Chapter 11 – Security and dependability. The objective of this chapter is to introduce software dependability and security. When you have read this chapter, you will: understand why dependability and security are usually more important than the functional characteristics of a software system; understand the four principal dimensions of dependability, namely availability, reliability, safety, and security; be aware of the specialized terminology that is used when discussing security and dependability;. | Chapter 11 – Security and Dependability Lecture 1 1 Chapter 11 Security and Dependability Topics covered Dependability properties The system attributes that lead to dependability. Availability and reliability Systems should be available to deliver service and perform as expected. Safety Systems should not behave in an unsafe way. Security Systems should protect themselves and their data from external interference. System dependability For many computer-based systems, the most important system property is the dependability of the system. The dependability of a system reflects the user’s degree of trust in that system. It reflects the extent of the user’s confidence that it will operate as users expect and that it will not ‘fail’ in normal use. Dependability covers the related systems attributes of reliability, availability and security. These are all inter-dependent. 3 Chapter 11 Security and Dependability Importance of dependability System failures may have widespread effects with . | Chapter 11 – Security and Dependability Lecture 1 1 Chapter 11 Security and Dependability Topics covered Dependability properties The system attributes that lead to dependability. Availability and reliability Systems should be available to deliver service and perform as expected. Safety Systems should not behave in an unsafe way. Security Systems should protect themselves and their data from external interference. System dependability For many computer-based systems, the most important system property is the dependability of the system. The dependability of a system reflects the user’s degree of trust in that system. It reflects the extent of the user’s confidence that it will operate as users expect and that it will not ‘fail’ in normal use. Dependability covers the related systems attributes of reliability, availability and security. These are all inter-dependent. 3 Chapter 11 Security and Dependability Importance of dependability System failures may have widespread effects with large numbers of people affected by the failure. Systems that are not dependable and are unreliable, unsafe or insecure may be rejected by their users. The costs of system failure may be very high if the failure leads to economic losses or physical damage. Undependable systems may cause information loss with a high consequent recovery cost. 4 Chapter 11 Security and Dependability Causes of failure Hardware failure Hardware fails because of design and manufacturing errors or because components have reached the end of their natural life. Software failure Software fails due to errors in its specification, design or implementation. Operational failure Human operators make mistakes. Now perhaps the largest single cause of system failures in socio-technical systems. 5 Chapter 11 Security and Dependability Principal dependability properties 6 Chapter 11 Security and Dependability Principal properties Availability The probability that the system will be up and running and able to deliver useful .
