Internet-Draft | Composite KEMs | October 2023 |
Ounsworth & Gray | Expires 25 April 2024 | [Page] |
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].¶
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.¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute 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 (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.¶
Changes affecting interoperability:¶
Re-worked wire format and ASN.1 to remove vestiges of Generics.¶
Changed all SEQUENCE OF SIZE (2..MAX)
to SEQUENCE OF SIZE (2)
.¶
Changed the definition of CompositeKEMPublicKey
from SEQUENCE OF SubjectPublicKeyInfo
to SEQUENCE OF BIT STRING
since with complete removal of Generic Composites, there is no longer any need to carry the component AlgorithmIdentifiers.¶
Removed CompositeKEMParams since all params are now explicit in the OID.¶
Defined KeyGen()
, Encaps()
, and Decaps()
for a composite KEM algorithm.¶
Removed the discussion of KeyTrans -> KEM and KeyAgree -> KEM promotions, and instead simply referenced [I-D.ietf-lamps-rfc5990bis] and [I-D.ounsworth-lamps-cms-dhkem].¶
Made RSA keys fixed-length at 2048 and 3072, both at the NIST Level 1 / AES-128 security level.¶
Re-worked section 4.1 (id-MLKEM768-RSA3072-KMAC256) to Reference 5990bis and its updated structures.¶
Removed RSA-KEM KDF params and make them implied by the OID; ie provide a profile of 5990bis.¶
Aligned combiner with draft-ounsworth-cfrg-kem-combiners-04.¶
Added id-MLKEM512-RSA2048-KMAC128 so that we have an RSA 2048 option.¶
Editorial changes:¶
Refactored to use MartinThomson github template.¶
Made this document standalone by folding in the minimum necessary content from composite-keys and dropping the cross-reference to composite-sigs.¶
Added a paragraph describing how to reconstitute component SPKIs.¶
Added an Implementation Consideration about FIPS validation where only one component algorithm is FIPS-approved.¶
Shortened the abstract (moved some content into Intro).¶
Brushed up the Security Considerations.¶
Made a proper IANA Considerations section.¶
Rename "Kyber" to "ML-KEM".¶
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.¶
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:¶
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.¶
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.¶
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.¶
[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.¶
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.¶
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.¶
The Encaps(pk) -> (ct, ss)
of a composite KEM algorithm is defined as:¶
where Combiner(ct1, ss1, ct2, ss2, fixedInfo)
is defined in Section 4.3 and CompositeCiphertextValue
is defined in Section 4.2.¶
The Decaps(sk, ct) -> ss
of a composite KEM algorithm is defined as:¶
where Combiner(ct1, ss1, ct2, ss2, fixedInfo)
is defined in {sec-kem-combiner}.¶
The composite algorithm combinations defined in this document were chosen according to the following guidelines:¶
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.¶
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.¶
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.¶
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.¶
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.¶
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.¶
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)¶
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 } }¶
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].¶
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:¶
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.¶
This specification references KEM combiner instantiations according to the following names:¶
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.¶
END EDNOTE¶
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, "")¶
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¶
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 3072 | KMAC128/256 |
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:¶
ECDH: There does not appear to be a single IETF definition of ECDH, so we refer to the following:¶
ECDH NIST: SHALL be Elliptic Curve Cryptography Cofactor Diffie-Hellman (ECC CDH) as defined in section 5.7.1.2 of [SP.800-56Ar3].¶
ECDH BSI / brainpool: SHALL be Elliptic Curve Key Agreement algorithm (ECKA) as defined in section 4.3.1 of [BSI-ECC]¶
ML-KEM: [I-D.ietf-lamps-kyber-certificates] and [FIPS.203-ipd]¶
RSA-KEM: [I-D.ietf-lamps-rfc5990bis]¶
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.¶
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:¶
RSA-KEM Parameter | Value |
---|---|
keyDerivationFunction | kda-kdf3 with id-sha3-256 |
keyLength | 128 |
where:¶
kda-kdf3
is defined in [I-D.ietf-lamps-rfc5990bis] which references it from [ANS-X9.44].¶
mda-shake256
is defined in [I-D.housley-lamps-cms-sha3-hash].¶
<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>¶
EDNOTE to IANA: OIDs will need to be replaced in both the ASN.1 module and in Table 2.¶
id-MLKEM512-ECDH-P256-KMAC128¶
id-MLKEM512-ECDH-brainpoolP256r1-KMAC128¶
id-MLKEM512-X25519-KMAC128¶
id-MLKEM768-RSA3072-KMAC256¶
id-MLKEM768-ECDH-P256-KMAC256¶
id-MLKEM768-ECDH-brainpoolP256r1-KMAC256¶
id-MLKEM768-X25519-KMAC256¶
id-MLKEM1024-ECDH-P384-KMAC256¶
id-MLKEM1024-ECDH-brainpoolP384r1-KMAC256¶
id-MLKEM1024-X448-KMAC256¶
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.¶
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.¶
TBD¶
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.¶
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.¶
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.¶
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.¶
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].¶