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Several protocols have been proposed to defend against wormholes in ad hoc networks by adopting positioning devices, synchronized clocks, or directional antennas. In this paper, we propose a mechanism, MDS-VOW, to detect wormholes in a sensor network. MDS-VOW first reconstructs the layout of the sensors using multi-dimensional scaling. To compensate the distortions caused by distance measurement errors, a surface smoothing scheme is adopted. MDS-VOW then detects the wormhole by visualizing the anomalies introduced by the attack. The anomalies, which are caused by the fake connections through the wormhole, bend the reconstructed surface to pull the sensors that are faraway to each other. Through detecting the bending feature, the wormhole is located and the fake connections are identified. The contributions of MDS-VOW are: (1) it does not require the sensors to be equipped with special hardware, (2) it adopts and combines the techniques from social science, computer graphics, and scientific visualization to attack the problem in network security. We examine the accuracy of the proposed mechanism when the sensors are deployed in a circle area and one wormhole exists in the network. The results show that MDS-VOW has a low false alarm ratio when the distance measurement errors are not large.

Multimedia data secmity is important for multimedia commerce. Previous cryptography studies have focused on text data. The encryption algorithms devdoped to secure text data may not be suitable to multimedia applications becattse of large data sizes and real time constraint. For multimedia applications, light weight encryption algorithms are attractive.We present a novel MPEG Video Encryption Algorithm, called VEA The basic idea of VEA is to use a secret key randomly changing the sign bits of all of the DCT coefficients of MPEG video. VEA'S encryption effects are achieved by the IDCT during MPEG video decompression processing. VEA adds minimum overhead to MPEG codecj one Mm&e XOR operation to each none zero DCT coefficient. A software implementation of VEA is fast enough to meet the real time requirement of MPEG video applications. Our experimental results show that VEA achieves satisfying results. We believe that it can be used to secure video-on-demand, tideo conferencing and video email applications.

Providing secure and efficient access to large scale outsourced data is an important component of cloud computing. In this paper, we propose a mechanism to solve this problem in owner-write-users-read applications. We propose to encrypt every data block with a different key so that flexible cryptography-based access control can be achieved. Through the adoption of key derivation methods, the owner needs to maintain only a few secrets. Analysis shows that the key derivation procedure using hash functions will introduce very limited computation overhead. We propose to use over-encryption and/or lazy revocation to prevent revoked users from getting access to updated data blocks. We design mechanisms to handle both updates to outsourced data and changes in user access rights. We investigate the overhead and safety of the proposed approach, and study mechanisms to improve data access efficiency.

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