11 Feb 2014Computer networks1 Network administrators are here to help you! Open a ticket on .

11 Feb 2014 Computer networks 1

Computer networks

Network administrators are here to help you!

Open a ticket on http://support.unibz.it


Computer networks What is a network

Computers External connection Terminals Printers Stand-alone hard disks VoIP telephones

Server-client architecture


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


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


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


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


Search engines Crawler technique (8 billions web

pages!) Google scoring system Search tricks:

Use many keywords Quotations Advanced search Search for images


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


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


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


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


Encryption

Scrambling technique to make text unreadable Public key for encrypting Private key for decrypting 128 bits to be sure


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


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


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


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


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)


Passwords


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


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


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


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


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


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


Phishing


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


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


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


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


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


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!


JBOD


RAID 1


RAID 0


RAID 10

11 Feb 2014Computer networks1 Network administrators are here to help you! Open a ticket on .

Documents

decrypt slide

mbps slide

standard computer

sure slide

second slide

images slide

days slide

distance slide