Lecture01 Internet

8/10/2019 Lecture01 Internet

1/28


2/28

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


3/28

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


4/28

The User Perspective have little laptopat home in NJ

want to exchange informationwith big serverin California(or Japan or )


5/28

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)


6/28

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


7/28

ISPDHCP

Router ARouter B

DNS

www.google.com

fiber opticlines

ISP: Internet ServiceProvider

DHCP: Dynamic HostConfig. Protocol

DNS: Domain NameServer


8/28


9/28

The Data: IP Packetwww.google.com

(66.102.1.147)

(149.150.254.102)


10/28

The Data: IP Packetwww.google.com

(66.102.1.147)

(149.150.254.102)


11/28

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


12/28

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


13/28

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


14/28


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


15/28


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


16/28


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 ...


17/28

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


18/28

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


19/28

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 /


20/28

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)


21/28

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


22/28

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?)


23/28

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


24/28

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


25/28

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


26/28

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


27/28

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


28/28

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

Lecture01 Internet

Documents

Transcript of Lecture01 Internet