1、外文资料 Parts of computer technique brief introduction Compendium Computer technique more the renewal being placed in continuously changes the on behalf inside, each a strenuous efforts for new technical emergence all coagulating numerous person.In this article, we simple introduction some of that. Sea
2、rch Engines Internet search tools fall into two camps： search engines, such as HotBot and AltaVista， and online directories， such as Yahoo and Lycos The difference between the two is related to how they compile their site listings Of course， there are exceptions to every rule Some search utilities s
3、uch as Ask Jeeves， combine the search engine and directory approaches into a single package， hoping to provide users with the best of both worlds In directory-based search services ， the Web site listings are compiled manually For example， the everpopular Yahoo dedicates staff resources to accept si
4、te suggestions from users review and categorize them， and add them to a specific directory on the Yahoo site You can usually submit your Web site simply by filling out an online form On Yahoo,forexample,youll find submission information at Because human intervention is necessary to process， verify，
5、 and review submission requests， expect a delay before your site secures a spot in a directory-based search service On the flip side， search engines completely automate the compilation process，removing the human component entirely A software robot， called a spider or crawler， automatically fetches s
6、ites all over the Web， reading pages and following associated links By design， a spider will return to a site periodically to check for new pages and changes to existing pages Results from spidering are recorded in the search engine s index or catalog Given the wealth of information available on the
7、 Internet， it is not surprising that indexes grow to very large sizes For example， the AltaVista index has recently been increased to top out at 350 million pages This may seem like a mammoth number， but by all estimates it still represents less than 35 percent of all pages on the Web Because of the
8、 depth and breadth of information being indexed， there is usually a delay， sometimes up to several weeks， between the time a site has been“ spidered”and when it appears in a search index Until this two-step process has been completed，a site remains unavailable to search queries Finally， the heart of
9、 each search engine is an algorithm that matches keyword queries against the information in the index， ranking results in the order the algorithm deems most relevant Because the spiders， resulting indexes， and search algorithms of each search engine differ， so do the search results and rankings acro
10、ss the various search engines This explains why a top 10 site in HotBot may not appear near the top of Alta Vista when the same keyword search criterion is entered In addition， many， but not all， search utilities also reference metatags invisible HTML tags within documents that describe their conten
11、t as a way to control how content is indexed As a result， proper use of metatags throughout a site can also boost search engine ranking Advanced Encryption Standard For the past three years， the National Institute of Standards and Technology (NIST) has been working to develop a new encryption standa
12、rd to keep government information secure The organization is in the final stages of an open process of selecting one or more algorithms， or data-scrambling formulas， for the new Advanced Encryption Standard (AES) and plans to make adecision by late summer or early fall The standard is slated to go i
13、nto effect next year AES is intended to be a stronger， more efficient successor to Triple Data Encryption Standard (3DES)， which replaced the aging DES， which was cracked in less than three days in July 1998 “ Until we have the AES， 3DES will still offer protection for years to come So there is no n
14、eed to immediately switch over，” says Edward Roback， acting chief of the computer security division at NIST and chairman of the AES selection committee“ What AES will offer is a more efficient algorithm It will be a federal standard， but it will be widely implemented in the IT community” According t
15、o Roback， efficiency of the proposed algorithms is measured by how fast they can encrypt and decrypt information， how fast they can present an encryption key and how much information they can encrypt The AES review committee is also looking at how much space the algorithm takes up on a chip and how
16、much memory it requires Roback says the selection of a more efficient AES will also result in cost savings and better use of resources “ DES was designed for hardware implementations， and we are now living in a world of much more efficient software， and we have learned an awful lot about the design
17、of algorithms，” says Roback“ When you start multiplying this with the billions of implementations done daily， the saving on overhead on the networks will be enormous” The process of selecting the algorithm for AES has been notable for its openness and transparency This is a marked departure from the
18、 governments past inclination toward secrecy in discussing encryption standards， which led to the public cracking of DES after critics questioned the governments assertion that the standard was still secure NIST kicked off the selection process in September 1997 Conferences were held in August 1998
19、and March 1999； cryptographers from around the world discussed the algorithm candidates and helped narrow the list to 15 and then to five finalists： IBMs MARS； RSA Laboratories* RC6 ； Joan Daemen and Vincent RijmensRijndael； Ross Andersen， Eli Baham and Lars Knudsens Serpent； and Counterpane Labs* T
20、wofish While most evaluators of the algorithms want to avoid complexity by selecting one to serve as a standard， theres a minority that wants to select more than one Digital Wallets A digital wallet is software that enables users to pay for goods on the Web. It holds credit-card numbers and other pe
21、rsonal information such as a shipping address Once entered， the data automatically populates order fields at merchant sites. When using a digital wallet， consumers dont need to fill out order forms on each site when they purchase an item because the information has already been stored and is automat
22、ically updated and entered into the order fields across merchant sites. Consumers also benefit when using digital wallets because their information is encrypted or protected by a private software code. And merchants benefit by receiving protection against fraud Digital wallets are available to consumers free of charge， and theyre fairly easy to obtain For example， when a consumer makes a purchase at a merchant site thats set up to handle server-side digital wallets， he types his name and payment and
