Information Security Fundamentals and Security Models
This domain covers the vocabulary and models that every later domain assumes: what security protects, how it is decomposed, and the formal rules that describe access control. NISP Level 1 questions here are usually definitional, so precision matters more than depth.
Core vocabulary and the CIA triad
Confidentiality, integrity and availability are the three classic goals; authenticity, non-repudiation and accountability are added as supporting properties. A threat is a potential cause of harm, a vulnerability is a weakness a threat can exploit, and risk combines threat, vulnerability and impact. Controls are preventive, detective or corrective, and can be administrative, technical or physical.
Formal security models
- Bell-LaPadula - confidentiality. No read up (simple security property), no write down (*-property), plus the discretionary property.
- Biba - integrity. No read down, no write up: the mirror image of Bell-LaPadula.
- Clark-Wilson - integrity via well-formed transactions and separation of duties; users act on data only through approved transformation procedures.
- Brewer-Nash (Chinese Wall) - prevents conflicts of interest by dynamically restricting access once a user touches a competing dataset.
- Harrison-Ruzzo-Ullman - an access matrix whose rights can be granted and revoked; used to reason about safety.
Worked example
An analyst cleared at Secret tries to open a Top Secret report. Bell-LaPadula's simple security property forbids reading up, so the request is denied even though the analyst is trusted. If the same analyst then tries to write a Secret note into a Top Secret file, the *-property forbids writing up as well. Bell-LaPadula protects confidentiality, not integrity; Biba would give the opposite answers.
Traps
- Mixing the direction of the rules; remember that Bell-LaPadula protects secrets and Biba protects correctness.
- Treating a model as a product feature rather than a policy abstraction.
- Confusing a vulnerability (the weakness) with the risk (the possible loss).
- Forgetting that least privilege, need-to-know and separation of duties are principles, not formal models.