Determining the security category of an information system requires slightly more analysis and must consider the security categories of all information types resident on the information system. For an information system, the potential impact values assigned to the respective security objectives (confidentiality, integrity, availability) shall be the highest values (i.e., high water mark) from among those security categories that have been determined for each type of information resident on the information system.'

The generalized format for expressing the security category, SC, of an information system is:

SC information system = {(confidentiality, impact), (integrity, impact), (availability, impact)}, where the acceptable values for potential impact are LOW, MODERATE, or HIGH.

Note that the value of not applicable cannot be assigned to any security objective in the context of establishing a security category for an information system. This is in recognition that there is a low minimum potential impact (i.e., low water mark) on the loss of confidentiality, integrity, and availability for an information system due to the fundamental requirement to protect the system-level processing functions and information critical to the operation of the information system.

EXAMPLE 4: An information system used for large acquisitions in a contracting organization contains both sensitive, pre-solicitation phase contract information and routine administrative information. The management within the contracting organization determines that: (i) for the sensitive contract information, the potential impact from a loss of confidentiality is moderate, the potential impact from a loss of integrity is moderate, and the potential impact from a loss of availability is low; and (ii) for the routine administrative information (non-privacy-related information), the potential impact from a loss of confidentiality is low, the potential impact from a loss of integrity is low, and the potential impact from a loss of availability is low.

The resulting security categories, SC, of these information types are expressed as:

SC contract information = {(confidentiality, MODERATE), (integrity, MODERATE), (availability, LOW)},

and

SC administrative information = {(confidentiality, LOW), (integrity, LOW), (availability, LOW)}.

The resulting security category of the information system is expressed as:

SC acquisition system = {(confidentiality, MODERATE), (integrity, MODERATE), (availability, LOW)},

representing the high water mark or maximum potential impact values for each security objective from the information types resident on the acquisition system.

It is recognized that information systems are composed of both programs and information. Programs in execution within an information system (i.e., system processes) facilitate the processing, storage, and transmission of information and are necessary for the organization to conduct its essential mission-related functions and operations. These system processing functions also require protection and could be subject to security categorization as well. However, in the interest of simplification, it is assumed that the security categorization of all information types associated with the information system provide an appropriate worst case potential impact for the overall information system—thereby obviating the need to consider the system processes in the security categorization of the information system.

EXAMPLE 5: A power plant contains a SCADA (supervisory control and data acquisition) system controlling the distribution of electric power for a large military installation. The SCADA system contains both real-time sensor data and routine administrative information. The management at the power plant determines that: (i) for the sensor data being acquired by the SCADA system, there is no potential impact from a loss of confidentiality, a high potential impact from a loss of integrity, and a high potential impact from a loss of availability; and (ii) for the administrative information being processed by the system, there is a low potential impact from a loss of confidentiality, a low potential impact from a loss of integrity, and a low potential impact from a loss of availability.

The resulting security categories, SC, of these information types are expressed as:

SC sensor data = {(confidentiality, NA), (integrity, HIGH), (availability, HIGH)},

and

SC administrative information = {(confidentiality, LOW), (integrity, LOW), (availability, LOW)}.

The resulting security category of the information system is initially expressed as:

SC SCADA system = {(confidentiality, LOW), (integrity, HIGH), (availability, HIGH)},

representing the high water mark or maximum potential impact values for each security objective from the information types resident on the SCADA system. The management at the power plant chooses to increase the potential impact from a loss of confidentiality from low to moderate reflecting a more realistic view of the potential impact on the information system should there be a security breach due to the unauthorized disclosure of system-level information or processing functions. The final security category of the information system is expressed as:

SC SCADA system = {(confidentiality, MODERATE), (integrity, HIGH), (availability, HIGH)}.

 

Table 1 summarizes the potential impact definitions for each security objective—confidentiality, integrity, and availability.