Internet DRAFT - draft-ietf-ipsecme-g-ikev2
draft-ietf-ipsecme-g-ikev2
Network Working Group V. Smyslov
Internet-Draft ELVIS-PLUS
Obsoletes: 6407 (if approved) B. Weis
Updates: 7296 (if approved) Independent
Intended status: Standards Track 26 February 2024
Expires: 29 August 2024
Group Key Management using IKEv2
draft-ietf-ipsecme-g-ikev2-11
Abstract
This document presents an extension to the Internet Key Exchange
version 2 (IKEv2) protocol for the purpose of a group key management.
The protocol is in conformance with the Multicast Security (MSEC) key
management architecture, which contains two components: member
registration and group rekeying. Both components are required for a
GCKS (Group Controller/Key Server) to provide authorized Group
Members (GMs) with IPsec group security associations. The group
members then exchange IP multicast or other group traffic as IPsec
packets.
This document obsoletes RFC 6407. This documents also updates RFC
7296 by renaming a transform type 5 from "Extended Sequence Numbers
(ESN)" to the "Replay Protection (RP)" and by renaming IKEv2
authentication method 0 from "Reserved" to "NONE".
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 29 August 2024.
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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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 6
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. G-IKEv2 Protocol . . . . . . . . . . . . . . . . . . . . . . 8
2.1. G-IKEv2 Integration into IKEv2 Protocol . . . . . . . . . 8
2.1.1. G-IKEv2 Transport and Port . . . . . . . . . . . . . 9
2.2. G-IKEv2 Payloads . . . . . . . . . . . . . . . . . . . . 9
2.3. G-IKEv2 Member Registration and Secure Channel
Establishment . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1. GSA_AUTH exchange . . . . . . . . . . . . . . . . . . 11
2.3.2. GSA_REGISTRATION Exchange . . . . . . . . . . . . . . 13
2.3.3. GM Registration Operations . . . . . . . . . . . . . 14
2.3.4. GCKS Registration Operations . . . . . . . . . . . . 16
2.4. Group Maintenance Channel . . . . . . . . . . . . . . . . 18
2.4.1. GSA_REKEY . . . . . . . . . . . . . . . . . . . . . . 19
2.4.2. GSA_INBAND_REKEY Exchange . . . . . . . . . . . . . . 25
2.4.3. Deletion of SAs . . . . . . . . . . . . . . . . . . . 25
2.5. Counter-based modes of operation . . . . . . . . . . . . 26
2.5.1. Allocation of Sender-ID . . . . . . . . . . . . . . . 27
2.5.2. GM Usage of Sender-ID . . . . . . . . . . . . . . . . 28
2.6. Replay Protection for Multicast Data-Security SAs . . . . 29
2.7. Encryption Transforms with Implicit IV . . . . . . . . . 29
3. Group Key Management and Access Control . . . . . . . . . . . 30
3.1. Key Wrap Keys . . . . . . . . . . . . . . . . . . . . . . 30
3.1.1. Default Key Wrap Key . . . . . . . . . . . . . . . . 31
3.2. GCKS Key Management Semantics . . . . . . . . . . . . . . 31
3.2.1. Forward Access Control Requirements . . . . . . . . . 31
3.3. GM Key Management Semantics . . . . . . . . . . . . . . . 32
3.4. SA Keys . . . . . . . . . . . . . . . . . . . . . . . . . 34
4. Header and Payload Formats . . . . . . . . . . . . . . . . . 35
4.1. G-IKEv2 Header . . . . . . . . . . . . . . . . . . . . . 35
4.2. Group Identification Payload . . . . . . . . . . . . . . 35
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4.3. Security Association - GM Supported Transforms Payload . 35
4.4. Group Security Association Payload . . . . . . . . . . . 35
4.4.1. Group Policies . . . . . . . . . . . . . . . . . . . 36
4.4.2. Group Security Association Policy Substructure . . . 37
4.4.3. Group Associated Policy Substructure . . . . . . . . 43
4.5. Key Download Payload . . . . . . . . . . . . . . . . . . 45
4.5.1. Key Bags . . . . . . . . . . . . . . . . . . . . . . 46
4.5.2. Group Key Bag Substructure . . . . . . . . . . . . . 46
4.5.3. Member Key Bag Substructure . . . . . . . . . . . . . 48
4.5.4. Key Wrapping . . . . . . . . . . . . . . . . . . . . 51
4.6. Delete Payload . . . . . . . . . . . . . . . . . . . . . 53
4.7. Notify Payload . . . . . . . . . . . . . . . . . . . . . 53
4.7.1. INVALID_GROUP_ID Notification . . . . . . . . . . . . 53
4.7.2. AUTHORIZATION_FAILED Notification . . . . . . . . . . 54
4.7.3. REGISTRATION_FAILED Notification . . . . . . . . . . 54
4.7.4. SENDER Notification . . . . . . . . . . . . . . . . . 54
4.7.5. REKEY_IS_NEEDED Notification . . . . . . . . . . . . 54
4.8. Authentication Payload . . . . . . . . . . . . . . . . . 54
5. Usigng G-IKEv2 Attributes . . . . . . . . . . . . . . . . . . 55
6. Interaction with IKEv2 Protocol Extensions . . . . . . . . . 58
6.1. Mixing Preshared Keys in IKEv2 for Post-quantum
Security . . . . . . . . . . . . . . . . . . . . . . . . 58
7. GDOI Protocol Extensions . . . . . . . . . . . . . . . . . . 60
8. Security Considerations . . . . . . . . . . . . . . . . . . . 60
8.1. GSA Registration and Secure Channel . . . . . . . . . . . 60
8.2. GSA Maintenance Channel . . . . . . . . . . . . . . . . . 60
8.2.1. Authentication/Authorization . . . . . . . . . . . . 60
8.2.2. Confidentiality . . . . . . . . . . . . . . . . . . . 60
8.2.3. Man-in-the-Middle Attack Protection . . . . . . . . . 60
8.2.4. Replay/Reflection Attack Protection . . . . . . . . . 61
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 61
9.1. New Registries . . . . . . . . . . . . . . . . . . . . . 61
9.2. Changes in the Existing IKEv2 Registries . . . . . . . . 63
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 65
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 65
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 66
12.1. Normative References . . . . . . . . . . . . . . . . . . 66
12.2. Informative References . . . . . . . . . . . . . . . . . 67
Appendix A. Use of LKH in G-IKEv2 . . . . . . . . . . . . . . . 71
A.1. Notation . . . . . . . . . . . . . . . . . . . . . . . . 71
A.2. Group Creation . . . . . . . . . . . . . . . . . . . . . 72
A.3. Simple Group SA Rekey . . . . . . . . . . . . . . . . . . 73
A.4. Group Member Exclusion . . . . . . . . . . . . . . . . . 73
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 74
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1. Introduction and Overview
This document presents an extension to IKEv2 [RFC7296] called
G-IKEv2, which allows performing a group key management. A group key
management protocol provides IPsec keys and policy to a set of IPsec
devices which are authorized to communicate using a Group Security
Association (GSA) defined in [RFC3740]. The data communications
within the group (e.g., IP multicast packets) are protected by a key
pushed to the group members (GMs) by the Group Controller/Key Server
(GCKS).
G-IKEv2 conforms to the Multicast Group Security Architecture
[RFC3740], Multicast Extensions to the Security Architecture for the
Internet Protocol [RFC5374] and the Multicast Security (MSEC) Group
Key Management Architecture [RFC4046]. G-IKEv2 replaces GDOI
[RFC6407], which defines a similar group key management protocol
using IKEv1 [RFC2409] (since deprecated by IKEv2). When G-IKEv2 is
used, group key management use cases can benefit from the simplicity,
increased robustness and cryptographic improvements of IKEv2 (see
Appendix A of [RFC7296]).
G-IKEv2 is composed of two phases: registration and rekeying. In the
registration phase a GM contacts a GCKS to register to a group and to
receive the necessary policy and the keying material to be able
communicate with the other GMs in the group as well as with the GCKS.
The rekeying phase allows the GCKS to periodically renew the keying
material for both GM-to-GM communications as well as for
communication between the GM and the GCKS.
G-IKEv2 defines two ways to perform registration. When a GM first
contacts a GCKS it uses the GSA_AUTH exchange (Section 2.3.1) to
register to a group. This exchange follows the IKE_SA_INIT exchange
(similarly to the IKE_AUTH exchange in IKEv2) and results in
establishing an IKE SA between the GM and the GCKS. During this
exchange the GCKS authenticates and authorizes the GM, then pushes
policy and keys used by the group to the GM. The other one is the
GSA_REGISTRATION exchange (Section 2.3.2), which a GM can use within
the already established IKE SA with the GCKS (e.g. for registering to
another group).
Refreshing the group keys can be performed either in an unicast mode
via the GSA_INBAND_REKEY exchange (Section 2.4.2) performed over an
specific IKE SA between a GM and a GCKS or in an multicast mode with
the GSA_REKEY pseudo exchange (Section 2.4.1), when new keys are
being distributed to all GMs.
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Large and small groups may use different sets of these mechanisms.
When a large group of devices are communicating, the GCKS is likely
to use the GSA_REKEY message for efficiency. This is shown in
Figure 1, where multicast communications indicated with double line.
(Note: For clarity, IKE_SA_INIT is omitted from Figure 1 and
Figure 2).
+--------+
+----IKEv2---->| GCKS |<----IKEv2----+
| +--------+ |
| || ^ |
| || | |
| || GSA_AUTH |
| || or |
| || GSA_REGISTRATION |
| || | |
GSA_AUTH || IKEv2 GSA_AUTH
or || | or
GSA_REGISTRATION GSA_REKEY | GSA_REGISTRATION
| || | |
| *==========**================* |
| || || | || |
v \/ \/ v \/ v
+-------+ +--------+ +-------+
| GM | ... | GM | ... | GM |
+-------+ +--------+ +-------+
|| || ||
*=====ESP/AH=====**=====ESP/AH====*
Figure 1: G-IKEv2 used in large groups
Alternatively, a small group may simply use the GSA_AUTH or
GSA_REGISTRATION as registration protocols, where the GCKS issues
rekeys using the GSA_INBAND_REKEY within the same IKE SA.
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GSA_AUTH or GSA_REGISTRATION, GSA_INBAND_REKEY
+--------------------IKEv2----------------------+
| |
| GSA_AUTH or GSA_REGISTRATION, |
| GSA_INBAND_REKEY |
| +-----------IKEv2-------------+ |
| | | |
| |GSA_AUTH or GSA_REGISTRATION,| |
| | GSA_INBAND_REKEY | |
| | +--IKEv2-+ | |
v v v v v v
+---------+ +----+ +----+ +----+
| GCKS/GM | | GM | | GM | | GM |
+---------+ +----+ +----+ +----+
|| || || ||
*==ESP/AH==**=====ESP/AH====**===ESP/AH===*
Figure 2: G-IKEv2 used in small groups
A combination of these approaches is also possible. For example, the
GCKS may use more robust GSA_INBAND_REKEY to provide keys for some
GMs (for example, those acting as senders in the group) and GSA_REKEY
for the rest. Note also, that GCKS may also be a GM (as shown in
Figure 2).
IKEv2 message semantics are preserved in that all communications
consists of message request-response pairs. The exception to this
rule is the GSA_REKEY pseudo-exchange, which is a single message
delivering group updates to the GMs.
1.1. Requirements Notation
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. Terminology
It is assumed that readers are familiar with the IPsec architecture
[RFC4301], and its extension for multicast [RFC5374]. This document
defines an extension to the IKEv2 protocol [RFC7296], so it is
assumed that readers have an understanding of this protocol. This
document uses a notation and conventions from [RFC7296] for
describing G-IKEv2 payloads and exchanges.
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The following key terms are used throughout this document (mostly
borrowed from [RFC3740], [RFC5374] and [RFC6407]).
Group
A set of IPsec devices that communicate to each other using
multicast.
Group Member (GM)
An IPsec device that belongs to a group. A Group Member is
authorized to be a Group Sender and/or a Group Receiver.
Group Receiver
A Group Member that is authorized to receive packets sent to a
group by a Group Sender.
Group Sender
A Group Member that is authorized to send packets to a group.
Group Key Management (GKM) Protocol
A key management protocol used by a GCKS to distribute IPsec
Security Association policy and keying material. A GKM protocol
is needed because a group of IPsec devices require the same SAs.
For example, when an IPsec SA describes an IP multicast
destination, the sender and all receivers need to have the group
SA.
Group Controller/Key Server (GCKS)
A Group Key Management (GKM) protocol server that manages IPsec
state for a group. A GCKS authenticates and provides the IPsec SA
policy and keying material to GMs.
Data-Security SA
A multicast SA between each multicast sender and the group's
receivers. The Data-Security SA protects data between member
senders and member receivers. One or more SAs are required for
the multicast transmission of data-messages from the Group Sender
to other group members. This specification relies on ESP and AH
as protocols for Data-Security SAs.
Rekey SA
A single multicast SA between the GCKS and all of the group
members. This SA is used for multicast transmission of key
management messages from the GCKS to all GMs.
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Group Security Association (GSA)
A collection of Data-Security SAs and Rekey SA necessary for a
Group Member to receive key updates. A GSA describes the working
policy for a group. Refer to [RFC4046] for additional
information.
Traffic Encryption Key (TEK)
The symmetric cipher key used in a Data-Security SA (e.g., IPsec
ESP) to protect traffic.
Key Encryption Key (KEK)
The symmetric cipher key used in a Rekey SA to protect
distribution of new keys.
Key Wrap Key (KWK)
The symmetric cipher key used to protect another key.
Group Associated Policy (GAP)
Group-wide policy not related to a particular SA.
Sender-ID
A unique identifier of a Group Sender in the context of an active
GSA, used to form Initialization Vector (IV) in counter-based
cipher modes.
Logical Key Hierarchy (LKH)
A group management method defined in Section 5.4 of [RFC2627].
2. G-IKEv2 Protocol
2.1. G-IKEv2 Integration into IKEv2 Protocol
G-IKEv2 is an extension to IKEv2 that provides group authorization,
secure policy and keys download from the GCKS to GMs.
G-IKEv2 is compatible with most IKEv2 extensions defined so far. In
particular, it is assumed that, if necessary, the IKE_INTERMEDIATE
exchanges [RFC9242] may be utilized while establishing the
registration SA. It is also believed that future IKEv2 extensions
will be possible to use with G-IKEv2, however, some IKEv2 extensions
require special handling when used with G-IKEv2. See Section 6 for
more details.
It is assumed that readers are familiar with the IKEv2 protocol, so
this document skips many details that are described in [RFC7296].
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2.1.1. G-IKEv2 Transport and Port
As IKEv2 extension, G-IKEv2 SHOULD use the IKEv2 ports (500, 4500).
G-IKEv2 MAY also use TCP transport for registration (unicast) IKE SA,
as defined in [RFC9329]. G-IKEv2 MAY also use UDP port 848, the same
as GDOI [RFC6407], because they serve a similar function. The
version number in the IKE header distinguishes the G-IKEv2 protocol
from GDOI protocol [RFC6407].
Section 2.23 of [RFC7296] describes how IKEv2 supports paths with
NATs. G-IKEv2 registration SA doesn't create any unicast IPsec SAs,
thus if a NAT is present between the GM and the GCKS, there is no
unicast ESP traffic to encapsulate in UDP. However, the actions
described in this section regarding the IKE SA MUST be honored. The
behavior of GMs and GCKS MUST NOT depend on the port used to create
the initial IKE SA. For example, if the GM and the GCKS used UDP
port 848 for the IKE_SA_INIT exchange, they will operate the same as
if they had used UDP port 500.
2.2. G-IKEv2 Payloads
In the following descriptions, the payloads contained in the G-IKEv2
messages are indicated by names as listed below.
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+==========+============================+=============+
| Notation | Payload | Defined in |
+==========+============================+=============+
| AUTH | Authentication | [RFC7296] |
+----------+----------------------------+-------------+
| CERT | Certificate | [RFC7296] |
+----------+----------------------------+-------------+
| CERTREQ | Certificate Request | [RFC7296] |
+----------+----------------------------+-------------+
| D | Delete | [RFC7296] |
+----------+----------------------------+-------------+
| GSA | Group Security Association | Section 4.4 |
+----------+----------------------------+-------------+
| HDR | IKEv2 Header | [RFC7296] |
+----------+----------------------------+-------------+
| IDg | Identification - Group | Section 4.2 |
+----------+----------------------------+-------------+
| IDi | Identification - Initiator | [RFC7296] |
+----------+----------------------------+-------------+
| IDr | Identification - Responder | [RFC7296] |
+----------+----------------------------+-------------+
| KD | Key Download | Section 4.5 |
+----------+----------------------------+-------------+
| KE | Key Exchange | [RFC7296] |
+----------+----------------------------+-------------+
| Ni, Nr | Nonce | [RFC7296] |
+----------+----------------------------+-------------+
| N | Notify | [RFC7296] |
+----------+----------------------------+-------------+
| SA | Security Association | [RFC7296] |
+----------+----------------------------+-------------+
| SAg | Security Association - GM | Section 4.3 |
| | Supported Transforms | |
+----------+----------------------------+-------------+
| SK | Encrypted | [RFC7296] |
+----------+----------------------------+-------------+
Table 1: Payloads used in G-IKEv2
Payloads defined as part of other IKEv2 extensions MAY also be
included in these messages. Payloads that may optionally appear in
G-IKEv2 messages will be shown in brackets, such as [CERTREQ].
G-IKEv2 defines several new payloads not used in IKEv2:
* IDg (Group ID) -- The GM requests the GCKS for membership into the
group by sending its IDg payload.
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* SAg (Security Association -- GM Supported Transforms) -- the GM
optionally sends supported transforms, so that GCKS may select a
policy appropriate for all members of the group (which is not
negotiated, unlike SA parameters in IKEv2).
* GSA (Group Security Association) -- The GCKS sends the group
policy to the GM using this payload.
* KD (Key Download) -- The GCKS sends the keys and the security
parameters to the GMs using this payload.
The details of the contents of each payload are described in
Section 4.
2.3. G-IKEv2 Member Registration and Secure Channel Establishment
Registration consists of a minimum of two exchanges, IKE_SA_INIT and
GSA_AUTH; member registration may have a few more messages exchanged
if the EAP method, cookie challenge (for DoS protection), negotiation
of Diffie-Hellman group or IKEv2 extensions based on [RFC9242] are
used. Each exchange consists of request/response pairs. The first
exchange IKE_SA_INIT is defined in IKEv2 [RFC7296]. This exchange
negotiates cryptographic algorithms, exchanges nonces and computes a
shared key between the GM and the GCKS. In addition to the
cryptographic algorithms negotiated for use in IKEv2 SA, a key wrap
algorithm is also negotiated in this exchange. This is achieved by
augmenting each proposed Encryption Algorithm transform with a new
"Key Wrap Algorithm" attribute. See Section 4.5.4 for details.
The second exchange GSA_AUTH is similar to the IKEv2 IKE_AUTH
exchange [RFC7296]. It authenticates the previously exchanged
messages, exchanges identities and certificates. The GSA_AUTH
messages are encrypted and integrity protected with keys established
through the previous exchanges, so the identities are hidden from
eavesdroppers and all fields in all the messages are authenticated.
The GCKS authorizes group members to be allowed into the group as
part of the GSA_AUTH exchange. Once the GCKS accepts a GM to join a
group it will provide the GM with the data-security keys (TEKs) and/
or group key encrypting key (KEK) as part of the GSA_AUTH response
message.
2.3.1. GSA_AUTH exchange
After the GM and GCKS complete the IKE_SA_INIT exchange, the GSA_AUTH
exchange MUST complete before any other exchanges defined in this
document can be done. GSA_AUTH is used to authenticate the previous
exchanges, exchange identities and certificates. G-IKEv2 also uses
this exchange for group member registration and authorization.
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The GSA_AUTH exchange is similar to the IKE_AUTH exchange with the
difference that its goal is to establish multicast Data-Security SAs
and optionally provide GM with the keys for Rekey SA. The set of
payloads in the GSA_AUTH exchange is slightly different, because
policy is not negotiated between the group member and the GCKS, but
instead provided by the GCKS for the GM. Note also, that GSA_AUTH
has its own exchange type, which is different from the IKE_AUTH
exchange type.
Note, that due to the similarities between IKE_AUTH and GSA_AUTH,
most IKEv2 extensions to the IKE_AUTH exchange (like [RFC6467]) can
also be used with the GSA_AUTH exchange.
Initiator (GM) Responder (GCKS)
-------------------- ------------------
HDR, SK{IDi, [CERT,] [CERTREQ,] [IDr,]
AUTH, IDg, [SAg,] [N(SENDER),] [N]} -->
Figure 3: GSA_AUTH Request
A group member initiates a GSA_AUTH request to join a group indicated
by the IDg payload. The GM may include an SAg payload declaring
which Transforms it is willing to accept. A GM that intends to act
as Group Sender SHOULD include a Notify payload status type of
SENDER, which enables the GCKS to provide any additional policy
necessary by group senders.
Initiator (GM) Responder (GCKS)
-------------------- ------------------
<-- HDR, SK{IDr, [CERT,]
AUTH, GSA, KD, [N]}
Figure 4: GSA_AUTH Normal Response
The GCKS responds with IDr, optional CERT, and AUTH payloads with the
same meaning as in IKE_AUTH. It also informs the group member of the
cryptographic policies of the group in the GSA payload and the key
material in the KD payload.
In addition to the IKEv2 error handling, the GCKS can reject the
registration request when the IDg is invalid or authorization fails,
etc. In these cases, see Section 4.7, the GSA_AUTH response will not
include the GSA and KD, but will include a Notify payload indicating
errors. If a GM included an SAg payload, and the GCKS chooses to
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evaluate it, and the GCKS detects that the group member cannot
support the security policy defined for the group, then the GCKS
SHOULD return a NO_PROPOSAL_CHOSEN. Other types of error
notifications can be INVALID_GROUP_ID, AUTHORIZATION_FAILED or
REGISTRATION_FAILED.
Initiator (GM) Responder (GCKS)
-------------------- ------------------
<-- HDR, SK{IDr, [CERT,] AUTH, N}
Figure 5: GSA_AUTH Error Response
If the group member finds the policy sent by the GCKS is
unacceptable, the member SHOULD initiate GSA_REGISTRATION exchange
sending IDg and the Notify NO_PROPOSAL_CHOSEN (see Section 2.3.2)).
2.3.2. GSA_REGISTRATION Exchange
Once the IKE SA between the GM and the GCKS is established, the GM
can use it for other registration requests, if this is needed. In
this scenario the GM will use the GSA_REGISTRATION exchange.
Payloads in the exchange are generated and processed as defined in
Section 2.3.1.
Initiator (GM) Responder (GCKS)
-------------------- ------------------
HDR, SK{IDg, [SAg,]
[N(SENDER),] [N]} -->
<-- HDR, SK{GSA, KD, [N]}
Figure 6: GSA_REGISTRATION Normal Exchange
As with GSA_AUTH exchange, the GCKS can reject the registration
request when the IDg is invalid or authorization fails, or GM cannot
support the security policy defined for the group (which can be
concluded by GCKS by evaluation of SAg payload). In this case the
GCKS returns an appropriate error notification as described in
Section 2.3.1.
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Initiator (GM) Responder (GCKS)
-------------------- ------------------
HDR, SK{IDg, [SAg,]
[N(SENDER),] [N]} -->
<-- HDR, SK{N}
Figure 7: GSA_REGISTRATION Error Exchange
This exchange can also be used if the group member finds the policy
sent by the GCKS is unacceptable. The group member SHOULD notify the
GCKS by sending IDg and the Notify type NO_PROPOSAL_CHOSEN, as shown
below. The GCKS in this case MUST remove the GM from the group IDg.
Initiator (GM) Responder (GCKS)
-------------------- ------------------
HDR, SK{IDg, N} -->
<-- HDR, SK{}
Figure 8: GM Reporting Errors in GSA_REGISTRATION Exchange
2.3.3. GM Registration Operations
A GM requesting registration contacts the GCKS using the IKE_SA_INIT
exchange. This exchange is unchanged from IKE_SA_INIT in the IKEv2
protocol. The IKE_SA_INIT exchange may optionally be followed by one
or more the IKE_INTERMEDIATE exchanges if the GM and the GCKS
negotiated use of IKEv2 extensions based on this exchange.
Next the GM sends the GSA_AUTH request message with the IKEv2
payloads from IKE_AUTH (without the SAi2, TSi and TSr payloads) along
with the Group ID informing the GCKS of the group the GM wishes to
join. An GM intending to emit data traffic SHOULD send a SENDER
Notify payload status. The SENDER notification not only signifies
that it is a sender, but provides the GM the ability to request
Sender-ID values, in case the Data-Security SA supports a counter
mode cipher. Section 2.5 includes guidance on requesting Sender-ID
values.
A GM may be limited in the Transforms IDs that it is able or willing
to use, and may find it useful to inform the GCKS which Transform IDs
it is willing to accept for different security protocols by including
the SAg payload into the request message. Proposals for Rekey SA
(with protocol GIKE_REKEY) and for Data-Security (AH [RFC4302] and/or
ESP [RFC4303]) SAs may be included into SAg. Each Proposal contains
a list of Transforms that the GM is able and willing to support for
that protocol. Valid transform types depend on the protocol (AH,
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ESP, GIKE_REKEY) and are defined in Figure 16. Other transform types
SHOULD NOT be included. The SPI length of each Proposal in an SAg is
set to zero, and thus the SPI field is empty. The GCKS MUST ignore
SPI length and SPI fields in the SAg payload.
Generally, a single Proposal for each protocol (GIKE_REKEY, AH/ESP)
will suffice, because the transforms are not negotiated, the GM
simply alerts the GCKS to restrictions it may have. In particular,
the restriction from Section 3.3 of [RFC7296] that AEAD and non-AEAD
transforms not be combined in a single proposal doesn't hold when the
SAg payload is being formed. However if the GM has restrictions on
combination of algorithms, this can be expressed by sending several
proposals.
Proposal Num field in Proposal substructure is treated specially in
SAg payload: it allows a GM to indicate that algorithms used in Rekey
SA and in Data-Security (AH and/or ESP) SAs are dependent. In
particular, Proposals for different protocols having the same value
in Proposal Num field are treated as a set, so that if GCKS uses
transforms from one of such Proposal for one protocol, then it MUST
only use transforms from one of the Proposals with the same value in
Proposal Num field for other protocols. For example, a GM may
support algorithms X and Y for both Rekey and Data-Security SAs, but
with a restriction that if X is used in Rekey SA, then only X can be
used in Data-Security SAs, and the same for Y. Use of the same value
in the Proposal Num field of different proposals indicates that the
GM expects these proposals to be used in conjunction with each other.
In the simplest case when no dependency between transforms exists,
all Proposals in SAg payload will have the same value in Proposal Num
field.
Although the SAg payload is optional, it is RECOMMENDED for the GM to
include this payload into the GSA_AUTH request to allow the GCKS to
select an appropriate policy.
A GM MAY also indicate the support for IPcomp by inclusion one or
more the IPCOMP_SUPPORTED notifications along with the SAg payload.
The Compression Parameter Index (CPI) in these notifications is set
to zero and MUST be ignored by the GCKS.
Upon receiving the GSA_AUTH response, the GM parses the response from
the GCKS authenticating the exchange using the IKEv2 method, then
processes the GSA and KD payloads.
The GSA payload contains the security policy and cryptographic
protocols used by the group. This policy describes the optional
Rekey SA (KEK), Data-Security SAs (TEK), and optional Group
Associated policy (GAP). If the policy in the GSA payload is not
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acceptable to the GM, it SHOULD notify the GCKS by initiating a
GSA_REGISTRATION exchange with a NO_PROPOSAL_CHOSEN Notify payload
(see Section 2.3.2). Note, that this should normally not happen if
the GM includes SAg payload in the GSA_AUTH request and the GCKS
takes it into account. Finally the KD payload is parsed providing
the keying material for the TEK and/or KEK. The KD payload contains
a list of key bags, where each key bag includes the keying material
for SAs distributed in the GSA payload. Keying material is matched
by comparing the SPIs in the key bags to SPIs previously included in
the GSA payloads. Once TEK keys and policy are matched, the GM
provides them to the data-security subsystem, and it is ready to send
or receive packets matching the TEK policy.
The GSA KEK policy MUST include the attribute GSA_INITIAL_MESSAGE_ID
with a first Message ID the GM should expect to receive if it is non-
zero. The value of the attribute MUST be checked by a GM against any
previously received Message ID for this group. If it is less than
the previously received number, it should be considered stale and
MUST be ignored. This could happen if two GSA_AUTH exchanges
happened in parallel, and the Message ID changed. This attribute is
used by the GM to prevent GSA_REKEY message replay attacks. The
first GSA_REKEY message that the GM receives from the GCKS will have
a Message ID greater or equal to the Message ID received in the
GSA_INITIAL_MESSAGE_ID attribute.
Once a GM successfully registers to the group it MUST replace any
information related to this group (policy, keys) that it might have
as a result of a previous registration with a new one.
Once a GM has received GIKE_REKEY policy during a registration, the
IKE SA MAY be closed. By convention, the GCKS closes the IKE SA.
The GKCS MAY choose to keep the IKE SA open for inband rekey,
especially for small groups. If inband rekey is used, then the
initial IKE SA can be rekeyed with the standard IKEv2 mechanism
described in Section 1.3.2 of [RFC7296]. If for some reason the IKE
SA is closed and no GIKE_REKEY policy is received during the
registration process, the GM MUST consider itself excluded from the
group. To continue participating in the group, the GM needs to re-
register.
2.3.4. GCKS Registration Operations
A G-IKEv2 GCKS passively listens for incoming requests from group
members. When the GCKS receives an IKE_SA_INIT request, it selects
an IKE proposal and generates a nonce and DH to include them in the
IKE_SA_INIT response.
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Upon receiving the GSA_AUTH request, the GCKS authenticates the group
member via the GSA_AUTH exchange. The GCKS then authorizes the group
member according to group policy before preparing to send the
GSA_AUTH response. If the GCKS fails to authorize the GM, it SHOULD
respond with an AUTHORIZATION_FAILED notify message. The GCKS SHOULD
also respond with an INVALID_GROUP_ID notify message if the requested
group is unknown to the GCKS or with an REGISTRATION_FAILED notify
message if there is a problem with the requested group (for example
the capacity of the group is exceeded).
The GSA_AUTH response will include the group policy in the GSA
payload and keys in the KD payload. If the GCKS policy includes a
group rekey option, it MUST include the GSA_INITIAL_MESSAGE_ID
attribute, specifying the starting Message ID the GCKS will use when
sending the GSA_REKEY message to the group members if this Message ID
is non-zero. This Message ID is used to prevent GSA_REKEY message
replay attacks and will be increased each time a GSA_REKEY message is
sent to the group. The GCKS data traffic policy is included in the
GSA TEK and keys are included in the KD TEK. The GAP MAY also be
included to provide the ATD and/or DTD (Section 4.4.3.1.1) specifying
activation and deactivation delays for SAs generated from the TEKs.
If the group member has indicated that it is a sender of data traffic
and one or more Data Security SAs distributed in the GSA payload
included a counter mode of operation, the GCKS responds with one or
more Sender-ID values (see Section 2.5).
[RFC5374] defines two modes of operation for multicast Data-Security
SAs: transport mode and tunnel mode with address preservation. In
the latter case outer source and destination addresses are taken from
the inner IP packet.
If the GCKS receives a GSA_REGISTRATION exchange with a request to
register a GM to a group, the GCKS will need to authorize the GM with
the new group (IDg) and respond with the corresponding group policy
and keys. If the GCKS fails to authorize the GM, it will respond
with the AUTHORIZATION_FAILED notification. The GCKS may also
respond with an INVALID_GROUP_ID or REGISTRATION_FAILED notify
messages for the reasons described above.
If a group member includes an SAg in its GSA_AUTH or GSA_REGISTRATION
request, the GCKS may evaluate it according to an implementation
specific policy.
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* The GCKS could evaluate the list of Transforms and compare it to
its current policy for the group. If the group member did not
include all of the ESP, AH or GIKE_REKEY Transforms that match the
current group policy or the capabilities of all other currently
active GMs, then the GCKS SHOULD return a NO_PROPOSAL_CHOSEN
Notification.
* The GCKS could store the list of Transforms, with the goal of
migrating the group policy to a different Transforms when all of
the group members indicate that they can support that Transforms.
* The GCKS could store the list of Transforms and adjust the current
group policy based on the capabilities of the devices as long as
they fall within the acceptable security policy of the GCKS.
Depending on its policy, the GCKS may have no further need for the
IKE SA (e.g., it does not plan to initiate an GSA_INBAND_REKEY
exchange). If the GM does not initiate another registration exchange
or Notify (e.g., NO_PROPOSAL_CHOSEN), and also does not close the IKE
SA and the GCKS is not intended to use the SA, then after a short
period of time the GCKS SHOULD close the IKE SA.
2.4. Group Maintenance Channel
The GCKS is responsible for rekeying the secure group per the group
policy. Rekeying is an operation whereby the GCKS provides
replacement TEKs and KEK, deleting TEKs, and/or excluding group
members. The GCKS may initiate a rekey message if group membership
and/or policy has changed, or if the keys are about to expire. Two
forms of group maintenance channels are provided in G-IKEv2 to push
new policy to group members.
GSA_REKEY
The GSA_REKEY is a pseudo-exchange, consisting of a one-way IKEv2
message sent by the GCKS, where the rekey policy is delivered to
group members using IP multicast as a transport. This method is
valuable for large and dynamic groups, and where policy may change
frequently and a scalable rekey method is required. When the
GSA_REKEY is used, the IKE SA protecting the member registration
exchanges is usually terminated, and group members await policy
changes from the GCKS via the GSA_REKEY messages.
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GSA_INBAND_REKEY
The GSA_INBAND_REKEY is a normal IKEv2 exchange using the IKE SA
that was setup to protecting the member registration exchange.
This exchange allows the GCKS to rekey without using an
independent GSA_REKEY pseudo-exchange. The GSA_INBAND_REKEY
exchange provides a reliable policy delivery and is useful when
G-IKEv2 is used with a small group of cooperating devices.
Depending on its policy the GCKS MAY combine these two methods. For
example, it may use the GSA_INBAND_REKEY to deliver key to the GMs in
the group acting as senders (as this would provide reliable keys
delivery), and the GSA_REKEY for the rest GMs.
2.4.1. GSA_REKEY
The GCKS initiates the G-IKEv2 Rekey by sending a protected message
to the GMs, usually using IP multicast. Since the Rekey messages do
not require responses and they are sent to multiple GMs, the
windowing mechanism described in Section 2.3 of [RFC7296] MUST NOT be
used for the Rekey messages. The GCKS rekey message replaces the
rekey GSA KEK or KEK array (e.g. in case of LKH), and/or creates a
new Data-Security GSA TEK. The GM_SENDER_ID attribute in the Key
Download payload (defined in Section 4.5.3.3) MUST NOT be part of the
Rekey Exchange as this is sender specific information and the Rekey
Exchange is group specific. The GCKS initiates the GSA_REKEY pseudo-
exchange as following:
GMs (Receivers) GCKS (Sender)
----------------- ---------------
<-- HDR, SK{GSA, KD, [N] [AUTH]}
Figure 9: GSA_REKEY Pseudo-Exchange
HDR is defined in Section 4.1. The Message ID in this message will
start with the value the GCKS sent to the group members in the
attribute GSA_INITIAL_MESSAGE_ID or from zero if this attribute
wasn't sent. The Message ID will be incremented each time a new
GSA_REKEY message is sent to the group members.
The GSA payload contains the current policy for rekey and Data-
Security SAs. The GSA may contain a new Rekey SA and/or a new Data-
Security SAs Section 4.4.
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The KD payload contains the keys for the policy included in the GSA.
If the Data-Security SA is being refreshed in this rekey message, the
IPsec keys are updated in the KD, and/or if the rekey SA is being
refreshed in this rekey message, the rekey Key or the LKH KEK array
(e.g. in case of LKH) is updated in the KD payload.
A Delete payload MAY be included to instruct the GM to delete
existing SAs. See Section 4.6 for more detail.
The AUTH payload MUST be included to authenticate the GSA_REKEY
message if the authentication method is based on public key
signatures and MUST NOT be included if authentication is implicit.
In the latter case, the fact that a GM can decrypt the GSA_REKEY
message and verify its ICV proves that the sender of this message
knows the current KEK, thus authenticating the sender as a member of
the group. Note, that implicit authentication doesn't provide source
origin authentication. For this reason using implicit authentication
for GSA_REKEY is NOT RECOMMENDED unless source origin authentication
is not required (for example, in a small group of highly trusted
GMs). See more about authentication methods in Section 4.4.2.1.1.
During group member registration, the GCKS sends the authentication
key in the KD payload, AUTH_KEY attribute, which the group member
uses to authenticate the key server. Before the current
authentication key expires, the GCKS will send a new AUTH_KEY to the
group members in a GSA_REKEY message. The authentication key that is
sent in the rekey message may be not the same as the authentication
key sent during the GM registration. If implicit authentication is
used, then AUTH_KEY MUST NOT be sent to GMs.
2.4.1.1. GSA_REKEY Messages Authentication
The content of the AUTH payload generally depends on the
authentication method from the Authentication Method transform
(Section 4.4.2.1.1). This specification defines the use of only one
authentication method - Digital Signature, and the AUTH payload
contains digital signature calculated over the content of the not yet
encrypted GSA_REKEY message.
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The digital signing is applied to the concatenation of two chunks: A
and P. The chunk A starts with the first octet of the G-IKEv2 header
(not including prepended four octets of zeros, if port 4500 is used)
and continues to the last octet of the Encrypted Payload header. The
chunk P consists of the not yet encrypted content of the Encrypted
payload, excluding the Initialization Vector, the Padding, the Pad
Length and the Integrity Checksum Data fields (see 3.14 of [RFC7296]
for description of the Encrypted payload). In other words, the P
chunk is the inner payloads of the Encrypted payload in plaintext
form. Figure 10 illustrates the layout of the P and A chunks in the
GSA_REKEY message.
Before the calculation of the AUTH payload the inner payloads of
Encrypted payload must be fully formed and ready for encryption,
except for the content of the AUTH payload. The AUTH payload must
have correct values in the Payload Header, the Auth Method and the
RESERVED fields. The Authentication Data field is zeroed, but the
ASN.1 Length and the AlgorithmIdentifier fields must be properly
filled in, see [RFC7427].
For the purpose of the AUTH payload calculation the Length field in
the IKE header and the Payload Length field in the Encrypted Payload
header are adjusted so that they don't count the lengths of
Initialization Vector, Integrity Checksum Data and Padding (along
with Pad Length field). In other words, the Length field in the IKE
header (denoted as AdjustedLen in Figure 10 ) is set to the sum of
the lengths of A and P, and the Payload Length field in the Encrypted
Payload header (denoted as AdjustedPldLen in Figure 10) is set to the
length of P plus the size of the Payload header (four octets).
The input to the digital signature algorithm that computes the
content of the AUTH payload can be described as:
DataToAuthenticate = A | P
GsaRekeyMessage = GenIKEHDR | EncPayload
GenIKEHDR = [ four octets 0 if using port 4500 ] | AdjustedIKEHDR
AdjustedIKEHDR = SPIi | SPIr | . . . | AdjustedLen
EncPayload = AdjustedEncPldHdr | IV | InnerPlds | Pad | PadLen | ICV
AdjustedEncPldHdr = NextPld | C | RESERVED | AdjustedPldLen
A = AdjustedIKEHDR | AdjustedEncPldHdr
P = InnerPlds
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ^ ^
| G-IKEv2 SA Initiator's SPI | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I |
| G-IKEv2 SA Responder's SPI | K |
| | E |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Next Payload | MjVer | MnVer | Exchange Type | Flags | H A
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ d |
| Message ID | r |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| AdjustedLen | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ x |
| Next Payload |C| RESERVED | AdjustedPldLen | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | v
| | |
~ Initialization Vector ~ E
| | n
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ c ^
| | r |
~ Inner payloads (not yet encrypted) ~ P
| | P |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ l v
~ Padding (0-255 octets) | Pad Length | d
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
~ Integrity Checksum Data ~ |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ v
Figure 10: Data to Authenticate in the GSA_REKEY Messages
The authentication data is calculated using the authentication
algorithm from the Authentication Method transform
(Section 4.4.2.1.1) and the current authentication key provided in
the AUTH_KEY attribute (Section 4.5.3.2). The calculated
authentication data is placed into the AUTH payload, the Length
fields in the IKE Header and the Encryption Payload header are
restored, the content of the Encrypted payload is encrypted and the
ICV is computed using the current KEK keys.
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2.4.1.2. IKE Fragmentation
IKE fragmentation [RFC7383] can be used to perform fragmentation of
large GSA_REKEY messages; however, when the GSA_REKEY message is
emitted as an IP multicast packet there is a lack of response from
the GMs. This has the following implications.
* Policy regarding the use of IKE fragmentation is implicit. If a
GCKS detects that all GMs have negotiated support of IKE
fragmentation in IKE_SA_INIT, then it MAY use IKE fragmentation on
large GSA_REKEY messages.
* The GCKS must always use IKE fragmentation based on a pre-
configured fragmentation threshold, as there is no way to check if
fragmentation is needed by first sending unfragmented messages and
waiting for response. Section 2.5.1 of [RFC7383] contains
recommendation on selecting the fragmentation threshold.
* PMTU mechanism, defined in Section 2.5.2 of [RFC7383], cannot be
used due to lack of GSA_REKEY response messages.
The calculation of authentication data MUST be applied to whole
messages only, before possible IKE Fragmentation. If the message was
received in fragmented form, it should be reconstructed before
verifying its authenticity as if it were received unfragmented. The
RESERVED field in the reconstructed Encrypted Payload header MUST be
set to the value of the RESERVED field in the Encrypted Fragment
payload header from the first fragment (that with Fragment Number
equal to 1).
2.4.1.3. GSA_REKEY GCKS Operations
The GCKS builds the rekey message with a Message ID value that is one
greater than the value included in the previous rekey message. The
first message sent over a new Rekey SA MUST use Message ID of 0. The
GSA, KD, N and D payloads follow with the same characteristics as in
the GSA Registration exchange. The AUTH payload (if present) is
created as defined in Section 2.4.1.1.
Because GSA_REKEY messages are not acknowledged and could be
discarded by the network, one or more GMs may not receive the new
policy. To mitigate such lost messages, during a rekey event the
GCKS may transmit several copies of an encrypted GSA_REKEY message
with the new policy. The (encrypted) retransmitted messages MUST be
bitwise identical and SHOULD be sent within a short time interval (a
few seconds) to ensure that time-to-live would not be substantially
skewed for the GMs that would receive different copies of the
messages.
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GCKS may also include one or several GSA_NEXT_SPI attributes
specifying SPIs for the prospected rekeys, so that listening GMs are
able to detect lost rekey messages and recover from this situation.
See Sections Section 4.4.2.2.3 for more detail.
2.4.1.4. GSA_REKEY GM Operations
When a group member receives the Rekey message from the GCKS it
decrypts the message and verifies its integrity using the current
KEK. If the AUTH payload is present in the decrypted message, then
the GM validates authenticity of the message using the key retrieved
in a previous G-IKEv2 exchange. Then the GM verifies the Message ID,
and processes the GSA and KD payloads. The group member then
downloads the new Data-Security SA and/or new Rekey SA. The parsing
of the payloads is identical to the parsing done in the registration
exchange.
Replay protection is achieved by a group member rejecting a GSA_REKEY
message which has a Message ID smaller than the current Message ID
that the GM is expecting. The GM expects the Message ID in the first
GSA_REKEY message it receives to be equal or greater than the Message
ID it receives in the GSA_INITIAL_MESSAGE_ID attribute. Note, that
if the GSA_INITIAL_MESSAGE_ID attribute is not received for the Rekey
SA, the GM MUST assume zero as the first expected Message ID. The GM
expects the Message ID in subsequent GSA_REKEY messages to be greater
than the last valid GSA_REKEY message ID it received.
GSA_REKEY messages are sent infrequently (typically one per several
hours or, in extreme cases, several minutes), which is much greater
than typical network packet reordering intervals.
If the GSA payload includes a Data-Security SA using cipher in a
counter-modes of operation and the receiving group member is a sender
for that SA, the group member uses its current Sender-ID value with
the Data-Security SAs to create counter-mode nonces. If it is a
sender and does not hold a current Sender-ID value, it MUST NOT
install the Data-Security SAs. It MAY initiate a GSA_REGISTRATION
exchange to the GCKS in order to obtain an Sender-ID value (along
with the current group policy).
Once a new Rekey SA is installed as a result of GSA_REKEY message,
the current Rekey SA (over which the message was received) MUST be
silently deleted after waiting DEACTIVATION_TIME_DELAY interval
regardless of its expiration time. If the message includes Delete
payload for existing Data-Security SA, then after installing a new
Data-Security SA the old one, identified by the Protocol and SPI
fields in the Delete payload, MUST be silently deleted after waiting
DEACTIVATION_TIME_DELAY interval regardless of its expiration time.
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If a Data-Security SA is not rekeyed yet and is about to expire (a
"soft lifetime" expiration is described in Section 4.4.2.1 of
[RFC4301]), the GM SHOULD initiate a registration to the GCKS. This
registration serves as a request for current SAs, and will result in
the download of replacement SAs, assuming the GCKS policy has created
them. A GM SHOULD also initiate a registration request if a Rekey SA
is about to expire and not yet replaced with a new one.
2.4.2. GSA_INBAND_REKEY Exchange
When the IKE SA protecting the member registration exchange is
maintained while group member participates in the group, the GCKS can
use the GSA_INBAND_REKEY exchange to individually provide policy
updates to the group member.
GM (Responder) GCKS (Initiator)
---------------- ------------------
<-- HDR, SK{GSA, KD, [N]}
HDR, SK{} -->
Figure 11: GSA_INBAND_REKEY Exchange
Because this is a normal IKEv2 exchange, the HDR is treated as
defined in [RFC7296].
2.4.2.1. GSA_INBAND_REKEY GCKS Operations
The GSA, KD, N and D payloads are built in the same manner as in a
registration exchange.
2.4.2.2. GSA_INBAND_REKEY GM Operations
The GM processes the GSA, KD, N and D payloads in the same manner as
if they were received in a registration exchange.
2.4.3. Deletion of SAs
There are occasions when the GCKS may want to signal to group members
to delete policy at the end of a broadcast, or if group policy has
changed. Deletion of SAs is accomplished by sending the G-IKEv2
Delete Payload [RFC7296], section 3.11 as part of the GSA_REKEY
pseudo-exchange as shown below.
GMs (Receivers) GCKS (Sender)
---------------- ---------------
<-- HDR, SK{D, [N,] [AUTH]}
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Figure 12: SA Deletion in GSA_REKEY
If GCKS has a unicast SA with group member then it can use the
GSA_INBAND_REKEY exchange to delete SAs.
GM (Responder) GCKS (Initiator)
--------------- ------------------
<-- HDR, SK{D, [N,]}
HDR, SK{} -->
Figure 13: SA Deletion in GSA_INBAND_REKEY
The GCKS MAY specify the remaining active time of the policy by using
the GAP_DTD attribute in the GSA GAP substructure. If a GCKS has no
further SAs to send to group members, the GSA and KD payloads MUST be
omitted from the message.
There may be circumstances where the GCKS may want to start over with
a clean state, for example in case it runs out of available Sender-
IDs. The GCKS can signal deletion of all the Data-Security SAs by
sending a Delete payload with an SPI value equal to zero. For
example, if the GCKS wishes to remove the Rekey SA and all the Data-
Security SAs, the GCKS sends a Delete payload with an SPI of zero and
Protocol ID of AH or ESP, followed by another Delete payload with a
SPI of zero and Protocol ID of GIKE_REKEY.
If a group member receives a Delete payload with zero SPI and
protocol ID of GIKE_REKEY either via multicast Rekey SA or via
unicast SA using the GSA_INBAND_REKEY exchange, it means that the
group member is excluded from the group. The group member MUST re-
register if it wants to continue participating in this group. The
registration is performed as described in Section 2.3. Note, that if
the GSA_INBAND_REKEY exchange is used to exclude a group member from
the group, and thus the unicast SA between the group member and the
GCKS exists, then this SA persists after this exchange and the group
member may use the GSA_REGISTRATION exchange to re-register.
2.5. Counter-based modes of operation
Several counter-based modes of operation have been specified for ESP
(e.g., AES-CTR [RFC3686], AES-GCM [RFC4106], AES-CCM [RFC4309],
ChaCha20-Poly1305 [RFC7634], AES-GMAC [RFC4543]) and AH (e.g., AES-
GMAC [RFC4543]). These counter-based modes require that no two
senders in the group ever send a packet with the same Initialization
Vector (IV) using the same cipher key and mode. This requirement is
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met in G-IKEv2 when the following measures are taken:
* The GCKS distributes a unique key for each Data-Security SA.
* The GCKS uses the method described in [RFC6054], which assigns
each sender a portion of the IV space by provisioning each sender
with one or more unique Sender-ID values.
2.5.1. Allocation of Sender-ID
When at least one Data-Security SA included in the group policy
includes a counter-based mode of operation, the GCKS automatically
allocates and distributes one Sender-ID to each group member acting
in the role of sender on the Data-Security SA. The Sender-ID value
is used exclusively by the group sender to which it was allocated.
The group sender uses the same Sender-ID for each Data-Security SA
specifying the use of a counter-based mode of operation. A GCKS MUST
distribute unique keys for each Data-Security SA including a counter-
based mode of operation in order to maintain unique key and nonce
usage.
During registration, the group sender can choose to request one or
more Sender-ID values. Requesting a value of 1 is not necessary
since the GCKS will automatically allocate exactly one to the group
sender. A group sender MUST request as many Sender-ID values
matching the number of encryption modules in which it will be
installing the TEKs in the outbound direction. Alternatively, a
group sender MAY request more than one Sender-ID and use them
serially. This could be useful when it is anticipated that the group
sender will exhaust their range of Data- Security SA nonces using a
single Sender-ID too quickly (e.g., before the time-based policy in
the TEK expires).
When the group policy includes a counter-based mode of operation, a
GCKS SHOULD use the following method to allocate Sender-ID values,
which ensures that each Sender-ID will be allocated to just one group
sender.
1. A GCKS maintains an Sender-ID counter, which records the Sender-
IDs that have been allocated. Sender-IDs are allocated
sequentially, with zero as the first allocated value.
2. Each time an Sender-ID is allocated, the current value of the
counter is saved and allocated to the group sender. The Sender-
ID counter is then incremented in preparation for the next
allocation.
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3. When the GCKS specifies a counter-based mode of operation in the
Data-Security SA a group sender may request a count of Sender-IDs
during registration in a Notify payload information of type
SENDER. When the GCKS receives this request, it increments the
Sender-ID counter once for each requested Sender-ID, and
distributes each Sender-ID value to the group sender. The GCKS
SHOULD have a policy-defined upper bound for the number of
Sender-ID values that it will return irrespective of the number
requested by the GM.
4. A GCKS allocates new Sender-ID values for each registration
operation by a group sender, regardless of whether the group
sender had previously contacted the GCKS. In this way, the GCKS
is not required to maintaining a record of which Sender-ID values
it had previously allocated to each group sender. More
importantly, since the GCKS cannot reliably detect whether the
group sender had sent data on the current group Data-Security SAs
it does not know what Data-Security counter-mode nonce values
that a group sender has used. By distributing new Sender-ID
values, the key server ensures that each time a conforming group
sender installs a Data-Security SA it will use a unique set of
counter-based mode nonces.
5. When the Sender-ID counter maintained by the GCKS reaches its
final Sender-ID value, no more Sender-ID values can be
distributed. Before distributing any new Sender-ID values, the
GCKS MUST exclude all group members from the group as described
in Section 2.4.3. This will result in the group members
performing re-registration, during which they will receive new
Data-Security SAs and group senders will additionally receive new
Sender-ID values. The new Sender-ID values can safely be used
because they are only used with the new Data-Security SAs.
2.5.2. GM Usage of Sender-ID
A GM applies the Sender-ID to Data-Security SA as follows.
* The most significant bits of the IV indicated in the
GAP_SENDER_ID_BITS attribute (Section 4.4.3.1.2) are taken to be
the Sender-ID field of the IV.
* The Sender-ID is placed in the least significant bits of the
Sender-ID field, where any unused most significant bits are set to
zero. If the Sender-ID value doesn't fit into the number of bits
from the GAP_SENDER_ID_BITS attributes, then the GM MUST treat
this as a fatal error and re-register to the group.
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2.6. Replay Protection for Multicast Data-Security SAs
IPsec provides replay protection as part of its security services.
With multicast extension for IPsec replay protection is not always
possible to achieve (see Section 6.1 of [RFC3740]). In particular,
if there are many group senders for a Data-Security SA, then each of
them will independently increment the Sequence Number field in the
ESP header (see Section 2 of [RFC4303]) thus making it impossible for
the group receivers to filter out replayed packets. However, if
there is only one group sender for a Data-Security SA, then it is
possible to achieve replay protection with some restrictions (see
Section 4.4.2.1.3). The GCKS may create several Data-Security SAs
with the same traffic selectors allowing only a single group sender
in each SA if it is desirable to get replay protection with multiple
(but still limited number) of group senders.
IPsec architecture assumes that it is a local matter for an IPsec
receiver whether replay protection is active or not. In other words,
an IPsec sender always increments the Sequence Number field in the
ESP header and a receiver decides whether to check for replayed
packets or not. With multicast extension for IPsec this approach
generally isn't applicable, since group members don't know how many
group senders exist for a particular Data-Security SA. For this
reason the status or replay protection must be part of the policy
downloaded to GMs by GCKS.
For this purpose this specification re-uses the "Extended Sequence
Numbers" transform, defined in Section 3.3.2 [RFC7296]. This
specification renames this transform to "Replay Protection" and adds
a new value for possible Transform IDs: "Not Used" (<TBA by IANA>).
The GCKS MUST include this transform in the GSA payload for every
Data-Security SA. Note, that this specification prohibits using
Extended Sequence Numbers (see Section 4.4.2.1.3).
2.7. Encryption Transforms with Implicit IV
IKEv2 IANA registry for Encryption Algorithm Transform IDs
[IKEV2-IANA] defines several transforms with implicit IV. These
transforms rely on ESP Sequence Number for constructing IV (see
[RFC8750] for details). It requires replay protection to be enabled
for an ESP SA using these encryption transforms. Unless replay
protection is active for a multicast ESP SA (see Section 2.6,
encryption transforms that rely on Sequence Number for IV
construction MUST NOT be used. In any case, such transforms MUST NOT
be used for any G-IKEv2 SA (both unicast and multicast).
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3. Group Key Management and Access Control
Through the G-IKEv2 rekey, G-IKEv2 supports algorithms such as
Logical Key Hierarchy (LKH) that have the property of denying access
to a new group key by a member removed from the group (forward access
control) and to an old group key by a member added to the group
(backward access control). An unrelated notion to PFS, "forward
access control" and "backward access control" have been called
"perfect forward security" and "perfect backward security" in the
literature [RFC2627].
Group management algorithms providing forward and backward access
control other than LKH have been proposed in the literature,
including OFT [OFT] and Subset Difference [NNL]. These algorithms
could be used with G-IKEv2, but are not specified as a part of this
document.
The Group Key Management Method transform from the GSA policy
specifies how members of the group obtain group keys. This document
specifies a single method for the group key management -- Wrapped Key
Download. This method assumes that all group keys are sent to the
GMs by the GCKS encrypted with some other keys, called Key Wrap Keys
(KWK).
3.1. Key Wrap Keys
Every GM always knows at least one KWK -- the KWK that is associated
with the IKE SA or multicast Rekey SA the wrapped keys are sent over.
In this document it is called default KWK and is denoted as GSK_w.
The GCKS may also send other keys to GMs that will be used as Key
Wrap Keys for the purpose of building key hierarchy. Each KWK is
associated with an encryption algorithm from the Encryption Algorithm
transform used for the SA the key is sent over. The size of a KWK
MUST be of the size of the key for this Encryption Algorithm
transform (taking into consideration the Key Length attribute for
this transform if present). This association persists even if the
key is used later in the context of another SA with possibly
different Encryption Algorithm transform.
To have an ability to provide forward access control the GCKS
provides each GM with a personal key at the time of registration.
Besides, several intermediate keys that form a key hierarchy and are
shared among several GMs may be provided by the GCKS.
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3.1.1. Default Key Wrap Key
The default KWK (GSK_w) is only used in the context of a single IKE
SA. Every IKE SA (unicast IKE SA or multicast Rekey SA) will have
its own GSK_w. The GSK_w is used with the algorithm from the
Encryption Algorithm transform for the SA the GSK_w is used in the
context of.
For the unicast IKE SA (used for the GM registration and for the
GSA_INBAND_REKEY exchanges, if they are take place) the GSK_w is
computed as follows:
GSK_w = prf+(SK_d, "Key Wrap for G-IKEv2")
where the string "Key Wrap for G-IKEv2" is 20 ASCII characters
without null termination.
For the multicast Rekey SA the GSK_w is provided along with other SA
keys as defined in Section 3.4.
3.2. GCKS Key Management Semantics
Wrapped Key Download method allows the GCKS to employ various key
management methods
* A simple key management methods -- when the GCKS always sends
group SA keys encrypted with the GSK_w.
* An LKH key management method -- when the GCKS provides each GM
with an individual key at the time of the GM registration
(encrypted with GSK_w). Then the GCKS forms an hierarchy of keys
so that the group SA keys are encrypted with other keys which are
encrypted with other keys and so on, tracing back to the keys for
each GM.
Other key policies may also be employed by the GCKS.
3.2.1. Forward Access Control Requirements
When group membership is altered using a group management algorithm
new Data-Security SAs and their associated keys are usually also
needed. New Data-Security SAs and keys ensure that members who were
denied access can no longer participate in the group.
If forward access control is a desired property of the group, new TEK
policy and the associated keys MUST NOT be included in a G-IKEv2
rekey message which changes group membership. This is required
because the GSA TEK policy and the associated keys are not protected
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with the new KEK. A second G-IKEv2 rekey message can deliver the new
GSA TEKS and their associated keys because it will be protected with
the new KEK, and thus will not be visible to the members who were
denied access.
If forward access control policy for the group includes keeping group
policy changes from members that are denied access to the group, then
two sequential G-IKEv2 rekey messages changing the group KEK MUST be
sent by the GCKS. The first G-IKEv2 rekey message creates a new KEK
for the group. Group members, which are denied access, will not be
able to access the new KEK, but will see the group policy since the
G-IKEv2 rekey message is protected under the current KEK. A
subsequent G-IKEv2 rekey message containing the changed group policy
and again changing the KEK allows complete forward access control. A
G-IKEv2 rekey message MUST NOT change the policy without creating a
new KEK.
If other methods of using LKH or other group management algorithms
are added to G-IKEv2, those methods MAY remove the above restrictions
requiring multiple G-IKEv2 rekey messages, providing those methods
specify how the forward access control policy is maintained within a
single G-IKEv2 rekey message.
3.3. GM Key Management Semantics
This specification defines a GM Key Management semantics in such a
way, that it doesn't depend on the key management method employed by
the GCKS. This allows having all the complexity of key management in
the GCKS, which is free to implement various key management methods,
such as direct transmitting of group SA keys or using some kind of
key hierarchy (e.g. LKH). For all these policies the GM behavior is
the same.
Each key that a GM receives in G-IKEv2 is identified by a 32-bit
number called Key ID. Zero Key ID has a special meaning -- it always
contains keying material from which the keys for protecting Data-
Security SAs and Rekey SA are taken.
All keys in G-IKEv2 are transmitted in encrypted form, as specified
in Section 4.5.4. This format includes a Key ID (ID of a key that is
encrypted) and a KWK ID (ID of a key that was used to encrypt this
key). Keys may be encrypted either with default KWK (GSK_w) or with
other keys, which the GM has received in the WRAP_KEY attributes. If
a key was encrypted with GSK_w, then the KWK ID field is set to zero,
otherwise the KWK ID field identifies the key used for encryption.
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When a GM receives a message from the GCKS installing new Data-
Security or Rekey SA, it will contain a KD payload with an SA_KEY
attribute containing keying material for this SA. For a Data-
Security SA exactly one SA_KEY attribute will be present with both
Key ID and KWK ID fields set to zero. This means that the default
KWK (GSK_w) should be used to extract this keying material.
For a multicast Rekey SA multiple SA_KEY attributes may be present
depending on the key management method employed by the GCKS. If
multiple SA_KEY attributes are present then all of them MUST contain
the same keying material encrypted using different KWKs. The GM in
general is unaware of the key management method used by the GCKS and
can always use the same procedure to get the keys. The GM tries to
decrypt at least one of the SA_KEY attributes using either the GSK_w
or the keys from the WRAP_KEY attributes that are present in the same
message or were receives in previous messages.
We will use the term "Key Path" to describe an ordered sequence of
keys where each subsequent key was used to encrypt the previous one.
The GM keeps its own Key Path (called Working Key Path) in the memory
associated with each group it is registered to and updates it when
needed. When the GSA_REKEY message is received the GM processes the
received SA_KEY attributes one by one trying to construct a new key
path that starts from this attributes and ends with any key in the
Working Key Path or with the default KWK (GSK_w).
In the simplest case the SA_KEY attribute is encrypted with GSK_w so
that the new Key Path is empty. If more complex key management
methods are used then a Key Path will contain intermediate keys from
the WRAP_KEY attributes received by a GM so far starting from its
registration to the group. If the GM is able to construct a new Key
Path using intermediate keys it has, then it is able to decrypt the
SA_KEY attribute and use its content to form new SA keys. If it is
unable to build a new Key Path, then in means that the GM is excluded
from the group.
Depending on the new Key Path the GM should do the following actions
to be prepared for future key updates:
* If the new Key Path is empty then no actions are needed. This may
happen if no WRAP_KEY attributes from the received message were
used.
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* If the new Key Path is non-empty and it ends with the default KWK
(GSK_w), then the whole new Key Path is stored by the GM as the
GM's Working Key Path. This situation may only happen at the time
the GM is registering to the group, when the GCKS is providing it
with its personal key and the other keys from the key tree that
are needed for this GM. These keys form an initial Working Key
Path for this GM.
* In all other cases the new Key Path will end at some intermediate
key from the GM's current Working Key Path. In this case the new
Key Path is constructed by replacing a part of the GM's current
Working Key Path from the beginning and up to (but not including)
the key that the GM has used to decrypt the last key in the new
Key Path.
Appendix A contains an example of how this algorithm works in case of
LKH key management method.
3.4. SA Keys
The keys that are used for Data-Security SAs or Rekey SA (called here
SA keys) are downloaded to GMs in the form of keying material. The
keys for each algorithm employed in an SA are taken from this keying
material as if they were concatenated to form it.
For a Data-Security SA the keys are taken in accordance to the third
bullet from Section 2.17 of [RFC7296]. In particular, for the ESP
and AH SAs the encryption key (if any) MUST be taken from the
leftmost bits of the keying material and the integrity key (if any)
MUST be taken from the remaining bits.
For a Rekey SA the following keys are taken from the keying material:
GSK_e | GSK_a | GSK_w = KEYMAT
where GSK_e and GSK_a are the keys used for the Encryption Algorithm
and the Integrity Algorithm transforms for the corresponding SA and
GSK_w is a default KWK for this SA. Note, that GSK_w is also used
with the Encryption Algorithm transform as well as GSK_e. If an AEAD
algorithm is used for encryption, then SK_a key will not be used (GM
can use the formula above assuming the length of SK_a is zero).
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4. Header and Payload Formats
The G-IKEv2 is an IKEv2 extension and thus inherits its wire format
for data structures. However, the processing of some payloads are
different. Several new payloads are defined: Group Identification
(IDg, Section 4.2), Security Association - GM Supported Transforms
(SAg, Section 4.3), Group Security Association (GSA, Section 4.4),
and Key Download (KD, Section 4.5). G-IKEv2 header (Section 4.1),
IDg payload and SAg payload reuse IKEv2 format for the IKEv2 header,
IDi/IDr payloads and SA payload respectively. New exchange types
GSA_AUTH, GSA_REGISTRATION, GSA_REKEY and GSA_INBAND_REKEY are also
added.
This section describes new payloads and the differences in processing
of existing IKEv2 payloads.
4.1. G-IKEv2 Header
G-IKEv2 uses the same IKE header format as specified in [RFC7296]
section 3.1. Major Version is 2 and Minor Version is 0 as in IKEv2.
IKE SA Initiator's SPI, IKE SA Responder's SPI, Flags, Message ID,
and Length are as specified in [RFC7296].
4.2. Group Identification Payload
The Group Identification (IDg) payload allows the group member to
indicate which group it wants to join. The payload is constructed by
using the IKEv2 Identification Payload (section 3.5 of [RFC7296]).
ID type ID_KEY_ID MUST be supported. ID types ID_IPV4_ADDR, ID_FQDN,
ID_RFC822_ADDR, ID_IPV6_ADDR SHOULD be supported. ID types
ID_DER_ASN1_DN and ID_DER_ASN1_GN are not expected to be used. The
Payload Type for the Group Identification payload is fifty (50).
4.3. Security Association - GM Supported Transforms Payload
The Security Association - GM Supported Transforms Payload (SAg)
payload declares which Transforms a GM is willing to accept. The
payload is constructed using the format of the IKEv2 Security
Association payload (section 3.3 of [RFC7296]). The Payload Type for
SAg is identical to the SA Payload Type -- thirty-three (33).
4.4. Group Security Association Payload
The Group Security Association (GSA) payload is used by the GCKS to
assert security attributes for both Rekey SA and Data-Security SAs.
The Payload Type for the Group Security Association payload is fifty-
one (51).
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Group Policies> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: GSA Payload Format
The Security Association Payload fields are defined as follows:
* Next Payload, C, RESERVED, Payload Length fields comprise the
IKEv2 Generic Payload Header and are defined in Section 3.2. of
[RFC7296].
* Group Policies (variable) -- A set of group policies for the
group.
4.4.1. Group Policies
Group policies are comprised of two types of policy -- Group SA (GSA)
policy and Group Associated policy (GAP). GSA policy defines
parameters for the Security Association for the group. Depending on
the employed security protocol GSA policies may further be classified
as Rekey SA policy (GSA KEK) and Data-Security SA policy (GSA TEK).
GSA payload may contain zero or one GSA KEK policy, zero or more GSA
TEK policies, and zero or one GAP, where either one GSA KEK or GSA
TEK policy MUST be present.
This latitude allows various group policies to be accommodated. For
example if the group policy does not require the use of a Rekey SA,
the GCKS would not need to send a GSA KEK policy to the group member
since all SA updates would be performed using the GSA_INBAND_REKEY
exchange via the unicast IKE SA. Alternatively, group policy might
use a Rekey SA but choose to download a KEK to the group member only
as part of the unicast IKE SA. Therefore, the GSA KEK policy would
not be necessary as part of the GSA_REKEY message.
Specifying multiple GSA TEKs allows multiple related data streams
(e.g., video, audio, and text) to be associated with a session, but
each protected with an individual security association policy.
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A GAP allows for the distribution of group-wise policy, such as
instructions for when to activate and de-activate SAs.
Policies are distributed in substructures to the GSA payload. The
format of the substructures is defined below in Section 4.4.2 (for
GSA policy) and in Section 4.4.3 (for GAP). The first octet of the
substructure unambiguously determines its type -- it is zero for GAP
and non-zero (actually, it is a security protocol ID) for GSA
policies.
4.4.2. Group Security Association Policy Substructure
The GSA policy substructure contains parameters for the SA used with
this group. Depending on the security protocol the SA is either a
Rekey SA or a Data-Security SA (ESP and AH). It is NOT RECOMMENDED
that the GCKS distribute both ESP and AH policies for the same set of
Traffic Selectors.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | SPI Size | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ SPI ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Source Traffic Selector ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Destination Traffic Selector ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <GSA Transforms> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <GSA Attributes> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 15: GSA Policy Substructure Format
The GSA policy fields are defined as follows:
* Protocol (1 octet) -- Identifies the security protocol for this
group SA. The values are defined in the IKEv2 Security Protocol
Identifiers in [IKEV2-IANA]. The valid values for this field are:
<TBA> (GIKE_REKEY) for Rekey SA and 2 (AH) or 3 (ESP) for Data-
Security SAs.
* SPI Size (1 octet) -- Size of Security Parameter Index (SPI) for
the SA. SPI size depends on the SA protocol. For GIKE_REKEY it
is 16 octets, while for AH and ESP it is 4 octets.
* Length (2 octets, unsigned integer) -- Length of this substructure
including the header.
* SPI (variable) -- Security Parameter Index for the group SA. The
size of this field is determined by the SPI Size field. As
described above, these SPIs are assigned by the GCKS. In case of
GIKE_REKEY the SPI is the IKEv2 Header SPI pair where the first 8
octets become the "Initiator's SPI" field in the G-IKEv2 rekey
message IKEv2 HDR, and the second 8 octets become the "Responder's
SPI" in the same HDR. When selecting SPI the GCKS MUST make sure
that the sole first 8 octets (corresponding to "Initiator's SPI"
field in the IKEv2 header) uniquely identify the Rekey SA.
* Source & Destination Traffic Selectors (variable) -- Substructures
describing the source and destination of the network identities.
The format for these substructures is defined in IKEv2 [RFC7296],
section 3.13.1. For the Rekey SA (with the GIKE_REKEY protocol)
the destination traffic selectors MUST define a single multicast
IP address, an IP protocol (assumed to be UDP) and a single port
the GSA_REKEY messages will be destined to. The source traffic
selector in this case MUST either define a single IP address, an
IP protocol (assumed to be UDP) and a single port the GSA_REKEY
messages will be originated from or be a wildcard selector. For
the Data-Security (AH and ESP) SAs the destination traffic
selectors SHOULD define a single multicast IP address. The source
traffic selector in this case SHOULD define a single IP address or
be a wildcard selector. IP protocol and ports define the
characteristics of traffic protected by this Data-Security SA. If
the Data-Security SAs are created in tunnel mode, then it MUST be
tunnel mode with address preservation (see [RFC5374]. UDP
encapsulation [RFC3948] is not used for the multicast Data-
Security SAs.
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* GSA Transforms (variable) -- A list of Transform Substructures
specifies the policy information for the SA. The format is
defined in IKEv2 [RFC7296], section 3.3.2. The "Last Substruc"
field in each Transform Substructure is set to 3 except for the
last Transform Substructure, where it is set to 0.
Section 4.4.2.1 describes using IKEv2 transforms in GSA policy
substructure.
* GSA Attributes (variable) -- Contains policy attributes associated
with the group SA. The following sections describe the possible
attributes. Any or all attributes may be optional, depending on
the protocol and the group policy. Section 4.4.2.2 defines
attributes used in GSA policy substructure.
4.4.2.1. GSA Transforms
GSA policy is defined by means of transforms in the GSA policy
substructure. For this purpose the transforms defined in [RFC7296]
are used. In addition, new transform types are defined for using in
G-IKEv2: Authentication Method (AUTHMETH) and Group Key Management
Method (GKM), see Section 9.
Valid Transform Types depend on the SA protocol and are summarized in
the table below.
Protocol Mandatory Types Optional Types
----------------------------------------------------------------
GIKE_REKEY ENCR, INTEG*, PRF, AUTHMETH**, GKM**
ESP ENCR INTEG, RP
AH INTEG RP
Figure 16: Valid Transform Types
(*) If AEAD encryption algorithm is used, then INTEG transform MUST
NOT be specified, otherwise it MUST be specified.
(**) May only appear at the time of a GM registration, (in the
GSA_AUTH and GSA_REGISTRATION exchanges).
4.4.2.1.1. Authentication Method Transform
The Authentication Method (AUTHMETH) transform is used in the
GIKE_REKEY policy to convey information of how GCKS will authenticate
the GSA_REKEY messages. This values are from the IKEv2
Authentication Method registry [IKEV2-IANA]. Note, that this
registry defines only values in a range 0-255, so even that Transform
ID field in the Transform substructure allows for 65536 possible
values, in case of the Authentication Method transform the values
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256-65535 MUST NOT appear. This document renames the "Reserved" (0)
value in the "IKEv2 Authentication Method" registry [IKEV2-IANA] to
"NONE".
Among the currently defined authentication methods in the IKEv2
Authentication Method registry, only the following are allowed to be
used in the Authentication Method transform: NONE (0) and Digital
Signature (14). Other currently defined authentication methods MUST
NOT be used. The following semantics is associated with each of the
allowed methods.
NONE -- No authentication of the GSA_REKEY messages will be provided
by the GCKS besides the ability for the GMs to correctly
decrypt them and verify their ICV. In this case the GCKS MUST
NOT include the AUTH_KEY attribute into the KD payload.
Additionally, the AUTH payload MUST NOT be included in the
GIKE_REKEY messages.
Digital Signature -- Digital signatures will be used by the GCKS to
authenticate the GSA_REKEY messages. In this case the GCKS
MUST include the AUTH_KEY attribute containing the public key
into the KD payload at the time the GM is registered to the
group. To specify the details of the signature algorithm a new
attribute Signature Algorithm Identifier (<TBA by IANA>) is
defined. This attribute contains DER-encoded ASN.1 object
AlgorithmIdentifier, which would specify the signature
algorithm and the hash function that the GCKS will use for
authentication. The AlgorithmIdentifier object is defined in
section 4.1.1.2 of [RFC5280], see also [RFC7427] for the list
of common AlgorithmIdentifier values used in IKEv2. In case of
using digital signature the GCKS MUST include the Signature
Algorithm Identifier attribute in the Authentication Method
transform.
The authentication method MUST NOT change as a result of rekey
operations. This means that the Authentication Method transform may
not appear in the rekey messages, it may only appear in the
registration exchange (either GSA_AUTH or GSA_REGISTRATION).
The type of the Authentication Method Transform is <TBA by IANA>.
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4.4.2.1.2. Group Key Management Method Transform
The Group Key Management Method (GKM) transform is used in the
GIKE_REKEY policy to convey information of how GCKS will manage the
group keys to provide forward and backward access control (i.e., used
to exclude group members). Possible key management methods are
defined in a new IKEv2 registry "Transform Type <TBA> -- Group Key
Management Methods" (see Section 9). This document defines one
values for this registry:
Wrapped Key Download (<TBA by IANA>) -- Keys are downloaded by GCKS
to the GMs in encrypted form. This algorithm may provide
forward and backward access control if some form of key
hierarchy is used and each GM is provided with a personal key
at the time of registration. Otherwise no access control is
provided.
The group key management method MUST NOT change as a result of rekey
operations. This means that the Group Key Management Method
transform may not appear in the rekey messages, it may only appear in
the registration exchange (either GSA_AUTH or GSA_REGISTRATION).
The type of the Group Key Management Method transform is <TBA by
IANA>.
4.4.2.1.3. Replay Protection Transform
The "Extended Sequence Number (ESN)" Transform is defined in
[RFC7296]. This specification renames this transform to "Replay
Protection (RP)". This transform allows to specify whether the
64-bit Extended Sequence Numbers (ESN) are to be used in ESP and AH.
Since both AH [RFC4302] and ESP [RFC4303] are defined in such a way,
that high-order 32 bits of extended sequence numbers are never
transmitted, it makes using ESN in multicast Data-Security SAs
problematic, because GMs that join group long after it is created
will have to somehow learn the current high order 32 bits of ESN for
each sender in the group. The algorithm for doing this described in
[RFC4302] and [RFC4303] is resource-consuming and is only suitable
when a receiver is able to guess the high-order 32 bits close enough
to its real value, which is not the case for multicast SAs. For this
reason extended sequence numbers MUST NOT be used for multicast Data-
Security SAs and thus the value "Extended Sequence Numbers" (1) for
the Replay Protection transform type MUST NOT be used in the GSA
Payload. The GCKS MUST estimate the data rate and rekey Data-
Security SAs frequently enough so that Sequence Numbers (SN) don't
wrap.
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4.4.2.2. GSA Attributes
GSA attributes are generally used to provide GMs with additional
parameters for the GSA policy. Unlike security parameters
distributed via transforms, which are expected not to change over
time (unless policy changes), the parameters distributed via GSA
attributes may depend on the time the provision takes place, on the
existence of others group SAs or on other conditions.
This document creates a new IKEv2 IANA registry for the types of the
GSA attributes which is initially filled as described in Section 9.
In particular, the following attributes are initially added.
GSA Attributes Value Type Multi-Valued Protocol
---------------------------------------------------------------------
Reserved 0
GSA_KEY_LIFETIME 1 V NO GIKE_REKEY, AH, ESP
GSA_INITIAL_MESSAGE_ID 2 V NO GIKE_REKEY
GSA_NEXT_SPI 3 V YES GIKE_REKEY, AH, ESP
The attributes follow the format defined in the IKEv2 [RFC7296]
section 3.3.5. In the table, attributes that are defined as TV are
marked as Basic (B); attributes that are defined as TLV are marked as
Variable (V).
4.4.2.2.1. GSA_KEY_LIFETIME Attribute
The GSA_KEY_LIFETIME attribute (1) specifies the maximum time for
which the SA is valid. The value is a 4 octet unsigned integer in a
network byte order, specifying a valid time period in seconds. When
the lifetime expires, the group security association and all
associated keys MUST be deleted. The GCKS may delete the SA at any
time before the end of the validity period.
A single attribute of this type MUST be included into any GSA policy
substructure if multicast rekey is employed by the GCKS. This
attribute SHOULD NOT be used if inband rekey (via the
GSA_INBAND_REKEY exchange) is employed by the GCKS for the GM.
4.4.2.2.2. GSA_INITIAL_MESSAGE_ID Attribute
The GSA_INITIAL_MESSAGE_ID attribute (2) defines the initial Message
ID to be used by the GCKS in the GSA_REKEY messages. The Message ID
is a 4 octet unsigned integer in network byte order.
A single attribute of this type MUST be included into the GSA KEK
policy substructure if the initial Message ID of the Rekey SA is non-
zero. Note, that it is always the case if GMs join the group after
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some multicast rekey operations have already taken place, so in these
cases this attribute will be included into the GSA policy at the time
of GMs' registration.
This attribute MUST NOT be used if inband rekey (via the
GSA_INBAND_REKEY exchange) is employed by the GCKS for the GM.
4.4.2.2.3. GSA_NEXT_SPI Attribute
The optional GSA_NEXT_SPI attribute (3) contains SPI that the GCKS
reserved for the next Rekey SA or Data-Security SAs replacing the
current ones. The length of the attribute data is determined by the
SPI Size field in the GSA Policy substructure the attribute resides
in (see Section 4.4.2), and the attribute data contains SPI as it
would appear on the network. Multiple attributes of this type MAY be
included, meaning that any of the supplied SPIs can be used in the
replacement group SA.
The GM MAY store these values and if later the GM starts receiving
messages with one of these SPIs without seeing a rekey message over
the current Rekey SA, this may be used as an indication, that the
rekey message got lost on its way to this GM. In this case the GM
SHOULD re-register to the group.
Note, that this method of detecting lost rekey messages can only be
used by group receivers. Additionally there is no point to include
this attribute in the GSA_INBAND_REKEY messages, since they use
reliable transport. Note also, that the GCKS is free to forget its
promises and not to use the SPIs it sent in the GSA_NEXT_SPI
attributes before (e.g. in case of the GCKS is rebooted), so the GM
must only treat these information as a "best effort" made by the GCKS
to prepare for future rekeys.
This attribute MUST NOT be used if inband rekey (via the
GSA_INBAND_REKEY exchange) is employed by the GCKS for the GM.
4.4.3. Group Associated Policy Substructure
Group specific policy that does not belong to any SA policy can be
distributed to all group member using Group Associated Policy (GAP)
substructure.
The GAP substructure is defined as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | RESERVED | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <GAP Attributes> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: GAP Substructure Format
The GAP substructure fields are defined as follows:
* Protocol (1 octet) -- MUST be zero. This value is reserved in
Section 9 and is never used for any security protocol, so it is
used here to indicate that this substructure contains policy not
related to any specific protocol.
* RESERVED ( octet) -- MUST be zero on transmission, MUST be ignored
on receipt.
* Length (2 octets, unsigned integer) -- Length of this substructure
including the header.
* GAP Attributes (variable) -- Contains policy attributes associated
with no specific SA. The following sections describe possible
attributes. Any or all attributes may be optional, depending on
the group policy.
4.4.3.1. GAP Attributes
This document creates a new IKEv2 IANA registry for the types of the
GAP attributes which is initially filled as described in Section 9.
In particular, the following attributes are initially added.
GAP Attributes Value Type Multi-Valued
--------------------------------------------------------
Reserved 0
GAP_ATD 1 B NO
GAP_DTD 2 B NO
GAP_SENDER_ID_BITS 3 B NO
The attributes follow the format defined in the IKEv2 [RFC7296]
section 3.3.5. In the table, attributes that are defined as TV are
marked as Basic (B); attributes that are defined as TLV are marked as
Variable (V).
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4.4.3.1.1. GAP_ATD And GAP_DTD Attributes
Section 4.2.1 of [RFC5374] specifies a key rollover method that
requires two values be provided to group members -- Activation Time
Delay (ATD) and Deactivation Time Delay (DTD).
The GAP_ATD attribute (1) allows a GCKS to set the Activation Time
Delay for Data-Security SAs of the group. The ATD defines how long
active members of the group (those who sends traffic) should wait
after receiving new SAs before staring sending traffic over them.
Note, that to achieve smooth rollover passive members of the group
should activate the SAs immediately once they receive them.
The GAP_DTD attribute (2) allows the GCKS to set the Deactivation
Time Delay for previously distributed SAs. The DTD defines how long
after receiving a request to delete Data-Security SAs passive group
members should wait before actually deleting them. Note that active
members of the group should stop sending traffic over these old SAs
once new replacement SAs are activated (after time specified in the
GAP_ATD attribute).
The GAP_ATD and GAP_DTD attributes contain 16 bit unsigned integer in
a network byte order, specifying the delay in seconds. These
attributes are OPTIONAL. If one of them or both are not sent by the
GCKS, then no corresponding delay should be employed.
4.4.3.1.2. GAP_SENDER_ID_BITS Attribute
The GAP_SENDER_ID_BITS attribute (3) declares how many bits of the
cipher nonce are taken to represent a Sender-ID value. The bits are
applied as the most significant bits of the IV, as shown in Figure 1
of [RFC6054] and specified in Section 2.5.2. Guidance for a GCKS
choosing the value is provided in Section 3 of [RFC6054]. This value
is applied to each Sender-ID value distributed in the KD payload.
The GCKS MUST include this attribute if there are more than one
sender in the group and any of the Data-Security SAs use counter-
based cipher mode. The number of Sender-ID bits is represented as 16
bit unsigned integer in network byte order.
4.5. Key Download Payload
The Key Download (KD) payload contains the group keys for the SAs
specified in the GSA Payload. The Payload Type for the Key Download
payload is fifty-two (52).
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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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Key Bags> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: Key Download Payload Format
The Key Download payload fields are defined as follows:
* Next Payload, C, RESERVED, Payload Length fields comprise the
IKEv2 Generic Payload Header and are defined in Section 3.2. of
[RFC7296].
* Key Bags (variable) -- A set of Key Bag substructures.
4.5.1. Key Bags
Keys are distributed in a substructures called key bags. Each key
bag contains one or more keys that are logically related -- either
these are keys for a single SA (Data-Security SA or Rekey SA) or
these are keys for a single group member (in the latter case besides
keys the key bag may also contain security parameters for this group
member).
For this reason two types of key bags are defined -- Group Key Bag
and Member Key Bag. The type is unambiguously determined by the first
byte of the key bag substructure -- for member key bag it is zero and
for group key bag it represents the protocol number, which along with
the following SPI, identify the SA the keys in the bag are for.
4.5.2. Group Key Bag Substructure
The Group Key Bag substructure contains SA key information. This key
information is associated with some group SAs: either with Data-
Security SAs or with group Rekey SA.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | SPI Size | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ SPI ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Group Key Bag Attributes> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: Group Key Bag Substructure Format
* Protocol (1 octet) -- Identifies the security protocol for this
key bag. The values are defined in the IKEv2 Security Protocol
Identifiers in [IKEV2-IANA]. The valid values for this field are:
<TBA> (GIKE_REKEY) for KEK Key packet and 2 (AH) or 3 (ESP) for
TEK key bag.
* SPI Size (1 octet) -- Size of Security Parameter Index (SPI) for
the corresponding SA. SPI size depends on the security protocol.
For GIKE_REKEY it is 16 octets, while for AH and ESP it is 4
octets.
* Length (2 octets, unsigned integer) -- Length of this substructure
including the header.
* SPI (variable) -- Security Parameter Index for the corresponding
SA. The size of this field is determined by the SPI Size field.
In case of GIKE_REKEY the SPI is the IKEv2 Header SPI pair where
the first 8 octets become the "Initiator's SPI" field in the
G-IKEv2 rekey message IKEv2 HDR, and the second 8 octets become
the "Responder's SPI" in the same HDR. When selecting SPI the
GCKS MUST make sure that the sole first 8 octets (corresponding to
"Initiator's SPI" field in the IKEv2 header) uniquely identify the
Rekey SA.
* Group Key Bag Attributes (variable) -- Contains Key information
for the corresponding SA.
This document creates a new IKEv2 IANA registry for the types of the
Group Key Bag attributes which is initially filled as described in
Section 9. In particular, the following attributes are initially
added.
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Group Key Bag
Attributes Value Type Multi-Valued Protocol
------------------------------------------------------------
Reserved 0
SA_KEY 1 V NO/YES* GIKE_REKEY,
NO AH, ESP
(*) Multiple SA_KEY attributes may only appear for the GIKE_REKEY
protocol in the GSA_REKEY exchange if the GCKS uses the Group Key
Management method that allows excluding GMs from the group (like
LKH).
The attributes follow the format defined in the IKEv2 [RFC7296]
section 3.3.5. In the table, attributes that are defined as TV are
marked as Basic (B); attributes that are defined as TLV are marked as
Variable (V).
4.5.2.1. SA_KEY Attribute
The SA_KEY attribute (1) contains a keying material for the
corresponding SA. The content of the attribute is formatted
according to Section 4.5.4 with a precondition that the Key ID field
MUST always be zero. The size of the keying material MUST be equal
to the total size of the keys needed to be taken from this keying
material (see Section 3.4) for the corresponding SA.
If the key bag is for a Data-Security SA (AH or ESP protocols), then
exactly one SA_KEY attribute MUST be present with both Key ID and KWK
ID fields set to zero.
If the key bag is for a Rekey SA (GIKE_REKEY protocol), then in the
GSA_AUTH, GSA_REGISTRATION and GSA_INBAND_REKEY exchanges exactly one
SA_KEY attribute MUST be present. In the GSA_REKEY exchange at least
one SA_KEY attribute MUST be present, and more attributes MAY be
present (depending on the key management method employed by the
GCKS).
4.5.3. Member Key Bag Substructure
The Member Key Bag substructure contains keys and other parameters
that are specific for a member of the group and are not associated
with any particular group SA.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | RESERVED | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Member Key Bag Attributes> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: Member Key Bag Substructure Format
The Member Key Bag substructure fields are defined as follows:
* Protocol (1 octet) -- MUST be zero. This value is reserved in
Section 9 and is never used for any security protocol, so it is
used here to indicate that this key bag is not associated with any
particular SA.
* RESERVED ( octet) -- MUST be zero on transmission, MUST be ignored
on receipt.
* Length (2 octets, unsigned integer) -- Length of this substructure
including the header.
* Member Key Bag Attributes (variable) -- Contains Key information
and other parameters exclusively for a particular member of the
group.
The member Key Bag substructure contains sensitive information for a
single GM, for this reason it MUST NOT be sent in GSA_REKEY messages
and MUST only be sent via unicast SA at the time the GM registers to
the group (in either GSA_AUTH or GSA_REGISTRATION exchanges).
This document creates a new IKEv2 IANA registry for the types of the
Member Key Bag attributes which is initially filled as described in
Section 9. In particular, the following attributes are initially
added.
Member Key Bag
Attributes Value Type Multi-Valued
----------------------------------------------------
Reserved 0
WRAP_KEY 1 V YES
AUTH_KEY 2 V NO
GM_SENDER_ID 3 V YES
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The attributes follow the format defined in the IKEv2 [RFC7296]
section 3.3.5. In the table, attributes that are defined as TV are
marked as Basic (B); attributes that are defined as TLV are marked as
Variable (V).
4.5.3.1. WRAP_KEY Attribute
The WRAP_KEY attribute (1) contains a key that is used to encrypt
other keys. One or more these attributes are sent to GMs if the GCKS
key management method relies on some key hierarchy (e.g. LKH). This
attribute MUST NOT be used if inband rekey (via the GSA_INBAND_REKEY
exchange) is employed by the GCKS for the GM.
The content of the attribute has a format defined in Section 4.5.4
with a precondition that the Key ID field MUST NOT be zero. The
algorithm associated with the key is from the Encryption Transform
for the SA the WRAP_KEY attributes was sent in. The size of the key
MUST be equal to the key size for this algorithm.
Multiple instances of the WRAP_KEY attributes MAY be present in the
key bag.
4.5.3.2. AUTH_KEY Attribute
The AUTH_KEY attribute (2) contains the key that is used to
authenticate the GSA_REKEY messages. The content of the attribute
depends on the authentication method the GCKS specified in the
Authentication Method transform in the GSA payload.
* If digital signatures are used for the GSA_REKEY messages
authentication then the content of the AUTH_KEY attribute is a
public key used for digital signature authentication. The public
key MUST be represented as DER-encoded ASN.1 object
SubjectPublicKeyInfo, defined in section 4.1.2.7 of [RFC5280].
The signature algorithm that will use this key was specified in
the Signature Algorithm Identifier attribute of the Authentication
Method transform. The key MUST be compatible with this algorithm.
An RSA public key format is defined in [RFC8017], Section A.1.
DSS public key format is defined in [RFC3279] Section 2.3.2. For
ECDSA Public keys, use format described in [RFC5480] Section 2.
Other algorithms added to the IKEv2 Authentication Method registry
are also expected to include a format of the SubjectPublicKeyInfo
object included in the algorithm specification.
Multiple instances of the AUTH_KEY attributes MUST NOT be sent. This
attribute MUST NOT appear in the rekey operations (in the GSA_REKEY
or GSA_INBAND_REKEY exchanges).
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4.5.3.3. GM_SENDER_ID Attribute
The GM_SENDER_ID attribute (3) is used to download one or more
Sender-ID values for the exclusive use of a group member. One or
more of this attributes MUST be sent by the GCKS if the GM informed
the GCKS that it would be a sender (by inclusion the SENDER
notification to the request) and at least one of the Data-Security
SAs included in the GSA payload uses counter-based mode of
encryption.
If the GMs has requested multiple Sender-ID values in the SENDER
notification, then the GCKS SHOULD provide it with the requested
number of Sender-IDs by sending multiple instances of the
GM_SENDER_ID attribute. The GCKS MAY send fewer values than
requested by the GM (e.g. if it is running out of Sender-IDs), but it
MUST NOT send more than requested.
This attribute MUST NOT appear in the rekey operations (in the
GSA_REKEY or GSA_INBAND_REKEY exchanges).
4.5.4. Key Wrapping
Symmetric keys in G-IKEv2 are never sent in clear inside G-IKEv2
messages. They are always protected with other symmetric keys. This
protection is called key wrapping. Algorithms used for key wrapping
are usually based on generic encryption algorithms, but their mode of
operation is optimized for protecting short high-entropy data with
minimal additional overhead. While in general key wrap algorithms
can be generic, in practice they are often tied to the underlying
encryption algorithms. For example, [RFC5649] defines key wrapping
using AES and [ARX-KW] defines key wrapping using Chacha20.
In G-IKEv2 the key wrap algorithm MUST be negotiated in the
IKE_SA_INIT exchange, so that the GCKS be able to send encrypted keys
to the GM in the GSA_AUTH exchange. In addition, if the GCKS the
multicast Rekey SA for group rekey, then it MUST specify the key wrap
algorithm in the GSA payload. If SAg payload is included in the
GSA_AUTH request, then it MUST also indicate which key wrap
algorithms are supported by the GM.
The key wrap algorithm is specified by augmenting the Encryption
Algorithm transform with a new "Key Wrap Algorithm" attribute (<TBA
by IANA>). This way the key wrap algorithm is tied to the encryption
algorithm.
This document creates a new IKEv2 IANA registry for the key wrap
algorithms which is initially filled as described in Section 9. In
particular, the following entries are initially added.
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Key Wrap Algorithm Value
-------------------------------------
Reserved 0
KW_5649 1
ARX_KW 2
These algorithms are defined as follows.
* KW_5649 -- Key wrap algorithm defined in [RFC5649]. This
algorithm is designed for use with AES block cipher, but can also
be used with other block ciphers.
* ARX_KW -- The ARX-KW-8-2-4-GX key wrap algorithm defined in
[ARX-KW]. This algorithm is designed for use with Chacha20 stream
cipher.
More key wrap algorithms may be defined in future. The requirement
is that these algorithms MUST be able to wrap key material of size up
to 256 bytes.
The key wrap algorithm is used with the encryption algorithm that
protects the message the wrapped keys are sent in: in case of unicast
IKE SA (used for GMs registration and rekeying with GSA_INBAND_REKEY)
the encryption algorithm will be the one negotiated during the IKE SA
establishment, while for a GSA_REKEY message the algorithm will be
provided by the GCKS in the Encryption Algorithm transform in the GSA
payload when this multicast SA was being established. Note that key
wrap algorithms for these SAs may be different - for the unicast SA
the key wrap algorithms is negotiated between the GM and the GCKS,
while for the multicast Rekey SA the key wrap algorithm is provided
by the GCKS to the group members as part of the group policy.
The format of the wrapped key is shown in Figure 21.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| KWK ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Encrypted Key ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: Wrapped Key Format
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The Wrapped Key fields are defined as follows:
* Key ID (4 octets) -- ID of the encrypted key. The value zero
means that the encrypted key contains SA keys (in the form of
keying material, see Section 3.4)), otherwise it contains some
intermediate key.
* KWK ID (4 octets) -- ID of the key that was used to encrypt key
with specified Key ID. The value zero means that the default KWK
was used to encrypt the key, otherwise some intermediate key was
used.
* Encrypted Key (variable) -- The encrypted key bits. These bits
comprise either a single encrypted key or a result of encryption
of a concatenation of keys (key material) for several algorithms.
The format of this fields is determined by the key wrap algorithm
for the SA the wrapped key is sent over.
4.6. Delete Payload
Delete payload is used in G-IKEv2 when the GCKS wants to delete Data-
Security and Rekey SAs. The interpretation of the Protocol field in
the Delete payload is extended, so that zero protocol indicates
deletion of whole Group SA (i.e. all Data-Security SAs and Rekey SA).
See Section 2.4.3 for detail.
4.7. Notify Payload
G-IKEv2 uses the same Notify payload as specified in [RFC7296],
section 3.10.
There are additional Notify Message types introduced by G-IKEv2 to
communicate error conditions and status (see Section 9).
4.7.1. INVALID_GROUP_ID Notification
INVALID_GROUP_ID (45) is a new error type notification that indicates
that the group ID sent during the registration process is invalid.
The Protocol ID and SPI Size fields in the Notify payload MUST be
zero. There is no data associated with this notification and the
content of the Notification Data field MUST be ignored on receipt.
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4.7.2. AUTHORIZATION_FAILED Notification
AUTHORIZATION_FAILED (46) is a new error type notification that is
sent in the response to a GSA_AUTH or GSA_REGISTRATION message when
authorization failed. The Protocol ID and SPI Size fields in the
Notify payload MUST be zero. There is no data associated with this
notification and the content of the Notification Data field MUST be
ignored on receipt.
4.7.3. REGISTRATION_FAILED Notification
REGISTRATION_FAILED (<TBA>) is a new error type notification that is
sent by the GCKS when the GM registration request cannot be satisfied
for the reasons not related to this particular GM, for example if the
capacity of the group is exceeded. The Protocol ID and SPI Size
fields in the Notify payload MUST be zero. There is no data
associated with this notification and the content of the Notification
Data field MUST be ignored on receipt.
4.7.4. SENDER Notification
SENDER (16429) is a new status type notification that is sent in the
GSA_AUTH or the GSA_REGISTRATION exchanges to indicate that the GM
intends to be sender of data traffic. The data includes a count of
how many Sender-ID values the GM desires. The count MUST be 4 octets
long and contain the big endian representation of the number of
requested Sender-IDs. The Protocol ID and SPI Size fields in the
Notify payload MUST be zero.
4.7.5. REKEY_IS_NEEDED Notification
REKEY_IS_NEEDED (<TBA>) is a new status type notification that is
sent in the GSA_AUTH response message to indicate that the GM has to
perform an immediate rekey of IKE SA to make it secure against
quantum computers and then start a registration request over. The
Protocol ID and SPI Size fields in the Notify payload MUST be zero.
There is no data associated with this notification and the content of
the Notification Data field MUST be ignored on receipt.
4.8. Authentication Payload
G-IKEv2 uses the same Authentication payload as specified in
[RFC7296], section 3.8, to authenticate the rekey message. However,
if it is used in the GSA_REKEY messages the content of the payload is
computed differently, as described in Section 2.4.1.1.
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5. Usigng G-IKEv2 Attributes
G-IKEv2 defines a number of attributes, that are used to convey
information from GCKS to GMs. There are some restrictions on where
and when these attributes can appear in G-IKEv2 messages, which are
defined when the attributes are introduced. For convenience these
restrictions are summarized in Table 2 (for multicast rekey
operations) and Table 3 (for inband rekey operations) below.
The following notation is used:
S A single attribute of this type MUST be present
M Multiple attributes of this type MAY be present
[] Attribute is OPTIONAL
- Attribute MUST NOT be present
Note, that the restrictions are defined per a substructure
corresponding attributes are defined for and not per whole G-IKEv2
message.
+========================+==================+===========+=======+
| Attributes | GSA_AUTH | GSA_REKEY | Notes |
| | GSA_REGISTRATION | | |
+========================+==================+===========+=======+
| GSA Attributes (Section 4.4.2.2) |
+========================+==================+===========+=======+
| GSA_KEY_LIFETIME | S | S | |
+------------------------+------------------+-----------+-------+
| GSA_INITIAL_MESSAGE_ID | [S] | [S] | |
+------------------------+------------------+-----------+-------+
| GSA_NEXT_SPI | [M] | [M] | |
+========================+==================+===========+=======+
| GAP Attributes (Section 4.4.3.1) |
+========================+==================+===========+=======+
| GAP_ATD | [S] | [S] | |
+------------------------+------------------+-----------+-------+
| GAP_DTD | [S] | [S] | |
+------------------------+------------------+-----------+-------+
| GAP_SENDER_ID_BITS | S | - | 1 |
+========================+==================+===========+=======+
| Key Bag Attributes (Section 4.5.1) |
+========================+==================+===========+=======+
| SA_KEY | S | S[M] | 2 |
+------------------------+------------------+-----------+-------+
| WRAP_KEY | [M] | [M] | 3 |
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+------------------------+------------------+-----------+-------+
| AUTH_KEY | S | [S] | 4 |
+------------------------+------------------+-----------+-------+
| GM_SENDER_ID | S[M] | - | 1 |
+------------------------+------------------+-----------+-------+
| Notes: |
| |
| (1) The GAP_SENDER_ID_BITS attribute MUST be present if the |
| GCKS policy includes at least one cipher in counter |
| mode of operation and the GM included the SENDER notify |
| into the registration request. Otherwise it MUST NOT |
| be present. At least one GM_SENDER_ID attribute MUST |
| be present in the former case (and more MAY be present |
| if the GM requested more Sender-IDs) and it MUST NOT be |
| present in the latter case. |
| |
| (2) For a Data-Security SA exactly one SA_KEY attribute |
| MUST be present. For a Rekey SA one SA_KEY attribute |
| MUST be present in all cases and more these attributes |
| MAY be present in GSA_REKEY exchange. |
| |
| (3) The WRAP_KEY attributes MAY be present if the GCKS |
| employs key management method that relies on key tree |
| (like LKH). |
| |
| (4) The AUTH_KEY attribute MUST be present in the GSA_AUTH |
| / GSA_REGISTRATION exchanges if the GCKS employs |
| authentication method of rekey operations based on |
| digital signatures and MUST NOT be present if implicit |
| authentication is employed. The AUTH_KEY attribute |
| MUST be present in the GSA_REKEY exchange if the GCKS |
| employs authentication method based on digital |
| signatures and wants to change the public key for the |
| following multicast rekey operations. |
+---------------------------------------------------------------+
Table 2: Attributes in G-IKEv2 exchanges with multicast rekey
operations
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+========================+================+==================+=====+
| Attributes | GSA_AUTH | GSA_INBAND_REKEY |Notes|
| |GSA_REGISTRATION| | |
+========================+================+==================+=====+
| GSA Attributes (Section 4.4.2.2) |
+========================+================+==================+=====+
| GSA_KEY_LIFETIME | [S] | [S] | |
+------------------------+----------------+------------------+-----+
| GSA_INITIAL_MESSAGE_ID | - | - | |
+------------------------+----------------+------------------+-----+
| GSA_NEXT_SPI | - | - | |
+========================+================+==================+=====+
| GAP Attributes (Section 4.4.3.1) |
+========================+================+==================+=====+
| GAP_ATD | [S] | [S] | |
+------------------------+----------------+------------------+-----+
| GAP_DTD | [S] | [S] | |
+------------------------+----------------+------------------+-----+
| GAP_SENDER_ID_BITS | S | - | 1 |
+========================+================+==================+=====+
| Key Bag Attributes (Section 4.5.1) |
+========================+================+==================+=====+
| SA_KEY | S | S | |
+------------------------+----------------+------------------+-----+
| WRAP_KEY | - | - | |
+------------------------+----------------+------------------+-----+
| AUTH_KEY | - | - | |
+------------------------+----------------+------------------+-----+
| GM_SENDER_ID | S[M] | - | 1 |
+------------------------+----------------+------------------+-----+
| Notes: |
| |
| (1) The GAP_SENDER_ID_BITS attribute MUST be present if the |
| GCKS policy includes at least one cipher in counter mode |
| of operation and the GM included the SENDER notify into |
| the registration request. Otherwise it MUST NOT be |
| present. At least one GM_SENDER_ID attribute MUST be |
| present in the former case (and more MAY be present if the |
| GM requested more Sender-IDs) and it MUST NOT be present |
| in the latter case. |
+------------------------------------------------------------------+
Table 3: Attributes in G-IKEv2 exchanges with inband rekey
operations
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6. Interaction with IKEv2 Protocol Extensions
A number of IKEv2 extensions is defined that can be used to extend
protocol functionality. G-IKEv2 is compatible with most of them. In
particular, EAP authentication defined in [RFC7296] can be used to
establish registration IKE SA, as well as EAP-only authentication
[RFC5998] and Secure Password authentication [RFC6467]. G-IKEv2 is
compatible with and can use IKEv2 Redirect Mechanism [RFC5685] and
IKEv2 Session Resumption [RFC5723]. G-IKEv2 is also compatible with
Multiple Key Exchanges in IKEv2 framework, defined in [RFC9370].
The above list of compatible IKEv2 extensions is not exhaustive,
however some IKEv2 extensions require special handling if used in
G-IKEv2.
6.1. Mixing Preshared Keys in IKEv2 for Post-quantum Security
G-IKEv2 can take advantage of the protection provided by Postquantum
Preshared Keys (PPK) for IKEv2 [RFC8784]. However, the use of PPK
leaves the initial IKE SA susceptible to quantum computer (QC)
attacks. While group SA keys are protected with the default KWK
(GSK_w), which is derived from SK_d and thus cannot be broken even by
attacker equipped with a QC, authentication of these keys relies on
authentication of IKE SA messages, which is not secure against QC
until the initial IKE SA is rekeyed. In additional, the other
content of IKE SA messages may also be visible to an attacker with a
QC. See Section 6 of [RFC8784] for details.
For these reasons the GCKS MUST NOT send GSA and KD payloads in the
GSA_AUTH response message and MUST return a new notification
REKEY_IS_NEEDED instead. Upon receiving this notification in the
GSA_AUTH response the GM MUST perform an IKE SA rekey and then
initiate a new GSA_REGISTRATION request for the same group. This is
illustrated below.
The GM starts the IKE_SA_INIT exchange requesting using PPK, and the
GCKS responds with agreement to do it, or aborts according to its
"mandatory_or_not" flag:
Initiator (GM) Responder (GCKS)
-------------------- ------------------
HDR, SAi1, KEi, Ni, N(USE_PPK) -->
<-- DR, SAr1, KEr, Nr, [CERTREQ],
N(USE_PPK)
Figure 22: IKE_SA_INIT Exchange requesting using PPK
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The GM then starts the GSA_AUTH exchange with the PPK_ID; if using
PPK is not mandatory for the GM, the NO_PPK_AUTH notification is
included in the request:
Initiator (GM) Responder (GCKS)
-------------------- ------------------
HDR, SK{IDi, AUTH, IDg,
[SAg,] [N(SENDER),]
N(PPK_IDENTITY), N(NO_PPK_AUTH)} -->
Figure 23: GSA_AUTH Request using PPK
Assuming the GCKS has the proper PPK it continues with a request to
the GM to immediately perform a rekey by sending the REKEY_IS_NEEDED
notification:
Initiator (GM) Responder (GCKS)
-------------------- ------------------
<-- HDR, SK{IDr, AUTH, N(PPK_IDENTITY),
N(REKEY_IS_NEEDED) }
Figure 24: GSA_AUTH Response using PPK
The GM initiates the CREATE_CHILD_SA exchange to rekey the initial
IKE SA and then makes a new registration request for the same group
over the new IKE SA4 the GM also have to delete initial SA:
Initiator (GM) Responder (GCKS)
-------------------- ------------------
<initial IKE SA>
HDR, SK{SA, Ni, KEi} -->
<-- HDR, SK{SA, Nr, KEr}
HDR, SK{D} -->
<-- HDR, SK{}
<new IKE SA>
HDR, SK{IDg, [SAg,] [N(SENDER)]} --->
<-- HDR, SK{GSA, KD}
Figure 25: Rekeying IKE SA followed by GSA_REGISTRATION Exchange
Note, that [I-D.smyslov-ipsecme-ikev2-qr-alt] MAY be used to make the
initial IKE SA secure against QC.
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7. GDOI Protocol Extensions
Few extensions were defined for GDOI protocol [RFC6407], like
[RFC8052] or [RFC8263]. It is expected that these extensions will be
redefined for G-IKEv2 in separate documents, if needed.
8. Security Considerations
8.1. GSA Registration and Secure Channel
G-IKEv2 registration exchange uses IKEv2 IKE_SA_INIT protocols,
inheriting all the security considerations documented in the
Section 5 of [RFC7296], including authentication, confidentiality,
protection against man-in-the-middle, protection against replay/
reflection attacks, and denial of service protection. The GSA_AUTH
and GSA_REGISTRATION exchanges also take advantage of those
protections. In addition, G-IKEv2 brings in the capability to
authorize a particular group member regardless of whether they have
the IKEv2 credentials.
8.2. GSA Maintenance Channel
The GSA maintenance channel is cryptographically and integrity
protected using the cryptographic algorithm and key negotiated in the
GSA member registration exchange.
8.2.1. Authentication/Authorization
The authentication key is distributed during the GM registration, and
the receiver of the rekey message uses that key to verify the message
came from the authorized GCKS. An implicit authentication can also
be used, in which case the ability of the GM to decrypt and to verify
ICV of the received message proved that a sender of the message is a
member of the group. However, implicit authentication doesn't
provide source origin authentication, so the GM cannot be sure that
the message came from the GCKS. For this reason using implicit
authentication is NOT RECOMMENDED unless in a small group of trusted
parties.
8.2.2. Confidentiality
Confidentiality is provided by distributing a confidentiality key as
part of the GSA member registration exchange.
8.2.3. Man-in-the-Middle Attack Protection
GSA maintenance channel is integrity protected by using a digital
signature.
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8.2.4. Replay/Reflection Attack Protection
The GSA_REKEY message includes a monotonically increasing sequence
number to protect against replay and reflection attacks. A group
member will recognize a replayed message by comparing the Message ID
number to that of the last received rekey message, any rekey message
containing a Message ID number less than or equal to the last
received value MUST be discarded. Implementations should keep a
record of recently received GSA rekey messages for this comparison.
9. IANA Considerations
9.1. New Registries
A new set of registries is created for G-IKEv2 on IKEv2 parameters
page [IKEV2-IANA]. The terms Reserved, Expert Review and Private Use
are to be applied as defined in [RFC8126].
This document creates a new IANA registry "Transform Type <TBA> -
Group Key Management Methods". The initial values of the new
registry are:
Value Group Key Management Method
-------------------------------------------------------
Reserved 0
Wrapped Key Download 1
Unassigned 2-1023
Private Use 1024-65535
Changes and additions to the unassigned range of this registry are by
the Expert Review Policy [RFC8126].
This document creates a new IANA registry "GSA Attributes". The
initial values of the new registry are:
GSA Attributes Value Type Multi-Valued Protocol
---------------------------------------------------------------------
Reserved 0
GSA_KEY_LIFETIME 1 V N GIKE_REKEY, AH, ESP
GSA_INITIAL_MESSAGE_ID 2 V N GIKE_REKEY
GSA_NEXT_SPI 3 V Y GIKE_REKEY, AH, ESP
Unassigned 5-16383
Private Use 16384-32767
Changes and additions to the unassigned range of this registry are by
the Expert Review Policy [RFC8126].
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This document creates a new IANA registry "GAP Attributes". The
initial values of the new registry are:
GAP Attributes Value Type Multi-Valued
--------------------------------------------------------
Reserved 0
GAP_ATD 1 B NO
GAP_DTD 2 B NO
GAP_SENDER_ID_BITS 3 B NO
Unassigned 4-16383
Private Use 16384-32767
Changes and additions to the unassigned range of this registry are by
the Expert Review Policy [RFC8126].
This document creates a new IANA registry "Group Key Bag Attributes".
The initial values of the new registry are:
Group Key Bag
Attributes Value Type Multi-Valued Protocol
------------------------------------------------------------
Reserved 0
SA_KEY 1 V YES GIKE_REKEY,
NO AH, ESP
Unassigned 2-16383
Private Use 16384-32767
Changes and additions to the unassigned range of this registry are by
the Expert Review Policy [RFC8126].
This document creates a new IANA registry "Member Key Bag
Attributes". The initial values of the new registry are:
Member Key Bag
Attributes Value Type Multi-Valued
----------------------------------------------------
Reserved 0
WRAP_KEY 1 V YES
AUTH_KEY 2 V NO
GM_SENDER_ID 3 V YES
Unassigned 4-16383
Private Use 16384-32767
Changes and additions to the unassigned range of this registry are by
the Expert Review Policy [RFC8126].
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This document creates a new IANA registry "Key Wrap Algorithms". The
initial values of the new registry are:
Key Wrap Algorithm Value
-----------------------------
Reserved 0
KW_5649 1
ARX_KW 2
Unassigned 3-1023
Private Use 1024-65535
Changes and additions to the unassigned range of this registry are by
the Expert Review Policy [RFC8126].
9.2. Changes in the Existing IKEv2 Registries
This document defines new Exchange Types in the "IKEv2 Exchange
Types" registry:
Value Exchange Type
----------------------------
39 GSA_AUTH
40 GSA_REGISTRATION
41 GSA_REKEY
<TBA> GSA_INBAND_REKEY
This document defines new Payload Types in the "IKEv2 Payload Types"
registry:
Value Next Payload Type Notation
----------------------------------------------------
50 Group Identification IDg
51 Group Security Association GSA
52 Key Download KD
This document makes the following changes to the "Transform Type
Values" registry:
* Defines two new transform types -- "Authentication Method
(AUTHMETH)" and "Group Key Management Method (GKM)";
* Renames existing transform type "Extended Sequence Numbers (ESN)"
to "Replay Protection (RP)";
* Changes the "Used In" column for the existing allocations as
follows;
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Type Description Used In
---------------------------------------------------------------------
1 Encryption Algorithm (ENCR) IKE, GIKE_REKEY and ESP
2 Pseudo-random Function (PRF) IKE, GIKE_REKEY
3 Integrity Algorithm (INTEG) IKE, GIKE_REKEY, AH,
optional in ESP
4 Diffie-Hellman Group (D-H) IKE, optional in AH, ESP
5 Replay Protection (RP) AH and ESP
<TBA> Authentication Method (AUTHMETH) GIKE_REKEY
<TBA> Group Key Management Method (GKM) GIKE_REKEY
This document defines two new Attribute Types in the "IKEv2 Transform
Attribute Types" registry:
Value Attribute Type Format
------------------------------------------------------
<TBA> Signature Algorithm Identifier TLV
<TBA> Key Wrap Algorithm TV
This document renames the "Transform Type 5 - Extended Sequence
Numbers Transform IDs" registry to "Transform Type 5 - Replay
Protection Transform IDs" and also adds a new value into this
registry:
Number Name
---------------------
<TBA> Not Used
This document defines new Notify Message Types in the "Notify Message
Types - Error Types" registry:
Value Notify Messages - Error Types
-----------------------------------------
45 INVALID_GROUP_ID
46 AUTHORIZATION_FAILED
<TBA> REGISTRATION_FAILED
This document defines new Notify Message Types in the "Notify Message
Types - Status Types" registry:
Value Notify Messages - Status Types
------------------------------------------
16429 SENDER
The Notify type with the value 16429 was allocated earlier in the
development of G-IKEv2 document with the name SENDER_REQUEST_ID.
This specification changes its name to SENDER.
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This document defines a new Security Protocol Identifier in the
"IKEv2 Security Protocol Identifiers" registry:
Protocol ID Protocol
--------------------------
<TBA> GIKE_REKEY
This document renames the "Reserved" value in the "IKEv2
Authentication Method" registry to "NONE".
10. Acknowledgements
The authors thank Lakshminath Dondeti and Jing Xiang for first
exploring the use of IKEv2 for group key management and providing the
basis behind the protocol. Mike Sullenberger and Amjad Inamdar were
instrumental in helping resolve many issues in several versions of
the document.
The authors are grateful to Tero Kivinen, Daniel Migault, Gorry
Fairhurst and Russ Housley for their careful reviews and valuable
proposals for improving the document quality.
11. Contributors
The following individuals made substantial contributions to early
versions of this memo.
Sheela Rowles
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-527-7677
Email: sheela@cisco.com
Aldous Yeung
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-853-2032
Email: cyyeung@cisco.com
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Paulina Tran
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-526-8902
Email: ptran@cisco.com
Yoav Nir
Dell EMC
9 Andrei Sakharov St
Haifa 3190500
Israel
Email: ynir.ietf@gmail.com
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/info/rfc2119>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
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[RFC6054] McGrew, D. and B. Weis, "Using Counter Modes with
Encapsulating Security Payload (ESP) and Authentication
Header (AH) to Protect Group Traffic", RFC 6054,
DOI 10.17487/RFC6054, November 2010,
<https://www.rfc-editor.org/info/rfc6054>.
[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>.
[RFC7427] Kivinen, T. and J. Snyder, "Signature Authentication in
the Internet Key Exchange Version 2 (IKEv2)", RFC 7427,
DOI 10.17487/RFC7427, January 2015,
<https://www.rfc-editor.org/info/rfc7427>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
12.2. Informative References
[ARX-KW] Shinichi, S., "ARX-KW, a family of key wrapping
constructions using SipHash and ChaCha", January 2020,
<https://eprint.iacr.org/2020/059.pdf>.
[I-D.smyslov-ipsecme-ikev2-qr-alt]
Smyslov, V., "Alternative Approach for Mixing Preshared
Keys in IKEv2 for Post-quantum Security", Work in
Progress, Internet-Draft, draft-smyslov-ipsecme-ikev2-qr-
alt-09, 19 October 2023,
<https://datatracker.ietf.org/doc/html/draft-smyslov-
ipsecme-ikev2-qr-alt-09>.
[IKEV2-IANA]
IANA, "Internet Key Exchange Version 2 (IKEv2)
Parameters", <http://www.iana.org/assignments/ikev2-
parameters/ikev2-parameters.xhtml#ikev2-parameters-7>.
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[NNL] Naor, D., Noal, M., and J. Lotspiech, "Revocation and
Tracing Schemes for Stateless Receivers", Advances in
Cryptology, Crypto '01, Springer-Verlag LNCS 2139, 2001,
pp. 41-62, 2001,
<http://www.wisdom.weizmann.ac.il/~naor/PAPERS/2nl.pdf>.
[OFT] McGrew, D. and A. Sherman, "Key Establishment in Large
Dynamic Groups Using One-Way Function Trees",
Manuscript, submitted to IEEE Transactions on Software
Engineering, 1998, <https://pdfs.semanticscholar.org/
d24c/7b41f7bcc2b6690e1b4d80eaf8c3e1cc5ee5.pdf>.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,
<https://www.rfc-editor.org/info/rfc2409>.
[RFC2627] Wallner, D., Harder, E., and R. Agee, "Key Management for
Multicast: Issues and Architectures", RFC 2627,
DOI 10.17487/RFC2627, June 1999,
<https://www.rfc-editor.org/info/rfc2627>.
[RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April
2002, <https://www.rfc-editor.org/info/rfc3279>.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode With IPsec Encapsulating Security Payload
(ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004,
<https://www.rfc-editor.org/info/rfc3686>.
[RFC3740] Hardjono, T. and B. Weis, "The Multicast Group Security
Architecture", RFC 3740, DOI 10.17487/RFC3740, March 2004,
<https://www.rfc-editor.org/info/rfc3740>.
[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets",
RFC 3948, DOI 10.17487/RFC3948, January 2005,
<https://www.rfc-editor.org/info/rfc3948>.
[RFC4046] Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,
"Multicast Security (MSEC) Group Key Management
Architecture", RFC 4046, DOI 10.17487/RFC4046, April 2005,
<https://www.rfc-editor.org/info/rfc4046>.
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[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
(GCM) in IPsec Encapsulating Security Payload (ESP)",
RFC 4106, DOI 10.17487/RFC4106, June 2005,
<https://www.rfc-editor.org/info/rfc4106>.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM
Mode with IPsec Encapsulating Security Payload (ESP)",
RFC 4309, DOI 10.17487/RFC4309, December 2005,
<https://www.rfc-editor.org/info/rfc4309>.
[RFC4543] McGrew, D. and J. Viega, "The Use of Galois Message
Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543,
DOI 10.17487/RFC4543, May 2006,
<https://www.rfc-editor.org/info/rfc4543>.
[RFC5374] Weis, B., Gross, G., and D. Ignjatic, "Multicast
Extensions to the Security Architecture for the Internet
Protocol", RFC 5374, DOI 10.17487/RFC5374, November 2008,
<https://www.rfc-editor.org/info/rfc5374>.
[RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
"Elliptic Curve Cryptography Subject Public Key
Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
<https://www.rfc-editor.org/info/rfc5480>.
[RFC5649] Housley, R. and M. Dworkin, "Advanced Encryption Standard
(AES) Key Wrap with Padding Algorithm", RFC 5649,
DOI 10.17487/RFC5649, September 2009,
<https://www.rfc-editor.org/info/rfc5649>.
[RFC5685] Devarapalli, V. and K. Weniger, "Redirect Mechanism for
the Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5685, DOI 10.17487/RFC5685, November 2009,
<https://www.rfc-editor.org/info/rfc5685>.
[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/info/rfc5723>.
[RFC5998] Eronen, P., Tschofenig, H., and Y. Sheffer, "An Extension
for EAP-Only Authentication in IKEv2", RFC 5998,
DOI 10.17487/RFC5998, September 2010,
<https://www.rfc-editor.org/info/rfc5998>.
[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
of Interpretation", RFC 6407, DOI 10.17487/RFC6407,
October 2011, <https://www.rfc-editor.org/info/rfc6407>.
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[RFC6467] Kivinen, T., "Secure Password Framework for Internet Key
Exchange Version 2 (IKEv2)", RFC 6467,
DOI 10.17487/RFC6467, December 2011,
<https://www.rfc-editor.org/info/rfc6467>.
[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>.
[RFC7634] Nir, Y., "ChaCha20, Poly1305, and Their Use in the
Internet Key Exchange Protocol (IKE) and IPsec", RFC 7634,
DOI 10.17487/RFC7634, August 2015,
<https://www.rfc-editor.org/info/rfc7634>.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
<https://www.rfc-editor.org/info/rfc8017>.
[RFC8052] Weis, B., Seewald, M., and H. Falk, "Group Domain of
Interpretation (GDOI) Protocol Support for IEC 62351
Security Services", RFC 8052, DOI 10.17487/RFC8052, June
2017, <https://www.rfc-editor.org/info/rfc8052>.
[RFC8263] Weis, B., Mangla, U., Karl, T., and N. Maheshwari, "Group
Domain of Interpretation (GDOI) GROUPKEY-PUSH
Acknowledgement Message", RFC 8263, DOI 10.17487/RFC8263,
November 2017, <https://www.rfc-editor.org/info/rfc8263>.
[RFC8750] Migault, D., Guggemos, T., and Y. Nir, "Implicit
Initialization Vector (IV) for Counter-Based Ciphers in
Encapsulating Security Payload (ESP)", RFC 8750,
DOI 10.17487/RFC8750, March 2020,
<https://www.rfc-editor.org/info/rfc8750>.
[RFC8784] Fluhrer, S., Kampanakis, P., McGrew, D., and V. Smyslov,
"Mixing Preshared Keys in the Internet Key Exchange
Protocol Version 2 (IKEv2) for Post-quantum Security",
RFC 8784, DOI 10.17487/RFC8784, June 2020,
<https://www.rfc-editor.org/info/rfc8784>.
[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>.
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[RFC9329] Pauly, T. and V. Smyslov, "TCP Encapsulation of Internet
Key Exchange Protocol (IKE) and IPsec Packets", RFC 9329,
DOI 10.17487/RFC9329, November 2022,
<https://www.rfc-editor.org/info/rfc9329>.
[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>.
Appendix A. Use of LKH in G-IKEv2
Section 5.4 of [RFC2627] describes the LKH architecture, and how a
GCKS uses LKH to exclude group members. This section clarifies how
the LKH architecture is used with G-IKEv2.
A.1. Notation
In this section we will use the notation X{Y} where a key with ID Y
is encrypted with the key with ID X. The notation GSK_w{Y} means
that the default wrap key GSK_w (with zero KWK ID)is used to encrypt
key Y, and the notation X{K_sa} means key X is used to encrypt the SA
key K_sa (wich always has zero Key ID). Note, that GSK_w{K_sa} means
that the SA key is encrypted with the default wrap key, in which case
both KWK ID and Key ID are zero. For simplicity we will assume that
The content of the KD payload will be shown as a sequence of key
bags. The Group Key Bag substructure will be denoted as GP(SAn)(),
when n is an SPI for the SA, and the Member Key Bag substructure will
be denoted as MP(). The content of the key bags is shown as SA_KEY
and WRAP_KEY attributes with the notation described above. For
simplicity the type of the attribute will not be shown, because it is
implicitly defined by the type of key bag.
Here is the example of KD payload.
KD(GP1(X{K_sa}),MP(Y{X},Z{Y},GSK_w{Z})
For simplicity any other attributes in the KD payload are omitted.
We will also use the notation X->Y->Z to describe the Key Path. In
this case key Y is needed to decrypt key X and key Z is needed to
decrypt key Y. In the example above the keys had the following
relation: K_sa->X->Y->Z->GSK_w.
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A.2. Group Creation
When a GCKS forms a group, it creates a key tree as shown in the
figure below. The key tree contains logical keys (which are
represented as the values of their Key IDs in the figure) and a
private key shared with only a single GM (the GMs are represented as
letters followed by the corresponding key ID in parentheses in the
figure). The root of the tree contains the multicast Rekey SA key
(which is represented as SAn(K_san). The figure below assumes that
the Key IDs are assigned sequentially; this is not a requirement and
only used for illustrative purposes. The GCKS may create a complete
tree as shown, or a partial tree which is created on demand as
members join the group.
SA1(K_sa1)
+------------------------------+
1 2
+---------------+ +---------------+
3 4 5 6
+-------+ +-------+ +--------+ +--------+
A(7) B(8) C(9) D(10) E(11) F(12) G(13) H(14)
Figure 26: Initial LKH tree
When GM A joins the group, the GCKS provides it with the keys in the
KD payload of the GSA_AUTH or GSA_REGISTRATION exchange. Given the
tree shown in figure above, the KD payload will be:
KD(GP(SA1)(1{K_sa1}),MP(3{1},7{3},GSK_w{7})
Figure 27: KD Payload for the Group Member A
From these attributes the GM A will construct the Key Path
K_sa1->1->3->7->GSK_w and since it ends up with GSK_w, it will use
all the WRAP_KEY attributes present in the path as its Working Key
Path: 1->3->7.
Similarly, when other GMs will be joining the group they will be
provided with the corresponding keys, so after all the GMs will have
the following Working Key Paths:
A: 1->3->7 B: 1->3->8 C: 1->4->9, D: 1->4->10
E: 2->5->11 F: 2->5->12 G: 2->6->13 H: 2->6->14
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A.3. Simple Group SA Rekey
If the GCKS performs a simple SA rekey without changing group
membership, it will only send group key bag in the KD payload with a
new SA key encrypted with the default KWK.
KD(GP(SA2)(GSK_w{K_sa2}))
Figure 28: KD Payload for the Simple Group SA Rekey
All the GMs will be able to decrypt it and no changes in their
Working Key Paths will happen.
A.4. Group Member Exclusion
If the GKCS has reason to believe that a GM should be excluded, then
it can do so by sending a GSA_REKEY message that includes a set of
GM_KEY attributes which would allow all GMs except for the excluded
one to get a new SA key.
In the example below the GCKS excludes GM F. For this purpose it
changes the key tree as follows, replacing the key 2 with the key 15
and the key 5 with the key 16. It also generates a new SA key for a
new SA3.
SA3(K_sa3)
+------------------------------+
1 15
+---------------+ +---------------+
3 4 16 6
+-------+ +-------+ +---- +--------+
A(7) B(8) C(9) D(10) E(11) F(12) G(13) H(14)
Figure 29: LKH tree after F has been excluded
Then it sends the following KD payload for the new Rekey SA3:
KD(GP(SA3)(1{K_sa3},15{K_sa3}),MP(6{15},16{15},11{16})
Figure 30: KD Payload for the Group Member F
While processing this KD payload:
* GMs A, B, C and D will be able to decrypt the SA_KEY attribute
1{K_sa3} by using the "1" key from their key path. Since no new
GM_KEY attributes are in the new Key Path, they won't update their
Working Key Paths.
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* GMs G and H will construct new Key Path 15->6 and will be able to
decrypt the intermediate key 15 using the key 6 from their Working
Key Paths. So, they will update their Working Key Paths replacing
their beginnings up to the key 6 with the new Key Path (thus
replacing the key 2 with the key 15).
* GM E will construct new Key Path 16->15->11 and will be able to
decrypt the intermediate key 16 using the key 11 from its Working
Key Path. So, it will update its Working Key Path replacing its
beginnings up to the key 11 with the new Key Path (thus replacing
the key 2 with the key 15 and the key 5 with the key 16).
* GM F won't be able to construct any Key Path leading to any key he
possesses, so it will be unable to decrypt the new SA key for the
SA3 and thus it will be excluded from the group once the SA3 is
used.
Finally, the GMs will have the following Working Key Paths:
A: 1->3->7 B: 1->3->8 C: 1->4->9, D: 1->4->10
E: 15->16->11 F: excluded G: 15->6->13 H: 15->6->14
Authors' Addresses
Valery Smyslov
ELVIS-PLUS
PO Box 81
Moscow (Zelenograd)
124460
Russian Federation
Phone: +7 495 276 0211
Email: svan@elvis.ru
Brian Weis
Independent
United States of America
Email: bew.stds@gmail.com
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