U4. Security Models & Policy

U4. Security Models & Policy

1. Policy

   • Policy= captures the requirements and describes the steps to be taken to achieve security
   • Organisatonal Security Policy
     • Rules that regulate how an organisation manages security
       • Must be well defined
   • Automated Security Policy
     • Restrictions & properties that specify how a computing system prevents violations of the organisational security policy

2. Models

   • Models = an 'idealised' implementation of an organisation’s security policy.
     • Models enforce the Access Control Structure policy and ensure "need to know"
       • Models allow formal validation of your implementation against the security policy. Benchmarking
     • Can be used to illustrate the Fundamental Design Principles
   • State Machine Model (automaton)
     • an abstract model that records relevant features of a system (IE: its security) at a particular point in tim
       • A state may change to another state at some later point in time, triggered possibly by a clock or some input event
         • movement from one state to another is known as a transition
           • the more states you try capture, the more complicated the model will become (more difficult to analyse).

3. Basic Security Theorem

   • If we can do these 3 things then we know that 'security' is preserved by all transitions and so the system will always be secure
     • 1. Define the State Set so that it captures some aspect of 'security
     • 2. Check that every state transition that begins in a 'secure' state ends in a 'secure' state
     • 3. Check that the initial state of the system is 'secure'.
     • Ensure you define what "secure" is!