Computer security is the protection of the assets of a computer or computer system.
Assets and Their Value
Types of assets: hardware, software, data, people, processes, or combinations of these.
Asset value:
- Depends on the asset owner’s or user’s perspective.
- May be independent of monetary cost, depending instead on factors such as replacement cost.
- May be time or event dependent.
The value of an asset influences the threats it faces. The type of an asset has a bearing on its vulnerabilities.
Vulnerability-Threat-Control Paradigm
- Vulnerability
A weakness in a system, in procedures, design, or implementation, that might be exploited to cause loss or harm.
Example: A network service with a buffer overflow bug. - Threat
A set of circumstances with the potential to cause loss or harm to a computing system.
Example: An attacker capable of sending crafted input to trigger the overflow and run arbitrary code. - Control
An action, device, procedure, or technique that removes or reduces a vulnerability.
Example: A patch that fixes the overflow, or a firewall rule that blocks external access to the service.
Threats to data, systems, and services originate from 3 sources:
- Non-human origin
Hardware, software, network, or power failure. - Human origin, benign intent
Human error in initiating a wrong action or giving wrong input. - Human origin, malicious intent
Autonomous attacks initiated by humans, either random (worms, viruses, malicious web pages or scripts, phishing emails) or directed (spear phishing, impersonation).
Attackers can be individuals, groups, organizations, or nation states.
Advanced Persistent Threat
An advanced persistent threat (APT) is a directed attack designed to snare a high value target, e.g. stealing a company CEO’s email password, or cause extremely high damage, e.g. destroying a uranium enrichment plant.
APT attacks are executed by coordinated human actions rather than through program code alone. Attackers are skilled, motivated, organized, and well funded.
- Advanced
Attackers have a full spectrum of intelligence-gathering techniques at their disposal. - Persistent
Attackers have specific objectives, rather than opportunistically seeking information for financial or other gain. - Threat
Attackers constitute a high-level threat because they have both capability and intent for severe damage or loss.
Potential harm to an asset is viewed from 2 perspectives:
- What bad things can happen to assets.
- Who or what can cause or allow those bad things to happen.
Security Properties
3 basic properties for an asset:
- Confidentiality
Ability of a system to ensure an asset is viewed (read) only by authorized parties. - Integrity
Ability of a system to ensure an asset is modified (write) only by authorized parties. - Availability
Ability of a system to ensure an asset can be used by any authorized parties.
These 3 properties (CIA) are both basic security properties and the objects of security threats.
Communication over networks introduces additional properties:
- Authentication
Ability of a system to confirm the identity of a sender. - Nonrepudiation
Aka. accountability, the ability of a system to confirm that a sender cannot convincingly deny having sent something. - Auditability
Ability of a system to trace all actions related to a given asset.
Acts Causing Security Harm
The CIA triad can be viewed from the perspective of the nature of the harm caused to assets, characterized by 4 acts:
- Interception
Confidentiality suffers if someone intercepts data. - Interruption
Availability is lost if someone or something interrupts a flow of data or access to a computer. - Modification
Integrity fails if someone or something modifies data. - Fabrication
Integrity also fails if someone or something fabricates false data.
Attackers are broadly categorized as passive or active.
