Tree-Based Index Overlay in Hybrid Peer-to-Peer Systems

Hybrid Peer-to-Peer （P2P） systems that construct overlay networks structured among superpeers have great potential in that they can give the benefits such as scalability, search speed and network traffic, taking advantages of superpeer-based and the structured P2P systems. In this article, we enhance keyword search in hybrid P2P systems by constructing a tree-based index overlay among directory nodes that maintain indices, according to the load and popularity of a keyword. The mathematical analysis shows that the keyword search based on semi-structured P2P overlay can improve the search performance, reducing the message traffic and maintenance costs.

Towards Risk Evaluation of Denial-of-Service Vulnerabilities in Security Protocols

Denial-of-Service （DOS） attacks are virulent to both computer and networked systems. Modeling and evaluating DoS attacks are very important issues to networked systems; they provide both mathematical foundations and theoretic guidelines to security system design. As defense against DoS has been built more and more into security protocols, this paper studies how to evaluate the risk of DoS in security protocols. First, we build a formal framework to model protocol operations and attacker capabilities. Then we propose an economic model for the risk evaluation. By characterizing the intruder capability with a probability model, our risk evaluation model specifies the ＂Value-at-Risk＂ （VaR） for the security protocols. Tile ＂Value-at-Risk＂ represents how much computing resources are expected to lose with a given level of confidence. The proposed model can help users to have a better understanding of the protocols they are using, and in the meantime help designers to examine their designs and get clues of improvement. Finally we apply the proposed model to analyze a key agreement protocol used in sensor networks and identify a DoS flaw there, and we also validate the applicability and effectiveness of our risk evaluation model by applying it to analyze and compare two public key authentication protocols.

A Multi-Key Pirate Decoder Against Traitor Tracing Schemes

In this paper we introduce an architecture for a multi-key pirate decoder which employs decryption keys from multiple traitors. The decoder has built-in monitoring and self protection functionalities and is capable of defeating most multiple-round based traitor tracing schemes such as the schemes based on the black-box confirmation method. In particular, the proposed pirate decoder is customized to defeat the private key and the public key fully collusion resistant traitor tracing （FTT） schemes, respectively. We show how the decoder prolongs a trace process so that the tracer has to give up his effort. FTT schemes are designed to identify all the traitors. We show that decoder enables the FTT schemes to identify at most 1 traitors. Finally, assuming the decoder is embedded with several bytes of memory, we demonstrate how the decoder is able to frame innocent users at will.

Level-of-Detail Rendering of Large-Scale Irregular Volume Datasets Using Particles

This paper describes a level-of-detail rendering technique for large-scale irregular volume datasets.It is well known that the memory bandwidth consumed by visibility sorting becomes the limiting factor when carrying out volume rendering of such datasets.To develop a sorting-free volume rendering technique,we previously proposed a particle-based technique that generates opaque and emissive particles using a density function constant within an irregular volume cell and projects the particles onto an image plane with sub-pixels.When the density function changes significantly in an irregular volume cell,the cell boundary may become prominent,which can cause blocky noise.When the number of the sub-pixels increases,the required frame buffer tends to be large.To solve this problem,this work proposes a new particle-based volume rendering which generates particles using metropolis sampling and renders the particles using the ensemble average. To confirm the effectiveness of this method,we applied our proposed technique to several irregular volume datasets,with the result that the ensemble average outperforms the sub-pixel average in computational complexity and memory usage. In addition,the ensemble average technique allowed us to implement a level of detail in the interactive rendering of a 71-million-cell hexahedral volume dataset and a 26-million-cell quadratic tetrahedral volume dataset.