Lecture01 Internet
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Transcript of Lecture01 Internet
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What we will coverWhat is the Internet
Client/server examples
Deciphering alphabet soup: ISP, DHCP, DNS, http,https, HTML, smtp, pop3, telnet, ftp, sftp, ssh
Network security:
How to send anonymous emails
How to hack into a system
How a Firewall works
Encrypted communications
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Internet HistoryThe Internetis a global network of interconnected computers, enablingusers to share information along multiple channels.
http://en.wikipedia.org/wiki/Internet
Started in 1969 as ARPANET funded byDARPA (Defense Advanced ResearchProjects Agency)
Build as packet switching network torecover from a nuclear attack byautomatically rerouting data through
surviving links
When I took office, only high energy physicistshad ever heard of what is called the World WideWeb... Now even my cat has it's own page.Bill Clinton
http://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Internet -
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The User Perspective have little laptopat home in NJ
want to exchange informationwith big serverin California(or Japan or )
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Basic Setup Each computer must have a unique identifier
IP number and IP name Computers must be able to exchange data (electrons,
photons, drum beats)
Wireless cards, fiber optics, or Ethernet connections
Unit of data is bit (zero or one, on/off, 2 states) Everyone involved must speak the same language
TCPIP (Transmission Control Protocol/Internet Protocol)
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Network Member Identifier Every computer on the Internet has at least one unique
identifier, usually two: IP Number: #.#.#.#, where # is an 8 bit number
What is the range for each sub-number? How many machines can be on the Internet? What is your computers IP number?
IP Name for easy reference What is your computers IP name?
Homework: What is the IP number of google What is the IP number of www.shu.edu What is the IP name of 149.150.254.102
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ISPDHCP
Router ARouter B
DNS
www.google.com
fiber opticlines
ISP: Internet ServiceProvider
DHCP: Dynamic HostConfig. Protocol
DNS: Domain NameServer
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The Data: IP Packetwww.google.com
(66.102.1.147)
(149.150.254.102)
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The Data: IP Packetwww.google.com
(66.102.1.147)
(149.150.254.102)
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The ProtocolA mutually agreed-upon convention or standard thatcontrols or enables the connection, communication, anddata transfer between computing endpoints.
http://en.wikipedia.org/wiki/Protocol_(computing)
Regulates the data exchange and interpretation
Defines who says what at which time
Defines how to interpret data that is exchanged
Regulates what constitutes an error and what to do ifone occurs
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ClientServer Model Communication on the Internet usually takes place
between a client and a server program/computer: Server program: program without a user interface
running on a large computer with access to manyresources (also called the server computer)
Client program: a program with extensive interfacecapabilities but few resources running on a smallcomputer (also called the client computer)
One server computer usually run several serverprograms, each of which can service multiple clientprogramssimultaneously
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ClientServer Example (1)I want to view the main web page from www.shu.edu
Server computer: www.shu.edu
Client computer: 192.168.1.2
Server program: web server program (httpd) running on
www.shu.edu with access to lots of stored web pages Client program: Internet Explorer or Firefox with
extensive formatting and display capabilities but no data todisplay
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ClientServer Example (2)I want to view the main web page from www.shu.edu
Client: start IE and enter: http://www.shu.edu/ Client sends packet to DNS: who is www.shu.edu
DNS sends packet back: www.shu.edu = 149.150.51.69
Client sends packet to 149.150.51.69:give me main page
Server:receives request for page from 192.168.1.2 Retrieves the web page from disk (or database)
Sends data to 192.168.1.2: here is the data
Client: formats data and display it nicely
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ClientServer Example (3)I want to view the main web page from www.shu.edu
Client:sends give me main pageServer:sends data to 192.168.1.2
http(Hypertext Transport Protocol): regulates how aweb server and client communicate
Client:formats data and display it nicely HTML(Hypertext Markup Language): defines how text
is supposed to look and where to place it
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ClientServer Example (4)I want to view the main web page from www.shu.edu
Action http 1.0 specs
http uses port 80 by general agreement
Client:give me main page GET / HTTP/1.0
Server: returns data fixed header:how many bytesare coming,
type of data
page text ...
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ClientServer Example (5)Telnet:
universal text client used to connect to anothercomputer and work on that computer in text-basedmode
usually connects to a telnet server but can also
connect to any server computer and any serverprogram
shows text data in raw unformatted form
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ClientServer: TelnetA Telnet client is build into Windows:
Click on Start
Pick Run and type cmd Type telnet
if you get error message in Vista, open Control Panel, selectPrograms, click Turn Windows features on or off, and checkTelnet client (not Telnet server). Then try again.
To open a connection to www.shu.edu, type:open www.shu.edu (will this work why not?)
Optional: to save a log of your session, type:set logfile log.txt
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Telneting to a Web Server Start telnet and type:
open www.shu.edu 80
Next type carefully and without errors (you might notsee what you type on the screen type anyway,including the empty line and capitals):
GET / HTTP/1.0
You have issued a request according to the HypertextTransfer Protocol, version 1.0, for the root web page /
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How email worksEmail systems have two parts, and consequently workwith two server programs and two protocols:
Retrieving email
uses either pop3(Post Office Protocol version 3 on port110) or IMAP(Internet message access protocol on port
143) Sending email
uses smtp(simple mail transport protocol on port 25)
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An smtp Conversation
Speaker TextServer: 220 Simple Mail Transfer Service ready
Client: HELO mycomputer.mydomain
Server: 250 kitten.shu.edu
Client: MAIL FROM:
Server: 250 OK
Client: RCPT TO:
Server: 250 OK
Client: DATA
Server: 354 Start mail input; end with .Client: Blah blah blah..
.
Server: 250 OK
Client: QUIT
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Homework1. Capture a web page from a web server2. Send me an (anonymous) email using Telnet (note that
the SHUsmtp server will only allow a connection if you are locatedon campus how does it know?)
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Hacking 101 Identify a target system
Find an open port
Check which server program services that port
Learn about vulnerabilities of that server program
Exploit vulnerability for evil purposes
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Firewall Protection Every packet transported over the
Internet contains theprotocol(port),sender address, and destinationaddress
Afirewallis a device that inspectseveryincoming (and outgoing)packetandincludes rules to block datadependingon the port, sender, or destination
A firewall is typically integrated into ahome wireless router
Mostfirewalls do not check the contentof a packet
ISP
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SPAM Protection Every Internet packet contains the port,
sender, destination, and content(data)usually unencrypted
A SPAM filteris a device that inspectsall email packetsand includes rules toblock messagesdepending on thecontent of the email.
A SPAM filter is typically integrated intoyou ISP or email provider
SPAM filters typically read your email!
ISP
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Privacy/Content Protection All Internet traffic ispublic! To protect content, the dataportion of IP packets
must be encrypted
To protect data between your wireless router andyour laptop, use e.g. WPA wireless encryption To protect data after it leaves your router, you must
use encrypted services (httpsinstead of http orsftpinstead of ftp)
Note: no standard encryption for email!
Sending email is like passing a postcard along a chain ofhundreds of people with a note: to Jane do not read if
youre not Jane
ISP
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EncryptionEncryption is usually based on a key that used to encrypt anddecrypt a message.
Pre-Shared Key (PSK) Encryption: both parties know a single key (e.g. WPA encryption: both your
router and your computers know the key)
Public Key Encryption: each party has two keys, a public and a private one. They swap
public keys: Bob uses Annies public key to send her anencrypted message, she can decrypt it using her private key
based on difficulty of factoring huge numbers into large primesand ease of multiplying them
See http://www.explainthatstuff.com/encryption.html
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Public Key Encryption requires: large semi-prime number x = p qExample:
public key x = 15 => private key is:
Homework: Find factorization of RSA-100, which is
15226050279225333605356183781326374297180681149613806886579084945801229632589528
97654000350692006139
More Info:
http://en.wikipedia.org/wiki/Public-key_cryptography http://en.wikipedia.org/wiki/RSA_numbers
http://primes.utm.edu/mersenne/
Enigmaby Robert Harris, and Enigma the Movie