FAQGLOBALFIPS 186-5 signature evidence

FIPS 186-5 digital signatures How should teams use them in FIPS-approved algorithm decisions?

Use FIPS 186-5 to select and evidence approved signature algorithms, then keep the algorithm, key-use, operating-environment, and module-validation claims separate.

This FAQ focuses on RSA, ECDSA, deterministic ECDSA, EdDSA, HashEdDSA, DSA verification, CAVP certificates, and CMVP module boundaries.

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Author
Sorena AI
Published
May 9, 2026
Updated
May 9, 2026
Questions
3

Structured answer sets in this page tree.

Primary sources
4

Cited legal and guidance references.

Publication metadata
Sorena AI
Published May 9, 2026
Updated May 9, 2026
Overview

Short answer: FIPS 186-5 is the digital-signature standard for approved RSA, ECDSA, deterministic ECDSA, EdDSA, and HashEdDSA use. It does not make every product using those names validated; teams still need implementation-specific CAVP evidence and, for FIPS 140-3 claims, CMVP module evidence.

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3 of 3 questions
Question 1

Which signature algorithms does FIPS 186-5 support?

Use FIPS 186-5 when the decision is about digital signature generation or verification for RSA, ECDSA, deterministic ECDSA, EdDSA, or HashEdDSA. The standard also states that DSA is no longer approved for digital signature generation, although DSA may be used to verify signatures generated before the implementation date.

The selection record should name the exact signature family, operation, parameters, key purpose, and approved hash or XOF relationship. For RSA, FIPS 186-5 permits signature generation or verification with modulus sizes at least 2048 bits, while CMVP implementation guidance explains how CAVP testing and Security Policy documentation handle sizes where CAVP testing is or is not available.

  • Record whether the service performs signature generation, signature verification, or both.
  • Separate RSA, ECDSA, deterministic ECDSA, EdDSA, HashEdDSA, and legacy DSA verification decisions; do not collapse them into a generic signature claim.
  • For RSA, document the modulus length, scheme such as RSASSA-PSS or RSASSA-PKCS1-v1.5, approved hash or XOF choice, and whether key generation is performed by the module.
Citations
Question 2

What evidence should support a FIPS 186-5 signature claim?

A useful evidence package starts with the standard citation but does not stop there. Keep the FIPS 186-5 algorithm decision, the CAVP algorithm-validation record, and the CMVP module claim as separate records that are linked only when the implementation name, version, parameters, and operating environment match.

For a CAVP check, capture the implementation name and version, vendor, certificate or validation-search entry, algorithm and mode, parameter set or modulus size, and tested operating environment. For a CMVP check, tie the signature service to the cryptographic module boundary, approved-mode service list, Security Policy, and any bound or embedded module caveats.

  • Use CAVP evidence to support the tested algorithm implementation, not to claim that the whole product or module is FIPS 140-3 validated.
  • Use CMVP evidence to support module validation, approved-mode operation, module boundary, and approved-service claims.
  • Refresh the evidence when the implementation version, operating environment, module boundary, processor acceleration path, key-generation path, or approved-service listing changes.
Citations
NIST CAVP validation search

Public search source for checking algorithm validation entries for signature implementations, modes, parameters, and environments.

Recommended next step

Separate algorithm selection, CAVP evidence, and CMVP module claims

Use this FAQ to review signature algorithm choices, key-use boundaries, operating environments, approved-mode services, and validation evidence before relying on a FIPS claim.

Assessment workflow
Check the signature boundary

Review whether signature algorithms, keys, parameters, and module claims point to the right validation records.

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Research workflow
Resolve a scoped FIPS question

Compare FIPS 186-5, CAVP, and CMVP source support when a signature claim depends on implementation details.

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Talk to Sorena
Talk through implementation

Review the product boundary, signature services, operating environment, and validation evidence in scope.

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Question 3

What FIPS 186-5 signature mistakes should teams avoid?

The first mistake is key reuse. FIPS 186-5 says digital signature key pairs must not be used for other purposes such as key establishment, and it repeats that RSA and ECDSA signature keys are signature-only. A key inventory should therefore show a signature-only purpose rather than a shared public-key bucket.

The second mistake is treating successful signature verification as the whole validation decision. For ECDSA and EdDSA, verifiers also need domain-parameter assurance; verifiers need public-key validity, claimed-signatory identity, and possession assurance before accepting a signature as valid. The third mistake is assuming conformance to FIPS 186-5 guarantees system security; the standard explicitly leaves implementation security and overall system assurance to the responsible implementer or authority.

  • Do not use a signature key pair for key establishment, encryption, or other non-signature purposes.
  • Do not claim DSA signature generation as approved under FIPS 186-5; limit DSA to the legacy verification context supported by the standard.
  • Do not reuse a CAVP certificate across a different implementation, version, operating environment, parameter set, or module boundary without confirming the scope.
Citations
Primary sources

References and citations

NIST CAVP validation search
csrc.nist.gov
Referenced sections
  • Public search source for checking algorithm validation entries for signature implementations, modes, parameters, and environments.
"Cryptographic Algorithm Validation Program"
NIST Cryptographic Module Validation Program
nist.gov
Referenced sections
  • Program source for cryptographic module validation, which is distinct from algorithm implementation testing.
"Cryptographic Module Validation Program"
NIST FIPS 140-3 Implementation Guidance
csrc.nist.gov
Referenced sections
  • Clarifies that approved-service indicators may depend on the signature algorithm, hash algorithm, and key size used by the service.
"signature generation algorithm, hashing algorithm, and key size"
NIST FIPS 186-5 Digital Signature Standard
doi.org
Referenced sections
  • Supports key-purpose separation, assurance checks before accepting signatures as valid, and the limits of conformance claims.
"shall not be used for any other purpose"
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