Security analysts organize the needs of a site in order to define a security policy. From this policy, analysts develop and implement mechanisms for enforcing the policy. The mechanisms may be procedural, technical, or physical. Part 3 describes the notion of policy and how it can be expressed and formalized, and how different types of policies affect accesses.

Chapter 4, “Security Policies,” presents the abstract notion of a security policy and some ways to represent policies. Policy languages abstract some of the common elements of policies and allow expression of policies both at abstract levels and in terms of the properties of the particular systems under consideration.

Chapter 5, “Confidentiality Policies,” discusses policies designed primarily for confidentiality. Many government organizations, especially the military, must keep information secret, as described by these policies. Chapter 5 focuses on the Bell-LaPadula security policy.

Chapter 6, “Integrity Policies,” discusses policies designed primarily for integrity. Banks, insurance companies, and other commercial and industrial firms worry more about data and programs being corrupted than about them being read, and use these policies.

Chapter 7, “Hybrid Policies,” presents policies that are hybrids of confidentiality and integrity security policies. One comes from the world of stock brokerage, and another from medical systems. Other types of policy models discussed here are originator controlled models and role-based models.

Chapter 8, “Noninterference and Policy Composition,” discusses the noninterference and nondeducibility models of security policies and the composition of security policies in general.