MODULE I-WEB TECHNOLOGY AND WEB SECURITY

1. WEB TECHNOLOGY ANDWEB SECURITY

2. WEB ESSENTIALS

3. SERVER • The software that distributes the information and the machine • where the information and software reside is called the server. • provides requested service to client • e.g., Web server sends requested Web page • Sending and receiving emails • Building and publishing websites

4. CLIENT • The software that resides on the remote machine, communicates with the server, fetches the information, processes it, and then displays it on the remote machine is called the client. • Initiates contact with server (―speaks first‖) • Typically requests service from server • Web: client implemented in browser

5. WEB SERVER • Software that delivers Web pages and other documents to browsers using the HTTP protocol • Sending the file to the client associated with the requested URL.

6. Example of web server • Apache HTTP Server. Developed by Apache Software Foundation, it is a free and open source web server for Windows, Mac OS X, Unix, Linux, Solaris and other operating systems; it needs the Apache license. • Microsoft Internet Information Services (IIS). Developed by Microsoft for Microsoft platforms; it is not open sourced, but widely used • Nginx. A popular open source web server for administrators because of its light resource utilization and scalability. It can handle many concurrent sessions due to its event-driven architecture. Nginx also can be used as a proxy server and load balancer. • Sun Java System Web Server. A free web server from Sun Microsystems that can run on Windows, Linux and Unix. It is well-equipped to handle medium to large websites.

7. WEB PAGE • A web page is a document or resource of information that is suitable for the World Wide Web and can be accessed through a web browser. • Information is transferred on the internet in page format. These pages are known as Web Pages. • Web Pages are displayed on the computer using special Web browsing software • Mozilla Firefox, Chromium, Microsoft Edge, Safari, etc. are examples of web browsers • A web page may contain text, graphics, and hyperlinks to other web pages and files. 

8. WEBSITE • A collection of pages on the World Wide Web that are accessible from the same URL and typically residing on the same server. • A webpage is a part of a website; it means a website contains different web pages. • Such as javaTpoint.com is a website, and • the page currently you are accessing is the webpage. • It can be understood as an example of a book. So, a Website is like a complete book, and a webpage is like a page of that book.

9. URL(UNIFORM RESOURCE LOCATOR) • Uniform Resource Locator, the unique address which identifies a resource on the Internet for routing purposes. • URL helps the user locate a web page, gopher service, library catalogue, image, or text file locations. • URLs are the standard addressing system of the www. • A complete URL provides the web client with all the information it needs to contact a server and make a request for information.

10. URLs divided into three essential parts: • Example: https://www.ecomputernotes.com/software  • Protocol(http ://) – The information appearing before the colon in any URL indicates the type of information server or protocol. For example, http:// indicates that the server to be connected is a www server.  • Domain name (www.ecomputernotes.com)– The second piece of information is the address of the server. In this example, ecomputernotes.com is the name of the machine at PS Exam on the World Wide Web.  • Resource name (software.htm) – The third piece of information is the path to the actual document requested. In this example, the URL indicates that the document in the system directory and is named software.htm. 

11. Client-server paradigm: •  In the client-server architecture, when the client computer sends a request for data to the server through the internet, the server accepts the requested process and deliver the data packets requested back to the client. • Clients do not share any of their resources. Examples of Client-Server Model are Email, World Wide Web, etc.

12. User enters the URL(Uniform Resource Locator) of the website or file. The Browser then requests the DNS(DOMAIN NAME SYSTEM) Server. • DNS Server lookup for the address of the WEB Server. • DNS Server responds with the IP address of the WEB Server. • Browser sends over an HTTP/HTTPS request to WEB Server’s IP (provided by DNS server). • Server sends over the necessary files of the website. • Browser then renders the files and the website is displayed. This rendering is done with the help of DOM (Document Object Model) interpreter, CSS interpreter and JS Engine collectively known as the JIT or (Just in Time) Compilers.

13. Advantages of Client-Server model: • Centralized system with all data in a single place. • Cost efficient requires less maintenance cost and Data recovery is possible. • The capacity of the Client and Servers can be changed separately. • Disadvantages of Client-Server model: • Clients are prone to viruses, Trojans and worms if present in the Server or uploaded into the Server. • Server are prone to Denial of Service (DOS) attacks. • Data packets may be spoofed or modified during transmission. • Phishing or capturing login credentials or other useful information of the user are common and MITM(Man in the Middle) attacks are common.

14. PROTOCOL • Protocols are agreed formats for transmitting data between devices. • The protocol determines: • i. The error checking required • ii. Data compression method used • iii. The way the end of a message is signaled • iv. The way the device indicates that it has received the message

15. INTERNET PROTOCOL • There are many protocols used by the Internet and the WWW: • TCP/IP • HTTP • FTP • Electronic mail protocols IMAP • POP

16. TCP/IP • The Internet uses two main protocols (developed by Vincent Cerf and Robert Kahn) Transmission control protocol (TCP): • Controls disassembly of message into packets at the origin reassembles at the destination Internet protocol • (IP):Specifies the addressing details for each packet Each packet is labelled with its origin and destination.

17. HYPER TEXT TRANFER PROTOCOL • The hypertext transfer protocol (HTTP) was developed by Tim Berners-Lee in 1991 • HTTP was designed to transfer pages between machines • The client (or Web browser) makes a request for a given page and the Server is responsible for finding it and returning it to the client • The browser connects and requests a page from the server • The server reads the page from the file system, sends it to the client and terminates the connection

19. Electronic Mail Protocol • Electronic mail uses the client/server model • • The organisation has an email server devoted to handling email • Stores and forwards email messages • • Individuals use email client software to read and send email • (e.g. Microsoft Outlook, or Netscape Messenger) • • Simple Mail Transfer Protocol (SMTP)

20. Specifies format of mail messages • • Post Office Protocol (POP) tells the email server to: • Send mail to the user’s computer and delete it from the server • Send mail to the user’s computer and do not delete it from the server • Ask whether new mail has arrived • The disadvantage of POP: You can only access messages from one PC

21. Interactive Mail Access Protocol (IMAP) • Newer than POP, provides similar functions with additional features. • e.g. can send specific messages to the client rather than all the messages. • A user can view email message headers and the sender’s name before downloading the entire message. • Allows users to delete and search mailboxes held on the email server. • The disadvantage of IMAP :Since email is stored on the email server, there is a need for more and more expensive (high speed) storage space.

22. HTTP • Hypertext Transfer Protocol (HTTP) is the communication protocol used by the Internet to transfer hypertext documents. • A protocol to transfer hypertext requests and information between servers and browsers • Hypertext is text, displayed on a computer, with references (hyperlinks) to other text that the reader can immediately follow, usually by a mouse HTTP is behind every request for a web document or graph, every click of a hypertext link, and every submission of a form.

23. HTTP specifies how clients request data, and how servers respond to these requests. • The client makes a request for a given page and the server is responsible for finding it and returning it to the client. • The browser connects and requests a page from the server. • The server reads the page from the file system and sends it to the client and then terminates the connection

25. Markup Language: • A markup language is a computer language that uses tags to define elements within a document. • It is human-readable, meaning markup files contain standard words, rather than typical programming syntax. • While several markup languages exist, the two most popular are HTML and XML.

26. HTML • HTML stands for Hypertext Markup Language. • HTML is used to create web pages and web applications. • HTML is widely used language on the web. • We can create a static website by HTML only. • Technically, HTML is a Markup language rather than a programming language

27. HTML5 • It is enriched with advance features which makes it easy and interactive for designer/developer and users. • It allows you to play a video and audio file. • It allows you to draw on a canvas. • It facilitate you to design better forms and build web applications that work offline. • It provides you advance features for that you would normally have to write JavaScript to do.

28. <!DOCTYPE html> <html lang="en-US"> <head> <title>Page Title</title> </head> <body> <h1>This is a heading</h1> <p>This is a paragraph.</p> </body> </html> <!DOCTYPE html><html><body><h1>My First Heading</h1><p>My first paragraph.</p></body></html>

31. FEATURES • HTML stands for Hyper Text Mark-up Language • It is used to organize text, graphics, audio, video on a web page • It is a formatting language used to design the decoration and contents of a web page • Hypertext means, the text which acts as a link • Mark up means symbols that are used to define structure of the text. It tells browser how to display the text (tags) • Language refers to the syntax • It was invented by Tim-Berners Lee at CERN • HTML 1.0 (1991), HTML 2.0 (1995), HTML 3.2 (1997), HTML 4.0 (1999), XHTML (2000), HTML5 (2014)

32. XHTML • XHTML stands for extensible hypertext markup language which is a connection between HTML (hypertext mark-up language) and XML (extensible markup language) also at most of the places XHTML is considered superior than HTML. • XHTML is easy to use with other data formats, and it creates more neat code as it is stricter than HTML. Therefore, it is more compatible with most browsers, and it maintains a standard of code that can be used for various devices.

33. <!DOCTYPE html PUBLIC "-// W //DT XHTML 1.2 //EN"  <!DOCTYPE html PUBLIC "-// W //DT XHTML 1.2 //EN"   " http : // www . myblogpost .org/T /xhtml12 / DT / xhtml12.dtd"> <htmlxmlns=http://www. myblogpost . org / 199 / xhtml> <head> <title> XHTML document </title> </head> <body> Wrong XHTML rule<br> Correct XHTML rule<br/> Wrong XHTML rule <hr> Correct XHTML rule <hr/> Wrong XHTML rule <imgsrc=" pic/ document / mypic.gif"alt=" picture of a boy playing in a field  "> Correct XHTML rule <imgsrc="pic/ document / mypic.gif"alt="picture of a boy playing in a field "/> </body> </html>

34. Advantages of XHTML • Here are the following advantages of XHTML, such as: • While using XHTML, the code of web applications becomes more stylish and easy to reuse. • It can help the developer create more advanced web projects due to the compatibility with various devices, and it also supports self-created markups like SVG (scalable vector graphics). • XHTML code can easily be converted to PDFs, RSS, and RFT, which allows the developer to work with a vast range of files. • XHTML reduce the loading time required by the browser to load an event which can result in overall speedy development, thus reducing time and energy • It contains closing tags which is an advantage for beginners, and this also makes the code look clean and easy to reuse.

35. Disadvantages of XHTML • XHTML also has some disadvantages, such as: • Very few browsers use XHTML. • Case sensitive as every part of code should be in lowercase. • It is mandatory to write < DOCTYPE > declaration. • And all the tags must be closed in the necessary order.