the internet
DESCRIPTION
The Internet. Overview. An introduction to HTML Dynamic HTML Encryption Public Key Infrastructure Development of the Internet Web Browsers. Top 10 uses of Internet at Work (2000). 1 . E-mail : 73 % 2 . Business related research : 35 3 . Academic Research : 23 - PowerPoint PPT PresentationTRANSCRIPT
The InternetThe InternetThe InternetThe Internet
Overview
An introduction to HTML Dynamic HTML Encryption Public Key Infrastructure Development of the Internet Web Browsers
Top 10 uses of Internet at Work (2000)
1. E-mail: 73% 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
Overall Structure of Internet
How does the World Wide Web works?
1. User must have a program called "browser" running on the computer: Internet Explorer (IE) or Netscape
2. User establishes a connection with an ISP (Internet Service Provider) via dial-up or LAN (local area network).
3. User types in an URL (Uniform Resource Locator) as the target webpage address in browser's address field. For example, http://www.csd.uwo.ca/~cs031
4. (4-6 are behind the scene) Through ISPs, the English URL is translated into a numerical IP (Internet Protocol) address. Eg:130.100.11.3
5. 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).
6. The web page that the user wants, HTML page, is sent back to user's browser.
7. 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)
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="http://www.cnn.com">CNN</a></ul>For more info about me, click my<a href="http://www.csd.uwo.ca/faculty/ling">home page at UWO.</a>
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, …
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!
HTML
HTML – HyperText Markup Language
A language used to define the content of, and the presentation instructions for, a Web document
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
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
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
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>
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
Document TagsDocument 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
The basic structure of an HTML document is
The <TITLE> within the <HEAD> is displayed in the title bar of the browser
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
Formatting Tags
HTML contains tag definitions that allow you to control Headings Style Ordered Lists Unordered Lists Definition Lists etc.
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
Heading Examples
Physical Style Tags
Used to control the display of text <B> - bold <I> - italics <U> - underline <TT> - typewriter type face
Physical Style Tag Example
Logical Style Tags
Examples of logical style tags <EM> - for emphasis <STRONG> - stronger emphasis <CITE> - citation <CODE> - computer code
Logical Style Tag Example
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
Layout Style Tag Example
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
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
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
Ordered List
Ordered List
Ordered List
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
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
Unordered List
Unordered List
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
Definition List
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
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) ftp://ftp.csd.uwo.ca
Email: mailto:[email protected] These protocols are sets of rules
that dictate how files are transmitted between computers
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
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
Image Formats
Standard image formats are needed so images can be stored retrieved transmitted over the Web
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
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
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
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
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
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
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
Image Tag
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
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
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
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>…
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>……
….You can see conclusions <a href=“#Conclusions_bookmark”>here</A>
…………
<A NAME=“Conclusions_bookmark”> </A><h2>Conclusions</h2>…
…You can see conclusions <a href=“#Conclusions_bookmark”>here</A>
In a long html file (say papers.html)
The form of the anchor tags used as a hypertext link is
<A HREF=“URL#Bookmark”>Link Item</A>
No.3 use: combining 1 and 2Anchors as Hyperlinksto bookmark in a different
document
An example of a link to a bookmark within another html document
Click <a href=“http://www.uwo.ca/papers.html#Conclusions_bookmark”>here</a> to jump to conclusions in that document.
See a real example inhttp://www.csd.uwo.ca/faculty/ling/cs031/simple.html
If linking to a bookmark in the same document, the URL is omitted
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
“http://www.uwo.ca/gifs/uwologo4.gif” 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
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 horizontal line A link to the heading at the top of the
page, using “Top” as the link text
DHTML
Dynamic HTML 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
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
Encryption
Encryption involves encoding a message to conceal the meaning
Consider the name
NORMA JEAN BAKER
OPSNB!KFBO!CBLFS
The name has been encrypted as
What is the encryption algorithm? How would you decode the
message?
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
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
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
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
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
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
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
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)
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
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.
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
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
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!
Key Length Broken in …
40 bits 3 hours
48 bits 13 days
56 bits 40 days
128 bits ???
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
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?
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
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
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)
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
Public Key Encryption is used by each application to establish the identity of the other application
Symmetric Encryption is used for data encryption
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
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
Received data is decrypted verified decompressed reassembled delivered to the client
Digital Trust
Public Key Infrastructure (PKI) manages all aspects of Digital Trust
In the digital world, trust requires Privacy Integrity Non-repudiation Authentication
Privacy
To ensure privacy, messages are encrypted
Encryption ensures that the message cannot be read in transit or by anyone except the recipient
Integrity
Verify the integrity of the message Ensure that the message that is
received is exactly what was sent
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
Authentication
Verify that the sender is who they claim to be
The Internet
Networks of networks Tens of thousands of computer
networks Reaches 100’s of millions of people How did the Internet develop?
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
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
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
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
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
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
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
The packets are individually routed from network to network until they reach their destination, where they are reassembled and presented to the user
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
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
Internet Development
There have been three generations of Internet development
They characterize the evolution of the Internet
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
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
Current systems use Multipurpose Internet Mail Extensions (MIME)
MIME allows the email system to transport Plain text, binary files, graphics and
sound MIME encodes and decodes
complex messages into a simpler form that SMTP can transport
Characteristics of email programs Composition Response Read Delete Organize Filter
Email Address
An email address consists of a local part and a host part
For example,
The local part is a user name, mailbox, login name or user id csdept
The host part is the name of an email server on the Internet csd.uwo.ca
POP and IMAP
Protocols like the Post Office Protocol (POP) and the Internet Message Access Protocol (IMAP) are used to transmit email from your computer to your email server your email server to your computer
Simple Mail Transfer Protocol
The Simple Mail Transfer Protocol (SMTP) is used to transmit email between email servers
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 email server
The email server uses the host part of the address to determine where to send the message
When the message arrives at the destination email 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
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, mccarthy.csd.uwo.ca
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 email address as the password Anonymous logon
File Transfer
The File Transfer Protocol (FTP) Used to copy (download) files over
the Internet
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
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 email address as the password
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
Tools
The first tool was Gopher Developed at the University of
Minnesota, where the mascot is a Golden Gopher!
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!
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
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
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
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!
Third Generation
The World Wide Web Tools
Browsers Search engines Directories
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!
The World Wide Web is a browsing and searching system
Built on the concept of hypertext and hypermedia
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
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
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
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.
Microsoft’s Web browser is Internet Explorer
All browsers have the same basic functionality, they just have a slightly different “look and feel”
Browser Functionality
Typical functionality Display HTML documents Create bookmarks Send and read email Read news Display and create the source HTML
for documents Debug script on DHTML pages
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
Directories
The top level of directories indicate general categories
As the user drills down into a category, they are presented with more specific categories
Consider WebCrawler and Google These two are typical World Web
Web tools They both provide basic and
advanced search capabilities as well as directories
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
Check out the WebCrawler and Google advanced search pages for examples of typical advanced search strategies
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