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SEC LAMPS Kyber KEM Certificate X.509 PKIX Module-Lattice-Based Key-Encapsulation Mechanism (ML-KEM), also known as Kyber, is a key-encapsulation mechanism (KEM). This document specifies algorithm identifiers and ASN.1 encoding format for ML-KEM in public key certificates. The encoding for public and private keys are also provided. [EDNOTE: This document is not expected to be finalized before the NIST PQC Project has standardized PQ algorithms. This specification will use object identifiers for the new algorithms that are assigned by NIST, and will use placeholders until these are released.] About This Document The latest revision of this draft can be found at . 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 .

Introduction Module-Lattice-Based Key-Encapsulation Mechanism (ML-KEM), also known as Kyber, is a key-encapsulation mechanism (KEM) standardized by the US NIST PQC Project . This document specifies the use of the ML-KEM algorithm at three security levels: ML-KEM-512, ML-KEM-768, and ML-KEM-1024, in X.509 public key certificates; see . Public and private key encodings are also specified.

ASN.1 and ML-KEM Identifiers An ASN.1 module is included for reference purposes. Note that as per , certificates use the Distinguished Encoding Rules; see . Also note that NIST defined the object identifiers for the ML-KEM algorithms in an ASN.1 modulle; see (TODO insert reference).

Applicability Statement ML-KEM certificates are used in protocols where the public key is used to generate and encapsulate a shared secret used to derive a symmetric key used to encrypt a payload; see . To be used in TLS, ML-KEM certificates could only be used as end-entity identity certificates and would require significant updates to the protocol; see .

Conventions and Definitions 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.

Algorithm Identifiers Certificates conforming to can convey a public key for any public key algorithm. The certificate indicates the algorithm through an algorithm identifier. An algorithm identifier consists of an object identifier and optional parameters. The AlgorithmIdentifier type, which is included herein for convenience, is defined as follows: The fields in AlgorithmIdentifier have the following meanings:

• algorithm identifies the cryptographic algorithm with an object identifier.
• parameters, which are optional, are the associated parameters for the algorithm identifier in the algorithm field.

includes object identifiers for ML-KEM-512, ML-KEM-768, and ML-KEM-1024. For all of these OIDs, the parameters MUST be absent.

ML-KEM Public Key Identifiers The AlgorithmIdentifier for a ML-KEM public key MUST use one of the id-alg-ml-kem object identifiers listed below, based on the security level. The parameters field of the AlgorithmIdentifier for the ML-KEM public key MUST be absent. When any of the ML-KEM AlgorithmIdentifier appears in the SubjectPublicKeyInfo field of an X.509 certificate, the key usage certificate extension MUST only contain keyEncipherment .

Subject Public Key Fields In the X.509 certificate, the subjectPublicKeyInfo field has the SubjectPublicKeyInfo type, which has the following ASN.1 syntax: The fields in SubjectPublicKeyInfo have the following meaning:

• algorithm is the algorithm identifier and parameters for the public key (see above).
• subjectPublicKey contains the byte stream of the public key. The algorithms defined in this document always encode the public key as TODO pick format e.g., exact multiple of 8 bits?.

The following is an example of a ML-KEM-512 public key encoded using the textual encoding defined in :

Private Key Format "Asymmetric Key Packages" describes how to encode a private key in a structure that both identifies what algorithm the private key is for and allows for the public key and additional attributes about the key to be included as well. For illustration, the ASN.1 structure OneAsymmetricKey is replicated below. The algorithm-specific details of how a private key is encoded are left for the document describing the algorithm itself. For the keys defined in this document, the private key is always an opaque byte sequence. The ASN.1 type PqckemPrivateKey is defined in this document to hold the byte sequence. Thus, when encoding a OneAsymmetricKey object, the private key is wrapped in a PqckemPrivateKey object and wrapped by the OCTET STRING of the "privateKey" field. The following is an example of a ML-KEM-512 private key encoded using the textual encoding defined in : The following example, in addition to encoding the ML-KEM-512 private key, has an attribute included as well as the public key. As with the prior example, the textual encoding defined in is used:

ASN.1 Module TODO ASN.1 Module

Security Considerations The Security Considerations section of applies to this specification as well.

IANA Considerations This document will have some IANA actions.

References Normative References ITU-T ITU-T 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] 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. 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. The Public Key Infrastructure using X.509 (PKIX) certificate format, and many associated formats, are expressed using ASN.1. The current ASN.1 modules conform to the 1988 version of ASN.1. This document updates those ASN.1 modules to conform to the 2002 version of ASN.1. There are no bits-on-the-wire changes to any of the formats; this is simply a change to the syntax. This document is not an Internet Standards Track specification; it is published for informational purposes. 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] Informative References National Institute of Standards and Technology (NIST) CryptoNext Security Entrust Limited This document describes the conventions for using a Key Encapsulation Mechanism algorithm (KEM) within the Cryptographic Message Syntax (CMS). The CMS specifies the envelopped-data content type, which consists of an encrypted content and encrypted content-encryption keys for one or more recipients. The mechanism proposed here can rely on either post-quantum KEMs, hybrid KEMs or classical KEMs but this document specifies the use of Kyber. PQShield Brave Software Radboud University and MPI-SP University of Waterloo This document gives a construction for a Key Encapsulation Mechanism (KEM)-based authentication mechanism in TLS 1.3. This proposal authenticates peers via a key exchange protocol, using their long- term (KEM) public keys. 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.

Acknowledgments TODO acknowledge.