Internet DRAFT - draft-pwouters-ipsecme-child-pfs-info

draft-pwouters-ipsecme-child-pfs-info







Network                                                       P. Wouters
Internet-Draft                                                     Aiven
Intended status: Standards Track                            3 March 2024
Expires: 4 September 2024


           IKEv2 support for Child SA PFS policy notification
                draft-pwouters-ipsecme-child-pfs-info-00

Abstract

   This document defines the CHILD_PFS_INFO Notify Message Status Type
   Payload for the Internet Key Exchange Protocol Version 2 (IKEv2) to
   support exchanging the policy for the Perfect Forward Secrecy (PFS)
   and Key Exchange (KE) method setting of the initial Child SA.

Status of This Memo

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   This Internet-Draft will expire on 4 September 2024.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Payload Format  . . . . . . . . . . . . . . . . . . . . .   3
   2.  CHILD_PFS_INFO Notify Status Message Payload  . . . . . . . .   3
   3.  Usage of the CHILD_PFS_INFO Notify  . . . . . . . . . . . . .   3
   4.  Operational Considerations  . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Libreswan . . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The IKEv2 [RFC7296] protocol uses the Keying Exchange (KE) payload,
   formerly known as the Diffie-Hellman Group Transform payload to
   create an ephemeral IKE connection.  During an IKE rekey, a new KE
   payload is used to create a new ephemeral IKE connection, resulting
   in Perfect Forward Secrecy (PFS).

   A Child SA optionally uses its own PFS settings by including its own
   KE payload and list of acceptable Keying Exchange methods.  During
   Child SA rekeys, KE payloads of acceptable eying Exchange methods are
   exchanged to create PFS.

   The Initial Exchanges establish both an IKE SA and a Child SA using
   the Keying Exchange method negotiated for the IKE SA.  Thus, after
   the Initial Exchange, the peers are not aware of each others PFS
   requirements for the existing Child SA.  It is common practise to
   either not do PFS for Child SAs, or to only use the same KE methods
   for both the IKE SA and all Child SAs.  But it is currently not
   possible to know this when the initial Child SA is established.  The
   peers find out about this problem only at the next Child SA rekey,
   which is typically 1 to 8 hours later.

   This document introduces the CHILD_PFS_INFO Notify payload to
   exchange this information during the Initial Exchanges









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1.1.  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.

1.2.  Payload Format

   All multi-octet fields representing integers are laid out in big
   endian order (also known as "most significant byte first", or
   "network byte order").

2.  CHILD_PFS_INFO Notify Status Message Payload

                       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        !
   +---------------+---------------+-------------------------------+
   !  Protocol ID  !   SPI Size    !      Notify Message Type      !
   +---------------+---------------+-------------------------------+
   ~ Key Eexchange methods list (KE list)                          ~
   +-------------------------------+-------------------------------+

   *  Protocol ID (1 octet) - MUST be 0.  MUST be ignored if not 0.

   *  SPI Size (1 octet) - MUST be 0.  MUST be ignored if not 0.

   *  Notify Status Message Type (2 octets) - set to [TBD1]

   *  list of one or more Key Exchange Methods

   The Key Exchange method list (KE list) contains KE values from the
   IANA "Transform Type 4 - Key Exchange Method Transform IDs" registry.
   Each entry is two octets.  If the KE list payload is a not a multiple
   of two, the entire payload MUST be ignored.

3.  Usage of the CHILD_PFS_INFO Notify

   The CHILD_PFS_INFO Notify payload is only sent during the IKE_AUTH
   Exchange that also contains the Key Exchange Method (KE) transform
   type.  This is typically the last (or only) IKE_AUTH Exchange.  When
   creating additional Child SA's using the CREATE_CHILD_SA Exchange,
   the Exchange already contains an optional KE payload and list of Key
   Exchange Method Transform IDs.  When rekeying such existing
   additional Child SA, a proper KE value (NONE or otherwise) is already



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   learned from the initial establishment of the Child SA during the
   initial CREATE_CHILD_SA Exchange and no CHILD_PFS_INFO is required.

   If PFS is completely disallowed, the KE list contains only the value
   0 (NONE).  If PFS is optional but allowed, the KE list contains the
   value 0 (NONE) as well as the other accepted values, eg 19 for
   "256-bit random ECP group".

   Unknown KE list entries MUST be ignored.

   A peer MUST return NO_PROPOSAL_CHOSEN if the CHILD_PFS_NOTIFY values
   received does not include an acceptable value that can be used for
   the KE payload and Transform Type 4 during a Child SA rekey.  This
   ensures that incomptabile peers will immediately fail the initial
   negotiation.

4.  Operational Considerations

   This document is a result of Operational Considers that have shown
   peers can run into broken IPsec connections at rekey time.  These are
   not obvious to the administrators as these usually do not sit around
   for a few hours to wait and see if the rekey process worked
   successfully.  The CHILD_PFS_INFO results in immediate negotiation
   failure that can be repaired before taking the IPsec connection into
   production.

   During rekey, the cryptographic strength of a rekeyed Child SA SHOULD
   remain at least as strong as the Child SA being rekeyed.  In practise
   this means the negotiated algorithms remain the same.  But some
   deployments use stronger settings for the IKE SA compared to its
   Child SAs, which means technically the initial Child SA uses a
   stronger KE method than for rekeys.  The CHILD_PFS_INFO payload
   exposes such settings to the peers during the Initial Exchanges, and
   peers can at that time accept or reject the child proposal.  Once the
   Initial Child SA containing CHILD_PFS_INFO is accepted, rekey
   proposals are guaranteed to be acceptable to both parties.  For
   example, an IKE SA could be using KE method 15 (3072-bit MODP) and
   specify in the CHILD_PFS_INFO that it accepts KE method 14 (2048-bit
   MODP) for this Child SA rekey.

   Deployments with a large number of Child SAs often use no PFS for
   their Child SAs.  It is computationally much cheaper to establish the
   large number of Child SAs and then immediately rekey the IKE SA.
   This method can also be used if the peer's Child SA KE methods are
   unacceptable.  If both peers accept the KE method of 0 (NONE), it can
   decide to rekey the Child SA without PFS and immediately rekey the
   IKE SA using its accepted KE method.




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5.  Security Considerations

   This document introduces no new security considerations, as it only
   causes an increased awareness of peer capabilities with respect to KE
   methods.

6.  Implementation Status

   [Note to RFC Editor: Please remove this section and the reference to
   [RFC6982] before publication.]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

   Authors are requested to add a note to the RFC Editor at the top of
   this section, advising the Editor to remove the entire section before
   publication, as well as the reference to [RFC7942].

6.1.  Libreswan

   Organization:  The Libreswan Project

   Name:  https://libreswan.org/

   Description:  An initial IKE implementation using the Private Use
      value 40961 for the Notify payload

   Level of maturity:  Beta

   Coverage:  Implements the draft's example reasons




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   Licensing:  GPLv2

   Implementation experience:  TBD

   Contact:  Libreswan Development: swan-dev@libreswan.org

7.  IANA Considerations

   This document defines one new IKEv2 Notify Message Type payload for
   the IANA "IKEv2 Notify Message Types - Status Types" registry.

         Value   Notify Type Messages - Status Types    Reference
         -----   ------------------------------    ---------------
         [TBD1]   CHILD_PFS_INFO                    [this document]

                                  Figure 1

8.  References

8.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

   [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>.

8.2.  Informative References

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982,
              DOI 10.17487/RFC6982, July 2013,
              <https://www.rfc-editor.org/info/rfc6982>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.





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Author's Address

   Paul Wouters
   Aiven
   Email: paul.wouters@aiven.io














































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