SC-33: Transmission Preparation Integrity

SC-33: Transmission Preparation Integrity requires you to protect the integrity of information as you prepare it for transmission, so content cannot be altered, corrupted, or substituted before it leaves the sender. Operationalize it by defining “transmission preparation” points, enforcing integrity checks (e.g., hashing/signing where appropriate), and retaining evidence that the checks run and exceptions are controlled. ¹

Key takeaways:

• Scope SC-33 to the systems and workflows that package, transform, queue, or serialize data for network transmission.
• Implement technical integrity controls (checksums/hashes, digital signatures, authenticated pipelines) plus procedural controls for exceptions.
• Keep assessor-ready evidence: design docs, configs, logs, and recurring attestations mapped to a named control owner. ²

SC-33 is easy to misunderstand because teams often assume “TLS already covers integrity in transit.” TLS helps once data is on the wire, but SC-33 focuses earlier: the last mile inside your environment where applications format payloads, generate files, transform records, create messages, and hand them to a transport service (API gateway, message broker, SFTP client, email relay, MFT, EDI tooling, etc.). That preparation layer is where subtle integrity failures show up: wrong file versions, partial exports, encoding/serialization bugs, tampered queues, injected attachments, or replayed messages.

For a Compliance Officer, CCO, or GRC lead, the fastest path is to treat SC-33 as a “data packaging integrity” control. You define which transmission types are in scope, assign ownership, choose integrity mechanisms proportionate to risk, and standardize evidence. Assessors typically care less about which cryptographic primitive you picked and more about whether you can prove the integrity mechanism is consistently applied, monitored, and governed.

This page gives requirement-level guidance you can hand to engineering and operations, with specific artifacts to collect for assessment readiness under NIST SP 800-53 Rev. 5. ¹

Regulatory text

Control: “NIST SP 800-53 control SC-33.” ²

Operator interpretation: Even though the excerpt in your source package is brief, SC-33’s title (“Transmission Preparation Integrity”) sets the expectation: you must ensure information is not improperly modified during the preparation steps that occur before transmission. Treat this as a requirement to (1) identify preparation points, (2) apply integrity protections at those points, and (3) prove the protections operate as intended through repeatable evidence. ¹

Plain-English interpretation (what SC-33 is really asking)

SC-33 expects you to prevent and detect integrity failures introduced during creation and packaging of outbound transmissions. “Preparation” commonly includes:

• Building outbound API payloads (JSON/XML), signing requests, adding headers, tokenizing fields
• Exporting data to flat files, reports, backups, batch feeds, EDI documents
• Compressing/encrypting/wrapping data, splitting files, adding manifests
• Enqueuing messages to brokers/queues, building events, serializing protobuf/avro
• Attaching documents to email/MFT workflows, generating PDFs, rendering invoices

Integrity failures here are often not “network” issues. They are workflow, pipeline, or access-control issues that cause the wrong bytes to be sent.

Who it applies to (entities + operational context)

Entity types: Federal information systems and contractor systems handling federal data. ²

Operational contexts where SC-33 matters most:

• Systems exchanging regulated or mission data with external parties (agencies, customers, other third parties)
• Batch jobs and ETL pipelines producing outbound feeds
• Message-driven architectures (queues, pub/sub, event buses)
• File transfer tooling (SFTP, managed file transfer, EDI)
• High-privilege integration points (API gateways, service accounts, CI/CD jobs that publish artifacts)

Common owners in practice (you must assign one):

• Primary: Security engineering or platform security (control design)
• Shared: App owners / integration engineers (implementation per interface)
• Operations/SRE: monitoring and evidence capture
• GRC: control narrative, mapping, sampling plan, exception governance

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

Use this sequence to move from requirement to an assessable implementation.

1) Define “transmission preparation” for your environment

Create a short scoping statement that answers:

• What outbound channels exist (API, MFT, SFTP, email relay, queues)?
• Where does preparation occur (service, job, gateway, integration platform)?
• What is considered “prepared” (serialized payload, rendered document, generated export)?

Deliverable: SC-33 scope statement + system list, owned by a named team. ¹

2) Inventory outbound data flows and classify integrity impact

For each flow, capture:

• Source system and destination
• Data type (records, files, events)
• Transformation steps (render, compress, encrypt, map fields)
• Operational frequency (real-time vs batch)
• Integrity impact if altered (business harm, safety, fraud, mission disruption)

Practical decision rule: If integrity loss would cause unauthorized actions, financial errors, incorrect decisions, or compliance reporting inaccuracies, treat the flow as high-integrity sensitivity and require stronger integrity controls plus monitoring.

Deliverable: Data flow register (can be a spreadsheet) linked to system owners.

3) Choose integrity controls per channel (design standard)

Pick a small set of approved patterns. Keep it boring; consistency is your friend in audits.

Patterns to standardize:

• Digital signatures for files/feeds: Sign outbound files (or a manifest listing filenames and hashes). Receiver verifies before processing.
• Hashes/checksums with manifests: Generate a checksum file for each outbound file set; store hashes in an immutable log location.
• Authenticated messaging: Use broker features and application-level message authentication where applicable; prevent unauthorized producers.
• API request signing (where appropriate): For high-risk integrations, sign requests or use mutual authentication plus payload integrity checks at the application layer.
• Immutable job outputs: Write prepared artifacts to write-once or append-only storage prior to transmission; restrict who can modify.

Deliverable: SC-33 engineering standard (“approved integrity mechanisms for transmission preparation”) and an exception path.

4) Implement guardrails in the preparation pipeline

This is where SC-33 succeeds or fails. You need controls that stop bad transmissions before they leave.

Minimum guardrails to implement:

• Access controls on preparation steps: Limit who can modify templates, mapping rules, export scripts, and integration configs.
• Build-time and run-time integrity: If a job prepares a file, hash/sign it at job completion and store the hash/signature separately from the file.
• Queue/topic permissions: Restrict producer identities; monitor for unexpected producers or schema violations.
• Change control: Treat integration mapping changes as production changes with peer review and traceability.

Deliverables: Config baselines (screenshots/exported configs), IAM role listings, change tickets, and pipeline/job definitions tied to flows. ¹

5) Monitoring and exception handling

Auditors will ask, “How do you know it ran?” and “What happens when it fails?”

Operational requirements:

• Alert on signature/hash verification failures (receiver-side) and signing/hashing job failures (sender-side).
• Triage runbooks that define: isolate artifact, re-run preparation, notify downstream, open incident if tampering suspected.
• Exception register for flows that cannot support signing/hashing (with compensating controls and a remediation plan).

Deliverables: Alert rules, sample alerts, runbooks, exception register approvals.

6) Map SC-33 to a control owner and recurring evidence

This is the fastest way to reduce assessment pain: document ownership, procedure, and what evidence you will produce each cycle. The recommended control in your source pack explicitly calls for this mapping. ²

Deliverables: Control narrative, RACI, evidence calendar, sampling methodology.

Practical tip: Daydream is useful here as a system of record for control ownership, procedures, and recurring evidence requests, so SC-33 doesn’t degrade into “tribal knowledge in Slack.”

Required evidence and artifacts to retain

Keep evidence aligned to (1) scope, (2) design, (3) operation, (4) exceptions.

Evidence type	What to retain	What it proves
Control narrative	SC-33 procedure, scope, owners, approved patterns	Control is defined and assignable
Flow inventory	List of outbound flows + classification	You know where preparation happens
Technical standards	File signing/hash standard; API/message guidance	Consistent design expectations
Config + code references	Job definitions, pipeline configs, broker ACLs, signing key configs	Control is implemented
Logs	Signing/hashing job logs; verification logs; immutable storage logs	Control operates
Monitoring artifacts	Alert definitions; sample incidents; runbooks	Failures get detected and handled
Exceptions	Exception register with approvals and compensating controls	Risk decisions are governed

Common exam/audit questions and hangups

Expect these questions and prepare answers with artifacts:

1. “Define transmission preparation.” Show your scope statement and flow register.
2. “How do you ensure outbound files weren’t modified after generation?” Show signing/hashing steps, storage controls, and logs.
3. “Where are keys managed?” Show key ownership, rotation approach, and access restrictions (avoid over-sharing sensitive details).
4. “How do you handle failures?” Provide runbooks and evidence of alerting.
5. “Are third parties involved?” Identify third-party transfer tooling or recipients and show boundary controls.

Hangup to avoid: claiming SC-33 is “covered by TLS.” Be ready to show integrity controls that apply before network transmission.

Frequent implementation mistakes (and how to avoid them)

• Mistake: No explicit scope. Fix: publish a one-page scoping memo and keep it version-controlled.
• Mistake: Integrity controls exist, but only for one channel. Fix: standardize patterns for API, messaging, and file transfers; document why some flows differ.
• Mistake: Hash stored next to the file in the same writable location. Fix: store hashes/signatures in a separate, access-restricted, preferably append-only location.
• Mistake: No evidence plan. Fix: define what logs and screenshots you will collect and how often; automate collection where you can.
• Mistake: Exceptions live in email. Fix: maintain an exception register with approvals and review cadence.

Enforcement context and risk implications

No public enforcement cases were provided in your source catalog for SC-33, so you should treat this as an assessment-readiness and operational risk control rather than a control with a direct enforcement narrative in this pack. ² Integrity failures during preparation often surface as misdirected payments, incorrect reporting, corrupted feeds, or unauthorized changes to outbound content. For federal systems and contractors, these issues translate to mission impact and audit findings.

Practical 30/60/90-day execution plan

First 30 days (stabilize and scope)

• Assign a control owner and backups; publish a control narrative for the sc-33: transmission preparation integrity requirement. ¹
• Build the outbound flow inventory and identify preparation points.
• Pick approved integrity patterns per channel; define an exception process.

Days 31–60 (implement the repeatable patterns)

• Implement signing/hashing for priority file-based and batch exports.
• Lock down preparation assets (templates, mapping configs, export scripts) with IAM and change control.
• Add monitoring and alerts for integrity failures and job anomalies.

Days 61–90 (operate, prove, and harden)

• Run an internal assessment: sample a set of flows and produce evidence end-to-end.
• Formalize the evidence calendar and automate evidence pulls where feasible (logs, config exports).
• Review exceptions; implement compensating controls and remediation tracking.

Frequently Asked Questions

Does TLS satisfy SC-33 by itself?

TLS addresses integrity in transit, but SC-33 focuses on integrity during preparation before data is transmitted. You should be able to show controls that prevent or detect modification between “artifact created” and “artifact sent.” ¹

What counts as “transmission preparation” in a microservices environment?

Preparation includes serialization, enrichment, signing, templating, and queuing steps that occur inside services or integration platforms. Document where payloads are constructed and handed off to the network boundary components.

Do I need digital signatures for every outbound message?

No single mechanism fits every flow. Use a risk-based standard: high-impact flows should have stronger integrity checks and monitoring, while lower-impact flows may rely on simpler checksums plus strong access control and change control.

How do I handle third-party managed file transfer tools?

Treat the tool as part of the transmission preparation chain. Ensure configuration control, restricted admin access, logging, and a method to verify that prepared files were not modified before transfer completes.

What evidence is most convincing to auditors?

A mapped control narrative plus “proof of operation” logs. Provide sample job runs showing hash/sign generation, storage of the hash/signature, and alerting/runbook steps for failures. ²

What should I do if a legacy integration cannot support signing or hashing?

Put it into an approved exception register and add compensating controls, such as tighter access controls, immutable staging storage, stronger monitoring, and receiver-side validation checks. Track a remediation plan to reach the standard over time.

Footnotes

1. NIST SP 800-53 Rev. 5

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