LAMPS S. Turner Internet-Draft sn3rd Intended status: Standards Track P. Kampanakis Expires: 5 September 2024 J. Massimo AWS B. Westerbaan Cloudflare 4 March 2024 Internet X.509 Public Key Infrastructure - Algorithm Identifiers for Module-Lattice-Based Key-Encapsulation Mechanism (ML-KEM) draft-ietf-lamps-kyber-certificates-03 Abstract 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 This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://lamps- wg.github.io/kyber-certificates/#go.draft-ietf-lamps-kyber- certificates.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-lamps-kyber- certificates/. Discussion of this document takes place on the Limited Additional Mechanisms for PKIX and SMIME (lamps) Working Group mailing list (mailto:spasm@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/spasm/. Subscribe at https://www.ietf.org/mailman/listinfo/spasm/. Source for this draft and an issue tracker can be found at https://github.com/lamps-wg/kyber-certificates. Turner, et al. Expires 5 September 2024 [Page 1] Internet-Draft ML-KEM in Certificates March 2024 Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 5 September 2024. Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. ASN.1 and ML-KEM Identifiers . . . . . . . . . . . . . . 3 1.2. Applicability Statement . . . . . . . . . . . . . . . . . 3 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. Algorithm Identifiers . . . . . . . . . . . . . . . . . . . . 3 4. ML-KEM Public Key Identifiers . . . . . . . . . . . . . . . . 4 5. Subject Public Key Fields . . . . . . . . . . . . . . . . . . 5 6. Private Key Format . . . . . . . . . . . . . . . . . . . . . 6 7. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 10.2. Informative References . . . . . . . . . . . . . . . . . 9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 9 Turner, et al. Expires 5 September 2024 [Page 2] Internet-Draft ML-KEM in Certificates March 2024 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction | WARNING: This I-D includes examples. These examples were | generated prior to NIST finalizing [DRAFTFIPS203]. 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 [DRAFTFIPS203]. 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 [RFC5280]. Public and private key encodings are also specified. 1.1. ASN.1 and ML-KEM Identifiers An ASN.1 module [X680] is included for reference purposes. Note that as per [RFC5280], certificates use the Distinguished Encoding Rules; see [X690]. Also note that NIST defined the object identifiers for the ML-KEM algorithms in an ASN.1 modulle; see (TODO insert reference). 1.2. 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 [I-D.ietf-lamps-kyber]. 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 [I-D.celi-wiggers-tls-authkem]. 2. 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. Algorithm Identifiers Certificates conforming to [RFC5280] 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: Turner, et al. Expires 5 September 2024 [Page 3] Internet-Draft ML-KEM in Certificates March 2024 AlgorithmIdentifier{ALGORITHM-TYPE, ALGORITHM-TYPE:AlgorithmSet} ::= SEQUENCE { algorithm ALGORITHM-TYPE.&id({AlgorithmSet}), parameters ALGORITHM-TYPE. &Params({AlgorithmSet}{@algorithm}) OPTIONAL } | NOTE: The above syntax is from [RFC5912] and is compatible with | the 2021 ASN.1 syntax [X680]. 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. Section 4 includes object identifiers for ML-KEM-512, ML-KEM-768, and ML-KEM-1024. For all of these OIDs, the parameters MUST be absent. | NOTE: It is possible to find systems that require the | parameters to be present. This can be due to either a defect | in the original 1997 syntax or a programming error where | developers never got input where this was not true. The | optimal solution is to fix these systems; where this is not | possible, the problem needs to be restricted to that subsystem | and not propagated to the Internet. 4. 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 Section 4.2.1.3 of [RFC5280]. Turner, et al. Expires 5 September 2024 [Page 4] Internet-Draft ML-KEM in Certificates March 2024 pk-ml-kem-512 PUBLIC-KEY ::= { IDENTIFIER id-alg-ml-kem-512 -- KEY no ASN.1 wrapping -- PARAMS ARE absent CERT-KEY-USAGE { keyEncipherment } --- PRIVATE-KEY no ASN.1 wrapping -- } pk-ml-kem-768 PUBLIC-KEY ::= { IDENTIFIER id-alg-ml-kem-768 -- KEY no ASN.1 wrapping -- PARAMS ARE absent CERT-KEY-USAGE { keyEncipherment } --- PRIVATE-KEY no ASN.1 wrapping -- } pk-ml-kem-1024 PUBLIC-KEY ::= { IDENTIFIER id-alg-ml-kem-1024 -- KEY no ASN.1 wrapping -- PARAMS ARE absent CERT-KEY-USAGE { keyEncipherment } --- PRIVATE-KEY no ASN.1 wrapping -- } | NOTE: As noted in Section 3, the values for these object | identifers will be assigned by NIST. Once assigned, they will | be added to a future revision of this document. 5. Subject Public Key Fields In the X.509 certificate, the subjectPublicKeyInfo field has the SubjectPublicKeyInfo type, which has the following ASN.1 syntax: SubjectPublicKeyInfo {PUBLIC-KEY: IOSet} ::= SEQUENCE { algorithm AlgorithmIdentifier {PUBLIC-KEY, {IOSet}}, subjectPublicKey BIT STRING } | NOTE: The above syntax is from [RFC5912] and is compatible with | the 2021 ASN.1 syntax [X680]. The fields in SubjectPublicKeyInfo have the following meaning: * algorithm is the algorithm identifier and parameters for the public key (see above). Turner, et al. Expires 5 September 2024 [Page 5] Internet-Draft ML-KEM in Certificates March 2024 * 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 [RFC7468]: | WARNING: This example was generated prior to NIST finalizing | [DRAFTFIPS203]. -----BEGIN PUBLIC KEY----- TODO insert example public key -----END PUBLIC KEY------- 6. Private Key Format "Asymmetric Key Packages" [RFC5958] 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. OneAsymmetricKey ::= SEQUENCE { version Version, privateKeyAlgorithm SEQUENCE { algorithm PUBLIC-KEY.&id({PublicKeySet}), parameters PUBLIC-KEY.&Params({PublicKeySet} {@privateKeyAlgorithm.algorithm}) OPTIONAL} privateKey OCTET STRING (CONTAINING PUBLIC-KEY.&PrivateKey({PublicKeySet} {@privateKeyAlgorithm.algorithm})), attributes [0] Attributes OPTIONAL, ..., [[2: publicKey [1] BIT STRING (CONTAINING PUBLIC-KEY.&Params({PublicKeySet} {@privateKeyAlgorithm.algorithm}) OPTIONAL, ... } PrivateKey ::= OCTET STRING PublicKey ::= BIT STRING Turner, et al. Expires 5 September 2024 [Page 6] Internet-Draft ML-KEM in Certificates March 2024 | NOTE: The above syntax is from [RFC5958] and is compatible with | the 2021 ASN.1 syntax [X680]. 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. PqckemPrivateKey ::= OCTET STRING The following is an example of a ML-KEM-512 private key encoded using the textual encoding defined in [RFC7468]: | WARNING: This example was generated prior to NIST finalizing | [DRAFTFIPS203]. -----BEGIN PRIVATE KEY----- TODO iser example private key -----END PRIVATE KEY------- 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 [RFC7468] is used: | WARNING: This example was generated prior to NIST finalizing | [DRAFTFIPS203]. -----BEGIN PRIVATE KEY----- TODO insert example private key with attribute -----END PRIVATE KEY------- | NOTE: There exist some private key import functions that have | not implemented the new ASN.1 structure OneAsymmetricKey that | is defined in [RFC5958]. This means that they will not accept | a private key structure that contains the public key field. | This means a balancing act needs to be done between being able | to do a consistency check on the key pair and widest ability to | import the key. 7. ASN.1 Module TODO ASN.1 Module Turner, et al. Expires 5 September 2024 [Page 7] Internet-Draft ML-KEM in Certificates March 2024 8. Security Considerations The Security Considerations section of [RFC5280] applies to this specification as well. | To Do: Discuss side-channels for Kyber TBD1. 9. IANA Considerations This document will have some IANA actions. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, . [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, DOI 10.17487/RFC5912, June 2010, . [RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, DOI 10.17487/RFC5958, August 2010, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [X680] ITU-T, "Information technology - Abstract Syntax Notation One (ASN.1): Specification of basic notation", ITU-T Recommendation X.680, ISO/IEC 8824-1:2021, February 2021, . Turner, et al. Expires 5 September 2024 [Page 8] Internet-Draft ML-KEM in Certificates March 2024 [X690] ITU-T, "Information technology - Abstract Syntax Notation One (ASN.1): ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1:2021, February 2021, . 10.2. Informative References [DRAFTFIPS203] National Institute of Standards and Technology (NIST), "DRAFT Module-Lattice-based Key-Encapsulation Mechanism Standard", FIPS PUB 203, August 2023, . [I-D.celi-wiggers-tls-authkem] Wiggers, T., Celi, S., Schwabe, P., Stebila, D., and N. Sullivan, "KEM-based Authentication for TLS 1.3", Work in Progress, Internet-Draft, draft-celi-wiggers-tls-authkem- 02, 18 August 2023, . [I-D.ietf-lamps-kyber] Prat, J. and M. Ounsworth, "Use of KYBER in the Cryptographic Message Syntax (CMS)", Work in Progress, Internet-Draft, draft-ietf-lamps-kyber-00, 10 November 2022, . [RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX, PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468, April 2015, . Acknowledgments TODO acknowledge. Authors' Addresses Sean Turner sn3rd Email: sean@sn3rd.com Panos Kampanakis AWS Turner, et al. Expires 5 September 2024 [Page 9] Internet-Draft ML-KEM in Certificates March 2024 Email: kpanos@amazon.com Jake Massimo AWS Email: jakemas@amazon.com Bas Westerbaan Cloudflare Email: bas@westerbaan.name Turner, et al. Expires 5 September 2024 [Page 10]