Composite Public and Private Keys For Use In Internet PKI

Composite Public and Private Keys For Use In Internet PKI Entrust Limited

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Security LAMPS Internet-Draft The migration to post-quantum cryptography is unique in the history of modern digital cryptography in that neither the old outgoing nor the new incoming algorithms are fully trusted to protect data for the required data lifetimes. The outgoing algorithms, such as RSA and elliptic curve, may fall to quantum cryptalanysis, while the incoming post-quantum algorithms face uncertainty about both the underlying mathematics as well as hardware and software implementations that have not had sufficient maturing time to rule out classical cryptanalytic attacks and implementation bugs. Cautious implementors may wish to layer cryptographic algorithms such that an attacker would need to break all of them in order to compromise the data being protected using either a Post-Quantum / Traditional Hybrid, Post-Quantum / Post-Quantum Hybrid, or combinations thereof. This document, and its companions, defines a specific instantiation of hybrid paradigm called "composite" where multiple cryptographic algorithms are combined to form a single key, signature, or key encapsulation mechanism (KEM) such that they can be treated as a single atomic object at the protocol level. This document defines the structures CompositePublicKey and CompositePrivateKey, which are sequences of the respective structure for each component algorithm. The generic composite variant is defined which allows arbitrary combinations of key types to be placed in the CompositePublicKey and CompositePrivateKey structures without needing the combination to be pre-registered or pre-agreed. The explicit variant is alxso defined which allows for a set of algorithm identifier OIDs to be registered together as an explicit composite algorithm and assigned an OID. This document is intended to be coupled with corresponding documents that define the structure and semantics of composite signatures and encryption, such as and .

Changes in version -03 Added the following explicit composite key types Explicit Composite Signature Keys id-Dilithium3-ECDSA-P256 id-Dilithium3-RSA id-Falcon512-ECDSA-P256 id-Falcon512-Ed25519 id-SPHINCSXXX-ECDSA-P256 id-Dilithium5-Falcon1024-ECDSA-P521 id-Dilithium5-Falcon1024-RSA Explicit Composite KEM Keys id-Kyber512-RSA id-Kyber512-ECDH-P256 id-Kyber512-x25519 Added samples of (most of) the above explic composites in appendices. Marked generic composite for prototyping; to be removed in final publication. Sycronized terminology with I-D.draft-driscoll-pqt-hybrid-terminology-01. Removed the section "Implementation Considerations > Asymmetric Key Packages (CMS)" since private key formats are now fully covered in the body and examples.

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 when, and only when, they appear in all capitals, as shown here. This document is consistent with all terminology from . In addition, the following terms are used in this document: BER: Basic Encoding Rules (BER) as defined in . CLIENT: Any software that is making use of a cryptographic key. This includes a signer, verifier, encrypter, decrypter. DER: Distinguished Encoding Rules as defined in . PKI: Public Key Infrastructure, as defined in . PUBLIC / PRIVATE KEY: The public and private portion of an asymmetric cryptographic key, making no assumptions about which algorithm.

Introduction During the transition to post-quantum cryptography (PQ or PQC), there will be uncertainty as to the strength of cryptographic algorithms; we will no longer fully trust traditional cryptography such as RSA, Diffie-Hellman, DSA and their elliptic curve variants, but we may also not fully trust their post-quantum replacements until further time has passed to allow additional scrutiny and the discovery of implementation bugs. Unlike previous cryptographic algorithm migrations, the choice of when to migrate and which algorithms to migrate to, is not so clear. Even after the migration period, it may be advantageous for an entity's cryptographic identity to be composed of multiple public-key algorithms by using a Post-Quantum/Traditional (PQ/T) or Post-Quantum/Post-Quantum (PQ/PQ) Hybrid scheme. The transition to PQC will face two challenges: 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. Migration: During the transition period, systems will require mechanisms that allow for staged migrations from fully traditional to fully post-quantum-aware cryptography. This document provides the composite mechanism, which is a specific instantiation of the PQ/T and PQ/PQ Hybrid paradigm to address algorithm strength uncertainty concerns by providing formats for encoding multiple public key and private key values into existing public key and private key fields. Backwards compatibility is not directly addressed via the composite mechanisms defined in the document, but some notes on how it can be obtained can be found in . This document is intended for general applicability anywhere that keys are used within PKIX or CMS structures.

Composite Key Structures In order to represent public keys and private keys that are composed of multiple algorithms, we define encodings consisting of a sequence of public key or private key primitives (aka "components") such that these structures can be used directly in existing public key fields such as those found in PKCS#10 , CMP , X.509 , CMS , and the Trust Anchor Format . A composite key is a single key object that performs an atomic cryptographic operation -- such a signing, verifying, encapsulating, or decapsulating -- using its encapsulated sequence of component keys as if it was a single key. This generally means that the complexity of combining algorithms can be deferred from the protocol layer to the cryptographic library layer.

CompositePublicKey Composite public key data is represented by the following structure:

A composite key MUST contain at least two component public keys. A CompositePublicKey MUST NOT contain a component public key which itself describes a composite key; i.e. recursive CompositePublicKeys are not allowed. EDNOTE: unclear that banning recursive composite keys actually accomplishes anything other than a general reduction in complexity and therefore reduction in attack surface. Each component SubjectPublicKeyInfo SHALL contain an AlgorithmIdentifier OID which identifies the public key type and parameters for the public key contained within it. See for specific algorithms defined in this document. Each element of a CompositePublicKey is a SubjectPublicKeyInfo object encoding a component public key. When the CompositePublicKey must be provided in octet string or bit string format, the data structure is encoded as specified in .

CompositePrivateKey This section provides an encoding for composite private keys intended for PKIX protocols and other applications that require an interoperable format for transmitting private keys, such as PKCS #12 or CMP / CRMF , . It is not intended to dictate a storage format in implementations not requiring interoperability of private key formats. In some 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. The establishment of correspondence between public keys in a CompositePublicKey and private keys not represented in a single composite structure is beyond the scope of this document. The composite private key data is represented by the following structure:

Each element is a OneAsymmetricKey object for a component private key. The parameters field MUST be absent. A CompositePrivateKey MUST contain at least two component private keys, and they MUST be in the same order as in the corresponding CompositePublicKey. EDNOTE: does this also need an explicit version? It would probably reduce attack surface of tricking a client into running the wrong parser and a given piece of data. ... maybe we get that for free if we use the explicit composite OIDs also for private keys?

Key Usage For protocols such as X.509 that specify key usage along with the public key, any key usage may be used with composite keys, with the requirement that the specified key usage MUST apply to all component keys. For example if a composite key is marked with a KeyUsage of digitalSignature, then all component keys MUST be capable of producing digital signatures. The composite mechanism MUST NOT be used to implement mixed-usage keys, for example, where a digitalSignature and a keyEncipherment key are combined together into a single composite key.

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.

EDNOTE: will this definition include an ASN.1 tag and length byte inside the OCTET STRING object? If so, that's probably an extra uneccessary layer. 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.

EDNOTE: See this LAMPS mailist discussion about BIT STRING vs OCTET STRING for public keys. I think we have dodged the issue, but may we worth re-visiting. https://mailarchive.ietf.org/arch/msg/spasm/Gv-ACiOpYZfOM0AJEZUX1jIhVq0/

Algorithm Identifiers This section defines the algorithm identifier for generic composite, as well as a framework for defining explicit combinations and a list of explicit composite algorithms covering a wide range of use cases. This section is not intended to be exhaustive and other authors may define others so long as they are compatible with the structures and processes defined in this and companion signature and encryption documents. Some use-cases desire the flexibility for client to use any combination of supported algorithms, while others desire the rigidity of explicitly-specified combinations of algorithms.

id-composite-key (Generic Composite Keys) Usage guidance: This mode is primarily for prototyping and for use in proprietary implementations; implementers MAY implement this section if there is a need for greater flexibility in algorithm combinations than is available by using the pre-defined composite algorithms defined below. EDNOTE: Does the WG feel strongly that this section should be removed prior to publication by the RFC Editors? IE remove it entirely from the standard? Are there enduring (ie non-prototyping) usecases that benefit from generic composite? The id-composite-key object identifier is used for identifying a generic composite public key and a generic composite private key. This allows arbitrary combinations of key types to be placed in the CompositePublicKey and CompositePrivateKey structures without needing the combination to be pre-registered or standardized.

EDNOTE: this is a temporary OID for the purposes of prototyping. We are requesting IANA to assign a permanent OID, see . The PUBLIC-KEY ASN.1 information object class is defined in . The PUBLIC-KEY information object for generic () and explicit () composite public and private keys has the following form:

The motivation for this variant is primarily for prototyping work prior to the standardization of algorithm identifiers for explicit combinations of algorithms. However, the authors envision that this variant will remain relevant beyond full standardization for example in environments requiring very high levels of crypto agility, for example where clients support a large number of algorithms or where a large number of keys will be used at a time and it is therefore prohibitive to define algorithm identifiers for every combination of pairs, triples, quadruples, etc of algorithms.

Explicit Composite Signature Keys This variant provides a rigid way of specifying supported combinations of key types. The motivation for this variant is to make it easier to reference and enforce specific combinations of algorithms. The authors envision this being useful for client-server negotiated protocols, protocol designers who wish to place constraints on allowable algorithm combinations in the protocol specification, as well as audited environments that wish to prove that only certain combinations will be supported by clients. Profiles need to define an explicit composite key type which consists of, at the minimum: A new algorithm identifier OID for the explicit algorithm. The PUBLIC-KEY information object of each component public key type. The algorithm identifiers and parameters to be contained in each of the component SubjectPublicKeyInfos and OneAsymmetricKeys. See for guidance on creating and registering OIDs for specific explicit combinations. In this variant, the public key is encoded as defined in and , however the PUBLIC-KEY.id SHALL be an OID which is registered to represent a specific combination of component public key types. See for examples. The SubjectPublicKeyInfo.algorithm for each component key is redundant information which MUST match -- and can be inferred from -- the specification of the explicit algorithm. It has been left here for ease of implementation as the component SubjectPublicKeyInfo structures are the same between generic and explicit, as well as with single-algorithm keys. However, it introduces the risk of mismatch and leads to the following security consideration: Security consideration: Implementations MUST check that the component AlgorithmIdentifier OIDs and parameters match those expected by the definition of the explicit algorithm. Implementations SHOULD first parse a component's SubjectPublicKeyInfo.algorithm, and ensure that it matches what is expected for that position in the explicit key, and then proceed to parse the SubjectPublicKeyInfo.subjectPublicKey. This is to reduce the attack surface associated with parsing the public key data of an unexpected key type, or worse; to parse and use a key which does not match the explicit algorithm definition. Similar checks MUST be done when handling the corresponding private key. Below are provided a set of explicit composite algorithms which have been selected to fill a wide range of use cases, with algorithms selected to match security levels across a group. The selections include pairs of {lattice, ECC/RSA} which should cover most short-term use cases, and also {hash-based, ECC} pairs and {lattice, lattice, ECC/RSA} triples for long-term use cases. Usage guidance is provided for each explicit combination. The algorithm set provided here is not intended to be exhaustive; additional use cases and cryptographic advances may require additional combinations to be defined in other documents by using the mechanim provided in .

id-Dilithium3-ECDSA-P256 Usage guidance: This signature key type is intended to be the standard composite signature, applicable for most use cases. The following object identifier is defined:

EDNOTE: this is a temporary OID for the purposes of prototyping. We are requesting IANA to assign a permanent OID, see . When used in an AlgorithmIdentifier, parameters SHALL be ABSENT. The PUBLIC-KEY SHALL be:

--- BEGIN EDNOTE --- EDNOTE: design decision needed: should it be CompositePublicKey and CompositePrivateKey, or should we define Dilithium3-ECDSA-P256-PublicKey and Dilithium3-ECDSA-P256-PrivateKey for each explicit type? Pros of a *-PublicKey for each explicit composite type: 1) the ASN.1 parser will do some of the heavy-lifting of checking that types match (but how much is up for debate..). 2) can further compress the encoding by removing the redundant inner component OIDs. Pros of CompositePublicKey (ie carrying full SPKIs for each component): 1) it becomes harder to write abstract code that takes advantange of the fact that all composite explicit types have the same wire encoding structure because each will have an independantly defined structure object. 2) The wire encoding carries a full SPKI, so for crypto libraries that require an SPKI for each component alg, clients need to reconstruct a full SPKI, including reconstituting the components OIDs, which needs the client to have a mapping table of explicit composite OIDs to component OIDs. --- END EDNOTE --- The public key encoding is defined in for id-Dilithium3-ECDSA-P256 SHALL have SIZE (2):

The first SubjectPublicKeyInfo (defined in ) SHALL contain:

where pk-dilithiumTBD and TBDDilithiumPublicKey are defined in . TODO: I don't think subjectPublicKey BIT STRING(DilithiumPublicKey) is correct ASN.1. EDNOTE: pk-dilithiumTBD and TBDPublicKey refer to and should be kept in sync with future versions of that draft. The second SubjectPublicKeyInfo SHALL contain:

where id-ecPublicKey, secp256r1, and ECPoint are defined in . The private key encoding is defined in , and for id-Dilithium3-ECDSA-P256 SHALL have SIZE (2):

The first OneAsymmetricKey, defined in SHALL contain

where id-dilithiumTBD and DilithiumPrivateKey are defined in . The publicKey remains OPTIONAL. The second OneAsymmetricKey SHALL contain

where ECPrivateKey is defined in . The publicKey remains OPTIONAL.

id-Dilithium3-RSA Usage guidance: This signature key type is intended to be the standard composite signature for environments that support RSA but not elliptic curve. The following object identifier is defined:

--- BEGIN EDNOTE --- EDNOTE: design decision needed: should it be CompositePublicKey + CompositePrivateKey, or should we define *-PublicKey and *-PrivateKey for each explicit type? Pros of a *-PublicKey for each explicit composite type: 1) the ASN.1 parser will do some of the heavy-lifting of checking that types match (but how much is up for debate..). 2) can further compress the encoding by removing the redundant inner component OIDs. Pros of CompositePublicKey (ie carrying full SPKIs for each component): 1) it becomes harder to write abstract code that takes advantange of the fact that all composite explicit types have the same wire encoding structure because each will have an independantly defined structure object. 2) The wire encoding carries a full SPKI, so for crypto libraries that require an SPKI for each component alg, clients need to reconstruct a full SPKI, including reconstituting the components OIDs, which needs the client to have a mapping table of explicit composite OIDs to component OIDs. --- END EDNOTE --- The public key encoding is defined in for id-Dilithium3-ECDSA-P256 SHALL have SIZE (2):

The first SubjectPublicKeyInfo (defined in ) SHALL contain:

where rsaEncryption and RSAPublicKey are defined in . The private key encoding is defined in , and for id-Dilithium3-ECDSA-P256 SHALL have SIZE (2):

The first OneAsymmetricKey, defined in SHALL contain

The publicKey remains OPTIONAL. The second OneAsymmetricKey SHALL contain

where ECPrivateKey is defined in . The publicKey remains OPTIONAL.

id-Falcon512-ECDSA-P256 Usage guidance: This signature key type is intended for constrained environments that need to use FIPS-approved elliptic curve. TODO: fill in details.

id-Falcon512-Ed25519 Usage guidance: This signature key type is intended for constrained environments that may use non-FIPS-approved elliptic curve. TODO: fill in details.

id-SPHINCSsha256256frobust-ECDSA-P256 Usage guidance: This signature key type is intended for long-term keys that desire the robustness to algorithmic attacks that comes from stateless hash-based signatures as well as the robustness to implementation bugs that comes from coupling with mature ECDSA implementations. TODO: fill in details.

id-Dilithium5-Falcon1024-ECDSA-P521 Usage guidance: This signature key type is intended for long-term keys that desire robustness to the break of a given lattice-based scheme, but also desire smaller signatures than stateless hash-based signatures. Note that this still has smaller pubkey + sig than SPHINCS+. TODO: fill in numbers. TODO: fill in details.

id-Dilithium5-Falcon1024-RSA Usage guidance: This signature key type is intended for long-term keys that desire robustness to the break of a given lattice-based scheme for environments that support RSA but not elliptic curve, but also desire smaller signatures than stateless hash-based signatures. Note that this still has smaller pubkey + sig than SPHINCS+. TODO: fill in numbers. TODO: fill in details.

Explicit Composite KEM Keys TODO: some text Ref to draft-ounsworth-pq-composite-kem

id-Kyber512-RSA TODO

id-Kyber512-ECDH-P256 TODO

id-Kyber512-x25519 TODO

Implementation Considerations This section addresses practical issues of how this draft affects other protocols and standards. EDNOTE 10: Possible topics to address: The size of these certs and cert chains. In particular, implications for (large) composite keys / signatures / certs on the handshake stages of TLS and IKEv2. If a cert in the chain is a composite cert then does the whole chain need to be of composite Certs? We could also explain that the root CA cert does not have to be of the same algorithms. The root cert SHOULD NOT be transferred in the authentication exchange to save transport overhead and thus it can be different than the intermediate and leaf certs.

Textual encoding of Composite Private Keys CompositePrivateKeys can be encoded to the Privacy-Enhanced Mail (PEM) format by placing a CompositePrivateKey into the privateKey field of a PrivateKeyInfo or OneAsymmetricKey object, and then applying the PEM encoding rules as defined in section 10 and 11 for plaintext and encrypted private keys, respectively.

Backwards Compatibility As noted in the introduction, the post-quantum cryptographic migration will face challenges in both ensuring cryptographic strength against adversaries of unknown capabilities, as well as providing ease of migration. The composite mechanisms defined in this document primarily address cryptographic strength, however this section contains notes on how backwards compatibility may be obtained. The term "ease of migration" is used here to mean that existing systems can be gracefully transitioned to the new technology without requiring large service disruptions or expensive upgrades. The term "backwards compatibility" is used here to mean something more specific; that existing systems, as they are deployed today, can interoperate with the upgraded systems of the future. These migration and interoperability concerns need to be thought about in the context of various types of protocols that make use of X.509 and PKIX with relation to public key objects, from online negotiated protocols such as TLS 1.3 and IKEv2 , to non-negotiated asynchronous protocols such as S/MIME signed and encrypted email , document signing such as in the context of the European eIDAS regulations , and publicly trusted code signing , as well as myriad other standardized and proprietary protocols and applications that leverage CMS signed or encrypted structures.

OR modes This document purposefully does not specify how clients are to combine component keys together to form a single cryptographic operation; this is left up to the specifications of signature and encryption algorithms that make use of the composite key type. One possible way to combine component keys is through an OR relation, or OR-like client policies for acceptable algorithm combinations, where senders and / or receivers are permitted to ignore some component keys. Some envisioned uses of this include environments where the client encounters a component key for which it does not possess a compatible algorithm implementation but wishes to proceed with the cryptographic operation using the subset of component keys for which it does have compatible implementations. Such a mechanism could be designed to provide ease of migration by allowing for composite keys to be distributed and used before all clients in the environment are fully upgraded, but it does not allow for full backwards compatibility since clients would at least need to be upgraded from their current state to be able to parse the composite structures.

Parallel PKIs We present the term "Parallel PKI" to refer to the setup where a PKI end entity possesses two or more distinct public keys or certificates for the same key type (signature, key establishment, etc) for the same identity (name, SAN), 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). This concept contains strong overlap with other documented approaches, such as and highlights the synergy between composite and non-composite hybrid approaches. 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 cryptographic operation. For negotiated protocols, the client could choose which public key(s) or certificate(s) to use based on the negotiated algorithms, or could combine two of the public keys for example in a non-composite hybrid method such as or . Note that it is possible to use the signature algorithm defined in as a way to carry the multiple signature values generated by a non-composite public mechanism in protocols where it is easier to support the composite signature algorithms than to implement such a mechanism in the protocol itself. There is also nothing precluding a composite public key from being one of the components used within a non-composite authentication operation; this may lead to greater convenience in setting up parallel PKI hierarchies that need to service a range of clients implementing different styles of post-quantum migration strategies. For non-negotiated protocols, the details for obtaining backwards compatibility will vary by protocol, but for example in CMS , the inclusion of multiple SignerInfo or RecipientInfo objects is often already treated as an OR relationship, so including one for each of the end entity's parallel PKI public keys would, in many cases, have the desired effect of allowing the receiver to choose one they are compatible with and ignore the others, thus achieving full backwards compatibility.

IANA Considerations This document registers the following in the SMI "Security for PKIX Algorithms (1.3.6.1.5.5.7.6)" registry:

Security Considerations

Reuse of keys in a Composite public key There is an additional security consideration that some use cases such as signatures remain secure against downgrade attacks if and only if component keys are never used outside of their composite context and therefore it is RECOMMENDED that component keys in a composite key are not to be re-used in other contexts. In particular, the components of a composite key SHOULD NOT also appear in single-key certificates. This is particularly relevant for protocols that use composite keys in a logical AND mode since the appearance of the same component keys in single-key contexts undermines the binding of the component keys into a single composite key by allowing messages signed in a multi-key AND mode to be presented as if they were signed in a single key mode in what is known as a "stripping attack".

Key mismatch in explicit composite This security consideration copied from . Implementations MUST check that that the component AlgorithmIdentifier OIDs and parameters match those expected by the definition of the explicit algorithm. Implementations SHOULD first parse a component's SubjectPublicKeyInfo.algorithm, and ensure that it matches what is expected for that position in the explicit key, and then proceed to parse the SubjectPublicKeyInfo.subjectPublicKey. This is to reduce the attack surface associated with parsing the public key data of an unexpected key type, or worse; to parse and use a key which does not match the explicit algorithm definition. Similar checks MUST be done when handling the corresponding private key.

Policy for Deprecated and Acceptable Algorithms Traditionally, a public key, certificate, or signature contains a single cryptographic algorithm. If and when an algorithm becomes deprecated (for example, RSA-512, or SHA1), it is obvious that clients performing signature verification or encryption operations should be updated to fail to validate or refuse to encrypt for these algorithms. 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, certificate, signature, or ciphertext MAY contain a mixture of deprecated and non-deprecated algorithms. Specifying behaviour in these cases is beyond the scope of this document, but should be considered by implementers and potentially in additional standards. EDNOTE: Max had proposed a CRL mechanism to accomplish this, which could be revived if necessary.

Protection of Private Keys Structures described in this document do not protect private keys in any way unless combined with a security protocol or encryption properties of the objects (if any) where the CompositePrivateKey is used. Protection of the private keys is vital to public key cryptography. The consequences of disclosure depend on the purpose of the private key. If a private key is used for signature, then the disclosure allows unauthorized signing. If a private key is used for key management, then disclosure allows unauthorized parties to access the managed keying material. The encryption algorithm used in the encryption process must be at least as 'strong' as the key it is protecting.

Checking for Compromised Key Reuse Certification Authority (CA) implementations need to be careful when checking for compromised key reuse, for example as required by WebTrust regulations; when checking for compromised keys, you MUST unpack the CompositePublicKey structure and compare individual component keys. In other words, for the purposes of key reuse checks, the composite public key structures need to be un-packed so that primitive keys are being compared. For example if the composite key {RSA1, PQ1} is revoked for key compromise, then the keys RSA1 and PQ1 need to be individually considered revoked. If the composite key {RSA1, PQ2} is submitted for certification, it SHOULD be rejected because the key RSA1 was previously declared compromised even though the key PQ2 is unique.

&RFC1421; &RFC2119; &RFC2986; &RFC5280; &RFC5480; &RFC5652; &RFC5912; &RFC5914; &RFC5915; &RFC5958; &RFC7468; &RFC8017; &RFC8174; &RFC8411; &I-D.draft-ounsworth-pq-composite-sigs-05; &I-D.draft-ounsworth-pq-composite-kem-00; &I-D.draft-massimo-lamps-pq-sig-certificates-00; Information technology - ASN.1 encoding Rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER) ITU-T &RFC3279; &RFC4210; &RFC4211; &RFC7292; &RFC7296; &RFC8446; &RFC8551; &I-D.draft-becker-guthrie-noncomposite-hybrid-auth-00; &I-D.draft-guthrie-ipsecme-ikev2-hybrid-auth-00; &I-D.draft-driscoll-pqt-hybrid-terminology-01; Transitioning to a quantum-resistant public key infrastructure Baseline Requirements for the Issuance and Management of Publicly-Trusted Code Signing Certificates v2.8 REGULATION (EU) No 910/2014 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 23 July 2014 on electronic identification and trust services for electronic transactions in the internal market and repealing Directive 1999/93/EC Chosen ciphertext attacks against protocols based on the RSA encryption standard PKCS# 1. Return Of {Bleichenbacher's} Oracle Threat (ROBOT). Cybersecurity in a Quantum World: will we be ready? Breaking rainbow takes a weekend on a laptop. An efficient key recovery attack on SIDH (preliminary version).

Creating explicit combinations The following ASN.1 Information Objects may be useful in defining and parsing explicit pairs of public key types. Given an ASN.1 2002 compliant ASN.1 compiler, these Information Objects will enforce the binding between the public key types specified in the instantiation of pk-explicitComposite, and the wire objects which implement it. The one thing that is not enforced automatically by this Information Object is that publicKey.params are intended to be absent if and only if they are absent for the declared public key type. This ASN.1 module declares them OPTIONAL and leaves it to implementers to perform this check explicitly. EDNOTE this ASN.1 needs to change. The current definition doesn't put a component AlgorithmIdentifier with each component key. Once we agree as a group that the text accurately describes what we want, we can spend a bit of time figuring out if the ASN.1 machinery lets us express it in a readable way and/or a way that will actually help people creating explicit pairs.

The following ASN.1 object class then automatically generates the public key structure from the types defined in pk-explicitComposite.

Using this module, it becomes trivial to define explicit pairs. For an example, see . To define explicit triples, quadruples, etc, these Information Objects can be extended to have thirdPublicKey, fourthPublicKey, etc throughout.

Examples These samples are reproduced here for completeness, but are also available in github: https://github.com/EntrustCorporation/draft-ounsworth-pq-composite-keys/tree/master/sampledata

Generic Composite Public Key Examples This is an example generic composite public key

which decodes as:

}, SubjectPublicKeyInfo { algorithm: AlgorithmIdentifier { algorithm: rsaEncryption parameters: NULL } subjectPublicKey: } } ]]> The corresponding explicit private key is as follows. Note that the PQ key comes from OpenQuantumSafe-openssl and is in the {privatekey || publickey} concatenated format. This may cause interoperability issues with some clients, and also makes the private keys appear larger than they would be if generated by a non-openssl client.

which decodes as:

}, OneAsymmetricKey { version: 0, privateKeyAlgorithm: PrivateKeyAlgorithmIdentifier{ algorithm: rseEncryption parameters: NULL } privateKey: } } ]]>

Explicit Composite Public Key Examples

pk-example-ECandRSA Assume that the following is a defined explicit pair:

Then the same key as above could be encoded as an explicit composite public key as:

which decodes as:

}, SubjectPublicKeyInfo { algorithm: AlgorithmIdentifier { algorithm: rsaEncryption parameters: NULL } subjectPublicKey: } } ]]> The corresponding explicit private key is:

which decodes as:

}, OneAsymmetricKey { version: 0, privateKeyAlgorithm: PrivateKeyAlgorithmIdentifier{ algorithm: rseEncryption parameters: NULL } privateKey: } } ]]>

id-Dilithium3-ECDSA-P256 This example uses the following OID as defined in Open Quantum Safe, which correspond to NIST Round3 candidates: https://github.com/open-quantum-safe/oqs-provider/blob/main/ALGORITHMS.md

A Dilithium3-ECDSA-P256 public key:

which decodes as:

}, SubjectPublicKeyInfo { algorithm: AlgorithmIdentifier { algorithm: ecPublicKey parameters: prime256v1 } subjectPublicKey: } } ]]> The corresponding explicit private key is as follows. Note that the PQ key comes from OpenQuantumSafe-openssl and is in the {privatekey || publickey} concatenated format. This may cause interoperability issues with some clients, and also makes the private keys appear larger than they would be if generated by a non-openssl client.

id-Dilithium3-RSA This example uses the following OID as defined in Open Quantum Safe, which correspond to NIST Round3 candidates: https://github.com/open-quantum-safe/oqs-provider/blob/main/ALGORITHMS.md

A Dilithium3-RSA public key:

which decodes as:

id-Falcon512-ECDSA-P256 This example uses the following OID as definid in Open Quantum Safe, which correspond to NIST Round3 candidates: https://github.com/open-quantum-safe/oqs-provider/blob/main/ALGORITHMS.md

A Falcon512-ECDSA-P256 public key:

which decodes as:

id-Falcon512-Ed25519 TODO

id-SPHINCSsha256256frobust-ECDSA-P256 This example uses the following OID as definid in Open Quantum Safe: https://github.com/open-quantum-safe/oqs-provider/blob/main/ALGORITHMS.md

A SPHINCSsha256256frobust-ECDSA-P256 public key:

which decodes as:

id-Dilithium5-Falcon1024-ECDSA-P521 This example uses the following OID as definid in Open Quantum Safe: https://github.com/open-quantum-safe/oqs-provider/blob/main/ALGORITHMS.md

A Dilithium5-Falcon1024-ECDSA-P521 public key:

which decodes as:

}, SubjectPublicKeyInfo { algorithm: AlgorithmIdentifier { algorithm: id-falcon1024 } subjectPublicKey: }, SubjectPublicKeyInfo { algorithm: AlgorithmIdentifier { algorithm: ecPublicKey parameters: secp521r1 } subjectPublicKey: } } ]]> The corresponding explicit private key is as follows. Note that the PQ key comes from OpenQuantumSafe-openssl and is in the {privatekey || publickey} concatenated format. This may cause interoperability issues with some clients, and also makes the private keys appear larger than they would be if generated by a non-openssl client.

id-Dilithium5-Falcon1024-RSA This example uses the following OID as definid in Open Quantum Safe: https://github.com/open-quantum-safe/oqs-provider/blob/main/ALGORITHMS.md

A Dilithium5-Falcon1024-RSA public key:

which decodes as:

}, SubjectPublicKeyInfo { algorithm: AlgorithmIdentifier { algorithm: id-falcon1024 } subjectPublicKey: }, SubjectPublicKeyInfo { algorithm: AlgorithmIdentifier { algorithm: rsaEncryption parameters: NULL } subjectPublicKey: } } ]]> The corresponding explicit private key is as follows. Note that the PQ key comes from OpenQuantumSafe-openssl and is in the {privatekey || publickey} concatenated format. This may cause interoperability issues with some clients, and also makes the private keys appear larger than they would be if generated by a non-openssl client.

id-Kyber512-RSA TODO

id-Kyber512-ECDH-P256 TODO

id-Kyber512-x25519 TODO

ASN.1 Module

Composite-Keys-2022 DEFINITIONS IMPLICIT TAGS ::= BEGIN EXPORTS ALL; IMPORTS PUBLIC-KEY, SIGNATURE-ALGORITHM, ParamOptions, AlgorithmIdentifier{} FROM AlgorithmInformation-2009 -- RFC 5912 [X509ASN1] { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-algorithmInformation-02(58) } SubjectPublicKeyInfo FROM PKIX1Explicit-2009 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) } OneAsymmetricKey FROM AsymmetricKeyPackageModuleV1 { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-asymmetricKeyPkgV1(50) } ; -- -- Object Identifiers -- der OBJECT IDENTIFIER ::= {joint-iso-itu-t asn1(1) ber-derived(2) distinguished-encoding(1)} -- To be replaced by IANA id-composite-key OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) entrust(114027) Algorithm(80) Composite(4) CompositeKey(1) -- COMPOSITE-KEY-ALGORITHM -- -- Describes the basic properties of a composite key algorithm -- -- &id - contains the OID identifying the composite algorithm -- &Params - if present, contains the type for the algorithm -- parameters; if absent, implies no parameters -- ¶mPresence - parameter presence requirement -- -- } COMPOSITE-KEY-ALGORITHM ::= CLASS { &id OBJECT IDENTIFIER UNIQUE, &Params OPTIONAL, ¶mPresence ParamOptions DEFAULT absent } WITH SYNTAX { IDENTIFIER &id [PARAMS [TYPE &Params] ARE ¶mPresence ] } CompositeAlgorithmIdentifier ::= AlgorithmIdentifier{COMPOSITE-KEY-ALGORITHM, {CompositeAlgorithmSet}} CompositeAlgorithmSet COMPOSITE-KEY-ALGORITHM ::= { CompositeAlgorithms, ... } -- -- Public Key -- pk-Composite PUBLIC-KEY ::= { IDENTIFIER id-composite-key KEY CompositePublicKey PARAMS TYPE CompositeAlgorithmIdentifier ARE optional PRIVATE-KEY CompositePrivateKey } CompositePublicKey ::= SEQUENCE SIZE (2..MAX) OF SubjectPublicKeyInfo CompositePublicKeyOs ::= OCTET STRING (CONTAINING CompositePublicKey ENCODED BY der) CompositePublicKeyBs ::= BIT STRING (CONTAINING CompositePublicKey ENCODED BY der) CompositePrivateKey ::= SEQUENCE SIZE (2..MAX) OF OneAsymmetricKey -- pk-explicitComposite - Composite public key information object pk-explicitComposite{OBJECT IDENTIFIER:id, PUBLIC-KEY:firstPublicKey, FirstPublicKeyType, PUBLIC-KEY:secondPublicKey, SecondPublicKeyType} PUBLIC-KEY ::= { IDENTIFIER id KEY ExplicitCompositePublicKey{firstPublicKey, FirstPublicKeyType, secondPublicKey, SecondPublicKeyType} PARAMS ARE absent } -- The following ASN.1 object class then automatically generates the -- public key structure from the types defined in pk-explicitComposite. -- ExplicitCompositePublicKey - The data structure for a composite -- public key sec-composite-pub-keys and SecondPublicKeyType are needed -- because PUBLIC-KEY contains a set of public key types, not a single -- type. -- TODO The parameters should be optional only if they are marked -- optional in the PUBLIC-KEY ExplicitCompositePublicKey{PUBLIC-KEY:firstPublicKey, FirstPublicKeyType, PUBLIC-KEY:secondPublicKey, SecondPublicKeyType} ::= SEQUENCE { firstPublicKey SEQUENCE { params firstPublicKey.&Params OPTIONAL, publicKey FirstPublicKeyType }, secondPublicKey SEQUENCE { params secondPublicKey.&Params OPTIONAL, publicKey SecondPublicKeyType } } END

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Intellectual Property Considerations

The following IPR Disclosure relates to this draft:

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


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

John Gray (Entrust),
Serge Mister (Entrust),
Scott Fluhrer (Cisco Systems),
Panos Kampanakis (Cisco Systems),
Daniel Van Geest (ISARA),
Tim Hollebeek (Digicert),
Klaus-Dieter Wirth (D-Trust), and
Francois Rousseau.

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" - .

Making contributions

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

https://github.com/EntrustCorporation/draft-ounsworth-pq-composite-keys