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Internet X.509 Public Key Infrastructure: Algorithm Identifiers for HSS and XMSS
draft-ietf-lamps-x509-shbs-04

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Authors Daniel Van Geest , Kaveh Bashiri , Scott Fluhrer , Stefan-Lukas Gazdag , Stavros Kousidis
Last updated 2024-09-19 (Latest revision 2024-07-25)
Replaces draft-gazdag-x509-shbs
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draft-ietf-lamps-x509-shbs-04
LAMPS - Limited Additional Mechanisms for PKIX and SMIME    D. Van Geest
Internet-Draft                                       CryptoNext Security
Intended status: Standards Track                              K. Bashiri
Expires: 26 January 2025                                             BSI
                                                              S. Fluhrer
                                                           Cisco Systems
                                                               S. Gazdag
                                                              genua GmbH
                                                             S. Kousidis
                                                                     BSI
                                                            25 July 2024

Internet X.509 Public Key Infrastructure: Algorithm Identifiers for HSS
                                and XMSS
                     draft-ietf-lamps-x509-shbs-04

Abstract

   This document specifies algorithm identifiers and ASN.1 encoding
   formats for the Stateful Hash-Based Signature Schemes (S-HBS)
   Hierarchical Signature System (HSS), eXtended Merkle Signature Scheme
   (XMSS), and XMSS^MT, a multi-tree variant of XMSS.  This
   specification applies to the Internet X.509 Public Key infrastructure
   (PKI) when those digital signatures are used in Internet X.509
   certificates and certificate revocation lists.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-lamps-x509-shbs/.

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

   Source for this draft and an issue tracker can be found at
   https://github.com/x509-hbs/draft-x509-shbs.

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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Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Use Cases of S-HBS in X.509 . . . . . . . . . . . . . . . . .   3
   4.  Algorithm Identifiers and Parameters  . . . . . . . . . . . .   4
     4.1.  HSS Algorithm Identifier  . . . . . . . . . . . . . . . .   4
     4.2.  XMSS Algorithm Identifier . . . . . . . . . . . . . . . .   5
     4.3.  XMSS^MT Algorithm Identifier  . . . . . . . . . . . . . .   5
   5.  Public Key Identifiers  . . . . . . . . . . . . . . . . . . .   5
     5.1.  HSS Public Keys . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  XMSS Public Keys  . . . . . . . . . . . . . . . . . . . .   6
     5.3.  XMSS^MT Public Keys . . . . . . . . . . . . . . . . . . .   7
   6.  Key Usage Bits  . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Signature Algorithms  . . . . . . . . . . . . . . . . . . . .   8
     7.1.  HSS Signature Algorithm . . . . . . . . . . . . . . . . .   8
     7.2.  XMSS Signature Algorithm  . . . . . . . . . . . . . . . .   8
     7.3.  XMSS^MT Signature Algorithm . . . . . . . . . . . . . . .   9
   8.  Key Generation  . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . . . . . .   9
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  11
   11. Backup and Restore Management . . . . . . . . . . . . . . . .  12

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   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     13.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Appendix A.  HSS X.509 v3 Certificate Example . . . . . . . . . .  15
   Appendix B.  XMSS X.509 v3 Certificate Example  . . . . . . . . .  18
   Appendix C.  XMSS^MT X.509 v3 Certificate Example . . . . . . . .  24
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  33
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  33

1.  Introduction

   Stateful Hash-Based Signature Schemes (S-HBS) such as HSS, XMSS and
   XMSS^MT combine Merkle trees with One Time Signatures (OTS) in order
   to provide digital signature schemes that remain secure even when
   quantum computers become available.  Their theoretic security is well
   understood and depends only on the security of the underlying hash
   function.  As such they can serve as an important building block for
   quantum computer resistant information and communication technology.

   The private key of S-HBS is a finite collection of OTS keys, hence
   only a limited number of messages can be signed and the private key's
   state must be updated and persisted after signing to prevent reuse of
   OTS keys.  While the right selection of algorithm parameters would
   allow a private key to sign a virtually unbounded number of messages
   (e.g. 2^60), this is at the cost of a larger signature size and
   longer signing time.  Due to the statefulness of the private key and
   the limited number of signatures that can be created, S-HBS might not
   be appropriate for use in interactive protocols.  However, in some
   use cases the deployment of S-HBS may be appropriate.  Such use cases
   are described and discussed later in Section 3.

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.  Use Cases of S-HBS in X.509

   As many cryptographic algorithms that are considered to be quantum-
   resistant, S-HBS have several pros and cons regarding their practical
   usage.  On the positive side they are considered to be secure against
   a classical as well as a quantum adversary, and a secure
   instantiation of S-HBS may always be built as long as a
   cryptographically secure hash function exists.  Moreover, S-HBS offer

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   small public key sizes, and, in comparison to other post-quantum
   signature schemes, the S-HBS can offer relatively small signature
   sizes (for certain parameter sets).  While key generation and
   signature generation may take longer than classical alternatives,
   fast and minimal verification routines can be built.  The major
   negative aspect is the statefulness.  Private keys always have to be
   handled in a secure manner, S-HBS necessitate a special treatment of
   the private key in order to avoid security incidents like signature
   forgery [MCGREW], [SP800208].  Therefore, for S-HBS, a secure
   environment MUST be used for key generation and key management.

   Note that, in general, root CAs offer such a secure environment and
   the number of issued signatures (including signed certificates and
   CRLs) is often moderate due to the fact that many root CAs delegate
   OCSP services or the signing of end-entity certificates to other
   entities (such as subordinate CAs) that use stateless signature
   schemes.  Therefore, many root CAs should be able to handle the
   required state management, and S-HBS offer a viable solution.

   As the above reasoning for root CAs usually does not apply for
   subordinate CAs, it is NOT RECOMMENDED for subordinate CAs to use
   S-HBS for issuing end-entity certificates.  Moreover, S-HBS MUST NOT
   be used for end-entity certificates.

   However, S-HBS MAY be used for code signing certificates, since they
   are suitable and recommended in such non-interactive contexts.  For
   example, see the recommendations for software and firmware signing in
   [CNSA2.0].  Some manufactures use common and well-established key
   formats like X.509 for their code signing and update mechanisms.
   Also there are multi-party IoT ecosystems where publicly trusted code
   signing certificates are useful.

4.  Algorithm Identifiers and Parameters

   In this document, we define new OIDs for identifying the different
   stateful hash-based signature algorithms.  An additional OID is
   defined in [I-D.draft-ietf-lamps-rfc8708bis] and repeated here for
   convenience.  For all of the OIDs, the parameters MUST be absent.

4.1.  HSS Algorithm Identifier

   The object identifier and public key algorithm identifier for HSS is
   defined in [I-D.draft-ietf-lamps-rfc8708bis].  The definitions are
   repeated here for reference.

   The object identifier for an HSS public key is id-alg-hss-lms-
   hashsig:

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   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 }

   Note that the id-alg-hss-lms-hashsig algorithm identifier is also
   referred to as id-alg-mts-hashsig.  This synonym is based on the
   terminology used 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/LMS tree.  [RFC8554] and [SP800208] define
   these values, but an IANA registry [IANA-LMS] permits the
   registration of additional identifiers in the future.

4.2.  XMSS Algorithm Identifier

   The object identifier for an XMSS public key is id-alg-xmss-hashsig:

   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, but an IANA registry [IANA-XMSS] permits the
   registration of additional identifiers in the future.

4.3.  XMSS^MT Algorithm Identifier

   The object identifier for an XMSS^MT public key is id-alg-xmssmt-
   hashsig:

   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, but an IANA registry [IANA-XMSS] permits the
   registration of additional identifiers in the future.

5.  Public Key Identifiers

   Certificates conforming to [RFC5280] can convey a public key for any
   public key algorithm.  The certificate indicates the algorithm
   through an algorithm identifier.  An algorithm identifier consists of
   an OID and optional parameters.

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   [RFC8554] and [RFC8391] define the raw octet string encodings of the
   public keys used in this document.  When used in a
   SubjectPublicKeyInfo type, the subjectPublicKey BIT STRING contains
   the raw octet string encodings of the public keys.

   This document defines ASN.1 OCTET STRING types for encoding the
   public keys when not used in a SubjectPublicKeyInfo.  The OCTET
   STRING is mapped to a subjectPublicKey (a value of type BIT STRING)
   as follows: the most significant bit of the OCTET STRING value
   becomes the most significant bit of the BIT STRING value, and so on;
   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 is as follows:

   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 } }

   The HSS public key is defined as follows:

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

   [RFC8554] defines the raw octet string encoding of an HSS public key
   using the hss_public_key structure.  See [SP800208] and [RFC8554] for
   more information on the contents and format of an HSS public key.
   Note that the single-tree signature scheme LMS is instantiated as HSS
   with number of levels being equal to 1.

5.2.  XMSS Public Keys

   The XMSS public key identifier is as follows:

   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 } }

   The XMSS public key is defined as follows:

   XMSS-HashSig-PublicKey ::= OCTET STRING

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   [RFC8391] defines the raw octet string encoding of an HSS public key
   using the xmss_public_key structure.  See [SP800208] and [RFC8391]
   for more information on the contents and format of an XMSS public
   key.

5.3.  XMSS^MT Public Keys

   The XMSS^MT public key identifier is as follows:

   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 } }

   The XMSS^MT public key is defined as follows:

   XMSSMT-HashSig-PublicKey ::= OCTET STRING

   [RFC8391] defines the raw octet string encoding of an HSS public key
   using the xmssmt_public_key structure.  See [SP800208] and [RFC8391]
   for more information on the contents and format of an XMSS^MT public
   key.

6.  Key Usage Bits

   The intended application for the key is indicated in the keyUsage
   certificate extension [RFC5280].  When one of the
   AlgorithmIdentifiers specified in this document appears in the
   SubjectPublicKeyInfo field of a certification authority (CA) X.509
   certificate [RFC5280], the certificate key usage extension MUST
   contain at least one of the following values: digitalSignature,
   nonRepudiation, keyCertSign, or cRLSign.  However, it MUST NOT
   contain other values.

   When one of these AlgorithmIdentifiers appears in the
   SubjectPublicKeyInfo field of an end entity X.509 certificate
   [RFC5280], the certificate key usage extension MUST contain at least
   one of the following values: digitalSignature or nonRepudiation.
   However, it MUST NOT contain other values.

   Note that for certificates that indicate id-alg-hss-lms-hashsig the
   above definitions are more restrictive than the requirement defined
   in Section 4 of [I-D.draft-ietf-lamps-rfc8708bis].

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7.  Signature Algorithms

   This section identifies OIDs for signing using HSS, XMSS, and
   XMSS^MT.  When these algorithm identifiers appear in the algorithm
   field as an AlgorithmIdentifier, the encoding MUST omit the
   parameters field.  That is, the AlgorithmIdentifier SHALL be a
   SEQUENCE of one component, one of the OIDs defined in the following
   subsections.

   When the signature algorithm identifiers described in this document
   are used to create a signature on a message, no digest algorithm is
   applied to the message before signing.  That is, the full data to be
   signed is signed rather than a digest of the data.

   For HSS, the signature value is described in section 6.4 of
   [RFC8554].  For XMSS and XMSS^MT the signature values are described
   in sections B.2 and C.2 of [RFC8391], respectively.  The octet string
   representing the signature is encoded directly in the OCTET STRING
   without adding any additional ASN.1 wrapping.  For the Certificate
   and CertificateList structures, the signature value is wrapped in the
   "signatureValue" OCTET STRING field.

7.1.  HSS Signature Algorithm

   The HSS public key OID is also used to specify that an HSS signature
   was generated on the full message, i.e. the message was not hashed
   before being processed by the HSS signature algorithm.

   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 }

   The HSS signature is defined as follows:

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

   See [SP800208] and [RFC8554] for more information on the contents and
   format of an HSS signature.

7.2.  XMSS Signature Algorithm

   The id-alg-xmss-hashsig public key OID is also used to specify that
   an XMSS signature was generated on the full message, i.e. the message
   was not hashed before being processed by the XMSS signature
   algorithm.

   The XMSS signature is defined as follows:

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   XMSS-HashSig-Signature ::= OCTET STRING

   See [SP800208] and [RFC8391] for more information on the contents and
   format of an XMSS signature.

   The signature generation MUST be performed according to 7.2 of
   [SP800208].

7.3.  XMSS^MT Signature Algorithm

   The id-alg-xmssmt-hashsig public key OID is also used to specify that
   an XMSS^MT signature was generated on the full message, i.e. the
   message was not hashed before being processed by the XMSS^MT
   signature algorithm.

   The XMSS^MT signature is defined as follows:

   XMSSMT-HashSig-Signature ::= OCTET STRING

   See [SP800208] and [RFC8391] for more information on the contents and
   format of an XMSS^MT signature.

   The signature generation MUST be performed according to 7.2 of
   [SP800208].

8.  Key Generation

   The key generation for XMSS and XMSS^MT MUST be performed according
   to 7.2 of [SP800208]

9.  ASN.1 Module

   For reference purposes, the ASN.1 syntax is presented as an ASN.1
   module here.  This ASN.1 Module builds upon the conventions
   established in [RFC5911].

   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(TBD) }

   DEFINITIONS IMPLICIT TAGS ::= BEGIN

   EXPORTS ALL;

   IMPORTS
     PUBLIC-KEY, SIGNATURE-ALGORITHM
       FROM AlgorithmInformation-2009  -- RFC 5911 [CMSASN1]
         { iso(1) identified-organization(3) dod(6) internet(1)

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           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
         { 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 [RFC8708]

   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 [RFC8708]

   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 [RFC8708]

   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 } }

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   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 } }

   --
   -- 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

   The security requirements of [SP800208] MUST be taken into account.

   For S-HBS it is crucial to stress the importance of a correct state
   management.  If an attacker were able to obtain signatures for two
   different messages created using the same OTS key, then it would
   become computationally feasible for that attacker to create forgeries
   [BH16].  As noted in [MCGREW] and [ETSI-TR-103-692], extreme care
   needs to be taken in order to avoid the risk that an OTS key will be
   reused accidentally.  This is a new requirement that most developers
   will not be familiar with and requires careful handling.

   Various strategies for a correct state management can be applied:

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   *  Implement a track record of all signatures generated by a key pair
      associated to a S-HBS instance.  This track record may be stored
      outside the device which is used to generate the signature.  Check
      the track record to prevent OTS key reuse before a new signature
      is released.  Drop the new signature and hit your PANIC button if
      you spot OTS key reuse.

   *  Use a S-HBS instance only for a moderate number of signatures such
      that it is always practical to keep a consistent track 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.  In this way the number of state synchronisations between
      nonvolatile and volatile memory is reduced.

11.  Backup and Restore Management

   Certificate Authorities have high demands in order to ensure the
   availability of signature generation throughout the validity period
   of signing key pairs.

   Usual backup and restore strategies when using a stateless signature
   scheme (e.g.  SLH-DSA) are to duplicate private keying material and
   to operate redundant signing devices or to store and safeguard a copy
   of the private keying material such that it can be used to set up a
   new signing device in case of technical difficulties.

   For S-HBS such straightforward backup and restore strategies will
   lead to OTS reuse with high probability as a correct state management
   is not guaranteed.  Strategies for maintaining availability and
   keeping a correct state are described in Section 7 of [SP800208].

12.  IANA Considerations

   One object identifier for the ASN.1 module in Appendix A is requested
   for the SMI Security for PKIX Module Identifiers (1.3.6.1.5.5.7.0)
   registry:

         +=========+========================+====================+
         | Decimal | Description            | References         |
         +=========+========================+====================+
         | TBD     | id-mod-pkix1-shbs-2024 | [EDNOTE: THIS RFC] |
         +---------+------------------------+--------------------+

                                  Table 1

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   IANA has updated the "SMI Security for PKIX Algorithms"
   (1.3.6.1.5.5.7.6) registry [SMI-PKIX] with two additional entries:

         +=========+=======================+====================+
         | Decimal | Description           | References         |
         +=========+=======================+====================+
         | 34      | id-alg-xmss-hashsig   | [EDNOTE: THIS RFC] |
         +---------+-----------------------+--------------------+
         | 35      | id-alg-xmssmt-hashsig | [EDNOTE: THIS RFC] |
         +---------+-----------------------+--------------------+

                                 Table 2

13.  References

13.1.  Normative References

   [I-D.draft-ietf-lamps-rfc8708bis]
              Housley, R., "Use of the HSS/LMS Hash-Based Signature
              Algorithm in the Cryptographic Message Syntax (CMS)",
              RFC 8708, DOI 10.17487/RFC8708, February 2020,
              <https://www.rfc-editor.org/rfc/rfc8708>.

   [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>.

   [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/rfc/rfc5280>.

   [RFC5911]  Hoffman, P. and J. Schaad, "New ASN.1 Modules for
              Cryptographic Message Syntax (CMS) and S/MIME", RFC 5911,
              DOI 10.17487/RFC5911, June 2010,
              <https://www.rfc-editor.org/rfc/rfc5911>.

   [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>.

   [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/rfc/rfc8391>.

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   [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>.

   [SP800208] National Institute of Standards and Technology (NIST),
              "Recommendation for Stateful Hash-Based Signature
              Schemes", 29 October 2020,
              <https://doi.org/10.6028/NIST.SP.800-208>.

13.2.  Informative References

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

   [CNSA2.0]  National Security Agency (NSA), "Commercial National
              Security Algorithm Suite 2.0 (CNSA 2.0) Cybersecurity
              Advisory (CSA)", 7 September 2022,
              <https://media.defense.gov/2022/Sep/07/2003071834/-1/-1/0/
              CSA_CNSA_2.0_ALGORITHMS_.PDF>.

   [ETSI-TR-103-692]
              European Telecommunications Standards Institute (ETSI),
              "State management for stateful authentication mechanisms",
              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)", n.d.,
              <https://www.iana.org/assignments/leighton-micali-
              signatures/>.

   [IANA-XMSS]
              IANA, "XMSS: Extended Hash-Based Signatures", n.d.,
              <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", 2 November 2016,
              <https://tubiblio.ulb.tu-darmstadt.de/id/eprint/101633>.

   [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/rfc/rfc3279>.

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   [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/rfc/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/rfc/rfc8411>.

   [SMI-PKIX] IANA, "SMI Security for PKIX Algorithms", n.d.,
              <https://www.iana.org/assignments/smi-numbers/smi-
              numbers.xhtml#smi-numbers-1.3.6.1.5.5.7.6>.

Appendix A.  HSS X.509 v3 Certificate Example

   This section shows a self-signed X.509 v3 certificate using HSS.

   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

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                   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:

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           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

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   -----BEGIN CERTIFICATE-----
   MIIGnjCCAXagAwIBAgIJAOiR1gaRT87zMA0GCyqGSIb3DQEJEAMRMD8xCzAJBgNV
   BAYTAlVTMQswCQYDVQQIDAJWQTEQMA4GA1UEBwwHSGVybmRvbjERMA8GA1UECgwI
   Qm9ndXMgQ0EwHhcNMjQwNTE0MDg1ODExWhcNMzQwNTE0MDg1ODExWjA/MQswCQYD
   VQQGEwJVUzELMAkGA1UECAwCVkExEDAOBgNVBAcMB0hlcm5kb24xETAPBgNVBAoM
   CEJvZ3VzIENBME4wDQYLKoZIhvcNAQkQAxEDPQAAAAABAAAABQAAAATAlhKL6jgw
   eOv2+0PXf5+egTnifLk0Tm5TGfDuaHWFg9Mr6XsURp5OxeNaGAsw5ROjYzBhMB0G
   A1UdDgQWBBRYFav0zwNpAmB6V03F1bNyihkhaDAfBgNVHSMEGDAWgBRYFav0zwNp
   AmB6V03F1bNyihkhaDAPBgNVHRMBAf8EBTADAQH/MA4GA1UdDwEB/wQEAwIBBjAN
   BgsqhkiG9w0BCRADEQOCBREAAAAAAAAAAAAAAAAEnDdS/7nX3/VbAbpQwlDMb/Ox
   c98MKuqz7ZYezudYBdqNp3chQjLZ+UpN9ysYKhxcaQPzHJyVbTGaycqETa6zi8Nx
   rD+HUb44tL/Z3JAfHlS9+RplcNRGtq1NbRa5+yn044ZCSj+kjwGEm0QLIyKcl23V
   uSY5EatGgr0QbLR6ZO3HQLAz8LWBHLRBVJww2dKTukiMT9AlQWB7kF4SILcwFhYe
   t+7YS+7tPHD8/zYYqiQjh5FlqJUtthzRAntwgYoYF8BFYv5HoT5pVDFnWJrh48mN
   7h4q0UZ16eSQZwFXklTbtOrei+fr/CeAm9Xa4I6wswjKb6Ec9EBlsPb4yaeXBMh8
   nlbsL0vNRYvX5qdQx+YhLBcxIxF6rpq1hF/mXIKZqDqpkYeaJFyDAZF8/M2+LpJQ
   +xIRlggNySQNu2/7WQWvf5a8o/RY4voKSvJM97Mbgd1KQaCx3VJMu23AqNm7Kcj8
   4374auVexOTofAsAhxV1ogZQl8YfFFJ5BKic7LHHakYzmLhj96cs1GJ4lBxdnU+m
   Cq45UIWyCY1iyUwRnwyRpawtEb1xtgzqNJhT/C7Me6ScLnqkjeLojAGpnD61NHcz
   ggHU73IE1lvl9iwbrobEcwJEhdb3rKPo9qm1XG1GiNpVuCt6TAya581dYorKyJbO
   jXF70sENmjVVK4Q+DqX61qB2jiOz38k7T2hWHuk8eVvTJVQRraasWBFJj03EwTmZ
   djqm0S9Xrb98nVfMNw0phCl7y0aFw4HFM5plwy8BSMpEbPGEPdBJwsEF23dMuXI9
   b85p8pHGFSWP2jh+71s+XzWrpngWKELBLC+eEVMsvcQke+nEzj3WQcddkpHDN8ty
   RNcNcIUTC6yzD7Dl4y5IuZy41z58UGkDel+u+GwJYZdrzs3l8FX+BfiXHZ6BZfX/
   mnqMltj4z9jcVc5negBr/bs/Gz1llMFatqCOvqS+JpBfHwbU6j+ml0COvxhckg8V
   4wVKFFEeI4Hvz/eoiHX4LSg3JocnY1wBUw5eU9KnGOsvwIJJBbBNM2+UEJF3+JCe
   yv67PcRC1omEmEL0JLO0214rZqn/bBjUefhyc1ObAu0Ec3ekaM9LvksWUGKH+UmZ
   46EMQpK8qeMtIoI1f3EViHBqAatEZK3lUtSX7rtEe24If92U/ckca1nRklEpA87s
   v0GlFGlUOrQ52URd8bL0XGufyV+7/MjHo4vh7OLQaVpAHJydij13O8FdwHJhSzfF
   loxti/hW2qw+PHIJzvbD/l3PN9lozafd95Zj2owd37gyz+uXEYP+a6q54kuy6mJz
   wxzpQJBWTxLDuvQr2RxQzOBR2Ou/ZygMLRONs28Tah2nVCC6glu45R+J8Wcmwdwb
   YFftpizyFwF/pedcZMk8CPLPSOyIhO8DwvXrBTF9/n88cUEoF2RfuexUedCzmPuE
   nDaLQwvUyewJSnATYvI2yLR1zCp3CKCd7xnWiNzisk5AYXHLx8PeFm9Jf17VFwAA
   AAV5RxKfzusdqP0NsBhEau9UKEbkGfYtPnS7nTYKrmdKKHobgDmgCCoooOxV7lWq
   ocyU1DYas1clMK0sXmO6Ivyqellk9tgDIChx+dwJ+kyBuWQbrerL2xgXXdiYvdKN
   xQR8W5Kaifa81lXHCF08WI4YrG+IqNee1O5d9SFOpYsZX+P0ZvklTfnGYGIxclw0
   NGcap2p9VKPYmx9b+AhBeVtD
   -----END CERTIFICATE-----

Appendix B.  XMSS X.509 v3 Certificate Example

   This section shows a self-signed X.509 v3 certificate using XMSS.

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   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:

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           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:
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           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:
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           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:

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           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:
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           91:72:fb:9b:ba:e8:92:56:fb:9a:5b:5d:3b:9d:d3:c5:c4:52:
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           b9:06:32:7c:ea:d1:36:f6:95:b8:57:41:1b:6e:66:31:2c:ee:
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           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:
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           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:
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           1a:f7:67:b5:5c:03:bf:bf:7a:e2:4d:a2:9b:5d:5d:5f:51:d0:

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           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

   -----BEGIN CERTIFICATE-----
   MIILSDCCAW+gAwIBAgIUVH5kcCmeA8V6pVx40SeHjFQ1F10wCgYIKwYBBQUHBiIw
   NTELMAkGA1UEBhMCRlIxDjAMBgNVBAcMBVBhcmlzMRYwFAYDVQQKDA1Cb2d1cyBY
   TVNTIENBMB4XDTI0MDcxMDA4MjcyNFoXDTM0MDcwODA4MjcyNFowNTELMAkGA1UE
   BhMCRlIxDjAMBgNVBAcMBVBhcmlzMRYwFAYDVQQKDA1Cb2d1cyBYTVNTIENBMFMw
   CgYIKwYBBQUHBiIDRQAAAAABK+u/ZhTeb5ZbTSpQAHutXCKwE3lyAhSpX/yW4Jt4
   jta+jBxwPNjdeLIaFEe+Hw10cj82dsLLGa0pkAuC3pt/36NjMGEwHQYDVR0OBBYE
   FGLONaVHd/8hhy68LSfnjvQ1a8/YMB8GA1UdIwQYMBaAFGLONaVHd/8hhy68LSfn
   jvQ1a8/YMA8GA1UdEwEB/wQFMAMBAf8wDgYDVR0PAQH/BAQDAgEGMAoGCCsGAQUF
   BwYiA4IJxQAAAAAA5YiouHOtTZL4XIHFimNXaqc7VKq2BorZ8cILyCceS6LP4tpE
   6ujyQKi5VJxJNhIk33St5SnvT9qIDSFdO2RjJ9CEtZV6MBg3zTQX3aydnkjbdAd5
   hCFa8CbNIWR7dzNIWGebLLKFbczsMUsvUVU6heHKBBXObkc59ekxRUHtccZPlvWu
   ZGq9ctCMFwKZEB0UNMrlR+P3ZpaWEdWXdnaD8YSltgBePmeXejLcyOtMKUZ3mdba
   ReZ7jEVttSlr/ZiiiY0MMEL1C3yXxbEd4tpnqUiknin0YD9NHUiDgjjv+ssdhhGh
   FZT71e5o+US5PVRw874XjdcuhS1c0KDFmVLMeeccGNluPQ9sBVEzKDXiAllfH+14
   CsZi8H3+c5YDTLRC4wDC18vrURDEDGS4N/6F0I4RbaYWd7EeAdke8xCc3QG8OHVe
   j1ieW2x7CkEIWTWpOoMZ4H2h9c+jHE4H4a0DlfLTi3kz+FIiUxseMpphP8R8mujV
   tSjxhGXVwfxNFpOIk2nK+pSglU4jrh5g4Oi0v/8WlXEPMXS7vrha6ySVi5UoE83j

Van Geest, et al.        Expires 26 January 2025               [Page 22]
Internet-Draft           HSS and XMSS for X.509                July 2024

   qWX39W6bqal6Bc6r8FRi2RL4oRpo368Vj4rfZyfJ7b3hgaaNmoTzkTbZiXSO74Tc
   XAMaCOTX8HL8bYoBNJTl/whRG4Bf5wfYnyXkHcP45dCcUM9mcfnM98Cn0GYBtxeg
   X2aXpP9irBygYw0wKOmQ1VmkSNgHhwJLP2gjpQTcs9dF9tyw7MaQphyh+H6EumN+
   WmQUeFj1dcD14R29SVfAQAgHmX9DLuIl2O2jGuN48XivAklUNlmO03KlC1IyvRei
   z+FHISg9urYk2Rj5RHM17SmkGLztaM1KmjTLGi+zX7pzmxjueqiSJWUlgQRjHCIr
   uLqBIbz5nah4mHW87UrGt2/AkSTrHfld4ON4TgX2NA97QVRJIKIwZpTx2sFsP14Q
   kpKjDH7oiyYRHNdoyTF5s6TVYwBow+OGLQmSSy1jfbgDpExgtCwS1QufFijqiC+7
   HBkLD0A9Z+gL+sbjOUSyvYo/Id2q7KOMSN1MmUOG10iBa+W5u1mfHA8/Efd8S2eo
   lcJ8yztmsHmmVW9tsCmKXnvuMGjz3UEpkfZ5ca6NIXB4HV3S98/nQjjRjFKmpvax
   OLErI4HhHyFtmT8Q67Gpc7g+MZnM3SvfWCfbC1opmY+xn+kxQtAm21O3fjBBlcPw
   B4O7sGO1FkjypmAvMl0iodp2TjcmUw2Vey25BS+TK9TfwQJb96WiTxFcgPTwvcfq
   PNtv4utsf8NY2TF3S033zrvWyGSjAdX5pI3o8O4JBiwLPKwKV9jkgXnqSr1RA4hM
   0EwLxAx+LeffG2diwNGcrbvT8HXdg6pwmSwZeD0mK0dvJMFgAh5LdQSRHwgcs3mg
   m9v7XT/H4wkfQT5ku60ZPTXhpvRpC6IEN0KVxsfl9FYOZ1t4NLsH8Y/nc1uH19/J
   LY2MQnaHFYVLIwMgNOEb9gwehFPZG07ZMUM4O4gShNgqOLHOD8cH1GMtl4kcs0SZ
   69TfMnS+DWMRIv36juILVhJWDEYWrUQQJpjcz8mVZz4RwXb6uBLqlvbZkay/Sbkc
   jhUFU6yeBNJbuIe/gVD3AqTAnBgPRax6gs9GFUJACTKJpeqQpZlo+ZMMe9Z6qOlR
   4pCeue0h29l+3txia0Rrn4HFdzmOHXgw3txTgODD+vqUaCiRmIb/hgSpvVh8MTcf
   25op88FIECBxX/w1E+t7EuJ9HMyX/o9cot320qOy6lGz77EeeQsAU/TyUnVa1xfF
   MaBUTisoLE9reic6LATasx0ETqROlFyokXCrwEt1n7NqqU6KIul//exT52ptMguL
   q0znfXLsBGIcGkUeM443rmovyPvzae0RAfP0V+kp1TsMnAzEy8M4XAHn1jHD2M4k
   175xm8iWE8pcXeSSQK+GoEv/p1U5cP2sCuGHxwFLw0E2xsYzj08lSo1wkqx8lcxJ
   qdzWamdSpVt/L7uR477WKPwi0HJm6AlzpyPGpok4C+XQs/FAOJxNF5YRF0Tv45RR
   kUxd/tntw3agLTvcjbkxFfZ1WHQvV7QpISltX+sGcQr02//GLxZzp3Zr0FunIVz9
   8BHob5vQycn+NXZKSmObukisr0+RZ5xcR9jjLQMSXvHLVjR1aZWtaJZs50qRcvub
   uuiSVvuaW107ndPFxFJCG/lKR0Ldd0naK73XlF97uGS5BjJ86tE29pW4V0EbbmYx
   LO6HelwZL9iVShaTSPOXJT0kYR7QYzfuOsmjRsWUoH4kzH9yjRSePDPszZrdtQiQ
   mBmVhTj//9Iev6bElxMrPUfpV1nTfZkBblNNwIKX+4nWfLcjDn1uI4hTBo8W/0AK
   G83VHpEBPnc6X8FXOnvG1VHX4uyJEmudA+Sdu31OAr9njQPKkFbwmpdLAi1MMYmC
   dpf+L9UKPeoNOGwwdV+ukVPXRWTfugsigESFbQ5cKX+CnlSjepW+lnlmnVui1i5H
   xpl9KzLc8rYCkW1j1JNFYMRCcRCe+5Av5nVxznhwwdr/4Uf+eSuOmoG/3QLjeDlx
   F7MjFBGdKY4hoZiwrANabJ5iZO9PA8o3pu3keNUNmSn1XGHmSMuXDl75LPa2x3wM
   pPca92e1XAO/v3riTaKbXV1fUdDWUo8qIGgIu/CcBQ7vs0kMKh2P+QO3YQlxiH3i
   jOS4rJgbw4BVoWvdE6IpT5OT09UBMT97OQ46V2zrXGpfG62XvZcjGJEFDiu0sRHu
   +FjHCNDeoj66VI09Y9qRUDokjRkYIy7PMI1d4+cCk/rI+OoF5usGgJBNFVg9JpgT
   S7Cs3ZAu0OHrcTKDXSqpubUk/OnsGMrJoQVZPvqv7U6Gsf5AR5tCd6+cK6DiPv1R
   qwJ36PE5RapUthTUFCD8NoHmBJiKoMCKz672tdy36yaG088cOGVUBLG1CUj1LQe6
   +OtJvdmxVOqswg0gEHnBy+ncLf9VUE/2BQJ4MTNvFX4kWmYjcLOyDBc5zhU4xf9g
   FjhgdHLJcNhZt4B/2vZnP9C6vhuhh9qSLaNsmSlXqsvRjWbxLclWYCRWSxmf9WWE
   iYZ9TYv4W2Ddry1mdmxm2cb1OSVs5XtDl2RcxSAePbXckrKc2Bsb4LxEe5yVxVNI
   kbKlRha/UK+lRMxUeD/tINguC0E98QSd3zxK14EE/4y3efhRjbcurCxU5vxDdo75
   voy4XK3EE6+wbjvRglce9VKEyszSaPMtBP8nCuai+sCpl9ZkRRhcb57BZCJm21YC
   w6hX/IcbXEMVjlj88gALT2pLoFza8uUbgkpr79tj132THS8geDcXIoLNa8GDYQWB
   mQwlKdZfIrwGZ31n
   -----END CERTIFICATE-----

Van Geest, et al.        Expires 26 January 2025               [Page 23]
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Appendix C.  XMSS^MT X.509 v3 Certificate Example

   This section shows a self-signed X.509 v3 certificate using XMSS^MT.

   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:

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           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:
           0d:4a:0c:b8:b0:ef:74:dd:6f:6f:dc:e5:83:e1:e3:c2:e8:58:
           17:b8:44:8a:2d:ec:df:54:f6:1f:67:a2:b3:c5:19:fb:b9:c7:
           1b:3c:ea:bd:2c:e1:43:65:d1:5a:17:dc:93:9d:c5:85:0c:55:
           34:13:49:15:92:e2:52:14:d1:81:aa:62:02:1a:ba:c9:b0:53:
           85:8e:7b:d1:4e:34:76:ac:79:d7:b3:48:92:bf:55:7e:2d:5c:
           cd:32:9b:c1:41:a7:a3:cd:b7:94:5c:96:1e:3e:27:4d:eb:f0:
           61:4b:a4:e3:3c:bb:69:85:37:e9:9c:98:f4:68:7a:61:77:8c:
           bd:b9:30:d6:f1:fd:69:78:3f:96:99:7b:69:39:90:b3:7c:b6:
           88:ed:cd:19:da:42:64:e5:32:4c:a2:30:f7:c4:e8:27:93:70:
           ed:fa:5e:ca:8e:7a:d1:13:af:15:b1:59:c9:9b:91:61:0b:06:
           d5:cc:2e:80:bb:49:93:dd:be:53:88:be:af:80:64:7c:5e:be:
           7b:8b:e7:5f:39:af:ab:67:42:6b:06:aa:ef:d6:69:af:a9:00:
           1f:a0:15:10:04:3e:db:93:b2:37:db:eb:85:59:43:a2:8d:8f:
           06:8c:cb:a2:1d:a8:3c:9f:f4:a4:7c:c8:cd:ff:f0:a8:79:0f:
           e7:d8:94:67:ec:17:3f:fa:6e:04:07:4f:bf:86:04:6c:fc:46:

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           87:b5:10:85:a4:07:e8:af:a9:ec:5d:28:5c:80:8c:31:cc:c7:
           b3:81:17:0b:4b:7d:1c:9e:74:02:1e:ef:de:0d:1b:c1:c0:04:
           4d:46:fd:dc:0b:a4:c6:33:e6:85:0a:60:39:4d:0b:f9:49:44:
           33:e0:15:99:19:bf:c7:8a:c6:96:04:93:37:6b:5d:e8:be:73:
           d4:80:b8:81:0f:9a:91:44:cf:72:02:d3:c9:f8:e0:7d:d2:9b:
           2b:ff:eb:42:6e:38:7e:dc:cd:a7:90:c5:2c:2b:a0:23:37:b9:
           64:10:a6:27:68:47:c5:f1:e8:8d:41:c1:49:e8:35:48:ce:c8:
           08:4c:ad:f2:ad:5d:e9:62:eb:c9:3c:61:85:18:c6:34:73:fd:
           26:a4:f0:50:83:9b:64:54:aa:55:6c:d8:a2:21:81:ff:9c:27:
           39:1f:c3:a2:0e:e5:53:b1:d7:fa:1f:ef:29:8b:c2:90:98:ea:
           2e:dd:45:bf:c3:6c:a3:93:47:99:03:18:25:e8:a5:ee:2e:77:
           eb:7f:f4:49:49:59:98:c1:fc:ab:1e:ad:20:bd:f8:24:fd:21:
           1b:da:5a:07:55:c8:50:05:31:50:93:b2:f8:6e:db:73:4d:5f:
           34:aa:f3:34:83:90:f0:41:6d:c8:43:56:d1:75:07:f5:16:20:
           b3:99:b2:c7:34:25:c4:0e:74:5a:51:0f:7b:3b:7f:6a:a9:41:
           17:b5:47:62:2d:4f:b9:61:97:60:e9:ae:ca:ad:31:6e:4b:0a:
           47:9c:53:66:a3:4e:c3:96:7c:01:a0:8e:ae:83:45:42:e6:92:
           12:8e:97:6f:e8:a0:b7:7d:a6:74:24:aa:20:b0:fa:9e:98:e8:
           7c:b4:da:30:e9:94:08:96:b7:b9:53:4f:75:5f:0c:4d:82:e3:
           cf:6e:bc:fa:23:4f:fa:33:17:7c:98:b6:1e:47:89:3e:d9:a1:
           aa:42:19:25:ae:9e:3f:53:44:ac:91:96:d8:55:c3:40:1d:fa:
           ad:86:38:62:bd:27:2f:26:34:be:ad:9a:01:44:42:c8:54:a5:
           3a:e9:0a:ff:f8:41:6d:38:1e:e2:3d:08:3a:94:4f:1e:60:d0:
           b1:c2:8e:94:34:f0:30:3e:f0:91:25:ee:98:34:b4:8d:95:4e:
           cf:ed:1d:61:89:c9:59:10:68:f2:bc:2e:5c:bd:c0:0f:1d:9c:
           2f:7c:c0:27:25:14:9b:de:a3:74:64:28:14:2c:a2:b2:90:3a:
           a4:6a:50:e9:8e:ca:78:e5:b6:74:56:e0:92:69:7d:b4:2e:e0:
           e7:66:92:16:92:a0:c3:db:4f:d3:d0:57:4d:4a:28:ee:b7:cc:
           04:ef:17:d9:fc:01:bb:1e:b2:5b:02:3d:1f:5a:85:73:a1:81:
           96:b7:33:5d:79:e5:6b:c9:29:73:34:01:69:ea:57:f0:01:be:
           4e:f3:5c:f3:0a:a7:37:08:ad:18:9c:c7:4c:59:d0:5d:bb:01:
           f1:53:76:cb:cd:d9:84:5e:bc:22:11:76:01:d9:e3:af:17:03:
           01:ef:38:4c:ad:c1:7d:a9:c6:61:2b:ba:9c:81:95:86:af:bb:
           73:90:dc:d9:2f:d1:3f:95:6a:b9:46:0f:fb:84:64:7c:7d:86:
           65:aa:10:71:56:19:5f:60:52:7f:19:fa:d5:5a:e0:90:e4:b9:
           62:55:71:2a:61:f9:37:2f:5e:07:71:43:cf:06:ca:6a:d5:52:
           c8:33:e1:ad:b2:3e:a4:61:01:00:bc:55:5d:0a:f3:e6:4f:35:
           06:c4:a8:3f:4c:8b:9b:c9:41:4b:f4:c1:57:ee:3c:c0:44:68:
           52:5a:2d:b9:a7:f2:41:da:c4:8d:7d:db:40:b6:fc:47:63:5a:
           69:a1:c7:8c:cc:3f:af:51:94:37:95:58:82:79:d2:16:4a:bf:
           12:0b:59:a5:a5:11:71:e6:1c:63:3b:ea:f0:2f:10:e0:97:9a:
           a1:04:53:d0:72:f4:3c:77:3b:78:ee:b5:aa:6b:f5:bb:5c:e9:
           35:4f:69:65:87:29:24:ec:47:7b:78:5a:a7:c1:e5:f1:73:7d:
           4d:79:ef:ef:4e:75:87:db:8f:36:fd:50:3e:74:dc:17:d4:c3:
           3f:4f:82:24:51:1b:12:16:26:61:db:93:15:19:39:55:f5:05:
           2c:6e:85:dd:b2:cc:4f:c0:09:0a:76:46:d8:e4:f2:11:92:a1:
           e0:36:a8:25:c7:45:19:6c:98:eb:9a:fa:c1:ec:80:18:ce:d1:
           f8:c4:23:9a:f9:b8:1f:05:67:8e:45:cb:e6:ee:0b:fa:db:67:

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           1f:62:2c:49:78:bb:55:98:1e:33:42:63:f2:db:ee:73:f7:60:
           80:6d:5f:9a:e8:8c:89:39:5b:b2:84:e2:c3:99:77:f3:5f:19:
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   -----BEGIN CERTIFICATE-----
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   -----END CERTIFICATE-----

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Acknowledgments

   Thanks for Russ Housley and Panos Kampanakis for helpful suggestions.

   This document uses a lot of text from similar documents [SP800208],
   ([RFC3279] and [RFC8410]) as well as
   [I-D.draft-ietf-lamps-rfc8708bis].  Thanks go to the authors of those
   documents.  "Copying always makes things easier and less error prone"
   - [RFC8411].

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 Gazdag
   genua GmbH
   Email: ietf@gazdag.de

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

Van Geest, et al.        Expires 26 January 2025               [Page 33]