proposed algorithm effectively ascertains the neuronal importance without assuming any coding model and provides a high performance with different decoding models. It shows better robustness of identifying the important neurons with noisy signals presented. The low demand of computational resources which, reflected by the fast convergence, indicates the feasibility of the method applied in portable BMI systems. The ascertainment of the important neurons helps to inspect neural patterns visually associated K Xu et al with the movement task. The elimination of irrelevant neurons greatly reduces the computational burden of mBMI systems and maintains the performance with better robustness.