chapter 1 - 1 adcs cs262/0898/v1 chapter 1 an introduction to computer security topics introduction...

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Chapter 1An Introduction To Computer Security

TOPICS

• Introduction• Threats to Computer Systems

– Threats, Vulnerabilities and Attacks– Characteristics of Computer Intrusion– Type of Threats– Points of Security Vulnerabilities– Methods of Defense

• Categories of Computer Attacks– Using an Attack Taxonomy– Consideration in Selecting an Attack

Taxonomy– Simple Attack Taxonomy– Risk Based Attack Taxonomy

• Examples of Common Attack Methods• Attack Prevention Methods• Summary

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Introduction

• Computer security protects computer and everything associated with it - building, terminals, printers, cabling, disks and tapes.

• Most importantly, computer security protects the information stored in a system. Hence often known as information security.

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Threats to Computer Systems

• Threats

• Vulnerabilities

• Attacks

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Threats

• Is defined as any potential occurrence, malicious or a possible danger that can affect the assets and resources associated with a computer system.

Example:

A person - a system cracker or a spy,

A thing - a faulty equipment or

An event - a fire or a flood.

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Vulnerabilities

• Is a point where a system is susceptible to attack. In other words the presence of vulnerabilities allows bad things to happen on a computer system.

Example:

Physical: buildings and computer rooms are vulnerable.

Natural: computers are very vulnerable to natural disasters such as fire, flood etc.

Human: people who administer and user computer system represent greatest vulnerability of all.

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Attack

• An attack on a computer system is some action taken by a malicious intruder that involves the exploitation of certain vulnerabilities to cause an existing threat to occur.

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Characteristic of Computer Intrusion

• The target of computer crime involves - hardware, software, media, data and people.

• In any system, the weakest point is the most serious vulnerability.

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Types of Threats

• Confidentiality threat:– To protect information from

unauthorised disclosure.

– Also known as secrecy or privacy.

• Integrity threat:– To ensure that information is

accurate, complete and authentic.

– Accuracy is more important than confidentiality of information.

• Availability threat:– To ensure that the computer systems

work efficiently.

– Able to recover quickly and completely if a disaster occurs.

– Opposite of availability is denial of service.

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Points of Security Vulnerabilities

• Attacks on hardware:– Computer hardware is so visible and

hence easy to attack.

– Includes power supply surge, unstable power supply etc.

• Attacks on Software:– Software can be destroyed maliciously

or modified, deleted or misplaced.

– Examples include time bomb, Trojan horse, computer bug etc.

• Attacks on data:– Available in many forms, such as

electronic, printout and media.

– Can be destroyed, changed, modified or deleted very easily.

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Categories of Computer Attacks

• Attack Taxonomy:– Defined as any generalised

categorisation of potential attacks that might occur on given computer system.

– Classes of system like real-time systems, databases and local area networks.

• Consideration in selecting attack taxonomy:– Completeness

– Appropriateness

– Internal and External threats

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Simple Attack Taxonomy

Programmers Internal External

Theft ofinformation

Unauthorisedaction

Via modem

Informationdestruction

Malicioussoftware

Malicioussoftware

Theft ofservices

Theft as user Unauthorisedaction

Via modem

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Risk Based Attack Taxonomy

• External information theft

• External abuse of resources

• Masquerading

• Pest programs

• Bypassing of internal controls

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Risk Based Attack Taxonomy

• External information theft:– Involves unauthorised access to

information without exploiting any mechanisms.

– Abuse of mechanisms without direct access to the system.

– Associated with disclosure threat.

– Example, an individual glancing at a colleague's terminal screen.

• External abuse of resources:– Involves physical destruction of

computer system hardware.

– Associated with the integrity threat.

– Example, direct vandalism.

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Risk Based Attack Taxonomy

• External masquerading:– Involves a malicious intruder

successfully impersonating another user.

– Associated with disclosure, integrity or denial of service threats.

– Example, intruder tapping into a communication media.

• Pest Program:– Programs that cause subsequent harm

to computer systemcan be viewed as a time bomb.

– Requires mechanisms internal to the computer systemassociated with integrity threat.

– Example, Trojan horse and computer virus attacks.

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Risk Based Attack Taxonomy

• Bypassing of Internal Controls:

– Involves the explicit avoidance of authorisation, access and authority controls.

– Associated with disclosure, integrity or denial of service threats.

– Example, cracking techniques that subvert protective approaches.

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Examples of Common Attack Methods

• Password spoof program

• Password theft by clever reasoning

• Logic bomb mail

• Schedule file removal

• Field separate attack

• Insertion of compiler Trojan horse

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Examples of Common Attack Methods

• Password spoof program:– Trojan horse program is used to fake

the normal login sequence.

– Involves spoofing a user for login and password information.

• Password theft by clever reasoning:– Users typically create passwords that

are mnemonic.

– Hackers gain access by guessing of password of individuals.

– Obtain a copy of password file and encryption function.

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Examples of Common Attack Methods

• Logic bomb mail:– Programs that remain dormant until

some predetermined logical condition on the target system becomes true.

– May cause harm after the malicious intruder has escaped.

– The login spoof might be viewed as a logic bomb.

• Schedule file removal:– A useful file offered on many types of

operating systems.

– Used to schedule program to be run at predetermined time.

– Command can be combined with attack programs.

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Examples of Common Attack Methods

• Field separate attack:– This attack relies on several technical

assumptions underlying operating system.

– Field separate can be redefined to include various characters.

– Also relies on existence of system program invoked by a normal user.

• Insertion of compiler Trojan horse:– Programs used by many different

users are the attractive target for Trojan horse for widespread damage.

– Hence, compilers are attractive targets for Trojan horse insertion.

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Attack PreventionMethods

• Individual screening

• Physical security

• Care in operations

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Attack Prevention Methods

• Individual screening:– Involves checking the background,

credentials and other personal attributes of individuals.

– Used to trust user not to spoof other user or create compiler Trojan horse.

• Physical security:– This method involves securing the

computer system facility.

– Computer centres that are guarded, locked and monitored demonstrate this type of security control.

– Advantage is external hardware damage is effectively controlled.

– Disadvantage is may not useful for remote access.

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Attack Prevention Methods

• Care in operations:

– Involves individuals being careful in their day-to-day activities to avoid common types of attacks.

– Users can often avoid password spoof attacks by clearing the terminals before login into system.

– Similarly compiler attacks can be avoided by simple access and configuration controls.