Computer Security

1. Computer Security CIS326 Dr Rachel Shipsey

2. This course will cover the following topics: • passwords • access controls • symmetric and asymmetric encryption • confidentiality • authentication and certification • security for electronic mail • key management

3. 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

4. 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

5. What is Security? Security is the protection of assets. The three main aspects are: • prevention • detection • re-action

6. 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

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

8. There is no single definition of security What features should a computer security system provide?

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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

16. 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.

17. 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.

18. Designing a Security System There 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?

19. 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.

20. Summary By 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)