In order to transmit the secure message, a deterministic secure quantum direct communication protocol which was called ＂Ping-pong＂ protocol was proposed by Bostrrm and Felbinger [Bostrom K, et al. Phys Rev Lett, 2002, 89： 187902]. But the protocol was proved very vulnerable, and can be attacked by an eavesdropper. An improved ＂Ping-pong＂ protocol is presented to overcome the problem. The GHZ state particles are used to detect eavesdroppers, and the classical XOR operation which serves as a one-time-pad is used to ensure the security of the protocol. During the security analysis, the method of the entropy theory is introduced, and three detection strategies are compared quantitatively by using the constraint between the information which an eavesdropper can obtain and the interference introduced. If the eavesdropper gets the full information, the detection rate of the original ＂Ping-pong＂ protocol is 50%; the detection rate of the second protocol which used two particles of EPR pair as detection particles is also 50%; and the detection rate of the presented protocol is 75%. In the end, the security of the pro-posed protocol is discussed. The analysis results show that the improved ＂Ping-pong＂ protocol in this paper is more secure than the other two.
Contextual advertising is a major revenue source for today＇s companies. Keyword extraction is a key step in this kind of advertising, through which appropriate advertising keywords are extracted from Web pages so that corresponding ads can be triggered. This paper describes a system that learns how to extract keywords from web pages for advertisement targeting. Firstly a text network for a single webpage is build, then PageRank is applied in the network to decide on the importance of a word, finally top-ranked words are selected as keywords of the webpage. The algorithm is tested on the corpus ofblog pages, and the experimental results prove practical and effective.
