LAMPS M. Ounsworth Internet-Draft J. Gray Intended status: Standards Track Entrust Expires: 3 September 2024 M. Pala OpenCA Labs J. Klaussner D-Trust GmbH S. Fluhrer Cisco Systems 2 March 2024 Composite ML-KEM for Use in the Internet X.509 Public Key Infrastructure and CMS draft-ietf-lamps-pq-composite-kem-03 Abstract This document defines Post-Quantum / Traditional composite Key Encapsulation Mechanism (KEM) algorithms suitable for use within X.509, 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 [I-D.ietf-lamps-rfc5990bis] 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/. Ounsworth, et al. Expires 3 September 2024 [Page 1] Internet-Draft Composite KEMs March 2024 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. 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 3 September 2024. Copyright Notice Copyright (c) 2024 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 -03 . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 2.2. Composite Design Philosophy . . . . . . . . . . . . . . . 6 2.3. Composite Key Encapsulation Mechanisms (KEMs) . . . . . . 7 2.3.1. Composite KeyGen . . . . . . . . . . . . . . . . . . 8 2.3.2. Composite Encaps . . . . . . . . . . . . . . . . . . 8 2.3.3. Composite Decaps . . . . . . . . . . . . . . . . . . 8 2.4. Component Algorithm Selection Criteria . . . . . . . . . 9 3. Composite Key Structures . . . . . . . . . . . . . . . . . . 10 3.1. pk-CompositeKEM . . . . . . . . . . . . . . . . . . . . . 10 3.2. CompositeKEMPublicKey . . . . . . . . . . . . . . . . . . 10 Ounsworth, et al. Expires 3 September 2024 [Page 2] Internet-Draft Composite KEMs March 2024 3.3. CompositeKEMPrivateKey . . . . . . . . . . . . . . . . . 11 3.4. Encoding Rules . . . . . . . . . . . . . . . . . . . . . 12 3.5. Key Usage Bits . . . . . . . . . . . . . . . . . . . . . 12 4. Composite KEM Structures . . . . . . . . . . . . . . . . . . 12 4.1. kema-CompositeKEM . . . . . . . . . . . . . . . . . . . . 12 4.2. CompositeCiphertextValue . . . . . . . . . . . . . . . . 13 4.3. KEM Combiner . . . . . . . . . . . . . . . . . . . . . . 13 4.3.1. KMAC-KDF . . . . . . . . . . . . . . . . . . . . . . 14 5. Example KEM Combiner instantiation . . . . . . . . . . . . . 15 6. Algorithm Identifiers . . . . . . . . . . . . . . . . . . . . 15 6.1. RSA-KEM Parameters . . . . . . . . . . . . . . . . . . . 17 7. Use in CMS . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.1. Underlying Components . . . . . . . . . . . . . . . . . . 18 7.2. RecipientInfo Conventions . . . . . . . . . . . . . . . . 20 7.3. Certificate Conventions . . . . . . . . . . . . . . . . . 20 7.4. SMIMECapabilities Attribute Conventions . . . . . . . . . 21 8. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . . . 21 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 9.1. Object Identifier Allocations . . . . . . . . . . . . . . 28 9.1.1. Module Registration - SMI Security for PKIX Module Identifier . . . . . . . . . . . . . . . . . . . . . 28 9.1.2. Object Identifier Registrations - SMI Security for PKIX Algorithms . . . . . . . . . . . . . . . . . . . . . 28 10. Security Considerations . . . . . . . . . . . . . . . . . . . 30 10.1. Policy for Deprecated and Acceptable Algorithms . . . . 30 10.2. KEM Combiner . . . . . . . . . . . . . . . . . . . . . . 30 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 11.1. Normative References . . . . . . . . . . . . . . . . . . 31 11.2. Informative References . . . . . . . . . . . . . . . . . 33 Appendix A. Samples . . . . . . . . . . . . . . . . . . . . . . 36 Appendix B. Implementation Considerations . . . . . . . . . . . 36 B.1. FIPS certification . . . . . . . . . . . . . . . . . . . 36 B.2. Backwards Compatibility . . . . . . . . . . . . . . . . . 36 B.2.1. Parallel PKIs . . . . . . . . . . . . . . . . . . . . 37 Appendix C. Intellectual Property Considerations . . . . . . . . 38 Appendix D. Contributors and Acknowledgments . . . . . . . . . . 38 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38 1. Changes in version -03 * Changed the title to reflect that it is specific to ML-KEM. * Added Max Pala, Jan Klaussner, and Scott Fluhrer as authors. * Added text to Introduction to justify where and why this mechanism would be used. * Added section "Use in CMS". Ounsworth, et al. Expires 3 September 2024 [Page 3] Internet-Draft Composite KEMs March 2024 * Switched all KDFs for both the combiner and the CMS KEMRI to use id-kmac128 or id-kmac256 from I-D.ietf-lamps-cms-sha3-hash. 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 catastrophic 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]. In particular, certain jurisdictions are recommending or requiring that PQC lattice schemes only be used within a PQ/T hybrid. As an example, we point to [BSI2021] which includes the following recommendation: "Therefore, quantum computer-resistant methods should not be used alone - at least in a transitional period - but only in hybrid mode, i.e. in combination with a classical method. For this purpose, protocols must be modified or supplemented accordingly. In addition, public key infrastructures, for example, must also be adapted" In addition, [BSI2021] specifically references this specification as a concrete example of hybrid X.509 certificates. Ounsworth, et al. Expires 3 September 2024 [Page 4] Internet-Draft Composite KEMs March 2024 A more recent example is [ANSSI2024], a document co-authored by French Cybersecurity Agency (ANSSI), Federal Office for Information Security (BSI), Netherlands National Communications Security Agency (NLNCSA), and Swedish National Communications Security Authority, Swedish Armed Forces which makes the following statement: "In light of the urgent need to stop relying only on quantum- vulnerable public-key cryptography for key establishment, the clear priority should therefore be the migration to post-quantum cryptography in hybrid solutions" This specification represents the straightforward implementation of the hybrid solutions called for by European cyber security agencies. 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. Ounsworth, et al. Expires 3 September 2024 [Page 5] Internet-Draft Composite KEMs March 2024 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 cryptographic 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. Ounsworth, et al. Expires 3 September 2024 [Page 6] Internet-Draft Composite KEMs March 2024 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]. Ounsworth, et al. Expires 3 September 2024 [Page 7] Internet-Draft Composite KEMs March 2024 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: Ounsworth, et al. Expires 3 September 2024 [Page 8] Internet-Draft Composite KEMs March 2024 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. Ounsworth, et al. Expires 3 September 2024 [Page 9] Internet-Draft Composite KEMs March 2024 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 8. 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. Ounsworth, et al. Expires 3 September 2024 [Page 10] Internet-Draft Composite KEMs March 2024 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. Ounsworth, et al. Expires 3 September 2024 [Page 11] Internet-Draft Composite KEMs March 2024 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) 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 KEM algorithm MUST contain only a keyEncipherment key usage, all other key usages MUST NOT be used. This is because the composite public key can only be used in situations that are appropriate for both component algorithms, so even if the classical component key supports both signing and encryption, the post-quantum algorithms do not. 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 } } Ounsworth, et al. Expires 3 September 2024 [Page 12] Internet-Draft Composite KEMs March 2024 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 probability. This document follows the construction of [I-D.ounsworth-cfrg-kem-combiners], which is repeated here for clarity and simplified to take two input 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 solely 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. Ounsworth, et al. Expires 3 September 2024 [Page 13] Internet-Draft Composite KEMs March 2024 See Section 10.2 for further discussion of the security considerations of this KEM combiner. 4.3.1. KMAC-KDF KMAC128-KDF and KMAC256-KDF are KMAC-based KDFs specified for use in CMS in [I-D.ietf-lamps-cms-sha3-hash]. Here, KMAC# indicates the use of either KMAC128-KDF or KMAC256-KDF. KMAC#(K, X, L, S) takes the following parameters: K: the input key-derivation key. In this document this is the shared secret outputted from the Encapsulate() or Decapsulate() functions. This corresponds to the IKM KDF input from Section 5 of [I-D.ietf-lamps-cms-kemri]. X: the context, which is the info KDF input. L: the output length, in bits. S: the optional customization label. In this document this parameter is unused, that is it is the zero-length string "". The object identifier for KMAC128-KDF is id-kmac128 as defined in [I-D.ietf-lamps-cms-sha3-hash]. The object identifier for KMAC256-KDF is id-kmac256 as defined in [I-D.ietf-lamps-cms-sha3-hash]. Since the customization label to KMAC# is not used, the parameter field MUST be absent when id-kmac128 or id-kmac256 is used as part of an algorithm identifier specifying the KDF to use for ML-KEM in KemRecipientInfo. This specification references KEM combiner instantiations according to the following names: +===================+============+============+ | KEM Combiner Name | KDF | outputBits | +===================+============+============+ | KMAC128/256 | id-kmac128 | 256 | +-------------------+------------+------------+ | KMAC256/384 | id-kmac256 | 384 | +-------------------+------------+------------+ | KMAC256/512 | id-kmac256 | 512 | +-------------------+------------+------------+ Table 1: KEM Combiners Ounsworth, et al. Expires 3 September 2024 [Page 14] Internet-Draft Composite KEMs March 2024 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 with the String "2.16.840.1.114027.80.5.2". TODO: OIDs to be replaced by IANA. Therefore .1 is equal to 2.16.840.1.114027.80.5.2.1 Ounsworth, et al. Expires 3 September 2024 [Page 15] Internet-Draft Composite KEMs March 2024 +========================+============+=========+===============+===========+ |Composite KEM OID |OID |First |Second |KEM | | | |Algorithm|Algorithm |Combiner | +========================+============+=========+===============+===========+ |id-MLKEM512-ECDH- |.1 |MLKEM512 |ECDH-P256 |KMAC128/256| |P256-KMAC128 | | | | | +------------------------+------------+---------+---------------+-----------+ |id-MLKEM512-ECDH- |.2 |MLKEM512 |ECDH- |KMAC128/256| |brainpoolP256r1-KMAC128 | | |brainpoolp256r1| | +------------------------+------------+---------+---------------+-----------+ |id- |.3 |MLKEM512 |X25519 |KMAC128/256| |MLKEM512-X25519-KMAC128 | | | | | +------------------------+------------+---------+---------------+-----------+ |id- |.13|MLKEM512 |RSA-KEM 2048 |KMAC128/256| |MLKEM512-RSA2048-KMAC128| | | | | +------------------------+------------+---------+---------------+-----------+ |id- |.4 |MLKEM512 |RSA-KEM 3072 |KMAC128/256| |MLKEM512-RSA3072-KMAC128| | | | | +------------------------+------------+---------+---------------+-----------+ |id-MLKEM768-ECDH- |.5 |MLKEM768 |ECDH-P256 |KMAC256/384| |P256-KMAC256 | | | | | +------------------------+------------+---------+---------------+-----------+ |id-MLKEM768-ECDH- |.6 |MLKEM768 |ECDH- |KMAC256/384| |brainpoolP256r1-KMAC256 | | |brainpoolp256r1| | +------------------------+------------+---------+---------------+-----------+ |id- |.7 |MLKEM768 |X25519 |KMAC256/384| |MLKEM768-X25519-KMAC256 | | | | | +------------------------+------------+---------+---------------+-----------+ |id-MLKEM1024-ECDH- |.8 |MLKEM1024|ECDH-P384 |KMAC256/512| |P384-KMAC256 | | | | | +------------------------+------------+---------+---------------+-----------+ |id-MLKEM1024-ECDH- |.9 |MLKEM1024|ECDH- |KMAC256/512| |brainpoolP384r1-KMAC256 | | |brainpoolP384r1| | +------------------------+------------+---------+---------------+-----------+ |id- |.10|MLKEM1024|X448 |KMAC256/512| |MLKEM1024-X448-KMAC256 | | | | | +------------------------+------------+---------+---------------+-----------+ Table 2: Composite KEM key types 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 8 for the explicit definitions of the above Composite signature algorithms. Full specifications for the referenced algorithms can be found as follows: Ounsworth, et al. Expires 3 September 2024 [Page 16] Internet-Draft Composite KEMs March 2024 * _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] * _X25519 / X448_: [RFC8410] 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 extraneous 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: +=======================+===========================+ | RSA-KEM Parameter | Value | +=======================+===========================+ | keyDerivationFunction | kda-kdf3 with id-sha3-256 | +-----------------------+---------------------------+ | keyLength | 128 | +-----------------------+---------------------------+ Table 3: RSA-KEM 2048 Parameters Ounsworth, et al. Expires 3 September 2024 [Page 17] Internet-Draft Composite KEMs March 2024 where: * kda-kdf3 is defined in [I-D.ietf-lamps-rfc5990bis] which references it from [ANS-X9.44]. * id-sha3-256 is defined in [I-D.ietf-lamps-cms-sha3-hash] which references it from [SHA3]. 7. Use in CMS [EDNOTE: The convention in LAMPS is to specify algorithms and their CMS conventions in separate documents. Here we have presented them in the same document, but this section has been written so that it can easily be moved to a standalone document.] Composite KEM algorithms MAY be employed for one or more recipients in the CMS enveloped-data content type [RFC5652], the CMS authenticated-data content type [RFC5652], or the CMS authenticated- enveloped-data content type [RFC5083]. In each case, the KEMRecipientInfo [I-D.ietf-lamps-cms-kemri] is used with the chosen composite KEM Algorithm to securely transfer the content-encryption key from the originator to the recipient. 7.1. Underlying Components A CMS implementation that supports a composite KEM algorithm MUST support at least the following underlying components: When a particular Composite KEM OID is supported, an implementation MUST support the corresponding KDF algorithm identifier in Table 4. When a particular Composite KEM OID is supported, an implementation MUST support the corresponding key-encryption algorithm identifier in Table 4. An implementation MAY also support other key-derivation functions and other key-encryption algorithms as well. The following table lists the REQUIRED KDF and key-encryption algorithms to preserve security and performance characteristics of each composite algorithm. Ounsworth, et al. Expires 3 September 2024 [Page 18] Internet-Draft Composite KEMs March 2024 +===============================+=============+====================+ | Composite KEM OID | KDF | Key Encryption Alg | +===============================+=============+====================+ | id-MLKEM512-ECDH-P256-KMAC128 | KMAC128/256 | id-aes128-Wrap | +-------------------------------+-------------+--------------------+ | id-MLKEM512-ECDH- | KMAC128/256 | id-aes128-Wrap | | brainpoolP256r1-KMAC128 | | | +-------------------------------+-------------+--------------------+ | id-MLKEM512-X25519-KMAC128 | KMAC128/256 | id-aes128-Wrap | +-------------------------------+-------------+--------------------+ | id-MLKEM512-RSA2048-KMAC128 | KMAC128/256 | id-aes128-Wrap | +-------------------------------+-------------+--------------------+ | id-MLKEM512-RSA3072-KMAC128 | KMAC128/256 | id-aes128-Wrap | +-------------------------------+-------------+--------------------+ | id-MLKEM768-ECDH-P256-KMAC256 | KMAC256/384 | id-aes192-Wrap | +-------------------------------+-------------+--------------------+ | id-MLKEM768-ECDH- | KMAC256/384 | id-aes192-Wrap | | brainpoolP256r1-KMAC256 | | | +-------------------------------+-------------+--------------------+ | id-MLKEM768-X25519-KMAC256 | KMAC256/384 | id-aes192-Wrap | +-------------------------------+-------------+--------------------+ | id-MLKEM1024-ECDH- | KMAC256/512 | id-aes256-Wrap | | P384-KMAC256 | | | +-------------------------------+-------------+--------------------+ | id-MLKEM1024-ECDH- | KMAC256/512 | id-aes256-Wrap | | brainpoolP384r1-KMAC256 | | | +-------------------------------+-------------+--------------------+ | id-MLKEM1024-X448-KMAC256 | KMAC256/512 | id-aes256-Wrap | +-------------------------------+-------------+--------------------+ Table 4: REQUIRED pairings for CMS KDF and WRAP where: * KMAC KDF instantiations are defined in Section 4.3.1. * id-aes*-Wrap are defined in [RFC3394]. Implementers MAY safely substitute stronger KDF and key-encryption algorithms than those indicated; for example id-alg-hkdf-with- sha3-512 and id-aes256-Wrap MAY be safely used in place of id-alg- hkdf-with-sha3-384and id-aes192-Wrap, for example, where SHA3-384 or AES-192 are not supported. Ounsworth, et al. Expires 3 September 2024 [Page 19] Internet-Draft Composite KEMs March 2024 7.2. RecipientInfo Conventions When a composite KEM Algorithm is employed for a recipient, the RecipientInfo alternative for that recipient MUST be OtherRecipientInfo using the KEMRecipientInfo structure [I-D.ietf-lamps-cms-kemri]. The fields of the KEMRecipientInfo MUST have the following values: version is the syntax version number; it MUST be 0. rid identifies the recipient's certificate or public key. kem identifies the KEM algorithm; it MUST contain one of the OIDs listed in Table 2. kemct is the ciphertext produced for this recipient; it contains the ct output from Encaps(pk) of the KEM algorithm identified in the kem parameter. kdf identifies the key-derivation function (KDF). Note that the KDF used for CMS RecipientInfo process MAY be different than the KDF used within the composite KEM Algorithm, which MAY be different than the KDFs (if any) used within the component KEMs of the composite KEM Algorithm. kekLength is the size of the key-encryption key in octets. ukm is an optional random input to the key-derivation function. wrap identifies a key-encryption algorithm used to encrypt the keying material. encryptedKey is the result of encrypting the keying material with the key-encryption key. When used with the CMS enveloped-data content type [RFC5652], the keying material is a content-encryption key. When used with the CMS authenticated-data content type [RFC5652], the keying material is a message-authentication key. When used with the CMS authenticated-enveloped-data content type [RFC5083], the keying material is a content-authenticated-encryption key. 7.3. Certificate Conventions The conventions specified in this section augment RFC 5280 [RFC5280]. The willingness to accept a composite KEM Algorithm MAY be signaled by the use of the SMIMECapabilities Attribute as specified in Section 2.5.2. of [RFC8551] or the SMIMECapabilities certificate extension as specified in [RFC4262]. Ounsworth, et al. Expires 3 September 2024 [Page 20] Internet-Draft Composite KEMs March 2024 The intended application for the public key MAY be indicated in the key usage certificate extension as specified in Section 4.2.1.3 of [RFC5280]. If the keyUsage extension is present in a certificate that conveys a composite KEM public key, then the key usage extension MUST contain only the following value: keyEncipherment The digitalSignature and dataEncipherment values MUST NOT be present. That is, a public key intended to be employed only with a composite KEM algorithm MUST NOT also be employed for data encryption or for digital signatures. This requirement does not carry any particular security consideration; only the convention that KEM keys be identified with the keyEncipherment key usage. 7.4. SMIMECapabilities Attribute Conventions Section 2.5.2 of [RFC8551] defines the SMIMECapabilities attribute to announce a partial list of algorithms that an S/MIME implementation can support. When constructing a CMS signed-data content type [RFC5652], a compliant implementation MAY include the SMIMECapabilities attribute that announces support for the RSA-KEM Algorithm. The SMIMECapability SEQUENCE representing a composite KEM Algorithm MUST include the appropriate object identifier as per Table 2 in the capabilityID field. 8. ASN.1 Module 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) } Ounsworth, et al. Expires 3 September 2024 [Page 21] Internet-Draft Composite KEMs March 2024 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) Ounsworth, et al. Expires 3 September 2024 [Page 22] Internet-Draft Composite KEMs March 2024 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 } SMIME-CAPS { IDENTIFIED BY id } } -- -- 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, Ounsworth, et al. Expires 3 September 2024 [Page 23] Internet-Draft Composite KEMs March 2024 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 ::= Ounsworth, et al. Expires 3 September 2024 [Page 24] Internet-Draft Composite KEMs March 2024 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 } Ounsworth, et al. Expires 3 September 2024 [Page 25] Internet-Draft Composite KEMs March 2024 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 } Ounsworth, et al. Expires 3 September 2024 [Page 26] Internet-Draft Composite KEMs March 2024 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 } -- -- Expand the S/MIME capabilities set used by CMS [RFC5911] -- SMimeCaps SMIME-CAPS ::= { kema-MLKEM512-ECDH-P256-KMAC128.&smimeCaps | kema-MLKEM512-ECDH-brainpoolP256r1-KMAC128.&smimeCaps | kema-MLKEM512-X25519-KMAC128.&smimeCaps | kema-MLKEM512-RSA2048-KMAC128.&smimeCaps | kema-MLKEM512-RSA3072-KMAC128.&smimeCaps | kema-MLKEM768-ECDH-P256-KMAC256.&smimeCaps | kema-MLKEM768-ECDH-brainpoolP256r1-KMAC256.&smimeCaps | kema-MLKEM768-X25519-KMAC256.&smimeCaps | kema-MLKEM1024-ECDH-P384-KMAC256.&smimeCaps | kema-MLKEM1024-ECDH-brainpoolP384r1-KMAC256.&smimeCaps | kema-MLKEM1024-X448-KMAC256.&smimeCaps, ... } END Ounsworth, et al. Expires 3 September 2024 [Page 27] Internet-Draft Composite KEMs March 2024 9. IANA Considerations 9.1. Object Identifier Allocations EDNOTE to IANA: OIDs will need to be replaced in both the ASN.1 module and in Table 2. 9.1.1. Module Registration - SMI Security for PKIX Module Identifier * Decimal: IANA Assigned - *Replace TBDMOD* * Description: Composite-KEM-2023 - id-mod-composite-kems * References: This Document 9.1.2. 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 Ounsworth, et al. Expires 3 September 2024 [Page 28] Internet-Draft Composite KEMs March 2024 - 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 Ounsworth, et al. Expires 3 September 2024 [Page 29] Internet-Draft Composite KEMs March 2024 - References: This Document 10. Security Considerations 10.1. 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 independently 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. 10.2. 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. Ounsworth, et al. Expires 3 September 2024 [Page 30] Internet-Draft Composite KEMs March 2024 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. 11. References 11.1. 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 , 2007. [BSI-ECC] Federal Office for Information Security (BSI), "Technical Guideline BSI TR-03111: Elliptic Curve Cryptography. Version 2.10", 1 June 2018. [FIPS.203-ipd] National Institute of Standards and Technology (NIST), "Module-Lattice-based Key-Encapsulation Mechanism Standard", August 2023, . [I-D.ietf-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-ietf-lamps-cms-kemri-08, 6 February 2024, . [I-D.ietf-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-ietf-lamps-cms-sha3-hash-01, 1 March 2024, . [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, 12 September 2023, . Ounsworth, et al. Expires 3 September 2024 [Page 31] Internet-Draft Composite KEMs March 2024 [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, 24 August 2023, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard (AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394, September 2002, . [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, . [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, September 2009, . [RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, DOI 10.17487/RFC5958, August 2010, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [RFC8411] Schaad, J. and R. Andrews, "IANA Registration for the Cryptographic Algorithm Object Identifier Range", RFC 8411, DOI 10.17487/RFC8411, August 2018, . Ounsworth, et al. Expires 3 September 2024 [Page 32] Internet-Draft Composite KEMs March 2024 [SHA3] National Institute of Standards and Technology (NIST), "SHA-3 Standard: Permutation-Based Hash and Extendable- Output Functions, FIPS PUB 202, DOI 10.6028/ NIST.FIPS.202", August 2015, . [SP.800-56Ar3] National Institute of Standards and Technology (NIST), "Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography", April 2018, . [SP.800-56Cr2] National Institute of Standards and Technology (NIST), "Recommendation for Key-Derivation Methods in Key- Establishment Schemes", August 2020, . [SP800-185] National Institute of Standards and Technology (NIST), "SHA-3 Derived Functions: cSHAKE, KMAC, TupleHash and ParallelHash", December 2016, . [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. 11.2. Informative References [ANSSI2024] French Cybersecurity Agency (ANSSI), Federal Office for Information Security (BSI), Netherlands National Communications Security Agency (NLNCSA), and Swedish National Communications Security Authority, Swedish Armed Forces, "Position Paper on Quantum Key Distribution", n.d., . Ounsworth, et al. Expires 3 September 2024 [Page 33] Internet-Draft Composite KEMs March 2024 [BSI2021] Federal Office for Information Security (BSI), "Quantum- safe cryptography - fundamentals, current developments and recommendations", October 2021, . [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, . [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, . [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, 20 February 2023, . [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, 28 March 2023, . [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, 11 January 2022, . [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- Ounsworth, et al. Expires 3 September 2024 [Page 34] Internet-Draft Composite KEMs March 2024 cfrg-kem-combiners-04, 8 July 2023, . [RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification Request Syntax Specification Version 1.7", RFC 2986, DOI 10.17487/RFC2986, November 2000, . [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, . [RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF)", RFC 4211, DOI 10.17487/RFC4211, September 2005, . [RFC5083] Housley, R., "Cryptographic Message Syntax (CMS) Authenticated-Enveloped-Data Content Type", RFC 5083, DOI 10.17487/RFC5083, November 2007, . [RFC5639] Lochter, M. and J. Merkle, "Elliptic Curve Cryptography (ECC) Brainpool Standard Curves and Curve Generation", RFC 5639, DOI 10.17487/RFC5639, March 2010, . [RFC5914] Housley, R., Ashmore, S., and C. Wallace, "Trust Anchor Format", RFC 5914, DOI 10.17487/RFC5914, June 2010, . [RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic Curve Cryptography Algorithms", RFC 6090, DOI 10.17487/RFC6090, February 2011, . [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, . [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, . Ounsworth, et al. Expires 3 September 2024 [Page 35] Internet-Draft Composite KEMs March 2024 [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves for Security", RFC 7748, DOI 10.17487/RFC7748, January 2016, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [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, . 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. Implementers 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 algorithm 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 Ounsworth, et al. Expires 3 September 2024 [Page 36] Internet-Draft Composite KEMs March 2024 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. Ounsworth, et al. Expires 3 September 2024 [Page 37] Internet-Draft Composite KEMs March 2024 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 Acknowledgments 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), 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 Email: mike.ounsworth@entrust.com John Gray Entrust Limited 2500 Solandt Road -- Suite 100 Ottawa, Ontario K2K 3G5 Canada Email: john.gray@entrust.com Ounsworth, et al. Expires 3 September 2024 [Page 38] Internet-Draft Composite KEMs March 2024 Massimiliano Pala OpenCA Labs 858 Coal Creek Cir 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 Scott Fluhrer Cisco Systems Email: sfluhrer@cisco.com Ounsworth, et al. Expires 3 September 2024 [Page 39]