Defense in depth (also known as Castle Approach) is an information assurance (IA) concept in which multiple layers of security controls (defense) are placed throughout an information technology (IT) system. Its intent is to provide redundancy in the event a security control fails or a vulnerability is exploited that can cover aspects of personnel, procedural, technical and physical for the duration of the system's life cycle.
Contents
Background
The idea behind the defense in depth approach is to defend a system against any particular attack using several independent methods. It is a layering tactic, conceived by the National Security Agency (NSA) as a comprehensive approach to information and electronic security.
Defense in depth is originally a military strategy that seeks to delay rather than prevent the advance of an attacker by yielding space to buy time. The placement of protection mechanisms, procedures and policies is intended to increase the dependability of an IT system, where multiple layers of defense prevent espionage and direct attacks against critical systems. In terms of computer network defense, defense in depth measures should not only prevent security breaches but also buy an organization time to detect and respond to an attack and so reduce and mitigate the consequences of a breach.
Controls
Defense in depth can be divided into three areas: Physical, Technical, and Administrative.
Physical controls
Physical controls are anything that physically limits or prevents access to IT systems. Fences, guards, dogs, and CCTV systems
Technical controls
Technical controls are hardware or software whose purpose is to protect systems and resources. Examples of technical controls would be disk encryption, fingerprint readers, and Windows Active Directory. Hardware technical controls differ from physical controls in that they prevent access to the contents of a system, but not the physical systems themselves.
Administrative controls
Administrative controls are an organization's policies and procedures. Their purpose is to ensure that there is proper guidance available in regards to security and that regulations are met. They include things such as hiring practices, data handling procedures, and security requirements.
Examples
Using more than one of the following layers constitutes defense in depth.