Nianmin Yao

A New Method to Protect Software from Cracking

There have been many methods to protect the commercial software from being cracked. But the crackers can always skip the protecting part through analyzing the assembly code of the software. A new protecting method is presented here. It breaks the original software into two parts. A part which is so important that it can’t be skipped, called key process of computing, is put at the remote server side and the rest runs on the local machine as usual. When the software runs into the departed part, it must call the remote part through RPC to get the right answer and goes on. We can see, in this method, the cracker can’t get the execution code of the remote part and he also can’t just skip the remote part. So the only way to crack the software protected by this method is to reimplement the key process of computing. If the key process of computing we select is complicated enough, to do it will be such a great work not less than reimplementing the whole software. This method is also easy to be deployed. The commercial software can be distributed by the internet and that is the cheapest way so far. The only shortcoming of it is that when the software is running, the machine must be connected onto the internet. That may not be a big problem when the internet can be connected to everywhere now.

Research of localization algorithm based on weighted Voronoi diagrams for wireless sensor network

Wireless sensor network (WSN) is formed by a large number of cheap sensors, which are communicated by an ad hoc wireless network to collect information of sensed objects of a certain area. The acquired information is useful only when the locations of sensors and objects are known. Therefore, localization is one of the most important technologies of WSN. In this paper, weighted Voronoi diagram-based localization scheme (W-VBLS) is proposed to extend Voronoi diagram-based localization scheme (VBLS). In this scheme, firstly, a node estimates the distances according to the strength of its received signal strength indicator (RSSI) from neighbor beacons and divides three beacons into groups, whose distances are similar. Secondly, by a triangle, formed by the node and two beacons of a group, a weighted bisector can be calculated out. Thirdly, an estimated position of the node with the biggest RSSI value as weight can be calculated out by three bisectors of the same group. Finally, the position of the node is calculated out by the weighted average of all estimated positions. The simulation shows that compared with centroid and VBLS, W-VBLS has higher positioning accuracy and lower computation complexity.

Fast Variants of the Backward-Oracle-Marching Algorithm

This study focuses on the faster exact single pattern string matching algorithms. In all solutions, two variants of BOM, EBOM and FBOM are very efficient. We improved them and presented two algorithms named Simplified-EBOM and Simplified-FBOM through removing the unnecessary branches and accomplishing the core calculation of the algorithm in a 1-dimensional array. The experimental results indicated that Simplified-EBOM is fast for short patterns and it is 12% faster than its basis algorithm on average.

Analyzing the performance of Aloha in string multi-hop underwater acoustic sensor networks

In this article, we intend to investigate the performance of channel access protocols in multi-hop underwater acoustic sensor networks, which are characterized by long propagation delays and limited channel bandwidth. An analytical model specifically designed for contention-based protocols in multi-hop underwater acoustic networks is identified and validated. The model is based on an underwater network model, called string topology network model, which provides a method for computing the expected network throughput and the probability of packets’ delivery to the gateway from an arbitrary sensor. This study demonstrates an improvement of an existing model, in which a node is implicitly assumed to be able to transmit two packets at the same time, which is not realistic due to the half-duplex character of underwater acoustic channels. Based on our findings, we propose a modified analytical model and evaluate it using NS-3 simulator. Results show that our analytical model is more precise than the existing one.

Tree-Mesh Based P2P Streaming Data Distribution Scheme

This paper presents the design of a novel P2P live streaming policy, tree-mesh based P2P Streaming Data Distribution Scheme(TMDS). Both the tree-based and the mesh-based structures have respective flaws while distributing the media data. The tree-based structure is highly vulnerable, so it is very suitable for the stable environment in small scale. And the mesh-based structure is quite stable, and can guarantee certain grade of service under the large-scale environment, but its costs of control are bigger, and also creates heavy load to the network. However TMDS can effectively solve these problems, and take advantage of their merits. Confirmed in the simulated environment, TMDS can: improve the quality of service; decrease the costs of system control, lighten the burden on the network; relieve the load on the transmitting end, enhance the stability of the system.

Cache Performance Simulation and Analysis under SimpleScalar Platform

Cache is an important component in computer architecture. It has great effects on the performance ofsystems. To provide references for the computer architecture designer, we analyzed various factors ofeffects on cache performance, and then carried out the simulation experiment of cache performance based on SimpleScalar tools set and SPEC2000 benchmark suite. We compared the effects on cache performance when L1-cache, L2-cache capacity and replacement methods are changed separately, and then we analyzed the experimental results in detail. The result is basically in keeping with the principle of architecture. At last we gave the reasonable cache parameters and conclusions.

A Fault Detection Service for Cluster-Based Ad Hoc Network

Ad Hoc Network becomes widely used for many specific fields. In case of frequently happened node failures and message losses, in order to expedite the development of applications, we propose a middleware service for the failure detection to support these applications. Based on the hierarchical-based and Gossip-based detection techniques, a fault detection service for cluster-based Ad Hoc Network integrating the proposed adaptive fault detector is proposed. Simulations show that the proposed detection service achieves a preferable system performance.

A New Key Management Scheme in Clustering Wireless Sensor Networks

Extension of life cycle has been one of the hot spots in Wireless Sensor Networks. Owing to limited capacity nodes fail as soon as energy is consumed, which tends to shorten survival time of entire wireless sensor network. Therefore, a clustering key management scheme based on hierarchical tree is proposed, furthermore dynamic update of networks is realized in the paper. In the hierarchical tree, child keys can be calculated according to their parent key, and nodes of different importance can be protected distinctively. The results show that it can not only ensure security of networks but also reduce the communication traffic, lower network overhead, and prolong life cycle of networks.

An Approximate Nearest Neighbor Query Algorithm Based on B^Z-Tree

R-tree can achieve better performance in low-dimensional space, but its performance suffers greatly in high-dimensional space. So the reduction of the dimensionality is the key to the problem. Z curve can fill d dimensional space linearly, divide the space into equal-size grids and map points lying in the grids into the linear space. BZ-tree is constructed using Z curve. BZ-tree is a balanced multi-branch tree. BZ-tree has the characteristic of B+-tree and R-tree. In BZ-tree, Z values of the points are the keywords, and all points are stored in leaf nodes, ordered by Z values. Using the reduction of the dimensionality of BZ-tree, the paper presents an approximate k-nearest neighbor query algorithm. According to the test, its running time is shorter than the Brute-Force method and the algorithm based on R-tree, and the quality of the approximate k-nearest neighbors is better.

Study on the data flow balance in NFS server with iSCSI

With the developing of the architecture of networked storage, a new type of storage servers acting as the data conduits over the network emerge, which is called pass-through servers. A typical example is the NFS servers based on iSCSI whose one end is connected to NFS clients and the other is connected to iSCSI storage device. As a store-and-forward device, the NFS servers experience heavy load, which includes protocols and data copying overhead, so a lot of CPU resource is consumed. In this paper, we build a mathematical model for the flow of data in pass-through servers using queuing theory and put forward a scheme of CPU time distribution. This scheme can allocate time of CPU to the service of iSCSI and NFS reasonably. Consequently, the flow rate of data inside servers is accelerated and the system performance is enhanced. We carry out both simulation experiments and real experiments to prove the conclusions. The results show that, if we properly adjust the CPU time distribution ratio according to different request sizes and different ratios of read/write requests, the system can improve the throughput more than 17% compared to the original one and can greatly reduce the mean response time of the data forwarding tasks.