IKEv2 support for Child SA PFS policy notification
draft-pwouters-ipsecme-child-pfs-info-00
| Document | Type | Active Internet-Draft (individual) | |
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| Author | Paul Wouters | ||
| Last updated | 2024-03-03 | ||
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draft-pwouters-ipsecme-child-pfs-info-00
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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