Security and Dependability Notes

System Dependability

  • Reflects user trust in the system.

  • Covers reliability, availability, and security.

  • Failures can have widespread effects and high costs.

Principal Properties

  • Availability: Probability of the system being up and running.

  • Reliability: Probability of the system delivering correct services.

  • Safety: Judgment of the likelihood of causing damage.

  • Security: Judgment of the system's resistance to intrusions.

Other Dependability Properties

  • Repairability: Extent to which the system can be repaired after failure.

  • Maintainability: Extent to which the system can be adapted to new requirements.

  • Survivability: Extent to which the system can deliver services under attack.

  • Error tolerance: Extent to which user input errors can be avoided and tolerated.

Availability and Reliability

  • Reliability: Probability of failure-free operation over time.

  • Availability: Probability that a system is operational at a point in time.

  • Both can be expressed quantitatively (e.g., availability of 0.999).

Reliability Achievement

  • Fault avoidance: Minimizing mistakes during development.

  • Fault detection and removal: Detecting and correcting errors before service.

  • Fault tolerance: Ensuring faults don't result in system failures.

Safety

  • Ability to operate without causing human injury or environmental damage.

  • Software safety is crucial due to software-based control systems.

  • Safety requirements exclude undesirable situations.

Safety Achievement

  • Hazard avoidance: Designing the system so hazards cannot arise.

  • Hazard detection and removal: Detecting and removing hazards before accidents.

  • Damage limitation: Minimizing damage from accidents.

Software Safety Benefits

  • Software enhances system safety through monitoring and control.

  • Reduces time spent in hazardous environments.

  • Detects and corrects safety-critical operator errors.

Security

  • System's ability to protect itself from external attacks.

  • Essential due to networked systems and internet access.

  • Pre-requisite for availability, reliability, and safety.

Security Assurance

  • Vulnerability avoidance: Designing the system to avoid vulnerabilities.

  • Attack detection and elimination: Detecting and neutralizing attacks.

  • Exposure limitation and recovery: Minimizing consequences of successful attacks.