11 Feb 2014 Computer networks 1
Computer networks
Network administrators are here to help you!
Open a ticket on http://support.unibz.it
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Computer networks What is a network
Computers External connection Terminals Printers Stand-alone hard disks VoIP telephones
Server-client architecture
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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
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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
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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
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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
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Search engines Crawler technique (8 billions web
pages!) Google scoring system Search tricks:
Use many keywords Quotations Advanced search Search for images
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Slow connections
Names EquipmentEffective
speedNotes
PSTNanalogic
aldial-up
telephone line and modem
56 KbpsTelephone is busy during connection
ISDNISDN telephone line and modem
128 Kbps
Telephone is busy during full speed connection
GPRSGSM mobile
phone100 Kbps
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Broadband connections
Name Equipment Effective speed Notes
ADSLtelephone line and modem
500 Kbps in upload
8-20 Mbps download
Congestion
Internet cable
some Gbps
UMTS3G
UMTS mobile phone
7 MbpsSpeed depends
strongly on environment
Wireless
Wi-Fiwireless card 30-300 Mbps
Speed depends on wireless
generation
WiMaxantenna in line
of sight and modem
40 Mbps Speed depends
strongly on distance
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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
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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
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Encryption
Scrambling technique to make text unreadable Public key for encrypting Private key for decrypting 128 bits to be sure
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Encryption for information exchange
G#4hg!
decryptencrypt
B
C
D
A
encrypt
encrypt
f@çd*s
È^£(iw,
decrypt
decrypt
message 1
message 2
message 3
message 1
message 2
message 3
D
B
C
message 1
message 2
message 3
G#4hg!
encrypt
encrypt
encrypt
f@çd*s
È^£(iw,
decrypt Trb:-ò°§
Dr4^\|ò9
%$&/òL
decrypt
decrypt
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Encryption for data storage
encrypt
decrypt
A secret data
D(£ò§*+]dH
secret
data A
encrypt decrypt
A secret data
D(£ò§*+]dH
%£)(“84jhg
ds?ì
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Digital signature
Law 82/2005 Private key for encrypting Public key for decrypting Keys given by certification authorities Combination with PEC Keys expiration
Temporal mark
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Digital signature
documentencryp
t decrypt
decrypt
decryptdocument
document
document
G#4$h&à?-2y
BC
D
A
false
document
encrypt decrypt
decrypt
decrypt2?=zx:-ki
2?=zx:-ki
2?=zx:-ki
Y&”:ò[fgj?’^
d
B
C
D
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Comparison with handwritten signature
Digital signature Handwritten signature
Who can signNeeds keys from certification authority and proper tools
Everybody instantly
Who can verify
Everybody (with proper tools)
Handwriting analysts
Verification reliability
Sure for some yearsSubjective in dubious cases, no time limit
Temporal duration
Some years (can be renewed)
Until other reliable signatures are available
Mass signatures
Some seconds for all documents (with proper tools)
Some seconds per document
Date reliability
Objective if temporal markBased on other subjective elements (paper’s and ink’s age)
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Passwords
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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
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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
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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
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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
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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
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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
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Phishing
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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
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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
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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
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Backup Why backup?
Source: The Cost of Lost Data. The importance of investing in that “ounce of prevention” by David M. Smith
40%
29%
13%
6%
9%3%
Hardware failureHuman errorSoftware corruptionVirusesTheftHardware destruc-tion
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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
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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!
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JBOD
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RAID 1
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RAID 0
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RAID 10
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