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Versions: 00 01

Network Working Group                                       D. Van Geest
Internet-Draft                                         ISARA Corporation
Intended status: Standards Track                              S. Fluhrer
Expires: April 13, 2019                                    Cisco Systems
                                                        October 10, 2018


  Algorithm Identifiers for HSS and XMSS for Use in the Internet X.509
                       Public Key Infrastructure
                    draft-vangeest-x509-hash-sigs-00

Abstract

   This document specifies algorithm identifiers and ASN.1 encoding
   formats for the 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 digital signatures are used to sign
   certificates and certificate revocation lists (CRLs).

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
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on April 13, 2019.

Copyright Notice

   Copyright (c) 2018 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
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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Subject Public Key Algorithms . . . . . . . . . . . . . . . .   3
     2.1.  HSS Public Keys . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  XMSS Public Keys  . . . . . . . . . . . . . . . . . . . .   4
     2.3.  XMSS^MT Public Keys . . . . . . . . . . . . . . . . . . .   4
   3.  Key Usage Bits  . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Signature Algorithms  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  HSS Signature Algorithm . . . . . . . . . . . . . . . . .   6
     4.2.  XMSS Signature Algorithm  . . . . . . . . . . . . . . . .   6
     4.3.  XMSS^MT Signature Algorithm . . . . . . . . . . . . . . .   7
   5.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
     6.1.  Algorithm Security Considerations . . . . . . . . . . . .  10
     6.2.  Implementation Security Considerations  . . . . . . . . .  10
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   The Hierarchical Signature System (HSS) is described in
   [I-D.mcgrew-hash-sigs].

   The eXtended Merkle Signature Scheme (XMSS), and its multi-tree
   variant XMSS^MT, are described in [RFC8391].

   These signature algorithms are based on well-studied Hash Based
   Signature (HBS) schemes, which can withstand known attacks using
   quantum computers.  They combine Merkle Trees with One Time Signature
   (OTS) schemes in order to create signature systems which can sign a
   large but limited number of messages per private key.  The private
   keys are stateful; a key's state must be updated and persisted after
   signing to prevent reuse of OTS keys.  If an OTS key is reused,
   cryptographic security is not guaranteed for that key.

   Due to the statefulness of the private key and the limited number of
   signatures that can be created, these signature algorithms might not
   be appropriate for use in interactive protocols.  While the right
   selection of algorithm parameters would allow a private key to sign a



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   virtually unbounded number of messages (e.g. 2^60), this is at the
   cost of a larger signature size and longer signing time.  Since these
   algorithms are already known to be secure against quantum attacks,
   and because roots of trust are generally long-lived and can take
   longer to be deployed than end-entity certificates, these signature
   algorithms are more appropriate to be used in root and subordinate CA
   certificates.  They are also appropriate in non-interactive contexts
   such as code signing.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Subject 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.

   In this document, we define two new OIDs for identifying the
   different hash-based signature algorithms.  A third OID is defined in
   [I-D.ietf-lamps-cms-hash-sig] and repeated here for convenience.  For
   all of the OIDs, the parameters MUST be absent.

2.1.  HSS Public Keys

   The object identifier and public key algorithm identifier for HSS is
   defined in [I-D.ietf-lamps-cms-hash-sig].  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
   [I-D.mcgrew-hash-sigs].

   The HSS public key's properties are defined as follows:







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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

   [I-D.ietf-lamps-cms-hash-sig] contains more information on the
   contents and format of an HSS public key.

2.2.  XMSS Public Keys

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

      id-xmss  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's properties are defined as follows:

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

      XMSS-PublicKey ::= OCTET STRING

   The format of an XMSS public key is is formally defined using XDR
   [RFC4506] and is defined in Appendix B.3 of [RFC8391].  In
   particular, the first 4 bytes represents the big-ending encoding of
   the XMSS algorithm type.

2.3.  XMSS^MT Public Keys

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

      id-xmssmt  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's properties are defined as follows:




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

      XMSSMT-PublicKey ::= OCTET STRING

   The format of an XMSS^MT public key is is formally defined using XDR
   [RFC4506] and is defined in Appendix C.3 of [RFC8391].  In
   particular, the first 4 bytes represents the big-ending encoding of
   the XMSS^MT algorithm type.

3.  Key Usage Bits

   The intended application for the key is indicated in the keyUsage
   certificate extension.

   If the keyUsage extension is present in an end-entity certificate
   that indicates id-xmss or id-xmssmt in SubjectPublicKeyInfo, then the
   keyUsage extension MUST contain one or both of the following values:

      nonRepudiation; and
      digitalSignature.

   If the keyUsage extension is present in a certification authority
   certificate that indicates id-xmss or id-xmssmt, then the keyUsage
   extension MUST contain one or more of the following values:

      nonRepudiation;
      digitalSignature;
      keyCertSign; and
      cRLSign.

   [I-D.ietf-lamps-cms-hash-sig] defines the key usage for id-alg-hss-
   lms-hashsig, which is the same as for the keys above.

4.  Signature Algorithms

   Certificates and CRLs conforming to [RFC5280] may be signed with any
   public key signature algorithm.  The certificate or CRL indicates the
   algorithm through an algorithm identifier which appears in the
   signatureAlgorithm field within the Certificate or CertificateList.
   This algorithm identifier is an OID and has optionally associated
   parameters.  This section identifies algorithm identifiers that MUST
   be used in the signatureAlgorithm field in a Certificate or
   CertificateList.



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   Signature algorithms are always used in conjunction with a one-way
   hash function.

   This section identifies OIDs for 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 below.

   The data to be signed (e.g., the one-way hash function output value)
   is directly signed by the hash-based signature algorithms without any
   additional formatting necessary.  The signature values is a large
   OCTET STRING.  This signature value is then ASN.1 encoded as a BIT
   STRING and included in the Certificate or CertificateList in the
   signature field.

4.1.  HSS Signature Algorithm

   The ASN.1 OIDs used to specify that an HSS signature was generated on
   a SHA-256 or SHA-512 hash of an object are, respectively:

      hss-with-SHA256  OBJECT IDENTIFIER ::= { itu-t(0)
         identified-organization(4) etsi(0) reserved(127)
         etsi-identified-organization(0) isara(15) algorithms(1)
         asymmetric(1) hss(12) 2 }

      hss-with-SHA512  OBJECT IDENTIFIER ::= { itu-t(0)
         identified-organization(4) etsi(0) reserved(127)
         etsi-identified-organization(0) isara(15) algorithms(1)
         asymmetric(1) hss(12) 1 }

   [I-D.ietf-lamps-cms-hash-sig] contains more information on the
   contents and format of an HSS signature.

4.2.  XMSS Signature Algorithm

   The ASN.1 OIDs used to specify that an XMSS signature was generated
   on a SHA-256 or SHA-512 hash of an object are, respectively:

      xmss-with-SHA256  OBJECT IDENTIFIER ::= { itu-t(0)
         identified-organization(4) etsi(0) reserved(127)
         etsi-identified-organization(0) isara(15) algorithms(1)
         asymmetric(1) xmss(13) 2 }

      xmss-with-SHA512  OBJECT IDENTIFIER ::= { itu-t(0)
         identified-organization(4) etsi(0) reserved(127)
         etsi-identified-organization(0) isara(15) algorithms(1)
         asymmetric(1) xmss(13) 1 }



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   The format of an XMSS signature is is formally defined using XDR
   [RFC4506] and is defined in Appendix B.2 of [RFC8391].

4.3.  XMSS^MT Signature Algorithm

   The ASN.1 OIDs used to specify that an XMSS^MT signature was
   generated on a SHA-256 or SHA-512 hash of an object are,
   respectively:

      xmssmt-with-SHA256  OBJECT IDENTIFIER ::= { itu-t(0)
         identified-organization(4) etsi(0) reserved(127)
         etsi-identified-organization(0) isara(15) algorithms(1)
         asymmetric(1) xmssmt(14) 2 }

      xmssmt-with-SHA512  OBJECT IDENTIFIER ::= { itu-t(0)
         identified-organization(4) etsi(0) reserved(127)
         etsi-identified-organization(0) isara(15) algorithms(1)
         asymmetric(1) xmssmt(14) 1 }

   The format of an XMSS^MT signature is is formally defined using XDR
   [RFC4506] and is defined in Appendix C.2 of [RFC8391].

5.  ASN.1 Module

   For reference purposes, the ASN.1 syntax is presented as an ASN.1
   module here.

   -- ASN.1 Module

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

   DEFINITIONS EXPLICIT TAGS ::=
   BEGIN

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










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   --
   -- HSS Signatures
   --

   -- OID for HSS signature generated with SHA-256 hash

   hss-with-SHA256  OBJECT IDENTIFIER ::= { itu-t(0)
      identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) hss(12) 2 }

   -- OID for HSS signature generated with SHA-512 hash

   hss-with-SHA512  OBJECT IDENTIFIER ::= { itu-t(0)
      identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) hss(12) 1 }

   --
   -- XMSS Keys and Signatures
   --

   -- OID for XMSS public keys

   id-xmss  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 }

   -- XMSS Public Keys

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

   XMSS-PublicKey ::= OCTET STRING

   -- OID for XMSS signature generated with SHA-256 hash

   xmss-with-SHA256  OBJECT IDENTIFIER ::= { itu-t(0)
      identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) xmss(13) 2 }





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   -- OID for XMSS signature generated with SHA-512 hash

   xmss-with-SHA512  OBJECT IDENTIFIER ::= { itu-t(0)
      identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) xmss(13) 1 }

   --
   -- XMSS^MT Keys and Signatures
   --

   -- OID for XMSS^MT public keys

   id-xmssmt  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 }

   -- XMSS^MT Public Keys

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

   XMSSMT-PublicKey ::= OCTET STRING

   -- OID for XMSS^MT signature generated with SHA-256 hash

   xmssmt-with-SHA256  OBJECT IDENTIFIER ::= { itu-t(0)
      identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) xmssmt(14) 2 }

   -- OID for XMSS^MT signature generated with SHA-512 hash

   xmssmt-with-SHA512  OBJECT IDENTIFIER ::= { itu-t(0)
      identified-organization(4) etsi(0) reserved(127)
      etsi-identified-organization(0) isara(15) algorithms(1)
      asymmetric(1) xmssmt(14) 1 }

   END







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6.  Security Considerations

6.1.  Algorithm Security Considerations

   The cryptographic security of the signatures generated by the
   algorithms mentioned in this document depends only on the hash
   algorithms used within the signature algorithms and the pre-hash
   algorithm used to create an X.509 certificate's message digest.
   Grover's algorithm [Grover96] is a quantum search algorithm which
   gives a quadratic improvement in search time to brute-force pre-image
   attacks.  The results of [BBBV97] show that this improvement is
   optimal, however [Fluhrer17] notes that Grover's algorithm doesn't
   parallelize well.  Thus, given a bounded amount of time to perform
   the attack and using a conservative estimate of the performance of a
   real quantum computer, the pre-image quantum security of SHA-256 is
   closer to 190 bits.  All parameter sets for the signature algorithms
   in this document currently use SHA-256 internally and thus have at
   least 128 bits of quantum pre-image resistance, or 190 bits using the
   security assumptions in [Fluhrer17].

   [Zhandry15] shows that hash collisions can be found using an
   algorithm with a lower bound on the number of oracle queries on the
   order of 2^(n/3) on the number of bits, however [DJB09] demonstrates
   that the quantum memory requirements would be much greater.
   Therefore a pre-hash using SHA-256 would have at least 128 bits of
   quantum collision-resistance as well as the pre-image resistance
   mentioned in the previous paragraph.

   Given the quantum collision and pre-image resistance of SHA-256
   estimated above, the algorithm identifiers hss-with-SHA256, xmss-
   with-SHA256 and xmssmt-with-SHA256 defined in this document provide
   128 bits or more of quantum security.  This is believed to be secure
   enough to protect X.509 certificates for well beyond any reasonable
   certificate lifetime, although the SHA-512 variants could be used if
   there are any doubts.

   The algorithm identifiers hss-with-SHA512, xmss-with-SHA512 and
   xmssmt-with-SHA512 are defined in order to provide 256 bits of
   classical security (256 bits of brute-force pre-image resistance with
   the signature algorithms' SHA-256 and 256 bits of birthday attack
   collision resistance with the SHA-512 pre-hash).

6.2.  Implementation Security Considerations

   Implementations must protect the private keys.  Compromise of the
   private keys may result in the ability to forge signatures.  Along
   with the private key, the implementation must keep track of which
   leaf nodes in the tree have been used.  Loss of integrity of this



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   tracking data can cause an one-time key to be used more than once.
   As a result, when a private key and the tracking data are stored on
   non-volatile media or stored in a virtual machine environment, care
   must be taken to preserve confidentiality and integrity.

   The generation of private keys relies on random numbers.  The use of
   inadequate pseudo-random number generators (PRNGs) to generate these
   values can result in little or no security.  An attacker may find it
   much easier to reproduce the PRNG environment that produced the keys,
   searching the resulting small set of possibilities, rather than brute
   force searching the whole key space.  The generation of quality
   random numbers is difficult.  [RFC4086] offers important guidance in
   this area.

   The generation of hash-based signatures also depends on random
   numbers.  While the consequences of an inadequate pseudo-random
   number generator (PRNGs) to generate these values is much less severe
   than the generation of private keys, the guidance in [RFC4086]
   remains important.

7.  Acknowledgements

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

8.  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 5.

9.  References

9.1.  Normative References

   [I-D.ietf-lamps-cms-hash-sig]
              Housley, R., "Use of the HSS/LMS Hash-based Signature
              Algorithm in the Cryptographic Message Syntax (CMS)",
              draft-ietf-lamps-cms-hash-sig-01 (work in progress),
              September 2018.

   [I-D.mcgrew-hash-sigs]
              McGrew, D., Curcio, M., and S. Fluhrer, "Hash-Based
              Signatures", draft-mcgrew-hash-sigs-13 (work in progress),
              September 2018.





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   [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>.

   [RFC4506]  Eisler, M., Ed., "XDR: External Data Representation
              Standard", STD 67, RFC 4506, DOI 10.17487/RFC4506, May
              2006, <https://www.rfc-editor.org/info/rfc4506>.

   [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>.

   [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>.

9.2.  Informative References

   [BBBV97]   Bennett, C., Bernstein, E., Brassard, G., and U. Vazirani,
              "Strengths and weaknesses of quantum computing", SIAM J.
              Comput. 26(5), 1510-1523, 1997.

   [DJB09]    Bernstein, D., "Cost analysis of hash collisions: Will
              quantum computers make SHARCS obsolete?", SHARCS 9, p.
              105, 2009.

   [Fluhrer17]
              Fluhrer, S., "Reassessing Grover's Algorithm", Cryptology
              ePrint Archive Report 2017/811, August 2017,
              <https://eprint.iacr.org/2017/811.pdf>.

   [Grover96]
              Grover, L., "A fast quantum mechanical algorithm for
              database search", 28th ACM Symposium on the Theory of
              Computing p. 212, 1996.

   [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>.






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   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <https://www.rfc-editor.org/info/rfc4086>.

   [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>.

   [Zhandry15]
              Zhandry, M., "A note on the quantum collision and set
              equality problems", Quantum Information & Computation 15,
              7-8, 557-567, May 2015.

Authors' Addresses

   Daniel Van Geest
   ISARA Corporation
   560 Westmount Rd N
   Waterloo, Ontario  N2L 0A9
   Canada

   Email: daniel.vangeest@isara.com


   Scott Fluhrer
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: sfluhrer@cisco.com












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