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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 implementers 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. Explicit pairings of algorithms are defined which should meet most Internet needs. This document is intended to be coupled with corresponding documents that define the structure and semantics of composite signatures and encryption, such as and . About This Document Status information for this document may be found at . Discussion of this document takes place on the Limited Additional Mechanisms for PKIX and SMIME (lamps) Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Changes in version -05

• Removed SPHINCS+ hybrids.
• Removed all references to generic composite.
• Added selection criteria note about requesting new explicit combinations.

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 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 . Other hybrid public key, signature, and KEM mechanisms exist, notably and / , which have their security and ease of migration properties discussed in more detail in . This document only specifies key formats; usage of these keys are covered in the corresponding composite signatures and composite KEM specifications. This document is intended for general applicability anywhere that keys are used within PKIX or CMS structures.

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

1. A single RSA combination is provided (but RSA modulus size not mandated), matched with NIST PQC Level 3 algorithms.
2. Elliptic curve algorithms are provided with combinations on each of the NIST , Brainpool , and Edwards curves. NIST PQC Levels 1 - 3 algorithms are matched with 256-bit curves, while NIST levels 4 - 5 are matched with 384-bit elliptic curves. This provides a balance between matching classical security levels of post-quantum and traditional algorithms, and also selecting elliptic curves which already have wide adoption.
3. NIST level 1 candidates (Falcon512 and Kyber512) are provided, matched with 256-bit elliptic curves, intended for constrained use cases. The authors wish to note that although all the composite structures defined in this and the companion documents and specifications are defined in such a way as to easily allow 3 or more component algorithms, it was decided to only specify explicit pairs. This also does not preclude future specification of explicit combinations with three or more components.

To maximize interoperability, use of the specific algorithm combinations specified in this document is encouraged. 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.

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 BCP14 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 .

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 . defines composites as:

• Composite Cryptographic Element: A cryptographic element that incorporates multiple component cryptographic elements of the same type in a multi-algorithm scheme.

Composite keys as defined here follow this definition and should be regarded as a single key that performs a single cryptographic operation such key generation, signing, verifying, encapsulating, or decapsulating -- using its encapsulated sequence of component keys as if it was a single key. This generally means that the complexity of combining algorithms can and should be ignored by application and protocol layers and deferred to the cryptographic library layer.

pk-Composite The following ASN.1 Information Object Class is a template to be used in defining all composite key types, with suitable replacements for the ASN.1 identifier pk-Composite and the OID id-composite-key as appropriate. See the ASN.1 Module in for parmeterized as well as signature and KEM versions. keyUsage is omitted here because composites may be formed for keys of any type, provided that any key usage specified MUST apply to all component keys. Composites MAY NOT be used to combine key types, for example to make a "dual-usage" key by combining a signing key with a KEM key.

CompositePublicKey Composite public key data is represented by the following structure: A composite key MUST contain at least two component public keys. When the composite key is used in conjunction with an explicit composite algorithm identifier defined under section , the order of the component keys is determined by that algorithm identifier's definition. A CompositePublicKey MUST NOT contain a component public key which itself describes a composite key; i.e. recursive CompositePublicKeys are not allowed. The purpose is a general reduction in complexity by not needing to consider nested key types. Each element of a CompositePublicKey is a SubjectPublicKeyInfo object encoding a component public key. 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. When the CompositePublicKey must be provided in octet string or bit string format, the data structure is encoded as specified in .

Key Usage Protocols such as X.509 that specify a key usage along with the public key. For composite keys, a single key usage is specified for the entire public key and it MUST apply to all component keys. For example if a composite key is marked with a key usage of digitalSignature, then all component keys MUST be capable of producing digital signatures and handled with policies appropriate for digital signature keys. 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. Specifications of explicit composite key types must specify allowable key usages for that type based on the types of the components.

Component Matching Many cryptographic libraries will require treating each component key independently and thus expect a full SubjectPublicKeyInfo for each component at some layer of the software stack. This left two design choices: either we carry full SPKI for each component within the CompositePublicKey, or we compress it by only carrying the raw key bytes and force implementations to carry OID and parameter mapping tables to be able to reconstruct component SPKIs. The authors decided to carry the full SPKIs in order to lessen the implementation complexity at the expense of a small amount of redundant data to transmit. This design choice has a non-obvious security risk in that the algorithm carried within each component SPKI is redundant information which MUST match -- and can be inferred from -- the specification of the explicit algorithm. Security consideration: Implementations SHOULD 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 SHOULD be done when handling the corresponding private key.

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 the order of the component keys is the same as the order defined in for the components of CompositePublicKey.

As a PrivateKeyInfo or OneAsymmetricKey A CompositePrivateKey can be stored in a OneAsymmetricKey structure (version 1 of which is also known as PrivateKeyInfo) . When this is done, the privateKeyAlgorithm field SHALL be set to the corresponding composite algorithm identifier defined according to , the privateKey field SHALL contain the CompositePrivateKey, and the publicKey field MUST NOT be present. Associated public key material MAY be present in the CompositePrivateKey.

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. 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.

Algorithm Identifiers This section defines algorithm identifiers, component algorithms and their ordering for composite combinations. The combinations registered in this section are intended to strike a balance between the overall number of combinations ("the combinatorial explosion problem"), while also covering the needs of a wide range of protocols, applications, and regulatory environments in which X.509-based technologies are used. This section is not intended to be exhaustive and other authors may define OIDs for new combinations so long as they are compatible with the structures and processes defined in this and the companion signature and encryption documents.

Signature public key types This table summarizes the list of explicit composite Signature algorithms by the key and signature OID and the two component algorithms which make up the explicit composite algorithm, as obtained by applying the selection criteria in section . These are denoted by First Signature Alg, and Second Signature Alg. 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 <CompSig> with the String "2.16.840.1.114027.80.5.1" Therefore <CompSig>.1 is equal to 2.16.840.1.114027.80.5.1.1 Note that a single OID is used for both the key type and the signature algorithm; ie there is a one-to-one correspondance between key types and signature algorithms, hence why these key type names contain more information than they strictly need to define a key type.

Composite Signature Key Type	OID	First Key Type	Second Key Type
id-Dilithium3-RSA-PSS	<CompSig>.14	Dilithium3	RSASSA-PSS
id-Dilithium3-RSA-PKCS15-SHA256	<CompSig>.1	Dilithium3	RSAES-PKCS-v1_5
id-Dilithium3-ECDSA-P256-SHA256	<CompSig>.2	Dilithium3	EC-P256
id-Dilithium3-ECDSA-brainpoolP256r1-SHA256	<CompSig>.3	Dilithium3	EC-brainpoolP256r1
id-Dilithium3-Ed25519	<CompSig>.4	Dilithium3	Ed25519
id-Dilithium5-ECDSA-P384-SHA384	<CompSig>.5	Dilithium5	EC-P384
id-Dilithium5-ECDSA-brainpoolP384r1-SHA384	<CompSig>.6	Dilithium5	EC-brainpoolP384r1
id-Dilithium5-Ed448	<CompSig>.7	Dilithium5	Ed448
id-Falcon512-ECDSA-P256-SHA256	<CompSig>.8	Falcon512	EC-P256
id-Falcon512-ECDSA-brainpoolP256r1-SHA256	<CompSig>.9	Falcon512	EC-brainpoolP256r1
id-Falcon512-Ed25519	<CompSig>.10	Falcon512	Ed25519

The table above contains everything needed to implement the listed explicit composite algorithms. See the ASN.1 module in section for the explicit definitions of the above Composite signature algorithms. Full specifications for the referenced algorithms can be found as follows:

• Dilithium:
• EC:
  • EC-P256: AlgorithmIdentifier.parameters MUST be secp256r1 as defined in .
  • EC-brainpoolP256r1: AlgorithmIdentifier.parameters MUST be brainpoolP256r1 as defined in .
  • EC-P384: AlgorithmIdentifier.parameters MUST be secp384r1 as defined in .
  • EC-brainpoolP384r1: AlgorithmIdentifier.parameters MUST be brainpoolP384r1 as defined in .
• Ed25519 / Ed448:
• Falcon: TBD
• RSAES-PKCS-v1_5:
• RSASSA-PSS:

The intended application for the key is indicated in the keyUsage certificate extension; see Section 4.2.1.3 of . If the keyUsage extension is present in a certificate that indicates signature public key types above in the SubjectPublicKeyInfo, then the at least one of following MUST be present: Requirements about the keyUsage extension bits defined in still apply.

KEM public key types This table summarizes the list of explicit composite Signature algorithms by the key and signature OID and the two component algorithms which make up the explicit composite algorithm. These are denoted by First Signature Alg, and Second Signature Alg. 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" Therefore <CompKEM>.1 is equal to 2.16.840.1.114027.80.5.2.1. Note that a single OID is used for both the key type and the KEM algorithm; ie there is a one-to-one correspondance between key types and KEM algorithms, hence why these key type names contain more information than they strictly need to define a key type. Composite KEM key types

Composite KEM Key Type	OID	First Key Type	Second Key Type
id-Kyber512-ECDH-P256-KMAC128	<CompKEM>.1	Kyber512	EC-P256
id-Kyber512-ECDH-brainpoolP256r1-KMAC128	<CompKEM>.2	Kyber512	EC-brainpoolP256r1
id-Kyber512-X25519-KMAC128	<CompKEM>.3	Kyber512	X25519
id-Kyber768-RSA-KMAC256	<CompKEM>.4	Kyber768	RSA-KEM
id-Kyber768-ECDH-P256-KMAC256	<CompKEM>.5	Kyber768	EC-P256
id-Kyber768-ECDH-brainpoolP256r1-KMAC256	<CompKEM>.6	Kyber768	EC-brainpoolP256r1
id-Kyber768-X25519-KMAC256	<CompKEM>.7	Kyber768	X25519
id-Kyber1024-ECDH-P384-KMAC256	<CompKEM>.8	Kyber1024	EC-P384
id-Kyber1024-ECDH-brainpoolP384r1-KMAC256	<CompKEM>.9	Kyber1024	EC-brainpoolP384r1
id-Kyber1024-X448-KMAC256	<CompKEM>.10	Kyber1024	X448

The table above contains everything needed to implement the listed explicit composite algorithms. See the ASN.1 module in section for the explicit definitions of the above Composite signature algorithms. Full specifications for the referenced algorithms can be found as follows:

• EC:
  • EC-P256: AlgorithmIdentifier.parameters within the component SKPI belonging to the EC key MUST be secp256r1 as defined in .
  • EC-brainpoolP256r1: AlgorithmIdentifier.parameters within the component SKPI belonging to the EC key MUST be brainpoolP256r1 as defined in .
  • EC-P384: AlgorithmIdentifier.parameters within the component SKPI belonging to the EC key MUST be secp384r1 as defined in .
  • EC-brainpoolP384r1: AlgorithmIdentifier.parameters within the component SKPI belonging to the EC key MUST be brainpoolP384r1 as defined in .
• Kyber:
• RSA-KEM:
• X25519 / X448:

Note: the inclusion of a hash function is so that these algorithm identifiers can double as both key types and KEM algorithms. The intended application for the key is indicated in the keyUsage certificate extension; see Section 4.2.1.3 of . If the keyUsage extension is present in a certificate that indicates any of the KEM public key types above in the SubjectPublicKeyInfo, then the following MUST be present: Requirements about the keyUsage extension bits defined in still apply.

ASN.1 Module !!Composite-Keys-2023.asn ]]>

IANA Considerations All sorts of OIDs in the ASN.1 module. Too many to list here (sorry). This document registers the following in the SMI "Security for PKIX Algorithms (1.3.6.1.5.5.7.6)" registry: TODO

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 SHOULD 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 SHOULD 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.

References Normative References This document defines message encryption and authentication procedures, in order to provide privacy-enhanced mail (PEM) services for electronic mail transfer in the Internet. [STANDARDS-TRACK] In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo represents a republication of PKCS #10 v1.7 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document, except for the security considerations section, is taken directly from the PKCS #9 v2.0 or the PKCS #10 v1.7 document. This memo provides information for the Internet community. This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] This document specifies the syntax and semantics for the Subject Public Key Information field in certificates that support Elliptic Curve Cryptography. This document updates Sections 2.3.5 and 5, and the ASN.1 module of "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3279. [STANDARDS-TRACK] This memo proposes several elliptic curve domain parameters over finite prime fields for use in cryptographic applications. The domain parameters are consistent with the relevant international standards, and can be used in X.509 certificates and certificate revocation lists (CRLs), for Internet Key Exchange (IKE), Transport Layer Security (TLS), XML signatures, and all applications or protocols based on the cryptographic message syntax (CMS). This document is not an Internet Standards Track specification; it is published for informational purposes. This document describes the Cryptographic Message Syntax (CMS). This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. [STANDARDS-TRACK] This document describes a structure for representing trust anchor information. A trust anchor is an authoritative entity represented by a public key and associated data. The public key is used to verify digital signatures, and the associated data is used to constrain the types of information or actions for which the trust anchor is authoritative. The structures defined in this document are intended to satisfy the format-related requirements defined in Trust Anchor Management Requirements. [STANDARDS-TRACK] This document defines the syntax for private-key information and a content type for it. Private-key information includes a private key for a specified public-key algorithm and a set of attributes. The Cryptographic Message Syntax (CMS), as defined in RFC 5652, can be used to digitally sign, digest, authenticate, or encrypt the asymmetric key format content type. This document obsoletes RFC 5208. [STANDARDS-TRACK] The RSA-KEM Key Transport Algorithm is a one-pass (store-and-forward) mechanism for transporting keying data to a recipient using the recipient's RSA public key. ("KEM" stands for "key encapsulation mechanism".) This document specifies the conventions for using the RSA-KEM Key Transport Algorithm with the Cryptographic Message Syntax (CMS). The ASN.1 syntax is aligned with an expected forthcoming change to American National Standard (ANS) X9.44. This note describes the fundamental algorithms of Elliptic Curve Cryptography (ECC) as they were defined in some seminal references from 1994 and earlier. These descriptions may be useful for implementing the fundamental algorithms without using any of the specialized methods that were developed in following years. Only elliptic curves defined over fields of characteristic greater than three are in scope; these curves are those used in Suite B. This document is not an Internet Standards Track specification; it is published for informational purposes. This document describes and discusses the textual encodings of the Public-Key Infrastructure X.509 (PKIX), Public-Key Cryptography Standards (PKCS), and Cryptographic Message Syntax (CMS). The textual encodings are well-known, are implemented by several applications and libraries, and are widely deployed. This document articulates the de facto rules by which existing implementations operate and defines them so that future implementations can interoperate. This memo specifies two elliptic curves over prime fields that offer a high level of practical security in cryptographic applications, including Transport Layer Security (TLS). These curves are intended to operate at the ~128-bit and ~224-bit security level, respectively, and are generated deterministically based on a list of required properties. This document provides recommendations for the implementation of public-key cryptography based on the RSA algorithm, covering cryptographic primitives, encryption schemes, signature schemes with appendix, and ASN.1 syntax for representing keys and for identifying the schemes. This document represents a republication of PKCS #1 v2.2 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series. By publishing this RFC, change control is transferred to the IETF. This document also obsoletes RFC 3447. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document specifies algorithm identifiers and ASN.1 encoding formats for elliptic curve constructs using the curve25519 and curve448 curves. The signature algorithms covered are Ed25519 and Ed448. The key agreement algorithms covered are X25519 and X448. The encoding for public key, private key, and Edwards-curve Digital Signature Algorithm (EdDSA) structures is provided. When the Curdle Security Working Group was chartered, a range of object identifiers was donated by DigiCert, Inc. for the purpose of registering the Edwards Elliptic Curve key agreement and signature algorithms. This donated set of OIDs allowed for shorter values than would be possible using the existing S/MIME or PKIX arcs. This document describes the donated range and the identifiers that were assigned from that range, transfers control of that range to IANA, and establishes IANA allocation policies for any future assignments within that range. Entrust Limited CableLabs With the widespread adoption of post-quantum cryptography will come the need for an entity to possess multiple public keys on different cryptographic algorithms. Since the trustworthiness of individual post-quantum algorithms is at question, a multi-key cryptographic operation will need to be performed in such a way that breaking it requires breaking each of the component algorithms individually. This requires defining new structures for holding composite signature data. This document defines the structures CompositeSignatureValue, and CompositeParams, which are sequences of the respective structure for each component algorithm. This document also defines processes for generating and verifying composite signatures. This document makes no assumptions about what the component algorithms are, provided that their algorithm identifiers and signature generation and verification processes are defined. Entrust Limited Entrust Limited 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 cryptanalysis, 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 Implementers 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. For digital signatures, this is referred to as "dual", and for encryption key establishment this as referred to as "hybrid". This document, and its companions, defines a specific instantiation of the dual and 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. EDNOTE: the terms "dual" and "hybrid" are currently in flux. We anticipate an Informational draft to normalize terminology, and will update this draft accordingly. This document defines a Composite key encapsulation mechanism (KEM) procedure, for use with Composite keys which consist of combinations of Encryption or KEM algorithms for each composite component algorithm. This document also introduces the idea of assigning an Object Identifier (OID) to a shared secret combiner so that stronger combiners can be implemented in the future without needing to re- issue this specification. This document is intended to be coupled with the composite keys structure define in [I-D.ounsworth-pq-composite-keys] and the CMS KEM-TRANS mechanism in [I-D.perret-prat-lamps-cms-pq-kem]. AWS AWS sn3rd Cloudflare Digital signatures are used within X.509 certificates, Certificate Revocation Lists (CRLs), and to sign messages. This document describes the conventions for using Dilithium quantum-resistant signatures in Internet X.509 certificates and certificate revocation lists. The conventions for the associated post-quantum signatures, subject public keys, and private key are also described. sn3rd AWS AWS Cloudflare This document specifies algorithm identifiers and ASN.1 encoding format for the United States National Institute of Standards and Technology's Post Quantum Cryptography Key Encapsulation Mechanism algorithms. The algorithms covered are Kyber TBD1. The encoding for public key and private key is also provided. [EDNOTE: This draft is not expected to be finalized before the NIST PQC Project has standardized PQ algorithms. After NIST has standardized its first algorithms, this document will replace TBD, with the appropriate algorithms and parameters before proceeding to ratification. The algorithm Kyber TBD1 has been added as an example in this draft, to provide a more detailed illustration of the content - it by no means indicates its inclusion in the final version. This specification will use object identifiers for the new algorithms that are assigned by NIST, and will use placeholders until these are released.] ITU-T Informative References This document describes the Internet X.509 Public Key Infrastructure (PKI) Certificate Management Protocol (CMP). Protocol messages are defined for X.509v3 certificate creation and management. CMP provides on-line interactions between PKI components, including an exchange between a Certification Authority (CA) and a client system. [STANDARDS-TRACK] This document describes the Certificate Request Message Format (CRMF) syntax and semantics. This syntax is used to convey a request for a certificate to a Certification Authority (CA), possibly via a Registration Authority (RA), for the purposes of X.509 certificate production. The request will typically include a public key and the associated registration information. This document does not define a certificate request protocol. [STANDARDS-TRACK] PKCS #12 v1.1 describes a transfer syntax for personal identity information, including private keys, certificates, miscellaneous secrets, and extensions. Machines, applications, browsers, Internet kiosks, and so on, that support this standard will allow a user to import, export, and exercise a single set of personal identity information. This standard supports direct transfer of personal information under several privacy and integrity modes. This document represents a republication of PKCS #12 v1.1 from RSA Laboratories' Public Key Cryptography Standard (PKCS) series. By publishing this RFC, change control is transferred to the IETF. This document describes version 2 of the Internet Key Exchange (IKE) protocol. IKE is a component of IPsec used for performing mutual authentication and establishing and maintaining Security Associations (SAs). This document obsoletes RFC 5996, and includes all of the errata for it. It advances IKEv2 to be an Internet Standard. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. This document defines Secure/Multipurpose Internet Mail Extensions (S/MIME) version 4.0. S/MIME provides a consistent way to send and receive secure MIME data. Digital signatures provide authentication, message integrity, and non-repudiation with proof of origin. Encryption provides data confidentiality. Compression can be used to reduce data size. This document obsoletes RFC 5751. National Security Agency National Security Agency National Security Agency The advent of cryptographically relevant quantum computers (CRQC) will threaten the public key cryptography that is currently in use in today's secure internet protocol infrastructure. To address this, organizations such as the National Institute of Standards and Technology (NIST) will standardize new post-quantum cryptography (PQC) that is resistant to attacks by both classical and quantum computers. After PQC algorithms are standardized, the widespread implementation of this cryptography will be contingent upon adapting current protocols to accommodate PQC. Hybrid solutions are one way to facilitate the transition between traditional and PQ algorithms: they use both a traditional and a PQ algorithm in order to perform encryption or authentication, with the guarantee that the given security property will still hold in the case that one algorithm fails. Hybrid solutions can be constructed in many ways, and the cryptographic community has already begun to explore this space. This document introduces non-composite hybrid authentication, which requires updates at the protocol level and limits impact to the certificate-issuing infrastructure. National Security Agency This document describes how to extend the Internet Key Exchange Protocol Version 2 (IKEv2) to allow hybrid non-composite authentication. The intended purpose for this extension is to enable the use of a Post-Quantum (PQ) digital signature and X.509 certificate in addition to the use of a traditional authentication method. This document enables peers to signify support for hybrid non-composite authentication, and send additional CERTREQ, AUTH, and CERT payloads to perform multiple authentications. ISARA Corporation ISARA Corporation Cisco Systems Cisco Systems Entrust Datacard, Ltd Entrust Datacard, Ltd This document describes a method of embedding alternative sets of cryptographic materials into X.509v3 digital certificates, X.509v2 Certificate Revocation Lists (CRLs), and PKCS #10 Certificate Signing Requests (CSRs). The embedded alternative cryptographic materials allow a Public Key Infrastructure (PKI) to use multiple cryptographic algorithms in a single object, and allow it to transition to the new cryptographic algorithms while maintaining backwards compatibility with systems using the existing algorithms. Three X.509 extensions and three PKCS #10 attributes are defined, and the signing and verification procedures for the alternative cryptographic material contained in the extensions and attributes are detailed. UK National Cyber Security Centre One aspect of the transition to post-quantum algorithms in cryptographic protocols is the development of hybrid schemes that incorporate both post-quantum and traditional asymmetric algorithms. This document defines terminology for such schemes. It is intended to ensure consistency and clarity across different protocols, standards, and organisations.

Work in Progress

Combiner modes (KofN) For content commitment use-cases, such as legally-binding non-repudiation, the signer (whether it be a CA or an end entity) needs to be able to specify how its signature is to be interpreted and verified. For now we have removed combiner modes (AND, OR, KofN) from this draft, but we are still discussing how to incorporate this for the cases where it is needed (maybe a X.509 v3 extension, or a signature algorithm param).

Samples 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

• TODO: move these to https://github.com/lamps-wg before publication

Explicit Composite Public Key Samples

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: 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: 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-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: 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.

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 (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.

CATALYST certificates CATALYST certificates, defined in and provides an alternative mechanism for placing multiple public keys and signatures into a certificate via the X.509v3 extensions subjectAltPublicKeyInfo, altSignatureAlgorithm, and altSignatureValue. specifies that only one of the keys is to be used at a time, so it is not in fact a hybrid mechinism in that it is not providing dual algorithm security; instead it is merely a migration mechanism. One could imagine obtaining dual algorithm security by using a CATALYST certificate in a mode other than that described in where both keys produce a signature and place them, for example, togeher in a CompositeSignatureValue. CALATYST certificates appear to have a backwards compatibility advantage in that these non-critical extensions will be ignored by legacy clients, thus making the certificate verification seamlessly verifiable by legacy clients. However, at the protocol level, the certificate holder still needs to know which algorithm the peer wants it to use in the protocol-level message. CATALYST certificates also have the disadvantage of needing to transmit the large post-quantum keys, signatures or key exchange data even if the client will not use them. Thus while CATALYST certificates may be advantageous in some applications that use multiple algorithms but can only handle a single certificate, it is in general not clear that they offer any strong advantage over a multi-cert hybrid in terms of ease of migration, or over composite in terms of security.

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),
Patrick Kelsey (Not for Radio LLC),
Anthony Hu (wolfSSL), 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