SC-20 Secure Name/Address Resolution Service (Authoritative Source)

Guidance: draftPolicy clause: draftWhat these mean

Baselines	Implementation level	Enhancements
Low, Moderate, High	System	1 (0 in a baseline)

Related controls: AU-10, SC-8, SC-12, SC-13, SC-21, SC-22

Control statement

• a. Provide additional data origin authentication and integrity verification artifacts along with the authoritative name resolution data the system returns in response to external name/address resolution queries; and
• b. Provide the means to indicate the security status of child zones and (if the child supports secure resolution services) to enable verification of a chain of trust among parent and child domains, when operating as part of a distributed, hierarchical namespace.

NIST discussion

Providing authoritative source information enables external clients, including remote Internet clients, to obtain origin authentication and integrity verification assurances for the host/service name to network address resolution information obtained through the service. Systems that provide name and address resolution services include domain name system (DNS) servers. Additional artifacts include DNS Security Extensions (DNSSEC) digital signatures and cryptographic keys. Authoritative data includes DNS resource records. The means for indicating the security status of child zones include the use of delegation signer resource records in the DNS. Systems that use technologies other than the DNS to map between host and service names and network addresses provide other means to assure the authenticity and integrity of response data.

Control enhancements

SC-20(2) Data Origin and Integrity

Baselines: Not in a baseline

Provide data origin and integrity protection artifacts for internal name/address resolution queries.

Discussion and assessment objectives for SC-20(2)

None.

Determine if:

• SC-20(02)[01] data origin artifacts are provided for internal name/address resolution queries;
• SC-20(02)[02] integrity protection artifacts are provided for internal name/address resolution queries.

Examine: System and communications protection policy; procedures addressing secure name/address resolution services (authoritative source); system design documentation; system configuration settings and associated documentation; system audit records; system security plan; other relevant documents or records.

Interview: System/network administrators; organizational personnel with information security responsibilities; organizational personnel with responsibilities for managing DNS.

Test: Mechanisms supporting and/or implementing data origin and integrity protection for internal name/address resolution service queries.

Withdrawn enhancements: SC-20(1).

Assessment objectives (SP 800-53A)

Objectives and methods for SC-20

Determine if:

• SC-20a.
  • SC-20a.[01] additional data origin authentication is provided along with the authoritative name resolution data that the system returns in response to external name/address resolution queries;
  • SC-20a.[02] integrity verification artifacts are provided along with the authoritative name resolution data that the system returns in response to external name/address resolution queries;
• SC-20b.
  • SC-20b.[01] the means to indicate the security status of child zones (and if the child supports secure resolution services) is provided when operating as part of a distributed, hierarchical namespace;
  • SC-20b.[02] the means to enable verification of a chain of trust among parent and child domains when operating as part of a distributed, hierarchical namespace is provided.

Examine: System and communications protection policy; procedures addressing secure name/address resolution services (authoritative source); system design documentation; system configuration settings and associated documentation; system security plan; other relevant documents or records.

Interview: System/network administrators; organizational personnel with information security responsibilities; organizational personnel with responsibilities for managing DNS.

Test: Mechanisms supporting and/or implementing secure name/address resolution services.

Policy statement

• The System owner shall ensure the system provides additional data origin authentication and integrity verification artifacts along with the authoritative name resolution data it returns in response to external name and address resolution queries. (SC-20a)
• When the system operates as part of a distributed, hierarchical namespace, the System owner shall ensure it provides the means to indicate the security status of child zones and, if a child supports secure resolution services, to enable verification of a chain of trust among parent and child domains. (SC-20b)

From the System and Communications Protection Policy template (draft). Highlighted fields are values your organization sets.

How to apply it

SC-20 asks the servers that answer for your domains to sign what they return, so anyone on the internet can check that an answer came from you and was not changed on the way. For the Domain Name System (DNS), that means DNS Security Extensions (DNSSEC): NIST’s discussion names DNSSEC signatures and keys as the additional artifacts, and delegation signer (DS) records as the way a parent zone indicates the security status of a child zone (SC-20b). It applies to the zones the organization publishes for external queries; systems that resolve names by something other than DNS need another way to protect their answers. SC-20 is in the Low, Moderate and High baselines.

Common implementations. Most organizations host their public zones with a managed DNS provider or their cloud provider’s DNS service, where DNSSEC signing is a setting, and then publish the DS record at the domain registrar or parent zone so the chain of trust is complete. NIST SP 800-81 Rev. 3, Secure Domain Name System (DNS) Deployment Guide (March 2026), recommends deploying DNSSEC to protect the integrity of DNS data, and section 3.8 covers signing:

• Algorithms from its Table 1, with ECDSA P-256 (algorithm 13) and the other elliptic curve options preferred to RSA because they keep responses small; RSA with SHA-256 needs keys of 2048 bits or more (section 3.8.1).
• Signing keys retired after at most one to three years, with zone-signing key rollovers automated; key-signing key rollovers need the parent zone too, so learn its process first. A hardware security module is recommended for the key-signing key of important zones (section 3.8.1).
• Signature validity on DNSKEY records kept short, for example five to seven days, to limit what a stolen key can forge (section 3.8.2).
• NSEC rather than NSEC3 as the more prudent choice, since NSEC3 adds load without reliably preventing zone walking (section 3.8.3).
• An authoritative, securely reached time source for the signer (section 3.8.7).

NIST posted a list of potential updates (errata) to the publication on July 10, 2026; they are editorial and change none of these points (as of October 2026). Signing internal zones is SC-20(2), in no baseline; section 3.8.6 says it is of limited value for most organizations and not recommended unless required.

Beyond signing, SP 800-81 Rev. 3 section 3.6 asks you to keep your public zones clean: remove CNAME records that point to names or addresses you no longer control, remove delegations to providers you no longer use, and watch for look-alike domains. A dangling record lets an attacker serve content under your name, and DNSSEC signs it just the same.

Organization-defined parameters. SC-20 has no parameters. In the System and Communications Protection policy, the system owner ensures the system provides data origin authentication and integrity verification artifacts with the authoritative name resolution data it returns to external queries, and, as part of a hierarchical namespace, indicates the security status of child zones and enables verification of a chain of trust.

Evidence assessors ask for.

• The list of zones the organization publishes, with who hosts each one
• The DNSSEC signing setting at the provider for each zone, and the DS record at the parent (an online DNSSEC analyzer or dig +dnssec shows the chain of trust and its status)
• For delegated subdomains, DS records in the parent zone for each signed child
• The key management settings: algorithm, key lengths, rollover schedule and where the key-signing key is held, recorded in the key inventory (SC-12)
• Monitoring that alerts before signatures expire or when validation of a zone fails

Inheritance. A managed DNS or cloud DNS service signs zones and handles zone-signing key rollovers, so that part is inherited from the provider; record it in the system security plan from the provider’s customer responsibility matrix. Turning signing on, publishing the DS record at the registrar and keeping zone content accurate stay with the organization. Public DNS is usually run once for the organization, so SC-20 is often a common control that systems inherit.

Common findings.

• Zones signed at the provider, but no DS record at the registrar, so the chain of trust is broken and nobody can validate the signatures.
• Some zones signed and others not, often domains added after the initial rollout or registered for a campaign or product.
• An expired signature or failed key rollover that made the domain fail validation, found by users rather than by monitoring.
• Dangling CNAME records or lame delegations to services the organization no longer uses.

Enhancements in the Moderate baseline. SC-20 has no enhancements in any baseline. SC-20(2) data origin and integrity for internal name and address resolution queries is in no baseline. SC-20(1) is withdrawn.

Artifacts

• System and Communications Protection Decision Worksheet
• System and Communications Protection Policy