Control statement
Synchronize system clocks within and between systems and system components.
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.
From control text to operational evidence
Use System Time Synchronization as a testable risk decision. Translate the official statement into accountable people, repeatable processes, configured technology, and evidence that demonstrates the outcome over time. In this family, pay particular attention to secure architecture, boundary protection, communications protection, cryptography, and system isolation.
Implementation workflow
- Define the control boundary, responsible owner, inherited portions, and systems or processes in scope.
- Resolve each organization-defined parameter before declaring the control implemented.
- Document how the implementation satisfies every clause of the official control statement.
- Collect evidence as a normal byproduct of operation rather than only before an assessment.
- Review exceptions, changes, and monitoring results on a risk-based cadence.
Evidence examples
- network and trust-boundary diagrams
- firewall and gateway configurations
- cryptographic configuration and key records
- segmentation and isolation test results
Common failure patterns
- diagrams omit cloud and third-party paths
- encryption enabled without key governance
- flat trust zones allow unnecessary lateral movement
- boundary rules accumulate without owner review
Questions practitioners should ask
- What risk decision is this control intended to support in this system?
- Which parts are implemented locally, inherited, shared, or not applicable—and what evidence supports that decision?
- Do the documented narrative, deployed configuration, operating process, and collected evidence agree?
- What event or threshold requires the implementation to be reviewed or changed?
Assessment objectives and methods
Show the assessment objective
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
Related controls
These relationships come from the official OSCAL catalog. They indicate useful dependencies or context, not automatic inheritance or equivalence.
Control enhancements
Enhancements add specificity, strength, or scope to the base control. Baseline badges show explicit selections in the official SP 800-53B OSCAL profiles.
SC-45(1) — Synchronization with Authoritative Time Source
- (a)Compare the internal system clocks [Organization-defined: frequency] with [Organization-defined: authoritative time source] ; and
- (b)Synchronize the internal system clocks to the authoritative time source when the time difference is greater than [Organization-defined: time period].
Official discussion
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.
Organization-defined parameters (3)
Assessment objectives and methods
- SC-45(01)(a)the internal system clocks are compared [Organization-defined: frequency] with [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 [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
- (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.
Official discussion
It may be necessary to employ geolocation information to determine that the secondary authoritative time source is in a different geographic region.
Assessment objectives and methods
- 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
Authoritative sources
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