Computer networks

1. Computer networks Network administrators are here to help you! Open a ticket on http://support.unibz.it Computer networks

2. Computer networks • What is a network • Computers • External connection • Terminals • Printers • Stand-alone hard disks • VoIP telephones • Server-client architecture Computer networks

3. Transfer speed • Network areas • Local Area Network (LAN, Intranet) • Wide Area Network (WAN, Internet) • Virtual Private Network (VPN) • Speed in “bits per second” (bps) • Ethernet 10 Mbps • Fast Ethernet 100 Mbps • Giga Ethernet 1 Gbps • Wireless 30-300 Mbps Computer networks

4. Communication programs • Web browser • Chrome (55% of the market) • Mozilla Firefox (25% of the market) • Internet Explorer (10% of the market) • Safari • Mail reader • Outlook, Mozilla Thunderbird • Webmail and Microsoft Outlook Web App http://webmail.unibz.it • Voice over IP • Costs Computer networks

5. Posta Elettronica Certificata – PEC • Standard email • No guarantee of sender’s e-mail address identity • No guarantee of sender’s identity • No guarantee that content has not been altered • No sent proof • No dispatched proof • No read proof • PEC to PEC: like a raccomandata con ricevuta di ritorno • Sent proof • Dispatched proof • (in practice also) sender’s address identity and unaltered content Computer networks

6. Posta Elettronica Certificata – PEC • PEC to standard email: like a raccomandata semplice • Sent proof • Standard email to PEC: like a normal letter • Sent and dispatched proves are legal proves • Every citizen may have a free PEC address to communicate with public administration Computer networks

7. Search engines • Crawler technique (8 billions web pages!) • Google scoring system • Search tricks: • Use many keywords • Quotations • Advanced search • Search for images Computer networks

8. Slow connections Computer networks

9. Broadband connections Computer networks

10. Broadband connections • ADSL Congestion • “minimum band guaranteed” contract • Digital divide • 5,400,000 Italians not covered by broadband • WiMax • 10 Kilometers range • “line of sight” problem Computer networks

11. Privacy • Law 196/2003 on privacy • authentication • permission • training • firewall and antivirus • 6-12 months update • backup every week • sensitive data • encryption • restore within 7 days Computer networks

12. Encryption • Scrambling technique to make text unreadable • Public key for encrypting • Private key for decrypting • 128 bits to be sure Computer networks

13. decrypt decrypt decrypt encrypt encrypt B B G#4hg! G#4hg! message 1 Trb:-ò°§ message 1 message 1 Encryption for information exchange A C C encrypt encrypt decrypt decrypt message 2 f@çd*s f@çd*s Dr4^\|ò9 message 2 message 2 encrypt encrypt decrypt D D message 3 %$&/òL message 3 message 3 È^£(iw, È^£(iw, Computer networks

14. secret data secretdata secretdata %£)(“84jhgds?ì A A A encrypt encrypt D(£ò§*+]dH D(£ò§*+]dH decrypt decrypt Encryption for data storage Computer networks

15. Digital signature • Law 82/2005 • Private key for encrypting • Public key for decrypting • Keys given by certification authorities • Combination with PEC • Keys expiration • Temporal mark Computer networks

16. B B 2?=zx:-ki document decrypt decrypt Digital signature A document falsedocument Y&”:ò[fgj?’^d G#4$h&à?-2y encrypt encrypt C C decrypt decrypt 2?=zx:-ki document decrypt decrypt D D 2?=zx:-ki document Computer networks

17. Comparison with handwritten signature Computer networks

18. Passwords Computer networks

19. Passwords • What can be done with your password? • Steal personal data • Steal other people’s data • Steal money • Delete and modify data • Steal identity • Start illegal activities • A standard computer can try 1 million passwords per second Computer networks

20. Passwords • Law 196/2003 • Avoid personal data in the password • Change password every 3 months • Minimum 8 characters • Better also: • Mix letters, strange characters and numbers • Do not use words • Use different passwords for different purposes • Beware of passwords stored in programs • What to do in case of employee’s absence • Alternative password devices • smartcard, token key, OTP with display, OTP USB, phone Computer networks

21. Viruses • What does a virus do? • Infect • Survive • Duplicate • Damage • Virus infection symptoms • computer is slow to start • unwanted and annoying pop-ups • many system errors Computer networks

22. Viruses • User’s responsible behaviors • downloaded files and email attachments • CD, DVD, USB pendrives • strange websites • updated programs • updated antivirus • Anti-viruses • Checking the whole hard disk • Checking suspect files • Always running Computer networks

23. Types of viruses • Trojan horse • looks like a good program • Key logger • records your keyboard activity (to get passwords) • Back door • opens a port on your computer (to let external users in) • Adware • displays advertisement • Spyware • spies your activity (to get passwords or for spam targeting) • Dialer • dials expensive numbers using your PSTN modem Computer networks

24. Spam • “unsolicited” “unwanted” “bulk” email • Advertisement: gambling, pornographic websites, medicines, risky investments, software… • Chain letters • Frauds • Phishing • Sender is always counterfeited • Do not click on links! Do not answer!!! • Where do they get my email address? • Antispam and blacklists Computer networks

25. Phishing Computer networks

26. Phishing example • 2,000,000 emails sent • 5% arrive to existing users: 100,000 • 5% of users read the email: 5,000 • 2% of readers believe in the email: 100 • $1,200 from each user •  Gain: $120,000 • In 2005 Mr. David Levi gained $360,000 from 160 people using Phishing on eBay website Computer networks

27. Safe navigating • Navigation security • Phishing • Viruses • Download  Save  Antivirus  Open • Avoid visiting and downloading from untrustworthy websites • Keep Explorer and Windows up-to-date • Intercept your data • Secure connection SSL: httpS Computer networks

28. Attacks from outside • Denial of Service • zombie computers • Firewall • which internal program • which external address • what amount of traffic • which kind of data • Windows Seven Firewall Computer networks

29. Backup • Why backup? Source: The Cost of Lost Data. The importance of investing in that “ounce of prevention” by David M. Smith Computer networks

30. Backup • What to backup? • Your data files • Emails and addresses; browser’s configuration • Program configuration files • Difficult-to-find stuff • Where to backup? • another hard disk • online backup systems: Dropbox, Mozy, Sugarsync • rewritable CD and DVD • RAID techniques Computer networks

31. RAID – Redundant Array of Independent Disks • JBOD – Just a Bunch Of Disks • 2 disks • RAID 0 • 2 disks, fast • RAID 1 • 2 disks but space as for 1, safe vs crash, 24h service • Most common solution • RAID 10 • 4 disks but space as for 2, fast, safe vs crash , 24h service • None of these techniques is safe versus viruses or human errors! Computer networks

32. JBOD Computer networks

33. RAID 1 Computer networks

34. RAID 0 Computer networks

35. RAID 10 Computer networks