Wei-Chung Teng

Clock Skew Based Node Identification in Wireless Sensor Networks

Node identification is one of the most important issues to wireless sensor network security. Current approaches use cryptographic authentication and certification tools to ensure the node identification, while this paper introduces an intuitive method to identify a node by measuring its clock skew. This method is based on our observation that every sensor node has a unique clock skew value that is different from any other node. We adopt Flooding Time Synchronization Protocol (FTSP) as the measuring tools, and the experimental data show that almost all measured clock skews of one sensor node vary inside a tiny bound. For any two nodes that their clock skews are very close to each other, a classifying function is proposed to check the line continuity of contiguous measured clock skews. The proposed method has successfully identified every node in our experiments, and its applications like Sybil attack detection is also discussed.

Distortion reduction for histogram modification-based reversible data hiding

Abstract The histogram modification (HM) method proposed by Ni et al. is very efficient for reversible data hiding (RDH). Besides the excellent execution-time performance, Ni et al.’s HM-based RDH (HMRDH) method has a high PSNR lower bound of marked images. In this short communication, an observation on Ni et al.’s HM-based RDH (HMRDH) method is pointed out that the distortion of the marked image from Ni et al.’s method is dependent on the number of 1’s in the watermark. From this observation, we first present a watermark complement scheme to reduce the distortion occurred in Ni et al.’s HMRDH method. Later, combinatorial analysis for average distortion ratio of the proposed scheme is provided. This analysis motivates us to present a block-based complement scheme to improve the distortion reduction further. The tradeoff between the distortion and the number of partitioned blocks is also investigated. Taking nine well-known trademarks as the test watermarks and two cover images with different types of content, experimental results demonstrated the distortion reduction and higher PSNR lower bound advantages of the proposed block-based watermark complement scheme.

Secured flooding time synchronization protocol with moderator

SUMMARY This work aims to address the security vulnerability of the Flooding Time Synchronization Protocol (FTSP), which is currently one of the most popular approaches for time synchronization in wireless sensor networks. FTSP has advanced features, such as implicitly dynamic topology and high time accuracy, but still has unresolved security issues. In order to defend against attacks from malicious nodes, we propose several technologies to reinforce the structure of FTSP. First, a reference node selecting mechanism is proposed to reduce the effect of multiple reference nodes, and four filters are proposed to defend against seqNum attack, global time attack and node replication attack. Experiment results show that the proposed sequence number blacklist filter and the global time blacklist filter are effective in defending against the aforementioned attacks. Second, a new root selection mechanism is proposed to secure the process of updating the root node. Combining the root selection mechanism with the global time black list filter, the proposed mechanisms successfully defend against traitor attacks on FTSP in our experiment. Copyright

A defense against clock skew replication attacks in wireless sensor networks

As studies to date have demonstrated that the clock skew of every physical device differs and so is suitable for device identification in network communications, the fact that any adversary can easily produce a fake clock skew by altering the timestamp of the sent packets remains a concern. This study contributes to this issue by realizing a replication attack of an indistinguishable fake clock skew and by developing its countermeasure in a wireless sensor network environment. In the first part of the study, a method of timestamp back calculation is developed for imitating the clock skew of a neighbor node. Given the relative clock skews of a victim node and an imitated node, our method calculates the time difference between the attacker node and the imitated one, which makes the biased timestamps of the attacker nodes packets, when measured by the victim node, derive to the exactly the same clock skew as the imitated node. Our experiment results show that the success rate of physical replication attacks ranges from 82.5% to 95%. In the second part of this study, a novel approach is proposed to defend against such clock skew replication attacks. This approach is based on our observation that a precise skew estimation can be performed only when the packets are sent at fixed time intervals. When the time period of the synchronization is changed frequently, our experiments show that the success rate of an attack is considerably reduced to less than 2.4%, or even 0% in most cases.

Versatile Humanoid Robots for Theatrical Performances

The purpose of this research is to develop multi-talented humanoid robots, based on technologies featuring high-computing and control abilities, to perform onstage. It has been a worldwide trend in the last decade to apply robot technologies in theatrical performance. The more robot performers resemble human beings, the easier it becomes for the emotions of audiences to be bonded with robotic performances. Although all kinds of robots can be theatrical performers based on programs, humanoid robots are more advantageous for playing a wider range of characters because of their resemblance to human beings. Thus, developing theatrical humanoid robots is becoming very important in the field of the robot theatre. However, theatrical humanoid robots need to possess the same versatile abilities as their human counterparts, instead of merely posing or performing motion demonstrations onstage, otherwise audiences will easily become bored. The four theatrical robots developed for this research have successfully performed in a public performance and participated in five programs. All of them were approved by most audiences.

Smart home at a finger tip: OSGi-based MyHome

This paper introduces MyHome, a framework of smart home by which household information is all at a finger tip. Through adopting Message Oriented Middleware (MOM) and Open Service Gateway Initiative (OSGi) technologies, MyHome offers reliable automatic operations, fault tolerant and configurable home automation, high extensibility and large scalability. In its design, MyHome system is composed of a residential gateway MyServer and Internet accessible GUI MyIcon and MyMobile. MyServer is used to provide services regarding home security, inventory tracking, facility management, GPS location recording and family care. Inherently an interactive and multitasking system driven by peripherals connected through wireless sensor networks, the overall MyServer architecture is designed with six core service modules operating on a MOM. Each of these modules is designed as an OSGi bundles and is implemented by a programming template utilizing event publish/subscribe messaging mechanism. To facilitate program demonstration, simulator and scenario editor are also developed. A successful implementation of the proposed MyServer is also demonstrated in an emulated home environment where peripherals are connected through ZigBee wireless sensor network with data integrated into a database. With these clearly defined service modules and pertinent infrastructure to integrate household peripherals, this paper presents a practical approach to the implementation of a smart home.

Clock Skew Based Client Device Identification in Cloud Environments

Along with the growth of cloud computing and mobile devices, the importance of client device identity concern over cloud environment is emerging. To provide a lightweight yet reliable method for device identification, an application layer approach based on clock skew fingerprint is proposed. The developed experimental platform adapts AJAX technology to collect the timestamps of client devices in the cloud server during connection time, then calculate the clock skews of client devices. Few methods based on linear regression and piecewise minimum algorithm are developed to optimize the precision and shorten timestamp collection process. A jump point detection scheme is also proposed to resolve the offset drifting problem, which is usually caused by switching network or temporary disconnection. Finally, two experiments are conducted to study the effectiveness of clock skew fingerprint, and the results illustrate that the false positive rate and the false negative rate, in the worst case, are both no more than 8% when the tolerance threshold is set appropriately.

Secured Flooding Time Synchronization Protocol

This research aims to complement security vulnerability of Flooding Time Synchronization Protocol (FTSP), which is currently one of the most sophisticated approaches for time synchronization in wireless sensor networks (WSNs). FTSP has advanced features like implicitly dynamic topology and high accuracy time, but its original design does not consider security issues. In order to defend against attacks from malicious nodes, we propose several techniques to reinforce the structure of FTSP. A reference node selecting mechanism is proposed to reduce the effect of multiple reference nodes, and four filters are proposed to defend against seqNum attack, global time attack, and node replication attack. Experiments of the above attacks are performed and the results show that all these attacks can be defended when sequence number blacklist filter and global time blacklist filter are adopted. Furthermore, fluctuation filter helps to reduce the data collection time from 10 sending cycles to 5 cycles when detecting global time attack.

Testbed Implementation of a Secure Flooding Time Synchronization Protocol

A fundamental building block in distributed wireless sensor networks is time synchronization. Given resource constrained nature of sensor networks, previous research has focused on developing various energy efficient time synchronization protocols tailored for these networks. However, many of these protocols have not been designed with security in mind. In this paper, we describe FTSP which is one of the major time synchronization protocols for sensor networks. We outline the adverse effects of the time synchronization attacks on some important sensor network applications, and explain the set of possible attacks on FTSP. We then propose a number of countermeasures to mitigate the effect of the security attacks. We implement these attack scenarios on a sensor network testbed and show the extent each attack is successful in desynchronizing the network. Finally, we implement the countermeasures on our sensor network testbed to validate their usefulness in mitigating security attacks. We show that adding a sequence number filter to the original FTSP helps mitigate the effect of attacks on this protocol.

A channel allocation scheme with dynamic priority for wireless mobile networks

A channel allocation scheme based on the technique of a guard channel employing dynamic priority with three queues (DPTQ) is proposed. DPTQ differs from most previously proposed schemes which focused only on reducing forced-termination for handoff calls. It tries to reduce blocking/dropping probabilities for new calls and data calls with a tolerable forced-termination probability for handoff calls in wireless networks. This scheme is especially suitable for operation in a hot spot in which fewer handoff calls may occur. In order to compare our scheme with the previously proposed dual-threshold bandwidth reservation (DTBR) scheme, in which no queue is employed, three queues are endowed with DTBR to form a dual-threshold with three queues (DTTQ) scheme. Through numeral comparisons, we show that DPTQ outperforms DTTQ in blocking/dropping probabilities for new calls and data calls with a bit increase of the forced-termination probability for handoff calls.