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Computer Security

CIS326

Dr Rachel Shipsey

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This course will cover the following topics:

• passwords

• access controls

• symmetric and asymmetric encryption

• confidentiality

• authentication and certification

• security for electronic mail

• key management

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The following books are recommended as additional reading to the CIS326 study guide

• Computer Security by Dieter Gollman• Secrets and Lies by Bruce Schneier• Security in Computing by Charles Pfleeger• Network Security Essentials by William Stallings• Cryptography - A Very Short Introduction by Fred

Piper and Sean Murphy• Practical Cryptography by Niels Ferguson and

Bruce Schneier

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There are also many websites dealing with the subjects discussed in this course.

For example, the following website provides links to a large number of sites who have security and cryptography course on-line:

http://avirubin.com/courses.html

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What is Security? Security is the protection of assets. The

three main aspects are:

• prevention

• detection

• re-action

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Some differences between traditional security and information security

• Information can be stolen - but you still have it

• Confidential information may be copied and sold - but the theft might not be detected

• The criminals may be on the other side of the world

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Computer Security deals with the prevention and detection of unauthorised actions by users of a computer system.

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There is no single definition of security

What features should a computer security system provide?

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Confidentiality

• The prevention of unauthorised disclosure of information.

• Confidentiality is keeping information secret or private.

• Confidentiality might be important for military, business or personal reasons.

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Integrity

• Integrity is the unauthorised writing or modification of information.

• Integrity means that there is an external consistency in the system - everything is as it is expected to be.

• Data integrity means that the data stored on a computer is the same as the source documents.

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Availability

• Information should be accessible and useable upon appropriate demand by an authorised user.

• Availability is the prevention of unauthorised withholding of information.

• Denial of service attacks are a common form of attack.

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Non-repudiation

• Non-repudiation is the prevention of either the sender or the receiver denying a transmitted message.

• A system must be able to prove that certain messages were sent and received.

• Non-repudiation is often implemented by using digital signatures.

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Authentication

• Proving that you are who you say you are, where you say you are, at the time you say it is.

• Authentication may be obtained by the provision of a password or a scan of your retina.

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Access Controls

• The limitation and control of access through identification and authentication.

• A system needs to be able to indentify and authenticate users for access to data, applications and hardware.

• In a large system there may be a complex structure determining which users and applications have access to which objects.

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Accountability

• The system managers are accountable to scrutiny from outside.

• Audit trails must be selectively kept and protected so that actions affecting security can be traced back to the responsible party

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Security systems

• A security system is not just a computer package. It also requires security conscious personnel who respect the procedures and their role in the system.

• Conversely, a good security system should not rely on personnel having security expertise.

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Risk Analysis

• The disadvantages of a security system are that they are time-consuming, costly, often clumsy, and impede management and smooth running of the organisation.

• Risk analysis is the study of the cost of a particular system against the benefits of the system.

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Designing a Security SystemThere are a number of design considerations:• Does the system focus on the data, operations or the users

of the system?

• What level should the security system operate from? Should it be at the level of hardware, operating system or applications package?

• Should it be simple or sophisticated?• In a distributed system, should the security be centralised

or spread?• How do you secure the levels below the level of the

security system?

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Security Models

A security model is a means for formally expressing the rules of the security policy in an abstract detached way.

The model should be:• easy to comprehend• without ambiguities• possible to implement• a reflection of the policies of the organisation.

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SummaryBy now you should have some idea about

• Why we need computer security (prevention, detection and re-action)

• What a computer security system does (confidentiality, integrity, availability, non-repudiation, authentication, access control, accountability)

• What computer security exerts do (design, implement and evaluate security systems)