Network Working Group A. Becker Internet-Draft M. Jenkins Obsoletes: 9212 (if approved) NSA Intended status: Informational 29 August 2025 Expires: 2 March 2026 Commercial National Security Algorithm (CNSA) Suite Profile for Secure/ Multipurpose Internet Mail Extensions (S/MIME) draft-becker-cnsa2-smime-profile-01 Abstract This document defines a base profile of S/MIME for use with the US Commercial National Security Algorithm (CNSA) 2.0 Suite, a cybersecurity advisory published by the United States Government which outlines quantum-resistant cryptographic algorithm policy for US national security applications. This profile applies to the capabilities, configuration, and operation of all components of US National Security Systems that employ S/MIME. It is also appropriate for all other US Government systems that process high-value information. This memo is not an IETF standard, and has not been shown to have IETF community consensus. This profile is made publicly available for use by developers and operators of these and any other system deployments. 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 2 March 2026. Becker & Jenkins Expires 2 March 2026 [Page 1] Internet-Draft CNSA2 S/MIME Profile August 2025 Copyright Notice Copyright (c) 2025 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. The Commercial National Security Algorithm Suite . . . . . . 3 4. Requirements and Assumptions . . . . . . . . . . . . . . . . 4 5. Message Digest . . . . . . . . . . . . . . . . . . . . . . . 4 6. Digital Signature . . . . . . . . . . . . . . . . . . . . . . 5 7. Key Establishment . . . . . . . . . . . . . . . . . . . . . . 6 7.1. KEM . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.2. KDF . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.3. AES Key Wrap . . . . . . . . . . . . . . . . . . . . . . 6 8. Content Encryption . . . . . . . . . . . . . . . . . . . . . 7 9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 11.1. Normative References . . . . . . . . . . . . . . . . . . 8 11.2. Informative References . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction This document specifies a profile of S/MIME [RFC8551] to comply with the National Security Agency's (NSA) Commercial National Security Algorithm (CNSA) 2.0 Suite [cnsafaq]. This profile applies to the capabilities, configuration, and operation of all components of US National Security Systems (NSS) [SP80059] that employ S/MIME. This profile is also appropriate for all other US Government systems that process high-value information, and is made publicly available for use by developers and operators of these and any other system deployments. Becker & Jenkins Expires 2 March 2026 [Page 2] Internet-Draft CNSA2 S/MIME Profile August 2025 This document does not define any cryptographic algorithm, and does not specify how to use any cryptographic algorithm not currently supported by S/MIME; instead, it profiles CNSA 2.0-compliant conventions for S/MIME, and uses algorithms already specified for use in S/MIME that are also allowed by the CNSA Suite 2.0. This document applies to all CNSA Suite solutions that make use of S/MIME. The reader is assumed to have familiarity with [RFC8551]. This memo is not an IETF standard, and has not been shown to have IETF community consensus. [ED NOTE: This document uses some details from [I-D.ietf-lamps-cms-kyber] to specify use of ML-KEM in CMS, and [I-D.ietf-lamps-cms-ml-dsa] to specify use of ML-DSA in CMS. We note that these drafts are not yet RFCs, and we may need to adjust this text accordingly based on the progress of these documents.] 2. 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Normative language does not apply beyond the scope of this profile. This is a profile of S/MIME [RFC8551]. Therefore, the requirements language in this memo may be different than that found in the underlying standards. All references to "CNSA" in this document refer to CNSA 2.0 [cnsafaq], unless otherwise stated. 3. The Commercial National Security Algorithm Suite The CNSA Suite is the set of approved commercial algorithms that can be used by vendors and IT users to meet cybersecurity and interoperability requirements for NSS. The initial suite of CNSA Suite algorithms, Suite B, established a baseline for use of commercial algorithms to protect classified information. The following suite, CNSA 1.0, served as a bridge between the original set and a fully quantum-resistant cryptographic capability. The current suite, CNSA 2.0, seeks to provide fully quantum-resistant protection [cnsafaq]. Becker & Jenkins Expires 2 March 2026 [Page 3] Internet-Draft CNSA2 S/MIME Profile August 2025 This profile uses CNSA 2.0 compliant algorithms: ML-DSA-87 [FIPS204] for signing, and ML-KEM-1024 [FIPS203] for key establishment. ML- DSA-87 and ML-KEM-1024 together with SHA384, SHA512, AES-256, LMS, and XMSS comprise the CNSA Suite 2.0. The NSA is authoring a set of RFCs, including this one, to provide updated guidance for using the CNSA 2.0 Suite in certain IETF protocols. These RFCs can be used in conjunction with other RFCs and cryptographic guidance (e.g., NIST Special Publications) to properly protect Internet traffic and data-at-rest for US Government NSS. 4. Requirements and Assumptions CMS values are generated using ASN.1 [X208], the Basic Encoding Rules (BER) [X209], and the Distinguished Encoding Rules (DER) [X509]. For key agreement, CNSA compliant implementations MUST use ML-KEM- 1024. Details provided in Section 7. For digital signature, CNSA compliant implementations MUST use ML- DSA-87. For CNSA Suite applications, public key certificates used to verify S/MIME signatures MUST be compliant with the CNSA Suite Certificate and Certificate Revocation List (CRL) profile specified in [I-D.jenkins-cnsa2-pkix-profile]. Within the CMS signed-data content type, signature algorithm identifiers are located in the signatureAlgorithm field of SignerInfo structures contained within the SignedData. In addition, signature algorithm identifiers are located in the SignerInfo signatureAlgorithm field of countersignature attributes. Specific requirements for digital signatures are given in Section 6; compliant implementations MUST consider signatures not meeting these requirements as invalid. This document assumes that the required trust anchors have been securely provisioned to the client. All implementations MUST use SHA-384 or SHA-512 for hashing and AES- GCM for encryption, the requirements for which are given in the following sections. 5. Message Digest CNSA-compliant implementations MUST use either SHA-384 or SHA-512 for message digest. Becker & Jenkins Expires 2 March 2026 [Page 4] Internet-Draft CNSA2 S/MIME Profile August 2025 [RFC5754] specifies the conventions for using SHA-384 or SHA-512 with the Cryptographic Message Syntax (CMS). CNSA-compliant S/MIME implementations MUST follow the conventions in [RFC5754]. Within the CMS signed-data content type, message digest algorithm identifiers are located in the SignedData digestAlgorithms field and the SignerInfo digestAlgorithm field. The SHA-384 message digest algorithm is defined in FIPS 180 [SHS], and the algorithm identifier for SHA-384 is defined in [RFC5754] as follows: id-sha384 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) nistalgorithm(4) hashalgs(2) 2 } The SHA-512 message digest algorithm is defined in FIPS 180 [SHS], and the algorithm identifier for SHA-512 is defined in [RFC5754] as follows: id-sha512 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) nistalgorithm(4) hashalgs(2) 3 } [RFC5754] defines the AlgorithmIdentifier parameters field as OPTIONAL. Implementations MUST accept SHA-384 and SHA-512 AlgorithmIdentifiers with absent parameters, or with NULL parameters. As specified in [RFC5754], implementations MUST generate SHA-384 or SHA-512 AlgorithmIdentifiers with absent parameters. 6. Digital Signature CNSA-compliant implementations MUST use ML-DSA-87 as the digital signature algorithm in S/MIME. [ED NOTE: The algorithm identifier for ML-DSA-87 is defined in Section 2 of [I-D.ietf-lamps-cms-ml-dsa], which is ongoing work detailing the conventions for using ML-DSA with the Cryptographic Message Syntax (CMS); This document will be updated accordingly as that work progresses. Note that [I-D.ietf-lamps-cms-ml-dsa] only specifies use of the pure mode (not pre-hash) of ML-DSA in CMS, which is also in accordance with CNSA. The "message digest" supplied to the signature algorithm is the entire message. Becker & Jenkins Expires 2 March 2026 [Page 5] Internet-Draft CNSA2 S/MIME Profile August 2025 [EDNOTE: This guidance is subject to change as conventions for External Mu, as defined in [I-D.ietf-lamps-dilithium-certificates], are further defined.] 7. Key Establishment 7.1. KEM CNSA-compliant implementations MUST use ML-KEM-1024 for key agreement. [ED NOTE:[I-D.ietf-lamps-cms-kyber] is ongoing work detailing the conventions for implementing ML-KEM in the KEMRecipientInfo structure in CMS to securely transfer the content-encryption key from the originator to the recipient. We also refer to guidance from [RFC9629].] A CMS originator MUST implement the Encapsulate algorithm from ML- KEM, and a CMS responder MUST implement the Decapsulate algorithm from ML-KEM. CNSA-compliant implementations MUST NOT support the user keying material (ukm) field defined in [RFC9629], and therefore ukm MUST NOT be included as input to the key-derivation function. 7.2. KDF A CNSA compliant implementation MUST use SHA-384 or SHA-512 for KDF computation. We note the KDF used to process the KEMRecipientInfo structure MAY be different from the KDF used in the ML-KEM-1024 algorithm. 7.3. AES Key Wrap Within the CMS enveloped-data content type, key wrap algorithm identifiers are located in the KeyWrapAlgorithm parameters within the EnvelopedData RecipientInfos KeyAgreeRecipientInfo keyEncryptionAlgorithm field. For CNSA-compliant implementations, the KeyWrapAlgorithm MUST be id-aes256-wrap-pad The required algorithm identifier, specified in [RFC5649] is: id-aes256-wrap-pad OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) Becker & Jenkins Expires 2 March 2026 [Page 6] Internet-Draft CNSA2 S/MIME Profile August 2025 nistAlgorithm(4) aes(1) 48 } 8. Content Encryption CNSA-compliant S/MIME implementations using the authenticated- enveloped-data content type [RFC5083] MUST use AES [AES] in Galois Counter Mode (GCM) [SP80038D] as the content authenticated encryption algorithm and MUST follow the conventions for using AES-GCM with the CMS defined in [RFC5084]. Within the CMS authenticated-enveloped-data content type, content- authenticated encryption algorithm identifiers are located in the AuthEnvelopedData EncryptedContentInfo contentEncryptionAlgorithm field. The content-authenticated encryption algorithm is used to encipher the content located in the AuthEnvelopedData EncryptedContentInfo encryptedContent field. The AES-GCM content-authenticated encryption algorithm is described in [GCM] and [SP80038D]. The algorithm identifier for AES-256 in GCM mode is: id-aes256-GCM OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4) aes(1) 46 } The AlgorithmIdentifier parameters field MUST be present, and the parameters field must contain GCMParameters: GCMParameters ::= SEQUENCE { ) aes-nonce OCTET STRING, aes-ICVlen AES-GCM-ICVlen DEFAULT 12 } The authentication tag length (aes-ICVlen) SHALL be 16 (indicating a tag length of 128 bits). The initialization vector (aes-nonce) MUST be generated in accordance with Section 8.2 of [SP80038D]. AES-GCM loses security catastrophically if a nonce is reused with a given key on more than one distinct set of input data. Therefore, a fresh content- authenticated encryption key MUST be generated for each message. Becker & Jenkins Expires 2 March 2026 [Page 7] Internet-Draft CNSA2 S/MIME Profile August 2025 9. Security Considerations Most of the security considerations for this document are described in [RFC8551] and [RFC9629]. Additional security considerations for the use of ML-KEM and ML-DSA in S/MIME can be found in [I-D.ietf-lamps-cms-kyber] and [I-D.ietf-lamps-cms-ml-dsa], respectively. 10. IANA Considerations This document has no IANA actions 11. References 11.1. Normative References [AES] National Institute of Standards and Technology, "Announcing the ADVANCED ENCRYPTION STANDARD (AES)", FIPS 197, DOI 10.6028/NIST.FIPS.197, November 2001, . [cnsafaq] National Security Agency, "The Commercial National Security Algorithm Suite 2.0 and Quantum Computing FAQ", December 2024, . [FIPS203] National Institute of Standards and Technology (2024), "Module-Lattice-Based Key-Encapsulation Mechanism Standard", (Department of Commerce, Washington, D.C.), Federal Information Processing Standards Publication (FIPS), NIST FIPS 203, . [FIPS204] National Institute of Standards and Technology (2024), "Module-Lattice-Based Digital Signature Standard", (Department of Commerce, Washington, D.C.), Federal Information Processing Standards Publication (FIPS), NIST FIPS 204, . [GCM] Dworkin, M., "Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC", NIST Special Publication 800-38D, DOI 10.6028/NIST.SP.800-38D, November 2007, . Becker & Jenkins Expires 2 March 2026 [Page 8] Internet-Draft CNSA2 S/MIME Profile August 2025 [I-D.ietf-lamps-cms-kyber] Prat, Julien., Ounsworth, Mike., and Daniel. Van Geest, "Use of ML-KEM in the Cryptographic Message Syntax (CMS)", August 2025, . [I-D.ietf-lamps-cms-ml-dsa] S, Ben., R, Adam., and Daniel. Van Geest, "Use of the ML- DSA Signature Algorithm in the Cryptographic Message Syntax (CMS)", January 2025, . [I-D.ietf-lamps-dilithium-certificates] Massimo, Jake., "Internet X.509 Public Key Infrastructure: Algorithm Identifiers for ML-DSA", February 2025, . [I-D.jenkins-cnsa2-pkix-profile] Jenkins, M. and A. Becker, "Commercial National Security Algorithm Suite Certificate and Certificate Revocation List Profile", January 2025, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5083] Housley, R., "Cryptographic Message Syntax (CMS) Authenticated-Enveloped-Data Content Type", RFC 5083, DOI 10.17487/RFC5083, November 2007, . [RFC5084] Housley, R., "Using AES-CCM and AES-GCM Authenticated Encryption in the Cryptographic Message Syntax (CMS)", RFC 5084, DOI 10.17487/RFC5084, November 2007, . [RFC5649] Housley, R. and M. Dworkin, "Advanced Encryption Standard (AES) Key Wrap with Padding Algorithm", RFC 5649, DOI 10.17487/RFC5649, September 2009, . Becker & Jenkins Expires 2 March 2026 [Page 9] Internet-Draft CNSA2 S/MIME Profile August 2025 [RFC5754] Turner, S., "Using SHA2 Algorithms with Cryptographic Message Syntax", RFC 5754, DOI 10.17487/RFC5754, January 2010, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Message Specification", RFC 8551, DOI 10.17487/RFC8551, April 2019, . [RFC9629] Housley, R., Gray, J., and T. Okubo, "Using Key Encapsulation Mechanism (KEM) Algorithms in the Cryptographic Message Syntax (CMS)", RFC 9629, DOI 10.17487/RFC9629, August 2024, . [SHS] National Institute of Standards and Technology (NIST), "Secure Hash Standard (SHS)", DOI 10.6028/NIST.FIPS.180-4, FIPS PUB 180-4, August 2015, . 11.2. Informative References [SP80038D] National Institute of Standards and Technology, "Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC, NIST Special Publication 800-38D", Special Publication 800-38D, DOI 10.6028/NIST.SP.800-38D, November 2007, >. [SP80059] National Institute of Standards and Technology, "Guideline for Identifying an Information System as a National Security System", Special Publication 59, DOI 10.6028/NIST.SP.800-59, August 2003, . [X208] CCITT, "Specification of Abstract Syntax Notation One (ASN.1)", CCITT Recommendation X.208 1998, . Becker & Jenkins Expires 2 March 2026 [Page 10] Internet-Draft CNSA2 S/MIME Profile August 2025 [X209] CCITT, "Specification of Basic Encoding Rules for Abstract Syntax Notation One (ASN.1)", CCITT Recommendation X.209 1998, . [X509] CCITT, "The Directory - Authentication Framework", CCITT Recommendation X.509 1998, . Authors' Addresses Alison Becker National Security Agency Email: aebecke@uwe.nsa.gov Michael Jenkins National Security Agency Email: mjjenki@cyber.nsa.gov Becker & Jenkins Expires 2 March 2026 [Page 11]