- An interlinked collected of hypertext document (web pages) residing on web server & other documents, menu and database, available via URLs.
- Web documents are marked for formatting and linking with HTML and web servers use HTTP to deliver web pages.
- WWW is a software application that makes it is and possible for nearly any one to publish and browse hypertext document on the internet.
- The World Wide Web is a collection of millions of file stored on thousands of computer called web servers all over the world.
- WWW is a most common access method of internet resources.
ELEMENTS OF WEB
- Web page is a resource of information that is suitable for the World Wide Web and can be accessed through web browser. This information is usually in HTML or XHTML format, and may provide navigation to other web pages via hypertext links.
- Web pages may be retrieved by local computer from a remote web server the web server may restrict access only to a private network for example corporate intranet.
- You can also publish pages on the world wide web WebPages are requested and served from web servers using HTTP.
- WebPages may consist of files or static text within web server's file system.
- The web server may construct XHTML for each webpage when it is requested by browser for dynamic WebPages.
- The first online website appeared in 1991; on 30th April 1995 the WWW would be free to anyone.
- A website is a collection of WebPages, images, videos or other digital assets that is hosted on the web server and accessible via internet.
- A webpage is documenting typically written in (X) HTML that is almost always accessible via HTTP.A protocol that transfers information from the web server to display in web browser.
- The pages of websites can usually be accessed from a common URL, some websites require a subscription to access some are free accessible.
- A web browser can have graphical user interface like internet explorer, Mozilla fire fox or opera or can be text based browser of lynx.
- Users of fully graphical browsers may still disable the download and viewing images and other media to save time, network bandwidth or just to simplify their browsing experience.
- Users may also prefer not to user the fonts, font sizes, styles and color schemes selected by the web page designer and may apply their own CSS styling to their viewed version of the page.
- The World Wide Web consortium (W3C) and web accessibility initiative (WAI) recommend that all web pages should designed with that criteria.
- A computer that runs program described above is call web server.web servers have also the capability of logging some detailed information about client requests and server responses to log files this allows the webmaster to collect statics by running log analyzers on log files.
- Web server is able to handling static as well as dynamic contents compression of content and transfer.
INTRODUCTION TO WEB LANGUAGES
HTML [Hypertext Markup Language]:-
- HTML stands for hyper text markup language. HTL provide instructions to web browser in order to control how documents are viewed and how they ate related to each other.
- HTML develops a few years ago as a subset of SGML (standard generalized markup language) which is a higher level markup language. That has long been a favorite of the department of defense.
- HTML is language interpreted by browser. Web pages are also called html document. Html is a set of special codes that can be embedded in text to add formatting and linking information.
- HTML is specified as TAGS in html document.HTML allows the individual elements on the web to be brought together and presented as collection of text, images, multimedia and other files can all be packaged together using html. It's basic structure element is <html>,<head>,<title> and <body>.
- Structure of HTML
<TITLE>:: Patel Kelvani Mandal ::</TITLE>
Any thing you write inside this body tag will be displayed on the browser.
DHTML [Dynamic Hypertext Markup Language]:-
- DHTML stands for dynamic hypertext markup language. DHTML is a Microsoft enhancement of HTML version 4.0 , with the help of DHTML you can created special effect such as rotating text and images , creating menus in the web page and give effect to user interface and also put validation on the form.
- Using java script you can create a dialog boxes and message boxes and put validation over each and every element of the form container. Using CSS [cascading style sheet] you can give effect to the text and different elements of web page by set the values of attributes.
VISUAL BASIC SCRIPT:
- VB script is a web scripting language. VBScript is created by Mocrosoft Corporation hence MSIE works with it while Netscape client doesn't support VB script.
- VBScript is embedded into html program in the head tag and body tag portion of the page.
- If it is refer to specific form object it must follows the body tag.
- The main different between VBScript and Java Script are in VBScript code terminates with a colon sign , where java script code terminates with semicolon.
<TITLE>:: Patel Kelvani Mandal ::</TITLE>
Msgbox "patel kelvani mandal college of technology":
Any thing you write inside this body tag will be displayed on the browser.
- Java script is web scripting language. Java script is created by Netscape hence. Java script works best with Netscape client.
- Java script can be embedded into html page that runs immediately on the client machine.
- Java script's first name was "LIVE SCRIPT" but Netscape decide to exchange of java popularity and rename the product as java script , java script is object based language.
- Java script is not a part of java language.
XML [Extended Markup Language]:
- Extended markup language is much like html & is a W3C specification
- XML is powerful medium of data exchange. It allows you to create your own tag to represent data and meta data.
- The power of xml is that it maintains the separation of the user interface from the structured data.
- Html specify how to display data in browser where as XML defines the contain for example, in html you use tag to display data as bold or italic.
- In XML you only use text to describe data such as city name, temperature, zip code etc.
- In XML you only use style sheets such as XSL [extended style sheet language] and CSS [cascading style sheet] to present the data in browser.
- There are many tools available to create XML documents and then to load, read XML documents and then to load, read validate and parse those documents this allows application running on totally different platform to exchange data because everybody understand "text" and XML document it nothing a tagged text document.
- All xml documents are having "*.xml" extension. XML use DTD document type definition to describe the data.
WML [Wireless markup language]:
- WML stands for wireless markup language .WML is formally called HDML [handled devices markup language].
- WML is a language that allows the text portions of web pages to be presented on cellular phone and PDA personal digital assistants via wireless access.
- WML is a part of the WAP [Wireless Application Protocol].
- WAP works on top of standard data link protocols such as global system for mobile communication CDMA [Code Division Multiple Access] and TDMA [Time Division Multiple Access].
- WML is a open language offered royalty free.WML is based on XML, It's pages are known as deck and decks are constructed as set of cards and card is basic unit of WML, WML is case sensitive language.
PHP [Personal Home Page]:
- PHP is also known as preprocessed hypertext its recursive full form of PHP. PHP is server side scripting language.PHP script is executed on the server.
- PHP supported many databases like Oracle, MS-SQL, MY-SQL etc.PHP is open source language and mostly used with open sourced database like MY-SQL.
- PHP file contains php script, HTML tags and Text also.
- It's having reach set of class and function. its object oriented version is PHP5 and up to PHP3 its procedure oriented language.
VRML [Virtual Reality Markup Language]:
- Is an attempt to extend the web into the domain of three dimension graphics VRML "world" can depict realistic or other worldly places which can contain objects that link to other html documents or vrml world on the web site.
- It is used to create virtual reality worlds that you can fly around in to find information although still in its infancy. It will most certainly be a language that dominates the future .web pages will most likely only be used to place in virtual world and accessing a document from a virtual book
- VRML is a simple ASCII text description of geometries that can be hired across various platforms like UNIX, MAC and Windows. It is based on open invent file format .it has been extended to support web oriented capabilities like hyperlinks and elective refinement.
- VRML is a recent invention intended to be a three-dimensional analog to hypertext markup language (HTML).
- VRML is intended to accomplish just that elaborate 3D environments can be designed and the browser allows you to move within the artificial 3D environment, and move from one environment to another by links.
- Latest version of VRML is 2.0 it is having extension "*.WRL" you can not directly run this page on MSIE you need one plug-in to be installed before run any VRML file its name is Microsoft VRML 2.0 viewer.
- Web surfing is typical approach for find information on the web because surfing is unstructured and random browsing.
- Web surfing is starting with particular web page in this approach is to follow links from one page to another.
- A number of tools have been developed that enable to find information very quickly and effectively from the web.
- Finding the information on the web using two independent approaches.
- Browsing through subject trees and hierarchies (using web index)
- Using keyword or phrases you can search (using web search engine).
- A web index is design to assist users with locating information on the web. Web indexes are also sometime referring as a directory.
- A web index collects and organize resources available via the web or www.There are number of web indexes are available on the web.
- Indexes may present information alphabetically. Web index is use hyper text to present of interest and also actually link directly to the resources from the index.
- Due to vast amount of information available via the web number of single index resources.
- Web index can link hundreds, thousands or more resources. Some web index has many resources that provides a searching capability for user to have to find out the resources within the web index.
WEB SEARCH ENGINE
- The ability to search the web for specific sites or files relies on one tiny factor it is existence of searching and indexing sites that you can access to perform the search.
- These sites are often known as web spiders, crawlers or robots because they endlessly and automatically search the web.
- Search site will create huge databases of all the words in all pages they have and you can search those databases simply by entering keywords you want to find.
- Despite the size of this vast store of information it can generally returns a result to the user within second or two.
- Each day search engine going to store lots of information in its serve and then as per the search criteria search engine will return the information.
META SEARCH ENGINE
- A met search engine or all in one search engine performs a search by calling on more than one other search engine to do the actual work. The results are collated. Duplicate retrievals are eliminated and the result are ranked according to how well they match your query. You are then presented with a list of URLs.
- The advantage of a meta search engine is that you can access a number of different search engines with a single query. The disadvantage is that you will often have a high noise-signal ratio that is a lot of "Matches" .that will not be of interest of you this means you will need to spend more time evaluating the results and deciding which hyperlinks to follow.
- For very specific , hard to locate topics , meta search engine can often be a good starting point for example, if you try to locate a topic using your favorite search engine, but fail to turn up anything useful you may want to query a meta search engine.
- There are some examples of meta search engine like
www.metasearch.com, www.metacrawler.com, www.metafind.com,etc.
- Some websites store information in a small text file on your computer this called a cookies.
- Cookies stored information such as personal information like user name , geographical area or personal references like background color, text font size, color or face etc.
- These are several types of cookies and you can choose whether to allow some none or all of them to be saved on your computer.
- A cookie is a file created by an internet site to store information on your computer such as your preferences when visiting that site. For example, If you inquire about flight schedule at an airline's web site, the site might create cookie that contains a records of the pages you looked at within the site you visited, whenever we can see next time it may be speedy.
- Once a cookie is saved on your computer, only the website that created the cookie can read it. A cookie file is easily accessed and modify by the user because it is stored on user system. there are following types of cookie.
- PERSISTENT COOKIE: It is one stored as file on your computer then, it remains there when you close internet explorer. The cookie can be read by the website that created it when you visit that site again.
- TEMPORARY COOKIES: A temporary or session cookie is stored only for your current browsing session, and is deleted from your computer when you close internet explorer.
- UNSATISFACTORY COOKIES: Unsatisfactory cookies are cookies that might allow access to personally identifiable information that could be used for a secondary purpose without your consent.
- FIRST-PARTY COOKIES: A first party cookie either originates on or is sent to the web site you are currently viewing these cookies are commonly used to store information, such as your preferences when visiting that site.
- THIRD-PARTY COOKIES:A third party cookie either originates on or is sent to a website different from the one you are currently viewing third party web-site usually provide some content on the web-site you are viewing for example, many sites advertising from third party websites and cookies. A common use for this type of cookie is to track your webpage use for advertising or other marketing purpose. Third party cookie either persistent or temporary cookies
- A firewall is dedicated application or software or hardware running on another computer which inspect network traffic passing through it, and denies or permits passage based on a set of rules.
- A firewall's basic tasks is to regulate some of the flow or traffic between computer networks of different trust levels typical examples are the internal network which a zone of higher trust so firewall will work between those zone internet and internal network.
- A firewall used to prevent network disturbance to the private network. Without proper configuration firewall can often became worthless those configuration requires detailed understanding of network application. For example AVG firewall, STGATE firewall, COMODO firewall are software firewalls. Some operating system like windows xp having its own inbuilt firewall.
- A hacker is a person intensely interested in the secret and complex workings of any computer operating system. Hackers are most often programmers. As such, hackers obtain advanced knowledge of operating systems and programming languages. They might discover holes within systems and the reasons for such holes. Hackers constantly seek further knowledge; freely share what they have discovered, and never intentionally damage data.
- Hackers (as opposed to crackers) are basically thrill-seekers who use information technology rather than fast cars or bungee cords. They spend their time learning how systems work at a deep level and exploit this information to roam the information highways seeking out adventure. They have bulletin boards for sharing information, regular meetings. . . .
- Hackers are "thrill-seekers", they learn how computer systems work, and they are adventure-seekers.
- "people who love to explore the hidden depths of computing systems"
- "Hackers are defined as computer enthusiasts who have an enthusiastic interest in learning about computer systems and how to use them in innovative ways."
- "A scatter group of people often called 'hackers' has been characterized as unethical, irresponsible, and a serious danger to society for actions related to breaking into computer systems . . . . Hackers are learns and explorers who want to help rather than cause damage, and who often have very high standards of behavior.
- It is against hacker ethics to alter any data aside from the logs that are needed to clean their tracks. They have no need of desire to destroy data as the malicious crackers. They are there to explore the system and learn more. The hacker has a constant yearning and thirst for knowledge that increases in intensity as their journey progresses.
- A cracker is one who breaks into or otherwise violates the system integrity of remote machines with cruel intent. Having gained unauthorized access, crackers destroy vital data; deny rightful users service, or cause problems for their targets. Crackers can easily be identified because their actions are cruel.
- Additionally, it should be mentioned that there are two major types of crackers. The first is fortunately few and far between. They are the expert crackers who discover new security holes and often write programs that take advantage of them. The second type, the script kiddies, only knows how to get these programs and run them. Script kiddies are more frequent, but much easier to stop and detect.
- A program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes, viruses can also replicate themselves.
- All computer viruses are manmade and simply virus that can make a copy of it over and over again is relatively easy to produce.
- Even such a simple virus is dangerous because it will quickly use all available memory and bring a system to halt. An even more dangerous type of virus is one capable of transmitting itself across network and bypassing security system.
- A worm is special kind or virus that can replicate itself and use memory, but cannot attach itself to other programs and harm data.
- A Trojan horse is full of as much trickery as mythological Trojan horse it was named after the Trojan horse because at first glance it will appear to be useful software but will actually do damage once installed or run on your computer like virus and worms will not reproduce itself.
- Mixture of all those is call blended threat. A blended threat is a sophisticated attack that bundles some of the worst aspects of viruses, worms and Trojan horses and malicious code into one threat.
- Blended threats use server and internet to initiate transmit and spread an attack. This combination of method and techniques means it will spread quickly and cause wide spread damage.
- Cryptography is science of securing data. Cryptography is the process of transforming original information into an unreadable form it may be sent over unsafe communication channel.
- Encryption is the transformation of data into an unreadable form using encryption and decryption key. There is two types of Encryption.
- Symmetric Encryption (Private Key Encryption)
- Symmetric encryption that the same key is used for message encryption and decryption process.
- For example sender would encrypt a message using a key and then send the message to receiver. Sender would separately communicate the key to receiver to allow him decrypt message to maintain security and privacy however sender and receiver both have to ensure that the key remains private to them.
- Symmetric encryption method is very simple but the simplicity of symmetric encryption is also the source of its problem.
- As the number of people increases. The management of the private keys becomes a costly and cumbersome exercise. Some well known example of this type of encryption DES [ data encryption standard] , IDES [international data encryption standard],AES[advanced encryption standard].
- Asymmetric Encryption (Public Key Encryption)
- Asymmetric or public key encryption differs from symmetric encryption by using a pair of keys instead of single key. one of the key is kept private while the second is made public key so that it can be accessed by any one.
- The key pair works in complementary manner information encrypted by one key can only be decrypted using the other. Only the recipient's private key can decrypt the message, As long as the private key remains secure , then the sender can be sure that only the intended recipient can possibly read the message.
- For example sender is sending a message to receiver and sender will creates a message then encrypts it using receiver's public key. When receiver having encrypted message then use secret private key to decrypt that message, As long as receiver's private key has not been compromised then both sender and receiver knows that message is secured.
- Digital Signature
- Digital signature is one type of asymmetric encryption but in digital signature message is encrypt and decrypt two times.
- It works as below figure.
- Before the sender will send plain text message, sender will do first encryption using the sender's private key which work as digital signature then sender will re-encrypt message using the receiver's public key after that process sender will send the encrypted message to receiver.
- When receiver will receive that message and then decrypt that message by using the receiver's private key and then receiver will re-decrypt that message using the sender's public key.
- Let us extend the example by declaring mr.A as a sender and mr.B as receiver.
- A will encrypt the message using his private key (digital signature)
- A will again encrypt the message using public key of mr.B (second encryption)
- A will send that message to B
- B will decrypt the message using his private key.(first decryption)
- B will re-decrypt message using mr.A's public key
- However this method is not efficient because it involves a lot of time and computer resources the encryption and decryption process are double it takes still longer time and more resources.
- A digital certificate is a file that identifies a person or organization. A digital certificate also known as digital signature
- The organization has gone to some certifying authority and gotten a digital signature.
- When organization server wants to convince your browser, it sends its certificate file. Your browser checks that the certifying authority is on the list that the browser manufacturer programmed into it. Then the server and the browser have a short conversation.
- Organization's server proves that it knows the private key that certificate says, your browser then ready to accept that it is dealing.