CMMC Level 2 Practice 3.8.6: Implement cryptographic mechanisms to protect the confidentiality of CUI stored on digital

CMMC Level 2 Practice 3.8.6 requires you to use cryptography to keep CUI confidential whenever it is stored digitally, across endpoints, servers, databases, backups, and removable media. To operationalize it fast, inventory where CUI is stored, enforce encryption with validated modules, control keys, and retain objective evidence that encryption is enabled and effective. ¹

Key takeaways:

• Encrypt CUI “at rest” everywhere it can land: user devices, file shares, cloud storage, backups, and portable media. ¹
• Treat key management as part of the requirement: ownership, rotation, access controls, recovery, and logging.
• Evidence wins assessments: show crypto settings, device posture, and repeatable checks mapped to 3.8.6. ²

The fastest path to meeting the cmmc level 2 practice 3.8.6: implement cryptographic mechanisms to protect the confidentiality of cui stored on digital requirement is to stop thinking about “encrypting systems” and start thinking about “encrypting CUI storage locations.” CUI spreads through normal operations: synced folders, email caches, local downloads, ticketing attachments, build artifacts, shared drives, and backups. Assessors typically look for two things: (1) whether CUI is actually encrypted wherever it rests, and (2) whether your encryption approach is governed and provable, not ad hoc.

This requirement is mapped to NIST SP 800-171 Rev. 2 control 3.8.6. ¹ In a CMMC Level 2 assessment context under the CMMC Program, you should be prepared to show objective evidence that cryptographic mechanisms are implemented, consistently applied across the CUI environment, and operationally maintained over time. ³

What follows is requirement-level implementation guidance you can hand to IT, Security, and GRC teams to execute, validate, and document.

Regulatory text

Requirement (mapped text): “Implement cryptographic mechanisms to protect the confidentiality of CUI stored on digital.” ¹

Operator meaning: You must ensure that when CUI is stored in any digital form, it is protected by encryption (or equivalent cryptographic confidentiality controls) appropriate to the system and storage medium. This includes endpoints, servers, cloud services, databases, virtual disks, backups, snapshots, and removable media where CUI may reside. ¹

What an assessor expects to see: a defined encryption standard, technical enforcement (not just a policy statement), key management controls, and recurring evidence that encryption remains enabled and effective. ²

Plain-English interpretation

• “Stored on digital” means at rest: data sitting on disk, SSD, phone storage, cloud object storage, VM volumes, database files, backup media, or exported archives.
• “Cryptographic mechanisms” means encryption that is implemented correctly and managed as an operational control (keys, access, rotation, recovery, and monitoring), not a one-time project.
• “Protect confidentiality” means an unauthorized party who obtains the storage medium (or a copy of it) cannot read the CUI without authorized access to the decryption keys.

Who it applies to (entity and operational context)

Applies to organizations seeking or maintaining CMMC Level 2 that store, process, or transmit CUI as part of DoD contracting performance, including primes and subcontractors where CUI is present in their environment. ³

Operationally, it applies wherever your CUI boundary runs, including:

• Corporate endpoints used to access CUI (laptops/desktops, privileged workstations)
• File servers, network shares, and collaboration platforms hosting CUI
• Cloud services used to store CUI (SaaS repositories, IaaS disks, PaaS storage)
• Backups and disaster recovery replicas that contain CUI
• Removable media workflows (if permitted) where CUI is copied or staged

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

1) Define and freeze “where CUI is allowed to be stored”

Create a short, enforceable CUI Storage Standard:

• Approved repositories (e.g., specific file share paths, specific cloud tenants/buckets)
• Prohibited storage (local desktop, personal cloud, unmanaged USB, email archives if you can’t control them)
• Required encryption method per storage type (endpoint full-disk encryption, database TDE, encrypted backups, etc.)
• Exceptions process (who approves, duration, compensating controls)

This is a governance move, but it determines whether you can technically enforce encryption everywhere CUI could land.

2) Inventory CUI storage locations (realistically)

Build a CUI storage inventory that includes:

• Endpoint populations that access CUI (by group, OU, MDM group, or device tags)
• Servers and file shares inside the CUI boundary
• Cloud storage services in scope
• Backup systems and destinations
• “Shadow” storage: synced folders, collaboration workspaces, engineering artifact stores

Practical tip: start with where CUI is supposed to be, then add “common escape points” discovered in incidents (downloads folder, email attachment caches, ticketing systems).

3) Implement encryption by storage class (with enforcement)

Use a control-by-control approach so you can prove coverage:

Endpoints (laptops/desktops)

• Enforce full-disk encryption via centralized policy (MDM/UEM or domain policy)
• Block access to CUI repositories from non-compliant devices (conditional access / NAC where feasible)
• Ensure recovery key escrow is controlled and auditable

Servers / file shares

• Encrypt underlying volumes or storage arrays where CUI resides
• Ensure administrators cannot bypass encryption controls through unmanaged mounts or exports
• Restrict and log privileged access to storage configurations

Cloud storage

• Require encryption at rest for storage services (tenant-level policy where possible)
• Control keys according to your design (provider-managed keys vs customer-managed keys), and document the decision and configuration
• Confirm logging and access controls are enabled for data access and key usage

Databases

• Use database encryption features appropriate to the platform
• Document scope: which schemas/tables contain CUI and are covered by encryption controls
• Ensure backups/exports from the database inherit encryption requirements

Backups, snapshots, archives

• Ensure backup jobs encrypt data before writing to media/destination
• Confirm retention copies and offsite replicas remain encrypted
• Treat backup encryption keys as production keys from a governance perspective (access, recovery, rotation)

Removable media (if allowed)

• Only allow encrypted media approved by policy
• Track issuance, return, and sanitization/destruction
• Block unapproved USB storage at the endpoint where feasible

4) Design key management that you can defend

Assessors will probe key handling because encryption without controlled keys is fragile.

Minimum operational decisions to document:

• Key ownership (system owner vs security)
• Access control model (who can decrypt, who can administer keys, who can recover keys)
• Key rotation and revocation approach (especially for staff departures and incidents)
• Backup and recovery process for keys (loss of keys can become an availability incident)
• Logging expectations (key access/admin actions)

Keep it simple. Centralized key management is easier to evidence than scattered local keys.

5) Add recurring verification and evidence capture (make it audit-ready)

Turn encryption into a monitored control:

• Automated reports showing endpoint encryption posture
• Periodic sampling of server volumes and cloud storage encryption settings
• Backup job configuration exports proving encryption is enabled
• Alerts/tickets when devices drift out of compliance

This aligns to the practical reality that CMMC assessments reward objective, repeatable evidence. ²

6) Map the control to your SSP and POA&M discipline

In your System Security Plan (SSP), document:

• Where CUI is stored
• The encryption mechanisms per storage class
• How keys are managed
• How you verify and maintain the control

If any scope areas cannot meet encryption quickly, track them in a POA&M with compensating controls and a closure plan consistent with your CMMC approach. ⁴

Required evidence and artifacts to retain

Keep evidence that answers “what is encrypted, how do you know, and who controls the keys?”

Suggested artifact set:

• CUI Storage Standard (approved repositories, prohibited locations, encryption requirements)
• SSP excerpt mapping 3.8.6 to implemented mechanisms ¹
• Endpoint encryption compliance reports (MDM/UEM export, screenshots, or compliance dashboards)
• Server/storage configuration evidence (volume encryption settings, storage policy exports)
• Cloud configuration evidence (policy settings, encryption-at-rest controls, key settings)
• Backup system configurations showing encryption enabled; restore test records (focus on verifying encrypted backups are recoverable)
• Key management procedures (access control list, role definitions, break-glass and recovery steps)
• Change tickets for encryption rollout, exceptions, and remediation actions
• Recurring control check records (monthly/quarterly checks, drift remediation)

Common exam/audit questions and hangups

Expect questions like:

• “Show me where CUI is stored and how it is encrypted in each location.” ¹
• “How do you prevent CUI from being stored on unmanaged endpoints?”
• “Who can access encryption keys, and how is that access approved and logged?”
• “Are backups encrypted? Show the job settings and a restore test.”
• “How do you detect if encryption is turned off or a new storage location appears?”

Hangup pattern: teams can explain encryption “in general” but cannot prove coverage for backups, exports, or developer tooling that stores artifacts.

Frequent implementation mistakes and how to avoid them

1. Encrypting endpoints but forgetting backups

• Fix: treat backups and replicas as first-class CUI stores; require encryption for every backup destination and job.

2. Relying on “the cloud encrypts by default” without evidence

• Fix: capture tenant policy screenshots/exports and document the control in the SSP; keep a recurring verification record.

3. Unbounded CUI sprawl

• Fix: restrict where CUI can live, enforce it with technical controls, and monitor for drift.

4. Weak key governance

• Fix: define roles, approvals, recovery, and termination handling. Document it and show access logs/tickets.

5. No recurring evidence

• Fix: schedule compliance exports and attach them to a control record. Daydream can help structure recurring evidence capture so you are not scrambling before an assessment. ²

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this specific practice. What matters operationally is that failure to encrypt stored CUI increases the impact of common events (lost devices, misconfigured storage, stolen backups) and can become an assessment finding if encryption is partial, inconsistent, or not provable. ⁵

A practical 30/60/90-day execution plan

First 30 days (stabilize scope and quick wins)

• Publish the CUI Storage Standard and identify approved repositories.
• Pull an inventory of endpoints and storage systems in the CUI boundary.
• Turn on and enforce endpoint full-disk encryption where centrally manageable.
• Identify backup platforms and confirm whether encryption is enabled; open remediation tickets for gaps.
• Start an evidence folder structure mapped to 3.8.6 (SSP excerpt, configs, reports). ²

Days 31–60 (close coverage gaps)

• Encrypt remaining server volumes and file shares hosting CUI.
• Implement cloud encryption policies and capture configuration evidence.
• Formalize key management procedures and access approval workflow.
• Restrict CUI access to compliant devices (conditional access/NAC approach where feasible).
• Add recurring checks (scheduled exports, sampling, drift remediation).

Days 61–90 (operationalize and prove durability)

• Run a tabletop or technical validation: simulate a lost endpoint and confirm data is unreadable; simulate a backup restore and confirm encrypted restore works.
• Conduct an internal assessment interview prep: rehearse “show me” evidence paths for each storage class.
• Tighten exception handling: short approvals, compensating controls, and documented closure.
• Move evidence capture to a recurring cadence with named owners; Daydream can track control operation and automate reminders for recurring artifacts tied to 3.8.6. ²

Frequently Asked Questions

Does full-disk encryption on laptops satisfy 3.8.6 by itself?

It covers CUI stored on those endpoints, but 3.8.6 also applies to servers, cloud storage, databases, backups, and removable media where CUI is stored. You need evidence for each storage location category. ¹

If our cloud provider encrypts storage by default, are we done?

Only if you can show the encryption setting is enabled for your tenant/services and you control access and keys appropriately. Keep configuration exports or screenshots and verify it on a recurring basis. ²

What about CUI inside SaaS tools like ticketing or collaboration platforms?

If CUI is stored there, it is in scope. Confirm the SaaS provides encryption at rest and document how you administer access, retention, and exports so CUI does not escape into unencrypted locations.

Are encrypted backups required?

If backups contain CUI, they are CUI stored on digital media and must be protected for confidentiality. Validate both encryption settings and restore capability so you don’t trade confidentiality for unrecoverable backups. ¹

Do we need customer-managed keys (CMK) to comply?

The requirement is to implement cryptographic mechanisms that protect confidentiality; it does not, by itself, mandate a specific key ownership model. Pick a model you can govern and evidence, then document the rationale and controls.

What evidence is most persuasive in a CMMC Level 2 assessment?

Objective evidence that is current and repeatable: encryption compliance reports, configuration exports, key access controls, and records of recurring verification. Map each artifact directly to 3.8.6 in your SSP/control narrative. ⁵

Footnotes

1. NIST SP 800-171 Rev. 2

2. DoD CMMC Program Guidance

3. 32 CFR Part 170; DoD CMMC Program Guidance

4. DoD CMMC Program Guidance; 32 CFR Part 170

5. DoD CMMC Program Guidance; NIST SP 800-171 Rev. 2