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The Internet.

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Presentation on theme: "The Internet."— Presentation transcript:

1 The Internet

2 Overview An introduction to HTML Dynamic HTML Encryption
Public Key Infrastructure Development of the Internet Web Browsers

3 Top 10 uses of Internet at Work (2000)
% 2. Business related research: 35 3. Academic Research: 23 4. General browsing/surfing: 17 5. IT information: 11 6. Downloading Software: 11 7. News information: 10 8. Searching for personal information: 9 9. Reading Magazines/Newspapers: 7 10. Sports information: 7

4 Overall Structure of Internet


6 How does the World Wide Web works?
User must have a program called "browser" running on the computer: Internet Explorer (IE) or Netscape User establishes a connection with an ISP (Internet Service Provider) via dial-up or LAN (local area network). User types in an URL (Uniform Resource Locator) as the target webpage address in browser's address field. For example,

7 (4-6 are behind the scene) Through ISPs, the English URL is translated into a numerical IP (Internet Protocol) address. Eg:   User's browser uses the IP address to establish a connection via local, regional, and/or national ISPs, with the target computer (a web server). The web page that the user wants, HTML page, is sent back to user's browser.  User's browser interprets HTML commands, and displays the page with nice format to the user. HTML pages can have Formatting information (text formatting, framing, etc.) Hyperlinks (user clicks on and browser repeats steps 3-6) Multimedia (pictures, audio, video, animations)

8 A Simple Example (simple.html)
<h1>A very simple web page</h1> My name is <b>Charles Ling</b> <br><br> Here is a picture of mine <br> <IMG SRC=../c_ling2.jpg width=150> <br><br> My favourite thing to do is <ul> <li>Adventurous travelling around the world <li>Watching good movies <li>Reading news at <a href="">CNN</a> </ul> For more info about me, click my <a href="">home page at UWO.</a>


10 Building Webpages Writing html files directly (using notepad or other text editors) Using MS Word and save as html Using specialized software: MS Frontpage, Dreamwaver, etc. Adding animations, forms, java, javascript, database functionality, …

11 Writing Simple html pages
Start notepad and writing html code directly Save it as an html file (eg, my.html) Start browser (eg, Internet Explore) Click file > open, click browse to locate and open the html file (eg, my.html). You will see how the html file is displayed!

12 HTML HTML – HyperText Markup Language
A language used to define the content of, and the presentation instructions for, a Web document

13 When a browser presents a Web document, the browser scans the document and applies the presentation instructions to the content Content that does not have presentation instructions will be presented using default instructions built into the browser

14 HTML documents must employ a simple format so anyone can create documents
HTML documents are stored in text (ASCII) files This type of document can be created using any editor that allows you to save the document as a text file

15 To combine the content and the presentation instructions in the same file, there must be a way to distinguish between these two components In HTML, the presentation instructions are inserted as “tags” Anything that isn’t a presentation instruction is content

16 HTML tags normally occur in pairs
The pair of tags surround the content to which they apply A start tag is indicated with angle brackets <TAG> An end tag is indicated with a slash after the opening angle bracket </TAG>

17 HTML has a set of predefined tags These tags can be used to
Control how the text in the document is displayed Insert images into the document Insert links to other documents

18 Document Tags HTML documents are enclosed within <HTML> and </HTML> tags Every HTML document will have a head and a body The document head is enclosed within the <HEAD> and </HEAD> tags The body is enclosed within the <BODY> and </BODY> tags

19 The basic structure of an HTML document is
The <TITLE> within the <HEAD> is displayed in the title bar of the browser

20 The <HEAD> of the document contains information used by the browser
All of the content for the document and the associated presentation instructions are placed inside the <BODY> tags

21 Formatting Tags HTML contains tag definitions that allow you to control Headings Style Ordered Lists Unordered Lists Definition Lists etc.

22 Heading Tags There are six heading levels
The levels are named H1, H2, H3, … H6 where H1 is the largest and H6 is the smallest To create a heading, you enclose the text of the heading inside the opening and closing tags for the heading level

23 Heading Examples

24 Physical Style Tags Used to control the display of text
<B> - bold <I> - italics <U> - underline <TT> - typewriter type face

25 Physical Style Tag Example

26 Logical Style Tags Examples of logical style tags
<EM> - for emphasis <STRONG> - stronger emphasis <CITE> - citation <CODE> - computer code

27 Logical Style Tag Example

28 Layout Style Tags Used to control text layout
<CENTER> - center the text <P> - new paragraph <BR> - break, start a new line <HR> - horizontal rule, draw a line

29 Layout Style Tag Example

30 Lists Lists of data can be defined using
Ordered List – enumerated lists Unordered List – bulleted lists Definition List – lists that are made of terms and their associated definitions

31 Ordered List Use the <OL> and </OL> tags to start and end an ordered list Within the ordered list, the list item (<LI>) tag is used to indicate the items on the list The VALUE tag can be used to set the value of a list item The START parameter is used to control the value of the first item

32 The TYPE parameter controls what enumeration scheme is used
The types are: 1 – numbers (default) a – lower case letters A – upper case letters i – small Roman numerals I – large Roman numerals

33 Ordered List

34 Ordered List

35 Ordered List

36 Unordered List Use the <UL> and </UL> tags to start and end an unordered list Within the unordered list, the list item (<LI>) tag is used to identify the items on the list

37 The TYPE parameter can be used to control the look of the list
The types are: Disc – a solid disc Circle – a hollow circle Square – a square symbol

38 Unordered List

39 Unordered List

40 Definition List The <DL> and </DL> tags define the Definition List The <DT> tag is used to indicate a definition term The <DD> tag is used to indicate a definition

41 Definition List

42 URL An URL is a Uniform Resource Locator
An URL contains information about The address of a document on the Internet The protocol that will be used to access the document

43 Protocols HTTP – HyperText Transfer Protocol
Designed to transmit files on the World Wide Web FTP – File Transfer Protocol Designed to transmit files over the Internet (before the Web developed) These protocols are sets of rules that dictate how files are transmitted between computers

44 URL Example In the following URL example, the protocol to be used is HTTP (before the “://”) The document is “browse.html” and it is located in the “selected” folder at the World Wide Web site for UWO in Canada

45 Images Images are added to documents using the <IMG> tag
A </IMG> tag is not required The SRC parameter is used to indicate the SouRCe of the image

46 Image Formats Standard image formats are needed so images can be
stored retrieved transmitted over the Web

47 Examples of image formats used on the Web are:
GIF – Graphics Interchange Format JPG ( JPEG ) – Joint Photographic Experts Group PNG – Portable Network Graphics BMP – Windows Bitmap

48 Graphics Interchange Format
Uses the Lempel-Ziv Welch (LZW) compression algorithm The algorithm searches the image for big blocks of the same color and then compresses these blocks This compression reduces the size of the image

49 The algorithm also uses an indexed color scheme, in which a custom color palette for the image is selected using only 256 of the over 16 million available colors This format is used when the image does not contain a wide range of colors or color shades

50 Joint Photographic Experts Group
Images can contain millions of colors Uses Lossy compression algorithm When the image is compressed it permanently loses some of its quality The algorithm looks for similar colors (like a range of reds) and chooses the same red for very close shades

51 If the original image had 1,000 shades of red, the compressed image may have only 500 shades
The human eye cannot detect all the shades so in general the lose will not be noticed This format is used when the image contains many colors and many color shades

52 Portable Network Graphics
Portable Network Graphics format was designed to replace GIF Uses loss less compression like GIF Provides better resolution and more colors like JPG Generates smaller files like GIF Is not supported by all versions of browsers

53 Windows Bitmap Every pixel in the image is represented by a piece of data The data represents the color of the pixel Bitmap images are very large Rarely used on Web pages because of the time required to download the image

54 Image Tag

55 Anchors Anchor tags (<A> and </A>) are used to insert hyperlinks and bookmarks into HTML documents A hyperlink is a link to another document on the World Wide Web A bookmark is a named location within an HTML document

56 No. 1 use of Anchors: Anchors as Hyperlinks
An example of a link to the UWO home page When the HTML is rendered the document will contain a link to UWO

57 The Link Item is the text or image that you click on to activate the link
The HREF parameter is the Hypertext REFerence parameter The HREF parameter is used to define the link destination

58 An Image as a Link

59 No. 2 use: Anchors as Bookmarks (in the same document)
An example of the definition of an (invisible) bookmark using the NAME parameter (normally in a long html file) <A NAME=“top”> </A> ….. <A NAME=“Conclusions_bookmark”> </A> <h2>Conclusions</h2>

60 An example of a link to a bookmark within the same document (in the same html document)
Note the use of # You can see conclusions <a href=“#Conclusions_bookmark”>here</A> <a href=“#top”>Back to top</a>

61 In a long html file (say papers.html)
…. You can see conclusions <a href=“#Conclusions_bookmark”>here</A> …… <A NAME=“Conclusions_bookmark”> </A> <h2>Conclusions</h2>

62 No.3 use: combining 1 and 2 Anchors as Hyperlinks to bookmark in a different document
The form of the anchor tags used as a hypertext link is <A HREF=“URL#Bookmark”>Link Item</A>

63 An example of a link to a bookmark within another html document
Click <a href=“”> here</a> to jump to conclusions in that document. See a real example in If linking to a bookmark in the same document, the URL is omitted

64 Web Page Example 1 Create a Web page with
“My First Web Page” as the title Your name as a level 2 heading An enumerated list of your three favorite University courses An image for the University. Try “” as the source URL. If this URL doesn’t work, look at the HTML source for the University’s home page to find an URL

65 Web Page Example 2 Create a Web Page with
A TV show name as a level 1 heading at the top of the page A paragraph of text about the show Bold the stars names and italicize the night that the show is broadcast within this text A horizontal line A link to a Web page for the show. Use the name of the show as the link text A link to the heading at the top of the page, using “Top” as the link text

66 DHTML Dynamic HTML DHTML allows the user to interact with a web page
Supported by fourth generation and later browsers (Netscape and IE) DHTML allows the user to interact with a web page The user can enter values and select buttons

67 The user of a DHTML page can enter data and then have the data sent (posted) to a web site
The computer hosting the web site can then process the data DHTML Example 1 DHTML Example 2

68 Encryption Encryption involves encoding a message to conceal the meaning Consider the name NORMA JEAN BAKER The name has been encrypted as OPSNB!KFBO!CBLFS What is the encryption algorithm? How would you decode the message?

69 For encryption to work there must be an algorithm that is applied to the original message
There must also be a way to decode the encrypted message to obtain the original message

70 Encryption algorithms use a binary “key” to encrypt and decrypt messages
There are two types of encryption algorithms used to secure Internet transmissions Symmetric Key Encryption Asymmetric (Public) Key Encryption

71 Symmetric Key Encryption
Symmetric Key Encryption can use the same key for both encryption and decryption The sender and the receiver must both know the key Both must ensure that the key is kept secret If the key becomes public then others can decrypt valid messages and create fake messages

72 Key Length For Symmetric Key Encryption, the typical key lengths are 40, 56 and 128 bits Key length is one measure of encryption strength Longer keys provide stronger encryption An additional bit in the key doubles the strength of the key

73 Data Encryption Standard
The Data Encryption Standard (DES) is the U.S. government’s standard for data encryption Uses the Data Encryption Algorithm (DEA) to encrypt/decrypt the message An improvement on the Lucifer algorithm developed by IBM in the early 1970s Uses a 56 bit key

74 Triple DES Uses a key three times as long as Standard DES
168 bit key Used for banks and other organizations that transmit highly sensitive data

75 Public Key Encryption Asymmetric Key Encryption
Uses a pair of keys, one public and one private Key length is a least 512 bits The public key is published so any sender can obtain it The private key is kept secret

76 Messages encrypted using the public key can only be decrypted by using the private key
There reverse is also true, messages encrypted using the private key can only be decrypted using the public key This is one way to generate a digital certificate (to sign a message)

77 Rhonda wants to send an email to Rick
Rhonda finds Rick’s Public Key through a Public Key directory She encrypts the message using Rick’s Public Key and sends the message Rick uses his Private Key to decrypt the message (his Public Key will NOT decrypt the message) For Rick to respond, he must use Rhonda’s Public Key to encrypt the message

78 Encryption Strength The strength of an encryption depends on the algorithm used and the length of the key The algorithms used in most implementations of Public Key Encryption are patented by RSA Data Security Inc.

79 RSA Algorithms The RSA Public Key Cryptosystem was developed in 1977 by Ronald Rivest Adi Shamir Leonard Adleman They have created a number of 128 bit key algorithms For example, RC2 and RC4

80 Code Breaking For Symmetric Key Encryption, the typical key lengths are 40, 56 and 128 bits Tests have been conducted to determine how long it will take to break messages encoded using various key lengths

81 The 128 bit encryption has not been broken yet!
Key Length Broken in … 40 bits 3 hours 48 bits 13 days 56 bits 40 days 128 bits ??? The 128 bit encryption has not been broken yet! “The sun will burn out first” is a frequent estimate of how long it will take!

82 US vs International Security
Under current U.S. policy, software manufacturers can only sell 40 bit key encryption systems overseas Some exceptions can use 56 bit keys International banks

83 In the U.S., 128 bit keys are recommended to ensure secure communications
Why would the U.S. want to restrict key length in software used in other countries?

84 Public Key Infrastructure
A Public Key Infrastructure is an encryption and digital certificate delivery system which makes secure electronic transactions possible The X.509 Standard

85 PKI uses Digital Certificates
A digital signature Digital Certificates carry the same legal weight as a written signature Provides a way for others to verify your identity Uses Public Key Encryption

86 A Digital Certificate relates you to a set of public and private keys
Digital Certificates are used to provide secure transactions through the Secure Sockets Layer Protocol (SSL)

87 SSL Protocol Developed by Netscape
Goal is to provide secure and reliable communication between applications For example, between a Web application (your browser) and a Web site

88 Public Key Encryption is used by each application to establish the identity of the other application
Symmetric Encryption is used for data encryption

89 Public Key Encryption is used to exchange the key used by the Symmetric Encryption of the data
The reliability of the message is ensured by including a Message Authentication Code (MAC) as part of the data

90 SSL takes the message to be transmitted and
fragments the data into manageable blocks optionally, compresses the data performs a message integrity check encrypts the data transmits the result

91 Received data is decrypted verified decompressed reassembled
delivered to the client

92 Digital Trust Public Key Infrastructure (PKI) manages all aspects of Digital Trust In the digital world, trust requires Privacy Integrity Non-repudiation Authentication

93 Privacy To ensure privacy, messages are encrypted
Encryption ensures that the message cannot be read in transit or by anyone except the recipient

94 Integrity Verify the integrity of the message
Ensure that the message that is received is exactly what was sent

95 Non-repudiation The sender cannot deny or repudiate a valid message
For example, when a stock broker receives an order for stock trades, the client cannot later claim that they didn’t send the message

96 Authentication Verify that the sender is who they claim to be

97 The Internet Networks of networks
Tens of thousands of computer networks Reaches 100’s of millions of people How did the Internet develop?

98 Started with ARPANET, an experimental project of the U. S
Started with ARPANET, an experimental project of the U.S. Department of Defense Advanced Research Projects Agency (DARPA) in 1969 The original purpose was to explore experimental networking technologies for the military

99 How large is the Internet?
Nobody knows for sure! According to the Internet Society (ISOC), a professional organization of Internet developers, influencers, and users, the Internet reaches more than 170 countries

100 Internet Growth Year Number of Hosts 1969 4 1974 62 1979 188 1984
1,024 1989 80,000 1994 2,217,000 1999 43,230,000

101 One of the reasons the Internet has been so successful is the commitment of its developers to producing “open” standards The specifications or rules that computers need to communicate are publicly and freely available; published so that everyone can obtain them

102 TCP/IP The standards that the Internet uses are known as TCP/IP
Transmission Control Protocol/Internet Protocol suite Without open standards, only computers from the same vendor could talk to one another

103 Computers and networks that conform to the same communications standards are able to “interoperate”, regardless of the manufacturer All of the networks and computers act as peers in the exchange of information and communication

104 Packets Communication on the Internet revolves around the concept of a packet, a basic building block All information and communications transmitted on the Internet are broken into packets, each of which is considered to be an independent entity

105 The packets are individually routed from network to network until they reach their destination, where they are reassembled and presented to the user

106 This method of networking is very flexible and robust
It allows diverse computers and systems to communicate by means of network software, not proprietary hardware

107 If a network goes “down” (breaks down), then the packets can be rerouted through other parts of the network of networks This dynamic alternate routing of information creates a very persistent means of communication

108 Internet Development There have been three generations of Internet development They characterize the evolution of the Internet

109 First Generation There were three main First Generation Tools
Electronic mail Remote logon File transfer These tools are still available on all parts of the Internet

110 Electronic Mail Uses Simple Mail Transfer Protocol (SMTP)
Standardized in 1983 Originally designed to transmit plain text Printable characters NOT binary files, graphics or sound

111 Current systems use Multipurpose Internet Mail Extensions (MIME)
MIME allows the system to transport Plain text, binary files, graphics and sound MIME encodes and decodes complex messages into a simpler form that SMTP can transport

112 Characteristics of email programs
Composition Response Read Delete Organize Filter

113 Address An address consists of a local part and a host part For example,

114 The local part is a user name, mailbox, login name or user id csdept The host part is the name of an server on the Internet

115 POP and IMAP Protocols like the Post Office Protocol (POP) and the Internet Message Access Protocol (IMAP) are used to transmit from your computer to your server your server to your computer

116 Simple Mail Transfer Protocol
The Simple Mail Transfer Protocol (SMTP) is used to transmit between servers

117 To send an email Construct the message on your computer
When you click on “Send”, the message is moved using POP or IMAP to your server The server uses the host part of the address to determine where to send the message

118 When the message arrives at the destination server, it is stored and the recipient is notified of its arrival When the recipient wants to read the message, it is moved using POP or IMAP to their computer

119 Remote Logon Allows you to logon to a computer over the Internet
A utility that handles remote logon is Telnet To remotely connect to a computer, you must know the address of the computer For example,

120 On most host computers, you must have an account on the computer
Some host computers allow you to logon as “Anonymous” or “Guest” with your address as the password Anonymous logon


122 File Transfer The File Transfer Protocol (FTP)
Used to copy (download) files over the Internet

123 FTP was designed to copy plain text files
HTTP was designed to transmit text files, graphics, sound, etc. FTP is faster than HTTP because FTP doesn't perform as many checks on the data during the download process

124 FTP allows you to connect to another computer list the files in a folder on the other computer copy files back and forth between the two computers Anonymous FTP allows you to logon as “Anonymous” or “Guest” with your address as the password


126 Second Generation The Second Generation saw large increases in
The amount of data being made public The number of Internet users There was an increasing need for tools that would aid users in finding resources

127 Tools The first tool was Gopher
Developed at the University of Minnesota, where the mascot is a Golden Gopher!

128 Gopher was a hierarchical system of menus
The top level menu contained general categories The information became more specific as you drilled down Looked a lot like Yahoo!

129 Veronica Very Easy Rodent-Oriented Net-wide Index to Computerized Archives The University of Nevada Gopher allowed you to search through the categories looking for interesting resources But it was a manual search Veronica allowed the user to submit keywords and the utility did a search of gopher space

130 Archie Archie is derived from the word archive
Developed at the McGill University School of Computer Science Maintained a database of all the names of files stored at known public FTP sites Helped find files at FTP sites

131 Network News - USENET USENET is a network within the Internet
Divided into newsgroups Each newsgroup is devoted to a topic To read or post to a newsgroup you need a news reader application

132 Newsgroups More than 80,000 newsgroups
Newsgroups are divided into hierarchies alt – 10,159 alternate groups microsoft – 991 groups bionet – 94 groups biz – 48 groups Newsgroups are added daily so these numbers are out of date!

133 Third Generation The World Wide Web Tools Browsers Search engines

134 World Wide Web Originally developed by the European Laboratory for Particle Physics (also known as CERN) by Tim Berners-Lee of Switzerland He developed a system to link together scholarly references The links from one document to another are imagined to form a web!

135 The World Wide Web is a browsing and searching system
Built on the concept of hypertext and hypermedia

136 The Web is a continuous distributed information construction project
Tens of thousands of people are adding knowledge to it daily by bringing up their own servers or posting documents on existing servers

137 Browsers A browser is application software
Browsers use HTML documents as their input The HTML tags in the document are applied to the content and the result is displayed in the browser

138 Mosaic The first popular graphical browser
It was developed at the National Center for Supercomputing Applications (NCSA) in Champaign, Illinois by Marc Andreessen Allows a user to click on text, graphics, buttons or icons that link to other resources

139 Netscape Developed by Netscape Communications Corporation
The company was founded in April of 1994 by Marc Andreessen, creator of the NCSA Mosaic software and Dr. James H. Clark, the founder of Silicon Graphics, Inc.

140 Microsoft’s Web browser is Internet Explorer
All browsers have the same basic functionality, they just have a slightly different “look and feel”

141 Browser Functionality
Typical functionality Display HTML documents Create bookmarks Send and read Read news Display and create the source HTML for documents Debug script on DHTML pages

142 Search Engines One of the most difficult tasks for a Web browser is to make it easy for the user to find resources Search engines allow users to do keyword searches These searches are actually database searches Search engines keep databases that match keywords to document URLs

143 Directories The top level of directories indicate general categories
As the user drills down into a category, they are presented with more specific categories

144 Consider WebCrawler and Google
These two are typical World Web Web tools They both provide basic and advanced search capabilities as well as directories

145 Advanced Searches Each search engine has its own syntax for describing a search Most engines AND together keywords The document must have all of the keywords The search engine should also support OR, NOT and exact phrases

146 Check out the WebCrawler and Google advanced search pages for examples of typical advanced search strategies

147 You can submit a page to be included in searches and directories
WebCrawler Google Search engine databases also get information about documents from programs called robots that explore the Web looking for documents to add to their database

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