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Computer networks
Network administrators
are here to help you!
Open a ticket on
http://support.unibz.it
11 Aug 2014
Computer networks
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Computer networks
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What is a network
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Computers
External connection
Terminals
Printers
Stand-alone hard disks
VoIP telephones
Server-client architecture
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Transfer speed
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Network areas
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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
Gigabit Ethernet 1 Gbps
Wireless 30-300 Mbps
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Communication programs
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Web browser
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Mail reader
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Chrome (55% of the market)
Mozilla Firefox (25% of the market)
Internet Explorer (10% of the market)
Safari
Outlook, Mozilla Thunderbird, Windows Live Mail
Webmail and Microsoft Outlook Web App
http://webmail.unibz.it
Voice over IP
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Costs
WhatsApp
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Posta Elettronica Certificata – PEC
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Standard email
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No
No
No
No
No
No
guarantee of sender’s e-mail address identity
guarantee of sender’s identity
guarantee that content has not been altered
sent proof
dispatched proof
read proof
PEC to PEC: like a raccomandata con ricevuta di
ritorno
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Sent proof
Dispatched proof
(in practice also) sender’s address identity and unaltered content
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Posta Elettronica Certificata – PEC
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PEC to standard email: like a raccomandata semplice
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Sent proof
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Standard email to PEC: like a normal letter
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Sent and dispatched proves are legal proves
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Every citizen may have a free PEC address to
communicate with public administration
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Search engines
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Crawler technique (8 billions web pages!)
Google scoring system
Search tricks:
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Use many keywords
Quotations
Advanced search
Search for images
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Slow connections
Names
Equipment
Effective
speed
Notes
PSTN
analogical
dial-up
telephone line
and modem
56 Kbps
Telephone is busy during
connection
128 Kbps
Telephone is busy during
full speed connection
100 Kbps
Telephone is busy during
connection
ISDN
GPRS
2G
EDGE
2.5 G
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ISDN
telephone line
and modem
GSM mobile
phone
modern GSM
phone
300 Kbps
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Broadband connections
Name
Equipment
Effective speed
Notes
ADSL
telephone line
and modem
500 Kbps in upload
8-20 Mbps download
Congestion
Internet
special contract
cable
UMTS
3G
3G mobile phone
HSDPA
LTE
LTE mobile phone
4G
Wireless
wireless card
Wi-Fi
WiMax
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antenna in line of
sight and modem
some Gbps
5 Mbps in upload
40 Mbps in download
Speed depends strongly on
environment
up to 100 Mbps
Depends on coverage and
contract
Speed depends on wireless
generation
30-300 Mbps
40 Mbps
Computer networks
Speed depends strongly on
distance
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Broadband connections
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ADSL Congestion
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“minimum band guaranteed” contract
Digital divide
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5,400,000 Italians not covered by broadband
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WiMax
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10 Kilometers range
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“line of sight” problem
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Law 196/2003 on privacy
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Data are divided into:
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personal data
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sensitive data
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race and ethnicity,
religious / philosophical / political opinions,
belonging to religious / philosophical / political / workers
organization
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sensitive data about health and sex
justice data (handled as sensitive data)
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genetic data (need extremely particular procedures)
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Law 196/2003 on privacy
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To personal users who do not communicate data
security requirements still apply
Requirements
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authentication with login + password or alternatives
permission
training or instructions
backup every week all data
security programs updated every 12 months (6 if sensitive)
sensitive data must be encrypted or unidentifiable
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Encryption
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Scrambling technique to make text
unreadable
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Public key for encrypting
Private key for decrypting
128 bits to be sure
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Encryption for information exchange
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message 1
encrypt
G#4hg!
decrypt
message 1
message 2
encrypt
f@çd*s
decrypt
message 2
message 3
encrypt
È^£(iw,
decrypt
message 3
message 1
encrypt
G#4hg!
decrypt
Trb:-ò°§
message 2
encrypt
f@çd*s
decrypt
Dr4^\|ò9
message 3
encrypt
decrypt
%$&/òL
È^£(iw,
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Encryption for data storage
secret
data
secret
data
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encrypt
encrypt
D(£ò§*
+]dH
decrypt
secret
data
D(£ò§*
+]dH
decrypt
%£)(“84
jhgds?ì
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Digital signature
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Law 82/2005
Private key for encrypting
Public key for decrypting
Keys given by certification authorities
Combination with PEC
Keys expiration
Temporal mark
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Digital signature
document
document
encrypt
G#4$h
&à?-2y
decrypt
document
document
2?=zx:-ki
false
document
encrypt
Y&”:ò[
fgj?’^d
decrypt
2?=zx:-ki
2?=zx:-ki
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Comparison with handwritten signature
Who can sign
Digital signature
Handwritten signature
Needs keys from certification
authority and proper tools
Everybody instantly
Who can verify Everybody (with proper tools)
Handwriting analysts
Verification
reliability
Sure for some years
Subjective 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
Objective if temporal mark
Based on other subjective
elements (paper’s and ink’s
age)
Date reliability
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Electronic vs digital signature
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Electronic signature
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Qualified electronic signature
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automatic signature through username and
password
and a certification authority guarantees it
Digital signature
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and uses encryption
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Passwords
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Passwords
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What can be done with your password?
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Steal personal data
Steal other people’s data
Steal money
Delete and modify data
Steal identity
Start illegal activities
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Passwords
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Most people have the following passwords:
password
dragon
monkey
123456
pussy
696969
12345678
baseball
abc123
1234
football
12345
qwerty
letmein
A standard computer can try 4 billion passwords per
second
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Passwords
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Law 196/2003
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Better also:
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Avoid personal data in the password
Change password every 6 months (3 if sensitive data)
Minimum 8 characters
Mix letters, strange characters and numbers
Do not use words
Use different passwords for different purposes
Beware of passwords stored in programs
Test your password robustness on
https://howsecureismypassword.net
What to do in case of employee’s absence
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Alternatives to password
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Law 196/2003 allows biometric identification methods
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fingerprints
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hand palm
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retina scanning
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voice identification
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Extra security
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Adding physical methods to standard password
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smartcard
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token key
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OTP with display
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OTP USB
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phone SMS
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phone call
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Viruses
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What does a virus do?
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Infect
Survive
Duplicate
Damage
Virus infection symptoms
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computer is slow to start
unwanted and annoying pop-ups
many system errors
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Viruses
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User’s responsible behaviors
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downloaded files and email attachments
CD, DVD, USB pendrives
strange websites
updated programs
updated antivirus
beware when installing free programs!
Anti-viruses
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Checking the whole hard disk
Checking suspect files
Always running
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Types of viruses
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Trojan horse
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Key logger
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displays advertisement
Spyware
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opens a port on your computer (to let external users in)
Adware
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records your keyboard activity (to get passwords)
Back door
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looks like a good program
spies your activity (to get passwords or for spam targeting)
Ransomware
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demands money to avoid damage or justice problems
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Spam
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“unsolicited” “unwanted” “bulk” email
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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
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Phishing example
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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
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Navigation security
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Phishing
Viruses
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Intercept your data
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Download  Save  Antivirus  Open
Avoid visiting and downloading from untrustworthy
websites
Keep Explorer and Windows up-to-date
Secure connection SSL: httpS
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Attacks from outside
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Denial of Service
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Firewall
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zombie computers
which internal program
which external address
what amount of traffic
which kind of data
Windows Seven Firewall
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Backup
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Why backup?
9%
3%
Hardware failure
6%
Human error
40%
Software corruption
Viruses
13%
Theft
Hardware destruction
29%
Source: The Cost of Lost Data. The importance of investing in that “ounce of prevention” by David M. Smith
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Backup
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Law 196/2003
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What to backup?
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backup every week
Your data files
emails, contacts, calendar
Program configuration files
Difficult-to-find stuff
Where to backup?
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another hard disk
online backup systems: Dropbox, GoogleDrive, Box, Amazon
RAID techniques
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RAID – Redundant Array of Independent Disks
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JBOD – Just a Bunch Of Disks
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RAID 0
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2 disks but space as for 1, safe vs crash, 24h service
Most common solution
RAID 10
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2 disks, fast
RAID 1
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2 disks
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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