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 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 4 September 2024. Copyright Notice Copyright (c) 2024 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. Wouters Expires 4 September 2024 [Page 1] Internet-Draft IKEv2 support for Child SA PFS policy no March 2024 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 Wouters Expires 4 September 2024 [Page 2] Internet-Draft IKEv2 support for Child SA PFS policy no March 2024 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 Wouters Expires 4 September 2024 [Page 3] Internet-Draft IKEv2 support for Child SA PFS policy no March 2024 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. Wouters Expires 4 September 2024 [Page 4] Internet-Draft IKEv2 support for Child SA PFS policy no March 2024 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 Wouters Expires 4 September 2024 [Page 5] Internet-Draft IKEv2 support for Child SA PFS policy no March 2024 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, . [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 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, . [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, . Wouters Expires 4 September 2024 [Page 6] Internet-Draft IKEv2 support for Child SA PFS policy no March 2024 Author's Address Paul Wouters Aiven Email: paul.wouters@aiven.io Wouters Expires 4 September 2024 [Page 7]