IPSECME Working Group S. Kampati
Internet-Draft Microsoft
Intended status: Standards Track W. Pan
Expires: 4 September 2025 Huawei
P. Wouters
Aiven
M. Bharath
Mavenir
M. Chen
CMCC
V. Smyslov
ELVIS-PLUS
3 March 2025
Optimized Rekeys in the Internet Key Exchange Protocol Version 2 (IKEv2)
draft-ietf-ipsecme-ikev2-sa-ts-payloads-opt-04
Abstract
This document describes a method for reducing the size of the
Internet Key Exchange version 2 (IKEv2) CREATE_CHILD_SA exchanges
used for rekeying of the IKE or Child SA by replacing the SA and TS
payloads with a Notify Message payload. Reducing size and complexity
of IKEv2 exchanges is especially useful for low power consumption
battery powered devices.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-ipsecme-ikev2-sa-ts-
payloads-opt/.
Discussion of this document takes place on the ipsec Working Group
mailing list (mailto:ipsec@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/ipsec/. Subscribe at
https://www.ietf.org/mailman/listinfo/ipsec/.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Kampati, et al. Expires 4 September 2025 [Page 1]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
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 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. Negotiation of Support for Optimized Rekey . . . . . . . . . 4
4. Optimized Rekey of IKE SA . . . . . . . . . . . . . . . . . . 5
5. Optimized Rekey of Child SAs . . . . . . . . . . . . . . . . 6
6. Payload Formats . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. OPTIMIZED_REKEY_SUPPORTED Notify . . . . . . . . . . . . 7
6.2. OPTIMIZED_REKEY Notify . . . . . . . . . . . . . . . . . 8
7. Interaction with IKEv2 Extensions . . . . . . . . . . . . . . 8
7.1. Multiple Key Exchanges . . . . . . . . . . . . . . . . . 8
7.2. IKE Session Resumption . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Operational Considerations . . . . . . . . . . . . . . . . . 9
10. Security Considerations . . . . . . . . . . . . . . . . . . . 10
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
12.1. Normative References . . . . . . . . . . . . . . . . . . 10
12.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
Kampati, et al. Expires 4 September 2025 [Page 2]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
1. Introduction
The Internet Key Exchange protocol version 2 (IKEv2) [RFC7296] is
used to negotiate Security Association (SA) parameters for the IKE SA
and the Child SAs. Cryptographic key material for these SAs have a
limited lifetime before it needs to be refreshed, a process referred
to as "rekeying". IKEv2 uses the CREATE_CHILD_SA exchange to rekey
either the IKE SA or the Child SAs.
When rekeying, a full set of negotiation parameters are exchanged.
However, most of these parameters will be the same as before. This
means that the security properties of the IKE or Child SA in practice
do not change during a typical rekey.
For example, the Traffic Selectors (TS) negotiated for the new Child
SA must cover the Traffic Selectors negotiated for the old Child SA.
And in practically all cases, a new Child SA does not need to cover a
wider set of traffic. In the rare case where this would be needed,
either a standard rekey could be used or a new Child SA could be
negotiated followed by a deletion of the replaced Child SA. Further,
per RFC 7296, the Traffic Selectors and algorithms should not change
when rekeying the Child SA.
This document specifies a method to omit these parameters and replace
them with a single Notify Message declaring that all these parameters
are identical to the originally negotiated parameters.
Large scale IKEv2 gateways such as Evolved Packet Data Gateway (ePDG)
in 4G networks or Centralized Radio Access Network (cRAN/Cloud)
gateways in 5G networks typically support more than 100,000 IKE/IPsec
connections. At any point in time, there will be hundreds or
thousands of IKE SAs and Child SAs that are being rekeyed. This
takes a large amount of bandwidth and CPU power and any protocol
simplification or bandwidth reducing would result in a significant
resource saving.
For Internet of Things (IoT) devices which utilize low power
consumption technology, reducing the size of the CREATE_CHILD_SA
exchange for rekeying reduces its power consumption, as sending bytes
over the air is usually the most power consuming operation of such a
device. Reducing the CPU operations required to verify the rekey
exchanges parameters will also save power and extend the lifetime for
these devices.
When using identical parameters for the IKE SA or Child SA rekey, the
SA and TS payloads can be omitted thanks to the optimization defined
in this document. For an IKE SA rekey, instead of the (large) SA
payload, only a Key Exchange (KE) payload, a Nonce payload, and a new
Kampati, et al. Expires 4 September 2025 [Page 3]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
Notify Type payload with the new Security Parameter Index (SPI) are
required. For a Child SA rekey, instead of the SA or TS payloads,
only an optional KE payload (when using PFS), a Nonce payload, and a
new Notify Type payload with the new SPI are needed. This makes the
rekey exchange packets much smaller and the peers do not need to
verify that the SA or TS parameters are compatible with the old SA
parameters.
2. Conventions Used in This Document
2.1. 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.
3. Negotiation of Support for Optimized Rekey
To indicate support for the optimized rekey negotiation, the
initiator includes the OPTIMIZED_REKEY_SUPPORTED notify payload in
the IKE_AUTH exchange request. If the responder supports this
optimized rekey and is configured to use it, then it includes the
OPTIMIZED_REKEY_SUPPORTED in the IKE_AUTH response message. If
multiple IKE_AUTH exchanges are sent, the OPTIMIZED_REKEY_SUPPORTED
notify payload should be in the first IKE_AUTH request and the last
IKE_AUTH response. During the IKE_AUTH exchanges, the entire SA and
TS payloads are included as normal. Note that the notify indicates
support for optimized rekey for both IKE and Child SAs.
A responder that does not support the optimized rekey exchange
processes the SA and TS payloads as normal, and does not include the
new Notify. As per regular IKEv2 processing, a responder that does
not recognize this new Notify, will ignore it. Responders may have
been administratively configured with the optimization turned off for
local reasons. The absence of the Notify indicates to the initiator
that the optimization is not available, and regular rekey should be
used.
The IKE_AUTH message exchange in this case is shown below:
Kampati, et al. Expires 4 September 2025 [Page 4]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
Initiator Responder
--------------------------------------------------------------------
HDR, SK {IDi, [CERT,] [CERTREQ,]
[IDr,] AUTH, SAi2, TSi, TSr,
N(OPTIMIZED_REKEY_SUPPORTED)} -->
<-- HDR, SK {IDr, [CERT,] AUTH,
SAr2, TSi, TSr,
N(OPTIMIZED_REKEY_SUPPORTED)}
If both peers have exchanged OPTIMIZED_REKEY_SUPPORTED notifies,
peers SHOULD use the optimized rekey method for rekeys. Non-
optimized, regular rekey requests MUST always be accepted. The
regular rekey can be retried when the optimized rekey fails.
Note that, except for the key and identification information such as
the SPI, the optimized rekey MUST inherit all other properties of the
SA being rekeyed. This means the configurations related to the SA
being rekeyed are supposed to have no changes. If there is a change
to the configurations, the regular rekey MUST be used instead. After
the regular rekey, the next rekey can use the optimized way if there
is no change to the configuration.
4. Optimized Rekey of IKE SA
The initiator of an optimized rekey request sends a CREATE_CHILD_SA
request with the OPTIMIZED_REKEY notify payload containing the new
SPI for the new IKE SA. It omits the SA payload.
The responder of an optimized rekey request replies with an included
OPTIMIZED_REKEY notify with its new IKE SPI and also omits the SA
payload.
Both parties send their nonce and KE payloads just as they would do
for a regular IKE SA rekey.
Using the old SPI from the IKE header and the two new SPIs
respectively from the initiator and responder's OPTIMIZED_REKEY
payloads, both parties can perform the IKE SA rekey operation.
The CREATE_CHILD_SA message exchange in this case is shown below:
Initiator Responder
--------------------------------------------------------------------
HDR, SK {N(OPTIMIZED_REKEY,newSPIi),
Ni, KEi} -->
<-- HDR, SK {N(OPTIMIZED_REKEY,newSPIr),
Nr, KEr}
Kampati, et al. Expires 4 September 2025 [Page 5]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
5. Optimized Rekey of Child SAs
The initiator of an optimized rekey request sends a CREATE_CHILD_SA
request with the OPTIMIZED_REKEY notify payload containing the new
SPI for the new Child SA. It omits the SA and TS payloads. If the
Child SA being rekeyed was negotiated with Perfect Forward Secrecy
(PFS), a KEi payload is included as well. If no PFS was negotiated
for the Child SA being rekeyed, a KEi payload is not included. If
the Child SA being rekeyed was created with IP compression, then
IPCOMP_SUPPORTED notifications MUST be sent as they contain the
required updated Compression Parameter Indexes (CPIs).
The responder of an optimized rekey request performs the same
process. It includes the OPTIMIZED_REKEY notify with its new SPI for
the new Child SA and omits the SA and TS payloads. Depending on the
PFS and IP compression negotiation of the Child SA being rekeyed, the
responder correspondingly includes a KEr payload and/or the
IPCOMP_SUPPORTED Notify payload.
Both parties send their nonce payloads just as they would do for a
regular Child SA rekey.
Using the old SPI from the REKEY_SA payload and the two new SPIs
respectively from the initiator and responder's OPTIMIZED_REKEY
payloads, both parties can perform the Child SA rekey operation.
Except for the key and identification information such as the SPI and
CPI, all other properties of the Child SA being rekeyed MUST be
inherited to the one newly created by the optimized rekey. Notify
payloads that can affect these properties, such as
USE_TRANSPORT_MODE, ESP_TFC_PADDING_NOT_SUPPORTED, ROHC_SUPPORTED
[RFC5857] or USE_AGGFRAG [RFC9347] MUST NOT be sent.
The CREATE_CHILD_SA message exchange in this case is shown below:
Initiator Responder
--------------------------------------------------------------------
HDR, SK {N(REKEY_SA,oldSPI), N(OPTIMIZED_REKEY,newSPIi),
Ni, [KEi,]} -->
<-- HDR, SK {N(OPTIMIZED_REKEY,newSPIr),
Nr, [KEr,]}
For the initial Child SA that was negotiated as part of an initial
IKE exchange (e.g., IKE_AUTH), at the time of its creation the
parameters of PFS and KE method for Child SAs are not negotiated.
Therefore, the KE method for the initial IKE SA should also be
recognized as the one for this initial Child SA.
Kampati, et al. Expires 4 September 2025 [Page 6]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
Two peers must have the same configurations for the parameters of PFS
and KE method for Child SAs.
If rekeying without PFS is required, the peer initiates the optimized
rekey request without a KEi payload. If rekeying with PFS is
required and the configured KE method for Child SAs is the same as
the one used by the Child SA being rekeyed, the peer initiates the
optimized rekey request with a KEi payload. The responder
correspondingly includes a KEr payload or not in its optimized rekey
response.
If the configured KE method for Child SAs is different from the one
used by the Child SA being rekeyed, this situation can be seen as
there is a configuration change, thus the regular rekey should be
used instead of the optimized rekey.
If the responder fails to process the optimized rekey request, e.g.,
receiving a request with a non-allowed PFS proposal, it MUST return
an error as the notification of type NO_PROPOSAL_CHOSEN. After
receiving the error response of the optimized rekey, the initiator
can retry a regular rekey.
6. Payload Formats
6.1. OPTIMIZED_REKEY_SUPPORTED Notify
The OPTIMIZED_REKEY_SUPPORTED Notify Message type notification is
used by the initiator and responder to indicate their support for the
optimized rekey negotiation.
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(=0)| SPI Size (=0) | Notify Message Type |
+---------------+---------------+-------------------------------+
* Protocol ID (1 octet) - MUST be 0.
* SPI Size (1 octet) - MUST be 0, meaning no SPI is present.
* Notify Message Type (2 octets) - MUST be set to the value TBD1.
This Notify Message type contains no data.
Kampati, et al. Expires 4 September 2025 [Page 7]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
6.2. OPTIMIZED_REKEY Notify
The OPTIMIZED_REKEY Notify Message type is used to perform an
optimized IKE SA or Child SA rekey.
0 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(=0)| SPI Size (=0) | Notify Message Type |
+---------------+---------------+-------------------------------+
| |
~ New SPI ~
| |
+---------------------------------------------------------------+
* Protocol ID (1 octet) - MUST be 0.
* SPI Size (1 octet) - MUST be 0. The "Security Parameter Index
(SPI)" field is not used in this Notify, and the new SPI is placed
in the "Notification Data" field.
* Notify Message Type (2 octets) - MUST be set to the value TBD2.
The Notification Data for this notify contains new SPI. Its size
depends on the type of SA being rekeyed. In case of IKE SA it MUST
be 8 octets. In case of Child SA it MUST be equal to the SPI Size
field in the REKEY_SA notification that identifies the SA being
rekeyed.
7. Interaction with IKEv2 Extensions
7.1. Multiple Key Exchanges
[RFC9370] defines the use of multiple key exchange methods for the
purpose of IKE SA and Child SA establishment in IKEv2. If multiple
key exchange methods are used for an SA, then optimized rekey of this
SA MUST use the same key exchange methods. It means that the
CREATE_CHILD_SA will be followed by some IKE_FOLLOWUP_KE exchanges
and the number of these exchanges will be determined by the number of
additional key exchange methods used for the SA being rekeyed.
7.2. IKE Session Resumption
IKE Session Resumption [RFC5723] defines an IKEv2 extension, that
allows peers to quickly restore IKE SA when it is for some reason
deleted. When used with optimized rekey, the following rules apply.
Kampati, et al. Expires 4 September 2025 [Page 8]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
* Support for optimized rekeys MUST be re-negotiated during the
resumption (in the IKE_AUTH exchange).
* If support for optimized rekey is negotiated during resumption,
then all IKE SA algorithms, including key exchange methods, are
taken from the resumption ticket (i.e., from the SA being
resumed), since they are not negotiated in the IKE_SA_RESUME
exchange.
* The initial Child SA created during the resumption is considered
as been created with key exchange methods for the IKE SA, that
were stored in the resumption ticket. This is despite the fact,
that during the resumption no key exhanges (e.g., Diffie-Hellman)
take place, the session keys are derived from the keys stored in
the resumption ticket.
8. IANA Considerations
This document defines two new Notify Message Types in the "IKEv2
Notify Message Types - Status Types" registry. IANA is requested to
assign codepoints in this registry.
NOTIFY messages: status types Value
----------------------------------------------------------
OPTIMIZED_REKEY_SUPPORTED TBD1
OPTIMIZED_REKEY TBD2
9. Operational Considerations
Some implementations allow sending rekey messages with a different
set of Traffic Selectors or cryptographic parameters in response to a
configuration update. IKEv2 [RFC7296] states this "SHOULD NOT" be
done. But if there is a configuration change that changes the
Traffic Selectors, cryptographic parameters, or other properties of
the SA, the regular rekey should be used to make the configuration
change active, since the optimized rekey can't express such changes.
Two peers' PFS policy and KE method configurations MUST be the same,
otherwise, the rekey of the Child SA created in the IKE_AUTH exchange
would fail. This issue is also discussed in detail in
[I-D.pwouters-ipsecme-child-pfs-info]. If the KE method for Child
SAs is negotiated during the creation of the initial Child SA via the
mechanism like [I-D.pwouters-ipsecme-child-pfs-info], this KE method
MUST be inherited when using the optimized method to rekey the
initial Child SA.
Kampati, et al. Expires 4 September 2025 [Page 9]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
10. Security Considerations
The optimized rekey removes sending unnecessary new parameters that
originally would have to be validated against the original
parameters. In that sense, this optimization enhances the security
of the rekey process by reducing the complexity and code required.
11. Acknowledgments
Special thanks go to Antony Antony and Tobias Brunner.
12. References
12.1. 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/rfc/rfc2119>.
[RFC5723] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange
Protocol Version 2 (IKEv2) Session Resumption", RFC 5723,
DOI 10.17487/RFC5723, January 2010,
<https://www.rfc-editor.org/rfc/rfc5723>.
[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/rfc/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/rfc/rfc8174>.
[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/rfc/rfc9370>.
12.2. Informative References
[I-D.pwouters-ipsecme-child-pfs-info]
Wouters, P., "IKEv2 support for Child SA PFS policy
notification", Work in Progress, Internet-Draft, draft-
pwouters-ipsecme-child-pfs-info-00, 3 March 2024,
<https://datatracker.ietf.org/doc/html/draft-pwouters-
ipsecme-child-pfs-info-00>.
Kampati, et al. Expires 4 September 2025 [Page 10]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
[RFC5857] Ertekin, E., Christou, C., Jasani, R., Kivinen, T., and C.
Bormann, "IKEv2 Extensions to Support Robust Header
Compression over IPsec", RFC 5857, DOI 10.17487/RFC5857,
May 2010, <https://www.rfc-editor.org/rfc/rfc5857>.
[RFC9347] Hopps, C., "Aggregation and Fragmentation Mode for
Encapsulating Security Payload (ESP) and Its Use for IP
Traffic Flow Security (IP-TFS)", RFC 9347,
DOI 10.17487/RFC9347, January 2023,
<https://www.rfc-editor.org/rfc/rfc9347>.
Authors' Addresses
Sandeep Kampati
Microsoft
India
Email: skampati@microsoft.com
Wei Pan
Huawei Technologies
101 Software Avenue, Yuhuatai District
Nanjing
Jiangsu,
China
Email: william.panwei@huawei.com
Paul Wouters
Aiven
Email: paul.wouters@aiven.io
Meduri S S Bharath
Mavenir Systems Pvt Ltd
Manyata Tech Park
Bangalore
Karnataka
India
Email: bharath.meduri@mavenir.com
Meiling Chen
China Mobile
32 Xuanwumen West Street, West District
Beijing
100053
China
Kampati, et al. Expires 4 September 2025 [Page 11]
Internet-Draft Optimized Rekey of IKE & Child SAs March 2025
Email: chenmeiling@chinamobile.com
Valery Smyslov
ELVIS-PLUS
PO Box 81
Moscow (Zelenograd)
124460
Russian Federation
Phone: +7 495 276 0211
Email: svan@elvis.ru
Kampati, et al. Expires 4 September 2025 [Page 12]