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Introduction to
Network Security
Source:
Chapter 1
Computer Security Fundamentals
Chuck Easttom, Prentice Hall, 2006
Modified by:
C F Yung
Objectives
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Identify top threats to a computer network
Assess the likelihood of an attack
Define key terms like cracker, sneaker,
firewall, and authentication (證明)
Compare and contrast perimeter and layered
approaches to network security
Use online resources
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Introduction
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Computer systems and networks are all
around us
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Online banking
Automated supermarket checkouts
Online classes
Online shopping
Online travel resources
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Introduction (cont.)
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How is personal information safeguarded (維
護)?
What are the vulnerabilities (弱點)?
What secures these systems?
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How Seriously Should You Take
Threats to Network Security?
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Which group do you belong to?
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“No one is coming after my computer.”
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“The sky is falling!”
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Assumes there is no real threat (威脅)
Reactive approach to security
Overestimate the dangers
Middle ground
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Identifying Types of Threats
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Malware – MALicious (懷惡意的) softWARE
Intrusions
DoS – Denial of Service attacks
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Malware
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Software with a malicious purpose
 Virus
 Trojan horse
 Worm
 Spyware
 Hoax/Phishing
Reference:

http://service1.symantec.com/SUPPORT/nav.nsf
/docid/1999041209131106
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Malware (cont.)
Virus
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A small program that replicates (複製) and hides itself inside
other programs, usually without the knowledge of the user.
Two criteria:
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Usually spreads through e-mail
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Must execute itself
Must replicate itself
Using victim’s email account to spread the virus
to everyone in their address book.
Uses system resources, causing slowdown or stoppage.
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Heavy network traffic caused by the virus
replication.
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Malware (cont.)
Trojan Horse
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The other most common kind of
malware.
Named after the wooden horse of
ancient history.
Appears to be benign (良好) software
but secretly downloading a virus or
other malware.
For a Trojan horse to spread, you must
invite these programs onto your
computers.
For example, by opening an email
attachment or downloading and running
a file from the Internet.
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Malware (cont.)
Trojan Horse
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Some may cause immediate damage, others
might be designed to provide remote access to
the system via a “back door”.
Some may sit and wait to perform actions as
instructed remotely, such as collecting and
sending keystrokes captured by a keylogger
program running in the background.
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Malware (cont.)
Worm
 Worms are programs that replicate
themselves from system to system without
the use of a host file.
 This is in contrast to viruses, which requires
the spreading of an infected host file.
 Use e-mail and network facilities to spread to
other resources.
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Malware (cont.)
Spyware
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Software that literally spies on what you do on your
computer.
The most rapidly growing type of malware
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Cookies
Key logger
Unlike viruses and worms, spyware does not usually selfreplicate.
Exploits infected computers for commercial gain.
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Typical tactics include delivery of unsolicited (未經請求) popup advertisements, theft of personal information (including
financial information such as credit card numbers)
Monitoring of Web-browsing activity for marketing purposes,
and routing of HTTP requests to advertising sites.
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Malware (cont.)
Hoax (惡作劇)
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Do not contain any code, instead relying on the gullibility of
the users to spread.
Often use emotional subjects such as a child's last wish.
Any e-mail message that asks you to forward copies to
everyone you know is almost certainly a hoax.
Phishing
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Phishing scams are targeted to gather personal information
in order to hijack your assets or steal your identity to open
credit accounts in your name.
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Sample: http://news.alibaba.com/article/detail/safetrading/100068729-1-fraud-email-samples.html
http://www.wikihow.com/Spot-an-Email-Hoax-or-PhishingScam
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Compromising System Security
損害系統安全
Intrusions
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Attacks attempt to gain unauthorized access to
your system resources.
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Hackers
Crackers
Social engineering
War-driving (wireless networks)
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Ref: http://www.pisa.org.hk/
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Denial of Service Attacks (DoS)
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The attacker does not intrude into the system,
just blocks access by authorized users.
To flood the targeted system with so many
false connection requests that the system
cannot respond to legitimate requests.
Reference:
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http://en.wikipedia.org/wiki/Denial-ofservice_attack
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Common Attacks on Your Network
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Viruses
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Catch up on new and refurbished viruses
http://www.hkcert.org
Unauthorized use of systems
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DoS attacks
Intrusions
Employee misuse
Insider attacks
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http://www.securityfocus.com/infocus/1546
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Basic Security Terminology
People
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Hackers (Experts on a particular system)
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White hats
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Black hats (Crackers)
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Conduct illegal activities for reasons they feel are ethical, such as
hacking into a system belonging to a corporation that the hacker
feels is engaged in unethical activities.
Script kiddies
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Once gain access to a system, their goal is to cause some type of
harm.
Gray hats
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Upon finding a vulnerability in a system, will report the
vulnerability to the vendor of the system.
Download utilities and scripts to perform some hacking tasks.
Ethical hackers (Sneakers)
 Employed to legally breaks into a system in order to
assess security deficiencies.
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Basic Security Terminology (cont.)
Devices
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Firewall
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Proxy server
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Filters network traffic
Hides IP address of internal host
Improve performance and filter requests
Intrusion Detection System (IDS)
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Monitors traffic, looking for attempted attacks (e.g.
scanning all ports of a system)
http://www.sans.org/reading_room/whitepapers/detectio
n/337.php
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Basic Security Terminology (cont.)
Activities
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Phreaking (盜用電話線路)
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Authentication
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Involves breaking into telephone systems, say to make free
long distance calls.
Determine if the credentials (username, password) are
authorized to access the resource.
Auditing (審核)
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Reviewing logs and records
Procedures to determine if these items meet standards
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Network Security Paradigms
網路安全範例
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How will we protect our network?
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Perimeter security approach
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Layered security approach
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Any technology or procedure to prevent unauthorized access
of the network.
Little or no effort is put into securing the systems within the
network.
Adequate for small organizations.
Firewalls, proxy servers, password policies.
Not only is perimeter secured, but individual systems within the
network are also secured.
Divide the network into segments and secure each segment.
Proactive versus reactive
Hybrid security method
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Online Security Resources
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CERT (Computer Emergency Response Team)
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The first computer incident-response team.
www.cert.org
Microsoft Security Advisor
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A portal to all Microsoft security information, tools, and updates.
www.microsoft.com/security/default.mspx
F-Secure
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A repository for detailed information on viruses, tools for cleaning
infected system.
www.f-secure.com/security_center/security_alerts.html
SANS
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A repository of security-related documentation.
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www.sans.org
(ISC)2
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A not-for-profit leader in educating and certifying information
security professionals
www.isc2.org
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Analysis Tools
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Nmap (Network Mapper)
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Snort
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Open source network intrusion prevention and detection
system.
www.snort.org
Nessus
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Free security scanner
www.insecure.org/nmap/index.html
Network vulnerability scanner
www.nessus.org
Microsoft Baseline Security Analyzer (MBSA)
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Free security and vulnerability assessment scan tool.
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Analysis Tools (cont.)
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Microsoft Baseline Security Analyzer (MBSA)
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Free security and vulnerability assessment scan
tool.
Knoppix STD
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A Live CD Linux distribution based on Knoppix
that focuses on computer security tools.
http://en.wikipedia.org/wiki/Knoppix_STD
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Summary
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Network security is a constantly changing
field.
You will require three levels of knowledge.
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First, take the courses necessary to train yourself
in the basic techniques.
Second, learn your enterprise system intimately,
with all its strengths and vulnerabilities.
Finally, keep current in the ever-changing
world of threats and exploits.
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