What Security Means

Security means that the systems have the properties of confidentiality, integrity, and availability, that users are authenticated and authorized correctly, and that transactions are non-repudiable.

The following explains each property.

• Confidentiality - Data is only available to the people intended to access it.
• Integrity - Data and system resources are only changed in appropriate ways by appropriate people.
• Availability - Systems are ready when needed and perform acceptably.
• Authentication - The identity of users is established (or you’re willing to accept anonymous users).
• Authorization - Users are explicitly allowed or denied access to resources.
• Nonrepudiation - Users can’t perform an action and later deny performing it.

The following maps threats to the properties that guard against them.

• Spoofing - Authentication
• Tampering - Integrity
• Repudiation - Non-repudiation
• Information disclosure - Confidentiality
• Denial of service - Availability
• Elevation of privilege - Authorization

Adopted from Threat Modeling: Uncover Security Design Flaws Using The STRIDE Approach.

Saltzer and Schroeder's Security Design Principles

Principles:

• Open design - Assume the attackers have the sources and the specs.
• Fail-safe defaults - Fail closed; no single point of failure.
• Least privilege - No more privileges than what is needed.
• Economy of mechanism - Keep it simple, stupid.
• Separation of privileges - Don’t permit an operation based on a single condition.
• Total mediation - Check everything, every time.
• Least common mechanism - Beware of shared resources.
• Psychological acceptability - Will they use it?

Adopted from Threat Modeling: Uncover Security Design Flaws Using The STRIDE Approach.