How does the Internet work ?

1. How does the Internet work ?

2. What we will cover • What 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. Internet History The Internet is a global network of interconnected computers, enabling users to share information along multiple channels. http://en.wikipedia.org/wiki/Internet • Started in 1969 as ARPANET funded by DARPA (Defense Advanced Research Projects Agency) • Build as packet switching network to recover from a nuclear attack by automatically 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

4. The User Perspective • have little laptop at home in NJ • want to exchange information with big server in California (or Japan or …)

5. 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. 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 computer’s IP number? • IP Name for easy reference • What is your computer’s 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. Router A Router B ISP DHCP fiber optic lines www.google.com ISP: Internet ServiceProvider DHCP: Dynamic HostConfig. Protocol DNS: Domain Name Server DNS

9. The Data: IP Packet www.google.com(66.102.1.147) (149.150.254.102)

10. The Data: IP Packet www.google.com(66.102.1.147) (149.150.254.102)

11. The Protocol A mutually agreed-upon convention or standard that controls or enables the connection, communication, and data 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 if one occurs

12. Client – Server 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 many resources (also called the server computer) • Client program: a program with extensive interface capabilities but few resources running on a “small” computer (also called the client computer) • One server computer usually run several server programs, each of which can service multiple client programs simultaneously

13. Client – Server 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 to display

14. Client – Server 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

15. Client – Server Example (3) I want to view the main web page from www.shu.edu • Client: sends “give me main page”Server: sends data to 192.168.1.2 • http (Hypertext Transport Protocol): regulates how a web 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. Client – Server Example (4) I want to view the main web page from www.shu.edu

17. Client – Server Example (5) Telnet: • universal text client used to connect to another computer and work on that computer in text-based mode • usually connects to a “telnet server” but can also connect to any server computer and any server program • shows text data in ‘raw’ unformatted form

18. Client – Server: Telnet A 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, select “Programs”, click “Turn Windows features on or off”, and check “Telnet 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. Telnet’ing to a Web Server • Start “telnet” and type: open www.shu.edu 80 • Next type carefully and without errors (you might not see 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 Hypertext Transfer Protocol, version 1.0, for the root web page /

20. How email works Email systems have two parts, and consequently work with two server programs and two protocols: • Retrieving email uses either pop3 (Post Office Protocol version 3 on port 110) or IMAP (Internet message access protocol on port 143) • Sending email uses smtp (simple mail transport protocol on port 25)

21. An smtp Conversation

22. Homework • Capture a web page from a web server • Send me an (anonymous) email using Telnet (note that the SHUsmtp server will only allow a connection if you are located on campus – how does it know?)

23. 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. Firewall Protection ISP • Every packet transported over the Internet contains the protocol (port), sender address, and destination address • A firewall is a device that inspectsevery incoming (and outgoing) packet and includes rules to block data depending on the port, sender, or destination • A firewall is typically integrated into a home wireless router • Most firewalls do not check the content of a packet

25. SPAM Protection ISP • Every Internet packet contains the port, sender, destination, and content (data) – usually unencrypted • A SPAM filter is a device that inspectsall email packets and includes rules to block messages depending on the content of the email. • A SPAM filter is typically integrated into you ISP or email provider • SPAM filters typically read your email!

26. Privacy/Content Protection ISP • All Internet traffic is public! • To protect content, the data portion of IP packets must be encrypted • To protect data between your wireless router and your laptop, use e.g. WPA wireless encryption • To protect data after it leaves your router, you must use encrypted services (https instead of http or sftp instead of ftp) • Note: no standard encryption for email! Sending email is like passing a postcard along a chain of hundreds of people with a note: “to Jane – do not read if you’re not Jane”

27. Encryption Encryption is usually based on a key that used to encrypt and decrypt 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 Annie’s public key to send her an encrypted message, she can decrypt it using her private key • based on difficulty of factoring huge numbers into large primes and ease of multiplying them See http://www.explainthatstuff.com/encryption.html

28. Public Key Encryption requires: • large “semi”-prime number x = p q Example: • public key x = 15 => private key is: Homework: Find factorization of RSA-100, which is1522605027922533360535618378132637429718068114961380688657908494580122963258952897654000350692006139 More Info: • http://en.wikipedia.org/wiki/Public-key_cryptography • http://en.wikipedia.org/wiki/RSA_numbers • http://primes.utm.edu/mersenne/ • Enigma by Robert Harris, and Enigma the Movie