Internet-Draft SLH-DSA for JOSE and COSE March 2026
Prorock, et al. Expires 16 September 2026 [Page]
Workgroup:
CBOR Object Signing and Encryption
Internet-Draft:
draft-ietf-cose-sphincs-plus-07
Published:
Intended Status:
Standards Track
Expires:
Authors:
M. Prorock
mesur.io
O. Steele
Tradeverifyd
H. Tschofenig
UniBw M.

SLH-DSA for JOSE and COSE

Abstract

This document specifies JSON Object Signing and Encryption (JOSE) and CBOR Object Signing and Encryption (COSE) serializations for Stateless Hash-Based Digital Signature Standard (SLH-DSA), a Post-Quantum Cryptography (PQC) digital signature scheme defined in US NIST FIPS 205.

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://cose-wg.github.io/draft-ietf-cose-sphincs-plus/draft-ietf-cose-sphincs-plus.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-cose-sphincs-plus/.

Discussion of this document takes place on the CBOR Object Signing and Encryption Working Group mailing list (mailto:cose@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/cose/. Subscribe at https://www.ietf.org/mailman/listinfo/cose/.

Source for this draft and an issue tracker can be found at https://github.com/cose-wg/draft-ietf-cose-sphincs-plus.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 16 September 2026.

▲

Table of Contents

1. Introduction

This document specifies JSON Object Signing and Encryption (JOSE) [RFC7515] and CBOR Object Signing and Encryption (COSE) [RFC9052] serializations for the Stateless Hash-Based Digital Signature Standard (SLH-DSA), which was derived from Version 3.1 of SPHINCS+, a Post-Quantum Cryptography (PQC) based digital signature scheme standardized in [FIPS-205].

This document builds on the Algorithm Key Pair (AKP) type, as defined in [I-D.ietf-cose-dilithium]. The AKP type enables flexible representation of keys used across different post-quantum cryptographic algorithms, including SLH-DSA.

2. Terminology

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. The SLH-DSA Algorithm Family

The SLH-DSA Signature Scheme is parameterized to support different security levels.

This document introduces the registration of the following algorithms in [IANA.jose]:

Table 1: JOSE Algorithms for SLH-DSA
Name alg Description
SLH-DSA-SHA2-128s SLH-DSA-SHA2-128s JSON Web Signature Algorithm for SLH-DSA-SHA2-128s
SLH-DSA-SHAKE-128s SLH-DSA-SHAKE-128s JSON Web Signature Algorithm for SLH-DSA-SHAKE-128s
SLH-DSA-SHA2-128f SLH-DSA-SHA2-128f JSON Web Signature Algorithm for SLH-DSA-SHA2-128f

This document introduces the registration of the following algorithms in [IANA.cose]:

Table 2: COSE Algorithms for SLH-DSA
Name alg Description
SLH-DSA-SHA2-128s TBD1 (-51) CBOR Object Signing Algorithm for SLH-DSA-SHA2-128s
SLH-DSA-SHAKE-128s TBD2 (-52) CBOR Object Signing Algorithm for SLH-DSA-SHAKE-128s
SLH-DSA-SHA2-128f TBD3 (-53) CBOR Object Signing Algorithm for SLH-DSA-SHA2-128f

4. SLH-DSA Keys

Private and public keys are produced to enable the sign and verify operations for each of the SLH-DSA algorithms.

The SLH-DSA Algorithm Family uses the Algorithm Key Pair (AKP) key type, as defined in [I-D.ietf-cose-dilithium]. This ensures compatibility across different cryptographic algorithms that use AKP for key representation.

The specific algorithms for SLH-DSA, such as SLH-DSA-SHA2-128s, SLH-DSA-SHAKE-128s, and SLH-DSA-SHA2-128f, are defined in this document and are used in the alg value of an AKP key representation to specify the corresponding algorithm.

Thumbprints for SLH-DSA keys are computed according to the process described in [I-D.ietf-cose-dilithium].

5. Security Considerations

The security considerations of [RFC7515], [RFC7517] and [RFC9053] apply to this specification as well.

A detailed security analysis of SLH-DSA is beyond the scope of this specification; see [FIPS-205] for additional details.

The following considerations apply to all parameter sets described in this specification.

5.1. Pre-Hash and Hashing Considerations

SLH-DSA, as specified in [FIPS-205], supports both pure and pre-hash modes. This document specifies only the pure mode of SLH-DSA for use with JOSE and COSE.

This document does not define or register separate HashSLH-DSA algorithm identifiers for JOSE or COSE. Doing so would require distinct algorithm registrations and would introduce additional implementation and interoperability complexity. The algorithm identifiers defined in this document therefore refer only to the pure SLH-DSA variants.

For many COSE use cases, this restriction is acceptable because the application can already structure the signed content in a way that limits the amount of data processed directly by the signature algorithm. In particular, applications that need to sign large payloads, detached content, or remotely held content may use the COSE Hash Envelope mechanism [I-D.ietf-cose-hash-envelope].

Hash Envelope can provide operational properties similar to those sought from a pre-hash signature mode, such as reduced data transfer to a signer, reduced buffering requirements, and simplified remote-signing workflows. However, Hash Envelope is not cryptographically identical to a standardized pre-hash variant of SLH-DSA. In Hash Envelope, a digest is carried and signed at the COSE layer, whereas in a pre-hash signature algorithm the hashing step is part of the algorithm definition itself.

Applications that use Hash Envelope together with SLH-DSA need to ensure that the digest is recomputed over the original content and compared with the signed digest before treating the signature as valid for that content. Profiles that rely on this construction SHOULD specify the permitted hash algorithms and the verification procedure explicitly.

If future deployment experience shows clear demand for algorithm-level pre-hash semantics in JOSE or COSE, separate registrations for HashSLH-DSA could be defined in a future specification.

5.2. Validating Public Keys

All algorithms that operate on public keys require validation before use. For sign, verify and proof schemes, the use of KeyValidate is REQUIRED.

5.3. Side-Channel Attacks

Implementations of the signing algorithm SHOULD protect the secret key from side-channel attacks. Any implementation of SLH-DSA signing algorithms SHOULD employ at least the following best practices:

  • Constant-time operation

  • Consistent instruction sequence and memory access

  • Uniform sampling without information leakage

5.4. Randomness considerations

All nonces MUST originate from a trusted and cryptographically secure source of randomness.

6. IANA Considerations

6.1. New COSE Algorithms

IANA is requested to add the following entries to the COSE Algorithms Registry.

The following registration templates are provided in accordance with the procedures described in [RFC9053] and [RFC9054].

6.1.1. SLH-DSA-SHA2-128s

  • Name: SLH-DSA-SHA2-128s

  • Value: TBD1 (requested assignment -51)

  • Description: CBOR Object Signing Algorithm for SLH-DSA-SHA2-128s

  • Capabilities: [kty]

  • Change Controller: IETF

  • Reference: RFC XXXX

  • Recommended: Yes

6.1.2. SLH-DSA-SHAKE-128s

  • Name: SLH-DSA-SHAKE-128s

  • Value: TBD2 (requested assignment -52)

  • Description: CBOR Object Signing Algorithm for SLH-DSA-SHAKE-128s

  • Capabilities: [kty]

  • Change Controller: IETF

  • Reference: RFC XXXX

  • Recommended: Yes

6.1.3. SLH-DSA-SHA2-128f

  • Name: SLH-DSA-SHA2-128f

  • Value: TBD3 (requested assignment -53)

  • Description: CBOR Object Signing Algorithm for SLH-DSA-SHA2-128f

  • Capabilities: [kty]

  • Change Controller: IETF

  • Reference: RFC XXXX

  • Recommended: Yes

6.2. New JOSE Algorithms

IANA is requested to add the following entries to the JSON Web Signature and Encryption Algorithms Registry.

The following completed registration templates are provided as described in [RFC7518].

6.2.1. SLH-DSA-SHA2-128s

  • Algorithm Name: SLH-DSA-SHA2-128s

  • Algorithm Description: SLH-DSA-SHA2-128s as described in FIPS 205.

  • Algorithm Usage Location(s): alg

  • JOSE Implementation Requirements: Optional

  • Change Controller: IETF

  • Specification Document(s): RFC XXXX

  • Algorithm Analysis Documents(s): [FIPS-205]

6.2.2. SLH-DSA-SHAKE-128s

  • Algorithm Name: SLH-DSA-SHAKE-128s

  • Algorithm Description: SLH-DSA-SHAKE-128s as described in FIPS 205.

  • Algorithm Usage Location(s): alg

  • JOSE Implementation Requirements: Optional

  • Change Controller: IETF

  • Specification Document(s): RFC XXXX

  • Algorithm Analysis Documents(s): [FIPS-205]

6.2.3. SLH-DSA-SHA2-128f

  • Algorithm Name: SLH-DSA-SHA2-128f

  • Algorithm Description: SLH-DSA-SHA2-128f as described in FIPS 205.

  • Algorithm Usage Location(s): alg

  • JOSE Implementation Requirements: Optional

  • Change Controller: IETF

  • Specification Document(s): RFC XXXX

  • Algorithm Analysis Documents(s): [FIPS-205]

7. References

7.1. Normative References

[FIPS-205]
"Stateless Hash-Based Digital Signature Standard", n.d., <https://doi.org/10.6028/NIST.FIPS.205>.
[I-D.ietf-cose-dilithium]
Prorock, M. and O. Steele, "ML-DSA for JOSE and COSE", Work in Progress, Internet-Draft, draft-ietf-cose-dilithium-11, , <https://datatracker.ietf.org/doc/html/draft-ietf-cose-dilithium-11>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC7515]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, , <https://www.rfc-editor.org/rfc/rfc7515>.
[RFC7517]
Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/RFC7517, , <https://www.rfc-editor.org/rfc/rfc7517>.
[RFC7518]
Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, , <https://www.rfc-editor.org/rfc/rfc7518>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC9052]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", STD 96, RFC 9052, DOI 10.17487/RFC9052, , <https://www.rfc-editor.org/rfc/rfc9052>.
[RFC9053]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053, , <https://www.rfc-editor.org/rfc/rfc9053>.
[RFC9054]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Hash Algorithms", RFC 9054, DOI 10.17487/RFC9054, , <https://www.rfc-editor.org/rfc/rfc9054>.

7.2. Informative References

[I-D.ietf-cose-hash-envelope]
Steele, O., Lasker, S., and H. Birkholz, "COSE Hash Envelope", Work in Progress, Internet-Draft, draft-ietf-cose-hash-envelope-10, , <https://datatracker.ietf.org/doc/html/draft-ietf-cose-hash-envelope-10>.
[IANA.cose]
IANA, "CBOR Object Signing and Encryption (COSE)", <https://www.iana.org/assignments/cose>.
[IANA.jose]
IANA, "JSON Object Signing and Encryption (JOSE)", <https://www.iana.org/assignments/jose>.

Appendix A. Examples

A.1. JOSE

A.1.1. Key Pair 

{
  "kty": "AKP",
  "alg": "SLH-DSA-SHA2-128s",
  "pub": "V53SIdVF...uvw2nuCQ",
  "priv": "V53SIdVF...cDKLbsBY"
}
Figure 1: Example SLH-DSA-SHA2-128s Private JSON Web Key 
{
  "kty": "AKP",
  "alg": "SLH-DSA-SHA2-128s",
  "pub": "V53SIdVF...uvw2nuCQ"
}
Figure 2: Example SLH-DSA-SHA2-128s Public JSON Web Key

A.1.2. JSON Web Signature 

eyJhbGciOiJ...LCJraWQiOiI0MiJ9\
.\
eyJpc3MiOiJ1cm46d...XVpZDo0NTYifQ\
.\
5MSEgQ0dZB4SeLC...AAAAAABIhMUE
Figure 3: Example SLH-DSA-SHA2-128s Compact JSON Web Signature

A.2. COSE

A.2.1. Key Pair 

{
  / kty AKP                / 1: 7,
  / alg SLH-DSA-SHA2-128s  / 3: -51,
  / kid                    / 2: h'736c682d6473612d313238732d6b6964',
  / public key             / -1:
h'f3eb7b23659086bd1d5196f8201898c189ae9fd5567be8941f135e54b261ca9d',
  / private key            / -2:
h'4d9884c45556898d0da29c5af418386d9abcdb84426e64ab44e5bcb3126c77de
  f3eb7b23659086bd1d5196f8201898c189ae9fd5567be8941f135e54b261ca9d'
}
Figure 4: Example SLH-DSA-SHA2-128s COSE Key

A.2.2. COSE Sign1 

18([
  <<{
    / alg SLH-DSA-SHA2-128s / 1: -51,
  }>>,
  / unprotected / {},
  / payload / h'66616b65',
  / signature /
h'66f177b396bbcb70fd813db15c6805d80c921ca441ff22c7f274c7e7309741de
  407015cb0f4b60cbb585dea1ac00b5807d6b2e8b5c3b2cb8cd52b37f9859c96b
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])
Figure 5: Example SLH-DSA-SHA2-128s COSE Sign1

Acknowledgments

We would like to thank Roy Williams, Cedric Fournet, Simo Sorce, Ilari Liusvaara, Neil Madden, Anders Rundgren, David Waite, and Russ Housley for their review feedback.

Contributors

Rafael Misoczki
Google
Michael Osborne
IBM
Christine Cloostermans
NXP

Authors' Addresses

Michael Prorock
mesur.io
Orie Steele
Tradeverifyd
Hannes Tschofenig
University of the Bundeswehr Munich
85577 Neubiberg
Germany