Internet-Draft Composite KEMs October 2023
Ounsworth & Gray Expires 25 April 2024 [Page]
Workgroup:
LAMPS
Internet-Draft:
draft-ietf-lamps-pq-composite-kem-01
Published:
Intended Status:
Standards Track
Expires:
Authors:
M. Ounsworth
Entrust
J. Gray
Entrust

Composite KEM For Use In Internet PKI

Abstract

This document defines Post-Quantum / Traditional composite Key Encapsulation Mechanism (KEM) algorithms suitable for use within X.509 and PKIX and CMS protocols. Composite algorithms are provided which combine ML-KEM with RSA-KEM and ECDH-KEM. The provided set of composite algorithms should meet most Internet needs.

This document assumes that all component algorithms are KEMs, and therefore it depends on [RFC5990] and [I-D.ounsworth-lamps-cms-dhkem] in order to promote RSA and ECDH respectively into KEMs. For the purpose of combining KEMs, the combiner function from [I-D.ounsworth-cfrg-kem-combiners] is used. For use within CMS, this document is intended to be coupled with the CMS KEMRecipientInfo mechanism in [I-D.housley-lamps-cms-kemri].

About This Document

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

The latest revision of this draft can be found at https://lamps-wg.github.io/draft-composite-kem/draft-ietf-lamps-pq-composite-kem.html#name-asn1-module. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-lamps-pq-composite-kem/.

Discussion of this document takes place on the LAMPS Working Group mailing list (mailto:spams@ietf.org), which is archived at https://datatracker.ietf.org/wg/lamps/about/. Subscribe at https://www.ietf.org/mailman/listinfo/spams/.

Source for this draft and an issue tracker can be found at https://github.com/lamps-wg/draft-composite-kem.

Status of This Memo

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

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This Internet-Draft will expire on 25 April 2024.

Table of Contents

1. Changes in version -01

Changes affecting interoperability:

Editorial changes:

Still to do in a future version:

[ ] We need PEM samples ... 118 hackathon? OQS friends? David @ BC? The right format for samples is probably to follow the hackathon ... a Dilithium or ECDSA trust anchor certificate, a composite KEM end entity certificate, and a CMS EnvolepedData sample encrypted for that composite KEM certificate.

2. Introduction

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 long data lifetimes. The outgoing algorithms, such as RSA and elliptic curve, may fall to quantum cryptalanysis, while the incoming post-quantum algorithms face uncertainty about both the underlying mathematics falling to classical algorithmic attacks as well as hardware and software implementations that have not had sufficient maturing time to rule out catestrophic implementation bugs. Unlike previous cryptographic algorithm migrations, the choice of when to migrate and which algorithms to migrate to, is not so clear.

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:

This document defines a specific instantiation of the PQ/T Hybrid paradigm called "composite" where multiple cryptographic algorithms are combined to form a single key encapsulation mechanism (KEM) key and ciphertext such that they 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 KEM algorithms are provided based on ML-KEM, RSA-KEM and ECDH-KEM. 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 key establishment or enveloped content encryption is used within PKIX or CMS structures.

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.

This document is consistent with all terminology from [I-D.driscoll-pqt-hybrid-terminology]. In addition, the following terms are used in this document:

COMBINER: A combiner specifies how multiple shared secrets are combined into a single shared secret.

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

KEM: A key encapsulation mechanism as defined in Section 2.3.

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

SHARED SECRET: A value established between two communicating parties for use as cryptographic key material, but which cannot be learned by an active or passive adversary. This document is concerned with shared secrets established via public key cryptagraphic operations.

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 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 Key Encapsulation Mechanisms (KEMs)

We borrow here the definition of a key encapsulation mechanism (KEM) from [I-D.ietf-tls-hybrid-design], in which a KEM 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.

  • Encaps(pk) -> (ct, ss): A probabilistic encapsulation algorithm, which takes as input a public key pk and outputs a ciphertext ct and shared secret ss.

  • Decaps(sk, ct) -> ss: A decapsulation algorithm, which takes as input a secret key sk and ciphertext ct and outputs a shared secret ss, or in some cases a distinguished error value.

The KEM interface defined above differs from both traditional key transport mechanism (for example for use with KeyTransRecipientInfo defined in [RFC5652]), and key agreement (for example for use with KeyAgreeRecipientInfo defined in [RFC5652]).

The KEM interface was chosen as the interface for a composite key establishment because it allows for arbitrary combinations of component algorithm types since both key transport and key agreement mechanisms can be promoted into KEMs. This specification uses the Post-Quantum KEM ML-KEM as specified in [I-D.ietf-lamps-kyber-certificates] and [FIPS.203-ipd]. For Traditional KEMs, this document relies on the RSA-KEM construction defined in [I-D.ietf-lamps-rfc5990bis] and the Elliptic Curve DHKEM defined in [I-D.ounsworth-lamps-cms-dhkem].

A composite KEM allows two or more underlying key transport, key agreement, or KEM algorithms to be combined into a single cryptographic operation by performing each operation, transformed to a KEM as outline above, and using a specified combiner function to combine the two or more component shared secrets into a single shared secret.

2.3.1. Composite KeyGen

The KeyGen() -> (pk, sk) of a composite KEM algorithm will perform the KeyGen() of the respective component KEM 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 Encaps

The Encaps(pk) -> (ct, ss) of a composite KEM algorithm is defined as:

Encaps(pk):
  # Split the component public keys
  pk1 = pk[0]
  pk2 = pk[1]

  # Perform the respective component Encaps operations
  (ct1, ss1) = ComponentKEM1.Encaps(pk1)
  (ct2, ss2) = ComponentKEM2.Encaps(pk2)

  # combine
  ct = CompositeCiphertextValue(ct1, ct2)
  ss = Combiner(ct1, ss1, ct2, ss2, algName)

  return (ct, ss)
Figure 1: Composite Encaps(pk)

where Combiner(ct1, ss1, ct2, ss2, fixedInfo) is defined in Section 4.3 and CompositeCiphertextValue is defined in Section 4.2.

2.3.3. Composite Decaps

The Decaps(sk, ct) -> ss of a composite KEM algorithm is defined as:

Decaps(sk, ct):
  # Sptil the component ciphertexts
  ct1 = ct[0]
  ct2 = ct[1]

  # Perform the respective component Decaps operations
  ss1 = ComponentKEM1.Encaps(sk1, ct1)
  ss2 = ComponentKEM2.Encaps(sk2, ct2)

  # combine
  ss = Combiner(ct1, ss1, ct2, ss2, algName)

  return ss
Figure 2: Composite Decaps(sk, ct)

where Combiner(ct1, ss1, ct2, ss2, fixedInfo) is defined in {sec-kem-combiner}.

2.4. Component Algorithm Selection Criteria

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

  1. RSA combinations are provided at key sizes of 2048 and 3072 bits. Since RSA 2048 and 3072 are considered to have 112 and 128 bits of classical security respectively, they are both matched with NIST PQC Level 1 algorithms and 128-bit symmetric algorithms.

  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 Key Structures

3.1. pk-CompositeKEM

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

pk-CompositeKEM {
  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 { keyEncipherment }
  }

As an example, the public key type pk-MLKEM512-ECDH-P256-KMAC128 is defined as:

pk-MLKEM512-ECDH-P256-KMAC128 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM512-ECDH-P256-KMAC128,
    OCTET STRING, ECPoint }

The full set of key types defined by this specification can be found in the ASN.1 Module in Section 7.

3.2. CompositeKEMPublicKey

Composite public key data is represented by the following structure:

CompositeKEMPublicKey ::= 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 6.

Some applications may need to reconstruct the SubjectPublicKeyInfo objects corresponding to each component public key. Table 2 in Section 6 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 CompositeKEMPublicKey and SubjectPublicKeyInfo.

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

3.3. CompositeKEMPrivateKey

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.

CompositeKEMPrivateKey ::= 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 CompositeKEMPublicKey.

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 6, the privateKey field SHALL contain the CompositeKEMPrivateKey, and the publicKey field MUST NOT be present. Associated public key material MAY be present in the CompositeKEMPrivateKey.

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 CompositeKEMPublicKey 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.

CompositeKEMPublicKeyOs ::= OCTET STRING (CONTAINING CompositeKEMPublicKey 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.

CompositeKEMPublicKeyBs ::= BIT STRING (CONTAINING CompositeKEMPublicKey ENCODED BY der)

4. Composite KEM Structures

4.1. kema-CompositeKEM

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

kema-CompositeKEM {
  OBJECT IDENTIFIER:id,
    PUBLIC-KEY:publicKeyType }
    KEM-ALGORITHM ::= {
         IDENTIFIER id
         VALUE CompositeCiphertextValue
         PARAMS ARE absent
         PUBLIC-KEYS { publicKeyType }
        }

4.2. CompositeCiphertextValue

The compositeCipherTextValue is a concatenation of the ciphertexts of the underlying component algorithms. It is represented in ASN.1 as follows:

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

A composite KEM and CompositeCipherTextValue MAY be associated with a composite KEM public key, but MAY also be associated with multiple public keys from different sources, for example multiple X.509 certificates, or multiple cryptographic modules. In the latter case, composite KEMs MAY be used as the mechanism for carrying multiple ciphertexts, for example, in a non-composite hybrid encryption equivalent of those described for digital signatures in [I-D.becker-guthrie-noncomposite-hybrid-auth].

4.3. KEM Combiner

TODO: as per https://www.enisa.europa.eu/publications/post-quantum-cryptography-integration-study section 4.2, might need to specify behaviour in light of KEMs with a non-zero failure probility.

This document follows the construction of [I-D.ounsworth-cfrg-kem-combiners], which is repeated here for clarity and simplified to take two imput shared secrets:

Combiner(ct1, ss1, ct2, ss2, fixedInfo) =
  KDF(counter || ct1 || ss1 || ct2 || ss2 || fixedInfo, outputBits)
Figure 3: Generic KEM combiner construction

where:

  • KDF(message, outputBits) represents a hash function suitable to the chosen KEMs according to {tab-kem-combiners}.

  • fixedInfo SHALL be the ASCII-encoded string name of the composite KEM algorithm as listed in Table 2.

  • counter SHALL be the fixed 32-bit value 0x00000001 which is placed here soly for the purposes of easy compliance with [SP.800-56Cr2].

  • || represents concatenation.

Each registered composite KEM algorithm must specify the choice of KDF, fixedInfo, and outputBits to be used.

See Section 9.2 for further discussion of the security coniserations of this KEM combiner.

4.3.1. Named KEM Combiner parameter sets

This specification references KEM combiner instantiations according to the following names:

Table 1: KEM Combiners
KEM Combiner Name KDF outputBits
KMAC128/256 KMAC128 256
KMAC256/384 KMAC256 384
KMAC256/512 KMAC256 512

KMAC is defined in NIST SP 800-185 [SP800-185]. The KMAC(K, X, L, S) parameters are instantiated as follows:

  • K: the ASCI value of the name of the Kem Type OID.

  • X: the message input to KDF(), as defined above.

  • L: integer representation of outputBits.

  • S: empty string.

BEGIN EDNOTE

these choices are somewhat arbitrary but aiming to match security level of the input KEMs. Feedback welcome.

  • ML-KEM-512: KMAC128/256

  • ML-KEM-768: KMAC256/384

  • ML-KEM-1024 KMAC256/512

END EDNOTE

5. Example KEM Combiner instantiation

For example, the KEM combiner used with the first entry of Table 2, id-MLKEM512-ECDH-P256-KMAC128 would be:

Combiner(ct1, ss1, ct2, ss2, "id-MLKEM512-ECDH-P256-KMAC128") =
           KMAC128( 0x00000001 || ss_1 || ss_2 ||
              "id-MLKEM512-ECDH-P256-KMAC128", 256, "")

6. Algorithm Identifiers

This table summarizes the list of composite KEM algorithms and lists the OID, two component algorithms, and the combiner function.

EDNOTE: The OID referenced are TBD and MUST be used only for prototyping and replaced with the final IANA-assigned OIDS. The following prefix is used for each: replace <CompKEM> with the String "2.16.840.1.114027.80.5.2".

TODO: OIDs to be replaced by IANA.

Therefore <CompKEM>.1 is equal to 2.16.840.1.114027.80.5.2.1

Table 2: Composite KEM key types
KEM Type OID OID First Algorithm Second Algorithm KEM Combiner
id-MLKEM512-ECDH-P256-KMAC128 <CompKEM>.1 MLKEM512 ECDH-P256 KMAC128/256
id-MLKEM512-ECDH-brainpoolP256r1-KMAC128 <CompKEM>.2 MLKEM512 ECDH-brainpoolp256r1 KMAC128/256
id-MLKEM512-X25519-KMAC128 <CompKEM>.3 MLKEM512 X25519 KMAC128/256
id-MLKEM512-RSA2048-KMAC128 <CompKEM>.13 MLKEM512 RSA-KEM 2048 KMAC128/256
id-MLKEM512-RSA3072-KMAC128 <CompKEM>.4 MLKEM512 RSA-KEM 2048 KMAC128/256
id-MLKEM768-RSA3072-KMAC256 <CompKEM>.4 MLKEM768 RSA-KEM 3072 KMAC256/384
id-MLKEM768-ECDH-P256-KMAC256 <CompKEM>.5 MLKEM768 ECDH-P256 KMAC256/384
id-MLKEM768-ECDH-brainpoolP256r1-KMAC256 <CompKEM>.6 MLKEM768 ECDH-brainpoolp256r1 KMAC256/384
id-MLKEM768-X25519-KMAC256 <CompKEM>.7 MLKEM768 X25519 KMAC256/384
id-MLKEM1024-ECDH-P384-KMAC256 <CompKEM>.8 MLKEM1024 ECDH-P384 KMAC256/512
id-MLKEM1024-ECDH-brainpoolP384r1-KMAC256 <CompKEM>.9 MLKEM1024 ECDH-brainpoolP384r1 KMAC256/512
id-MLKEM1024-X448-KMAC256 <CompKEM>.10 MLKEM1024 X448 KMAC256/512

The table above contains everything needed to implement the listed explicit composite algorithms, with the exception of some special notes found below in this section. See the ASN.1 module in section Section 7 for the explicit definitions of the above Composite signature algorithms.

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

Note that all ECDH as well as X25519 and X448 algorithms MUST be promoted into KEMs according to [I-D.ounsworth-lamps-cms-dhkem].

EDNOTE: I believe that [SP.800-56Ar3] and [BSI-ECC] give equivalent and interoperable algorithms, so maybe this is extranuous detail to include?

The "KEM Combiner" column refers to the definitions in Section 4.3.

6.1. RSA-KEM Parameters

Use of RSA-KEM [I-D.ietf-lamps-rfc5990bis] within id-MLKEM512-RSA2048-KMAC128 and id-MLKEM512-RSA3072-KMAC128 requires additional specification.

The RSA component keys MUST be generated at the 2048-bit and 3072-bit security level respectively.

As with the other composite KEM algorithms, when id-MLKEM512-RSA2048-KMAC128 or id-MLKEM512-RSA3072-KMAC128 is used in an AlgorithmIdentifier, the parameters MUST be absent. The RSA-KEM SHALL be instantiated with the following parameters:

Table 3: RSA-KEM 2048 Parameters
RSA-KEM Parameter Value
keyDerivationFunction kda-kdf3 with id-sha3-256
keyLength 128

where:

7. ASN.1 Module

<CODE STARTS>

Composite-KEM-2023
      {iso(1) identified-organization(3) dod(6) internet(1)
        security(5) mechanisms(5) pkix(7) id-mod(0)
        id-mod-composite-kems(TBDMOD) }

DEFINITIONS IMPLICIT TAGS ::= BEGIN

EXPORTS ALL;

IMPORTS

PUBLIC-KEY, 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) }

KEM-ALGORITHM, KEMAlgSet
  FROM KEMAlgorithmInformation-2023
      { iso(1) identified-organization(3) dod(6) internet(1)
        security(5) mechanisms(5) pkix(7) id-mod(0)
        id-mod-kemAlgorithmInformation-2023(99) }

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) }

;


--
-- Object Identifiers
--

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



--
-- Composite KEM basic structures
--

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

CompositeKEMPublicKeyOs ::= OCTET STRING (CONTAINING
                                CompositeKEMPublicKey ENCODED BY der)

CompositeKEMPublicKeyBs ::= BIT STRING (CONTAINING
                                CompositeKEMPublicKey ENCODED BY der)

CompositeKEMPrivateKey ::= SEQUENCE SIZE (2) OF OneAsymmetricKey

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


--
-- Information Object Classes
--

pk-CompositeKEM {
  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 { keyEncipherment }
  }

kema-CompositeKEM {
  OBJECT IDENTIFIER:id,
    PUBLIC-KEY:publicKeyType }
    KEM-ALGORITHM ::= {
         IDENTIFIER id
         VALUE CompositeCiphertextValue
         PARAMS ARE absent
         PUBLIC-KEYS { publicKeyType }
        }



--
-- Composite KEM Algorithms
--


-- TODO: OID to be replaced by IANA
id-MLKEM512-ECDH-P256-KMAC128 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 1 }

pk-MLKEM512-ECDH-P256-KMAC128 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM512-ECDH-P256-KMAC128,
    OCTET STRING, ECPoint }

kema-MLKEM512-ECDH-P256-KMAC128 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM512-ECDH-P256-KMAC128,
      pk-MLKEM512-ECDH-P256-KMAC128 }


-- TODO: OID to be replaced by IANA
id-MLKEM512-ECDH-brainpoolP256r1-KMAC128 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 2 }

pk-MLKEM512-ECDH-brainpoolP256r1-KMAC128 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM512-ECDH-brainpoolP256r1-KMAC128,
    OCTET STRING, ECPoint }

kema-MLKEM512-ECDH-brainpoolP256r1-KMAC128 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM512-ECDH-brainpoolP256r1-KMAC128,
      pk-MLKEM512-ECDH-brainpoolP256r1-KMAC128 }



-- TODO: OID to be replaced by IANA
id-MLKEM512-X25519-KMAC128 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 3 }

pk-MLKEM512-X25519-KMAC128 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM512-X25519-KMAC128,
    OCTET STRING, OCTET STRING }

kema-MLKEM512-X25519-KMAC128 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM512-X25519-KMAC128,
      pk-MLKEM512-X25519-KMAC128 }



-- TODO: OID to be replaced by IANA
id-MLKEM512-RSA2048-KMAC128 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 13 }

pk-MLKEM512-RSA2048-KMAC128 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM512-RSA2048-KMAC128,
    OCTET STRING, RSAPublicKey }

kema-MLKEM512-RSA2048-KMAC128 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM512-RSA2048-KMAC128,
      pk-MLKEM512-RSA2048-KMAC128 }



-- TODO: OID to be replaced by IANA
id-MLKEM512-RSA3072-KMAC128 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 4 }

pk-MLKEM512-RSA3072-KMAC128 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM512-RSA3072-KMAC128,
    OCTET STRING, RSAPublicKey }

kema-MLKEM512-RSA3072-KMAC128 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM512-RSA3072-KMAC128,
      pk-MLKEM512-RSA3072-KMAC128 }


-- TODO: OID to be replaced by IANA
id-MLKEM768-ECDH-P256-KMAC256 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 5 }

pk-MLKEM768-ECDH-P256-KMAC256 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM768-ECDH-P256-KMAC256,
    OCTET STRING, ECPoint }

kema-MLKEM768-ECDH-P256-KMAC256 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM768-ECDH-P256-KMAC256,
      pk-MLKEM768-ECDH-P256-KMAC256 }


-- TODO: OID to be replaced by IANA
id-MLKEM768-ECDH-brainpoolP256r1-KMAC256 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 6 }

pk-MLKEM768-ECDH-brainpoolP256r1-KMAC256 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM768-ECDH-brainpoolP256r1-KMAC256,
    OCTET STRING, ECPoint }

kema-MLKEM768-ECDH-brainpoolP256r1-KMAC256 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM768-ECDH-brainpoolP256r1-KMAC256,
      pk-MLKEM768-ECDH-brainpoolP256r1-KMAC256 }


-- TODO: OID to be replaced by IANA
id-MLKEM768-X25519-KMAC256 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 7 }

pk-MLKEM768-X25519-KMAC256 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM768-X25519-KMAC256,
    OCTET STRING, OCTET STRING }

kema-MLKEM768-X25519-KMAC256 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM768-X25519-KMAC256,
      pk-MLKEM768-X25519-KMAC256 }



-- TODO: OID to be replaced by IANA
id-MLKEM1024-ECDH-P384-KMAC256 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 8 }

pk-MLKEM1024-ECDH-P384-KMAC256 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM1024-ECDH-P384-KMAC256,
    OCTET STRING, ECPoint }

kema-MLKEM1024-ECDH-P384-KMAC256 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM1024-ECDH-P384-KMAC256,
      pk-MLKEM1024-ECDH-P384-KMAC256 }


-- TODO: OID to be replaced by IANA
id-MLKEM1024-ECDH-brainpoolP384r1-KMAC256 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 9 }

pk-MLKEM1024-ECDH-brainpoolP384r1-KMAC256 PUBLIC-KEY ::=
  pk-CompositeKEM{
    id-MLKEM1024-ECDH-brainpoolP384r1-KMAC256,
    OCTET STRING, ECPoint }

kema-MLKEM1024-ECDH-brainpoolP384r1-KMAC256 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM1024-ECDH-brainpoolP384r1-KMAC256,
      pk-MLKEM1024-ECDH-brainpoolP384r1-KMAC256 }


-- TODO: OID to be replaced by IANA
id-MLKEM1024-X448-KMAC256 OBJECT IDENTIFIER ::= {
  joint-iso-itu-t(2) country(16) us(840) organization(1)
  entrust(114027) algorithm(80) explicitcomposite(5) kem(2) 10 }

pk-MLKEM1024-X448-KMAC256 PUBLIC-KEY ::=
  pk-CompositeKEM {
    id-MLKEM1024-X448-KMAC256,
    OCTET STRING, OCTET STRING }

kema-MLKEM1024-X448-KMAC256 KEM-ALGORITHM ::=
    kema-CompositeKEM{
      id-MLKEM1024-X448-KMAC256,
      pk-MLKEM1024-X448-KMAC256 }

END

<CODE ENDS>

8. IANA Considerations

8.1. Object Identifier Allocations

EDNOTE to IANA: OIDs will need to be replaced in both the ASN.1 module and in Table 2.

8.1.1. Module Registration - SMI Security for PKIX Module Identifier

  • Decimal: IANA Assigned - Replace TBDMOD

  • Description: Composite-KEM-2023 - id-mod-composite-kems

  • References: This Document

8.1.2. Object Identifier Registrations - SMI Security for PKIX Algorithms

  • id-MLKEM512-ECDH-P256-KMAC128

    • Decimal: IANA Assigned

    • Description: id-MLKEM512-ECDH-P256-KMAC128

    • References: This Document

  • id-MLKEM512-ECDH-brainpoolP256r1-KMAC128

    • Decimal: IANA Assigned

    • Description: id-MLKEM512-ECDH-brainpoolP256r1-KMAC128

    • References: This Document

  • id-MLKEM512-X25519-KMAC128

    • Decimal: IANA Assigned

    • Description: id-MLKEM512-X25519-KMAC128

    • References: This Document

  • id-MLKEM768-RSA3072-KMAC256

    • Decimal: IANA Assigned

    • Description: id-MLKEM768-3072-KMAC256

    • References: This Document

  • id-MLKEM768-ECDH-P256-KMAC256

    • Decimal: IANA Assigned

    • Description: id-MLKEM768-ECDH-P256-KMAC256

    • References: This Document

  • id-MLKEM768-ECDH-brainpoolP256r1-KMAC256

    • Decimal: IANA Assigned

    • Description: id-MLKEM768-ECDH-brainpoolP256r1-KMAC256

    • References: This Document

  • id-MLKEM768-X25519-KMAC256

    • Decimal: IANA Assigned

    • Description: id-MLKEM768-X25519-KMAC256

    • References: This Document

  • id-MLKEM1024-ECDH-P384-KMAC256

    • Decimal: IANA Assigned

    • Description: id-MLKEM1024-ECDH-P384-KMAC256

    • References: This Document

  • id-MLKEM1024-ECDH-brainpoolP384r1-KMAC256

    • Decimal: IANA Assigned

    • Description: id-MLKEM1024-ECDH-brainpoolP384r1-KMAC256

    • References: This Document

  • id-MLKEM1024-X448-KMAC256

    • Decimal: IANA Assigned

    • Description: id-MLKEM1024-X448-KMAC256

    • References: This Document

9. Security Considerations

9.1. Policy for Deprecated and Acceptable Algorithms

Traditionally, a public key or certificate contains a single cryptographic algorithm. If and when an algorithm becomes deprecated (for example, RSA-512, or SHA1), it is obvious that the public keys or certificates using that algorithm are to be considered revoked.

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-MLKEM512-ECDH-P256-KMAC128 even after ECDH-P256 is deprecated.

The composite KEM design specified in this document, and especially that of the KEM combiner specified in Section 4.3 means that the overall composite KEM algorithm should be considered to have the security strength of the strongest of its component algorithms; ie as long as one component algorithm remains strong, then the overall composite algorithm remains strong.

9.2. KEM Combiner

This document uses directly the KEM Combiner defined in [I-D.ounsworth-cfrg-kem-combiners] and therefore IND-CCA2 of any of its ingredient KEMs, i.e. the newly formed combined KEM is IND-CCA2 secure as long as at least one of the ingredient KEMs is

[I-D.ounsworth-cfrg-kem-combiners] provides two different constructions depending on the properties of the component KEMs:

  • If both the secret share ss_i and the ciphertext ct_i are constant length, then k_i MAY be constructed concatenating the two values. If ss_i or ct_i are not guaranteed to have constant length, it is REQUIRED to append the rlen encoded length when concatenating, prior to inclusion in the overall construction.

The component KEMs used in this specification are RSA-KEM [I-D.ietf-lamps-rfc5990bis], ECDH KEM [I-D.ounsworth-lamps-cms-dhkem] and ML-KEM [FIPS.203-ipd] all of which meet the criteria of having constant-length shared secrets and ciphertexts and therefore we justify using the simpler construction that omits the length tag.

10. References

10.1. Normative References

[ANS-X9.44]
American National Standards Institute, "Public Key Cryptography for the Financial Services Industry -- Key Establishment Using Integer Factorization Cryptography", American National Standard X9.44 , .
[BSI-ECC]
Federal Office for Information Security (BSI), "Technical Guideline BSI TR-03111: Elliptic Curve Cryptography. Version 2.10", .
[FIPS.203-ipd]
National Institute of Standards and Technology (NIST), "Module-Lattice-based Key-Encapsulation Mechanism Standard", , <https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.203.ipd.pdf>.
[I-D.housley-lamps-cms-sha3-hash]
Housley, R., "Use of the SHA3 One-way Hash Functions in the Cryptographic Message Syntax (CMS)", Work in Progress, Internet-Draft, draft-housley-lamps-cms-sha3-hash-01, , <https://datatracker.ietf.org/doc/html/draft-housley-lamps-cms-sha3-hash-01>.
[I-D.ietf-lamps-rfc5990bis]
Housley, R. and S. Turner, "Use of the RSA-KEM Algorithm in the Cryptographic Message Syntax (CMS)", Work in Progress, Internet-Draft, draft-ietf-lamps-rfc5990bis-01, , <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-rfc5990bis-01>.
[I-D.ounsworth-lamps-cms-dhkem]
Ounsworth, M., Gray, J., and R. Housley, "Use of the DH-Based KEM (DHKEM) in the Cryptographic Message Syntax (CMS)", Work in Progress, Internet-Draft, draft-ounsworth-lamps-cms-dhkem-00, , <https://datatracker.ietf.org/doc/html/draft-ounsworth-lamps-cms-dhkem-00>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC5280]
Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, , <https://www.rfc-editor.org/info/rfc5280>.
[RFC5652]
Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, , <https://www.rfc-editor.org/info/rfc5652>.
[RFC5958]
Turner, S., "Asymmetric Key Packages", RFC 5958, DOI 10.17487/RFC5958, , <https://www.rfc-editor.org/info/rfc5958>.
[RFC5990]
Randall, J., Kaliski, B., Brainard, J., and S. Turner, "Use of the RSA-KEM Key Transport Algorithm in the Cryptographic Message Syntax (CMS)", RFC 5990, DOI 10.17487/RFC5990, , <https://www.rfc-editor.org/info/rfc5990>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8411>.
[SP.800-56Ar3]
National Institute of Standards and Technology (NIST), "Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography", , <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-56Ar3.pdf>.
[SP.800-56Cr2]
National Institute of Standards and Technology (NIST), "Recommendation for Key-Derivation Methods in Key-Establishment Schemes", , <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-56Cr2.pdf>.
[SP800-185]
National Institute of Standards and Technology (NIST), "SHA-3 Derived Functions: cSHAKE, KMAC, TupleHash and ParallelHash", , <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-185.pdf>.
[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, .

10.2. Informative References

[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, , <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, , <https://datatracker.ietf.org/doc/html/draft-driscoll-pqt-hybrid-terminology-01>.
[I-D.housley-lamps-cms-kemri]
Housley, R., Gray, J., and T. Okubo, "Using Key Encapsulation Mechanism (KEM) Algorithms in the Cryptographic Message Syntax (CMS)", Work in Progress, Internet-Draft, draft-housley-lamps-cms-kemri-02, , <https://datatracker.ietf.org/doc/html/draft-housley-lamps-cms-kemri-02>.
[I-D.ietf-lamps-kyber-certificates]
Turner, S., Kampanakis, P., Massimo, J., and B. Westerbaan, "Internet X.509 Public Key Infrastructure - Algorithm Identifiers for Kyber", Work in Progress, Internet-Draft, draft-ietf-lamps-kyber-certificates-01, , <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-kyber-certificates-01>.
[I-D.ietf-tls-hybrid-design]
Stebila, D., Fluhrer, S., and S. Gueron, "Hybrid key exchange in TLS 1.3", Work in Progress, Internet-Draft, draft-ietf-tls-hybrid-design-04, , <https://datatracker.ietf.org/doc/html/draft-ietf-tls-hybrid-design-04>.
[I-D.ounsworth-cfrg-kem-combiners]
Ounsworth, M., Wussler, A., and S. Kousidis, "Combiner function for hybrid key encapsulation mechanisms (Hybrid KEMs)", Work in Progress, Internet-Draft, draft-ounsworth-cfrg-kem-combiners-04, , <https://datatracker.ietf.org/doc/html/draft-ounsworth-cfrg-kem-combiners-04>.
[RFC2986]
Nystrom, M. and B. Kaliski, "PKCS #10: Certification Request Syntax Specification Version 1.7", RFC 2986, DOI 10.17487/RFC2986, , <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, , <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, , <https://www.rfc-editor.org/info/rfc4211>.
[RFC5639]
Lochter, M. and J. Merkle, "Elliptic Curve Cryptography (ECC) Brainpool Standard Curves and Curve Generation", RFC 5639, DOI 10.17487/RFC5639, , <https://www.rfc-editor.org/info/rfc5639>.
[RFC5914]
Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor Format", RFC 5914, DOI 10.17487/RFC5914, , <https://www.rfc-editor.org/info/rfc5914>.
[RFC6090]
McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic Curve Cryptography Algorithms", RFC 6090, DOI 10.17487/RFC6090, , <https://www.rfc-editor.org/info/rfc6090>.
[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, , <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, , <https://www.rfc-editor.org/info/rfc7296>.
[RFC7748]
Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves for Security", RFC 7748, DOI 10.17487/RFC7748, , <https://www.rfc-editor.org/info/rfc7748>.
[RFC8446]
Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <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, , <https://www.rfc-editor.org/info/rfc8551>.

Appendix A. Samples

TBD

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. The combiner presented in Section 4.3 was chosen to align with [SP.800-56Cr2] for this reason.

Implementors seeking FIPS certification of a composite KEM 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.

B.2. Backwards Compatibility

As noted in the introduction, the post-quantum cryptographic migration will face challenges in both ensuring cryptographic strength against adversaries of unknown capabilities, as well as providing ease of migration. The composite mechanisms defined in this document primarily address cryptographic strength, however this section contains notes on how backwards compatibility may be obtained.

The term "ease of migration" is used here to mean that existing systems can be gracefully transitioned to the new technology without requiring large service disruptions or expensive upgrades. 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.

These 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 key establishment and content encryption, 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], as well as myriad other standardized and proprietary protocols and applications that leverage CMS [RFC5652] encrypted structures.

B.2.1. Parallel PKIs

EDNOTE: remove this section?

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.

For non-negotiated protocols, the details for obtaining backwards compatibility will vary by protocol, but for example in CMS [RFC5652].

EDNOTE: I copied and pruned this text from I-D.ounsworth-pq-composite-sigs. It probably needs to be fleshed out more as we better understand the implementation concerns around composite encryption.

Appendix C. Intellectual Property Considerations

The following IPR Disclosure relates to this draft:

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

EDNOTE TODO: Check with Max Pala whether this IPR actually applies to this draft.

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), Ali Noman (Entrust), Scott Fluhrer (Cisco), Jan Klaussner (D-Trust), Max Pala (CableLabs), and Douglas Stebila (University of Waterloo).

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].

Authors' Addresses

Mike Ounsworth
Entrust Limited
2500 Solandt Road -- Suite 100
Ottawa, Ontario K2K 3G5
Canada
John Gray
Entrust Limited
2500 Solandt Road -- Suite 100
Ottawa, Ontario K2K 3G5
Canada