An Introduction to Intrusion Tolerance

Intrusion Detection and Intrusion Prevention are the security work that is classical. Intrusion Tolerance is a new approach that has its emersion in the past decade. Intrusion Tolerance means fault that is operational intentional which leads to failure of component.

Vulnerability to a certain extent of system should be accepted and assumed. Attacking on subsystems can have a successful happening sometimes. This should be accepted and assumed. The whole system should remain operational and secure. This should be assured by tolerance paradigm in security.

Integrity, Authenticity and Confidentiality are the various security properties. Maintaining security properties despite allowing compromise of certain components must be done by intrusion-tolerant system. Intruder should be able to modify or read data. Assumptions that there can be happening of intrusions are possible. It is impossible to state that here are no vulnerabilities in a system.

Security and Reliability: Application of “tolerance” paradigm was first done in Reliability.

Computing that is fault tolerant and reliability: Continuing delivering of the right service even in fault presence is the work of a fault-tolerant system. Input-output relation gives system, service and what is intended by system.

Fault types:

  • Electrical damage is suffered by chip (motor)
  • Wrong button is pushed by operator
  • Software defect
  • Burning out of fans
  • Fault that is transient, physical and design

System and components: Components make system. Each component makes each system.

Defense-in-depth approach:

  • Redundancy: Different components and systems are included such that anyone can do wanted function in case others fail.
  • Diversity: Usage of different components which is based on different principles and designs from various vendors.
  • Independence: This factor is got by physical separation, communication independence and electrical isolation between systems.


  • System’s Availability: Measurement of difference between incorrect and correct delivery service.
  • System’s Safety: Measurement of catastrophic failure time.
  • System’s Security: Prevent unauthorized information handling.
  • Maintainability: Measurement of restoration time.

Failure, Fault and Error:

  • If system does not deliver required service, we name it a failure.
  • Fault is cause of failure.
  • Error causes failure of system.
  • Error processing:
  • Error recovery and detection: Backward recovery, Forward recovery

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