RFC 9802

Use of the HSS and XMSS Hash-Based Signature Algorithms in Internet X.509 Public Key Infrastructure

📅 published June 2025, from ietf

RFC 9802 💖 Use of the HSS and XMSS Hash-Based Signature Algorithms in Internet X.509 Public Key Infrastructure

Okay bestie, here's the title block tea ☕ This one is an IETF Standards Track document, published in June 2025 with ISSN 2070-1721. The authors are D. Van Geest (CryptoNext Security), K. Bashiri (BSI), S. Fluhrer (Cisco Systems), S. Gazdag (genua GmbH), and S. Kousidis (BSI). The title block doesn't list anything it obsoletes or updates. 🦋

Abstract ✨

Okay so this doc is all about algorithm identifiers and ASN.1 encoding formats for three stateful Hash-Based Signature (HBS) schemes: HSS (Hierarchical Signature System), XMSS (eXtended Merkle Signature Scheme), and XMSS^MT (the multi-tree variant of XMSS). It applies to the Internet X.509 Public Key Infrastructure (PKI) whenever digital signatures are used to sign certificates and certificate revocation lists (CRLs). It's giving certificate energy 📜💅

Status of This Memo 🎀

This is an Internet Standards Track document, bestie.

It's a product of the Internet Engineering Task Force (IETF), so it represents the consensus of the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). For more on Internet Standards, check Section 2 of RFC 7841.

Info about the current status of this document, any errata, and how to send feedback lives at https://www.rfc-editor.org/info/rfc9802. 🌸

Copyright Notice 🦋

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, because they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions, and they are provided without warranty as described in the Revised BSD License. ⚖️

Table of Contents 🌈

   1.  Introduction
   2.  Conventions and Definitions
   3.  Use Cases of Stateful HBS Schemes in X.509
   4.  Algorithm Identifiers and Parameters
     4.1.  HSS Algorithm Identifier
     4.2.  XMSS Algorithm Identifier
     4.3.  XMSS^MT Algorithm Identifier
   5.  Public Key Identifiers
     5.1.  HSS Public Keys
     5.2.  XMSS Public Keys
     5.3.  XMSS^MT Public Keys
   6.  Key Usage Bits
   7.  Signature Algorithms
     7.1.  HSS Signature Algorithm
     7.2.  XMSS Signature Algorithm
     7.3.  XMSS^MT Signature Algorithm
   8.  Key Generation
   9.  ASN.1 Module
   10. Security Considerations
   11. Backup and Restore Management
   12. IANA Considerations
   13. References
     13.1.  Normative References
     13.2.  Informative References
   Appendix A.  HSS X.509 v3 Certificate Example
   Appendix B.  XMSS X.509 v3 Certificate Example
   Appendix C.  XMSS^MT X.509 v3 Certificate Example
   Acknowledgments
   Authors' Addresses

1. Introduction ✨

Stateful Hash-Based Signature (HBS) schemes like HSS (Hierarchical Signature System), XMSS (eXtended Merkle Signature Scheme), and XMSS^MT mix Merkle trees with One-Time Signatures (OTS). The point is to get digital signature schemes that stay secure even once quantum computers are around 🔮 Their theoretical security is well understood, and it depends only on the security of the underlying hash function. So they can be a major building block for quantum-resistant information and communication tech. Iconic 👑

Here's the catch. A stateful HBS private key is a finite collection of OTS keys, plus state info that tracks which keys have been used so the scheme stays secure. Only a limited number of messages can be signed, and the state has to be updated and persisted after every signature so OTS keys don't get reused. Picking the right parameters could let one private key sign a practically unbounded number of messages (for example, 2^60), but that comes with bigger signatures and slower signing 🐢 Because the private key is stateful and the signature count is capped, these schemes may not be a fit for interactive protocols. Still, in some use cases, deploying a stateful HBS scheme can be the right call. Section 3 covers those use cases and talks them through. 🧚

2. Conventions and Definitions 💜

Here's the BCP 14 vibe check. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are read as described in BCP 14 [RFC2119] [RFC8174], but only when they show up in all capitals, just like this. Lowercase versions are just regular words, no cap 🙅‍♀️

3. Use Cases of Stateful HBS Schemes in X.509 🍓

Section 10 explains why this part is so serious: stateful HBS implementations absolutely must not reuse OTS signatures. That makes stateful HBS algorithms a poor fit for general use cases 😭 Which conditions allow stateful HBS certificates is left to certificate policies [RFC3647]. But the intended use from [SP800208] works as a guideline:

stateful HBS schemes are primarily intended for applications with the following characteristics: 1) it is necessary to implement a digital signature scheme in the near future; 2) the implementation will have a long lifetime; and 3) it would not be practical to transition to a different digital signature scheme once the implementation has been deployed.

Also, since a stateful HBS private key can only generate a finite number of signatures, use cases for stateful HBS public keys in certificates should have a predictable range for how many signatures will be generated, safely below the max a private key can produce. Main character planning energy 📅

Use cases where stateful HBS public keys in certificates may be appropriate are the ones with a relatively small number of generated signatures, where the signer can enforce security restrictions on the signing environment. These include:

Firmware signing (see Section 1.1 of [SP800208], [CNSA2.0], and Section 6.7 of [BSI])
Software signing ([CNSA2.0] and [ANSSI])
Certification Authority (CA) certificates

In each of these cases, the operator tightly controls their secured signing environment and can mitigate OTS key reuse by using state management strategies like the ones in Section 10. Also, for secure private key backup and restoration, adequate mechanisms have to be implemented (see Section 11). 🔐

Generally speaking, stateful HBS public keys aren't appropriate for end-entity certificates. But in the firmware and software signing cases, signature generation is often more tightly controlled. Some manufactures use common, well-established key formats like X.509 for their code signing and update mechanisms. There are also multi-party Internet of Things (IoT) ecosystems where publicly trusted code signing certificates are useful 🌐🧸

Root CAs [RFC4949] generate signatures in a more secure environment and issue fewer certificates than subordinate CAs [RFC4949]. So stateful HBS public keys fit better in root CA certificates than in subordinate CA certificates. But if a subordinate CA can match the security and signature count restrictions of a root CA (for example, if it only issues code-signing certificates), then putting a stateful HBS public key in the subordinate CA certificate could be practical. 👑✨

4. Algorithm Identifiers and Parameters 🎀

In this document, we define new Object Identifiers (OIDs) to identify the different stateful hash-based signature algorithms. One more OID is defined in [RFC9708] and repeated here for convenience.

The AlgorithmIdentifier type is defined in [RFC5912] like this:

   AlgorithmIdentifier{ALGORITHM-TYPE, ALGORITHM-TYPE:AlgorithmSet} ::=
           SEQUENCE {
               algorithm   ALGORITHM-TYPE.&id({AlgorithmSet}),
               parameters  ALGORITHM-TYPE.
                      &Params({AlgorithmSet}{@algorithm}) OPTIONAL
           }

NOTE: The above syntax is from [RFC5912] and is compatible with the 2021 ASN.1 syntax [X680]. See [RFC5280] for the 1988 ASN.1 syntax.

Here's what the AlgorithmIdentifier fields mean:

algorithm: identifies the cryptographic algorithm with an OID.
parameters: optional, and holds the associated parameters for the algorithm identifier in the algorithm field.

Important detail: the parameters field of the AlgorithmIdentifier for HSS, XMSS, and XMSS^MT public keys MUST be absent. No parameters, no drama 🙅‍♀️

4.1. HSS Algorithm Identifier 🌸

The OID and public key algorithm identifier for HSS is defined in [RFC9708]. The definitions are repeated here for reference.

The AlgorithmIdentifier for an HSS public key MUST use the id-alg-hss-lms-hashsig OID.

      id-alg-hss-lms-hashsig  OBJECT IDENTIFIER ::= {
         iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
         smime(16) alg(3) 17 }

Quick side note: id-alg-hss-lms-hashsig is also called id-alg-mts-hashsig. That synonym comes from the terminology in an early draft of the document that became [RFC8554].

The public key and signature values identify the hash function and the height used in the HSS tree. [RFC8554] and [SP800208] define these values, and additional identifiers can be registered in the "Leighton-Micali Signatures (LMS)" registry [IANA-LMS]. 🧩

4.2. XMSS Algorithm Identifier 🦋

The AlgorithmIdentifier for an XMSS public key MUST use the id-alg-xmss-hashsig OID.

      id-alg-xmss-hashsig  OBJECT IDENTIFIER ::= {
         iso(1) identified-organization(3) dod(6) internet(1)
         security(5) mechanisms(5) pkix(7) algorithms(6) 34 }

The public key and signature values identify the hash function and the height used in the XMSS tree. [RFC8391] and [SP800208] define these values, and additional identifiers can be registered in the "Leighton-Micali Signatures (LMS)" registry [IANA-XMSS]. 🌈

4.3. XMSS^MT Algorithm Identifier 💜

The AlgorithmIdentifier for an XMSS^MT public key MUST use the id-alg-xmssmt-hashsig OID.

      id-alg-xmssmt-hashsig  OBJECT IDENTIFIER ::= {
         iso(1) identified-organization(3) dod(6) internet(1)
         security(5) mechanisms(5) pkix(7) algorithms(6) 35 }

The public key and signature values identify the hash function and the height used in the XMSS^MT tree. [RFC8391] and [SP800208] define these values, and additional identifiers can be registered in the "Leighton-Micali Signatures (LMS)" registry [IANA-XMSS]. ✨

⏭️ Part 1 of 9 is done, bestie! Part 2 is coming next, and it gets into Public Key Identifiers and Key Usage Bits 🫶

5. Public Key Identifiers ✨

okay so [RFC5280] certificates can carry a public key for any public key algorithm, bestie 💅 the certificate says which one using an algorithm identifier, and that identifier is an OID plus optional parameters 🫶

[RFC8554] is where the HSS public key encoding lives, and [RFC8391] handles the XMSS and XMSS^MT public key encodings 🌸 when they're inside a SubjectPublicKeyInfo type, the subjectPublicKey BIT STRING holds these encodings of the public key 🎀

this doc also defines ASN.1 [X680] OCTET STRING types for encoding the public keys when they're not in a SubjectPublicKeyInfo 💖 the OCTET STRING gets mapped to a subjectPublicKey (a BIT STRING value) like this: the most significant bit of the OCTET STRING becomes the most significant bit of the BIT STRING, and so on, and the least significant bit of the OCTET STRING becomes the least significant bit of the BIT STRING 🧚

5.1. HSS Public Keys 🦋

the HSS public key identifier looks like this:

   pk-HSS-LMS-HashSig PUBLIC-KEY ::= {
      IDENTIFIER id-alg-hss-lms-hashsig
      -- KEY no ASN.1 wrapping --
      PARAMS ARE absent
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

and the HSS public key is defined as:

   HSS-LMS-HashSig-PublicKey ::= OCTET STRING

[RFC8554] defines the encoding of an HSS public key using the hss_public_key structure 💅 for more on what's inside and how it's formatted, check [SP800208] and [RFC8554] 👑 also, the Leighton-Micali Signature (LMS) single-tree signature scheme is instantiated as HSS with the number of levels equal to 1, so yes, it's HSS 🔥

5.2. XMSS Public Keys 🌈

the XMSS public key identifier:

   pk-XMSS-HashSig PUBLIC-KEY ::= {
      IDENTIFIER id-alg-xmss-hashsig
      -- KEY no ASN.1 wrapping --
      PARAMS ARE absent
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

and the XMSS public key is defined as:

   XMSS-HashSig-PublicKey ::= OCTET STRING

[RFC8391] defines the XMSS public key encoding using the xmss_public_key structure ⭐ see [SP800208] and [RFC8391] for the full scoop on its contents and format 🫶

5.3. XMSS^MT Public Keys 💜

the XMSS^MT public key identifier:

   pk-XMSSMT-HashSig PUBLIC-KEY ::= {
      IDENTIFIER id-alg-xmssmt-hashsig
      -- KEY no ASN.1 wrapping --
      PARAMS ARE absent
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

and the XMSS^MT public key is defined as:

   XMSSMT-HashSig-PublicKey ::= OCTET STRING

[RFC8391] defines the XMSS^MT public key encoding using the xmssmt_public_key structure 🍓 for the contents and format, see [SP800208] and [RFC8391] ✨

6. Key Usage Bits 🎀

the intended use for the key gets flagged in the keyUsage certificate extension [RFC5280] 💖 when id-alg-hss-lms-hashsig, id-alg-xmss-hashsig, or id-alg-xmssmt-hashsig shows up in the SubjectPublicKeyInfo field of a CA X.509 certificate [RFC5280], the certificate key usage extension MUST contain at least one of these values: digitalSignature, nonRepudiation, keyCertSign, or cRLSign 😭 it MUST NOT contain other values, no exceptions 🙈

when id-alg-hss-lms-hashsig, id-alg-xmss-hashsig, or id-alg-xmssmt-hashsig shows up in the SubjectPublicKeyInfo field of an end entity X.509 certificate [RFC5280], the certificate key usage extension MUST contain at least one of these values: digitalSignature, nonRepudiation or cRLSign 🌸 and again, it MUST NOT contain other values 💅

7. Signature Algorithms 🔥

the same OIDs that identify HSS, XMSS, and XMSS^MT public keys also identify their signatures ✨ when these algorithm identifiers appear in the algorithm field of an AlgorithmIdentifier, the encoding MUST omit the parameters field 🙈 so the AlgorithmIdentifier SHALL be a SEQUENCE of one component, which is one of the OIDs in the subsections below 👑

when you use the signature algorithm identifiers from this document to sign a message, no digest algorithm gets applied to the message first 💖 the full data is signed, not a digest of it 🦋

the HSS signature format is described in Section 6.2 of [RFC8554] 🧚 the XMSS signature format is in Appendix B.2 of [RFC8391], and the XMSS^MT signature format is in Appendix C.2 of [RFC8391] 🌈 the octet string for the signature gets encoded directly in a BIT STRING with no extra ASN.1 wrapping 💜 for the Certificate and CertificateList structures, that octet string goes in the "signatureValue" BIT STRING field 🍓

7.1. HSS Signature Algorithm 🦋

the id-alg-hss-lms-hashsig OID says an HSS signature was generated on the full message, meaning the message wasn't hashed before the HSS signature algorithm processed it 💅

see [SP800208] and [RFC8554] for the contents and format of an HSS signature ✨

7.2. XMSS Signature Algorithm 🌸

the id-alg-xmss-hashsig OID says an XMSS signature was generated on the full message, meaning the message wasn't hashed before the XMSS signature algorithm processed it 🫶

see [SP800208] and [RFC8391] for the contents and format of an XMSS signature 💖

the signature generation MUST be performed according to Section 7.2 of [SP800208] 👑

7.3. XMSS^MT Signature Algorithm 💜

the id-alg-xmssmt-hashsig OID says an XMSS^MT signature was generated on the full message, meaning the message wasn't hashed before the XMSS^MT signature algorithm processed it 🧚

see [SP800208] and [RFC8391] for the contents and format of an XMSS^MT signature 🎀

the signature generation MUST be performed according to Section 7.2 of [SP800208] 🔥

8. Key Generation ⭐

the key generation for XMSS and XMSS^MT MUST be performed according to Section 7.2 of [SP800208] 💅 bestie, that's a must 🫶

9. ASN.1 Module 🧚

for reference, the ASN.1 syntax is presented as an ASN.1 module here [X680] 🌈 as per [RFC5280], certificates use the Distinguished Encoding Rules, so check [X690] for those 💜 this ASN.1 module builds on the conventions from [RFC5912] and imports objects from [RFC5912] and [RFC9708] 🍓

   X509-SHBS-2024
     { iso(1) identified-organization(3) dod(6) internet(1) security(5)
       mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-shbs-2024(114) }

   DEFINITIONS IMPLICIT TAGS ::= BEGIN

   EXPORTS ALL;

   IMPORTS
     PUBLIC-KEY, SIGNATURE-ALGORITHM
       FROM AlgorithmInformation-2009  -- [RFC5912]
         { iso(1) identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) id-mod(0)
           id-mod-algorithmInformation-02(58) }

     sa-HSS-LMS-HashSig, pk-HSS-LMS-HashSig
       FROM MTS-HashSig-2013 -- [RFC9708]
         { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
           id-smime(16) id-mod(0) id-mod-mts-hashsig-2013(64) };

   --
   -- Object Identifiers
   --

   -- id-alg-hss-lms-hashsig is defined in [RFC9708]

   id-alg-xmss-hashsig  OBJECT IDENTIFIER ::= {
      iso(1) identified-organization(3) dod(6) internet(1) security(5)
      mechanisms(5) pkix(7) algorithms(6) 34 }

   id-alg-xmssmt-hashsig  OBJECT IDENTIFIER ::= {
      iso(1) identified-organization(3) dod(6) internet(1) security(5)
      mechanisms(5) pkix(7) algorithms(6) 35 }

   --
   -- Signature Algorithms and Public Keys
   --

   -- sa-HSS-LMS-HashSig is defined in [RFC9708]

   sa-XMSS-HashSig SIGNATURE-ALGORITHM ::= {
      IDENTIFIER id-alg-xmss-hashsig
      PARAMS ARE absent
      PUBLIC-KEYS { pk-XMSS-HashSig }
      SMIME-CAPS { IDENTIFIED BY id-alg-xmss-hashsig } }

   sa-XMSSMT-HashSig SIGNATURE-ALGORITHM ::= {
      IDENTIFIER id-alg-xmssmt-hashsig
      PARAMS ARE absent
      PUBLIC-KEYS { pk-XMSSMT-HashSig }
      SMIME-CAPS { IDENTIFIED BY id-alg-xmssmt-hashsig } }

   -- pk-HSS-LMS-HashSig is defined in [RFC9708]

   pk-XMSS-HashSig PUBLIC-KEY ::= {
      IDENTIFIER id-alg-xmss-hashsig
      -- KEY no ASN.1 wrapping --
      PARAMS ARE absent
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

   XMSS-HashSig-PublicKey ::= OCTET STRING

   pk-XMSSMT-HashSig PUBLIC-KEY ::= {
      IDENTIFIER id-alg-xmssmt-hashsig
      -- KEY no ASN.1 wrapping --
      PARAMS ARE absent
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

   XMSSMT-HashSig-PublicKey ::= OCTET STRING

   --
   -- Public Key (pk-) Algorithms
   --
   PublicKeys PUBLIC-KEY ::= {
      -- This expands PublicKeys from RFC 5912
      pk-HSS-LMS-HashSig |
      pk-XMSS-HashSig |
      pk-XMSSMT-HashSig,
      ...
   }

   --
   -- Signature Algorithms (sa-)
   --
   SignatureAlgs SIGNATURE-ALGORITHM ::= {
      -- This expands SignatureAlgorithms from RFC 5912
      sa-HSS-LMS-HashSig |
      sa-XMSS-HashSig |
      sa-XMSSMT-HashSig,
      ...
   }

   END

10. Security Considerations 💀

this section is SERIOUS, bestie 😭 the security requirements of [SP800208] MUST be taken into account 🫶

stateful HBS private keys can only generate a limited number of signatures, so a user needs to know the total number of signatures they plan to generate in their use case 🙈 otherwise they risk exhausting the number of OTS keys in their private key 💀

for stateful HBS schemes, correct state management is crucial 🔥 if an attacker got signatures for two different messages made with the same OTS key, it would become computationally feasible for them to create forgeries [BH16] 😭 as noted in [MCGREW] and [ETSI-TR-103-692], you have to be extremely careful so an OTS key doesn't get reused by accident 🚨 this is a new requirement that most developers won't be familiar with, so it needs careful handling 💖

there are a few strategies for correct state management:

Keep a record of all signatures generated by a key pair associated with a stateful HBS instance, for example by logging the OTS key indexes as signatures are generated. This record may be stored outside the device used to generate the signature. Check the record to prevent OTS key reuse before a new signature is released. If OTS key reuse is detected, freeze all new signature generation by the private key, re-audit previously released signatures (possibly revoking the private key if previously released signatures showed OTS key reuse), and perform a post-failure audit.
Use a stateful HBS instance only for a moderate number of signatures, so it's always practical to keep a consistent record and be able to unambiguously trace back all generated signatures. 🧚
Apply the state reservation strategy described in Section 5 of [MCGREW], where upcoming states are reserved in advance by the signer. This way, the number of state synchronizations between nonvolatile and volatile memory is reduced. 👑

11. Backup and Restore Management 💾✨

Okay bestie, certificate authorities have really high standards 💅. They need signature generation to be available the whole time a signing key pair is valid, no exceptions 😭.

Some usual backup and restore moves when you're using a stateless signature scheme (like SLH-DSA) are:

duplicating your private keying material and running redundant signing devices 🔁
storing and protecting a copy of the private keying material, so you can set up a new signing device if something goes wrong technically 🛟

Stateful HBS schemes are a whole different vibe 🙈. Those straightforward backup and restore strategies will lead to OTS reuse with high probability, because correct state management is not guaranteed. Strategies for keeping things available and keeping the state correct are covered in Section 7 of [SP800208] and [S-HBS] 📚.

12. IANA Considerations 🗂️

IANA registered the following OID for the ASN.1 module (see Section 9) in the "SMI Security for PKIX Module Identifier" (1.3.6.1.5.5.7.0) registry. Iconic registration, honestly 👑:

          +=========+========================+============+
          | Decimal | Description            | References |
          +=========+========================+============+
          | 114     | id-mod-pkix1-shbs-2024 | RFC 9802   |
          +---------+------------------------+------------+

                               Table 1

IANA also registered the following entries in the "SMI Security for PKIX Algorithms" (1.3.6.1.5.5.7.6) registry [SMI-PKIX] 🦋:

          +=========+=======================+============+
          | Decimal | Description           | References |
          +=========+=======================+============+
          | 34      | id-alg-xmss-hashsig   | RFC 9802   |
          +---------+-----------------------+------------+
          | 35      | id-alg-xmssmt-hashsig | RFC 9802   |
          +---------+-----------------------+------------+

                              Table 2

13. References 📖🎀

13.1. Normative References 💜

[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/info/rfc2119.

[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, https://www.rfc-editor.org/info/rfc5280.

[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, DOI 10.17487/RFC5912, June 2010, https://www.rfc-editor.org/info/rfc5912.

[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/info/rfc8174.

[RFC8391] Huelsing, A., Butin, D., Gazdag, S., Rijneveld, J., and A. Mohaisen, "XMSS: eXtended Merkle Signature Scheme", RFC 8391, DOI 10.17487/RFC8391, May 2018, https://www.rfc-editor.org/info/rfc8391.

[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/info/rfc8554.

[RFC9708] Housley, R., "Use of the HSS/LMS Hash-Based Signature Algorithm in the Cryptographic Message Syntax (CMS)", RFC 9708, DOI 10.17487/RFC9708, January 2025, https://www.rfc-editor.org/info/rfc9708.

[SP800208] Cooper, D., Apon, D., Dang, Q., Davidson, M., Dworkin, M., and C. Miller, "Recommendation for Stateful Hash-Based Signature Schemes", NIST SP 800-208, DOI 10.6028/nist.sp.800-208, 29 October 2020, https://doi.org/10.6028/NIST.SP.800-208.

[X680] ITU-T, "Information technology - Abstract Syntax Notation One (ASN.1): Specification of basic notation", ITU-T Recommendation X.680, ISO/IEC 8824-1:2021, February 2021, https://www.itu.int/rec/T-REC-X.680.

[X690] ITU-T, "Information technology: ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1:2021, February 2021, https://www.itu.int/rec/T-REC-X.690.

13.2. Informative References 🌸

[ANSSI] Agence nationale de la sécurité des systèmes d'information (ANSSI), "ANSSI views on the Post-Quantum Cryptography transition (2023 follow up)", 21 December 2023, https://cyber.gouv.fr/sites/default/files/document/follow_up_position_paper_on_post_quantum_cryptography.pdf.

[BH16] Bruinderink, L. and S. Hülsing, "Oops, I did it again - Security of One-Time Signatures under Two-Message Attacks.", Cryptology ePrint Archive, Paper 2016/1042, 2016, https://eprint.iacr.org/2016/1042.

[BSI] Bundesamt für Sicherheit in der Informationstechnik (BSI), "Quantum-safe cryptography - fundamentals, current developments and recommendations", 18 May 2022, https://www.bsi.bund.de/SharedDocs/Downloads/EN/BSI/Publications/Brochure/quantum-safe-cryptography.pdf.

[CNSA2.0] National Security Agency (NSA), "The Commercial National Security Algorithm Suite 2.0 and Quantum Computing FAQ", 7 September 2022, https://media.defense.gov/2022/Sep/07/2003071836/-1/-1/0/CSI_CNSA_2.0_FAQ_.PDF.

[ETSI-TR-103-692] European Telecommunications Standards Institute (ETSI), "CYBER; State management for stateful authentication mechanisms", ETSI TR 103 692 v1.1.1, November 2021, https://www.etsi.org/deliver/etsi_tr/103600_103699/103692/01.01.01_60/tr_103692v010101p.pdf.

[IANA-LMS] IANA, "Leighton-Micali Signatures (LMS)", https://www.iana.org/assignments/leighton-micali-signatures/.

[IANA-XMSS] IANA, "XMSS: Extended Hash-Based Signatures", https://iana.org/assignments/xmss-extended-hash-based-signatures/.

[MCGREW] McGrew, D., Kampanakis, P., Fluhrer, S., Gazdag, S., Butin, D., and J. Buchmann, "State Management for Hash-Based Signatures", Cryptology ePrint Archive, Paper 2016/357, 2 November 2016, https://eprint.iacr.org/2016/357.

[RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April 2002, https://www.rfc-editor.org/info/rfc3279.

[RFC3647] Chokhani, S., Ford, W., Sabett, R., Merrill, C., and S. Wu, "Internet X.509 Public Key Infrastructure Certificate Policy and Certification Practices Framework", RFC 3647, DOI 10.17487/RFC3647, November 2003, https://www.rfc-editor.org/info/rfc3647.

[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, https://www.rfc-editor.org/info/rfc4949.

[RFC8410] Josefsson, S. and J. Schaad, "Algorithm Identifiers for Ed25519, Ed448, X25519, and X448 for Use in the Internet X.509 Public Key Infrastructure", RFC 8410, DOI 10.17487/RFC8410, August 2018, https://www.rfc-editor.org/info/rfc8410.

[RFC8411] Schaad, J. and R. Andrews, "IANA Registration for the Cryptographic Algorithm Object Identifier Range", RFC 8411, DOI 10.17487/RFC8411, August 2018, https://www.rfc-editor.org/info/rfc8411.

[S-HBS] Wiggers, T., Bashiri, K., Kölbl, S., Goodman, J., and S. Kousidis, "Hash-based Signatures: State and Backup Management", Work in Progress, Internet-Draft, draft-wiggers-hbs-state-02, 1 April 2025, https://datatracker.ietf.org/doc/html/draft-wiggers-hbs-state-02.

[SMI-PKIX] IANA, "SMI Security for PKIX Algorithms", https://www.iana.org/assignments/smi-numbers.

Appendix A. HSS X.509 v3 Certificate Example ✨

okay bestie, this appendix shows a self-signed X.509 v3 certificate using HSS 🦋 the decoded view comes first, then the PEM version 💜

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            e8:91:d6:06:91:4f:ce:f3
        Signature Algorithm: hss
        Issuer: C = US, ST = VA, L = Herndon, O = Bogus CA
        Validity
            Not Before: May 14 08:58:11 2024 GMT
            Not After : May 14 08:58:11 2034 GMT
        Subject: C = US, ST = VA, L = Herndon, O = Bogus CA
        Subject Public Key Info:
            Public Key Algorithm: hss
                hss public key:
                PQ key material:
                    00:00:00:01:00:00:00:05:00:00:00:04:c0:96:12:
                    8b:ea:38:30:78:eb:f6:fb:43:d7:7f:9f:9e:81:39:
                    e2:7c:b9:34:4e:6e:53:19:f0:ee:68:75:85:83:d3:
                    2b:e9:7b:14:46:9e:4e:c5:e3:5a:18:0b:30:e5:13
        X509v3 extensions:
            X509v3 Subject Key Identifier:
                58:15:AB:F4:CF:03:69:02:60:7A:57:4D:C5:D5:B3:72:
                8A:19:21:68
            X509v3 Authority Key Identifier:
                58:15:AB:F4:CF:03:69:02:60:7A:57:4D:C5:D5:B3:72:
                8A:19:21:68
            X509v3 Basic Constraints: critical
                CA:TRUE
            X509v3 Key Usage: critical
                Certificate Sign, CRL Sign
    Signature Algorithm: hss
    Signature Value:
        00:00:00:00:00:00:00:00:00:00:00:04:9c:37:52:ff:b9:d7:
        df:f5:5b:01:ba:50:c2:50:cc:6f:f3:b1:73:df:0c:2a:ea:b3:
        ed:96:1e:ce:e7:58:05:da:8d:a7:77:21:42:32:d9:f9:4a:4d:
        f7:2b:18:2a:1c:5c:69:03:f3:1c:9c:95:6d:31:9a:c9:ca:84:
        4d:ae:b3:8b:c3:71:ac:3f:87:51:be:38:b4:bf:d9:dc:90:1f:
        1e:54:bd:f9:1a:65:70:d4:46:b6:ad:4d:6d:16:b9:fb:29:f4:
        e3:86:42:4a:3f:a4:8f:01:84:9b:44:0b:23:22:9c:97:6d:d5:
        b9:26:39:11:ab:46:82:bd:10:6c:b4:7a:64:ed:c7:40:b0:33:
        f0:b5:81:1c:b4:41:54:9c:30:d9:d2:93:ba:48:8c:4f:d0:25:
        41:60:7b:90:5e:12:20:b7:30:16:16:1e:b7:ee:d8:4b:ee:ed:
        3c:70:fc:ff:36:18:aa:24:23:87:91:65:a8:95:2d:b6:1c:d1:
        02:7b:70:81:8a:18:17:c0:45:62:fe:47:a1:3e:69:54:31:67:
        58:9a:e1:e3:c9:8d:ee:1e:2a:d1:46:75:e9:e4:90:67:01:57:
        92:54:db:b4:ea:de:8b:e7:eb:fc:27:80:9b:d5:da:e0:8e:b0:
        b3:08:ca:6f:a1:1c:f4:40:65:b0:f6:f8:c9:a7:97:04:c8:7c:
        9e:56:ec:2f:4b:cd:45:8b:d7:e6:a7:50:c7:e6:21:2c:17:31:
        23:11:7a:ae:9a:b5:84:5f:e6:5c:82:99:a8:3a:a9:91:87:9a:
        24:5c:83:01:91:7c:fc:cd:be:2e:92:50:fb:12:11:96:08:0d:
        c9:24:0d:bb:6f:fb:59:05:af:7f:96:bc:a3:f4:58:e2:fa:0a:
        4a:f2:4c:f7:b3:1b:81:dd:4a:41:a0:b1:dd:52:4c:bb:6d:c0:
        a8:d9:bb:29:c8:fc:e3:7e:f8:6a:e5:5e:c4:e4:e8:7c:0b:00:
        87:15:75:a2:06:50:97:c6:1f:14:52:79:04:a8:9c:ec:b1:c7:
        6a:46:33:98:b8:63:f7:a7:2c:d4:62:78:94:1c:5d:9d:4f:a6:
        0a:ae:39:50:85:b2:09:8d:62:c9:4c:11:9f:0c:91:a5:ac:2d:
        11:bd:71:b6:0c:ea:34:98:53:fc:2e:cc:7b:a4:9c:2e:7a:a4:
        8d:e2:e8:8c:01:a9:9c:3e:b5:34:77:33:82:01:d4:ef:72:04:
        d6:5b:e5:f6:2c:1b:ae:86:c4:73:02:44:85:d6:f7:ac:a3:e8:
        f6:a9:b5:5c:6d:46:88:da:55:b8:2b:7a:4c:0c:9a:e7:cd:5d:
        62:8a:ca:c8:96:ce:8d:71:7b:d2:c1:0d:9a:35:55:2b:84:3e:
        0e:a5:fa:d6:a0:76:8e:23:b3:df:c9:3b:4f:68:56:1e:e9:3c:
        79:5b:d3:25:54:11:ad:a6:ac:58:11:49:8f:4d:c4:c1:39:99:
        76:3a:a6:d1:2f:57:ad:bf:7c:9d:57:cc:37:0d:29:84:29:7b:
        cb:46:85:c3:81:c5:33:9a:65:c3:2f:01:48:ca:44:6c:f1:84:
        3d:d0:49:c2:c1:05:db:77:4c:b9:72:3d:6f:ce:69:f2:91:c6:
        15:25:8f:da:38:7e:ef:5b:3e:5f:35:ab:a6:78:16:28:42:c1:
        2c:2f:9e:11:53:2c:bd:c4:24:7b:e9:c4:ce:3d:d6:41:c7:5d:
        92:91:c3:37:cb:72:44:d7:0d:70:85:13:0b:ac:b3:0f:b0:e5:
        e3:2e:48:b9:9c:b8:d7:3e:7c:50:69:03:7a:5f:ae:f8:6c:09:
        61:97:6b:ce:cd:e5:f0:55:fe:05:f8:97:1d:9e:81:65:f5:ff:
        9a:7a:8c:96:d8:f8:cf:d8:dc:55:ce:67:7a:00:6b:fd:bb:3f:
        1b:3d:65:94:c1:5a:b6:a0:8e:be:a4:be:26:90:5f:1f:06:d4:
        ea:3f:a6:97:40:8e:bf:18:5c:92:0f:15:e3:05:4a:14:51:1e:
        23:81:ef:cf:f7:a8:88:75:f8:2d:28:37:26:87:27:63:5c:01:
        53:0e:5e:53:d2:a7:18:eb:2f:c0:82:49:05:b0:4d:33:6f:94:
        10:91:77:f8:90:9e:ca:fe:bb:3d:c4:42:d6:89:84:98:42:f4:
        24:b3:b4:db:5e:2b:66:a9:ff:6c:18:d4:79:f8:72:73:53:9b:
        02:ed:04:73:77:a4:68:cf:4b:be:4b:16:50:62:87:f9:49:99:
        e3:a1:0c:42:92:bc:a9:e3:2d:22:82:35:7f:71:15:88:70:6a:
        01:ab:44:64:ad:e5:52:d4:97:ee:bb:44:7b:6e:08:7f:dd:94:
        fd:c9:1c:6b:59:d1:92:51:29:03:ce:ec:bf:41:a5:14:69:54:
        3a:b4:39:d9:44:5d:f1:b2:f4:5c:6b:9f:c9:5f:bb:fc:c8:c7:
        a3:8b:e1:ec:e2:d0:69:5a:40:1c:9c:9d:8a:3d:77:3b:c1:5d:
        c0:72:61:4b:37:c5:96:8c:6d:8b:f8:56:da:ac:3e:3c:72:09:
        ce:f6:c3:fe:5d:cf:37:d9:68:cd:a7:dd:f7:96:63:da:8c:1d:
        df:b8:32:cf:eb:97:11:83:fe:6b:aa:b9:e2:4b:b2:ea:62:73:
        c3:1c:e9:40:90:56:4f:12:c3:ba:f4:2b:d9:1c:50:cc:e0:51:
        d8:eb:bf:67:28:0c:2d:13:8d:b3:6f:13:6a:1d:a7:54:20:ba:
        82:5b:b8:e5:1f:89:f1:67:26:c1:dc:1b:60:57:ed:a6:2c:f2:
        17:01:7f:a5:e7:5c:64:c9:3c:08:f2:cf:48:ec:88:84:ef:03:
        c2:f5:eb:05:31:7d:fe:7f:3c:71:41:28:17:64:5f:b9:ec:54:
        79:d0:b3:98:fb:84:9c:36:8b:43:0b:d4:c9:ec:09:4a:70:13:
        62:f2:36:c8:b4:75:cc:2a:77:08:a0:9d:ef:19:d6:88:dc:e2:
        b2:4e:40:61:71:cb:c7:c3:de:16:6f:49:7f:5e:d5:17:00:00:
        00:05:79:47:12:9f:ce:eb:1d:a8:fd:0d:b0:18:44:6a:ef:54:
        28:46:e4:19:f6:2d:3e:74:bb:9d:36:0a:ae:67:4a:28:7a:1b:
        80:39:a0:08:2a:28:a0:ec:55:ee:55:aa:a1:cc:94:d4:36:1a:
        b3:57:25:30:ad:2c:5e:63:ba:22:fc:aa:7a:59:64:f6:d8:03:
        20:28:71:f9:dc:09:fa:4c:81:b9:64:1b:ad:ea:cb:db:18:17:
        5d:d8:98:bd:d2:8d:c5:04:7c:5b:92:9a:89:f6:bc:d6:55:c7:
        08:5d:3c:58:8e:18:ac:6f:88:a8:d7:9e:d4:ee:5d:f5:21:4e:
        a5:8b:19:5f:e3:f4:66:f9:25:4d:f9:c6:60:62:31:72:5c:34:
        34:67:1a:a7:6a:7d:54:a3:d8:9b:1f:5b:f8:08:41:79:5b:43

and now the PEM version 🎀

Appendix B. XMSS X.509 v3 Certificate Example ✨

this one's the XMSS version 🌈 it shows a self-signed X.509 v3 certificate using XMSS 🧚

Certificate: Data: Version: 3 (0x2) Serial Number: 54:7e:64:70:29:9e:03:c5:7a:a5:5c:78:d1:27:87:8c: 54:35:17:5d Signature Algorithm: xmss Issuer: C = FR, L = Paris, O = Bogus XMSS CA Validity Not Before: Jul 10 08:27:24 2024 GMT Not After : Jul 8 08:27:24 2034 GMT Subject: C = FR, L = Paris, O = Bogus XMSS CA Subject Public Key Info: Public Key Algorithm: xmss xmss public key: PQ key material: 00:00:00:01:2b:eb:bf:66:14:de:6f:96:5b:4d:2a: 50:00:7b:ad:5c:22:b0:13:79:72:02:14:a9:5f:fc: 96:e0:9b:78:8e:d6:be:8c:1c:70:3c:d8:dd:78:b2: 1a:14:47:be:1f:0d:74:72:3f:36:76:c2:cb:19:ad: 29:90:0b:82:de:9b:7f:df X509v3 extensions: X509v3 Subject Key Identifier: 62:CE:35:A5:47:77:FF:21:87:2E:BC:2D:27:E7:8E:F4: 35:6B:CF:D8 X509v3 Authority Key Identifier: 62:CE:35:A5:47:77:FF:21:87:2E:BC:2D:27:E7:8E:F4: 35:6B:CF:D8 X509v3 Basic Constraints: critical CA:TRUE X509v3 Key Usage: critical Certificate Sign, CRL Sign Signature Algorithm: xmss Signature Value: 00:00:00:00:e5:88:a8:b8:73:ad:4d:92:f8:5c:81:c5:8a:63: 57:6a:a7:3b:54:aa:b6:06:8a:d9:f1:c2:0b:c8:27:1e:4b:a2: cf:e2:da:44:ea:e8:f2:40:a8:b9:54:9c:49:36:12:24:df:74: ad:e5:29:ef:4f:da:88:0d:21:5d:3b:64:63:27:d0:84:b5:95: 7a:30:18:37:cd:34:17:dd:ac:9d:9e:48:db:74:07:79:84:21: 5a:f0:26:cd:21:64:7b:77:33:48:58:67:9b:2c:b2:85:6d:cc: ec:31:4b:2f:51:55:3a:85:e1:ca:04:15:ce:6e:47:39:f5:e9: 31:45:41:ed:71:c6:4f:96:f5:ae:64:6a:bd:72:d0:8c:17:02: 99:10:1d:14:34:ca:e5:47:e3:f7:66:96:96:11:d5:97:76:76: 83:f1:84:a5:b6:00:5e:3e:67:97:7a:32:dc:c8:eb:4c:29:46: 77:99:d6:da:45:e6:7b:8c:45:6d:b5:29:6b:fd:98:a2:89:8d: 0c:30:42:f5:0b:7c:97:c5:b1:1d:e2:da:67:a9:48:a4:9e:29: f4:60:3f:4d:1d:48:83:82:38:ef:fa:cb:1d:86:11:a1:15:94: fb:d5:ee:68:f9:44:b9:3d:54:70:f3:be:17:8d:d7:2e:85:2d: 5c:d0:a0:c5:99:52:cc:79:e7:1c:18:d9:6e:3d:0f:6c:05:51: 33:28:35:e2:02:59:5f:1f:ed:78:0a:c6:62:f0:7d:fe:73:96: 03:4c:b4:42:e3:00:c2:d7:cb:eb:51:10:c4:0c:64:b8:37:fe: 85:d0:8e:11:6d:a6:16:77:b1:1e:01:d9:1e:f3:10:9c:dd:01: bc:38:75:5e:8f:58:9e:5b:6c:7b:0a:41:08:59:35:a9:3a:83: 19:e0:7d:a1:f5:cf:a3:1c:4e:07:e1:ad:03:95:f2:d3:8b:79: 33:f8:52:22:53:1b:1e:32:9a:61:3f:c4:7c:9a:e8:d5:b5:28: f1:84:65:d5:c1:fc:4d:16:93:88:93:69:ca:fa:94:a0:95:4e: 23:ae:1e:60:e0:e8:b4:bf:ff:16:95:71:0f:31:74:bb:be:b8: 5a:eb:24:95:8b:95:28:13:cd:e3:a9:65:f7:f5:6e:9b:a9:a9: 7a:05:ce:ab:f0:54:62:d9:12:f8:a1:1a:68:df:af:15:8f:8a: df:67:27:c9:ed:bd:e1:81:a6:8d:9a:84:f3:91:36:d9:89:74: 8e:ef:84:dc:5c:03:1a:08:e4:d7:f0:72:fc:6d:8a:01:34:94: e5:ff:08:51:1b:80:5f:e7:07:d8:9f:25:e4:1d:c3:f8:e5:d0: 9c:50:cf:66:71:f9:cc:f7:c0:a7:d0:66:01:b7:17:a0:5f:66: 97:a4:ff:62:ac:1c:a0:63:0d:30:28:e9:90:d5:59:a4:48:d8: 07:87:02:4b:3f:68:23:a5:04:dc:b3:d7:45:f6:dc:b0:ec:c6: 90:a6:1c:a1:f8:7e:84:ba:63:7e:5a:64:14:78:58:f5:75:c0: f5:e1:1d:bd:49:57:c0:40:08:07:99:7f:43:2e:e2:25:d8:ed: a3:1a:e3:78:f1:78:af:02:49:54:36:59:8e:d3:72:a5:0b:52: 32:bd:17:a2:cf:e1:47:21:28:3d:ba:b6:24:d9:18:f9:44:73: 35:ed:29:a4:18:bc:ed:68:cd:4a:9a:34:cb:1a:2f:b3:5f:ba: 73:9b:18:ee:7a:a8:92:25:65:25:81:04:63:1c:22:2b:b8:ba: 81:21:bc:f9:9d:a8:78:98:75:bc:ed:4a:c6:b7:6f:c0:91:24: eb:1d:f9:5d:e0:e3:78:4e:05:f6:34:0f:7b:41:54:49:20:a2: 30:66:94:f1:da:c1:6c:3f:5e:10:92:92:a3:0c:7e:e8:8b:26: 11:1c:d7:68:c9:31:79:b3:a4:d5:63:00:68:c3:e3:86:2d:09: 92:4b:2d:63:7d:b8:03:a4:4c:60:b4:2c:12:d5:0b:9f:16:28: ea:88:2f:bb:1c:19:0b:0f:40:3d:67:e8:0b:fa:c6:e3:39:44: b2:bd:8a:3f:21:dd:aa:ec:a3:8c:48:dd:4c:99:43:86:d7:48: 81:6b:e5:b9:bb:59:9f:1c:0f:3f:11:f7:7c:4b:67:a8:95:c2: 7c:cb:3b:66:b0:79:a6:55:6f:6d:b0:29:8a:5e:7b:ee:30:68: f3:dd:41:29:91:f6:79:71:ae:8d:21:70:78:1d:5d:d2:f7:cf: e7:42:38:d1:8c:52:a6:a6:f6:b1:38:b1:2b:23:81:e1:1f:21: 6d:99:3f:10:eb:b1:a9:73:b8:3e:31:99:cc:dd:2b:df:58:27: db:0b:5a:29:99:8f:b1:9f:e9:31:42:d0:26:db:53:b7:7e:30: 41:95:c3:f0:07:83:bb:b0:63:b5:16:48:f2:a6:60:2f:32:5d: 22:a1:da:76:4e:37:26:53:0d:95:7b:2d:b9:05:2f:93:2b:d4: df:c1:02:5b:f7:a5:a2:4f:11:5c:80:f4:f0:bd:c7:ea:3c:db: 6f:e2:eb:6c:7f:c3:58:d9:31:77:4b:4d:f7:ce:bb:d6:c8:64: a3:01:d5:f9:a4:8d:e8:f0:ee:09:06:2c:0b:3c:ac:0a:57:d8: e4:81:79:ea:4a:bd:51:03:88:4c:d0:4c:0b:c4:0c:7e:2d:e7: df:1b:67:62:c0:d1:9c:ad:bb:d3:f0:75:dd:83:aa:70:99:2c: 19:78:3d:26:2b:47:6f:24:c1:60:02:1e:4b:75:04:91:1f:08: 1c:b3:79:a0:9b:db:fb:5d:3f:c7:e3:09:1f:41:3e:64:bb:ad: 19:3d:35:e1:a6:f4:69:0b:a2:04:37:42:95:c6:c7:e5:f4:56: 0e:67:5b:78:34:bb:07:f1:8f:e7:73:5b:87:d7:df:c9:2d:8d: 8c:42:76:87:15:85:4b:23:03:20:34:e1:1b:f6:0c:1e:84:53: d9:1b:4e:d9:31:43:38:3b:88:12:84:d8:2a:38:b1:ce:0f:c7: 07:d4:63:2d:97:89:1c:b3:44:99:eb:d4:df:32:74:be:0d:63: 11:22:fd:fa:8e:e2:0b:56:12:56:0c:46:16:ad:44:10:26:98: dc:cf:c9:95:67:3e:11:c1:76:fa:b8:12:ea:96:f6:d9:91:ac: bf:49:b9:1c:8e:15:05:53:ac:9e:04:d2:5b:b8:87:bf:81:50: f7:02:a4:c0:9c:18:0f:45:ac:7a:82:cf:46:15:42:40:09:32: 89:a5:ea:90:a5:99:68:f9:93:0c:7b:d6:7a:a8:e9:51:e2:90: 9e:b9:ed:21:db:d9:7e:de:dc:62:6b:44:6b:9f:81:c5:77:39: 8e:1d:78:30:de:dc:53:80:e0:c3:fa:fa:94:68:28:91:98:86: ff:86:04:a9:bd:58:7c:31:37:1f:db:9a:29:f3:c1:48:10:20: 71:5f:fc:35:13:eb:7b:12:e2:7d:1c:cc:97:fe:8f:5c:a2:dd: f6:d2:a3:b2:ea:51:b3:ef:b1:1e:79:0b:00:53:f4:f2:52:75: 5a:d7:17:c5:31:a0:54:4e:2b:28:2c:4f:6b:7a:27:3a:2c:04: da:b3:1d:04:4e:a4:4e:94:5c:a8:91:70:ab:c0:4b:75:9f:b3: 6a:a9:4e:8a:22:e9:7f:fd:ec:53:e7:6a:6d:32:0b:8b:ab:4c: e7:7d:72:ec:04:62:1c:1a:45:1e:33:8e:37:ae:6a:2f:c8:fb: f3:69:ed:11:01:f3:f4:57:e9:29:d5:3b:0c:9c:0c:c4:cb:c3: 38:5c:01:e7:d6:31:c3:d8:ce:24:d7:be:71:9b:c8:96:13:ca: 5c:5d:e4:92:40:af:86:a0:4b:ff:a7:55:39:70:fd:ac:0a:e1: 87:c7:01:4b:c3:41:36:c6:c6:33:8f:4f:25:4a:8d:70:92:ac: 7c:95:cc:49:a9:dc:d6:6a:67:52:a5:5b:7f:2f:bb:91:e3:be: d6:28:fc:22:d0:72:66:e8:09:73:a7:23:c6:a6:89:38:0b:e5: d0:b3:f1:40:38:9c:4d:17:96:11:17:44:ef:e3:94:51:91:4c: 5d:fe:d9:ed:c3:76:a0:2d:3b:dc:8d:b9:31:15:f6:75:58:74: 2f:57:b4:29:21:29:6d:5f:eb:06:71:0a:f4:db:ff:c6:2f:16: 73:a7:76:6b:d0:5b:a7:21:5c:fd:f0:11:e8:6f:9b:d0:c9:c9: fe:35:76:4a:4a:63:9b:ba:48:ac:af:4f:91:67:9c:5c:47:d8: e3:2d:03:12:5e:f1:cb:56:34:75:69:95:ad:68:96:6c:e7:4a: 91:72:fb:9b:ba:e8:92:56:fb:9a:5b:5d:3b:9d:d3:c5:c4:52: 42:1b:f9:4a:47:42:dd:77:49:da:2b:bd:d7:94:5f:7b:b8:64: b9:06:32:7c:ea:d1:36:f6:95:b8:57:41:1b:6e:66:31:2c:ee: 87:7a:5c:19:2f:d8:95:4a:16:93:48:f3:97:25:3d:24:61:1e: d0:63:37:ee:3a:c9:a3:46:c5:94:a0:7e:24:cc:7f:72:8d:14: 9e:3c:33:ec:cd:9a:dd:b5:08:90:98:19:95:85:38:ff:ff:d2: 1e:bf:a6:c4:97:13:2b:3d:47:e9:57:59:d3:7d:99:01:6e:53: 4d:c0:82:97:fb:89:d6:7c:b7:23:0e:7d:6e:23:88:53:06:8f: 16:ff:40:0a:1b:cd:d5:1e:91:01:3e:77:3a:5f:c1:57:3a:7b: c6:d5:51:d7:e2:ec:89:12:6b:9d:03:e4:9d:bb:7d:4e:02:bf: 67:8d:03:ca:90:56:f0:9a:97:4b:02:2d:4c:31:89:82:76:97: fe:2f:d5:0a:3d:ea:0d:38:6c:30:75:5f:ae:91:53:d7:45:64: df:ba:0b:22:80:44:85:6d:0e:5c:29:7f:82:9e:54:a3:7a:95: be:96:79:66:9d:5b:a2:d6:2e:47:c6:99:7d:2b:32:dc:f2:b6: 02:91:6d:63:d4:93:45:60:c4:42:71:10:9e:fb:90:2f:e6:75: 71:ce:78:70:c1:da:ff:e1:47:fe:79:2b:8e:9a:81:bf:dd:02: e3:78:39:71:17:b3:23:14:11:9d:29:8e:21:a1:98:b0:ac:03: 5a:6c:9e:62:64:ef:4f:03:ca:37:a6:ed:e4:78:d5:0d:99:29: f5:5c:61:e6:48:cb:97:0e:5e:f9:2c:f6:b6:c7:7c:0c:a4:f7: 1a:f7:67:b5:5c:03:bf:bf:7a:e2:4d:a2:9b:5d:5d:5f:51:d0: d6:52:8f:2a:20:68:08:bb:f0:9c:05:0e:ef:b3:49:0c:2a:1d: 8f:f9:03:b7:61:09:71:88:7d:e2:8c:e4:b8:ac:98:1b:c3:80: 55:a1:6b:dd:13:a2:29:4f:93:93:d3:d5:01:31:3f:7b:39:0e: 3a:57:6c:eb:5c:6a:5f:1b:ad:97:bd:97:23:18:91:05:0e:2b: b4:b1:11:ee:f8:58:c7:08:d0:de:a2:3e:ba:54:8d:3d:63:da: 91:50:3a:24:8d:19:18:23:2e:cf:30:8d:5d:e3:e7:02:93:fa: c8:f8:ea:05:e6:eb:06:80:90:4d:15:58:3d:26:98:13:4b:b0: ac:dd:90:2e:d0:e1:eb:71:32:83:5d:2a:a9:b9:b5:24:fc:e9: ec:18:ca:c9:a1:05:59:3e:fa:af:ed:4e:86:b1:fe:40:47:9b: 42:77:af:9c:2b:a0:e2:3e:fd:51:ab:02:77:e8:f1:39:45:aa: 54:b6:14:d4:14:20:fc:36:81:e6:04:98:8a:a0:c0:8a:cf:ae: f6:b5:dc:b7:eb:26:86:d3:cf:1c:38:65:54:04:b1:b5:09:48: f5:2d:07:ba:f8:eb:49:bd:d9:b1:54:ea:ac:c2:0d:20:10:79: c1:cb:e9:dc:2d:ff:55:50:4f:f6:05:02:78:31:33:6f:15:7e: 24:5a:66:23:70:b3:b2:0c:17:39:ce:15:38:c5:ff:60:16:38: 60:74:72:c9:70:d8:59:b7:80:7f:da:f6:67:3f:d0:ba:be:1b: a1:87:da:92:2d:a3:6c:99:29:57:aa:cb:d1:8d:66:f1:2d:c9: 56:60:24:56:4b:19:9f:f5:65:84:89:86:7d:4d:8b:f8:5b:60: dd:af:2d:66:76:6c:66:d9:c6:f5:39:25:6c:e5:7b:43:97:64: 5c:c5:20:1e:3d:b5:dc:92:b2:9c:d8:1b:1b:e0:bc:44:7b:9c: 95:c5:53:48:91:b2:a5:46:16:bf:50:af:a5:44:cc:54:78:3f: ed:20:d8:2e:0b:41:3d:f1:04:9d:df:3c:4a:d7:81:04:ff:8c: b7:79:f8:51:8d:b7:2e:ac:2c:54:e6:fc:43:76:8e:f9:be:8c: b8:5c:ad:c4:13:af:b0:6e:3b:d1:82:57:1e:f5:52:84:ca:cc: d2:68:f3:2d:04:ff:27:0a:e6:a2:fa:c0:a9:97:d6:64:45:18: 5c:6f:9e:c1:64:22:66:db:56:02:c3:a8:57:fc:87:1b:5c:43: 15:8e:58:fc:f2:00:0b:4f:6a:4b:a0:5c:da:f2:e5:1b:82:4a: 6b:ef:db:63:d7:7d:93:1d:2f:20:78:37:17:22:82:cd:6b:c1: 83:61:05:81:99:0c:25:29:d6:5f:22:bc:06:67:7d:67

Appendix C. XMSS^MT X.509 v3 Certificate Example 🎀

okay bestie, this is where we get to the XMSS^MT version 💅✨ the last cert was XMSS, and now we're doing the multi-tree flavour (XMSS^MT) 🌈

this section shows a self-signed X.509 v3 certificate using XMSS^MT 🫶 self-signed means the cert is signed by the same key it's certifying, so it's kind of its own hype person 💖 and yes, it's giving main character energy 👑🔥

The certificate example keeps going, and the signature bytes are the star of the show 💅✨

   Certificate:
       Data:
           Version: 3 (0x2)
           Serial Number:
               5c:22:ad:8a:06:51:9e:67:02:6a:2d:43:3e:8b:c7:23:
               43:77:80:c8
           Signature Algorithm: xmssmt
           Issuer: C = FR, L = Paris, O = Bogus XMSSMT CA
           Validity
               Not Before: Jul 10 08:28:04 2024 GMT
               Not After : Jul  8 08:28:04 2034 GMT
           Subject: C = FR, L = Paris, O = Bogus XMSSMT CA
           Subject Public Key Info:
               Public Key Algorithm: xmssmt
                   xmssmt public key:
                   PQ key material:
                       00:00:00:01:4b:a7:89:11:6f:fc:1d:fb:d3:e7:71:
                       73:b8:a2:48:ef:53:b9:9d:1f:c6:8a:7c:be:4f:8a:
                       29:fa:41:fd:bd:da:20:7f:f6:3b:b0:c5:b8:a7:c2:
                       f2:5a:f2:26:14:eb:36:f0:26:2f:87:74:fb:0e:d5:
                       7e:17:a0:d1:4d:b6:cf:51
           X509v3 extensions:
               X509v3 Subject Key Identifier:
                   7C:7D:59:B8:95:61:D5:03:6A:1E:3D:F1:24:AB:1D:ED:
                   04:CD:DB:5F
               X509v3 Authority Key Identifier:
                   7C:7D:59:B8:95:61:D5:03:6A:1E:3D:F1:24:AB:1D:ED:
                   04:CD:DB:5F
               X509v3 Basic Constraints: critical
                   CA:TRUE
               X509v3 Key Usage: critical
                   Certificate Sign, CRL Sign
       Signature Algorithm: xmssmt
       Signature Value:
           00:00:00:57:c4:98:89:ff:d9:0a:8e:6e:6f:16:95:8c:ec:35:
           42:21:c2:ca:56:ed:f8:81:f1:b2:4f:2b:6d:73:f4:37:55:fc:
           f4:4e:15:eb:6b:90:de:34:fe:d6:96:70:94:8d:c1:e7:4a:32:
           49:30:3a:40:a4:67:d2:fb:da:f8:d8:a1:7a:48:22:1c:e3:98:
           bc:d0:68:85:29:c9:e5:f7:5c:56:d8:9c:80:be:68:ed:11:eb:
           39:0f:ef:cb:09:b2:28:30:a6:2b:05:bc:de:11:22:be:c4:dc:
           08:9a:3d:b4:49:37:1f:54:5e:5f:2d:93:62:b0:95:c5:5d:23:
           92:f3:55:40:78:19:00:56:9e:a2:f1:0e:4b:ae:75:d6:92:09:
           b1:79:ec:c9:18:67:19:09:86:83:74:5d:0a:06:ab:da:f0:af:
           02:97:4d:d7:73:06:8b:a2:84:c7:09:af:dd:8b:15:39:e4:30:
           9f:c9:00:25:a8:33:4d:de:e8:25:b6:35:0b:51:bf:7a:34:a7:
           e8:84:e8:fa:39:5b:aa:37:6e:95:89:ac:26:4a:4e:ca:be:29:
           08:4b:3c:28:a7:85:6a:ad:5a:d2:93:eb:12:e1:9a:87:1c:40:
           3b:cf:15:6c:43:4e:88:21:54:52:7e:0d:6d:17:29:8d:15:6f:
           ef:42:5a:a9:25:d0:97:80:61:31:22:a4:9f:25:17:51:ad:0b:
           a1:cb:93:b4:f5:a6:b0:22:1b:6d:50:64:2a:48:bd:05:16:88:
           00:e3:7b:56:d0:03:b3:7a:2d:6a:0b:f3:de:a2:8c:6e:81:80:
           2c:8f:e9:d8:78:ed:5b:99:c9:13:d1:b6:eb:78:c3:40:2b:a1:
           7a:84:0a:ba:12:87:5e:1d:38:24:22:8f:c0:a3:65:1c:1c:ce:
           2d:8e:e5:2f:1f:be:93:5c:fe:1c:cd:a8:9d:7e:7e:cf:18:e2:
           9c:c5:54:dc:62:61:74:23:55:64:66:21:96:4c:a7:2e:8a:94:
           a6:35:10:a5:e8:5e:6e:91:ac:a8:cb:ed:51:2b:66:45:03:f5:
           87:ed:4d:8c:4e:6d:54:80:a1:33:8a:84:9d:23:31:90:c6:05:
           11:a7:9d:bd:51:0a:73:47:bc:08:49:11:b3:98:ff:01:14:69:
           d7:c0:a0:0c:55:e4:5e:e2:fa:84:ac:27:b3:85:2c:99:71:52:
           9c:33:f8:9d:8c:d2:13:bc:6e:18:79:15:a7:02:ee:15:eb:27:
           d8:af:24:38:02:9c:ca:30:f3:e2:30:41:2f:62:a2:2c:a5:81:
           1b:71:6d:b1:94:bd:c6:3d:9e:5e:51:45:de:5b:f4:d7:e6:35:
           e7:d8:7c:d5:98:ec:7e:0e:f8:9d:c1:a7:7b:b3:65:b1:a1:4b:
           2d:ec:d9:12:45:6b:1f:0b:1c:6b:3b:0a:66:76:39:f4:cc:9b:
           e1:b7:17:f7:53:fc:c3:a6:18:f7:2e:45:52:b1:18:99:75:d1:
           69:bb:77:c8:1a:84:5f:06:b5:8b:cb:02:b0:b2:0f:bf:17:18:
           65:3d:a7:72:5b:71:9f:92:7e:3a:df:84:cc:65:5c:c4:5b:70:
           fd:cc:38:9e:12:6e:f9:ff:1f:02:fc:ca:f5:68:86:fc:ca:71:
           f1:3d:7b:32:b4:d4:c3:a2:20:16:3f:12:07:71:95:3b:d4:b1:
           1e:fc:8c:1f:34:8c:c8:ab:8c:bb:75:93:c1:1a:d2:85:3e:9a:
           e6:04:86:88:de:27:46:ca:f3:f7:f3:8e:54:18:ea:aa:ae:14:
           02:b1:4a:6a:e0:24:77:40:28:8d:37:27:9c:87:6a:81:09:d2:
           01:4d:20:7f:de:84:a8:80:8c:8e:63:82:be:66:df:87:30:5c:
           b8:71:0a:e9:91:68:71:6e:97:97:f0:27:4e:fa:ae:6a:85:ac:
           80:cd:38:48:49:c1:2b:9d:db:54:c5:f0:bf:fa:06:e8:96:3a:
           c0:95:f0:88:bd:8e:80:78:3d:dc:ad:5d:0a:56:dd:c7:80:9f:
           fc:64:58:4d:6d:27:f6:d7:1a:8c:b2:1c:09:ea:7d:4f:74:99:
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okay bestie, quick heads up 🫶 this chunk is just a raw hex dump with no prose, section headings, or BCP 14 keywords, so there's nothing to rewrite in voice without making stuff up 😭 I've kept every byte exactly as given, verbatim, so nothing gets lost. If you paste the actual text for this part, I'll slay it in full 💅✨

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           21:78:6e:f4:7a:e2:04:e5:0e:21:52:bf:04:cd:0c:69:5d:d7:
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           8f:a9:31:0d:0f:9f:f4:2c:a1:3d:4f:b2:51:92:68:f0:ec:d8:
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           9e:56:07:cf:8f:98:9a:da:d7:db:7f:c7:d0:3a:0a:14:cd:5a:
           66:0c:eb:02:76:a0:d4:56:e6:e8:be:a1:f0:c7:23:b3:4f:86:
           90:1a:5a:16:8e:07:0d:24:d1:ee:03:98:9f

Acknowledgments ✨

Okay bestie, the cert is basically the ultimate receipt for everything we just walked through 🧾💖 Here's the whole thing, untouched:

Thanks to Russ Housley, Panos Kampanakis, Michael StJohns, and Corey Bonnell for their helpful suggestions and reviews. 🫶 Big thanks to them, the whole squad really showed up!

This document uses a lot of text from similar documents, including [SP800208], [RFC3279] and [RFC8410], as well as [RFC9708]. Thanks goes to the authors of those documents. 🙏 As [RFC8411] puts it: "Copying always makes things easier and less error prone" 💅 Honestly, iconic energy.

Authors' Addresses 🦋

Daniel Van Geest CryptoNext Security Email: daniel.vangeest@cryptonext-security.com

Kaveh Bashiri BSI Email: kaveh.bashiri.ietf@gmail.com

Scott Fluhrer Cisco Systems Email: sfluhrer@cisco.com

Stefan-Lukas Gazdag genua GmbH Email: ietf@gazdag.de

Stavros Kousidis BSI Email: kousidis.ietf@gmail.com

And that's a wrap on RFC 9802, bestie! 🌈👑 The whole crew of authors slayed this, periodt 💖

📦 where this page comes from

ietf: rfc9802 2025-06
💖 girlified by claude-haiku-5-5 on 2026-10-19: a language model's rewrite of the original, under its terms