Skip to main content

Composite Signatures For Use In Internet PKI
draft-ounsworth-pq-composite-sigs-10

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Mike Ounsworth , John Gray , Massimiliano Pala , Jan Klaußner
Last updated 2023-10-23 (Latest revision 2023-05-29)
RFC stream (None)
Formats
Stream Stream state (No stream defined)
Consensus boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date (None)
Responsible AD (None)
Send notices to (None)
draft-ounsworth-pq-composite-sigs-10
LAMPS                                                       M. Ounsworth
Internet-Draft                                                   J. Gray
Intended status: Standards Track                                 Entrust
Expires: 25 April 2024                                           M. Pala
                                                               CableLabs
                                                            J. Klaussner
                                                            D-Trust GmbH
                                                         23 October 2023

              Composite Signatures For Use In Internet PKI
                  draft-ounsworth-pq-composite-sigs-10

Abstract

   The migration to post-quantum cryptography is unique in the history
   of modern digital cryptography in that neither the old outgoing nor
   the new incoming algorithms are fully trusted to protect data for the
   required data lifetimes.  The outgoing algorithms, such as RSA and
   elliptic curve, may fall to quantum cryptanalysis, while the incoming
   post-quantum algorithms face uncertainty about both the underlying
   mathematics as well as hardware and software implementations that
   have not had sufficient maturing time to rule out classical
   cryptanalytic attacks and implementation bugs.

   Cautious implementers may wish to layer cryptographic algorithms such
   that an attacker would need to break all of them in order to
   compromise the data being protected using either a Post-Quantum /
   Traditional Hybrid, Post-Quantum / Post-Quantum Hybrid, or
   combinations thereof.  This document, and its companions, defines a
   specific instantiation of hybrid paradigm called "composite" where
   multiple cryptographic algorithms are combined to form a single key
   or signature such that they can be treated as a single atomic object
   at the protocol level.

   This document defines the structures CompositeSignaturePublicKey,
   CompositeSignaturePrivateKey and CompositeSignatureValue, which are
   sequences of the respective structure for each component algorithm.
   Composite signature algorithm identifiers are specified in this
   document which represent the explicit combinations of the underlying
   component algorithms.

Status of This Memo

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

Ounsworth, et al.         Expires 25 April 2024                 [Page 1]
Internet-Draft              PQ Composite Sigs               October 2023

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

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

   This Internet-Draft will expire on 25 April 2024.

Copyright Notice

   Copyright (c) 2023 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/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Changes in version -10  . . . . . . . . . . . . . . . . . . .   3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Composite Design Philosophy . . . . . . . . . . . . . . .   6
     2.3.  Composite Signatures  . . . . . . . . . . . . . . . . . .   7
       2.3.1.  Composite KeyGen  . . . . . . . . . . . . . . . . . .   7
       2.3.2.  Composite Sign  . . . . . . . . . . . . . . . . . . .   7
       2.3.3.  Composite Verify  . . . . . . . . . . . . . . . . . .   9
     2.4.  OID Concatenation . . . . . . . . . . . . . . . . . . . .  11
     2.5.  PreHashing the Message  . . . . . . . . . . . . . . . . .  13
     2.6.  Algorithm Selection Criteria  . . . . . . . . . . . . . .  13
   3.  Composite Signature Structures  . . . . . . . . . . . . . . .  14
     3.1.  pk-CompositeSignature . . . . . . . . . . . . . . . . . .  14
     3.2.  CompositeSignaturePublicKey . . . . . . . . . . . . . . .  15
     3.3.  CompositeSignaturePrivateKey  . . . . . . . . . . . . . .  15
     3.4.  Encoding Rules  . . . . . . . . . . . . . . . . . . . . .  16
     3.5.  Key Usage Bits  . . . . . . . . . . . . . . . . . . . . .  16
   4.  Composite Signature Structures  . . . . . . . . . . . . . . .  17
     4.1.  sa-CompositeSignature . . . . . . . . . . . . . . . . . .  17
     4.2.  CompositeSignatureValue . . . . . . . . . . . . . . . . .  18

Ounsworth, et al.         Expires 25 April 2024                 [Page 2]
Internet-Draft              PQ Composite Sigs               October 2023

   5.  Algorithm Identifiers . . . . . . . . . . . . . . . . . . . .  18
     5.1.  Notes on id-MLDSA44-RSA2048-PSS-SHA256 and
           id-MLDSA65-RSA3072-PSS-SHA256 . . . . . . . . . . . . . .  21
   6.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . . . . . .  22
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
     7.1.  Object Identifier Allocations . . . . . . . . . . . . . .  29
       7.1.1.  Module Registration - SMI Security for PKIX Module
               Identifier  . . . . . . . . . . . . . . . . . . . . .  29
       7.1.2.  Object Identifier Registrations - SMI Security for PKIX
               Algorithms  . . . . . . . . . . . . . . . . . . . . .  29
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  32
     8.1.  Policy for Deprecated and Acceptable Algorithms . . . . .  32
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  33
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  34
   Appendix A.  Samples  . . . . . . . . . . . . . . . . . . . . . .  37
     A.1.  Explicit Composite Signature Examples . . . . . . . . . .  37
       A.1.1.  MLDSA44-ECDSA-P256-SHA256 Public Key  . . . . . . . .  37
       A.1.2.  MLDSA44-ECDSA-P256 Private Key  . . . . . . . . . . .  37
       A.1.3.  MLDSA44-ECDSA-P256 Self-Signed X509 Certificate . . .  39
   Appendix B.  Implementation Considerations  . . . . . . . . . . .  41
     B.1.  FIPS certification  . . . . . . . . . . . . . . . . . . .  41
     B.2.  Backwards Compatibility . . . . . . . . . . . . . . . . .  42
       B.2.1.  Parallel PKIs . . . . . . . . . . . . . . . . . . . .  42
       B.2.2.  Hybrid Extensions (Keys and Signatures) . . . . . . .  43
   Appendix C.  Intellectual Property Considerations . . . . . . . .  43
   Appendix D.  Contributors and Acknowledgements  . . . . . . . . .  43
     D.1.  Making contributions  . . . . . . . . . . . . . . . . . .  44
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  44

1.  Changes in version -10

   Changes affecting interoperability:

   *  Changed all SEQUENCE OF SIZE (2..MAX) to SEQUENCE OF SIZE (2).

   *  Removed CompositeSignatureParams since all params are now explicit
      in the Object IDs

   *  Made RSA keys fixed-length at 3072

   *  Removee redundency of subject public key overhead since OID fully
      specifies the keytype and parameters

   *  Re-worked wire format of the composite signature by prehashing and
      concatenating the OID to each component signature.  This is
      believed to give the binding between the two component algorithms
      a stronger non-separability property.

Ounsworth, et al.         Expires 25 April 2024                 [Page 3]
Internet-Draft              PQ Composite Sigs               October 2023

   Editorial changes:

   *  Made this document standalone by folding in the minimum necessary
      content from composite-keys

   *  Added a paragraph describing how to reconstitute component Subject
      Public Key Infos

   *  Added a section showing the HEX encoding of the String Algorithm
      Names

   *  Added a section on pre-hashing

   *  Rename Dilithium to ML-DSA and Falcon to FN-DSA

   *  Added an Implementation Consideration about FIPS validation where
      only one component algorithm is FIPS-approved.

   *  Added a section on Signature APIs (Keygen, Sign, Verify) in
      introduction

   *  Added reference to draft-vaira-pquip-pqc-use-cases-00

   *  TODO Refactored to use MartinThomson github template

2.  Introduction

   During the transition to post-quantum cryptography, there will be
   uncertainty as to the strength of cryptographic algorithms; we will
   no longer fully trust traditional cryptography such as RSA, Diffie-
   Hellman, DSA and their elliptic curve variants, but we will also not
   fully trust their post-quantum replacements until they have had
   sufficient scrutiny and time to discover and fix implementation bugs.
   Unlike previous cryptographic algorithm migrations, the choice of
   when to migrate and which algorithms to migrate to, is not so clear.
   Even after the migration period, it may be advantageous for an
   entity's cryptographic identity to be composed of multiple public-key
   algorithms.

   Cautious implementers may wish to combine cryptographic algorithms
   such that an attacker would need to break all of them in order to
   compromise the data being protected.  Such mechanisms are referred to
   as Post-Quantum / Traditional Hybrids
   [I-D.driscoll-pqt-hybrid-terminology].

   PQ/T Hybrid cryptography can, in general, provide solutions to two
   migration problems:

Ounsworth, et al.         Expires 25 April 2024                 [Page 4]
Internet-Draft              PQ Composite Sigs               October 2023

   *  Algorithm strength uncertainty: During the transition period, some
      post-quantum signature and encryption algorithms will not be fully
      trusted, while also the trust in legacy public key algorithms will
      start to erode.  A relying party may learn some time after
      deployment that a public key algorithm has become untrustworthy,
      but in the interim, they may not know which algorithm an adversary
      has compromised.

   *  Ease-of-migration: During the transition period, systems will
      require mechanisms that allow for staged migrations from fully
      classical to fully post-quantum-aware cryptography.

   *  Safeguard against faulty algorithm implementations and compromised
      keys: Even for long known algorithms there is a non-negligible
      risk of severe implementation faults.  Latest examples are the
      ROCA attack and ECDSA psychic signatures.  Using more than one
      algorithms will mitigate these risks.

   This document defines a specific instantiation of the PQ/T Hybrid
   paradigm called "composite" where multiple cryptographic algorithms
   are combined to form a single signature such that it can be treated
   as a single atomic algorithm at the protocol level.  Composite
   algorithms address algorithm strength uncertainty because the
   composite algorithm remains strong so long as one of its components
   remains strong.  Concrete instantiations of composite signature
   algorithms are provided based on ML-DSA, Falcon, RSA and ECDSA.
   Backwards compatibility is not directly covered in this document, but
   is the subject of Appendix B.2.

   This document is intended for general applicability anywhere that
   digital signatures are used within PKIX and CMS structures.  For a
   more detailed use-case discussion for composite signatures, the
   reader is encouraged to look at [I-D.vaira-pquip-pqc-use-cases]

2.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The following terms are used in this document:

   ALGORITHM: A standardized cryptographic primitive, as well as any
   ASN.1 structures needed for encoding data and metadata needed to use
   the algorithm.  This document is primarily concerned with algorithms
   for producing digital signatures.

Ounsworth, et al.         Expires 25 April 2024                 [Page 5]
Internet-Draft              PQ Composite Sigs               October 2023

   BER: Basic Encoding Rules (BER) as defined in [X.690].

   CLIENT: Any software that is making use of a cryptographic key.  This
   includes a signer, verifier, encrypter, decrypter.

   COMPONENT ALGORITHM: A single basic algorithm which is contained
   within a composite algorithm.

   COMPOSITE ALGORITHM: An algorithm which is a sequence of two or more
   component algorithms, as defined in Section 3.

   DER: Distinguished Encoding Rules as defined in [X.690].

   LEGACY: For the purposes of this document, a legacy algorithm is any
   cryptographic algorithm currently is use which is not believe to be
   resistant to quantum cryptanalysis.

   PKI: Public Key Infrastructure, as defined in [RFC5280].

   POST-QUANTUM ALGORITHM: Any cryptographic algorithm which is believed
   to be resistant to classical and quantum cryptanalysis, such as the
   algorithms being considered for standardization by NIST.

   PUBLIC / PRIVATE KEY: The public and private portion of an asymmetric
   cryptographic key, making no assumptions about which algorithm.

   SIGNATURE: A digital cryptographic signature, making no assumptions
   about which algorithm.

   STRIPPING ATTACK: An attack in which the attacker is able to
   downgrade the cryptographic object to an attacker-chosen subset of
   original set of component algorithms in such a way that it is not
   detectable by the receiver.  For example, substituting a composite
   public key or signature for a version with fewer components.

2.2.  Composite Design Philosophy

   [I-D.driscoll-pqt-hybrid-terminology] defines composites as:

      _Composite Cryptographic Element_: A cryptographic element that
      incorporates multiple component cryptographic elements of the same
      type in a multi-algorithm scheme.

   Composite keys as defined here follow this definition and should be
   regarded as a single key that performs a single cryptographic
   operation such key generation, signing, verifying, encapsulating, or
   decapsulating -- using its internal sequence of component keys as if
   they form a single key.  This generally means that the complexity of

Ounsworth, et al.         Expires 25 April 2024                 [Page 6]
Internet-Draft              PQ Composite Sigs               October 2023

   combining algorithms can and should be handled by the cryptographic
   library or cryptographic module, and the single composite public key,
   private key, and ciphertext can be carried in existing fields in
   protocols such as PKCS#10 [RFC2986], CMP [RFC4210], X.509 [RFC5280],
   CMS [RFC5652], and the Trust Anchor Format [RFC5914].  In this way,
   composites achieve "protocol backwards-compatibility" in that they
   will drop cleanly into any protocol that accepts KEM algorithms
   without requiring any modification of the protocol to handle multiple
   keys.

2.3.  Composite Signatures

   Here we define the signature mechanism in which a signature is a
   cryptographic primitive that consists of three algorithms:

   *  KeyGen() -> (pk, sk): A probabilistic key generation algorithm,
      which generates a public key pk and a secret key sk.

   *  Sign(sk, Message) -> (signature): A signing algorithm which takes
      as input a secret key sk and a Message, and outputs a signature

   *  Verify(pk, Message, signature) -> true or false: A verification
      algorithm which takes as input a public key, a Message and
      signature and outputs true if the signature and public key can be
      used to verify the message.  Thus it proves the Message was signed
      with the secret key associated with the public key and verifies
      the integrity of the Message.  If the signature and public key
      cannot verify the Message, it returns false.

   A composite signature allows two or more underlying signature
   algorithms to be combined into a single cryptographic signature
   operation and can be used for applications that require signatures.

2.3.1.  Composite KeyGen

   The KeyGen() -> (pk, sk) of a composite signature algorithm will
   perform the KeyGen() of the respective component signature algorithms
   and it produces a composite public key pk as per Section 3.2 and a
   composite secret key sk is per Section 3.3.

2.3.2.  Composite Sign

   Generation of a composite signature involves applying each component
   algorithm's signature process to the input message according to its
   specification, and then placing each component signature value into
   the CompositeSignatureValue structure defined in Section 4.1.

   The following process is used to generate composite signature values.

Ounsworth, et al.         Expires 25 April 2024                 [Page 7]
Internet-Draft              PQ Composite Sigs               October 2023

Sign (sk, Message) -> (signature)
Input:
     K1, K2             Signing private keys for each component. See note below on
                        composite inputs.

     A1, A2             Component signature algorithms. See note below on
                        composite inputs.

     Message            The Message to be signed, an octet string

     HASH               The Message Digest Algorithm used for pre-hashing.  See section
                        on pre-hashing below.

     OID                The Composite Signature String Algorithm Name converted
                        from ASCII to bytes.  See section on OID concatenation
                        below.

Output:
     signature          The composite signature, a CompositeSignatureValue

Signature Generation Process:

   1. Compute a Hash of the Message

         M' = HASH(Message)

   2. Generate the n component signatures independently,
      according to their algorithm specifications.

         S1 := Sign( K1, A1, OID || M' )
         S2 := Sign( K2, A2, OID || M' )

   3. Encode each component signature S1 and S2 into a BIT STRING
      according to its algorithm specification.

        signature ::= Sequence { S1, S2 }

   4. Output signature

                Figure 1: Composite Sign(sk, Message)

Ounsworth, et al.         Expires 25 April 2024                 [Page 8]
Internet-Draft              PQ Composite Sigs               October 2023

   Note on composite inputs: the method of providing the list of
   component keys and algorithms is flexible and beyond the scope of
   this pseudo-code.  When passed to the Composite Sign(sk, Message) API
   the sk is a CompositePrivateKey.  It is possible to construct a
   CompositePrivateKey from component keys stored in separate software
   or hardware keystores.  Variations in the process to accommodate
   particular private key storage mechanisms are considered to be
   conformant to this document so long as it produces the same output as
   the process sketched above.

   Since recursive composite public keys are disallowed, no component
   signature may itself be a composite; ie the signature generation
   process MUST fail if one of the private keys K1 or K2 is a composite.

   A composite signature MUST produce, and include in the output, a
   signature value for every component key in the corresponding
   CompositePublicKey, and they MUST be in the same order; ie in the
   output, S1 MUST correspond to K1, S2 to K2.

2.3.3.  Composite Verify

   Verification of a composite signature involves applying each
   component algorithm's verification process according to its
   specification.

   In the absence of an application profile specifying otherwise,
   compliant applications MUST output "Valid signature" (true) if and
   only if all component signatures were successfully validated, and
   "Invalid signature" (false) otherwise.

   The following process is used to perform this verification.

Composite Verify(pk, Message, signature)
Input:
     P1, P2             Public verification keys. See note below on
                        composite inputs.

     Message            Message whose signature is to be verified,
                        an octet string

     signature          CompositeSignatureValue containing the component
                        signature values (S1 and S2) to be verified.

     A1, A2             Component signature algorithms. See note
                        below on composite inputs.

     HASH               The Message Digest Algorithm for pre-hashing.  See
                        section on pre-hashing the message below.

Ounsworth, et al.         Expires 25 April 2024                 [Page 9]
Internet-Draft              PQ Composite Sigs               October 2023

     OID                The Composite Signature String Algorithm Name converted
                        from ASCII to bytes.  See section on OID concatenation
                        below

Output:
    Validity (bool)    "Valid signature" (true) if the composite
                        signature is valid, "Invalid signature"
                        (false) otherwise.

Signature Verification Procedure::
   1. Check keys, signatures, and algorithms lists for consistency.

      If Error during Desequencing, or the sequences have
      different numbers of elements, or any of the public keys
      P1 or P2 and the algorithm identifiers A1 or A2 are
      composite then output "Invalid signature" and stop.

   2. Compute a Hash of the Message

         M' = HASH(Message)

   3. Check each component signature individually, according to its
       algorithm specification.
       If any fail, then the entire signature validation fails.

       if not verify( P1, OID || M', S1, A1 ) then
            output "Invalid signature"
       if not verify( P2, OID || M', S2, A2 ) then
            output "Invalid signature"

       if all succeeded, then
        output "Valid signature"

          Figure 2: Composite Verify(pk, Message, signature)

   Note on composite inputs: the method of providing the list of
   component keys and algorithms is flexible and beyond the scope of
   this pseudo-code.  When passed to the Composite Verify(pk, Message,
   signature) API the pk is a CompositePublicKey.  It is possible to
   construct a CompositePublicKey from component keys stored in separate
   software or hardware keystores.  Variations in the process to
   accommodate particular private key storage mechanisms are considered
   to be conformant to this document so long as it produces the same
   output as the process sketched above.

   Since recursive composite public keys are disallowed, no component
   signature may itself be a composite; ie the signature generation
   process MUST fail if one of the private keys K1 or K2 is a composite.

Ounsworth, et al.         Expires 25 April 2024                [Page 10]
Internet-Draft              PQ Composite Sigs               October 2023

2.4.  OID Concatenation

   As mentioned above, the OID input value for the Composite Signature
   Generation and verification process is the String representation of
   the OID converted from ASCII to bytes.  The following table shows the
   HEX encoding of the ASCII String representation for each Signature
   AlgorithmID

Ounsworth, et al.         Expires 25 April 2024                [Page 11]
Internet-Draft              PQ Composite Sigs               October 2023

   +=============================+==================================================================================+
   |Composite Signature          |HEX Encoding to be prepended to each Message                                      |
   |AlgorithmID                  |                                                                                  |
   +=============================+==================================================================================+
   |id-MLDSA44-RSA2048-PSS-SHA256|69642D4D4C44534134342D525341323034382D5053532D534841323536                        |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-                          |69642D4D4C44534134342D525341323034382D504B435331352D534841323536                  |
   |MLDSA44-RSA2048-PKCS15-SHA256|                                                                                  |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA44-Ed25519-SHA512    |69642D4D4C44534134342D456432353531392D534841353132                                |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA44-ECDSA-P256-SHA256 |69642D4D4C44534134342D45434453412D503235362D534841323536                          |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA44-ECDSA-            |69642D4D4C44534134342D45434453412D627261696E706F6F6C5032353672312D534841323536    |
   |brainpoolP256r1-SHA256       |                                                                                  |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA65-RSA3072-PSS-SHA256|69642D4D4C44534136352D525341333037322D5053532D534841323536                        |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-                          |69642D4D4C44534136352D525341333037322D504B435331352D534841323536                  |
   |MLDSA65-RSA3072-PKCS15-SHA256|                                                                                  |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA65-ECDSA-P256-SHA256 |69642D4D4C44534136352D45434453412D503235362D534841323536                          |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA65-ECDSA-            |69642D4D4C44534136352D45434453412D627261696E706F6F6C5032353672312D534841323536    |
   |brainpoolP256r1-SHA256       |                                                                                  |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA65-Ed25519-SHA512    |69642D4D4C44534136352D456432353531392D534841353132                                |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA87-ECDSA-P384-SHA384 |69642D4D4C44534138372D45434453412D503338342D534841333834                          |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA87-ECDSA-            |69642D4D4C44534138372D45434453412D627261696E706F6F6C5033383472312D534841333834    |
   |brainpoolP384r1-SHA384       |                                                                                  |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-MLDSA87-Ed448-SHAKE256    |69642D4D4C44534138372D45643434382D5348414B45323536                                |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-Falon512-ECDSA-P256-SHA256|69642D46616C6F6E3531322D45434453412D503235362D534841323536                        |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-Falcon512-ECDSA-          |69642D46616C636F6E3531322D45434453412D627261696E706F6F6C5032353672312D534841323536|
   |brainpoolP256r1-SHA256       |                                                                                  |
   +-----------------------------+----------------------------------------------------------------------------------+
   |id-Falcon512-Ed25519-SHA512  |69642D46616C636F6E3531322D456432353531392D534841353132                            |
   +-----------------------------+----------------------------------------------------------------------------------+

              Table 1: Composite Signature OID Concatenations

Ounsworth, et al.         Expires 25 April 2024                [Page 12]
Internet-Draft              PQ Composite Sigs               October 2023

2.5.  PreHashing the Message

   As noted in the composite signature generation process and composite
   signature verification process, the Message should be pre-hashed into
   M' with the digest algorithm specified in the composite signature
   algorithm identifier.  The choice of the digest algorithm was chosen
   with the following criteria:

   1.  For composites paired with RSA or ECDSA, the hashing algorithm
       SHA256 or SHA384 is used as part of the RSA or ECDSA signature
       algorithm and is therefore also used as the composite prehashing
       algorithm.

   2.  For Dilithium signing a digest of the message is allowed as long
       as the hash function provides at least y bits of classical
       security strength against both collision and second preimage
       attacks.  For MLDSA44 y is 128 bits, MLDSA65 y is 192 bits and
       for MLDSA87 y is 256 bits.  Therefore SHA256 paired with RSA and
       SHA256 and SHA384 paired with ECDSA match the appropriate
       security strength.

   3.  Ed25519 [RFC8032] uses SHA512 internally, therefore SHA512 is
       used to pre-hash the message when Ed25519 is a component
       algorithm.

   4.  Ed448 [RFC8032] uses SHAKE256 internally, therefore SHA256 with
       an output length of 512 bits is used to pre-hash the message when
       Ed448 is a component algorithm.  This is denoted in the table in
       Section 5 as SHAKE256/512.

   5.  TODO: For Falcon signing it is expected prehashing digest
       accomodations will be allowed.

2.6.  Algorithm Selection Criteria

   The composite algorithm combinations defined in this document were
   chosen according to the following guidelines:

   1.  A single RSA combination is provided at a key size of 3072 bits,
       matched with NIST PQC Level 3 algorithms.

Ounsworth, et al.         Expires 25 April 2024                [Page 13]
Internet-Draft              PQ Composite Sigs               October 2023

   2.  Elliptic curve algorithms are provided with combinations on each
       of the NIST [RFC6090], Brainpool [RFC5639], and Edwards [RFC7748]
       curves.  NIST PQC Levels 1 - 3 algorithms are matched with
       256-bit curves, while NIST levels 4 - 5 are matched with 384-bit
       elliptic curves.  This provides a balance between matching
       classical security levels of post-quantum and traditional
       algorithms, and also selecting elliptic curves which already have
       wide adoption.

   3.  NIST level 1 candidates are provided, matched with 256-bit
       elliptic curves, intended for constrained use cases.

   If other combinations are needed, a separate specification should be
   submitted to the IETF LAMPS working group.  To ease implementation,
   these specifications are encouraged to follow the construction
   pattern of the algorithms specified in this document.

   The composite structures defined in this specification allow only for
   pairs of algorithms.  This also does not preclude future
   specification from extending these structures to define combinations
   with three or more components.

3.  Composite Signature Structures

   In order for signatures to be composed of multiple algorithms, we
   define encodings consisting of a sequence of signature primitives
   (aka "component algorithms") such that these structures can be used
   as a drop-in replacement for existing signature fields such as those
   found in PKCS#10 [RFC2986], CMP [RFC4210], X.509 [RFC5280], CMS
   [RFC5652].

3.1.  pk-CompositeSignature

   The following ASN.1 Information Object Class is a template to be used
   in defining all composite Signature public key types.

   pk-CompositeSignature {
     OBJECT IDENTIFIER:id, FirstPublicKeyType,
     SecondPublicKeyType} PUBLIC-KEY ::=
     {
       IDENTIFIER id
       KEY SEQUENCE {
        BIT STRING (CONTAINING FirstPublicKeyType)
        BIT STRING (CONTAINING SecondPublicKeyType)
       }
       PARAMS ARE absent
       CERT-KEY-USAGE { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
     }

Ounsworth, et al.         Expires 25 April 2024                [Page 14]
Internet-Draft              PQ Composite Sigs               October 2023

   As an example, the public key type pk-MLDSA65-ECDSA-P256-SHA256 is
   defined as:

   pk-MLDSA65-ECDSA-P256-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA65-ECDSA-P256-SHA256,
     OCTET STRING, ECPoint}

   The full set of key types defined by this specification can be found
   in the ASN.1 Module in Section 6.

3.2.  CompositeSignaturePublicKey

   Composite public key data is represented by the following structure:

   CompositeSignaturePublicKey ::= SEQUENCE SIZE (2) OF BIT STRING

   A composite key MUST contain two component public keys.  The order of
   the component keys is determined by the definition of the
   corresponding algorithm identifier as defined in section Section 5.

   Some applications may need to reconstruct the SubjectPublicKeyInfo
   objects corresponding to each component public key.  Table 3 in
   Section 5 provides the necessary mapping between composite and their
   component algorithms for doing this reconstruction.  This also
   motivates the design choice of SEQUENCE OF BIT STRING instead of
   SEQUENCE OF OCTET STRING; using BIT STRING allows for easier
   transcription between CompositeSignaturePublicKey and
   SubjectPublicKeyInfo.

   When the CompositeSignaturePublicKey must be provided in octet string
   or bit string format, the data structure is encoded as specified in
   Section 3.4.

3.3.  CompositeSignaturePrivateKey

   Usecases that require an interoperable encoding for composite private
   keys, such as when private keys are carried in PKCS #12 [RFC7292],
   CMP [RFC4210] or CRMF [RFC4211] MUST use the following structure.

   CompositeSignaturePrivateKey ::= SEQUENCE SIZE (2) OF OneAsymmetricKey

   Each element is a OneAsymmetricKey` [RFC5958] object for a component
   private key.

   The parameters field MUST be absent.

   The order of the component keys is the same as the order defined in
   Section 3.2 for the components of CompositeSignaturePublicKey.

Ounsworth, et al.         Expires 25 April 2024                [Page 15]
Internet-Draft              PQ Composite Sigs               October 2023

   When a CompositePrivateKey is conveyed inside a OneAsymmetricKey
   structure (version 1 of which is also known as PrivateKeyInfo)
   [RFC5958], the privateKeyAlgorithm field SHALL be set to the
   corresponding composite algorithm identifier defined according to
   Section 5, the privateKey field SHALL contain the
   CompositeSignaturePrivateKey, and the publicKey field MUST NOT be
   present.  Associated public key material MAY be present in the
   CompositeSignaturePrivateKey.

   In some usecases the private keys that comprise a composite key may
   not be represented in a single structure or even be contained in a
   single cryptographic module; for example if one component is within
   the FIPS boundary of a cryptographic module and the other is not; see
   {sec-fips} for more discussion.  The establishment of correspondence
   between public keys in a CompositeSignaturePublicKey and private keys
   not represented in a single composite structure is beyond the scope
   of this document.

3.4.  Encoding Rules

   Many protocol specifications will require that the composite public
   key and composite private key data structures be represented by an
   octet string or bit string.

   When an octet string is required, the DER encoding of the composite
   data structure SHALL be used directly.

   CompositeSignaturePublicKeyOs ::= OCTET STRING (CONTAINING CompositeSignaturePublicKey ENCODED BY der)

   When a bit string is required, the octets of the DER encoded
   composite data structure SHALL be used as the bits of the bit string,
   with the most significant bit of the first octet becoming the first
   bit, and so on, ending with the least significant bit of the last
   octet becoming the last bit of the bit string.

   CompositeSignaturePublicKeyBs ::= BIT STRING (CONTAINING CompositeSignaturePublicKey ENCODED BY der)

   In the interests of simplicity and avoiding compatibility issues,
   implementations that parse these structures MAY accept both BER and
   DER.

3.5.  Key Usage Bits

   For protocols such as X.509 [RFC5280] that specify key usage along
   with the public key, then the composite public key associated with a
   composite signature MUST have a signing-type key usage.

Ounsworth, et al.         Expires 25 April 2024                [Page 16]
Internet-Draft              PQ Composite Sigs               October 2023

   If the keyUsage extension is present in a Certification Authority
   (CA) certificate that indicates a composite key, then any combination
   of the following values MAY be present:

   digitalSignature;
   nonRepudiation;
   keyCertSign; and
   cRLSign.

   If the keyUsage extension is present in an End Entity (EE)
   certificate that indicates a composite key, then any combination of
   the following values MAY be present:

   digitalSignature; and
   nonRepudiation;

4.  Composite Signature Structures

4.1.  sa-CompositeSignature

   The ASN.1 algorithm object for a composite signature is:

   sa-CompositeSignature {
     OBJECT IDENTIFIER:id,
       PUBLIC-KEY:publicKeyType }
       SIGNATURE-ALGORITHM ::= {
           IDENTIFIER id
           VALUE CompositeSignatureValue
           PARAMS ARE absent
           PUBLIC-KEYS { publicKeyType }
       }

   The following is an explanation how SIGNATURE-ALGORITHM elements are
   used to create Composite Signatures:

Ounsworth, et al.         Expires 25 April 2024                [Page 17]
Internet-Draft              PQ Composite Sigs               October 2023

    +=============================+===================================+
    | SIGNATURE-ALGORITHM element | Definition                        |
    +=============================+===================================+
    | IDENTIFIER                  | The Object ID used to identify    |
    |                             | the composite Signature Algorithm |
    +-----------------------------+-----------------------------------+
    | VALUE                       | The Sequence of BIT STRINGS for   |
    |                             | each component signature value    |
    +-----------------------------+-----------------------------------+
    | PARAMS                      | Parameters are absent             |
    +-----------------------------+-----------------------------------+
    | PUBLIC-KEYS                 | The composite key required to     |
    |                             | produce the composite signature   |
    +-----------------------------+-----------------------------------+

                                  Table 2

4.2.  CompositeSignatureValue

   The output of the composite signature algorithm is the DER encoding
   of the following structure:

   CompositeSignatureValue ::= SEQUENCE SIZE (2) OF BIT STRING

   Where each BIT STRING within the SEQUENCE is a signature value
   produced by one of the component keys.  It MUST contain one signature
   value produced by each component algorithm, and in the same order as
   specified in the object identifier.

   The choice of SEQUENCE SIZE (2) OF BIT STRING, rather than for
   example a single BIT STRING containing the concatenated signature
   values, is to gracefully handle variable-length signature values by
   taking advantage of ASN.1's built-in length fields.

5.  Algorithm Identifiers

   This section defines the algorithm identifiers for explicit
   combinations.  For simplicity and prototyping purposes, the signature
   algorithm object identifiers specified in this document are the same
   as the composite key object Identifiers.  A proper implementation
   should not presume that the object ID of a composite key will be the
   same as its composite signature algorithm.

   This section is not intended to be exhaustive and other authors may
   define others composite signature algorithms so long as they are
   compatible with the structures and processes defined in this and
   companion public and private key documents.

Ounsworth, et al.         Expires 25 April 2024                [Page 18]
Internet-Draft              PQ Composite Sigs               October 2023

   Some use-cases desire the flexibility for clients to use any
   combination of supported algorithms, while others desire the rigidity
   of explicitly-specified combinations of algorithms.

   The following table summarizes the details for each explicit
   composite signature algorithms:

   The OID referenced are TBD for prototyping only, and the following
   prefix is used for each:

   replace <CompSig> with the String "2.16.840.1.114027.80.7.1"

   Therefore <CompSig>.1 is equal to 2.16.840.1.114027.80.7.1.1

   Signature public key types:

Ounsworth, et al.         Expires 25 April 2024                [Page 19]
Internet-Draft              PQ Composite Sigs               October 2023

   +=============================+============+=========+=======================+============+
   |Composite Signature          |OID         |First    |Second Algorithm       |Pre-Hash    |
   |AlgorithmID                  |            |Algorithm|                       |            |
   +=============================+============+=========+=======================+============+
   |id-MLDSA44-RSA2048-PSS-SHA256|<CompSig>.1 |MLDSA44  |SHA256WithRSAEncryption|SHA256      |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-                          |<CompSig>.2 |MLDSA44  |SHA256WithRSAEncryption|SHA256      |
   |MLDSA44-RSA2048-PKCS15-SHA256|            |         |                       |            |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA44-Ed25519-SHA512    |<CompSig>.3 |MLDSA44  |Ed25519                |SHA512      |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA44-ECDSA-P256-SHA256 |<CompSig>.4 |MLDSA44  |SHA256withECDSA        |SHA256      |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA44-ECDSA-            |<CompSig>.5 |MLDSA44  |SHA256withECDSA        |SHA256      |
   |brainpoolP256r1-SHA256       |            |         |                       |            |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA65-RSA3072-PSS-SHA256|<CompSig>.6 |MLDSA65  |SHA256WithRSAPSS       |SHA256      |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-                          |<CompSig>.7 |MLDSA65  |SHA256WithRSAEncryption|SHA256      |
   |MLDSA65-RSA3072-PKCS15-SHA256|            |         |                       |            |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA65-ECDSA-P256-SHA256 |<CompSig>.8 |MLDSA65  |SHA256withECDSA        |SHA256      |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA65-ECDSA-            |<CompSig>.9 |MLDSA65  |SHA256withECDSA        |SHA256      |
   |brainpoolP256r1-SHA256       |            |         |                       |            |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA65-Ed25519-SHA512    |<CompSig>.10|MLDSA65  |Ed25519                |SHA512      |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA87-ECDSA-P384-SHA384 |<CompSig>.11|MLDSA87  |SHA384withECDSA        |SHA384      |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA87-ECDSA-            |<CompSig>.12|MLDSA87  |SHA384withECDSA        |SHA384      |
   |brainpoolP384r1-SHA384       |            |         |                       |            |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-MLDSA87-Ed448-SHAKE256    |<CompSig>.13|MLDSA87  |Ed448                  |SHAKE256/512|
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-Falon512-ECDSA-P256-SHA256|<CompSig>.14|Falcon512|SHA256withECDSA        |SHA256      |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-Falcon512-ECDSA-          |<CompSig>.15|Falcon512|SHA256withECDSA        |SHA256      |
   |brainpoolP256r1-SHA256       |            |         |                       |            |
   +-----------------------------+------------+---------+-----------------------+------------+
   |id-Falcon512-Ed25519-SHA512  |<CompSig>.16|Falcon512|Ed25519                |SHA512      |
   +-----------------------------+------------+---------+-----------------------+------------+

                  Table 3: Composite Signature Algorithms

Ounsworth, et al.         Expires 25 April 2024                [Page 20]
Internet-Draft              PQ Composite Sigs               October 2023

   The table above contains everything needed to implement the listed
   explicit composite algorithms.  See the ASN.1 module in section
   Section 6 for the explicit definitions of the above Composite
   signature algorithms.

   Full specifications for the referenced algorithms can be found as
   follows:

   *  _MLDSA_: [I-D.ietf-lamps-dilithium-certificates] and
      [FIPS.204-ipd]

   *  _ECDSA_: [RFC5480]

   *  _Ed25519 / Ed448_: [RFC8410]

   *  _Falcon_: TBD

   *  _RSAES-PKCS-v1_5_: [RFC8017]

   *  _RSASSA-PSS_: [RFC8017]

5.1.  Notes on id-MLDSA44-RSA2048-PSS-SHA256 and id-MLDSA65-RSA3072-PSS-
      SHA256

   Use of RSA-PSS [RFC8017] deserves a special explanation.

   The RSA component keys MUST be generated at the 2048-bit security
   level in order to match security level with ML-DSA-44 or at 3072-bits
   to match ML-DSA-65.

   As with the other composite signature algorithms, when id-
   MLDSA44-RSA2048-PSS-SHA256 or id-MLDSA65-RSA3072-PSS-SHA256 is used
   in an AlgorithmIdentifier, the parameters MUST be absent. id-
   MLDSA44-RSA2048-PSS-SHA256 and id-MLDSA65-RSA3072-PSS-SHA256 SHALL
   instantiate RSA-PSS with the following parameters:

                  +==========================+=========+
                  | RSA-PSS Parameter        | Value   |
                  +==========================+=========+
                  | Mask Generation Function | mgf1    |
                  +--------------------------+---------+
                  | Mask Generation params   | SHA-256 |
                  +--------------------------+---------+
                  | Message Digest Algorithm | SHA-256 |
                  +--------------------------+---------+

                      Table 4: RSA-PSS 2048 and 3072
                                Parameters

Ounsworth, et al.         Expires 25 April 2024                [Page 21]
Internet-Draft              PQ Composite Sigs               October 2023

   where:

   *  Mask Generation Function (mgf1) is defined in [RFC8017]

   *  SHA-256 is defined in [RFC6234].

6.  ASN.1 Module

   <CODE STARTS>

      Composite-Signatures-2023
        { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027)
          algorithm(80) id-composite-signatures-2023 (TBDMOD) }

   DEFINITIONS IMPLICIT TAGS ::= BEGIN

   EXPORTS ALL;

   IMPORTS
     PUBLIC-KEY, SIGNATURE-ALGORITHM, AlgorithmIdentifier{}
       FROM AlgorithmInformation-2009  -- RFC 5912 [X509ASN1]
         { iso(1) identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) id-mod(0)
           id-mod-algorithmInformation-02(58) }

     SubjectPublicKeyInfo
       FROM PKIX1Explicit-2009
         { iso(1) identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) id-mod(0)
           id-mod-pkix1-explicit-02(51) }

     OneAsymmetricKey
       FROM AsymmetricKeyPackageModuleV1
         { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
           pkcs-9(9) smime(16) modules(0)
           id-mod-asymmetricKeyPkgV1(50) }

     RSAPublicKey, ECPoint
       FROM PKIXAlgs-2009
         { iso(1) identified-organization(3) dod(6)
           internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
           id-mod-pkix1-algorithms2008-02(56) }

     sa-rsaSSA-PSS
       FROM PKIX1-PSS-OAEP-Algorithms-2009
          {iso(1) identified-organization(3) dod(6) internet(1) security(5)
          mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-rsa-pkalgs-02(54)}

Ounsworth, et al.         Expires 25 April 2024                [Page 22]
Internet-Draft              PQ Composite Sigs               October 2023

   ;

   --
   -- Object Identifiers
   --

   -- Defined in ITU-T X.690
   der OBJECT IDENTIFIER ::=
     {joint-iso-itu-t asn1(1) ber-derived(2) distinguished-encoding(1)}

   --
   -- Signature Algorithm
   --

   --
   -- Composite Signature basic structures
   --

   CompositeSignaturePublicKey ::= SEQUENCE SIZE (2) OF BIT STRING

   CompositeSignaturePublicKeyOs ::= OCTET STRING (CONTAINING
                                   CompositeSignaturePublicKey ENCODED BY der)

   CompositeSignaturePublicKeyBs ::= BIT STRING (CONTAINING
                                   CompositeSignaturePublicKey ENCODED BY der)

   CompositeSignaturePrivateKey ::= SEQUENCE SIZE (2) OF OneAsymmetricKey

   CompositeSignatureValue ::= SEQUENCE SIZE (2) OF OCTET STRING

   -- Composite Signature Value is just a sequence of OCTET STRINGS

   --   CompositeSignaturePair{FirstSignatureValue, SecondSignatureValue} ::=
   --     SEQUENCE {
   --      signaturevalue1 FirstSignatureValue,
   --      signaturevalue2 SecondSignatureValue }

      -- An Explicit Compsite Signature is a set of Signatures which
      -- are composed of OCTET STRINGS
   --   ExplicitCompositeSignatureValue ::= CompositeSignaturePair {
   --       OCTET STRING,OCTET STRING}

   --

Ounsworth, et al.         Expires 25 April 2024                [Page 23]
Internet-Draft              PQ Composite Sigs               October 2023

   -- Information Object Classes
   --

   pk-CompositeSignature {
        OBJECT IDENTIFIER:id, FirstPublicKeyType,
        SecondPublicKeyType} PUBLIC-KEY ::=
        {
          IDENTIFIER id
          KEY SEQUENCE {
           BIT STRING (CONTAINING FirstPublicKeyType)
           BIT STRING (CONTAINING SecondPublicKeyType)
          }
          PARAMS ARE absent
          CERT-KEY-USAGE { digitalSignature, nonRepudiation, keyCertSign, cRLSign }
        }

   sa-CompositeSignature{OBJECT IDENTIFIER:id,
      PUBLIC-KEY:publicKeyType }
         SIGNATURE-ALGORITHM ::=  {
            IDENTIFIER id
            VALUE CompositeSignatureValue
            PARAMS ARE absent
            PUBLIC-KEYS {publicKeyType}
         }

   -- TODO: OID to be replaced by IANA
   id-MLDSA44-RSA2048-PSS-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 1 }

   pk-MLDSA44-RSA2048-PSS-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA44-RSA2048-PSS-SHA256,
     OCTET STRING, RSAPublicKey}

   sa-MLDSA44-RSA2048-PSS-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA44-RSA2048-PSS-SHA256,
          pk-MLDSA44-RSA2048-PSS-SHA256 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA44-RSA2048-PKCS15-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 2 }

   pk-MLDSA44-RSA2048-PKCS15-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA44-RSA2048-PKCS15-SHA256,
     OCTET STRING, RSAPublicKey}

Ounsworth, et al.         Expires 25 April 2024                [Page 24]
Internet-Draft              PQ Composite Sigs               October 2023

   sa-MLDSA44-RSA2048-PKCS15-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA44-RSA2048-PKCS15-SHA256,
          pk-MLDSA44-RSA2048-PKCS15-SHA256 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA44-Ed25519-SHA512 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 3 }

   pk-MLDSA44-Ed25519-SHA512 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA44-Ed25519-SHA512,
     OCTET STRING, ECPoint}

   sa-MLDSA44-Ed25519-SHA512 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA44-Ed25519-SHA512,
          pk-MLDSA44-Ed25519-SHA512 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA44-ECDSA-P256-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 4 }

   pk-MLDSA44-ECDSA-P256-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA44-ECDSA-P256-SHA256,
     OCTET STRING, ECPoint}

   sa-MLDSA44-ECDSA-P256-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA44-ECDSA-P256-SHA256,
          pk-MLDSA44-ECDSA-P256-SHA256 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA44-ECDSA-brainpoolP256r1-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 5 }

   pk-MLDSA44-ECDSA-brainpoolP256r1-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA44-ECDSA-brainpoolP256r1-SHA256,
     OCTET STRING, ECPoint}

   sa-MLDSA44-ECDSA-brainpoolP256r1-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA44-ECDSA-brainpoolP256r1-SHA256,

Ounsworth, et al.         Expires 25 April 2024                [Page 25]
Internet-Draft              PQ Composite Sigs               October 2023

          pk-MLDSA44-ECDSA-brainpoolP256r1-SHA256 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA65-RSA3072-PSS-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 6 }

   pk-MLDSA65-RSA3072-PSS-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA65-RSA3072-PSS-SHA256,
     OCTET STRING, RSAPublicKey}

   sa-MLDSA65-RSA3072-PSS-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA65-RSA3072-PSS-SHA256,
          pk-MLDSA65-RSA3072-PSS-SHA256 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA65-RSA3072-PKCS15-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 7 }

   pk-MLDSA65-RSA3072-PKCS15-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA65-RSA3072-PKCS15-SHA256,
     OCTET STRING, RSAPublicKey}

   sa-MLDSA65-RSA3072-PKCS15-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA65-RSA3072-PKCS15-SHA256,
          pk-MLDSA65-RSA3072-PKCS15-SHA256 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA65-ECDSA-P256-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 8 }

   pk-MLDSA65-ECDSA-P256-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA65-ECDSA-P256-SHA256,
     OCTET STRING, ECPoint}

   sa-MLDSA65-ECDSA-P256-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA65-ECDSA-P256-SHA256,
          pk-MLDSA65-ECDSA-P256-SHA256 }

Ounsworth, et al.         Expires 25 April 2024                [Page 26]
Internet-Draft              PQ Composite Sigs               October 2023

   -- TODO: OID to be replaced by IANA
   id-id-MLDSA65-ECDSA-brainpoolP256r1-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 9 }

   pk-id-MLDSA65-ECDSA-brainpoolP256r1-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA65-ECDSA-brainpoolP256r1-SHA256,
     OCTET STRING, ECPoint}

   sa-id-MLDSA65-ECDSA-brainpoolP256r1-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-id-MLDSA65-ECDSA-brainpoolP256r1-SHA256,
          pk-id-MLDSA65-ECDSA-brainpoolP256r1-SHA256 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA65-Ed25519-SHA512 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 10 }

   pk-MLDSA65-Ed25519-SHA512 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA65-Ed25519-SHA512,
     OCTET STRING, ECPoint}

   sa-MLDSA65-Ed25519-SHA512 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA65-Ed25519-SHA512,
          pk-MLDSA65-Ed25519-SHA512 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA87-ECDSA-P384-SHA384 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 11 }

   pk-MLDSA87-ECDSA-P384-SHA384 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA87-ECDSA-P384-SHA384,
     OCTET STRING, ECPoint}

   sa-MLDSA87-ECDSA-P384-SHA384 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA87-ECDSA-P384-SHA384,
          pk-MLDSA87-ECDSA-P384-SHA384 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA87-ECDSA-brainpoolP384r1-SHA384 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)

Ounsworth, et al.         Expires 25 April 2024                [Page 27]
Internet-Draft              PQ Composite Sigs               October 2023

      entrust(114027) algorithm(80) composite(7) signature(1) 12 }

   pk-MLDSA87-ECDSA-brainpoolP384r1-SHA384 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA87-ECDSA-brainpoolP384r1-SHA384,
     OCTET STRING, ECPoint}

   sa-MLDSA87-ECDSA-brainpoolP384r1-SHA384 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA87-ECDSA-brainpoolP384r1-SHA384,
          pk-MLDSA87-ECDSA-brainpoolP384r1-SHA384 }

   -- TODO: OID to be replaced by IANA
   id-MLDSA87-Ed448-SHAKE256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 13 }

   pk-MLDSA87-Ed448-SHAKE256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA87-Ed448-SHAKE256,
     OCTET STRING, ECPoint}

   sa-MLDSA87-Ed448-SHAKE256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-MLDSA87-Ed448-SHAKE256,
          pk-MLDSA87-Ed448-SHAKE256 }

   -- TODO: OID to be replaced by IANA
   id-Falon512-ECDSA-P256-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 14 }

   pk-Falon512-ECDSA-P256-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-MLDSA87-Ed448-SHAKE256,
     OCTET STRING, ECPoint}

   sa-Falon512-ECDSA-P256-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-Falon512-ECDSA-P256-SHA256,
          pk-Falon512-ECDSA-P256-SHA256 }

   -- TODO: OID to be replaced by IANA
   id-Falcon512-ECDSA-brainpoolP256r1-SHA256 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 15 }

   pk-Falcon512-ECDSA-brainpoolP256r1-SHA256 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-Falcon512-ECDSA-brainpoolP256r1-SHA256,
     OCTET STRING, ECPoint}

Ounsworth, et al.         Expires 25 April 2024                [Page 28]
Internet-Draft              PQ Composite Sigs               October 2023

   sa-Falcon512-ECDSA-brainpoolP256r1-SHA256 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-Falcon512-ECDSA-brainpoolP256r1-SHA256,
          pk-Falcon512-ECDSA-brainpoolP256r1-SHA256 }

   -- TODO: OID to be replaced by IANA
   id-Falcon512-Ed25519-SHA512 OBJECT IDENTIFIER ::= {
      joint-iso-itu-t(2) country(16) us(840) organization(1)
      entrust(114027) algorithm(80) composite(7) signature(1) 16 }

   pk-Falcon512-Ed25519-SHA512 PUBLIC-KEY ::=
     pk-CompositeSignature{ id-Falcon512-Ed25519-SHA512,
     OCTET STRING, ECPoint}

   sa-Falcon512-Ed25519-SHA512 SIGNATURE-ALGORITHM ::=
       sa-CompositeSignature{
          id-Falcon512-Ed25519-SHA512,
          pk-Falcon512-Ed25519-SHA512 }

   END

   <CODE ENDS>

7.  IANA Considerations

7.1.  Object Identifier Allocations

   EDNOTE to IANA: OIDs will need to be replaced in both the ASN.1
   module and in Table 3.

7.1.1.  Module Registration - SMI Security for PKIX Module Identifier

   *  Decimal: IANA Assigned - *Replace TBDMOD*

   *  Description: Composite-Signatures-2023 - id-mod-composite-
      signatures

   *  References: This Document

7.1.2.  Object Identifier Registrations - SMI Security for PKIX
        Algorithms

   *  id-MLDSA44-RSA2048-PSS-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA44-RSA2048-PSS-SHA256

Ounsworth, et al.         Expires 25 April 2024                [Page 29]
Internet-Draft              PQ Composite Sigs               October 2023

   *  References: This Document

   *  id-MLDSA44-RSA2048-PKCS15-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA44-RSA2048-PKCS15-SHA256

   *  References: This Document

   *  id-MLDSA44-Ed25519-SHA512

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA44-Ed25519-SHA512

   *  References: This Document

   *  id-MLDSA44-ECDSA-P256-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA44-ECDSA-P256-SHA256

   *  References: This Document

   *  id-MLDSA44-ECDSA-brainpoolP256r1-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA44-ECDSA-brainpoolP256r1-SHA256

   *  References: This Document

   *  id-MLDSA65-RSA3072-PSS-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA65-RSA3072-PSS-SHA256

   *  References: This Document

   *  id-MLDSA65-RSA3072-PKCS15-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA65-RSA3072-PKCS15-SHA256

Ounsworth, et al.         Expires 25 April 2024                [Page 30]
Internet-Draft              PQ Composite Sigs               October 2023

   *  References: This Document

   *  id-MLDSA65-ECDSA-P256-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA65-ECDSA-P256-SHA256

   *  References: This Document

   *  id-MLDSA65-ECDSA-brainpoolP256r1-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA65-ECDSA-brainpoolP256r1-SHA256

   *  References: This Document

   *  id-MLDSA65-Ed25519-SHA512

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA65-Ed25519-SHA512

   *  References: This Document

   *  id-MLDSA87-ECDSA-P384-SHA384

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA87-ECDSA-P384-SHA384

   *  References: This Document

   *  id-MLDSA87-ECDSA-brainpoolP384r1-SHA384

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA87-ECDSA-brainpoolP384r1-SHA384

   *  References: This Document

   *  id-MLDSA87-Ed448-SHAKE256

   *  Decimal: IANA Assigned

   *  Description: id-MLDSA87-Ed448

Ounsworth, et al.         Expires 25 April 2024                [Page 31]
Internet-Draft              PQ Composite Sigs               October 2023

   *  References: This Document

   *  id-Falon512-ECDSA-P256-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-Falon512-ECDSA-P256-SHA256

   *  References: This Document

   *  id-Falcon512-ECDSA-brainpoolP256r1-SHA256

   *  Decimal: IANA Assigned

   *  Description: id-Falcon512-ECDSA-brainpoolP256r1-SHA256

   *  References: This Document

   *  id-Falcon512-Ed25519-SHA512

   *  Decimal: IANA Assigned

   *  Description: id-Falcon512-Ed25519

   *  References: This Document

8.  Security Considerations

8.1.  Policy for Deprecated and Acceptable Algorithms

   Traditionally, a public key, certificate, or signature contains a
   single cryptographic algorithm.  If and when an algorithm becomes
   deprecated (for example, RSA-512, or SHA1), then clients performing
   signatures or verifications should be updated to adhere to
   appropriate policies.

   In the composite model this is less obvious since implementers may
   decide that certain cryptographic algorithms have complementary
   security properties and are acceptable in combination even though one
   or both algorithms are deprecated for individual use.  As such, a
   single composite public key or certificate may contain a mixture of
   deprecated and non-deprecated algorithms.

   Since composite algorithms are registered independently of their
   component algorithms, their deprecation can be handled indpendently
   from that of their component algorithms.  For example a cryptographic
   policy might continue to allow id-MLDSA65-ECDSA-P256-SHA256 even
   after ECDH-P256 is deprecated.

Ounsworth, et al.         Expires 25 April 2024                [Page 32]
Internet-Draft              PQ Composite Sigs               October 2023

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <https://www.rfc-editor.org/info/rfc2986>.

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210,
              DOI 10.17487/RFC4210, September 2005,
              <https://www.rfc-editor.org/info/rfc4210>.

   [RFC4211]  Schaad, J., "Internet X.509 Public Key Infrastructure
              Certificate Request Message Format (CRMF)", RFC 4211,
              DOI 10.17487/RFC4211, September 2005,
              <https://www.rfc-editor.org/info/rfc4211>.

   [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>.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
              <https://www.rfc-editor.org/info/rfc5480>.

   [RFC5639]  Lochter, M. and J. Merkle, "Elliptic Curve Cryptography
              (ECC) Brainpool Standard Curves and Curve Generation",
              RFC 5639, DOI 10.17487/RFC5639, March 2010,
              <https://www.rfc-editor.org/info/rfc5639>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <https://www.rfc-editor.org/info/rfc5652>.

   [RFC5958]  Turner, S., "Asymmetric Key Packages", RFC 5958,
              DOI 10.17487/RFC5958, August 2010,
              <https://www.rfc-editor.org/info/rfc5958>.

Ounsworth, et al.         Expires 25 April 2024                [Page 33]
Internet-Draft              PQ Composite Sigs               October 2023

   [RFC6090]  McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
              Curve Cryptography Algorithms", RFC 6090,
              DOI 10.17487/RFC6090, February 2011,
              <https://www.rfc-editor.org/info/rfc6090>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <https://www.rfc-editor.org/info/rfc6234>.

   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, DOI 10.17487/RFC7748, January
              2016, <https://www.rfc-editor.org/info/rfc7748>.

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,
              <https://www.rfc-editor.org/info/rfc8032>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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>.

   [X.690]    ITU-T, "Information technology - ASN.1 encoding Rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER)", ISO/IEC 8825-1:2015, November 2015.

9.2.  Informative References

   [Bindel2017]
              Bindel, N., Herath, U., McKague, M., and D. Stebila,
              "Transitioning to a quantum-resistant public key
              infrastructure", 2017, <https://link.springer.com/
              chapter/10.1007/978-3-319-59879-6_22>.

Ounsworth, et al.         Expires 25 April 2024                [Page 34]
Internet-Draft              PQ Composite Sigs               October 2023

   [I-D.becker-guthrie-noncomposite-hybrid-auth]
              Becker, A., Guthrie, R., and M. J. Jenkins, "Non-Composite
              Hybrid Authentication in PKIX and Applications to Internet
              Protocols", Work in Progress, Internet-Draft, draft-
              becker-guthrie-noncomposite-hybrid-auth-00, 22 March 2022,
              <https://datatracker.ietf.org/doc/html/draft-becker-
              guthrie-noncomposite-hybrid-auth-00>.

   [I-D.driscoll-pqt-hybrid-terminology]
              D, F., "Terminology for Post-Quantum Traditional Hybrid
              Schemes", Work in Progress, Internet-Draft, draft-
              driscoll-pqt-hybrid-terminology-01, 20 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-driscoll-pqt-
              hybrid-terminology-01>.

   [I-D.guthrie-ipsecme-ikev2-hybrid-auth]
              Guthrie, R., "Hybrid Non-Composite Authentication in
              IKEv2", Work in Progress, Internet-Draft, draft-guthrie-
              ipsecme-ikev2-hybrid-auth-00, 25 March 2022,
              <https://datatracker.ietf.org/doc/html/draft-guthrie-
              ipsecme-ikev2-hybrid-auth-00>.

   [I-D.ietf-lamps-dilithium-certificates]
              Massimo, J., Kampanakis, P., Turner, S., and B.
              Westerbaan, "Internet X.509 Public Key Infrastructure:
              Algorithm Identifiers for Dilithium", Work in Progress,
              Internet-Draft, draft-ietf-lamps-dilithium-certificates-
              01, 6 February 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
              dilithium-certificates-01>.

   [I-D.massimo-lamps-pq-sig-certificates]
              Massimo, J., Kampanakis, P., Turner, S., and B.
              Westerbaan, "Algorithms and Identifiers for Post-Quantum
              Algorithms", Work in Progress, Internet-Draft, draft-
              massimo-lamps-pq-sig-certificates-00, 8 July 2022,
              <https://datatracker.ietf.org/doc/html/draft-massimo-
              lamps-pq-sig-certificates-00>.

   [I-D.ounsworth-pq-composite-kem]
              Ounsworth, M. and J. Gray, "Composite KEM For Use In
              Internet PKI", Work in Progress, Internet-Draft, draft-
              ounsworth-pq-composite-kem-01, 13 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ounsworth-pq-
              composite-kem-01>.

Ounsworth, et al.         Expires 25 April 2024                [Page 35]
Internet-Draft              PQ Composite Sigs               October 2023

   [I-D.pala-klaussner-composite-kofn]
              Pala, M. and J. Klaußner, "K-threshold Composite
              Signatures for the Internet PKI", Work in Progress,
              Internet-Draft, draft-pala-klaussner-composite-kofn-00, 15
              November 2022, <https://datatracker.ietf.org/doc/html/
              draft-pala-klaussner-composite-kofn-00>.

   [I-D.vaira-pquip-pqc-use-cases]
              Vaira, A., Brockhaus, H., Railean, A., Gray, J., and M.
              Ounsworth, "Post-quantum cryptography use cases", Work in
              Progress, Internet-Draft, draft-vaira-pquip-pqc-use-cases-
              00, 23 October 2023,
              <https://datatracker.ietf.org/api/v1/doc/document/draft-
              vaira-pquip-pqc-use-cases/>.

   [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>.

   [RFC7292]  Moriarty, K., Ed., Nystrom, M., Parkinson, S., Rusch, A.,
              and M. Scott, "PKCS #12: Personal Information Exchange
              Syntax v1.1", RFC 7292, DOI 10.17487/RFC7292, July 2014,
              <https://www.rfc-editor.org/info/rfc7292>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <https://www.rfc-editor.org/info/rfc7296>.

   [RFC8017]  Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
              "PKCS #1: RSA Cryptography Specifications Version 2.2",
              RFC 8017, DOI 10.17487/RFC8017, November 2016,
              <https://www.rfc-editor.org/info/rfc8017>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8551]  Schaad, J., Ramsdell, B., and S. Turner, "Secure/
              Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
              Message Specification", RFC 8551, DOI 10.17487/RFC8551,
              April 2019, <https://www.rfc-editor.org/info/rfc8551>.

Ounsworth, et al.         Expires 25 April 2024                [Page 36]
Internet-Draft              PQ Composite Sigs               October 2023

Appendix A.  Samples

A.1.  Explicit Composite Signature Examples

A.1.1.  MLDSA44-ECDSA-P256-SHA256 Public Key

   -----BEGIN PUBLIC KEY-----
   MIIFfzANBgtghkgBhvprUAcBBAOCBWwAMIIFZwSCBSA+LrUqGdS5RSYzFWfGEmNS
   ZhiNF7vW+lTyoUESmu1iWjPNA8ILNB8fyxMi3TApDYNHlniiz7ogh9VKvGuUWrgl
   IUoX+f2FaErDnh3Fz24xpO7n0j7E7dqZYU0iSUTFekex+rRxr0hCNtuZQ++qYVSa
   CQOxScsuWrLjSW6Q6KzVAeHGoJIAL28JckUZ8KCg6AaMyqZwIFIw6NJ678K4c+Zy
   mFSusvyQ7LorxqAkHl03RGLy4BjMohDA2SzVW3W3Eez6rjvWoM8XMu8pWN1kJaqi
   JQLQx/HPqgnu1qmgcFqmTWHil6Z0sRH7XSZyhYpU4rNZr9/1yxFCw0WjYymATrzt
   CAGpfSzf8Igg/NL4mhOpSNkCzDnnC7ge/kskDHgHCDVWGPB9myTcXmVRsgCd53rh
   CDhR8csztl29tzYwgSqkraNTnfrlMPY9iMCzi/V9ShMfh60DoOBRsLjxr4pDra88
   vzHekDm084lEIghrkNZdswmCxELZSGpsPsiVyn32k4y1MdTorhiRTZn1Q+NlSk7t
   YH5XzdnDY4DByL/azaAQ4IThHc9tn9fra8icox4Ov3pdDosvyu6pvUEPpQv8vfOM
   vm156SFgS4JEj/ykqGF35E+9F96IS0aM9GBTjLQnM52DTm85BYSELx+EYb2AHxAr
   jhD4fUXnjK/g5V1kxBLxFmAxBmU/PGNkYILrOdPxl8f79LH6+PCehgZS4QqzF943
   FqO53B62Cp7F+zE2xpvUXeZ2ThuGGHce2cEE6lADa3Y3vX0rON7oWRHpBXRbSeP0
   X85TS0M6svSpgR2bMou/a7V2+NFHcU/dHteOqszhL1w1wxDcEnoy+FKNnVS3U/pi
   bFcGWzG63mxEgQc/wU0n7bBvOaFj29jnSmm6KsQrC/2J+AlX3uYqGCA4F3vzhPIP
   bj34TfUWPCIvgdGey8M5PDbNpj9yVXELTN3EEViFTA4W3+yr7Pf8Z9GlwJ6Oxbic
   E57oif1mKLRa3eIQ8R6T2/bTYCON1OtU///WJn8kE0A1Yayyr7AlBula/tM69aW0
   WctoEda2TgcYbDmE4fdMtgwKCfCjw2zP88KLiQUs3m6ZcBvx/CqKmB6xZpx5pNYq
   WqP4/YxhYLiTK6BNjW3gw5N1V+zIcTokeCClwwIzP/roO/sS2sMu1Y6znLfmawsY
   7aK5bmb/icPQU+DPq/v6YIxwTq2FYNxrsXSjKs+JJG0PqYeRXJ8GJfLbYMHddSaR
   CEXgYFIvAw4vn1Zqqqpm7OnRaIbV4EtzzxXDdy+vZUnMFs6hPEpGYCb+/DHYCfND
   QMpb5Xxcn9ighN0dzyL3pPvliPQIFgmpniuPpXnv1eBAmjc4UQlfMgyhfCXngUNR
   CjOJjEhWF+p4+26cDf25kLhO77gpog2JrV963GkQhHSyXoipvs0tK2/35Ec4/+bt
   2mbT0kErQyRfQw73E0OHO3TmHVExqCvqLQFkonEyYL+tD9ne0m3TGFmokcIItgUk
   09dAfeUOlcfvRfGYZlIxLTIFgep6UamMK+XNuOUNoq9S0UA7JZM+8YwCB61jI3oG
   Vq9Y3ohtQAr5+3HYwatD9a2Poks6Fqr0UCc0F0CSPLaqdiEVbZW92b+z44c33KGo
   E7QJgNfLsMazHsI+6bC5Ss8edJ07tGUKpiDzvQhMlvTMN8aqIyREuqSqNFc1CbF6
   v2opDdRte5aeGJKrVp0H5EO9oIkAsDwJ/cfroye514dlJ/CQuBYzARnueVghPWti
   BEEE5WF0F9l42el2mFaXWuOx5LvkUe5rxqlps10b0sgHUls5PPOeslgT9bVzhLu7
   Uuwkv4949UUnIzx58SRKIJ3DJg== -----END PUBLIC KEY-----

A.1.2.  MLDSA44-ECDSA-P256 Private Key

   -----BEGIN PRIVATE KEY----- MIIPmQIBADANBgtghkgBhvprUAcBBASCD4Mwgg9/
   BIIPAD4utSoZ1LlFJjMVZ8YS Y1JmGI0Xu9b6VPKhQRKa7WJa8O4O357Umw24m9Pd/
   Jg06IDz9AmosfLTjayQT5j9
   tRaYa9SlMtuRa++YF0vtPF5KCc2GSbvH8nHNJaKc8to8JSCAYIKyJNtEchq1gIoG
   ZYDCZKIQkSDFaSRDKSKQcRmIYVkUSlsAAdoiKcTEZJQoLQGyTIgQAViyaWAkERwR
   DSNHYRhACcwWJhMRJROHLFoWScIGMpFIkQIBUEGEUIEyShPGCJPIjaPECZoYSACn
   jYNIToxGSIKgEViAkEgIQRDDhFsGbQwxjuJIMUumDBNIgRqnkQIxJQpDiknIaeJG
   ZcLGSQITclFEcJIojNMwQVsEDUA2ShsWiFlCAFA2Ssy4gNGiTQHISRMWglG4EEgi

Ounsworth, et al.         Expires 25 April 2024                [Page 37]
Internet-Draft              PQ Composite Sigs               October 2023

   ShFHCSDDYYQiTdgQcIgYLCMyERskMpIUMsM0aRJIgaAmhmCIBVlEQBSZSAEZcFoG
   iQGnQREmYgA3aBi1aQQzMGLIjcDEiSEATiE1EBmEcQwzIMnGUUAySYEicuOUZQuU
   CeNICaIETYKWjQOjkIuIcZQgRZyALQIiIsQEIJuSkBQjQAmDZSMXIKKCDYjGBWSA
   ZZAgKgwpDKEkkVlGJtS2cAMZQAyjTFRGjRyFaIg0JoRCjEgEIeQiENEikBoFiNw2
   TKKiBRA1UFwWheQiJhLDLeGITMwSCQPAIdioaaAGJNy2AGJILUwGgFImBsPEYcvG
   QZQGLokSaViyYco4TMQ2MJEyRIQiEKM4LFEkckmGiUCkbQFDbhIWYgOEbBwAjNCw
   AZlIEhEDYhmzMAoxStQ0LUQ2iJK2iCCDMFggTQklSJvGDMigMZnCSZM0LBMzLKIG
   BhA4MAFAQgGEjQTCAQKyJFoETCMUAgvFIWSIgIEEbQA0TdIIYRoXbiM1JFkiQIMU
   jWK2RQkBShEFiJCQDYhGCQHEDZkiBQmWQIwUTSAGDhMWhQuibaQSjcEIDFG4BQyH
   cJMGLgkUaMsQgEASghCkjEiQcIkiRtCyMAgFYMCkLRqjgRJJTJMUYIM2TVAwTtQm
   TQE2QiDCcQu4DKQQKQqQSYFAbZjGZASFRYgkZJQWhAoQRpnEgApATUA2IUoiDKQS
   ZhAhBRqVjQu1gRRCjpsEKtTEYYMAkEOQDRo3hJMybAlJRKhhTP0aKQwPSKB9pfN8
   dXgHTPuxm9SWLRPY/gp4oA0bg8Hi1uxCqZ9uuFIK8BmEpgsPO73JCbkyewPYmUmB
   /9neuGdRvAmmoNOoFxt9FlroZWFB3wMUxYXuKUiuT91s0HZC8n1duwJ6gMbmNZ4A
   sKiAZaJdKrKwF/pdx5qIgcXQ9wAngvTgGkiBH+EoNY2qLTnZ/4OdWFAho8DTOfxu
   ViRPNgpuKIKZti4Cjh7idxNbx3lIXoZOZOeqs8Cw6nw7JLpGlW1dCjebe6mKFjyL
   b0NaLc37kheNeyEUxL4hvsF9AdxDHaIJ6ARyH2Rg1by6XrvfXEIXz9KoYzGhuB+V
   3roTAuM5026aHNZGNhMU53xUomAPj97DQK6o5q0D+0vxb3xTrVHvZc/m8IMgxlLa
   mikqmxORaM/qr2EghWLkcMlgeO8VkrB/V7Oh9q8GVsiDN7BnyGd7LiUHdtFwEUZZ
   ezohR9jea6gfwxVeqeVHA8STfFZIP+/fYUG6p7X0ixvOGYlBGRKMoLtZqGnzO4Ii
   3subCMfNs9i+O1ZHPvd3O9jmalv5pMTWKbda2uQqDW9SkB2ZNSKJBzNfO0g71Tg3
   L1ObdgOWPxEC97GlKmeaI6zlJ5zeZqRURrj+7vnNqyxniC9YzPE8vNKa6JxAKjPm
   ubb6umaQeFOnKDuqM6g2/f+kAKZiZ8kmywFNQuizw7d2cXoWD4d4yRJgNd7clrUI
   yV5ZmX9rGayTckfcq1rqp9IhL3vhiMXxq1DXhf7EUVCVn3kRT3pFOfcajV/GdJk/
   wXmm25M5/zCFdls0AA1hjL8tvYxPwlAHNwVysdXsUPgy3WpeZumR52EM5twEcDbm
   +G/1xAkTLR2sCzAZz+Z1ieQGpchsj8bKZIsJ0h2r2sZgdyzXHT8UpYVGvSbObZAV
   +s3kiRzJfW0nZLd+zAtqXAl1fZhpGxBvFJz6bZ1YeYwfvR2gIkoJ8kYfmUC9OiIr
   UYwQ4nshLbUrkfkcotqlD0Dl9f4SZZuaezIcUWmpw7PGm9eEbIg9Kw1UBDoJ3eK7
   SBEEGyNDeYQJzuIkAlN++RL9kNV/86cSSvJraRSqAbDcABxvt5C1ltGz6546czCj
   CT21LFtEyjkWaSsc1/1GzEyJ7/dLBvB98IHeDECupp+5Qi3NOmq8mZ3qsAvbhDLW
   uYYJQQ7oKEv+R0Rr2TRRBghUVmVjSBb2B17kNBqDK6GiVzQQHR8tKymvx4x4O6qe
   E0Jh8paay+Vfe8lfjJ+kw244BETG/Nocxn/XTOdBlsqAed6wbpABRAQU4ih+xX/r
   KNNBs5HhtZKbVuyO8mItkjh2Waw6BVr2oKUiuwqtWfvgfF8/HwOUYNkjmyF0/cVB
   nUOK1z2Ae1H5SYbnWNKgdcvRp3PxAAnNhHezLwi0fmQ73JZMty4RaifZLjqLcNSd
   T5oKJFiNaow1etsRg2LkbJhQKwmI79KKhzTBs3fnkwgX5VFpX4EAfHeVNqHkCrok
   wUE3qAw2UogT64AWIftOZ1PoS3IdJey1aEVuZRcGzGSWwCPvnwYuGZ9PqWQpq6sa
   DIDbhJ/gR5LeqVjCtxPdq69NQ2FprkDgVCI1p6HVrzdT9e9GaGVotHnm6SmfURA9
   gUkccwkmdKbE5JzKNkqsv/n40KIm4g+70kCM3CPNlnSKfqUXTMUEeXfD9uycS4qv
   VcvI+wy71DtDgnvR/gatUvCwhxLxbNSavd2rqvVBVUPgL3yysptalzY4awvYHG5g
   9MfjVoiJ/eJMIAGOdg3g93W1dt4mPzYOWffwvmDXa1Z1HPMSaQjky566xV51UlTZ
   fA6iMlepUJvHE62gHl7AdqU2SFKQ476M2rDajfezVRbCaqTvDyjR7qiaNZ2aG9Ij
   183yiv3CNzXpFDpU8mrhK2X4N48iKCBDleC7Qn2/PTzdN/77DZAM72qbOmrf1DeB
   v9xPq1tGa8drPI7/KmzMR2lJr4f3IjNteGmcOtOe0i/wdIyN483JluYFc85oc6WC
   zR/RGtBEaxWNaQdC3SeqV9t0z1HZRqf25Sis2Gv/MBmEvg2co7sv7b7o0NSZBKzr
   dbnrm74uLtysUxCRoC6Ld5UES0tQr7Euv8qHHCsw2qOMzLpnYcrsL/KFTQFGOoAI
   YSVTdZoz/gWvC3NbLGDDAzCHRIlkNBZrMi/MTYn8s3njHLnA2YWqUg+eE8GDmDl0
   0//8ckvv5hNXpTT4i0NaNq8QPi61KhnUuUUmMxVnxhJjUmYYjRe71vpU8qFBEprt
   YlozzQPCCzQfH8sTIt0wKQ2DR5Z4os+6IIfVSrxrlFq4JSFKF/n9hWhKw54dxc9u

Ounsworth, et al.         Expires 25 April 2024                [Page 38]
Internet-Draft              PQ Composite Sigs               October 2023

   MaTu59I+xO3amWFNIklExXpHsfq0ca9IQjbbmUPvqmFUmgkDsUnLLlqy40lukOis
   1QHhxqCSAC9vCXJFGfCgoOgGjMqmcCBSMOjSeu/CuHPmcphUrrL8kOy6K8agJB5d
   N0Ri8uAYzKIQwNks1Vt1txHs+q471qDPFzLvKVjdZCWqoiUC0Mfxz6oJ7tapoHBa
   pk1h4pemdLER+10mcoWKVOKzWa/f9csRQsNFo2MpgE687QgBqX0s3/CIIPzS+JoT
   qUjZAsw55wu4Hv5LJAx4Bwg1VhjwfZsk3F5lUbIAned64Qg4UfHLM7Zdvbc2MIEq
   pK2jU5365TD2PYjAs4v1fUoTH4etA6DgUbC48a+KQ62vPL8x3pA5tPOJRCIIa5DW
   XbMJgsRC2UhqbD7Ilcp99pOMtTHU6K4YkU2Z9UPjZUpO7WB+V83Zw2OAwci/2s2g
   EOCE4R3PbZ/X62vInKMeDr96XQ6LL8ruqb1BD6UL/L3zjL5teekhYEuCRI/8pKhh
   d+RPvRfeiEtGjPRgU4y0JzOdg05vOQWEhC8fhGG9gB8QK44Q+H1F54yv4OVdZMQS
   8RZgMQZlPzxjZGCC6znT8ZfH+/Sx+vjwnoYGUuEKsxfeNxajudwetgqexfsxNsab
   1F3mdk4bhhh3HtnBBOpQA2t2N719Kzje6FkR6QV0W0nj9F/OU0tDOrL0qYEdmzKL
   v2u1dvjRR3FP3R7XjqrM4S9cNcMQ3BJ6MvhSjZ1Ut1P6YmxXBlsxut5sRIEHP8FN
   J+2wbzmhY9vY50ppuirEKwv9ifgJV97mKhggOBd784TyD249+E31FjwiL4HRnsvD
   OTw2zaY/clVxC0zdxBFYhUwOFt/sq+z3/GfRpcCejsW4nBOe6In9Zii0Wt3iEPEe
   k9v202AjjdTrVP//1iZ/JBNANWGssq+wJQbpWv7TOvWltFnLaBHWtk4HGGw5hOH3
   TLYMCgnwo8Nsz/PCi4kFLN5umXAb8fwqipgesWaceaTWKlqj+P2MYWC4kyugTY1t
   4MOTdVfsyHE6JHggpcMCMz/66Dv7EtrDLtWOs5y35msLGO2iuW5m/4nD0FPgz6v7
   +mCMcE6thWDca7F0oyrPiSRtD6mHkVyfBiXy22DB3XUmkQhF4GBSLwMOL59Waqqq
   Zuzp0WiG1eBLc88Vw3cvr2VJzBbOoTxKRmAm/vwx2AnzQ0DKW+V8XJ/YoITdHc8i
   96T75Yj0CBYJqZ4rj6V579XgQJo3OFEJXzIMoXwl54FDUQoziYxIVhfqePtunA39
   uZC4Tu+4KaINia1fetxpEIR0sl6Iqb7NLStv9+RHOP/m7dpm09JBK0MkX0MO9xND
   hzt05h1RMagr6i0BZKJxMmC/rQ/Z3tJt0xhZqJHCCLYFJNPXQH3lDpXH70XxmGZS
   MS0yBYHqelGpjCvlzbjlDaKvUtFAOyWTPvGMAgetYyN6BlavWN6IbUAK+ftx2MGr
   Q/Wtj6JLOhaq9FAnNBdAkjy2qnYhFW2Vvdm/s+OHN9yhqBO0CYDXy7DGsx7CPumw
   uUrPHnSdO7RlCqYg870ITJb0zDfGqiMkRLqkqjRXNQmxer9qKQ3UbXuWnhiSq1ad
   B+RDvaCJALA8Cf3H66MnudeHZSfwkLgWMwEZ7nlYIT1rYgR5MHcCAQEEICNcwpss
   HyyHcp4sFiQfXGBHkt4Ful/+xUioOUgxpmhZoAoGCCqGSM49AwEHoUQDQgAE5WF0
   F9l42el2mFaXWuOx5LvkUe5rxqlps10b0sgHUls5PPOeslgT9bVzhLu7Uuwkv494
   9UUnIzx58SRKIJ3DJg== -----END PRIVATE KEY-----

A.1.3.  MLDSA44-ECDSA-P256 Self-Signed X509 Certificate

   -----BEGIN CERTIFICATE-----
   MIIP9zCCBhigAwIBAgIUQDaCiOd3IecnO16Hko3aeFCPLnAwDQYLYIZIAYb6a1AH
   AQQwEjEQMA4GA1UEAwwHb3FzdGVzdDAeFw0yMzEwMTgyMDQ2MTZaFw0yNDEwMTcy
   MDQ2MTZaMBIxEDAOBgNVBAMMB29xc3Rlc3QwggV/MA0GC2CGSAGG+mtQBwEEA4IF
   bAAwggVnBIIFID4utSoZ1LlFJjMVZ8YSY1JmGI0Xu9b6VPKhQRKa7WJaM80Dwgs0
   Hx/LEyLdMCkNg0eWeKLPuiCH1Uq8a5RauCUhShf5/YVoSsOeHcXPbjGk7ufSPsTt
   2plhTSJJRMV6R7H6tHGvSEI225lD76phVJoJA7FJyy5asuNJbpDorNUB4cagkgAv
   bwlyRRnwoKDoBozKpnAgUjDo0nrvwrhz5nKYVK6y/JDsuivGoCQeXTdEYvLgGMyi
   EMDZLNVbdbcR7PquO9agzxcy7ylY3WQlqqIlAtDH8c+qCe7WqaBwWqZNYeKXpnSx
   EftdJnKFilTis1mv3/XLEULDRaNjKYBOvO0IAal9LN/wiCD80viaE6lI2QLMOecL
   uB7+SyQMeAcINVYY8H2bJNxeZVGyAJ3neuEIOFHxyzO2Xb23NjCBKqSto1Od+uUw
   9j2IwLOL9X1KEx+HrQOg4FGwuPGvikOtrzy/Md6QObTziUQiCGuQ1l2zCYLEQtlI
   amw+yJXKffaTjLUx1OiuGJFNmfVD42VKTu1gflfN2cNjgMHIv9rNoBDghOEdz22f
   1+tryJyjHg6/el0Oiy/K7qm9QQ+lC/y984y+bXnpIWBLgkSP/KSoYXfkT70X3ohL
   Roz0YFOMtCcznYNObzkFhIQvH4RhvYAfECuOEPh9ReeMr+DlXWTEEvEWYDEGZT88
   Y2Rggus50/GXx/v0sfr48J6GBlLhCrMX3jcWo7ncHrYKnsX7MTbGm9Rd5nZOG4YY

Ounsworth, et al.         Expires 25 April 2024                [Page 39]
Internet-Draft              PQ Composite Sigs               October 2023

   dx7ZwQTqUANrdje9fSs43uhZEekFdFtJ4/RfzlNLQzqy9KmBHZsyi79rtXb40Udx
   T90e146qzOEvXDXDENwSejL4Uo2dVLdT+mJsVwZbMbrebESBBz/BTSftsG85oWPb
   2OdKaboqxCsL/Yn4CVfe5ioYIDgXe/OE8g9uPfhN9RY8Ii+B0Z7Lwzk8Ns2mP3JV
   cQtM3cQRWIVMDhbf7Kvs9/xn0aXAno7FuJwTnuiJ/WYotFrd4hDxHpPb9tNgI43U
   61T//9YmfyQTQDVhrLKvsCUG6Vr+0zr1pbRZy2gR1rZOBxhsOYTh90y2DAoJ8KPD
   bM/zwouJBSzebplwG/H8KoqYHrFmnHmk1ipao/j9jGFguJMroE2NbeDDk3VX7Mhx
   OiR4IKXDAjM/+ug7+xLawy7VjrOct+ZrCxjtorluZv+Jw9BT4M+r+/pgjHBOrYVg
   3GuxdKMqz4kkbQ+ph5FcnwYl8ttgwd11JpEIReBgUi8DDi+fVmqqqmbs6dFohtXg
   S3PPFcN3L69lScwWzqE8SkZgJv78MdgJ80NAylvlfFyf2KCE3R3PIvek++WI9AgW
   CameK4+lee/V4ECaNzhRCV8yDKF8JeeBQ1EKM4mMSFYX6nj7bpwN/bmQuE7vuCmi
   DYmtX3rcaRCEdLJeiKm+zS0rb/fkRzj/5u3aZtPSQStDJF9DDvcTQ4c7dOYdUTGo
   K+otAWSicTJgv60P2d7SbdMYWaiRwgi2BSTT10B95Q6Vx+9F8ZhmUjEtMgWB6npR
   qYwr5c245Q2ir1LRQDslkz7xjAIHrWMjegZWr1jeiG1ACvn7cdjBq0P1rY+iSzoW
   qvRQJzQXQJI8tqp2IRVtlb3Zv7PjhzfcoagTtAmA18uwxrMewj7psLlKzx50nTu0
   ZQqmIPO9CEyW9Mw3xqojJES6pKo0VzUJsXq/aikN1G17lp4YkqtWnQfkQ72giQCw
   PAn9x+ujJ7nXh2Un8JC4FjMBGe55WCE9a2IEQQTlYXQX2XjZ6XaYVpda47Hku+RR
   7mvGqWmzXRvSyAdSWzk8856yWBP1tXOEu7tS7CS/j3j1RScjPHnxJEogncMmoyEw
   HzAdBgNVHQ4EFgQUze7w0J16DyVsWiqhvpM3hNBk7h4wDQYLYIZIAYb6a1AHAQQD
   ggnIADCCCcMDggl1AH/cre4zsO0NbpYSzDlrLOsMVsBGd5a+KHjIKGSU/CqA25Qs
   XO9Z4BGo9tz061A1cF0bYV+/r6Eu/9CmTlWoeoUKo0D4yOZq0RuIyyho/6i7XlVK
   PNffhQe20/scjXm0+dB09bBl8SFQEVj/02erYvTqQzkkLGTwHVuCPCpHD+8UDBt/
   7fR74Ty5Y40zz92O+t94nTd7x81/qhCGw5Ga93wHmrtQp8mNq9iqPkJ1e6uxGPXn
   6PV2d0rpdMnE7oBklxh64Qu0RvqvtwsOTj3kT21/jNpnKMm8Ge4MJxn1CZNbtN3e
   aUzcT2nnnYj82oCeFb2imb0r5HbvFyuWBTKGDPrkxJVk1wvAHC+ads4py2v1BQsU
   v5q05yQK6VnWS2M6CeqFnV2GNPn4eAinoZcGVXOLLzPzokdWnwMlSeIAMN1aFzb8
   iI4i1icnBZWGXRoR0F5PKHF2rz3/tz8YQnbBcxq2GXlX6ifj1iJw/1iDCa9qZ9GC
   GuYd4HeNH+OravwKZYOd0lkxkBRaPAR4EmfmPBL22s7XxOLNa7RIC1eyGG9X6euR
   1bS8rIcB43oFerVQU7cX/zx1TPyoqyWDOk5t2rRCT6whbzfj1W/a6nEpt1ivz/Me
   Bfq7l4WtfniBbe/jlbGumDqfH+JLrfGDbtU7MBLgUbE0mFZWkqx3iE8WAGYM4LeH
   CTfzJGgqch+JPFvay9UjrJyryzYt/Z6cdG41nEsASbgNCPjnBAIqrm3lRtqMCK4j
   X/V61lM4gvkTpJtwSoU8vLltpDqd3JRrDX/K1oZCOShGdTKrkaD2r5GIl37iavKV
   kxAcUICZ7exlj9bX9oLO6TM2RXhD4KoPZDesxMNw/CVzNxYrT2g/cpPai+wDzJqz
   EF/MwK0DomQlnmU1f3L+pTfV+2Bk8ipFJmquJB/Mb0/nXeimpnyMxI1nrR5AupR+
   GjNY9szss++RJ/wMALUtHDOqGUfcSsktOlPyyuj4QHPKt25xS6WcfkgfzQfDT4NW
   Q3VHvfGdhnNaVlqpN7kTBRQqCWlGOQS/S6I+O0yGruo1BPIfYxOatHbRdLsZTm56
   hmgTDSLgo16JOIij+Ly4qn8dmsdY34wSqfvWRGF63GTscCPcbcHwLAyVqGYhg9ph
   8r0M1fzLUiYYnBiWKY/P1O3J1t1TyJA/34c8di5aFXaHz/SWvFVIr1DgHiNR7r66
   txgIcmf/qc6RsODSJ731fJu0Jnl9yR4KyaHy4HTr6NZd3NGyCzQS2yEcxBa2QaGz
   Tf1//tO5jTZBEow+NEQw4h73khQ6PMKVeWuyrrTIa67EvLGOsTsZKrV3zww/6eK2
   1TqN+9EMWL3KAE5U3NYZNy7LhKHtk1DEsz4c2MWFvy6qc9gN66RwUCMJYP3uQq/H
   sHrJuKrpbX9a6ShNBJRSl3CNRrjF6vOwyhigtBFmF7NEL50RHAUl2ExmgC92C8O7
   N48VPig4/jlmInMgbPWA55x1yGiN3UFZcOW4kjmSGT+eAHN/Z/5coJhch/Z6n38V
   pt4dsWBy3+omfZ2i8J0fV3BdwmlwQ3lWiGCYHQc+66UE/rU03C46QPsGlqV5j95O
   DDTGHxp+cQ6APr6uvNSPOQ/JkqY5G0ukxtQsufP2uVnFZ4J9LYJ6bmMvkMRspGct
   RisSzlFI/aM5iDQAwMKEgdGbvDQicsgmWnajQ3VdWPDlrEXc9j1eU+HZMJi+yH0Y
   lENwGMvqCtlm3VYfHYNAxEH0A5b66Jyr55fnZuK0YQFqVa/iXNnBP5zSNh5gbnTu
   8yEbLZunDUR2qYQMQOc2J21CdpXB8oO9iyGG0Be7RHIEyVLRjui/iAycAV7uTicq
   nshPO4NIz+Gqe65nsPpOyQP6pNd/BJt5U8MJx90OccKBAfLhBduNlVZiCgfCvQGK

Ounsworth, et al.         Expires 25 April 2024                [Page 40]
Internet-Draft              PQ Composite Sigs               October 2023

   l6j+aBvCKD58BmTtK4yyccvwYrDrbQUOyuehs6DNCFkP1uMbaDvoO8ksWDNA4r9l
   yqRqmRGJ+4B5bqtf/3d9YlUI0Ri20DVRbCA2vH0QCWGpT1MnhDunWmMO0RFPm9U8
   vl4Q5t5Fjz/x4DS9/eRb9JOwZcMsWdlLrHeVPSBZXyg8WCgarEjBton6WksmIBfw
   cpRTIvVb5EPwHZYUrF4NXzHJvvfIPFYgDMlKwRQPaEeEWol8onKxaAYrnDoNhdyO
   CyfH0EmuLEaPVu6R3UvO0u9fiphLwD523tjGx1zT2zSADOjvo6WgvKsrMuiH3plu
   b/NcPeZPgWpaA/rSg2xN53qa4f56SO1hKCDh9c8npd8iu1axmyu6Yk5jdbD2vZRO
   CVHTyds6gIzkm+UrxO5OLWLOASrLR/UOpslqgOM/uiAyWnKZ78ijmRVHlBzNtVi6
   /2G8Mp7OnhX7CrYrjG13ma++LD9pupAKqUMhmiAC4eBvPXo88VNBG7iUL8i1FiMJ
   in+tBqZjVPnoTCtiMu+O7NTA+3XqjukxbxRYXOvIu2np6jBlWKVWPWxuPH/x5MM1
   KWWOaDAubAOGKpmt74fluwBhsJhE3V3VxvDZ2Bsl07PFKl5TRnak/mfay93op+U9
   OBETCW7doNvI7hLg7P7kx/HjGr1P1Ioy4D2dlai/D158C5p5KNagL83FTZY2DjAX
   b1dwzSUI7WzelEFr/hjVaiYosllMQHt/BXoYTBEbPMpmWA/Nfz9DB0bYOcjz2coB
   9UXjSMpMeKNaC2gXx3g0jq9OukfKRKN6HZIW5WVc+jEa3c3vQQkKbuHvT5+fyIrz
   iKedQO9bpaKC+79VPY315Ay44tws2bUmOqfyR+9WGlEWH3NHVsDJf0UVChLGbAt4
   0o73qsrcGMr3NgGU3MuFzITEhYqB4s/YzP4R14k1iyx7z97JzrjWGBRA9KUGYb+T
   8plXUoTS1Qjf5yDrR/KMEY4747YqST/UVe2epb7xFWW7lTnqryXBvn3E8TM1s/uU
   +vgLBbkW9d9yNzswBQQ1YDAYv8rh0NCXsnKAn8pxgqSYJhTK45KhZxmRgk3jDec9
   E1wp9huoFqzmEy71XGOL94HFPEXANJd0j7dHegBg83IC7kjUpRTcBiFow2CPldtg
   6zm4pmx7pIECrbAANoW9wCbv1DUnRUS4kiZf3GD6nxDZYML7R1KDmOc1zrM3ExUY
   HT9NXmx/l7DQ3P8aHjU+coPCxyA0P0tPVFWgprC3xM/7CFNUXWRwcoPN7fP3AAAA
   AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAOFiQwA0gAMEUCIBZgPd/De2z8
   KVaX4IdLzKwgoTxOvQbM2VFO79bQmwhVAiEAw7plaHGiHrVngE1TDaTjNpVZKpMh
   6VjbIrd6yvAdXUA= -----END CERTIFICATE-----

Appendix B.  Implementation Considerations

B.1.  FIPS certification

   One of the primary design goals of this specification is for the
   overall composite algorithm to be able to be considered FIPS-approved
   even when one of the component algorithms is not.

   Implementors seeking FIPS certification of a composite Signature
   algorithm where only one of the component algorithms has been FIPS-
   validated or FIPS-approved should credit the FIPS-validated component
   algorithm with full security strength, the non-FIPS-validated
   component algorith with zero security, and the overall composite
   should be considered full strength and thus FIPS-approved.

   The authors wish to note that this gives composite algorithms great
   future utility both for future cryptographic migrations as well as
   bridging across jurisdictions; for example defining composite
   algorithms which combine FIPS cryptography with cryptography from a
   different national standards body.

Ounsworth, et al.         Expires 25 April 2024                [Page 41]
Internet-Draft              PQ Composite Sigs               October 2023

B.2.  Backwards Compatibility

   The term "backwards compatibility" is used here to mean something
   more specific; that existing systems as they are deployed today can
   interoperate with the upgraded systems of the future.  This draft
   explicitly does not provide backwards compatibility, only upgraded
   systems will understand the OIDs defined in this document.

   If backwards compatibility is required, then additional mechanisms
   will be needed.  Migration and interoperability concerns need to be
   thought about in the context of various types of protocols that make
   use of X.509 and PKIX with relation to digital signature objects,
   from online negotiated protocols such as TLS 1.3 [RFC8446] and IKEv2
   [RFC7296], to non-negotiated asynchronous protocols such as S/MIME
   signed email [RFC8551], document signing such as in the context of
   the European eIDAS regulations [eIDAS2014], and publicly trusted code
   signing [codeSigningBRsv2.8], as well as myriad other standardized
   and proprietary protocols and applications that leverage CMS
   [RFC5652] signed structures.  Composite simplifies the protocol
   design work because it can be implemented as a signature algorithm
   that fits into existing systems.

B.2.1.  Parallel PKIs

   We present the term "Parallel PKI" to refer to the setup where a PKI
   end entity possesses two or more distinct public keys or certificates
   for the same identity (name), but containing keys for different
   cryptographic algorithms.  One could imagine a set of parallel PKIs
   where an existing PKI using legacy algorithms (RSA, ECC) is left
   operational during the post-quantum migration but is shadowed by one
   or more parallel PKIs using pure post quantum algorithms or composite
   algorithms (legacy and post-quantum).

   Equipped with a set of parallel public keys in this way, a client
   would have the flexibility to choose which public key(s) or
   certificate(s) to use in a given signature operation.

   For negotiated protocols, the client could choose which public key(s)
   or certificate(s) to use based on the negotiated algorithms, or could
   combine two of the public keys for example in a non-composite hybrid
   method such as [I-D.becker-guthrie-noncomposite-hybrid-auth] or
   [I-D.guthrie-ipsecme-ikev2-hybrid-auth].  Note that it is possible to
   use the signature algorithms defined in Section 5 as a way to carry
   the multiple signature values generated by one of the non-composite
   public mechanism in protocols where it is easier to support the
   composite signature algorithms than to implement such a mechanism in
   the protocol itself.  There is also nothing precluding a composite
   public key from being one of the components used within a non-

Ounsworth, et al.         Expires 25 April 2024                [Page 42]
Internet-Draft              PQ Composite Sigs               October 2023

   composite authentication operation; this may lead to greater
   convenience in setting up parallel PKI hierarchies that need to
   service a range of clients implementing different styles of post-
   quantum migration strategies.

   For non-negotiated protocols, the details for obtaining backwards
   compatibility will vary by protocol, but for example in CMS
   [RFC5652], the inclusion of multiple SignerInfo objects is often
   already treated as an OR relationship, so including one for each of
   the signer's parallel PKI public keys would, in many cases, have the
   desired effect of allowing the receiver to choose one they are
   compatible with and ignore the others, thus achieving full backwards
   compatibility.

B.2.2.  Hybrid Extensions (Keys and Signatures)

   The use of Composite Crypto provides the possibility to process
   multiple algorithms without changing the logic of applications, but
   updating the cryptographic libraries: one-time change across the
   whole system.  However, when it is not possible to upgrade the crypto
   engines/libraries, it is possible to leverage X.509 extensions to
   encode the additional keys and signatures.  When the custom
   extensions are not marked critical, although this approach provides
   the most backward-compatible approach where clients can simply ignore
   the post-quantum (or extra) keys and signatures, it also requires all
   applications to be updated for correctly processing multiple
   algorithms together.

Appendix C.  Intellectual Property Considerations

   The following IPR Disclosure relates to this draft:

   https://datatracker.ietf.org/ipr/3588/

Appendix D.  Contributors and Acknowledgements

   This document incorporates contributions and comments from a large
   group of experts.  The Editors would especially like to acknowledge
   the expertise and tireless dedication of the following people, who
   attended many long meetings and generated millions of bytes of
   electronic mail and VOIP traffic over the past year in pursuit of
   this document:

   Serge Mister (Entrust), Scott Fluhrer (Cisco Systems), Panos
   Kampanakis (Cisco Systems), Daniel Van Geest (ISARA), Tim Hollebeek
   (Digicert), and Francois Rousseau.

Ounsworth, et al.         Expires 25 April 2024                [Page 43]
Internet-Draft              PQ Composite Sigs               October 2023

   We are grateful to all, including any contributors who may have been
   inadvertently omitted from this list.

   This document borrows text from similar documents, including those
   referenced below.  Thanks go to the authors of those documents.
   "Copying always makes things easier and less error prone" -
   [RFC8411].

D.1.  Making contributions

   Additional contributions to this draft are welcome.  Please see the
   working copy of this draft at, as well as open issues at:

   https://github.com/EntrustCorporation/draft-ounsworth-composite-sigs

Authors' Addresses

   Mike Ounsworth
   Entrust Limited
   2500 Solandt Road -- Suite 100
   Ottawa, Ontario  K2K 3G5
   Canada
   Email: mike.ounsworth@entrust.com

   John Gray
   Entrust Limited
   2500 Solandt Road -- Suite 100
   Ottawa, Ontario  K2K 3G5
   Canada
   Email: john.gray@entrust.com

   Massimiliano Pala
   CableLabs
   858 Coal Creek Circle
   Louisville, Colorado,  80027
   United States of America
   Email: director@openca.org

   Jan Klaussner
   D-Trust GmbH
   Kommandantenstr. 15
   10969 Berlin
   Germany
   Email: jan.klaussner@d-trust.net

Ounsworth, et al.         Expires 25 April 2024                [Page 44]