(3) The World Wide Web PDF

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Download (3) The World Wide Web PDF

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Introduction: ● Invented by Tim Berners-Lee at CERN in Geneva, Switzerland in 1989. ● WWW is a way of accessing information on the internet, in which information is encapsulated in a web page and viewed in a web browser. ● Web pages are linked to one another via hypertext links. Hypertext Transfer Protocol (HTTP): ● It is a method of requesting and transmitting web pages. ● When a user clicks on a link/enters URL, a request is sent to the HTTP port of the associated web server. The server then responds to the client’s request - valid and resource is available = server transmits the resource; otherwise the server responds with an error message or not at all. ● Exchange is for all resources - images, videos, script files, etc. Search Engines: ● It’s a system that searches the web and catalogues the content of web pages. ● Users provide search criteria and the search engine presents a collection of web content that satisfies some/all of the criteria. ● Search criteria can be in the form of text, and can be combined with Boolean operators to improve specificity. ● Search results can be filtered, based on the geographic origin, timeframe, and content type. Web Analytics: ● Collection and analysis of data regarding website usage. ● Typically used by website owners to track the number and behaviours of users visiting their sites. ● Essentially, it tracks and reports everything that happens to an associated webpage. Hypertext Markup Language (HTML): ● Defines content of web page as a text file, with an.html extension. ● Tags (< or >) are used to specify content characteristics. ● Lines between significant tags are usually indented for human readability. Special Characters: ● Escape characters: ○ Characters such as “, &, need to be represented by a character sequence. ● Special characters: ○ Characters such as €, can be entered in Unicode, using dec/hex notation. Cascading Style Sheets (CSS): ● CSS describes how HTML elements are to be displayed on screen, or in other media. ● It defines the styles of text and other classes of content, such as background, images, etc. ● By controlling the layout of multiple web pages all at once, CC saves a lot of work. ● CSS can be added to the HTML elements by: ○ Inline - by using the style attribute in HTML elements. ○ Internal - by using a element in the section. ○ External - by using an external CSS file. JavaScript: ● JavaScript is a programming language significantly different from Java. It appears as an executable source code embedded in an HTML file. ● When executed, it can change the web page, or run a code on the client’s computer. ● Programming basics:

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Code is surrounded by braces { }. Functions and if-statements are used to indicate the demand. Events indicate the specific action or occurrence. A variable is used to name data and store values.

Forms: ● Allow users to provide information that is sent to a server for storage and/or processing. ● All input is joined together and sent to the server in a long string of named values. Cookies: ● Cookies are used to store permanent ID about a client’s visit to a specific web server, such as: ○ Identification information like username and credentials. ○ Display preferences like categories. ○ Shopping information like browsing history. ○ Regional/language preferences. ● Cookies are encrypted using JavaScript to read and write cookies, and is often not readable to humans. ● Cookies can be used to track down identity and location as well as other information. Web Security: ● Tracking is used to gain (unsolicited) info about you to be used for their (commercial) gain or even your loss. Tracking mechanisms include: cookies, browser fingerprinting, web beacon, JavaScript. Security Risks: ● On the client site: ○ Phishing: scams for client’s to provide personal information such as identity, credentials, bank information, etc. ○ Malware: malicious software. Includes: ■ Virus: can corrupt/delete/steal data or disrupt a computer system. Is spread by infecting other files and activated when file is run or opened. ■ Worms: able to replicate itself autonomously over networks. Generates network traffic and consumes resources. ■ Trojan: poses as a legit software that can be used for nefarious purposes. Capable of key logging, encrypt user data and RAT (remote administration tool). ● On the server site: ○ Servers can be hacked to steal data, or render the server inoperable. ○ Denial of service (DOS) attacks on the server results in the server gets overwhelmed with malicious and illegitimate requests. ■ Attack can be distributed using zombies, a compromised computer. A network of zombie computers are known as a botnet. ■ Due to the multiple number of sources of attack, it cannot be effectively blocked. ● On the communication links: ○ Data can be intercepted between you and the destination server. ○ Uses HTTPS connections when available, and often utilizes a virtual private network (VPN) service....