SI-4(10): Visibility of Encrypted Communications

SI-4(10): Visibility of Encrypted Communications requires you to ensure encrypted network communications are still observable by your security monitoring function, so threats do not hide inside TLS, VPN, or other encrypted channels. Operationally, you must define which encrypted traffic needs inspection, implement an approved visibility method, and retain evidence that monitoring works and is governed. ¹

Key takeaways:

• You need a documented, approved approach for monitoring encrypted traffic without breaking business-critical encryption use cases. ¹
• Auditors will focus on scope decisions (what traffic), method selection (how you see it), and repeatable evidence (logs, configs, test results). ¹
• The fastest path is to assign ownership, map data flows, pick standard patterns (proxy, endpoint telemetry, key access), then validate detection coverage. ¹

Encrypted traffic is now the default for user browsing, SaaS, APIs, service-to-service calls, and remote access. That’s good for confidentiality, but it creates a monitoring blind spot: malware can beacon over HTTPS, data can be exfiltrated via TLS, and command-and-control can ride inside a VPN tunnel. SI-4(10) exists to close that blind spot by requiring “provisions” that make encrypted communications visible to whatever you designate as your monitoring capability. ¹

For a Compliance Officer, CCO, or GRC lead, the trap is treating this as a single tool purchase (“we have an IDS”) or a vague policy statement (“we monitor the network”). Assessors usually want to see clear scoping decisions, technical implementation details, and proof the controls operate over time. You also need governance: visibility into encrypted communications can create privacy, legal, and key-management concerns, so you must show your approach is approved, limited to defined use cases, and monitored for misuse.

This page gives requirement-level guidance you can operationalize quickly: what SI-4(10) means in plain English, who it applies to, practical implementation options, evidence to retain, and a phased execution plan you can run with.

Regulatory text

Control excerpt: “Make provisions so that {{ insert: param, si-04.10_odp.01 }} is visible to {{ insert: param, si-04.10_odp.02 }}.” ¹

Operator interpretation of the placeholders: NIST expresses SI-4(10) using organization-defined parameters. In practice, you define:

• What encrypted communications matter for monitoring (for example: outbound internet egress, remote access VPN, east-west service traffic, SaaS access).
• Who/what must see it (for example: SOC analysts, SIEM, NDR, IDS/IPS, EDR telemetry pipelines, or a managed detection provider).

What you must do: Put technical and procedural measures in place so your security monitoring function can detect and investigate threats that would otherwise be hidden by encryption, and document those measures as part of your monitoring strategy. ¹

Plain-English requirement (what SI-4(10) is really asking)

You are allowed to use encryption. You are not allowed to accept “we can’t see anything because it’s encrypted” as a standing limitation for security monitoring. SI-4(10) expects you to make deliberate design choices so monitoring remains effective, even when traffic is encrypted. ¹

Think of SI-4(10) as a three-part requirement:

1. Define scope: which encrypted channels must be monitored.
2. Implement visibility: choose a method that provides usable security signals.
3. Prove operations: show evidence the method is deployed, governed, and producing detections/telemetry.

Who it applies to

Entity scope: Federal information systems and contractor systems handling federal data commonly inherit or are assessed against NIST SP 800-53 control expectations. ¹

Operational scope (where this bites in real environments):

• Enterprise egress to the internet (web browsing, API calls, software updates).
• Remote access (user VPN, zero trust access, VDI).
• Cloud workloads (service-to-service TLS, Kubernetes ingress/egress).
• SaaS traffic (SSO, email, file sharing).
• Third-party connectivity (B2B VPNs, private links, managed services).

If your boundary or internal traffic is largely encrypted, SI-4(10) becomes a primary determinant of whether your monitoring program is credible.

Implementation options (choose a pattern, don’t freestyle)

You do not need to decrypt everything to meet the intent. You need to ensure meaningful visibility. Common implementation patterns include:

Pattern	What you can see	Where it fits	Key governance concerns
TLS inspection at a proxy / secure web gateway	Decrypted content for scoped flows; URLs/headers; malware scanning	Centralized egress, managed endpoints	Certificate management, privacy restrictions, exceptions list
Decryption at network security devices (firewall/NDR) for specific segments	Deep packet inspection for scoped traffic	Data center edges, ingress/egress points	Key handling, performance, segmentation design
Endpoint-based visibility (EDR + browser/process telemetry)	Process-to-network correlation, DNS, SNI, cert info, file write events	Remote workforce, SaaS-first environments	Endpoint coverage, logging standards, tamper protection
Metadata-only monitoring (JA3/JA4 fingerprints, SNI, NetFlow/IPFIX, DNS logs)	Behavioral signals without decryption	Privacy-sensitive contexts, high volume links	May be insufficient for content-based detections
Controlled key access (HSM/KMS integrated) for authorized inspection	Decrypt selected workloads where keys are centrally managed	Cloud-native services with strict key control	Separation of duties, key escrow policy, audit trails

Your job as the control owner is to pick the pattern(s) that match your architecture and risk appetite, then document why that provides “visibility” for your defined encrypted communications. ¹

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

Step 1: Assign ownership and write the control statement

• Name a control owner (typically Security Operations, Network Security, or Security Architecture).
• Write an SI-4(10) implementation statement that answers: Which encrypted communications are in scope, what visibility method is used, and what the SOC receives. ¹

Daydream tip: Put SI-4(10) in your control library with a single “source of truth” mapping: owner, system scope, procedure, and recurring evidence artifacts. This is the fastest way to avoid evidence gaps during assessment. ¹

Step 2: Define “encrypted communications” scope with a traffic inventory

Build (or reuse) a data flow inventory that covers:

• Ingress points, egress points, and major east-west paths
• Remote access paths
• Cloud VPC/VNet flow paths and interconnects
• Third-party connections

Deliverable: a scope table that marks each flow as in scope for visibility or out of scope with justification (for example: regulated privacy traffic, technical infeasibility with compensating controls).

Step 3: Decide what “visible” means for your SOC

Define minimum monitoring outputs for in-scope traffic, such as:

• Session metadata (source/destination, ports, byte counts)
• Identity context (user, device, workload identity)
• DNS and certificate signals
• Content inspection for defined categories (malware download, known bad domains, data exfil indicators) where approved

Write these into a monitoring requirement that your SOC and engineers can test.

Step 4: Implement the technical visibility method(s)

Common actions:

• Route in-scope egress through a proxy or inspection point.
• Deploy enterprise root CA and manage certificate pinning exceptions (if doing TLS interception).
• Ensure EDR is installed and logging is forwarded for endpoints that generate encrypted traffic.
• Enable network telemetry exports (NetFlow/IPFIX), DNS logging, and certificate/SNI logging where supported.
• Forward logs to SIEM and confirm parsers and retention.

Step 5: Add governance guardrails (this is where audits get sticky)

You need written decisions on:

• Which traffic is decrypted vs monitored via metadata.
• Who can access decrypted content (role-based access, SOC need-to-know).
• Approvals and exceptions (who can exempt apps or destinations; expiry and review of exceptions).
• Key management and separation of duties if inspection requires access to private keys. ¹

Step 6: Validate visibility with repeatable tests

Run validation that produces artifacts an auditor can read:

• Test that a known TLS flow generates the expected logs in SIEM.
• Test that blocking/detection content rules work on the inspection device (where applicable).
• Test that exempted traffic is actually exempted and documented.

Do not treat “it’s configured” as proof. Treat “we tested it and kept results” as proof.

Step 7: Operationalize: monitoring, tuning, and review

• Create SOC runbooks for encrypted-traffic investigations (what logs to pull, how to pivot).
• Review exceptions regularly and remove stale bypasses.
• Track coverage gaps (segments without inspection, unmanaged devices, shadow IT).

Required evidence and artifacts to retain

Auditors typically want to see a chain from requirement → decision → implementation → operation. Build an evidence packet with:

1. Control narrative / implementation statement for SI-4(10), including scoped encrypted channels and visibility approach. ¹
2. Network/data flow inventory marking encrypted flows in scope and out of scope with justification.
3. Architecture diagrams showing where inspection/telemetry is collected (proxy, firewall, NDR, endpoint).
4. Configuration evidence (sanitized screenshots or exports) showing:
   • TLS inspection policies (if applicable)
   • Log forwarding to SIEM
   • Exceptions list and approval mechanism
5. Test records demonstrating visibility for representative encrypted flows (test plan + results).
6. SOC procedures/runbooks for investigating alerts tied to encrypted traffic signals.
7. Access control evidence for decrypted content (RBAC, audit logs of access where available).
8. Exception governance (tickets/approvals, risk acceptance, review notes).

If you use Daydream to map SI-4(10) to owner, procedure, and recurring artifacts, you can standardize this packet so it is always assessment-ready instead of assembled under pressure. ¹

Common exam/audit questions and hangups

• “Define ‘encrypted communications’ for your environment.” Expect to show your scoped inventory and boundary assumptions. ¹
• “What can your SOC see for TLS traffic?” Be ready to show sample logs and an investigation path.
• “Do you decrypt traffic? If yes, which categories and why?” This often triggers privacy, labor, or legal review.
• “How do you manage inspection exceptions?” Auditors dislike permanent bypasses with no expiry.
• “What about unmanaged devices or BYOD?” Your answer needs compensating controls (segmentation, restricted access paths, conditional access).

Frequent implementation mistakes (and how to avoid them)

1. Mistake: Equating “encrypted” with “unmonitorable.”
   Fix: Document visibility requirements (metadata + endpoint correlation at minimum), then prove it in SIEM.

2. Mistake: TLS interception turned on broadly with no governance.
   Fix: Write a decryption scope, approvals, and access restrictions; keep an exceptions register.

3. Mistake: Logs exist but aren’t actionable.
   Fix: Validate parsers, dashboards, and alert rules; train the SOC on pivots for encrypted traffic.

4. Mistake: Ignoring east-west encryption.
   Fix: Identify high-risk internal encrypted flows (identity, secrets, critical apps) and add telemetry or inspection at strategic choke points.

5. Mistake: No evidence over time.
   Fix: Schedule recurring control evidence pulls (policy export, exceptions list, sample logs, test reruns) and store them in your GRC system.

Risk implications (why this control fails in real incidents)

Encrypted channels are a common hiding place for command-and-control, staged payload downloads, and data exfiltration. If you cannot observe meaningful indicators in encrypted traffic, incident response slows down and root cause analysis becomes guesswork. SI-4(10) is a monitoring credibility control: it forces you to show that encryption does not create a free pass around detection. ¹

Practical 30/60/90-day execution plan

First 30 days (establish decisions and scope)

• Assign SI-4(10) control owner and publish a control narrative with defined scope and “visible to” monitoring capability. ¹
• Build an encrypted-traffic flow inventory and identify top monitoring blind spots (remote access, egress, cloud).
• Choose your primary visibility pattern(s) and document rationale and constraints (privacy, technical).

Days 31–60 (implement and integrate)

• Implement routing to inspection/telemetry points for in-scope flows (proxy, firewall, NDR, endpoint telemetry).
• Configure log forwarding into SIEM and confirm data quality (fields, timestamps, identity context).
• Stand up exception governance: request, approval, expiry, and review workflow.

Days 61–90 (prove operations and harden)

• Execute a repeatable test plan for representative encrypted flows; store results as evidence.
• Deliver SOC runbooks for encrypted-traffic investigations and escalation paths.
• Review the exception list and reduce bypasses; document compensating controls where decryption is not approved.

Frequently Asked Questions

Do we have to decrypt all TLS traffic to satisfy SI-4(10)?

The control requires “provisions” for visibility, not universal decryption. Define what “visible” means for your monitoring function and show that in-scope encrypted traffic produces usable security signals. ¹

What counts as “visible” to the monitoring capability?

Visibility should be sufficient to detect and investigate threats in encrypted channels, which often means session metadata plus identity and endpoint correlation, and sometimes content inspection for scoped flows. Document your definition and validate it with tests and SIEM evidence. ¹

How do we handle privacy or labor concerns with TLS inspection?

Limit decryption scope, restrict access to decrypted content, document approvals, and maintain an exceptions process for sensitive categories. Auditors respond well to clear governance and separation of duties around keys and access. ¹

We use SaaS heavily. Where should we implement SI-4(10) controls?

Start at enterprise egress and endpoints: proxy/SWG policies for managed devices, and EDR plus DNS/cert telemetry for remote users. Then address cloud-to-SaaS and service-to-service flows based on risk and feasibility. ¹

What evidence is most persuasive in an assessment?

A scoped traffic inventory, the inspection/telemetry configuration, sample SIEM logs for encrypted flows, and a documented test record that confirms ongoing visibility. Pair that with exception approvals and SOC runbooks. ¹

How can Daydream help with SI-4(10) specifically?

Daydream is most valuable for mapping SI-4(10) to a named owner, a repeatable implementation procedure, and recurring evidence artifacts, so you can produce the same assessment-ready packet each cycle. This directly addresses the common gap of missing implementation evidence. ¹

Footnotes

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