According To Filter Safe Application Study Of Technical E-mail Of The Net Pass

E-mail is one of import application in the Internet. Corporations can use e-mail doing electronic business affairs. The e-mail's security problems must be ensured with. It has four basic aspects: confidentiality, integrality, rationality and validity. Now security problems have been mainly exist in two facts: one is security defect of mail transfer protocol, the other is security defect of mail system. Security defect of mail system mainly is that hacker utilizing security defect of mail system directly bring about attack, such as the defect of outlook can be attacked by hacker. The security defect of mail transfer protocol mainly is that mail transfer protocol exist security defect in itself, because of establishment step not take into account security problems. Based on mail transfers is accomplished by mail system and mending mail transfer protocol is difficult. The necessity of choice to solute this problem is to mend mail system in order to strengthen mail's security.Now, mail system can satisfy with commonly e-mail confidentiality, integrality and validity. But the request of e-mail rationality can't be recognized (e-mail rationality is that e-mail haven't content of transgressing and lawless, blowing the gaff, or junk mail.). E-mail security can be improved by mending mail system. If a mail filter gateway can be placed in the entry of mail system and internet, or between MUA and MTA, or between MTA and MDA, e-mail security should be mended greatly. The mail filter gateway will ensure security of e-mail transfers by adopting technology of encrypting technology and digital signature to ensure e-mail confidentiality, integrality and validity. On the other hand, mail filter gateway strengthen filtrating e-mail content to ensure e-mail rationality. Now mail filter gateway that is a part of e-mail system can be more and more recognized. It is a good method which a mail filter gateway placed in the entry of mail system for corporation filter come-and-go e-mail's content. So investigation of e-mail filter gateway is greatly necessary.In this paper, we firstly analyze the weak points of conventional mail transfer protocol, especially the weak points of the mail filtering. Thus, we gives out the goalof the research work. In this paper, we give out an design of the mail filter gateway for corporation use. The design use SMTP, POP3, HTTP transfer protocol, and adopt 'servlet' technology to make software module more agility and expansion in deploy. In this paper, we discuss how to filter mail's content, and make clear the architecture and the theory of them. We represent the four-layer architecture of the mail filter gateway, including mail received layer, the mail's data transfer layer, the mail content analysis layer and the mail storage layer. Based on the idea, we finally bring forward each layer's mechanism, the implement detail of the gateway and the enhanced algorithm.Mail received layer is lowest layer in mail gateway. It answer for receiving e-mail data in network.. Receiving e-mail data in network come from 25 port and 110 port. Data coming from 25 port is data that can be used in SMTP transfer protocol. Data coming from 110 port is data that can be used in POP3 transfer protocol. Mail received layer running two thread. The primary thread answer for primary process initialization. Monitoring thread answer for receiving data in network by utilizing monitoring technology,analyzing data to subject data and straight matter data and carry these data to mail content analysis layer. Communication technology in two layers mainly is servlet technology. With containing some request to http request two layers realize separation. In addition mail received layer notice mail security by adopting technology of timing connect and holding back buffer overflow.Mail's data transfer layer is the second layer in mail gateway. It contain some model. The first model's function is to decode mail data receiving from mail received layer based on MIME coding,carry these data to the mail content analysis layer, such as mail's length, transmitting single, and return control single. Another model's function is to decode data based on subject data, if mail data were encrypted.The mail content analysis layer collaborating with the mail's data transfer layer filtrate e-mail content based on rule database, mainly is to filtrate text content. The filtration include subject filtration and content filtration. Filtrating technology is keyword matching technology in this paper. To filtrate subject adopt integral matching technology and to filtrate text content adopt multi-pattern matching technology. Ruledatabase include rule table and info table. Rule table include some 'black list' which comprise of some keyword set up by administrator. Info table is some table storing each client information and convenient for people consulting or storing mail information. The mail content analysis layer touch off different control single based on filtrating result and carry these single to mail received layer by mail's data transfer layer. The mail content analysis layer running two thread: primary thread and filtrating thread. The primary thread answer for primary process initialization and respond in request from other layer. The filtrating thread answer for filtrating mail content based on rule database.The mail storage layer have two model. The first model's function is to receive data from the mail content analysis layer and store them in mailbox's name. The second model's function is to offer to some service for clients, such as storing service.