SC-45 System Time Synchronization

Guidance: nonePolicy clause: noneWhat these mean

Baselines	Implementation level	Enhancements
Not in a baseline	System	2 (0 in a baseline)

Related controls: AC-3, AU-8, IA-2, IA-8

Control statement

Synchronize system clocks within and between systems and system components.

NIST discussion

Time synchronization of system clocks is essential for the correct execution of many system services, including identification and authentication processes that involve certificates and time-of-day restrictions as part of access control. Denial of service or failure to deny expired credentials may result without properly synchronized clocks within and between systems and system components. Time is commonly expressed in Coordinated Universal Time (UTC), a modern continuation of Greenwich Mean Time (GMT), or local time with an offset from UTC. The granularity of time measurements refers to the degree of synchronization between system clocks and reference clocks, such as clocks synchronizing within hundreds of milliseconds or tens of milliseconds. Organizations may define different time granularities for system components. Time service can be critical to other security capabilities—such as access control and identification and authentication—depending on the nature of the mechanisms used to support the capabilities.

Control enhancements

SC-45(1) Synchronization with Authoritative Time Source

Baselines: Not in a baseline

• (a) Compare the internal system clocks [Assignment: organization-defined frequency] with [Assignment: organization-defined authoritative time source] ; and
• (b) Synchronize the internal system clocks to the authoritative time source when the time difference is greater than [Assignment: organization-defined time period].

Discussion and assessment objectives for SC-45(1)

Synchronization of internal system clocks with an authoritative source provides uniformity of time stamps for systems with multiple system clocks and systems connected over a network.

Determine if:

• SC-45(01)(a) the internal system clocks are compared [Assignment: organization-defined frequency] with [Assignment: organization-defined authoritative time source];
• SC-45(01)(b) the internal system clocks are synchronized with the authoritative time source when the time difference is greater than [Assignment: organization-defined time period].

Examine: System and communications protection policy; procedures addressing time synchronization; system design documentation; system configuration settings and associated documentation; system audit records; system security plan; other relevant documents or records.

Interview: System/network administrators; organizational personnel with information security responsibilities; organizational personnel installing, configuring, and/or maintaining the system.

Test: Mechanisms supporting and/or implementing system time synchronization.

SC-45(2) Secondary Authoritative Time Source

Baselines: Not in a baseline

• (a) Identify a secondary authoritative time source that is in a different geographic region than the primary authoritative time source; and
• (b) Synchronize the internal system clocks to the secondary authoritative time source if the primary authoritative time source is unavailable.

Discussion and assessment objectives for SC-45(2)

It may be necessary to employ geolocation information to determine that the secondary authoritative time source is in a different geographic region.

Determine if:

• SC-45(02)(a) a secondary authoritative time source is identified that is in a different geographic region than the primary authoritative time source;
• SC-45(02)(b) the internal system clocks are synchronized to the secondary authoritative time source if the primary authoritative time source is unavailable.

Examine: System and communications protection policy; procedures addressing time synchronization; system design documentation; system configuration settings and associated documentation; system audit records; system security plan; other relevant documents or records.

Interview: System/network administrators; organizational personnel with information security responsibilities; organizational personnel installing, configuring, and/or maintaining the system.

Test: Mechanisms supporting and/or implementing system time synchronization with secondary authoritative time sources.

Assessment objectives (SP 800-53A)

Objectives and methods for SC-45

Determine if system clocks are synchronized within and between systems and system components.

Examine: System and communications protection policy; procedures addressing time synchronization; system design documentation; system configuration settings and associated documentation; system audit records; system security plan; other relevant documents or records.

Interview: System/network administrators; organizational personnel with information security responsibilities; organizational personnel installing, configuring, and/or maintaining the system.

Test: Mechanisms supporting and/or implementing system time synchronization.