Internet-Draft | Composite ML-KEM | July 2024 |
Ounsworth, et al. | Expires 9 January 2025 | [Page] |
This document introduces a set of Key Encapsulation Mechanism (KEM) schemes that use pairs of cryptographic elements such as public keys and cipher texts to combine their security properties. These schemes effectively mitigate risks associated with the adoption of post-quantum cryptography and are fully compatible with existing X.509, PKIX, and CMS data structures and protocols. This document defines eleven specific pairwise combinations, namely ML-KEM Composite Schemes, that blend ML-KEM with traditional algorithms such as RSA-OAEP, ECDH, X25519, and X448. For use within CMS, this document is intended to be coupled with the CMS KEMRecipientInfo mechanism in [I-D.housley-lamps-cms-kemri]. These combinations are tailored to meet security best practices and regulatory requirements.¶
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/.¶
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This Internet-Draft will expire on 9 January 2025.¶
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.¶
Specified the fixedInfo domain separators as the DER encoded object identifiers.¶
Adjusted the combiner to be compliant with NIST SP800-56C as per https://mailarchive.ietf.org/arch/msg/spasm/nlyQF1i7ndp5A7zzcTsdYF_S9mI/ -- also aligns with X-Wing changes below.¶
Removed reference to draft-ounsworth-cfrg-kem-combiners so that we don't end up in a downref situation.¶
Changes inspired by X-Wing:¶
Since all combinations use ML-KEM; changed the document title to "Composite ML-KEM".¶
In the "Use in CMS > Underlying Components" section, the MLKEM768 combinations were lifted from id-aes192-Wrap to id-aes256-Wrap because the latter is believed to have better general adoption.¶
Added an appendix "Fixed Component Algorithm Identifiers" -- not finished, needs more work.¶
Added a section "Promotion of RSA-OAEP into a KEM".¶
Removed references to I-D.ounsworth-lamps-cms-dhkem since we'll just inline a simplified version of RFC9180's DHKEM.¶
Still to do in a future version:¶
[ ]
We need PEM samples ... 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 EnvelopedData sample encrypted for that composite KEM certificate.¶
[ ]
Open question: do we need to include the ECDH, X25519, X448, and RSA public keys in the KDF? X-Wing does, but previous versions of this spec do not. In general existing ECC and RSA hardware decrypter implementations might not know their own public key.¶
The advent of quantum computing poses a significant threat to current cryptographic systems. Traditional cryptographic algorithms such as RSA-OAEP, ECDH and their elliptic curve variants are vulnerable to quantum attacks. During the transition to post-quantum cryptography (PQC), there is considerable uncertainty regarding the robustness of both existing and new cryptographic algorithms. While we can no longer fully trust traditional cryptography, we also cannot immediately place complete trust in post-quantum replacements until they have undergone extensive scrutiny and real-world testing to uncover and rectify potential implementation flaws.¶
Unlike previous migrations between cryptographic algorithms, the decision of when to migrate and which algorithms to adopt is far from straightforward. Even after the migration period, it may be advantageous for an entity's cryptographic identity to incorporate multiple public-key algorithms to enhance security.¶
Cautious implementers may opt to combine cryptographic algorithms in such a way that an attacker would need to break all of them simultaneously to compromise the protected data. These mechanisms are referred to as Post-Quantum/Traditional (PQ/T) Hybrids [I-D.driscoll-pqt-hybrid-terminology].¶
Certain jurisdictions are already recommending or mandating that PQC lattice schemes be used exclusively within a PQ/T hybrid framework. The use of Composite scheme provides a straightforward implementation of hybrid solutions compatible with (and advocated by) some governments and cybersecurity agencies [BSI2021].¶
In addition, [BSI2021] specifically references this specification as a concrete example of hybrid X.509 certificates.¶
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-OAEP and ECDH. Backwards compatibility is not directly covered in this document, but is the subject of Appendix C.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 cryptographic 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 as 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 uses the RSA-OAEP algorithm defined in [RFC3560], the Elliptic Curve Diffie-Hellman key agreement schemes ECDH defined in section 5.7.1.2 of [SP.800-56Ar3], and X25519 / X448 which are defined in [RFC8410]. A combiner function is used to combine the two 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.¶
CompositeKEM.KeyGen(): (compositePK[0], compositeSK[0]) = MLKEM.KeyGen() (compositePK[1], compositeSK[1]) = TradKEM.KeyGen() return (compositePK, compositeSK)¶
The RSA Optimal Asymmetric Encryption Padding (OAEP), more specifically the RSAES-OAEP key transport algorithm as specified in [RFC3560] is a public key encryption algorithm used to transport key material from a sender to a receiver. It is promoted into a KEM by having the sender generate a random 256 bit secret and encrypt it.¶
DHKEM.Encaps(pkR): shared_secret = SecureRandom(ss_len) enc = RSA-OAEP.Encrypt(pkR, shared_secret) return enc, shared_secret¶
Decaps(sk, ct) -> ss
is accomplished in the analogous way.¶
DHKEM.Decap(skR, enc): shared_secret = RSA-OAEP.Decrypt(skR, enc) return shared_secret¶
The value of ss_len
as well as the RSA-OAEP parameters used within this specification can be found in Section 5.2.¶
An elliptic curve Diffie-Hellman key agreement is promoted into a KEM Encaps(pk) -> (ct, ss)
using a simplified version of the DHKEM definition from [RFC9180].¶
DHKEM.Encaps(pkR): skE, pkE = GenerateKeyPair() shared_secret = DH(skE, pkR) enc = SerializePublicKey(pkE) return enc, shared_secret¶
Decaps(sk, ct) -> ss
is accomplished in the analogous way.¶
DHKEM.Decap(skR, enc): pkE = DeserializePublicKey(enc) shared_secret = DH(skR, pkE) return shared_secret¶
This construction applies for all variants of elliptic curve Diffie-Hellman used in this specification: ECDH, X25519, and X448.¶
The simplifications from the DHKEM definition in [RFC9180] is that since the ciphertext and receiver's public key are included explicitly in the composite KEM combiner, there is no need to construct the kem_context
object, and since a domain separator is included explicitly in the composite KEM combiner there is no need to perform the labelled steps of ExtractAndExpand()
.¶
The Encaps(pk) -> (ct, ss)
of a composite KEM algorithm is defined as:¶
CompositeKEM.Encaps(pk): # Split the component public keys mlkemPK = pk[0] tradPK = pk[1] # Perform the respective component Encaps operations (mlkemCT, mlkemSS) = MLKEM.Encaps(mlkemPK) (tradCT, tradSS) = TradKEM.Encaps(tradPK) # Combine # note that the order of the traditional and ML-KEM components # is flipped here in order to satisfy NIST SP800-56Cr2. ct = CompositeCiphertextValue(ct1, ct2) ss = Combiner(tradSS, mlkemSS, tradCT, tradPK, domSep) return (ct, ss)¶
where Combiner(tradSS, mlkemSS, tradCT, tradPK, domSep)
is defined in general in Section 4.3 with specific values for domSep
per composite KEM algorithm in Section 5 and CompositeCiphertextValue
is defined in Section 4.2.¶
The Decaps(sk, ct) -> ss
of a composite KEM algorithm is defined as:¶
CompositeKEM.Decaps(ct, mlkemSK, tradSK): # split the component ciphertexts mlkemCT = ct[0] tradCT = ct[1] # Perform the respective component Decaps operations mlkemSS = MLKEM.Decaps(mlkemSK, mlkemCT) tradSS = TradKEM.Decaps(tradSK, tradCT) # Combine # note that the order of the traditional and ML-KEM components # is flipped here in order to satisfy NIST SP800-56Cr2. ss = Combiner(tradSS, mlkemSS, tradCT, tradPK, domSep) return ss¶
where Combiner(tradSS, mlkemSS, tradCT, tradPK, domSep)
is defined in general in Section 4.3 with specific values for domSep
per composite KEM algorithm in Section 5. CompositeCiphertextValue
is defined in Section 4.2.¶
Here the secret key values mlkemSK
and tradSK
may be interpreted as either literal secret key values, or as a handle to a cryptographic module which holds the secret key and is capable of performing the secret key operation.¶
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
is defined as:¶
pk-MLKEM512-ECDH-P256 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM512-ECDH-P256, 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 5.¶
Some applications may need to reconstruct the SubjectPublicKeyInfo
objects corresponding to each component public key. Table 1 in Section 5 provides the necessary mapping between composite and their component algorithms for doing this reconstruction. This also motivates the design choice of SEQUENCE OF BIT STRING
instead of SEQUENCE OF OCTET STRING
; using BIT STRING
allows for easier transcription between 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.¶
Use cases that require an inter-operable 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 5, 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 use-cases 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 Appendix C.1 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)¶
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.¶
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¶
The order of the component ciphertexts is the same as the order defined in Section 3.2.¶
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.¶
The KEM combiner construction is as follows:¶
where:¶
KDF(message, outputBits)
represents a hash function suitable to the chosen KEMs according to {tab-kem-combiners}.¶
counter
SHALL be the fixed 32-bit value 0x00000001
which is placed here solely for the purposes of compliance with [SP.800-56Cr2].¶
tradSS
is the shared secret from the traditional component (elliptic curve or RSA).¶
mlkemSS
is the shared secret from the ML-KEM componont.¶
tradCT
is the ciphertext from the traditional component (elliptic curve or RSA).¶
tradPK
is the public key of the traditional component (elliptic curve or RSA).¶
domSep
SHALL be the DER encoded value of the object identifier of the composite KEM algorithm as listed in Section 5.1.¶
||
represents concatenation.¶
Each registered composite KEM algorithm must specify the choice of KDF
, demSep
, and outputBits
to be used.¶
Some of the design choices for the combiner, specifically to place tradSS
first, and to allow tradCT || tradPK || domSep
to be treated together as a FixedInfo block are made for the purposes of compliance with [SP.800-56Cr2]; see Section 4.4 for more discussion.¶
See Section 9.3 for further discussion of the security considerations of this KEM combiner.¶
This specification is compliant with [SP.800-56Cr2] which allows for multiple sources of shared secret material to be combined into a single shared secret and the combined shared secret to be considered FIPS compliant so long as the first input shared secret is the result of a FIPS compliant algorithm. In order to ease FIPS compliance issues during the transition period, this specification uses the traditional algorithm as the first input to the combiner so that the combiner is FIPS compliant so long as the traditional component is FIPS compliant.¶
This construction is specifically designed to conform with Section 4.1 Option 1 (when KDF is SHA3) or Option 3 (when KDF is KMAC) in the following way:¶
In both cases we match exactly the construction using the allowed "hybrid" shared secret of the form Z' = Z || T
to yield the construction¶
counter || Z || T || FixedInfo
¶
where:¶
Z = tradSS
is the algorithm assumed to always be FIPS-approved from a FIPS-certified implementation which is expected to be true during the period where organizations are migrating their existing deployments to add ML-KEM implementations which may not yet have received FIPS certification,¶
T = mlkemSS
, and¶
FixedInfo = tradCT || tradPK || domSep
.¶
In the case that KDF is KMAC, the message to be hashed MUST be post-pended with H_outputBits
and the byte string 01001011 || 01000100 || 01000110
, which represents the sequence of characters "K", "D," and "F" in 8-bit ASCII, as required by [SP.800-56Cr2] section 4.1 Option 3. salt
is left empty since KMAC is only required to behave as a hash function and not as a keyed MAC.¶
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¶
Composite KEM | OID | First Algorithm | Second Algorithm | KDF |
---|---|---|---|---|
id-MLKEM512-ECDH-P256 | <CompKEM>.1 | MLKEM512 | ECDH-P256 | SHA3-256 |
id-MLKEM512-ECDH-brainpoolP256r1 | <CompKEM>.2 | MLKEM512 | ECDH-brainpoolp256r1 | SHA3-256 |
id-MLKEM512-X25519 | <CompKEM>.3 | MLKEM512 | X25519 | SHA3-256 |
id-MLKEM512-RSA2048 | <CompKEM>.13 | MLKEM512 | RSA-OAEP 2048 | SHA3-256 |
id-MLKEM512-RSA3072 | <CompKEM>.4 | MLKEM512 | RSA-OAEP 3072 | SHA3-256 |
id-MLKEM768-ECDH-P256 | <CompKEM>.5 | MLKEM768 | ECDH-P256 | SHA3-384 |
id-MLKEM768-ECDH-brainpoolP256r1 | <CompKEM>.6 | MLKEM768 | ECDH-brainpoolp256r1 | SHA3-384 |
id-MLKEM768-X25519 | <CompKEM>.7 | MLKEM768 | X25519 | SHA3-384 |
id-MLKEM1024-ECDH-P384 | <CompKEM>.8 | MLKEM1024 | ECDH-P384 | SHA3-512 |
id-MLKEM1024-ECDH-brainpoolP384r1 | <CompKEM>.9 | MLKEM1024 | ECDH-brainpoolP384r1 | SHA3-512 |
id-MLKEM1024-X448 | <CompKEM>.10 | MLKEM1024 | X448 | SHA3-512 |
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]¶
EDNOTE: I believe that [SP.800-56Ar3] and [BSI-ECC] give equivalent and inter-operable algorithms, so maybe this is extraneous detail to include?¶
The KEM combiner defined in section Section 4.3 requires a domain separator domSep
input. The following table shows the HEX-encoded domain separator for each Composite KEM AlgorithmID; to use it, the value should be HEX-decoded and used in binary form. The domain separator is simply the DER encoding of the composite algorithm OID.¶
EDNOTE: Should the domain separator values be the SHA-256 hash of the DER encoding of the corresponding composite algorithm OID? That way they would be fixed-length even if the OIDs are different lengths. See https://github.com/lamps-wg/draft-composite-sigs/issues/19¶
Composite KEM AlgorithmID | Domain Separator (in Hex encoding) |
---|---|
id-MLKEM512-ECDH-P256 | 060B6086480186FA6B50050201 |
id-MLKEM512-ECDH-brainpoolP256r1 | 060B6086480186FA6B50050202 |
id-MLKEM512-X25519 | 060B6086480186FA6B50050203 |
id-MLKEM512-RSA2048 | 060B6086480186FA6B5005020D |
id-MLKEM512-RSA3072 | 060B6086480186FA6B50050204 |
id-MLKEM768-ECDH-P256 | 060B6086480186FA6B50050205 |
id-MLKEM768-ECDH-brainpoolP256r1 | 060B6086480186FA6B50050206 |
id-MLKEM768-X25519 | 060B6086480186FA6B50050207 |
id-MLKEM1024-ECDH-P384 | 060B6086480186FA6B50050208 |
id-MLKEM1024-ECDH-brainpoolP384r1 | 060B6086480186FA6B50050209 |
id-MLKEM1024-X448 | 060B6086480186FA6B5005020A |
EDNOTE: these domain separators are based on the prototyping OIDs assigned on the Entrust arc. We will need to ask for IANA early allocation of these OIDs so that we can re-compute the domain separators over the final OIDs.¶
Use of RSA-OAEP [RFC3560] within id-MLKEM512-RSA2048
and id-MLKEM512-RSA3072
requires additional specification.¶
First, a quick note on the choice of RSA-OAEP as the supported RSA encryption primitive. RSA-KEM [RFC5990] is more straightforward to work with, but it has fairly limited adoption and therefore is of limited backwards compatibility value. Also, while RSA-PKCS#1v1.5 [RFC8017] is still everywhere, but hard to make secure and no longer FIPS-approved as of the end of 2023 [SP800-131Ar2], so it is of limited forwards value. This leaves RSA-OAEP [RFC3560] as the remaining choice.¶
The RSA component keys MUST be generated at the 2048-bit and 3072-bit security levels respectively.¶
As with the other composite KEM algorithms, when id-MLKEM512-RSA2048
or id-MLKEM512-RSA3072
is used in an AlgorithmIdentifier, the parameters MUST be absent. The RSA-OAEP SHALL be instantiated with the following hard-coded parameters which are the same for both the 2048 and 3072 bit security levels.¶
RSA-OAEP Parameter | Value |
---|---|
hashFunc | id-sha2-256 |
maskGenFunc | mgf1SHA256Identifier |
pSourceFunc | DEFAULT pSpecifiedEmptyIdentifier |
ss_len | 256 bits |
where:¶
[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.¶
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.¶
The following table lists the REQUIRED KDF and key-encryption algorithms to preserve security and performance characteristics of each composite algorithm.¶
Composite KEM OID | KDF | Key Encryption Alg |
---|---|---|
id-MLKEM512-ECDH-P256 | SHA3-256 | id-aes128-Wrap |
id-MLKEM512-ECDH-brainpoolP256r1 | SHA3-256 | id-aes128-Wrap |
id-MLKEM512-X25519 | SHA3-256 | id-aes128-Wrap |
id-MLKEM512-RSA2048 | SHA3-256 | id-aes128-Wrap |
id-MLKEM512-RSA3072 | SHA3-256 | id-aes128-Wrap |
id-MLKEM768-ECDH-P256 | SHA3-384 | id-aes256-Wrap |
id-MLKEM768-ECDH-brainpoolP256r1 | SHA3-384 | id-aes256-Wrap |
id-MLKEM768-X25519 | SHA3-384 | id-aes256-Wrap |
id-MLKEM1024-ECDH-P384 | SHA3-512 | id-aes256-Wrap |
id-MLKEM1024-ECDH-brainpoolP384r1 | SHA3-512 | id-aes256-Wrap |
id-MLKEM1024-X448 | SHA3-512 | id-aes256-Wrap |
Note: id-aes256-Wrap
is stronger than necessary for the MLKEM768 combinations at the NIST level 3 192 bit security level, however id-aes256-Wrap
was chosen because it has better general adoption than id-aes192-Wrap
.¶
where:¶
SHA3-* KDF instantiations are defined in [I-D.ietf-lamps-cms-sha3-hash].¶
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 1.¶
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.¶
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].¶
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.¶
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-OAEP Algorithm.¶
The SMIMECapability SEQUENCE representing a composite KEM Algorithm MUST include the appropriate object identifier as per Table 1 in the capabilityID field.¶
<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 } SMIME-CAPS { IDENTIFIED BY id } } -- -- Composite KEM Algorithms -- -- TODO: OID to be replaced by IANA id-MLKEM512-ECDH-P256 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM512-ECDH-P256, OCTET STRING, ECPoint } kema-MLKEM512-ECDH-P256 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM512-ECDH-P256, pk-MLKEM512-ECDH-P256 } -- TODO: OID to be replaced by IANA id-MLKEM512-ECDH-brainpoolP256r1 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM512-ECDH-brainpoolP256r1, OCTET STRING, ECPoint } kema-MLKEM512-ECDH-brainpoolP256r1 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM512-ECDH-brainpoolP256r1, pk-MLKEM512-ECDH-brainpoolP256r1 } -- TODO: OID to be replaced by IANA id-MLKEM512-X25519 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM512-X25519, OCTET STRING, OCTET STRING } kema-MLKEM512-X25519 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM512-X25519, pk-MLKEM512-X25519 } -- TODO: OID to be replaced by IANA id-MLKEM512-RSA2048 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM512-RSA2048, OCTET STRING, RSAPublicKey } kema-MLKEM512-RSA2048 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM512-RSA2048, pk-MLKEM512-RSA2048 } -- TODO: OID to be replaced by IANA id-MLKEM512-RSA3072 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM512-RSA3072, OCTET STRING, RSAPublicKey } kema-MLKEM512-RSA3072 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM512-RSA3072, pk-MLKEM512-RSA3072 } -- TODO: OID to be replaced by IANA id-MLKEM768-ECDH-P256 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM768-ECDH-P256, OCTET STRING, ECPoint } kema-MLKEM768-ECDH-P256 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM768-ECDH-P256, pk-MLKEM768-ECDH-P256 } -- TODO: OID to be replaced by IANA id-MLKEM768-ECDH-brainpoolP256r1 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM768-ECDH-brainpoolP256r1, OCTET STRING, ECPoint } kema-MLKEM768-ECDH-brainpoolP256r1 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM768-ECDH-brainpoolP256r1, pk-MLKEM768-ECDH-brainpoolP256r1 } -- TODO: OID to be replaced by IANA id-MLKEM768-X25519 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM768-X25519, OCTET STRING, OCTET STRING } kema-MLKEM768-X25519 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM768-X25519, pk-MLKEM768-X25519 } -- TODO: OID to be replaced by IANA id-MLKEM1024-ECDH-P384 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM1024-ECDH-P384, OCTET STRING, ECPoint } kema-MLKEM1024-ECDH-P384 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM1024-ECDH-P384, pk-MLKEM1024-ECDH-P384 } -- TODO: OID to be replaced by IANA id-MLKEM1024-ECDH-brainpoolP384r1 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 PUBLIC-KEY ::= pk-CompositeKEM{ id-MLKEM1024-ECDH-brainpoolP384r1, OCTET STRING, ECPoint } kema-MLKEM1024-ECDH-brainpoolP384r1 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM1024-ECDH-brainpoolP384r1, pk-MLKEM1024-ECDH-brainpoolP384r1 } -- TODO: OID to be replaced by IANA id-MLKEM1024-X448 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 PUBLIC-KEY ::= pk-CompositeKEM { id-MLKEM1024-X448, OCTET STRING, OCTET STRING } kema-MLKEM1024-X448 KEM-ALGORITHM ::= kema-CompositeKEM{ id-MLKEM1024-X448, pk-MLKEM1024-X448 } -- -- 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 <CODE ENDS>¶
EDNOTE to IANA: OIDs will need to be replaced in both the ASN.1 module and in Table 1.¶
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.¶
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
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.¶
TODO¶
EDNOTE: the exact text to put here depends on the outcome of the CFRG KEM Combiners and X-Wing discussion. If CFRG doesn't move fast enough for us, then we may need to leverage this security consideration directly on top of the X-Wing paper [X-Wing].¶
The notion of a ciphertext collision resistant KEM is defined in [X-Wing] being the property that it is computationally difficult to find two different ciphertexts that will decapsulate to the same shared secret under the same public key. In [X-Wing] it is proven that ML-KEM has this property and therefore the ML-KEM ciphertext can safely be omitted from the KEM combiner. Ciphertext collision resistance is not guaranteed for either RSA-OAEP or ECDH, therefore these ciphertexts are bound to the key derivation.¶
TBD¶
The following table lists explicitly the DER encoded AlgorithmID
that MUST be used when reconstructing SubjectPublicKeyInfo
objects for each component public key, which may be required for example if cryptographic library requires the public key in this form in order to process each component algorithm. The public key BIT STRING
should be taken directly from the respective component of the CompositeKEMPublicKey.¶
Composite KEM | First AlgorithmID | Second AlgorithmID |
---|---|---|
TODO | TODO | TODO |
TODO: see https://github.com/lamps-wg/draft-composite-kem/issues/20¶
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.¶
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 inter-operate 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), 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].¶