



IP Security Maintenance and Extensions                      G. Wang, Ed.
Internet-Draft                                       Huawei Int. Pte Ltd
Intended status: Standards Track                             L. Bruckert
Expires: 8 May 2026                            secunet Security Networks
                                                              V. Smyslov
                                                              ELVIS-PLUS
                                                         4 November 2025


      Post-quantum Hybrid Key Exchange in the IKEv2 with FrodoKEM
              draft-wang-ipsecme-hybrid-kem-ikev2-frodo-02

Abstract

   Multiple key exchanges in the Internet Key Exchange Protocol Version
   2 (IKEv2) [RFC9370] specifies a framework that supports multiple key
   encapsulation mechanisms (KEMs) in the Internet Key Exchange Protocol
   Version 2 (IKEv2) by allowing up to 7 layers of additional KEMs to
   derive the final shared secret keys for IPsec protocols.  The primary
   goal is to mitigate the “harvest now and decrypt later” threat posed
   by cryptanalytically relevant quantum computers (CRQC).  For this
   purpose, usually one or more post-quantum KEMs are performed in
   addition to the traditional (EC)DH key exchange.  This draft
   specifies how the post-quantum KEM FrodoKEM is instantiated in the
   IKEv2 as an additional key exchange mechanism.

   [EDNOTE: IANA KE code points for FrodoKEM may need to be assigned, as
   the code points for ML-KEM has been considered in [I-D.KR24]. ]

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 8 May 2026.






Wang, et al.               Expires 8 May 2026                   [Page 1]

Internet-Draft           Hybrid KEM in the IKEv2           November 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
     1.1.  Notes of Change . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  KEMs and FrodoKEM . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  KEMs  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  FrodoKEM  . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Comparison to ML-KEM  . . . . . . . . . . . . . . . . . .   6
   4.  FrodoKEM in the IKEv2 . . . . . . . . . . . . . . . . . . . .   6
     4.1.  FrodoKEM in IKE_INTERMEDIATE  . . . . . . . . . . . . . .   6
     4.2.  FrodoKEM in IKE_FOLLOWUP_KE . . . . . . . . . . . . . . .  10
     4.3.  IKEv2 Payloads for FrodoKEM . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .  12
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

1.1.  Notes of Change

   Three main changes have been made in version 02, as a response to
   comments received since July of 2025.

   *  Reduced code points from 6 in v01 to 4 now (revised Sections 3.3
      and 6).

   *  Explained why variants for both AES and SHAKE are necessary
      (revised Section 3.2).




Wang, et al.               Expires 8 May 2026                   [Page 2]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   *  Added KEi and KEr payloads for using FrodoKEM in IKEv2 (added new
      Sections 4.3).

   Two main changes have been made in version 01, as a response to
   comments received at 122 meeting:

   *  Restructured the draft.

   *  Reduced the point codes from 12 to 6 (eFrodoKEM).

1.2.  Introduction

   Cryptographically-relevant quantum computers (CRQC) pose a threat to
   cryptographically protected data.  In particular, the so-called
   harvest-now-and-decrypt-later (HNDL) attack is considered an imminent
   threat.  To mitigate this threat the concept of hybrid key
   encapsulation mechanisms (KEMs) has been proposed to achieve secure
   key exchange if at least one of the KEMs is still secure. “Multiple
   key exchanges in the Internet Key Exchange Protocol Version 2 (IKEv2)
   [RFC9370] specifies a framework to perform hybrid key encapsulation
   in the IKEv2 by allowing multiple key exchanges to take place for
   deriving shared secret keys during a Security Association (SA) setup.
   Essentially, this specification employs the IKE_INTERMEDIATE
   exchange, which is a new IKEv2 message introduced in “Intermediate
   Exchange in the Internet Key Exchange Protocol Version 2 (IKEv2)”
   [RFC9242], so that multiple key exchanges can be run to establish an
   IKE SA via exchanging additional PQ public keys and ciphertexts
   between a client and a server.  RFC 9370 also introduces
   IKE_FOLLOWUP_KE, a new IKEv2 exchange for realizing the same purpose
   when the IKE SA is being rekeyed or additional Child SAs are created.

   However, [RFC9370] just specifies the framework of hybrid KEMs and
   has to be been instantiated for concrete KEMs by separate documents.
   [I-D.KR24] describes how the framework given by [RFC9370] can be run
   with the ML-KEM [FIPS203], previously called Kyber, which has been
   standardized by NIST in August 2024.  However, on the one hand,
   [RFC9370] allows up to 7 layers of additional KEMs to derive final
   shared secret keys for the IKEv2.  On the other hand, for some
   applications (e.g. financial services) demanding high security level,
   additional PQ KEMs may be desired for use with [RFC9370].  Currently,
   ISO is standardizing three PQ KEM algorithms (EDNOTE: we may want to
   change the wording since the ISO standard will be finished
   eventually): Kyber, FrodoKEM, and Classic McEliece.  Note that
   FrodoKEM [FrodoKEM] [I-D.LBES25] is unstructured lattice based KEM,
   whose security is more conservative compared to ML-KEM, which is
   based on structured lattice.  Therefore, this draft is motivated to
   describe concretely how the frame of hybrid KEMs for the IKEv2
   specified in RFC 9370 can be instantiated with FrodoKEM.  FrodoKEM



Wang, et al.               Expires 8 May 2026                   [Page 3]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   should be used together with a traditional key exchange mechanism
   such as ECDH and in addition, may be used with further KEMs, e.g. ML-
   KEM.

   Here are a few reasons for explaining why such diversity of KEMs is
   important for the IKEv2 (and also other security protocols).

   *  The availability of various PQ algorithms is beneficial to
      applications as different PQ algorithms could be selected
      according to practical performance and security requirements.

   *  Generally speaking, post-quantum algorithms are still not mature
      yet.  Some algorithms may turn out to be insecure after a number
      of years’ study and/or standardization.  An example is SIKE, which
      had been in the NIST standardization progres for several years
      until it was totally broken in July of 2022 [CD22].

   *  Cryptographic agility shall play a crucial role in the PQ
      migration [OPM23].  To facilitate cryptographic agility, not only
      should the systems and protocols be engineered agile but also
      there should be a good number of standardized PQC algorithms
      available, which may be based on different hard problems.

   However, the performance of FrodoKEM is not as good as ML-KEM.  In
   particular, the sizes of pulic key and ciphtertext of FrodoKEM are
   roughly 10 times larger than those of ML-KEM.  Consequently, this
   will almost unavoidably trigger IKE fragmentation.

2.  Requirements Language

   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.  KEMs and FrodoKEM

3.1.  KEMs

   Key encapsulation mechanism (KEM) is a kind of key exchange, which
   allows one entity to encapsulate a secret key under a (long-term or
   ephemeral) public key of another entity.  By following the definiton
   given in [I-D.KR24], a KEM consists of three algorithms:

   *  KeyGen(k) -> (pk, sk): A probabilistic key generation algorithm,
      which generates a public encapsulation key pk and a secret
      decapsulation key sk, when a security parameter k is given.



Wang, et al.               Expires 8 May 2026                   [Page 4]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   *  Encaps(pk) -> (ct, ss): A probabilistic encapsulation algorithm,
      which takes as input a public encapsulation key pk and outputs a
      ciphertext ct and shared secret ss.

   *  Decaps(sk, ct) -> ss: A decapsulation algorithm, which takes as
      input a secret decapsulation key sk and ciphertext ct and outputs
      a shared secret ss.

3.2.  FrodoKEM

   FrodoKEM [I-D.LBES25] is one of three KEMs in the process of ISO
   standardization [FrodoKEM].  Its security is based on a well-studied
   hard problem in unstructured lattices, called the learning with
   errors problem.  The algorithm details of FrodoKEM are specified in
   [I-D.LBES25].

   In total, FrodoKEM [FrodoKEM] has 12 variants.  Namely, it offers 3
   NIST security levels 1, 3, and 5; the pseudorandom generator (PRG)
   uses AES128 or SHAKE 128; and the KEM public key can be a long-term
   key (standard mode) or a short-term key (ephemeral mode).

   FrodoKEM has two main variants: a "standard" variant and an
   "ephemeral" variant.  As specified in Section of 8 in [I-D.LBES25],
   "standard FrodoKEM is recommended for applications in which the
   number of ciphertexts produced for a single public key is expected to
   be equal or greater than 2^8".  "Ephemeral FrodoKEM MUST be used for
   applications in which that same figure is expected to be smaller than
   2^8".  In this document, FrodoKEM is specified for ephemeral key
   exchange in the IKEv2 and one temporarily generated public key MUST
   be used just once.  So, only eFrodoKEM, which stands for Ephemeral
   FrodoKEM, SHALL be specified in this draft.

   FrodoKEM has both AES and SHAKE variants to offer optimized
   performance across different hardware platforms.  AES variants are
   highly suitable for devices with hardware acceleration for AES (like
   AES-NI on Intel processors).  SHAKE variants provide competitive or
   better performance on platforms lacking AES hardware acceleration
   (such as many embedded systems and general-purpose CPUs).  To cover
   both scenarios, this specification SHALL include both variants.

   According to the current standardization progress in ISO, FrodoKEM
   will be standardized for only 8 variants for NIST security levels 3
   and 5.  Namely, there are (e)FrodoKEM-976 and (e)FrodoKEM-1344, but
   not (e)FrodoKEM-640 for security level 1.  To align with ISO, this
   specification SHALL not include varaints for security level 1 as
   well.





Wang, et al.               Expires 8 May 2026                   [Page 5]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   Based on the above, this document specifies only four variants of
   eFrodoKEM for the IKEv2 ephemeral key exchange.  Namely, eFrodoKEM-
   976-<AES> and eFrodoKEM-976-<SHAKE> for security level 3, and
   eFrodoKEM-1344-<AES> and eFrodoKEM-1344-<SHAKE> for security level 5.

3.3.  Comparison to ML-KEM

   ML-KEM and FrodoKEM are two well-known post-quantum KEMs based on
   lattices.  More specifically, ML-KEM [FIPS203], originally called
   Kyber, has been standardized as the only one KEM scheme by NIST in
   August of 2024.  It is a Module-Lattice based Key-Encapsulation
   Mechanism, so called ML-KEM.  ML-KEM is also specified as an Internet
   Draft in IETF [I-D.Kyber24].

   However, the perfomace of FrodoKEM is not as good as ML-KEM.
   Specifically, as shown in Table 1, the sizes of pulic key and
   ciphtertext of FrodoKEM are roughly 10 times larger than those of ML-
   KEM.  Consequently, this will almost unavoidably trigger IKE
   fragmentation [RFC7383] [RFC9242], when FrodoKEM is used in the
   IKEv2.

  +===============+============+============+============+===============+
  |   Algorithms  | secret key | public key | ciphterext | shared secret |
  |               |    sk      |    pk      |     ct     |      ss       |
  +===============+============+============+============+===============+
  | ML-KEM-768    |    1,184   |   2,400    |    1,088   |      32       |
  +---------------+------------+------------+------------+---------------+
  | ML-KEM-1024   |    1,568   |   3,168    |    1,568   |      32       |
  +---------------+------------+------------+------------+---------------+
  | eFrodoKEM-976 |    31,296  |   15,632   |    15,744  |      24       |
  +---------------+------------+------------+------------+---------------+
  | eFrodoKEM-1344|    43,088  |   21,520   |    21,632  |      32       |
  +---------------+------------+------------+---------------+------------+
  Table 1: Size (in bytes) of keys and ciphertexts of ML-KEM and eFrodoKEM

4.  FrodoKEM in the IKEv2

4.1.  FrodoKEM in IKE_INTERMEDIATE

   As specified in [RFC9370], to run PQ KEMs in IEKv2, the initiator and
   the responder SHALL run traditional key exchange first and then PQ
   KEMs.  This is because the size of PQ KEM public key or the
   ciphertext is normally large, such that the first exchange in IKEv2
   cannot accommodate them (together with other necessary informaiton)
   without exceeding MTU (Maximum Transmission Unit), which is genreally
   set as 1500 byes.





Wang, et al.               Expires 8 May 2026                   [Page 6]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   Namely, in the first IKE_SA_INIT exchanges in IKEv2, the initiator
   sends KEi(0) payload to the responder, and the responder sends KEr(0)
   payload to the initiator for completing traditional ephemeral DH or
   ephemeral ECDH key exhange.  Once these procedures are done
   successully, the two entities SHALL share the same raw key SK(0).
   And from SK(0), a series of keying materials are derived, which are
   called as SKEYSEED(0), SK_d(0), SK_a[i/r](0), SK_e[i/r](0), and
   SK_p[i/r](0) (refere to section 2.2.2 in [RFC9370]).

   To run FrodoKEM (or any PQ KEM) in IKEv2, both the initiator and the
   responder MUST declare their support of both the ADDKE Transform
   Types and the IKE_INTERMEDIATE exchange in the IKE_SA_INIT exchanges
   between them.  At the same time, the initiator SHALL present its
   intended FrodoKEM variants via one or more ADDKE Transform Types,
   which are presented in one or more Proposals.  Then, the responder
   MAY select a variant of FrodoKEM (or one or more PQ KEMs) from the
   initiator's proposals, and then sends the corresponding ADDKE
   Transform ID (or IDs) to the initiator.

   Once the initiator receives one ADDKE Transform ID, which is for
   FrodoKEM (or any PQ KEM), it SHALL run KeyGen(k) to generate an
   ephemeral public and private KEM key pairs (pk, sk), and sends the
   value of public key pk to the responder via KEi(1) payload.
   Corrrespondingly, once retrived public key pk from KEi(1) payload,
   the responder SHALL run Encaps(pk) to obtain a pair (ct1, ss1).
   Here, ss1 is the raw key to be shared, and ct1 is the ciphertext
   encapsulated ss1.  Then, the responder SHALL send ct1 via KEr(1)
   payload that contains ct1 to the initiator.  After that, the
   initiator can retrieve ct1 from KEr(1) payload and then decapsulate
   ct1 to obtain the shared sceret ss1.  Here, both KEi(1) and KEr(1)
   payloads SHALL be sent via the IKE_INTERMEDIATE exchanges between the
   two entities.  Also, note that during these procedures, KEi(1) and
   KEr(1) payloads SHALL be protected via using keys SK_a[i/r](0) and
   SK_e[i/r](0).

   Once ss1 is successfully shared, the two entities SHALL set
   SK(1)=ss1, and then stir SK(1) with SK_d(0) to derive SKEYSEED(1).
   And then, from SKEYSEED(1), a series of SK_d(1), SK_a[i/r](1),
   SK_e[i/r](1), and SK_p[i/r](1) SHALL be derived.  If there are more
   ADDKE exchanges for PQ KEMs, these procedures SHALL continute until
   the final ADDKE finishes.  Then, the final updated key values,
   SKEYSEED(n), SK_d(n), SK_a[i/r](n), SK_e[i/r](n), and SK_p[i/r](n),
   SHALL be used to protect the following IKEv2 exchanges, in particual
   the IKEv2 authenticaion messages.

   The structure of KEi(1) and KEr(1) payloads and their lengths for
   eFrodoKEMs listed in Table 1 will be given in Section 4.3.




Wang, et al.               Expires 8 May 2026                   [Page 7]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   Following generalexmaples given in Appendix A of [RFC9370], here is
   an example to show that the initiator proposes to use additional key
   exchanges for establishing an IKE SA.  Here, the initiator proposes
   three sets of additional key exchanges.  Namely, the first set is
   TBD36 (ml-kem-768), TBD37 (ml-kem-1024) [I-D.KR24] or NONE; the
   second set is TBD40 (eFrodoKEM-976-<AES>), TBD41 (eFrodoKEM-
   976-<SHAKE>) or NONE; and the third set is TBD43 (eFrodoKEM-
   1344-<SHAKE>) or NONE (refer to Section 6).  As all of the three
   additional key exchanes are optional, the responder can choose NONE
   for some or all of the additional exchanges if the proposed key
   exchange methods are not supported or for whatever reasons the
   responder decides not to perform the additional key exchange.







































Wang, et al.               Expires 8 May 2026                   [Page 8]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


Initiator                     Responder
---------------------------------------------------------------------
HDR(IKE_SA_INIT), SAi1(.. ADDKE*...), --->
KEi(Curve25519), Ni, N(IKEV2_FRAG_SUPPORTED),
N(INTERMEDIATE_EXCHANGE_SUPPORTED)
    Proposal #1
    Transform ENCR (ID = ENCR_AES_GCM_16,
                    256-bit key)
    Transform PRF (ID = PRF_HMAC_SHA2_512)
    Transform KE (ID = Curve25519)
    Transform ADDKE1 (ID = TBD36)
    Transform ADDKE1 (ID = TBD37)
    Transform ADDKE1 (ID = NONE)
    Transform ADDKE2 (ID = TBD40)
    Transform ADDKE2 (ID = TBD41)
    Transform ADDKE2 (ID = NONE)
    Transform ADDKE3 (ID = TBD43)
    Transform ADDKE3 (ID = NONE)

                   <--- HDR(IKE_SA_INIT), SAr1(.. ADDKE*...),
                        KEr(Curve25519), Nr, N(IKEV2_FRAG_SUPPORTED),
                        N(INTERMEDIATE_EXCHANGE_SUPPORTED)
                        Proposal #1
                          Transform ENCR (ID = ENCR_AES_GCM_16,
                                         256-bit key)
                          Transform PRF (ID = PRF_HMAC_SHA2_512)
                          Transform KE (ID = Curve25519)
                          Transform ADDKE1 (ID = TBD36)
                          Transform ADDKE2 (ID = TBD40)
                          Transform ADDKE3 (ID = NONE)

HDR(IKE_INTERMEDIATE), SK {KEi(1)(TBD36)} -->
                   <--- HDR(IKE_INTERMEDIATE), SK {KEr(1)(TBD36)}
HDR(IKE_INTERMEDIATE), SK {KEi(2)(TBD40)} -->
                   <--- HDR(IKE_INTERMEDIATE), SK {KEr(2)(TBD40)}

HDR(IKE_AUTH), SK{ IDi, AUTH, SAi2, TSi, TSr } --->
                   <--- HDR(IKE_AUTH), SK{IDr, AUTH, SAr2,TSi, TSr}
Fig. 1 Hybrid KEMs of ECDH, TBD36 (ml-kem-768), and TBD40 (eFrodoKEM-976-<AES>)

   In the above example, the responder chooses to run two additional key
   exchanges.  Namely, it selects TBD36 (ml-kem-768), TBD40 (eFrodoKEM-
   976-<AES>), and NONE, respectively for the first, second, and third
   additional key exchanges.  According to the IKEv2 specification
   [RFC7296], a set of keying materials can be derived, in particular
   SK_d, SK_a[i/r], and SK_e[i/r], when the IKE_SA_INIT exchange has
   been completed by the initiator and the responder with a successful
   execution of ECDH based on the curve 25519.  After that, both peers



Wang, et al.               Expires 8 May 2026                   [Page 9]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   will perform an IKE_INTERMEDIATE exchange, carrying TBD36 payload,
   which is protected with SK_e[i/r] and SK_a[i/r] keys.  After the
   completion of this IKE_INTERMEDIATE exchange, the SKEYSEED is updated
   using SK(1), which is the TBD36 shared secret.  Next, an
   IKE_INTERMEDIATE exchange for TBD40 payload will be performed so that
   the SKEYSEED will be updated again.

   After the completion of both IKE_INTERMEDIATE exchanges for TBD36 and
   TBD43, the initiator and the responder will continue the IKE_AUTH
   exchange phase.

4.2.  FrodoKEM in IKE_FOLLOWUP_KE

   FrodoKEM can also be used for creating additional Child SAs and
   rekeying the IKE SA or Child SAs.  FrodoKEM may be used as the only
   key exchange in CREATE_CHILD_SA exchange or as an additional key
   exchange method.  In the latter case, the IKE_FOLLOWUP_KE exchange as
   defined in [RFC9370] is used.

   IKE_FOLLOWUP_KE is an additional exchange for the purpose of using
   multiple key exchanges with the CREATE_CHILD_SA Exchange.  If the use
   of additional key exchange methods is negotiated in the
   CREATE_CHILD_SA exchange, these are performed subsequently in a
   series of IKE_FOLLOWUP_KE exchanges.  After all key exchanges are
   completed, SKEYSEED or KEYMAT are computed as specified in section
   2.2.4 of [RFC9370].

4.3.  IKEv2 Payloads for FrodoKEM

   For completeness, the KE (Key Exchange) payload is given below and
   all fields inside keep the same meaning as specified in Section 3.4
   of the IKEv2 standard [RFC7296].  This also means that the initiator
   SHALL prepare KEi(0) and KEi(1) payloads according to Fig. 2.
   Namely, the Key Exchange Data will be filled with KEi(0) or KEi(1).
   This applies for the responder to prepare KEr(0) and KEr(1) as well.

                         1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Key Exchange Method Num    |           RESERVED             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                       Key Exchange Data                       ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Fig. 2 Key Exchange Payload



Wang, et al.               Expires 8 May 2026                  [Page 10]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   Table 2 lists the lengths in octets for the KE payload with four
   variants of eFrodoKEM specified in this document.

      +============+==============+================+================+
      | KE         | KEM          | Payload Length | Data Size in   |
      | Method No. |              |  (for pk/ct)   |Octets (KEi/KEr)|
      +============+==============+================+================+
      | TBD38      |eFrodoKEM-976 |  15,640/       |  15,632/       |
      |            |-<AES>        |  15,752        |  15,744        |
      +------------+--------------+----------------+----------------+
      | TBD39      |eFrodoKEM-976 |  15,640/       |  15,632/       |
      |            |-<SHAKE>      |  15,752        |  15,744        |
      +------------+--------------+----------------+----------------+
      | TBD40      |eFrodoKEM-1344|  21,528/       |  21,520/       |
      |            |-<AES>        |  21,640        |  21,632        |
      +------------+------------- +---------------------+-----------+
      | TBD41      |eFrodoKEM-1344|  21,528/       |  21,520/       |
      |            |-<SHAKE>      |  21,640        |  21,632        |
      +------------+--------------+----------------+----------------+

      Table 2: Lengths of Key Payload for 4 variants of eFrodoKEM.

5.  Security Considerations

   Basically, security considerations from [RFC7383], [RFC9242] and
   [RFC9370] apply to hybrid KEM exchange of ECDH, ML-KEM, and FrodoKEM
   described in this draft.

   Downgrade attacks on the authentication part of IKEv2 has been
   identied and repaired in "Prevention Downgrade Attacks on the
   Internet Key Exchange Protocol Version 2 (IKEv2)" [SP25].  Due to a
   flaw without authenticating the whole message received from the other
   peer, these attacks may lead an attacker to misleading the two peers
   to finally negotiate a weak KEM for key exchange.  These attacks
   apply to the IKEv2 [RFC7296], [RFC9370], and all extensions.  So,
   this specifictaion MUST be implemented with the updated mechanism for
   authenticaiton given by [SP25].

6.  IANA Considerations

   As specified in Section 3.2, this draft is to asking 4 values for
   registration in the "Transform Type 4 - Key Exchange Method Transform
   IDs" registry [IANA-IKEv2], maintained by IANA.  Namely, they are:
   "eFrodoKEM-976-<AES>", "eFrodoKEM-976-<SHAKE>", "eFrodoKEM-
   1344-<AES>", and "eFrodoKEM-1344-<SHAKE>".






Wang, et al.               Expires 8 May 2026                  [Page 11]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   Table 2 below gives the list of 6 IANA values for the 6 versions of
   eFrodoKEM.  The Recipient Tests field should point to this document
   as well.

      +========+===============+========+===============+============+
      | Number  | Name         | Status | Recipient     | Reference  |
      |         |              |        | Tests         |            |
      +=========+==============+========+===============+============+
      | TBD38   |eFrodoKEM-976 |        | [TBD, this    | [TBD, this |
      |         |-<AES>        |        | draft]        | draft]     |
      +---------+--------------+--------+---------------+------------+
      | TBD39   |eFrodoKEM-976 |        | [TBD, this    | [TBD, this |
      |         |-<SHAKE>      |        | draft]        | draft]     |
      +---------+--------------+--------+---------------+------------+
      | TBD40   |eFrodoKEM-1344|        | [TBD, this    | [TBD, this |
      |         |-<AES>        |        | draft]        | draft]     |
      +---------+------------- +--------+---------------+------------+
      | TBD41   |eFrodoKEM-1344|        | [TBD, this    | [TBD, this |
      |         |-<SHAKE>      |        | draft]        | draft]     |
      +---------+--------------+--------+---------------+------------+

      Table 3: Updates to the IANA "Transform Type 4 - Key Exchange"

7.  Acknowledgments

   To be added later.

8.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

   [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>.

   [RFC7383]  Smyslov, V., "Internet Key Exchange Protocol Version 2
              (IKEv2) Message Fragmentation", RFC 7383,
              DOI 10.17487/RFC7383, November 2014,
              <https://www.rfc-editor.org/info/rfc7383>.




Wang, et al.               Expires 8 May 2026                  [Page 12]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   [RFC9242]  Smyslov, V., "Intermediate Exchange in the Internet Key
              Exchange Protocol Version 2 (IKEv2)", RFC 9242,
              DOI 10.17487/RFC9242, May 2022,
              <https://www.rfc-editor.org/info/rfc9242>.

   [RFC9370]  Tjhai, CJ., Tomlinson, M., Bartlett, G., Fluhrer, S., Van
              Geest, D., Garcia-Morchon, O., and V. Smyslov, "Multiple
              Key Exchanges in the Internet Key Exchange Protocol
              Version 2 (IKEv2)", RFC 9370, DOI 10.17487/RFC9370, May
              2023, <https://www.rfc-editor.org/info/rfc9370>.

   [IANA-IKEv2]
              "Internet Key Exchange Version 2 (IKEv2) Parameters", the
              Internet Assigned Numbers Authority (IANA). ,
              <https://www.iana.org/assignments/ikev2-parameters/
              ikev2-parameters.xhtml>.

   [FrodoKEM] Alkim, E., Bos, J. W., Ducas, L., Longa, P., Mironov, I.,
              Naehrig, N., Nikolaenko, V., Peikert, C., Raghunathan, A.,
              and D. Stebila, "FrodoKEM: Learning With Errors Key
              Encapsulation", Preliminary Standardization Proposal
              submitted to ISO , December 2024,
              <https://frodokem.org/files/
              FrodoKEM_standard_proposal_20241205.pdf>.

9.  Informative References

   [I-D.D24]  F. Driscoll, F., "Terminology for Post-Quantum Traditional
              Hybrid Schemes", Work in Progress, Internet-Draft,
              February 2024, <https://datatracker.ietf.org/doc/draft-
              ietf-pquip-pqt-hybrid-terminology/>.

   [I-D.KR24] Kampanakis, K. and G. Ravago, "Post-quantum Hybrid Key
              Exchange with ML-KEM in the Internet Key Exchange Protocol
              Version 2 (IKEv2)", Work in Progress, Internet-Draft,
              November 2024, <https://datatracker.ietf.org/doc/draft-
              kampanakis-ml-kem-ikev2/>.

   [I-D.Kyber24]
              Schwabe, P. and B. Westerbaan, "Kyber Post-Quantum KEM",
              Work in Progress, Internet-Draft, January 2024,
              <https://datatracker.ietf.org/doc/draft-cfrg-schwabe-
              kyber/>.

   [OPM23]    Ott, D., Paterson, K., and D. Moreau, "Where Is the
              Research on Cryptographic Transition and Agility?",
              Communications of the ACM, 66(4): 29-32, January 2023.




Wang, et al.               Expires 8 May 2026                  [Page 13]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   [I-D.LBES25]
              Longa, P., Bos, J. W., Ehlen, S., and D. Stebila,
              "FrodoKEM: key encapsulation from learning with errors",
              Work in Progress, Internet-Draft, March 2025,
              <https://datatracker.ietf.org/doc/draft-longa-cfrg-
              frodokem/>.

   [FIPS203]  National Institute of Standards and Technology, "FIPS 203:
              Module-Lattice-Based Key-Encapsulation Mechanism
              Standard", Federal Information Processing Standards
              Publication , August 2024,
              <https://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.203.pdf>.

   [CD22]     Castryck, W. and T. Decru, "An Efficient Key Recovery
              Attack on SIDH", Formal version published in the
              proceddings of EUROCRYPT 2023 , July 2022,
              <https://eprint.iacr.org/2022/975>.

   [SP25]     Smyslov, V. and C. Patton, "Prevention Downgrade Attacks
              on the Internet Key Exchange Protocol Version 2 (IKEv2)",
              Work in Progress, Internet-Draft (Group Documet of
              IPSECME, IETF), October 2025,
              <https://datatracker.ietf.org/doc/draft-ietf-ipsecme-
              ikev2-downgrade-prevention/>.

Authors' Addresses

   Guilin Wang (editor)
   Huawei Int. Pte Ltd
   9 North Buona Vista Drive, #13-01
   The Metropolis Tower 1
   SINGAPORE 138588
   Singapore
   Email: wang.guilin@huawei.com


   Leonie Bruckert
   secunet Security Networks
   Ammonstr. 74
   01067 Dresden
   Germany
   Email: Leonie.Bruckert@secunet.com


   Valery Smyslov
   ELVIS-PLUS
   Russian Federation



Wang, et al.               Expires 8 May 2026                  [Page 14]

Internet-Draft           Hybrid KEM in the IKEv2           November 2025


   Email: smyslov.ietf@gmail.com


















































Wang, et al.               Expires 8 May 2026                  [Page 15]
