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AC-4(4) AC · Access Control

Flow Control of Encrypted Information

LOW MODERATE ✓ HIGH
1 Overlay 1 Related Control
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Requirements NIST SOURCE

Prevent encrypted information from bypassing [information flow control mechanisms] by [one of: decrypting the information; blocking the flow of the encrypted information; terminating communications sessions attempting to pass encrypted information; ].

Discussion (NIST Supplemental Guidance)

Flow control mechanisms include content checking, security policy filters, and data type identifiers. The term encryption is extended to cover encoded data not recognized by filtering mechanisms.

Implementation Guidance

Engineering Interpretation

Original engineering commentary written for this explorer — not NIST source text and not authoritative guidance.

No engineering interpretation has been authored for AC-4(4) yet. This section is architected to receive it — see the Requirements and Assessment sections above for the authoritative NIST source content in the meantime.

Assessment

NIST SP 800-53A REV 5.2.0

Assessment Objectives

  1. information flow control mechanisms that encrypted information is prevented from bypassing are defined;
  2. one or more of the following PARAMETER VALUES is/are selected: {decrypting the information; blocking the flow of the encrypted information; terminating communications sessions attempting to pass encrypted information; <AC-04(04)_ODP[03] organization-defined procedure or method>};
  3. the organization-defined procedure or method used to prevent encrypted information from bypassing information flow control mechanisms is defined (if selected);
  4. encrypted information is prevented from bypassing <AC-04(04)_ODP[01] information flow control mechanisms> by <AC-04(04)_ODP[02] SELECTED PARAMETER VALUES>.

Examine

[SELECT FROM: Access control policy; information flow control policies; procedures addressing information flow enforcement; system design documentation; system configuration settings and associated documentation; system audit records; system security plan; other relevant documents or records].

Interview

[SELECT FROM: System/network administrators; organizational personnel with information security responsibilities; system developers].

Test

[SELECT FROM: Mechanisms implementing information flow enforcement policy].

Overlays

Showing the OT/ICS overlay for the parent control AC-4 — see the AC-4(4) entries within each baseline below.

OT/ICS Overlay SP 800-82r3

NIST SP 800-82r3 Appendix F, Table 22. Blank baseline means the control/control enhancement is not selected in that initial OT baseline.

LOW

Not applicable at this tier.

MODERATE

  • Base control: Included (matches standard baseline)

HIGH

  • Base control: Included (matches standard baseline)
  • Included: (4)

STIGs & CCIs

No STIG checks or CCI mappings are currently loaded for AC-4(4). This section is architected to display, per product: STIG ID, Finding ID, Severity, Title, Description, Check, Fix, CCI, and NIST control mapping — but nothing is populated here until a real DISA STIG/CCI dataset is ingested.

Learn more about STIG/CCI integration →

Evidence

Potential Evidence — Derived

Categorized from the SP 800-53A "Examine"/"Test" artifact list above by keyword — not an authoritative NIST evidence list.

Policy

  • Access control policy
  • information flow control policies
  • system security plan

Configuration

  • system design documentation
  • system configuration settings and associated documentation

Testing

  • Mechanisms implementing information flow enforcement policy

Other Records

  • procedures addressing information flow enforcement
  • system audit records
  • other relevant documents or records