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CIT 380: Securing Computer Systems

Introduction

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About Me http://www.nku.edu/~waldenj1

James Walden– Assistant Professor of Computer Science– waldenj@nku.edu– Interests:

• Software Security• Programming Languages• Software Engineering• Network Security

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Course Administration

Web Site– Notes, readings, and assignments on web site.– http://www.nku.edu/~waldenj1

Assignment submission– Use submit command on kosh.

Contact Information– Email: waldenj@nku.edu– Phone: (859) 572-5571

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CIT 380 within the Curriculum

CIT 140 CIT 370 CIT 380Security

CIT 484Network Security

CIT 430Forensics

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Syllabus

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Course Goals1. What is computer security?2. How do computer systems fail?3. How can the risks to a system be evaluated?4. How well does a particular security solution mitigate the

risks to a system?5. How can the costs and trade-offs of a security solution be

balanced?6. What are the essential problems and solutions of network

security?7. How do viruses and worms propagate and how can they be

stopped?8. How can intrusions be detected and investigated to

determine the nature of the attackand the attacker?9. What are the ethical impacts of security technologies?

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GradingGrades are based on

– Midterm Exam (30%)– Final Exam (40%)– Assignments (30%)

A 90-100B 80-89C 70-79D 60-69F 0-60

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Topics

A first look at four important questions:– What is security?– How do we evaluate risks of various threats?– How does security mitigate these risks?– How do we balance the costs and trade-offs of

our security solutions?

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9/11

Most devastating terrorist attack in history.– Low-tech.– Innovative.

• Completely different than earlier hijackings.• We thought we had solved airplane bombings by

ensuring passengers were on same flight as baggage.– What were the security responses?

• How effective were the responses?• What were the costs?

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What is Security?

Security is the prevention of certain types of intentional actions from occuring in a system.– These potential actions are threats.– Threats that are carried out are attacks.– Intentional attacks are carried out by an attacker.– Objects of attacks are assets.

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Safety vs Security Adversary: An intelligent attacker who

intentionally causes the system to fail.

Security• Home: door lock.• Car: alarm.• Computer: Login

password.

Safety• Home: fire alarm.• Car: crumple zones.• Computer: UPS.

Safety and security can interact: Who is watching your computer room after the fire alarm was pulled?

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Goals of SecurityPrevention

– Prevent attackers from violating security policy

Detection– Detect attackers’ violation of security policy

Recovery– Stop attack, assess and repair damage

Survivability– Continue to function correctly even if attack succeeds

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NSTISSC Security Model

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Components of Security

Confidentiality– Keeping data and resources hidden. Privacy.

Integrity– Preventing unauthorized changes to data or

resources.

Availability– Enabling access to data and resources

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ConfidentialityAuthentication

Passwords, mother’s maiden name

CorporationsTrade secrets, e.g., the formula for Coca Cola.

DatabasesSSN, Driver’s license

GovernmentsNational securityEmbarrassing information: www.thememoryhole.org

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Integrity

Data Integrity– content of the information.– ex: 2005 Walmart $1.5 million bar code scam.

Origin Integrity (authentication)– source of the information.– ex: 1997 Kurt Vonnegut MIT commencement

address email. Vonnegut was not the 1997 speaker and the content wasn’t his.

Prevention vs Detection

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Availability

Prevent loss of system access.

Denial of service attacks common.– Easy to launch, difficult to track down.– Can be just part of another attack

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States of Information

1. StorageInformation not currently being accessed.

2. ProcessingInformation currently being used by processor.

3. TransmissionInformation in transit btw one node and another.

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Security Measures

Technology.– Hardware/software used to ensure

confidentiality, integrity, or availability.

Policy and practice.– Security requirements and activities.

Education, training, and awareness.– Understanding of threats and vulnerabilities and

how to protect against them.

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How to evaluate security solutions?

1. What assets are you trying to protect?2. What are the risks to those assets?3. How well does the security solution

mitigate those risks?4. What other risks does the security solution

cause?5. What costs and trade-offs does the security

solution impose?

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Aspects of Risks

To evaluate a risk, we need to evaluate both:– Probability of risk occurring.– Cost incurred by risk if it occurs.

Minimize product of probability and cost.Risks are impacted by environment.

– Building a house in a flood plain incurs additional risks beyond that of house itself.

– Similarly, installion and configuration options impact risk of software systems.

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Security is a matter of Trade-offs

Security is only one of many system goals:• Functionality• Ease of Use• Efficiency• Time to market• Cost• Security

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Cost-Benefit Analysis

Is it cheaper to prevent violation or recover?– Cost of good network security:

• Money, time, reduced functionality, annoyed users.• Large and ongoing.

– Risks of bad network security:• Angry customers, bad press, network downtime.• Small and temporary.

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Airport SecurityLet’s consider the issue of airport security again from

the standpoint of what we’ve learned. Develop a solution, keeping the 5 questions in mind:

1. What assets are you trying to protect?2. What are the risks to those assets?3. How well does the security solution mitigate

those risks?4. What other risks does the security solution cause?5. What costs and trade-offs does the security

solution impose?

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Human Issues: People Problems

Social engineering– Kevin Mitnick testified before Congress “I was

so successful in that line of attack that I rarely had to resort to a technical attack.”

Circumvention– Users write down passwords, leave screens

unlocked.

Insider attacks

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Human Issues: OrganizationsLow priority

– Security costs, but doesn’t produce income.– Lack of liability reduces costs of bad security.

Variable impact– Cost of security violation highly variable.– Insurance converts variable risk to fixed cost, but

risk too variable for much involvement so far.Power and responsibility

– Personnel responsible for security often don’t have power to enforce security.

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Security: Laws and Customs

Are desired security measures illegal?– cryptography export before 2000– is it legal to monitor security breakins?– international commerce

Will users circumvent them?– writing down passwords– removing file ACLs

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Security Liability

Product liability:– Tires: Continental recalled Ford SUV tires in

2002 due to wire and vibration problems.– Software: Manufacturer not liable for security

flaws.

Since Microsoft isn’t liable for Windows security failures, why would they want to sacrifice money, time, functionality, and ease of use for security?

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Assumptions• Security rests on assumptions specific to

type of security required and environment.• Example:

– TCP/IP designed for pre-commercial Internet.• Assumed only legitimate admins had root access.• Trusted IP addresses, since only root can set IP addr.• What happens to network when Windows 95 systems

added to network, where desktop user has all privileges?

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Assurance

How much can you trust a system?Example:

– Purchasing aspirin from a drugstore.– Bases for trust:

• Certification of drug by FDA.• Reputation of manufacturer.• Safety seal on bottle.

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How much do you trust? Ken Thompson’s compiler hack from

“Reflections on Trusting Trust.”– Modified C compiler does two things:

• If compiling a compiler, inserts the self-replicating code into the executable of the new compiler.

• If compiling login, inserts code to allow a backdoor password.

– After recompiling and installing old C compiler:• Source code for Trojan horse does not appear

anywhere in login or C compiler.• Only method of finding Trojan is analyzing binary.

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Key Points• Components of security

– Confidentiality– Integrity– Availability

• States of information– Storage, Processing, Transmission

• Evaluating risk and security solutions.– Security is a matter of trade-offs.

• Security is a human problem.

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References1. Ross Anderson, Security Engineering, Wiley,

2001.2. Matt Bishop, Introduction to Computer Security,

Addison-Wesley, 2005.3. Peter Neumann, (moderator), Risks Digest,

http://catless.ncl.ac.uk/Risks/4. Bruce Schneier, Beyond Fear, Copernicus Books,

2003.5. Ken Thompson, “Reflections on Trusting Trust”,

Communication of the ACM, Vol. 27, No. 8, August 1984, pp. 761-763 (http://www.acm.org/classics/sep95/)