Basic Components:

Computer Security:

Measures and controls that ensure the confidentiality, integrity and availability of computer resources including the software, hardware, firmware and information being processed, stored and communicated.

1. Confidentiality:

Confidentiality is the concealment of information or resources. The need for keeping information secret arises from the use of computers in institutions with sensitive information such as government and industry.

2. Integrity:

Integrity refers to the trustworthiness of data or resources, and it is usually phrased in terms of preventing improper or unauthorised change.

Integrity includes data integrity (the content of the information) and origin integrity (the source of the data, often called authentication).

Integrity mechanisms fall into two classes: prevention mechanisms and detection mechanisms.

Prevention mechanisms seek to maintain the integrity of the data by blocking any unauthorised attempts to change the data or any attempts to change the data in unauthorised ways.

Detection mechanisms do not try to prevent violations of integrity; they simply report that the data’s integrity is no longer trustworthy.

3. Availability:

Availability refers to the ability to use information or resources. Availability is an important aspect of reliability as well as of system design because an unavailable system is at least as bad as no system at all.

System designs usually assume a statistical model to analyse expected patterns of use, and mechanisms ensure availability when that statistical model holds. Someone may be able to manipulate use (or parameters that control use, such as network traffic) so that the assumptions of the statistical model are no longer valid.

This means that the mechanisms for keeping the resource or data available are working in an environment for which they were not designed. As a result, they will often fail.

Additional Goals:

1. Accountability: Undeniably trace back actions to unique entity
2. Authenticity: property of being genuine and being able to be verified and trusted
3. Non-Repudiation: inability to dispute that a certain action was take by an entity
4. Anonymity: remaining unidentified for certain actions
5. Un-linkability: inability to link two entities who are in fact the same

Note

Not all security goals can be met at the same time Ex: anonymity vs accountability

Model for Computer Security

Threats:

A threat is a potential violation of security.

The violation need not actually occur for there to be a threat. The fact that the violation might occur means that those actions that could cause it to occur must be guarded against.

the three security services - confidentiality, integrity and availability counter threats to the security of the system.

Attacks can be divided into four broad classes:

1. disclosure: unauthorised access to resources
2. deception: acceptance of false data
3. disruption: interruption or prevention of correct operation
4. usurpation: unauthorised control of some part of the system

Policy and Mechanism:

A security policy is a statement of what is and what is not allowed.

Policy consists of a set of axioms that the policy makers believe can be enforced. Designers of policies always make two assumptions.

1. The policy correctly and unambiguously partitions the set of system states into secure and insecure states
2. The security mechanisms prevent the system from entering insecure state

If either of the above two assumptions is erroneous the system will be insecure.

A security mechanism is a method, tool or procedure for enforcing a security policy. The security mechanisms are either secure, precise or broad.

Let,

• $P$ - set of all possible states
• $Q$ - set of secure states (specified by the policy)
• $R$ - set of states the security mechanisms restrict the system to be in

Then, security mechanism is

• secure if $R \subseteq Q$
• broad if $r \in R$ and $r \notin Q$

In practice, the security mechanisms are broad, i.e. they allow the system to be in nonsecure states.

Security Model:

• Asset/System Resource: Hardware, software, Data, networks
• Adversaries pose threats to assets i.e. violation of security goals, exploiting vulnerabilities etc
• Owners of assets impose counter measures/security mechanisms to enforce security policies to reduce the risk to their assets from threats
• Thread modelling or attacker modelling identify possible threats and their mitigations in protecting a specific asset.
• Attacks are threats that are carried out.
  • Active: an attempt to alter system resources or affect their operation
  • Passive: an attempt to learn or make use of information from the system that does not affect system resources.
• Attack Surface:
  • Network
  • Hardware
  • Software
  • Human