SC-31: Covert Channel Analysis

SC-31 requires you to perform and document a covert channel analysis for your system’s communications to identify potential avenues for covert channels, then track the results into design or operational decisions. To operationalize it quickly, scope the analysis to your real communication paths, run a structured review for storage and timing channels, record findings and mitigations, and retain assessor-ready evidence. ¹

Key takeaways:

• You need a repeatable covert channel analysis process tied to system communications, not a one-time paper exercise. ¹
• Auditors will ask for scope, method, findings, and proof that outcomes influenced configuration or architecture decisions. ²
• The fastest path is to assign an owner, define analysis triggers, and produce a single “SC-31 Covert Channel Analysis Report” with traceable artifacts. ¹

SC-31: covert channel analysis requirement is easy to misread as “do a pen test” or “run a network scan.” That’s not what it asks. SC-31 is narrower and more technical: you must analyze communications within the system to identify aspects that could serve as covert channels, meaning paths that can carry information in ways you did not intend to authorize or monitor. ¹

For a CCO, GRC lead, or Compliance Officer, the operational challenge is twofold. First, you need to translate a security-engineering activity into a compliance deliverable that stands up in an assessment. Second, you need to right-size it: deep enough to be credible, scoped enough to complete without stalling delivery teams.

This page gives you a requirement-level implementation playbook: what it means in plain English, who owns it, how to execute it step-by-step, what evidence to keep, and where audits commonly get stuck. It is written to help you produce assessor-ready artifacts quickly while still improving real system security. ¹

Regulatory text

Control requirement (excerpt): “Perform a covert channel analysis to identify those aspects of communications within the system that are potential avenues for covert [organization-defined] channels; and” ²

Operator interpretation:

• You must perform an analysis, not just state that covert channels are “out of scope.” ¹
• The analysis must focus on communications within the system, including how components exchange data, signals, metadata, and resources that could be repurposed to transfer information. ²
• The control includes an organization-defined parameter (the excerpt shows “[organization-defined]”). You must define what types of covert channels you consider (for example, timing channels, storage channels, or other classes relevant to your architecture) and reflect that in your procedure and report. ²

Plain-English interpretation (what SC-31 is asking you to prove)

You can explain SC-31 to non-engineers like this:

1. You identified where information could “hide” in normal system communications (including unintended signals such as timing, shared resource contention, header fields, queue depths, cache behavior, or error conditions).
2. You assessed whether those paths are plausible for your threat model and environment.
3. You either mitigated the risk (design/config changes) or accepted it with a documented rationale and monitoring/constraints.

The compliance deliverable is not a perfect theoretical proof. It is a defensible analysis tied to actual system behavior and documented decisions. ¹

Who it applies to (entity and operational context)

SC-31 commonly applies where NIST SP 800-53 is the governing control baseline, including:

• Federal information systems and programs assessed against NIST SP 800-53. ¹
• Contractor systems handling federal data where NIST SP 800-53 controls are contractually flowed down or used for assessment. ¹

Operationally, SC-31 is most relevant when you have:

• Multi-tenant or multi-level environments (shared compute, shared clusters, shared networks).
• Segmented networks with “high-to-low” or “restricted-to-less-restricted” boundaries.
• Strong separation claims (microsegmentation, container isolation, enclaves) where hidden signaling would undercut the separation story.

If you run a simple single-tenant application with minimal internal communication, your analysis may be smaller. If you run shared infrastructure, your analysis must be deeper and more explicit.

What you actually need to do (step-by-step)

Step 1: Assign ownership and define triggers

• Assign a control owner (usually Security Architecture or Product Security) and a compliance coordinator (GRC).
• Define triggers for re-analysis: major architecture changes, new shared services, new cross-domain interfaces, or changes to isolation boundaries.

Output: SC-31 procedure (1–2 pages) + named owner and re-review triggers. ¹

Step 2: Build an inventory of “communication surfaces”

Create a scoped list of communication paths “within the system,” such as:

• Service-to-service calls (APIs, message buses, RPC)
• Shared storage and caches
• Shared compute resources (nodes, hypervisors, container runtime features)
• Authentication/authorization side effects (error messages, response codes)
• Observability paths (logs, metrics, tracing)
• Control plane vs data plane paths (Kubernetes API, CI/CD runners, admin channels)

Tip for speed: start from your data-flow diagrams and network segmentation diagrams, then add shared resource notes from your platform team.

Output: “SC-31 Communications Scope” table. ¹

Step 3: Run a structured covert channel analysis (storage + timing)

Use a repeatable worksheet approach so you can show method, not just conclusions.

A practical structure:

A. Storage channel review (information hidden in a shared state)

• Shared files, database fields, message headers, object metadata
• Shared caches (application cache, CDN headers, broker queues)
• Shared configuration stores, feature flags, service discovery metadata
• Shared logs/metrics that one tenant can influence and another can read

B. Timing channel review (information encoded in timing/latency patterns)

• Variable response times across trust boundaries
• Backpressure and queue depth effects
• Rate limiting behavior that differs by secret state
• Resource contention that a lower-trust process can observe (CPU, cache, IO)

For each communication surface, document:

• The potential covert channel type (storage/timing/other you define)
• Preconditions (attacker position, permissions, co-residency)
• Impacted data types (sensitive data categories used in the system)
• Feasibility judgment (high/medium/low, with reasoning)
• Existing controls that reduce feasibility (segmentation, isolation, quotas)

Output: Covert channel analysis worksheet with per-surface findings. ²

Step 4: Decide treatment and implement mitigations where warranted

Common mitigation patterns you can document without overpromising:

• Strengthen isolation boundaries (reduce co-residency, tighten segmentation)
• Reduce shared state or make it unidirectional where feasible
• Normalize error messages and response behavior to reduce signaling
• Add quotas and controls on shared resources to limit contention-based signaling
• Add monitoring for unusual patterns (for example, repeated crafted requests across boundaries)

Your artifact must show that findings resulted in one of:

• A tracked engineering change (ticket/PR)
• A risk acceptance with rationale and approver
• A compensating control plan with owner and due date

Output: Remediation tracker entries tied back to findings. ¹

Step 5: Produce an assessor-ready SC-31 report

Keep it short and auditable:

• Scope and assumptions
• Method used (storage/timing categories, threat assumptions)
• Findings summary and risk treatment decisions
• Evidence references (diagrams, configs, tickets)

This is where Daydream fits naturally: teams often do the analysis but fail to retain evidence in a single place. Daydream can map SC-31 to a named owner, a written procedure, and a recurring evidence bundle so you can answer assessor requests in minutes instead of re-creating work from engineering chat logs. ²

Required evidence and artifacts to retain

Minimum set that holds up in audits:

• SC-31 procedure (owner, scope approach, triggers, frequency logic). ¹
• System communications scope artifact (data-flow diagram or communications inventory). ¹
• Covert Channel Analysis Report (dated, versioned, tied to a system release/architecture). ²
• Findings register with disposition (mitigate/accept/transfer) and approvals.
• Change evidence: tickets/PRs/config diffs proving mitigations were implemented where required.
• Review/attestation record: sign-off from Security Architecture and system owner.

Common exam/audit questions and hangups

Auditors and assessors tend to probe these points:

• “Show me which communications you analyzed and why those represent the system’s true boundaries.”
• “What do you mean by ‘covert channel’ in your environment? Where is that defined?” ²
• “What changed after the analysis? Show tickets or configuration changes.”
• “How do you ensure the analysis stays current after architecture changes?”
• “If you accepted risk, who approved it and what compensating controls exist?”

Hangup pattern: teams provide a generic secure design document with no mapping to actual communication paths. SC-31 expects an analysis tied to communications “within the system.” ²

Frequent implementation mistakes (and how to avoid them)

Mistake	Why it fails	How to fix it
Treating SC-31 as a network scan	Scans find exposed services, not covert channels	Use a worksheet that explicitly covers storage and timing channels
Over-scoping into “analyze everything”	Teams stall and never ship evidence	Start from real trust boundaries and shared resources, then expand only if needed
No organization-defined parameter	The control expects you to define what you analyze	Write a short definition section in the procedure aligned to your architecture 2
Findings without outcomes	Assessors need proof decisions were made	Tie each finding to a ticket, PR, or risk acceptance record
Evidence scattered across tools	You cannot respond to an evidence request quickly	Centralize artifacts in one control record (Daydream or your GRC system) 1

Risk implications (why SC-31 is assessed seriously)

Covert channels undermine the security claims you make elsewhere: isolation, segmentation, least privilege, and data separation can all look correct on paper while hidden signaling paths still exist. In regulated environments, that turns into assessment risk: inability to demonstrate SC-31 can read as a control design gap, even if your security posture is otherwise strong. ¹

Practical 30/60/90-day execution plan

No sourced durations are provided for SC-31, so treat this as a planning template you can adjust to your SDLC pace.

First 30 days (establish control mechanics)

• Assign SC-31 owner and reviewer roles.
• Draft SC-31 procedure with your organization-defined covert channel categories. ²
• Build the communications scope inventory from existing diagrams.
• Pick one “representative” system boundary (highest risk segment or most shared environment) for the first analysis pass.

Days 31–60 (execute and produce auditable artifacts)

• Complete the covert channel analysis worksheet for in-scope communications.
• Create a findings register with explicit dispositions.
• Open remediation tickets for high-priority items and link them to findings.
• Publish the SC-31 Covert Channel Analysis Report and store it with the control record.

Days 61–90 (operationalize and make it repeatable)

• Add SC-31 trigger checks to architecture review or change management.
• Validate that mitigations were implemented; retain change evidence.
• Run a tabletop review with engineering and GRC: can you answer the common audit questions from this page using your stored artifacts?
• If you use Daydream, configure SC-31 to collect recurring evidence automatically (report, worksheet, sign-off, remediation links) so the next review is incremental, not a re-start. ¹

Frequently Asked Questions

Do we need a specialist to perform a covert channel analysis?

You need someone who understands your architecture and isolation model; that is often Security Architecture plus a platform engineer. Your GRC team should focus on scope, method repeatability, and evidence quality. ¹

Is SC-31 satisfied by a penetration test report?

Usually no. A pen test can be a supporting input, but SC-31 calls for an analysis of communications paths as potential covert channel avenues, which pen tests do not systematically document. ²

What does “organization-defined” mean in SC-31?

You must define what covert channel types or classes you will consider in your environment and document that definition in your procedure and report. Keep it aligned to your architecture so it is defensible. ²

How do we scope SC-31 for a cloud-native microservices platform?

Start with trust boundaries and shared resources: cluster multi-tenancy, service mesh paths, shared caches, and observability pipelines. Then analyze the highest-risk cross-boundary communications first and document why you scoped it that way. ¹

What evidence do auditors ask for most often?

A dated analysis report tied to the current architecture, plus proof that findings led to tracked decisions (tickets, PRs, or risk acceptance approvals). Assessors also ask who owns the control and how re-analysis is triggered. ¹

How often do we need to redo the analysis?

NIST does not specify a fixed interval in the provided excerpt; set triggers based on architectural change and risk. Document the trigger logic in your SC-31 procedure and follow it consistently. ¹

Footnotes

1. NIST SP 800-53 Rev. 5

2. NIST SP 800-53 Rev. 5 OSCAL JSON