What is the difference between addressable and required implementation specifications in the Security Rule?

Answer:

If an implementation specification is described as “required,” the specification must be implemented. The concept of "addressable implementation specifications" was developed to provide covered entities additional flexibility with respect to compliance with the security standards. In meeting standards that contain addressable implementation specifications, a covered entity will do one of the following for each addressable specification: (a) implement the addressable implementation specifications; (b) implement one or more alternative security measures to accomplish the same purpose; (c) not implement either an addressable implementation specification or an alternative. The covered entity’s choice must be documented. The covered entity must decide whether a given addressable implementation specification is a reasonable and appropriate security measure to apply within its particular security framework. For example, a covered entity must implement an addressable implementation specification if it is reasonable and appropriate to do so, and must implement an equivalent alternative if the addressable implementation specification is unreasonable and inappropriate, and there is a reasonable and appropriate alternative. This decision will depend on a variety of factors, such as, among others, the entity's risk analysis, risk mitigation strategy, what security measures are already in place, and the cost of implementation. The decisions that a covered entity makes regarding addressable specifications must be documented in writing.  The written documentation should include the factors considered as well as the results of the risk assessment on which the decision was based.