path: root/doc/rfc/rfc9206.txt

Independent Submission                                       L. Corcoran
Request for Comments: 9206                                    M. Jenkins
Category: Informational                                              NSA
ISSN: 2070-1721                                            February 2022


  Commercial National Security Algorithm (CNSA) Suite Cryptography for
                   Internet Protocol Security (IPsec)

Abstract

   The United States Government has published the National Security
   Agency's Commercial National Security Algorithm (CNSA) Suite, which
   defines cryptographic algorithm policy for national security
   applications.  This document specifies the conventions for using the
   United States National Security Agency's CNSA Suite algorithms in
   Internet Protocol Security (IPsec).  It applies to the capabilities,
   configuration, and operation of all components of US National
   Security Systems (described in NIST Special Publication 800-59) that
   employ IPsec.  This document is also appropriate for all other US
   Government systems that process high-value information.  It is made
   publicly available for use by developers and operators of these and
   any other system deployments.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not candidates for any level of Internet Standard;
   see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9206.

Copyright Notice

   Copyright (c) 2022 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.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  The Commercial National Security Algorithm Suite
   4.  CNSA-Compliant IPsec Overview
   5.  IPsec User Interface Suites
     5.1.  Suite CNSA-GCM-256-ECDH-384
     5.2.  Suite CNSA-GCM-256-DH-3072
     5.3.  Suite CNSA-GCM-256-DH-4096
   6.  IKEv2 Authentication
   7.  Certificates
   8.  IKEv2 Security Associations (SAs)
   9.  The Key Exchange Payload in the IKE_SA_INIT Exchange
   10. Generating Key Material for the IKE SA
   11. Additional Requirements
   12. Guidance for Applications with Long Data-Protection
           Requirements
   13. Security Considerations
   14. IANA Considerations
   15. References
     15.1.  Normative References
     15.2.  Informative References
   Authors' Addresses

1.  Introduction

   This document specifies the conventions for using the United States
   National Security Agency's (NSA's) Commercial National Security
   Algorithm (CNSA) Suite algorithms [CNSA] in Internet Protocol
   Security (IPsec).  It defines CNSA-based User Interface suites ("UI
   suites") describing sets of security configurations for Internet Key
   Exchange Protocol Version 2 (IKEv2) and IP Encapsulating Security
   Payload (ESP) protocol use, and specifies certain other constraints
   with respect to algorithm selection and configuration.  It applies to
   the capabilities, configuration, and operation of all components of
   US National Security Systems (described in NIST Special Publication
   800-59 [SP80059]) that employ IPsec.  This document is also
   appropriate for all other US Government systems that process high-
   value information.  It is made publicly available for use by
   developers and operators of these and any other system deployments.

   The reader is assumed to have familiarity with the following:

   *  "IP Encapsulating Security Payload (ESP)" [RFC4303]

   *  "Internet X.509 Public Key Infrastructure Certificate and
      Certificate Revocation List (CRL) Profile" [RFC5280]

   *  "Internet Key Exchange Protocol Version 2 (IKEv2)" [RFC7296]

   *  "Cryptographic Algorithm Implementation Requirements and Usage
      Guidance for Encapsulating Security Payload (ESP) and
      Authentication Header (AH)" [RFC8221]

   *  "Commercial National Security Algorithm (CNSA) Suite Certificate
      and Certificate Revocation List (CRL) Profile" [RFC8603]

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.

   AES refers to the Advanced Encryption Standard.  ECDSA and ECDH refer
   to the use of the Elliptic Curve Digital Signature Algorithm (ECDSA)
   and Elliptic Curve Diffie-Hellman (ECDH), respectively.  DH refers to
   Diffie-Hellman key establishment.  RSA refers to an RSA signature.

3.  The Commercial National Security Algorithm Suite

   The NSA profiles commercial cryptographic algorithms and protocols as
   part of its mission to support secure, interoperable communications
   for US Government National Security Systems.  To this end, it
   publishes guidance to both (1) assist with the US Government
   transition to new algorithms and (2) provide vendors -- and the
   Internet community in general -- with information concerning their
   proper use and configuration.

   Recently, cryptographic transition plans have become overshadowed by
   the prospect of the development of a cryptographically relevant
   quantum computer.  The NSA has established the Commercial National
   Security Algorithm (CNSA) Suite to provide vendors and IT users near-
   term flexibility in meeting their information assurance
   interoperability requirements.  The purpose behind this flexibility
   is to avoid vendors and customers making two major transitions in a
   relatively short timeframe, as we anticipate a need to shift to
   quantum-resistant cryptography in the near future.

   The NSA is authoring a set of RFCs, including this one, to provide
   updated guidance concerning the use of certain commonly available
   commercial algorithms in 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 National Security Systems.

4.  CNSA-Compliant IPsec Overview

   CNSA-compliant implementations for IPsec MUST use IKEv2 [RFC7296].

   Implementing a CNSA-compliant IPsec system requires cryptographic
   algorithm selection for both the IKEv2 and ESP protocols.  The
   following CNSA requirements apply to IPsec:

   Encryption:

      AES [FIPS197] (with key size 256 bits)

   Digital Signature:

      ECDSA [FIPS186] (using the NIST P-384 elliptic curve)
      RSA [FIPS186] (with a modulus of 3072 bits or larger)

   Key Establishment:

      ECDH [SP80056A] (using the NIST P-384 elliptic curve)
      DH [RFC3526] (with a prime modulus of 3072 or larger)

   To facilitate selection of appropriate combinations of compliant
   algorithms, this document provides CNSA-compliant User Interface
   suites (UI suites) [RFC4308] to implement IPsec on National Security
   Systems.

   The approved CNSA hash function for all purposes is SHA-384, as
   defined in [FIPS180].  However, PRF_HMAC_SHA_512 is specified for the
   IKEv2 Pseudorandom Function (PRF) instead of PRF_HMAC_SHA_384, due to
   availability.  See Section 8 below.

   For CNSA Suite applications, public key certificates MUST be
   compliant with the CNSA Suite Certificate and CRL Profile specified
   in [RFC8603].

   Under certain conditions, such as applications having long-lived
   data-protection requirements, systems that do not comply with the
   requirements of this document are acceptable; see Section 12.

5.  IPsec User Interface Suites

   User Interface (UI) suites [RFC4308] are named suites that cover some
   typical security policy options for IPsec.  Use of UI suites does not
   change the IPsec protocol in any way.  The following UI suites
   provide cryptographic algorithm choices for ESP [RFC4303] and for
   IKEv2 [RFC7296].  The selection of a UI suite will depend on the key
   exchange algorithm.  The suite names indicate the Advanced Encryption
   Standard [FIPS197] mode, AES key length specified for encryption, and
   the key exchange algorithm.

   Although RSA is also a CNSA-approved key establishment algorithm,
   only DH and ECDH are specified for key exchange in IKEv2 [RFC7296].
   RSA in IPsec is used only for digital signatures.  See Section 6.

   ESP requires negotiation of both a confidentiality algorithm and an
   integrity algorithm.  However, algorithms for Authenticated
   Encryption with Associated Data (AEAD) [RFC5116] do not require a
   separate integrity algorithm to be negotiated.  In particular, since
   AES-GCM is an AEAD algorithm, ESP implementing AES-GCM MUST either
   offer no integrity algorithm or indicate the single integrity
   algorithm NONE (see Section 3.3 of [RFC7296]).

   To be CNSA compliant, IPsec implementations that use the following UI
   suites MUST use the suite names listed below.  IPsec implementations
   SHOULD NOT use names different than those listed here for the suites
   that are described and MUST NOT use the names listed here for suites
   that do not match these values.  These requirements are necessary for
   interoperability.

   Transform names are as listed in the IANA "Internet Key Exchange
   Version 2 (IKEv2) Parameters" registry.  Definitions of the
   transforms are contained in the references specified in that
   registry.

   Other UI suites may be acceptable for CNSA compliance.  See Section 8
   for details.

5.1.  Suite CNSA-GCM-256-ECDH-384

   ESP SA:
      Encryption:  ENCR_AES_GCM_16 (with key size 256 bits)
      Integrity:  NONE
   IKEv2 SA:
      Encryption:  ENCR_AES_GCM_16 (with key size 256 bits)
      PRF:  PRF_HMAC_SHA2_512
      Integrity:  NONE
      Diffie-Hellman group:  384-bit random ECP group

5.2.  Suite CNSA-GCM-256-DH-3072

   ESP SA:
      Encryption:  ENCR_AES_GCM_16 (with key size 256 bits)
      Integrity:  NONE
   IKEv2 SA:
      Encryption:  ENCR_AES_GCM_16 (with key size 256 bits)
      PRF:  PRF_HMAC_SHA2_512
      Integrity:  NONE
      Diffie-Hellman group:  3072-bit MODP group

5.3.  Suite CNSA-GCM-256-DH-4096

   ESP SA:
      Encryption:  ENCR_AES_GCM_16 (with key size 256 bits)
      Integrity:  NONE
   IKEv2 SA:
      Encryption:  ENCR_AES_GCM_16 (with key size 256 bits)
      PRF:  PRF_HMAC_SHA2_512
      Integrity:  NONE
      Diffie-Hellman group:  4096-bit MODP group

6.  IKEv2 Authentication

   Authentication of the IKEv2 Security Association (SA) requires
   computation of a digital signature.  To be CNSA compliant, digital
   signatures MUST be generated with SHA-384 as defined in [RFC8017]
   together with either ECDSA-384 as defined in [RFC4754] or RSA with
   3072-bit or greater modulus.  (For applications with long data-
   protection requirements, somewhat different rules apply; see
   Section 12.)

   Initiators and responders MUST be able to verify ECDSA-384 signatures
   and MUST be able to verify RSA with 3072-bit or 4096-bit modulus and
   SHA-384 signatures.

   For CNSA-compliant systems, authentication methods other than
   ECDSA-384 or RSA MUST NOT be accepted for IKEv2 authentication.  A
   3072-bit modulus or larger MUST be used for RSA.  If the relying
   party receives a message signed with any authentication method other
   than an ECDSA-384 or RSA signature, it MUST return an
   AUTHENTICATION_FAILED notification and stop processing the message.
   If the relying party receives a message signed with RSA using less
   than a 3072-bit modulus, it MUST return an AUTHENTICATION_FAILED
   notification and stop processing the message.

7.  Certificates

   To be CNSA compliant, the initiator and responder MUST use X.509
   certificates that comply with [RFC8603].  Peer authentication
   decisions must be based on the Subject or Subject Alternative Name
   from the certificate that contains the key used to validate the
   signature in the Authentication Payload as defined in Section 3.8 of
   [RFC7296], rather than the Identification Data from the
   Identification Payload that is used to look up policy.

8.  IKEv2 Security Associations (SAs)

   Section 5 specifies three UI suites for ESP and IKEv2 Security
   Associations.  All three use AES-GCM for encryption but differ in the
   key exchange algorithm.  Galois/Counter Mode (GCM) [RFC4106] combines
   counter (CTR) mode with a secure, parallelizable, and efficient
   authentication mechanism.  Since AES-GCM is an AEAD algorithm, ESP
   implements AES-GCM with no additional integrity algorithm (see
   Section 3.3 of [RFC7296]).

   An initiator proposal SHOULD be constructed from one or more of the
   following suites:

   *  CNSA-GCM-256-ECDH-384
   *  CNSA-GCM-256-DH-3072
   *  CNSA-GCM-256-DH-4096

   A responder SHOULD accept proposals constructed from at least one of
   the three named suites.  Other UI suites may result in acceptable
   proposals (such as those based on PRF_HMAC_SHA2_384); however, these
   are provided to promote interoperability.

   Nonce construction for AES-GCM using a misuse-resistant technique
   [RFC8452] conforms with the requirements of this document and MAY be
   used if a Federal Information Processing Standard (FIPS) validated
   implementation is available.

   The named UI suites specify PRF_HMAC_SHA2_512 for the IKEv2 SA PRF
   transform, as PRF_HMAC_SHA2_384 is not listed among required PRF
   transforms in [RFC8247]; therefore, implementation of the latter is
   likely to be scarce.  The security level of PRF_HMAC_SHA2_512 is
   comparable, and the difference in performance is negligible.
   However, SHA-384 is the official CNSA algorithm for computing a
   condensed representation of information.  Therefore, the
   PRF_HMAC_SHA2_384 transform is CNSA compliant if it is available to
   the initiator and responder.  Any PRF transform other than
   PRF_HMAC_SHA2_384 or PRF_HMAC_SHA2_512 MUST NOT be used.

   If none of the proposals offered by the initiator consist solely of
   transforms based on CNSA algorithms (such as those in the UI suites
   defined in Section 5), the responder MUST return a Notify payload
   with the error NO_PROPOSAL_CHOSEN when operating in CNSA-compliant
   mode.

9.  The Key Exchange Payload in the IKE_SA_INIT Exchange

   The key exchange payload is used to exchange Diffie-Hellman public
   numbers as part of a Diffie-Hellman key exchange.  The CNSA-compliant
   initiator and responder MUST each generate an ephemeral key pair to
   be used in the key exchange.

   If the Elliptic Curve Diffie-Hellman (ECDH) key exchange is selected
   for the SA, the initiator and responder both MUST generate an
   elliptic curve (EC) key pair using the P-384 elliptic curve.  The
   ephemeral public keys MUST be stored in the key exchange payload as
   described in [RFC5903].

   If the Diffie-Hellman (DH) key exchange is selected for the SA, the
   initiator and responder both MUST generate a key pair using the
   appropriately sized MODP group as described in [RFC3526].  The size
   of the MODP group will be determined by the selection of either a
   3072-bit or greater modulus for the SA.

10.  Generating Key Material for the IKE SA

   As noted in Section 7 of [RFC5903], the shared secret result of an
   ECDH key exchange is the 384-bit x value of the ECDH common value.
   The shared secret result of a DH key exchange is the number of octets
   needed to accommodate the prime (e.g., 384 octets for 3072-bit MODP
   group) with leading zeros as necessary, as described in Section 2.1.2
   of [RFC2631].

   IKEv2 allows for the reuse of Diffie-Hellman private keys; see
   Section 2.12 of [RFC7296].  However, there are security concerns
   related to this practice.  Section 5.6.3.3 of [SP80056A] states that
   an ephemeral private key MUST be used in exactly one key
   establishment transaction and MUST be destroyed (zeroized) as soon as
   possible.  Section 5.8 of [SP80056A] states that any shared secret
   derived from key establishment MUST be destroyed (zeroized)
   immediately after its use.  CNSA-compliant IPsec systems MUST follow
   the mandates in [SP80056A].

11.  Additional Requirements

   The IPsec protocol AH MUST NOT be used in CNSA-compliant
   implementations.

   A Diffie-Hellman group MAY be negotiated for a Child SA as described
   in Section 1.3 of [RFC7296], allowing peers to employ Diffie-Hellman
   in the CREATE_CHILD_SA exchange.  If a transform of type 4 is
   specified for an SA for ESP, the value of that transform MUST match
   the value of the transform used by the IKEv2 SA.

   Per [RFC7296], if a CREATE_CHILD_SA exchange includes a KEi payload,
   at least one of the SA offers MUST include the Diffie-Hellman group
   of the KEi.  For CNSA-compliant IPsec implementations, the Diffie-
   Hellman group of the KEi MUST use the same group used in the
   IKE_INIT_SA.

   For IKEv2, rekeying of the CREATE_CHILD_SA MUST be supported by both
   parties.  The initiator of this exchange MAY include a new Diffie-
   Hellman key; if it is included, it MUST use the same group used in
   the IKE_INIT_SA.  If the initiator of the exchange includes a Diffie-
   Hellman key, the responder MUST include a Diffie-Hellman key, and it
   MUST use the same group.

   For CNSA-compliant systems, the IKEv2 authentication method MUST use
   an end-entity certificate provided by the authenticating party.
   Identification Payloads (IDi and IDr) in the IKE_AUTH exchanges MUST
   NOT be used for the IKEv2 authentication method but may be used for
   policy lookup.

   The administrative User Interface (UI) for a system that conforms to
   this profile MUST allow the operator to specify a single suite.  If
   only one suite is specified in the administrative UI, the IKEv2
   implementation MUST only offer algorithms for that one suite.

   The administrative UI MAY allow the operator to specify more than one
   suite; if it allows this, it MUST allow the operator to specify a
   preferred order for the suites that are to be offered or accepted.
   If more than one suite is specified in the administrative UI, the
   IKEv2 implementation MUST only offer algorithms of those suites.
   (Note that although this document does not define a UI suite
   specifying PRF_HMAC_SHA2_384, a proposal containing such a transform
   is CNSA compliant.)

12.  Guidance for Applications with Long Data-Protection Requirements

   The CNSA mandate is to continue to use current algorithms with
   increased security parameters, then transition to approved post-
   quantum resilient algorithms when they are identified.  However, some
   applications have data-in-transit-protection requirements that are
   long enough that post-quantum resilient protection must be provided
   now.  Lacking approved asymmetric post-quantum resilient
   confidentiality algorithms, that means approved symmetric techniques
   must be used as described in this section until approved post-quantum
   resilient asymmetric algorithms are identified.

   For new applications, confidentiality and integrity requirements from
   the sections above MUST be followed, with the addition of a Pre-
   Shared Key (PSK) mixed in as defined in [RFC8784].

   Installations currently using IKEv1 with PSKs MUST (1) use AES in
   cipher block chaining mode (AES-CBC) in conjunction with a CNSA-
   compliant integrity algorithm (e.g., AUTH_HMAC_SHA2_384_192) and (2)
   transition to IKEv2 with PSKs [RFC8784] as soon as implementations
   become available.

   Specific guidance for systems not compliant with the requirements of
   this document, including non-GCM modes and PSK length, and PSK
   randomness, will be defined in solution-specific requirements
   appropriate to the application.  Details of those requirements will
   depend on the program under which the commercial National Security
   Systems solution is developed (e.g., an NSA Commercial Solutions for
   Classified Capability Package).

13.  Security Considerations

   This document inherits all of the security considerations of the
   IPsec and IKEv2 documents, including [RFC7296], [RFC4303], [RFC4754],
   and [RFC8221].

   The security of a system that uses cryptography depends on both the
   strength of the cryptographic algorithms chosen and the strength of
   the keys used with those algorithms.  The security also depends on
   the engineering and administration of the protocol used by the system
   to ensure that there are no non-cryptographic ways to bypass the
   security of the overall system.

   When selecting a mode for the AES encryption [RFC5116], be aware that
   nonce reuse can result in a loss of confidentiality.  Nonce reuse is
   catastrophic for GCM, since it also results in a loss of integrity.

14.  IANA Considerations

   IANA has added the UI suites defined in this document to the
   "Cryptographic Suites for IKEv1, IKEv2, and IPsec" registry located
   at <https://www.iana.org/assignments/crypto-suites>:

                   +=======================+===========+
                   |       Identifier      | Reference |
                   +=======================+===========+
                   | CNSA-GCM-256-ECDH-384 | RFC 9206  |
                   +-----------------------+-----------+
                   | CNSA-GCM-256-DH-3072  | RFC 9206  |
                   +-----------------------+-----------+
                   | CNSA-GCM-256-DH-4096  | RFC 9206  |
                   +-----------------------+-----------+

                                  Table 1

15.  References

15.1.  Normative References

   [CNSA]     Committee for National Security Systems, "Use of Public
              Standards for Secure Information Sharing", CNSSP 15,
              October 2016,
              <https://www.cnss.gov/CNSS/Issuances/Policies.htm>.

   [FIPS180]  National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", Federal Information Processing
              Standard 180-4, DOI 10.6028/NIST.FIPS.180-4, August 2015,
              <https://csrc.nist.gov/publications/detail/fips/180/4/
              final>.

   [FIPS186]  National Institute of Standards and Technology, "Digital
              Signature Standard (DSS)", NIST Federal Information
              Processing Standard 186-4, DOI 10.6028/NIST.FIPS.186-4,
              July 2013,
              <https://csrc.nist.gov/publications/detail/fips/186/4/
              final>.

   [FIPS197]  National Institute of Standards and Technology, "Advanced
              Encryption Standard (AES)", Federal Information Processing
              Standard 197, DOI 10.6028/NIST.FIPS.197, November 2001,
              <https://csrc.nist.gov/publications/detail/fips/197/
              final>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2631]  Rescorla, E., "Diffie-Hellman Key Agreement Method",
              RFC 2631, DOI 10.17487/RFC2631, June 1999,
              <https://www.rfc-editor.org/info/rfc2631>.

   [RFC3526]  Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
              Diffie-Hellman groups for Internet Key Exchange (IKE)",
              RFC 3526, DOI 10.17487/RFC3526, May 2003,
              <https://www.rfc-editor.org/info/rfc3526>.

   [RFC4106]  Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
              (GCM) in IPsec Encapsulating Security Payload (ESP)",
              RFC 4106, DOI 10.17487/RFC4106, June 2005,
              <https://www.rfc-editor.org/info/rfc4106>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [RFC4308]  Hoffman, P., "Cryptographic Suites for IPsec", RFC 4308,
              DOI 10.17487/RFC4308, December 2005,
              <https://www.rfc-editor.org/info/rfc4308>.

   [RFC4754]  Fu, D. and J. Solinas, "IKE and IKEv2 Authentication Using
              the Elliptic Curve Digital Signature Algorithm (ECDSA)",
              RFC 4754, DOI 10.17487/RFC4754, January 2007,
              <https://www.rfc-editor.org/info/rfc4754>.

   [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
              Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
              <https://www.rfc-editor.org/info/rfc5116>.

   [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,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5903]  Fu, D. and J. Solinas, "Elliptic Curve Groups modulo a
              Prime (ECP Groups) for IKE and IKEv2", RFC 5903,
              DOI 10.17487/RFC5903, June 2010,
              <https://www.rfc-editor.org/info/rfc5903>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <https://www.rfc-editor.org/info/rfc7296>.

   [RFC8017]  Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
              "PKCS #1: RSA Cryptography Specifications Version 2.2",
              RFC 8017, DOI 10.17487/RFC8017, November 2016,
              <https://www.rfc-editor.org/info/rfc8017>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8221]  Wouters, P., Migault, D., Mattsson, J., Nir, Y., and T.
              Kivinen, "Cryptographic Algorithm Implementation
              Requirements and Usage Guidance for Encapsulating Security
              Payload (ESP) and Authentication Header (AH)", RFC 8221,
              DOI 10.17487/RFC8221, October 2017,
              <https://www.rfc-editor.org/info/rfc8221>.

   [RFC8247]  Nir, Y., Kivinen, T., Wouters, P., and D. Migault,
              "Algorithm Implementation Requirements and Usage Guidance
              for the Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 8247, DOI 10.17487/RFC8247, September 2017,
              <https://www.rfc-editor.org/info/rfc8247>.

   [RFC8603]  Jenkins, M. and L. Zieglar, "Commercial National Security
              Algorithm (CNSA) Suite Certificate and Certificate
              Revocation List (CRL) Profile", RFC 8603,
              DOI 10.17487/RFC8603, May 2019,
              <https://www.rfc-editor.org/info/rfc8603>.

   [RFC8784]  Fluhrer, S., Kampanakis, P., McGrew, D., and V. Smyslov,
              "Mixing Preshared Keys in the Internet Key Exchange
              Protocol Version 2 (IKEv2) for Post-quantum Security",
              RFC 8784, DOI 10.17487/RFC8784, June 2020,
              <https://www.rfc-editor.org/info/rfc8784>.

   [SP80056A] National Institute of Standards and Technology,
              "Recommendation for Pair-Wise Key Establishment Schemes
              Using Discrete Logarithm Cryptography", NIST Special
              Publication 800-56A, Revision 3,
              DOI 10.6028/NIST.SP.800-56Ar3, April 2018,
              <https://csrc.nist.gov/publications/detail/sp/800-56a/rev-
              3/final>.

15.2.  Informative References

   [RFC8452]  Gueron, S., Langley, A., and Y. Lindell, "AES-GCM-SIV:
              Nonce Misuse-Resistant Authenticated Encryption",
              RFC 8452, DOI 10.17487/RFC8452, April 2019,
              <https://www.rfc-editor.org/info/rfc8452>.

   [SP80059]  National Institute of Standards and Technology, "Guideline
              for Identifying an Information System as a National
              Security System", Special Publication 800-59,
              DOI 10.6028/NIST.SP.800-59, August 2003,
              <https://csrc.nist.gov/publications/detail/sp/800-59/
              final>.

Authors' Addresses

   Laura Corcoran
   National Security Agency
   Email: lscorco@nsa.gov


   Michael Jenkins
   National Security Agency - Center for Cybersecurity Standards
   Email: mjjenki@cyber.nsa.gov