Trustworthy Frameworks

Trustworthy frameworks Framework constancy • For some computer-based systems, the main system property is the reliability of the system. • The reliability of a system reflects the user's level of confidence in that system. It reflects the degree of the user's certainty that it will work as expected and that it won't "fail" in normal use. • Reliability covers the related system attributes of dependability, availability, and security. These are interdependent. Significance of reliability • System failures can have far-reaching impacts with large numbers of people affected by the failure. • Systems that are not reliable and are considered risky, dangerous, or uncertain might be rejected by their users. • The costs of system failure can be extremely high if the failure leads to financial losses or physical damage. • Unreliable systems might cause data loss with high subsequent recovery costs. Reasons for failure • Hardware failure o • Software failure o • Hardware fails due to design and manufacturing errors or because components have reached the end of their natural life. Software fails due to errors in its specification, design, or implementation. Operational failure o Human operators make mistakes. This is currently perhaps the largest single cause of system failures in socio-technical systems. Head properties • Availability o The likelihood that the system will be operational and able to deliver useful services to users. 1 • Reliability o • Safety o • A judgment of how likely it is that the system will cause harm to people or its environment. Security o • The likelihood that the system will correctly deliver services as expected by users. A judgment of how likely it is that the system can resist accidental or deliberate interruptions. Resilience o A judgment of how well a system can maintain the continuity of its critical services in the face of disruptive events such as hardware failure and cyberattacks. Other trustworthiness properties • Repairability • Flexibility • Fault tolerance Trustworthiness characteristic conditions • Safe system operation relies on the system being available and working reliably. • A system might be unreliable because its data has been corrupted by an external attack. • If a system is infected with a virus, you cannot be sure about its reliability or safety. Reliability accomplishment • Avoid the introduction of accidental errors during the development of the system. • Design V and V cycles that are effective in finding residual errors in the system. • Design systems to be fault-tolerant so they can continue operating when faults occur. • Design protection mechanisms that defend against external attacks. 2 • Configure the system appropriately for its operating environment. • Integrate system capabilities to detect and resist cyberattacks. • Incorporate recovery mechanisms to help restore normal system service after a failure. Reliability costs • Reliability costs tend to increase significantly as higher levels of reliability are required. • There are two reasons for this: o The use of more expensive development methods and hardware needed to achieve higher levels of reliability. o The increased testing and system validation required to convince the system user and regulators that the necessary levels of reliability have been achieved. Reliability economics • Due to the very high costs of achieving reliability, it may be more economical to accept unreliable systems and pay for failure costs. • However, this depends on social and political factors. A reputation for products that can't be relied upon may lose future business. • It also depends on the system type — for business systems, modest levels of reliability may be acceptable. 3