Internet X.509 Public Key Infrastructure: Algorithm Identifiers for HSS and XMSS
draft-gazdag-x509-shbs-00

Network Working Group                                         K. Bashiri
Internet-Draft                                                       BSI
Intended status: Informational                                S. Fluhrer
Expires: 25 August 2024                                    Cisco Systems
                                                               S. Gazdag
                                                              genua GmbH
                                                            D. Van Geest
                                                     CryptoNext Security
                                                             S. Kousidis
                                                                     BSI
                                                        22 February 2024

Internet X.509 Public Key Infrastructure: Algorithm Identifiers for HSS
                                and XMSS
                       draft-gazdag-x509-shbs-00

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-gazdag-x509-shbs/.

   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.

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Notation  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Use Cases of S-HBS in X.509 . . . . . . . . . . . . . . . . .   4
   5.  Public Key Algorithms . . . . . . . . . . . . . . . . . . . .   4
     5.1.  HSS Public Keys . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  XMSS Public Keys  . . . . . . . . . . . . . . . . . . . .   5
     5.3.  XMSS^MT Public Keys . . . . . . . . . . . . . . . . . . .   6
   6.  Key Usage Bits  . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Signature Algorithms  . . . . . . . . . . . . . . . . . . . .   7
     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
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     13.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

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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 4.

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.  Notation

   The parameter 'n' is the security parameter, given in bytes.  In
   practice this is typically aligned to the standard output length of
   the hash function in use, i.e. either 24, 32 or 64 bytes.  The height
   of a single tree is typically given by the parameter 'h'.  The number
   of levels of trees is either called 'L' (HSS) or 'd' (XMSS, XMSS^MT).

   [EDNOTE: Should we delete this section?  The parameters are not used
   in this document.]

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4.  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
   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.

5.  Public Key Algorithms

   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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   In this document, we define new OIDs for identifying the different
   stateful hash-based signature algorithms.  An additional OID is
   defined in [RFC8708] and repeated here for convenience.  For all of
   the OIDs, the parameters MUST be absent.

5.1.  HSS Public Keys

   The object identifier and public key algorithm identifier for HSS is
   defined in [RFC8708].  The definitions are repeated here for
   reference.

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

   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 HSS public key identifier is as follows:

   pk-HSS-LMS-HashSig PUBLIC-KEY ::= {
      IDENTIFIER id-alg-hss-lms-hashsig
      KEY HSS-LMS-HashSig-PublicKey
      PARAMS ARE absent
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

   The HSS public key is defined as follows:

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

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

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   id-alg-xmss-hashsig  OBJECT IDENTIFIER ::= {
      itu-t(0) identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) xmss(13) 0 }

   The XMSS public key identifier is as follows:

   pk-XMSS-HashSig PUBLIC-KEY ::= {
      IDENTIFIER id-alg-xmss-hashsig
      KEY XMSS-HashSig-PublicKey
      PARAMS ARE absent
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

   The XMSS public key is defined as follows:

   XMSS-HashSig-PublicKey ::= OCTET STRING

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

5.3.  XMSS^MT Public Keys

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

   id-alg-xmssmt-hashsig  OBJECT IDENTIFIER ::= {
      itu-t(0) identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) xmssmt(14) 0 }

   The XMSS^MT public key identifier is as follows:

   pk-XMSSMT-HashSig PUBLIC-KEY ::= {
      IDENTIFIER id-alg-xmssmt-hashsig
      KEY XMSSMT-HashSig-PublicKey
      PARAMS ARE absent
      CERT-KEY-USAGE
         { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

   The XMSS^MT public key is defined as follows:

   XMSSMT-HashSig-PublicKey ::= OCTET STRING

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

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6.  Key Usage Bits

   The intended application for the key is indicated in the keyUsage
   certificate extension [RFC5280].  If the keyUsage extension is
   present in a certificate that indicates id-alg-hss-lms-hashsig, id-
   alg-xmss-hashsig, or id-alg-xmssmt-hashsig, then the following
   requirements given in this section MUST be fulfilled.

   If the keyUsage extension is present in a code signing certificate,
   then it MUST contain at least one of the following values:

   nonRepudiation; or
   digitalSignature.

   However, it MUST NOT contain other values.

   If the keyUsage extension is present in a certification authority
   certificate, then it MUST contain at least one of the following
   values:

   nonRepudiation; or
   digitalSignature; or
   keyCertSign; or
   cRLSign.

   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 [RFC8708].

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.

   The data to be signed is prepared for signing.  For the algorithms
   used in this document, the data is signed directly by the signature
   algorithm, the data is not hashed before processing.  Then, a private
   key operation is performed to generate the signature value.

   [EDNOTE: Should we delete the preceding paragraph?]

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   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 XMSS 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.

   id-alg-xmss-hashsig  OBJECT IDENTIFIER ::= {
      itu-t(0) identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) xmss(13) 0 }

   The XMSS signature is defined as follows:

   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].

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7.3.  XMSS^MT Signature Algorithm

   The XMSS^MT 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.

   id-alg-xmssmt-hashsig  OBJECT IDENTIFIER ::= {
      itu-t(0) identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) xmssmt(14) 0 }

   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].

--
-- ASN.1 Module
--

<CODE STARTS>

Hashsigs-pkix-0 -- TBD - IANA assigned module OID

DEFINITIONS IMPLICIT TAGS ::= BEGIN

EXPORTS ALL;

IMPORTS
  PUBLIC-KEY, SIGNATURE-ALGORITHM
  FROM AlgorithmInformation-2009
    {iso(1) identified-organization(3) dod(6) internet(1) security(5)

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    mechanisms(5) pkix(7) id-mod(0) id-mod-algorithmInformation-02(58)};

--
-- Object Identifiers
--

-- id-alg-hss-lms-hashsig is defined in [RFC8708]

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 }

id-alg-xmss-hashsig  OBJECT IDENTIFIER ::= { itu-t(0)
   identified-organization(4) etsi(0) reserved(127)
   etsi-identified-organization(0) isara(15) algorithms(1)
   asymmetric(1) xmss(13) 0 }

id-alg-xmssmt-hashsig  OBJECT IDENTIFIER ::= { itu-t(0)
   identified-organization(4) etsi(0) reserved(127)
   etsi-identified-organization(0) isara(15) algorithms(1)
   asymmetric(1) xmssmt(14) 0 }

--
-- Signature Algorithms and Public Keys
--

-- sa-HSS-LMS-HashSig is defined in [RFC8708]

sa-HSS-LMS-HashSig SIGNATURE-ALGORITHM ::= {
   IDENTIFIER id-alg-hss-lms-hashsig
   PARAMS ARE absent
   PUBLIC-KEYS { pk-HSS-LMS-HashSig }
   SMIME-CAPS { IDENTIFIED BY id-alg-hss-lms-hashsig } }

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]

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pk-HSS-LMS-HashSig PUBLIC-KEY ::= {
   IDENTIFIER id-alg-hss-lms-hashsig
   KEY HSS-LMS-HashSig-PublicKey
   PARAMS ARE absent
   CERT-KEY-USAGE
      { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

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

pk-XMSS-HashSig PUBLIC-KEY ::= {
   IDENTIFIER id-alg-xmss-hashsig
   KEY XMSS-HashSig-PublicKey
   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 XMSSMT-HashSig-PublicKey
   PARAMS ARE absent
   CERT-KEY-USAGE
      { digitalSignature, nonRepudiation, keyCertSign, cRLSign } }

XMSSMT-HashSig-PublicKey ::= OCTET STRING

END

<CODE ENDS>

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

   IANA is requested to assign a module OID from the "SMI for PKIX
   Module Identifier" registry for the ASN.1 module in Section 6.

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/rfc/rfc2119>.

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   [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>.

   [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>.

   [RFC8708]  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>.

   [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>.

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   [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>.

   [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>.

   [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>.

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 [RFC8708].  Thanks go to the
   authors of those documents.  "Copying always makes things easier and
   less error prone" - [RFC8411].

Authors' Addresses

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

   Scott Fluhrer
   Cisco Systems
   Email: sfluhrer@cisco.com

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   Stefan Gazdag
   genua GmbH
   Email: ietf@gazdag.de

   Daniel Van Geest
   CryptoNext Security
   Email: daniel.vangeest.ietf@gmail.com

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

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