Digital signatures are long-lived interoperability commitments with strong evidence expectations.
This guide covers FIPS 186-5 and FIPS 204 with a practical selection and governance lens.
Structured answer sets in this page tree.
Cited legal and guidance references.
FIPS 186-5, published on 3 February 2023, is the current Digital Signature Standard. It approves use of RSA signatures through RFC 8017, specifies ECDSA, approves deterministic ECDSA through RFC 6979, and approves EdDSA with additional requirements. FIPS 204, published on 13 August 2024, adds ML-DSA as a post-quantum digital signature standard. The engineering challenge is choosing the right scheme, controlling key purpose, pinning digest behavior, and keeping signatures verifiable for years.
FIPS 186-5 is broader than older DSS summaries suggest. It approves RSA signature implementations based on RFC 8017, specifies ECDSA, includes deterministic ECDSA, and approves EdDSA with additional requirements.
It also changes legacy assumptions. The standard no longer approves DSA for digital signature generation, although DSA may still be used to verify signatures generated before the implementation date under the older standard.
FIPS 204 specifies ML-DSA, a module-lattice-based digital signature algorithm published on 13 August 2024. It is part of the post-quantum transition stack and should be planned as a crypto-agility move, not just a library upgrade.
For many teams, the real decision is not classic versus post-quantum. It is which verification domains need classic compatibility, which ones can move first, and where hybrid evidence or parallel support is required.
FIPS 186-5 and FIPS 205 both reinforce a simple rule: digital signature key pairs are for signatures, not for unrelated purposes. This matters because key-purpose drift is a common production failure in complex systems.
Use separate keys for code signing, document signing, identity assertions, and protocol authentication unless the policy explicitly justifies reuse.
Digest selection is part of signature-system interoperability. FIPS 186-5 references FIPS 180 and FIPS 202, and specific algorithms carry specific digest rules. For example, Ed25519 uses SHA-512 and Ed448 uses SHAKE256 inside the standard.
If hash or XOF choices drift between signer and verifier, the result is broken verification or ambiguous evidence. Treat digest and parameter choices as policy, not as incidental implementation detail.
Signature systems are often reviewed for non-repudiation, software integrity, identity, or procurement reasons. Good evidence proves the selected schemes, the key-purpose controls, and the long-term verification story.
The evidence pack should be able to answer who signed, with which scheme and parameters, under which policy, and how the system proves that later.
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