Composite FN-DSA and LMS Digital Signature Algorithm for use in X.509 Public Key Infrastructure
draft-gray-lamps-composite-fndsa-lms-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | John Gray , Jean-Pierre Fiset | ||
| Last updated | 2026-07-06 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-gray-lamps-composite-fndsa-lms-00
Limited Additional Mechanisms for PKIX and SMIME J. Gray
Internet-Draft Entrust
Intended status: Standards Track J. P. Fiset
Expires: 7 January 2027 Crypto4a
6 July 2026
Composite FN-DSA and LMS Digital Signature Algorithm for use in X.509
Public Key Infrastructure
draft-gray-lamps-composite-fndsa-lms-00
Abstract
This document defines a composite signature scheme combining the FN-
DSA (Falcon) digital signature algorithm with the Leighton-Micali
Signature (LMS) scheme defined in RFC 8554. This construction is
designed for use within X.509 Public Key Infrastructure (PKI) and
follows the composite signature paradigm defined in
[I-D.ietf-lamps-pq-composite-sigs].
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://johngray-
dev.github.io/draft-gray-lamps-composite-fndsa-lms/draft-gray-lamps-
composite-fndsa-lms.html. Status information for this document may
be found at https://datatracker.ietf.org/doc/draft-gray-lamps-
composite-fndsa-lms/.
Discussion of this document takes place on the Limited Additional
Mechanisms for PKIX and SMIME Working Group mailing list
(mailto:spasm@ietf.org), which is archived at
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https://www.ietf.org/mailman/listinfo/spasm/.
Source for this draft and an issue tracker can be found at
https://github.com/johngray-dev/draft-gray-lamps-composite-fndsa-lms.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Overview of the Composite FN-DSA-LMS Scheme . . . . . . . . . 3
3.1. Pre-hashing . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Prefix, Label, and Context . . . . . . . . . . . . . . . 4
4. Composite Functions . . . . . . . . . . . . . . . . . . . . . 4
4.1. Key Generation . . . . . . . . . . . . . . . . . . . . . 4
4.2. Sign . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.3. Verify . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Serialization of Public and Privates Keys and
Sigantures . . . . . . . . . . . . . . . . . . . . . . . 5
4.4.1. Public Key . . . . . . . . . . . . . . . . . . . . . 5
4.4.2. Private Key . . . . . . . . . . . . . . . . . . . . . 5
4.4.3. Signature . . . . . . . . . . . . . . . . . . . . . . 6
5. Use within X.509 and PKIX . . . . . . . . . . . . . . . . . . 6
6. Algorithm Identifiers . . . . . . . . . . . . . . . . . . . . 6
6.1. id-FNDSA512-LMS_M24-SHAKE . . . . . . . . . . . . . . . . 6
6.2. id-FNDSA512-LMS_M32-SHAKE . . . . . . . . . . . . . . . . 6
6.3. id-FNDSA1024-LMS_M32-SHAKE . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7.1. LMS Statefulness Requirement . . . . . . . . . . . . . . 7
7.2. Hybrid Security . . . . . . . . . . . . . . . . . . . . . 7
7.3. SUF-CMA . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.4. Key Reuse . . . . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
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9. Normative References . . . . . . . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document defines a composite signature scheme combining:
* FN-DSA (Falcon), a lattice-based signature algorithm
* LMS, a stateful hash-based signature algorithm [RFC8554]
The reason for this choice of algorithm combination:
* Both FN-DSA and LMS are believed to be quantum resistant
algorithms (PQ/PQ Hybrid).
* They use completely different hardness problems (lattice based
versus stateful hash based).
* If relevent attacks or implementations bugs are found in either
algorithm there is resiliency.
* FN-DSA can help mitigate the risk of operational errors that lead
to state failure in LMS.
* Combined together they produce a compact PQ/PQ composite signature
ideally suited for high value assets in constrained environments.
The composite construction presents a single algorithm interface
while internally invoking both primitives.
This specification follows the composite design framework described
in [I-D.ietf-lamps-pq-composite-sigs].
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Overview of the Composite FN-DSA-LMS Scheme
Composite FN-DSA-LMS is a hybrid signature scheme formed by combining
FN-DSA and LMS.
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The construction follows the composite signature combiner approach:
M' := Prefix || Label || len(ctx) || ctx || PH(M)
Both component algorithms independently sign M'.
3.1. Pre-hashing
Composite FN-DSA-LMS uses a pre-hash function PH:
PH(M)
This is incorporated into the message representative:
M' := Prefix || Label || len(ctx) || ctx || PH(M)
3.2. Prefix, Label, and Context
Prefix: Always set to "CompositeAlgorithmSignatures2025" as in
[I-D.ietf-lamps-pq-composite-sigs].
Label: Unique per algorithm OID (defined in Algorithm Identifier
section below)
ctx: Application-defined context (0–255 bytes).
4. Composite Functions
4.1. Key Generation
Composite-FNDSA-LMS.KeyGen() -> (pk, sk)
Steps:
1. Generate component keys:
(fndsaPK, fndsaSK) = FNDSA.KeyGen()
(lmsPK, lmsSK) = LMS.KeyGen()
2. Output:
pk = SerializePublicKey(fndsaPK, lmsPK)
sk = SerializePrivateKey(fndsaSK, lmsSK)
4.2. Sign
Signing follows a similar procedure as in
[I-D.ietf-lamps-pq-composite-sigs].
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Composite-FNDSA-LMS.Sign(sk, M, ctx) -> s
Steps:
1. Check:
if len(ctx) > 255: error
2. Compute:
M' := Prefix || Label || len(ctx) || ctx || PH(M)
3. Deserialize keys:
(fndsaSK, lmsSK) = DeserializePrivateKey(sk)
4. Sign:
fndsaSig = FNDSA.Sign(fndsaSK, M')
lmsSig = LMS.Sign(lmsSK, M')
5. Output:
s = SerializeSignatureValue(fndsaSig, lmsSig)
4.3. Verify
Composite-FNDSA-LMS.Verify(pk, M, s, ctx) -> boolean
Steps:
1. Deserialize:
(fndsaPK, lmsPK) = DeserializePublicKey(pk)
(fndsaSig, lmsSig) = DeserializeSignatureValue(s)
2. Compute:
M' := Prefix || Label || len(ctx) || ctx || PH(M)
3. Verify:
FNDSA.Verify(fndsaPK, M', fndsaSig)
LMS.Verify(lmsPK, M', lmsSig)
Both FNDSA.Verify() and LMS.Verify() MUST verify correctly.
4.4. Serialization of Public and Privates Keys and Sigantures
4.4.1. Public Key
SerializePublicKey(fndsaPK, lmsPK):
return fndsaPK || lmsPK
4.4.2. Private Key
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SerializePrivateKey(fndsaSK, lmsSK):
return fndsaSK || lmsSK
4.4.3. Signature
LMS signatures are variable length. Parsing relies on the fixed size
of the FN-DSA signature.
SerializeSignatureValue(fndsaSig, lmsSig):
return fndsaSig || lmsSig
5. Use within X.509 and PKIX
Composite FN-DSA-LMS is used identically to other composite
algorithms.
* Public key encoded as BIT STRING
* Signature encoded as BIT STRING
* Raw serialized values used without ASN.1 wrapping
6. Algorithm Identifiers
6.1. id-FNDSA512-LMS_M24-SHAKE
* Label: COMPSIG-FNDSA512-LMS_M24-SHAKE
* PH: SHAKE256
* FN-DSA: FN-DSA-512
* LMS: LMS_SHAKE_M24_H10
6.2. id-FNDSA512-LMS_M32-SHAKE
* Label: COMPSIG-FNDSA512-LMS_M32-SHAKE
* PH: SHAKE256
* FN-DSA: FN-DSA-512
* LMS: LMS_SHAKE_M32_H10
6.3. id-FNDSA1024-LMS_M32-SHAKE
* Label: COMPSIG-FNDSA1024-LMS_M32-SHAKE
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* PH: SHAKE256
* FN-DSA: FN-DSA-1024
* LMS: LMS_SHAKE_M32_H15
TODO: Define other combinations here. We want to keep the list as
small as possible.
7. Security Considerations
7.1. LMS Statefulness Requirement
LMS private keys are stateful.
Each invocation of LMS.Sign MUST use a unique leaf index. Reuse of a
leaf index results in catastrophic loss of security.
7.2. Hybrid Security
Composite FN-DSA-LMS is EUF-CMA secure if at least one component
remains secure.
7.3. SUF-CMA
Composite FN-DSA-LMS is NOT SUF-CMA secure.
7.4. Key Reuse
Component keys MUST NOT be reused between:
* composite vs standalone
* multiple composites
8. IANA Considerations
IANA is requested to assign OIDs under:
1.3.6.1.5.5.7.6
TODO for each combination
9. Normative References
[I-D.ietf-lamps-fn-dsa-certificates]
Massimo, J., Kampanakis, P., Turner, S., and B.
Westerbaan, "Internet X.509 Public Key Infrastructure --
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Algorithm Identifiers for the Fast-Fourier Transform over
NTRU-Lattice-Based Digital Signature Algorithm (FN-DSA)",
Work in Progress, Internet-Draft, draft-ietf-lamps-fn-dsa-
certificates-00, 20 May 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
fn-dsa-certificates-00>.
[I-D.ietf-lamps-pq-composite-sigs]
Ounsworth, M., Gray, J., Pala, M., Klaußner, J., and S.
Fluhrer, "Composite Module-Lattice-Based Digital Signature
Algorithm (ML-DSA) for use in X.509 Public Key
Infrastructure", Work in Progress, Internet-Draft, draft-
ietf-lamps-pq-composite-sigs-19, 21 April 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
pq-composite-sigs-19>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8554] McGrew, D., Curcio, M., and S. Fluhrer, "Leighton-Micali
Hash-Based Signatures", RFC 8554, DOI 10.17487/RFC8554,
April 2019, <https://www.rfc-editor.org/rfc/rfc8554>.
[RFC9858] Fluhrer, S. and Q. Dang, "Additional Parameter Sets for
HSS/LMS Hash-Based Signatures", RFC 9858,
DOI 10.17487/RFC9858, October 2025,
<https://www.rfc-editor.org/rfc/rfc9858>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
John Gray
Entrust
2500 Solandt Road – Suite 100
Ottawa, Ontario K2K 3G5
Canada
Email: john.gray@entrust.com
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Jean-Pierre Fiset
Crypto4a
Canada
Email: jp@crypto4a.com
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