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Comply Defense
Category: Cryptography & Encryption

Encryption in Transit

Also known as: Encryption for Data-in-Transit, Data-in-Transit Encryption
Simply put

Encryption in transit is the practice of scrambling data while it moves between two points on a network, such as between an end user and a cloud service or between two services, so that anyone who intercepts the communication cannot read it. It helps protect information during transmission, though the data may be stored in an unencrypted form at either end. It is one control among several and does not by itself constitute a complete data-protection strategy.

Formal definition

Encryption in transit refers to the application of encryption algorithms to data as it is transferred between nodes of a network, protecting confidentiality (and, depending on the protocol, integrity) of communications against interception while data is in motion. In typical implementations it secures traffic between an end user and a service provider or between internal services, using cryptographic mechanisms so that only parties holding the appropriate decryption keys can access the plaintext. It is generally treated as a foundational security control that is distinct from and complementary to encryption at rest; per the evidence, it is not on its own a complete data-protection strategy. This entry describes the general concept and does not specify particular cryptographic algorithms, key lengths, protocol versions, or the control baselines, impact levels, or agency-specific requirements (for example under NIST SP 800-53, NIST SP 800-171, FedRAMP, or the DoD RMF) that a reader must confirm against current authoritative sources.

Why it matters

Data is often at its most exposed while moving across a network. When information travels between an end user and a cloud service, or between two internal services, it can be intercepted in transit by an adversary positioned on the communication path. Encryption in transit addresses this exposure by scrambling the data so that anyone who intercepts the communication cannot read the plaintext, protecting the confidentiality of the information while it is in motion. For organizations handling sensitive information such as Controlled Unclassified Information (CUI), this control is generally treated as a foundational safeguard, though the specific requirements that apply depend on the governing framework and baseline (for example under NIST SP 800-53, NIST SP 800-171, FedRAMP, or the DoD RMF), which a reader must confirm against current authoritative sources.

A critical point that experts insist on is that encryption should not be equated with complete security or complete data protection. As the evidence notes, encryption is a foundational control for protecting data at rest and in transit, but it is not a complete data-protection strategy on its own. Encryption in transit protects data while it moves; it does not protect data once it comes to rest at either endpoint, where it may be stored in an unencrypted form. It is therefore one control among several and must be paired with complementary controls, including encryption at rest, access controls, and key management, rather than treated as a substitute for a broader security posture.

Misunderstanding the scope of this control can create a false sense of assurance. Because data may still be stored unencrypted at either end of a protected communication, an organization that relies solely on encryption in transit leaves gaps that adversaries can exploit at the endpoints. Compliance officers and system security personnel should treat encryption in transit as a distinct, complementary layer within a defense-in-depth approach and verify how it maps to the specific control requirements applicable to their systems.

Who it's relevant to

Information System Security Managers and System Owners
Those responsible for securing systems that transmit sensitive data should treat encryption in transit as a foundational but partial control. They must ensure it is combined with complementary safeguards such as encryption at rest and endpoint protections, since data may be stored unencrypted at either end of a protected communication. The specific implementation and baseline requirements should be confirmed against the applicable governing framework.
Compliance Officers and Auditors
Personnel assessing whether systems meet applicable requirements should verify how encryption in transit maps to the relevant control baselines and should not treat its presence as evidence of complete data protection. Because requirements vary by framework, impact level, and agency tailoring, auditors should confirm the precise obligations against current authoritative sources rather than assuming a uniform standard.
Government Contractors Handling CUI
Organizations that transmit Controlled Unclassified Information across networks or to cloud services should understand that encryption in transit protects data while it moves but not once it rests at an endpoint. Contractors should determine which specific requirements apply to their systems and confirm implementation details, including any framework-specific expectations, against the governing publications and their contractual obligations.
Cloud Service and Endpoint Architects
Those designing communications between end users and cloud services, or between internal services, rely on encryption in transit to protect data against interception on the network path. They should account for the fact that data may be stored in unencrypted form at the endpoints and design complementary controls accordingly, rather than relying on transit encryption as a sole protection mechanism.

Inside Encryption in Transit

Data in Transit
Information actively moving between systems, such as across networks, between endpoints, or between a client and a server, as distinguished from data at rest (stored) or data in use (being processed). Encryption in transit protects this data from interception or modification while it moves.
Transport Layer Security (TLS)
A widely used cryptographic protocol for securing communications over a network. TLS is commonly relied upon to protect data in transit for web and application traffic. Readers should verify the specific protocol versions and configurations acceptable under their applicable requirements, as permitted versions change over time.
Cryptographic Module Validation
In many federal and defense contexts, encryption used to protect sensitive information generally must employ validated cryptographic modules. The FIPS 140 series (as maintained by NIST) is frequently cited for validating cryptographic modules; practitioners should confirm the current validation requirements and the applicable revision against authoritative NIST sources.
Applicable Data Categories
The requirement to encrypt data in transit and the strength expected generally depend on the information category involved, such as Controlled Unclassified Information (CUI), federal civilian agency data under FISMA, DoD systems under the RMF, or classified systems governed by separate authorities. Obligations and acceptable methods can differ by category and by agency tailoring.
Relevant Control References
Control frameworks such as NIST SP 800-53 (maintained by NIST for federal information systems) and NIST SP 800-171 (addressing protection of CUI in nonfederal systems) include controls addressing transmission confidentiality and integrity. The specific control identifiers and expectations depend on the applicable publication revision and any agency or contractual tailoring, which the reader should verify.

Common questions

Answers to the questions practitioners most commonly ask about Encryption in Transit.

Does encrypting data in transit mean my system is compliant with applicable requirements?
No. Encryption in transit is one technical safeguard, not a substitute for compliance. Compliance generally requires satisfying a broader set of controls addressing access control, configuration management, monitoring, and documentation, as tailored under the applicable framework (for example NIST SP 800-53 for FISMA systems or NIST SP 800-171 for CUI in most defense contexts). Encryption also does not equate to security overall; it protects confidentiality and, depending on the mechanism, integrity of data as it moves between endpoints, but it does not address threats at rest, at the endpoints, or in the surrounding environment. Confirm your obligations against the current authoritative text for your system category.
If I use FIPS-validated encryption for data in transit, does that automatically satisfy both FedRAMP and DoD requirements?
Not necessarily. FedRAMP authorization and DoD authorization under the RMF are distinct processes maintained by different authorities, and a FedRAMP authorization does not automatically satisfy DoD requirements. DoD systems and cloud services handling defense information may be subject to additional DoD-specific criteria, impact levels, and continuous monitoring expectations beyond a baseline FedRAMP authorization. Using validated cryptography addresses a specific control expectation but does not itself confer any authorization. Verify the specific requirements for your target environment against current official sources, as these evolve across revisions.
How do I determine which cryptographic modules are acceptable for encryption in transit?
In most federal and defense implementations, agencies expect cryptographic modules to be validated under the applicable cryptographic module validation program rather than merely claiming to use a strong algorithm. Acceptability generally depends on the system category, the sensitivity of the data (for example CUI versus classified information under the NISPOM), and any agency-specific tailoring. Because the list of acceptable modules and the status of individual validations change over time, confirm current validation status and any agency-specific direction against the authoritative program listings rather than relying on vendor marketing claims.
What should I document to demonstrate encryption in transit during an assessment?
Assessors generally look for evidence that the control is both implemented and effective, so documentation typically includes where encryption is applied, which protocols and cryptographic modules are used, configuration settings, and how the implementation maps to the relevant control statements in your system security plan. Keep in mind that an assessment evaluates whether controls are implemented correctly, while authorization is a separate decision made by an authorizing official; passing an assessment does not by itself grant an Authority to Operate. Align your documentation with the specific control requirements applicable to your system and revision.
How does encryption in transit relate to continuous monitoring after authorization?
An Authority to Operate is time-bound and subject to continuous monitoring, so an encryption-in-transit control must be maintained, not treated as a one-time checkbox at authorization. In most programs this means monitoring for deprecated protocols, expired or misconfigured certificates, and configuration drift, and updating implementations as guidance and cryptographic recommendations evolve across revisions. Changes that materially affect the control may need to be reflected in your security documentation and reported through your continuous monitoring process. Confirm the specific monitoring cadence and reporting expectations for your system.
Do requirements for encryption in transit differ across federal civilian, defense, and state or local systems?
Yes, scope boundaries matter. Civilian agency systems generally operate under FISMA using NIST SP 800-53 baselines, defense systems typically follow the RMF with DoD-specific tailoring, protection of CUI in the defense contractor base commonly draws on NIST SP 800-171, and classified systems fall under separate national security requirements such as those associated with the NISPOM. State, local, tribal, and territorial obligations may differ and can be driven by their own policies or by conditions attached to specific federal programs. Verify which regime applies to your particular system before selecting an implementation approach.

Common misconceptions

Encrypting data in transit means the data is fully secured.
Encryption in transit only protects data while it moves between systems. It does not address data at rest or data in use, and compliance with an encryption requirement is not equivalent to overall security. A complete protection strategy generally also considers stored data, access controls, and other safeguards.
Any encryption is sufficient to meet federal or defense requirements.
Many federal and defense contexts generally expect encryption to use validated cryptographic modules (commonly referenced through the FIPS 140 series maintained by NIST), not merely any cryptographic method. Acceptable algorithms, protocol versions, and validation status change over time, so practitioners should confirm current requirements against authoritative sources.
The same encryption-in-transit requirement applies uniformly across all systems.
Requirements can differ by information category and governing authority, for example, CUI in nonfederal systems, civilian agency systems under FISMA, DoD systems under the RMF, and classified systems under separate authorities. State, local, tribal, and territorial obligations may also differ, and agency tailoring can affect the specifics.

Best practices

Identify the information category being transmitted (such as CUI, federal civilian data, or DoD system data) and confirm which governing authority and control set apply before selecting an encryption approach.
Where validated cryptography is required, confirm that the cryptographic modules in use hold current validation (commonly referenced through the FIPS 140 series maintained by NIST) rather than assuming any encryption satisfies the requirement.
Verify acceptable protocol versions and configurations against the current authoritative guidance, since permitted TLS versions and cryptographic settings change across revisions.
Map your transmission-protection measures to the specific controls in the applicable publication (for example NIST SP 800-53 or NIST SP 800-171) and its current revision, accounting for any agency or contractual tailoring.
Treat encryption in transit as one layer of protection and pair it with safeguards for data at rest and data in use, rather than equating encryption with complete security or compliance.
Confirm all specific control identifiers, protocol versions, and validation requirements against current official sources before implementation, as these change over time and by agency.