Network Working Group B. Weis
Internet-Draft Independent
Obsoletes: 6407 (if approved) V. Smyslov
Intended status: Standards Track ELVIS-PLUS
Expires: January 9, 2020 July 8, 2019
Group Key Management using IKEv2
draft-yeung-g-ikev2-16
Abstract
This document presents a set of IKEv2 exchanges that comprise a group
key management protocol. The protocol is in conformance with the
Multicast Security (MSEC) key management architecture, which contains
two components: member registration and group rekeying. Both
components require a Group Controller/Key Server to download IPsec
group security associations to authorized members of a group. The
group members then exchange IP multicast or other group traffic as
IPsec packets. This document obsoletes RFC 6407.
Status of This Memo
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This Internet-Draft will expire on January 9, 2020.
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Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
1.2. G-IKEv2 Integration into IKEv2 Protocol . . . . . . . . . 5
1.2.1. G-IKEv2 Transport and Port . . . . . . . . . . . . . 5
1.2.2. IKEv2 Header Initialization . . . . . . . . . . . . . 6
1.3. G-IKEv2 Protocol . . . . . . . . . . . . . . . . . . . . 6
1.3.1. G-IKEv2 Payloads . . . . . . . . . . . . . . . . . . 6
1.4. G-IKEv2 Member Registration and Secure Channel
Establishment . . . . . . . . . . . . . . . . . . . . . . 7
1.4.1. GSA_AUTH exchange . . . . . . . . . . . . . . . . . . 7
1.4.2. GSA_REGISTRATION Exchange . . . . . . . . . . . . . . 9
1.4.3. GM Registration Operations . . . . . . . . . . . . . 10
1.4.4. GCKS Registration Operations . . . . . . . . . . . . 11
1.4.5. Group Maintenance Channel . . . . . . . . . . . . . . 12
1.4.6. Counter-based modes of operation . . . . . . . . . . 19
1.5. Interaction with IKEv2 Protocol Extensions . . . . . . . 21
1.5.1. Postquantum Preshared Keys for IKEv2 . . . . . . . . 21
2. Header and Payload Formats . . . . . . . . . . . . . . . . . 23
2.1. The G-IKEv2 Header . . . . . . . . . . . . . . . . . . . 23
2.2. Group Identification (IDg) Payload . . . . . . . . . . . 24
2.3. Security Association - GM Supported Transforms (SAg) . . 24
2.4. Group Security Association Payload . . . . . . . . . . . 24
2.4.1. GSA Policy . . . . . . . . . . . . . . . . . . . . . 24
2.4.2. KEK Policy . . . . . . . . . . . . . . . . . . . . . 26
2.4.3. GSA TEK Policy . . . . . . . . . . . . . . . . . . . 29
2.4.4. GSA Group Associated Policy . . . . . . . . . . . . . 33
2.5. Key Download Payload . . . . . . . . . . . . . . . . . . 34
2.5.1. TEK Download Type . . . . . . . . . . . . . . . . . . 36
2.5.2. KEK Download Type . . . . . . . . . . . . . . . . . . 37
2.5.3. LKH Download Type . . . . . . . . . . . . . . . . . . 38
2.5.4. SID Download Type . . . . . . . . . . . . . . . . . . 40
2.6. Delete Payload . . . . . . . . . . . . . . . . . . . . . 42
2.7. Notify Payload . . . . . . . . . . . . . . . . . . . . . 42
2.8. Authentication Payload . . . . . . . . . . . . . . . . . 43
3. Security Considerations . . . . . . . . . . . . . . . . . . . 43
3.1. GSA Registration and Secure Channel . . . . . . . . . . . 43
3.2. GSA Maintenance Channel . . . . . . . . . . . . . . . . . 44
3.2.1. Authentication/Authorization . . . . . . . . . . . . 44
3.2.2. Confidentiality . . . . . . . . . . . . . . . . . . . 44
3.2.3. Man-in-the-Middle Attack Protection . . . . . . . . . 44
3.2.4. Replay/Reflection Attack Protection . . . . . . . . . 44
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4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
4.1. New Registries . . . . . . . . . . . . . . . . . . . . . 44
4.2. New Payload and Exchange Types Added to the Existing
IKEv2 Registry . . . . . . . . . . . . . . . . . . . . . 45
4.3. Changes to Previous Allocations . . . . . . . . . . . . . 45
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 45
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 46
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.1. Normative References . . . . . . . . . . . . . . . . . . 47
7.2. Informative References . . . . . . . . . . . . . . . . . 48
Appendix A. Use of LKH in G-IKEv2 . . . . . . . . . . . . . . . 50
A.1. Group Creation . . . . . . . . . . . . . . . . . . . . . 50
A.2. Group Member Exclusion . . . . . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
1. Introduction and Overview
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). This document presents a set of IKEv2
[RFC7296] exchanges that comprise a group key management protocol.
A GM begins a "registration" exchange when it first joins the group.
With G-IKEv2, the GCKS authenticates and authorizes GMs, then pushes
policy and keys used by the group to the GM. G-IKEv2 includes two
"registration" exchanges. The first is the GSA_AUTH exchange (
Section 1.4.1), which follows an IKE_SA_INIT exchange. The second is
the GSA_REGISTRATION exchange ( Section 1.4.2), which a GM can use
within an established IKE SA. Group rekeys are accomplished using
either the GSA_REKEY exchange (a single message distributed to all
GMs, usually as a multicast message), or as a GSA_INBAND_REKEY
exchange delivered individually to group members using existing IKE
SAs).
Large and small groups may use different sets of these protocols.
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. (Note: For clarity, IKE_SA_INIT is omitted from the
figure.)
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+--------+
+------------->| GCKS |<-------------+
| +--------+ |
| | ^ |
| | | |
| | GSA_AUTH |
| | or |
| | GSA_REGISTRATION |
| | | |
GSA_AUTH | | GSA_AUTH
or GSA_REKEY | or
GSA_REGISTRATION | | GSA_REGISTRATION
| | | |
| +------------+-----------------+ |
| | | | | |
v v v v v v
+-------+ +--------+ +-------+
| GM | ... | GM | ... | GM |
+-------+ +--------+ +-------+
^ ^ ^
| | |
+-------ESP-------+-------ESP------+
Figure 1: G-IKEv2 used in large groups
Alternatively, a small group may simply use the GSA_AUTH as a
registration protocol, where the GCKS issues rekeys using the
GSA_INBAND_REKEY within the same IKEv2 SA. The GCKS is also likely
to be a GM in a small group (as shown in Figure 2.)
GSA_AUTH, GSA_INBAND_REKEY
+-----------------------------------------------+
| |
| GSA_AUTH, GSA_INBAND_REKEY |
| +-----------------------------+ |
| | | |
| | GSA_AUTH, GSA_INBAND_REKEY | |
| | +--------+ | |
v v v v v v
+---------+ +----+ +----+ +----+
| GCKS/GM | | GM | | GM | | GM |
+---------+ +----+ +----+ +----+
^ ^ ^ ^
| | | |
+----ESP-----+------ESP-------+-----ESP-----+
Figure 2: G-IKEv2 used in small groups
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IKEv2 message semantics are preserved in that all communications
consists of message request-response pairs. The exception to this
rule is the GSA_REKEY exchange, which is a single message delivering
group updates to the GMs.
G-IKEv2 conforms with the Multicast Group Security Architecture
[RFC3740], 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].
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. G-IKEv2 Integration into IKEv2 Protocol
G-IKEv2 uses the security mechanisms of IKEv2 (peer authentication,
confidentiality, message integrity) to ensure that only authenticated
devices have access to the group policy and keys. The G-IKEv2
exchange further provides group authorization, and secure policy and
key download from the GCKS to GMs. Some IKEv2 extensions require
special handling if used with G-IKEv2. See Section 1.5 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].
1.2.1. G-IKEv2 Transport and Port
G-IKEv2 SHOULD use UDP port 848, the same as GDOI [RFC6407], because
they serve a similar function. They can use the same ports, just as
IKEv1 and IKEv2 can share port 500. The version number in the IKE
header distinguishes the G-IKEv2 protocol from GDOI protocol
[RFC6407]. G-IKEv2 MAY also use the IKEv2 ports (500, 4500), which
would provide a better integration with IKEv2. G-IKEv2 MAY also use
TCP transport for registration (unicast) IKE SA, as defined in
[RFC8229].
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1.2.2. IKEv2 Header Initialization
The Major Version is (2) and Minor Version is (0) according to IKEv2
[RFC7296], and maintained in this document. The G-IKEv2 IKE_SA_INIT,
GSA_AUTH, GSA_REGISTRATION and GSA_INBAND_REKEY use the IKE SPI
according to IKEv2 [RFC7296], section 2.6.
1.3. G-IKEv2 Protocol
1.3.1. G-IKEv2 Payloads
In the following descriptions, the payloads contained in the G-IKEv2
messages are indicated by names as listed below.
Notation Payload
------------------------------------------------------------
AUTH Authentication
CERT Certificate
CERTREQ Certificate Request
GSA Group Security Association
HDR IKEv2 Header
IDg Identification - Group
IDi Identification - Initiator
IDr Identification - Responder
KD Key Download
KE Key Exchange
Ni, Nr Nonce
SA Security Association
SAg Security Association - GM Supported Transforms
Payloads defined as part of other IKEv2 extensions MAY also be
included in these messages. Payloads that may optionally appear will
be shown in brackets, such as [ CERTREQ ], to indicate that a
certificate request payload can optionally be included.
G-IKEv2 defines several new payloads not used in IKEv2:
o IDg (Group ID) - The GM requests the GCKS for membership into the
group by sending its IDg payload.
o GSA (Group Security Association) - The GCKS sends the group policy
to the GM using this payload.
o KD (Key Download) - The GCKS sends the control and data keys to
the GM using the KD payload.
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o SAg (Security Association - GM Supported Transforms) - the GM
sends supported transforms, so that GCKS may select a policy
appropriate for all members of the group.
The details of the contents of each payload are described in
Section 2.
1.4. G-IKEv2 Member Registration and Secure Channel Establishment
The registration protocol consists of a minimum of two messages
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) or negotiation of Diffie-Hellman group is included.
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 does a Diffie-Hellman
exchange between the group member (GM) and the Group Controller/Key
Server (GCKS).
The second exchange GSA_AUTH authenticates the previous messages,
exchanges identities and certificates. These messages are encrypted
and integrity protected with keys established through the IKE_SA_INIT
exchange, so the identities are hidden from eavesdroppers and all
fields in all the messages are authenticated. The GCKS SHOULD
authorize group members to be allowed into the group as part of the
GSA_AUTH exchange. Once the GCKS accepts a group member to join a
group it will download the data security keys (TEKs) and/or group key
encrypting key (KEK) or KEK array as part of the GSA_AUTH response
message.
1.4.1. GSA_AUTH exchange
After the group member and GCKS use the IKE_SA_INIT exchange to
negotiate cryptographic algorithms, exchange nonces, and perform a
Diffie-Hellman exchange as defined in IKEv2 [RFC7296], the GSA_AUTH
exchange MUST complete before any other exchanges can be done. The
security properties of the GSA_AUTH exchange are the same as the
properties of the IKE_AUTH exchange. It is used to authenticate the
IKE_SA_INIT messages, exchange identities and certificates. G-IKEv2
also uses this exchange for group member registration and
authorization. Even though the IKE_AUTH does contain the SA2, TSi,
and TSr payload the GSA_AUTH does not. They are not needed because
policy is not negotiated between the group member and the GCKS, but
instead downloaded from the GCKS to the group member.
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Initiator (Member) Responder (GCKS)
-------------------- ------------------
HDR, SK { IDi, [CERT,] [CERTREQ, ] [IDr, ]
AUTH, IDg, [SAg, ] [N ] } -->
Figure 3: GSA_AUTH Request
After the IKE_SA_INIT exchange completes, the 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 that it is
willing to accept. A GM that intends to emit data packets SHOULD
include a Notify payload status type of SENDER, which enables the
GCKS to provide any additional policy necessary by group senders.
Initiator (Member) Responder (GCKS)
-------------------- ------------------
<-- HDR, SK { IDr, [CERT, ]
AUTH, [ GSA, KD, ] [D, ] }
Figure 4: GSA_AUTH Normal Response
The GCKS responds with IDr, optional CERT, and AUTH material as if it
were an 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. The GCKS can also include a Delete (D)
payload instructing the group member to delete existing SAs it might
have as the result of a previous group member registration. Note,
that since the GCKS generally doesn't know which SAs the GM has, the
SPI field in the Delete payload(s) SHOULD be set to zero in this
case. (See more discussion on the Delete payload in Section 2.6.)
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 2.7, the GSA_AUTH response will not
include the GSA and KD, but will include a Notify payload indicating
errors. If the group member included an SAg payload, and the GCKS
chooses to evaluate it, and it detects that that group member cannot
support the security policy defined for the group, then the GCKS
SHOULD return a NO_PROPOSAL_CHOSEN. Other types of notifications can
be AUTHORIZATION_FAILED or REGISTRATION_FAILED.
Initiator (Member) Responder (GCKS)
-------------------- ------------------
<-- HDR, SK { IDr, [CERT, ] AUTH, N }
Figure 5: GSA_AUTH Error Response
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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 1.4.2)).
1.4.2. GSA_REGISTRATION Exchange
When a secure channel is already established between a GM and the
GCKS, the GM registration for a group can reuse the established
secure channel. In this scenario the GM will use the
GSA_REGISTRATION exchange. Payloads in the exchange are generated
and processed as defined in Section 1.4.1.
Initiator (Member) Responder (GCKS)
-------------------- ------------------
HDR, SK {IDg, [SAg, ][N ] } -->
<-- HDR, SK { GSA, KD, [D ] }
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 1.4.1.
Initiator (Member) Responder (GCKS)
-------------------- ------------------
HDR, SK {IDg, [SAg, ][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 or for some reason wants to
unregister itself from the group. The group member SHOULD notify the
GCKS by sending IDg and the Notify type NO_PROPOSAL_CHOSEN or
REGISTRATION_FAILED, as shown below. The GCKS MUST unregister the
group member.
Initiator (Member) Responder (GCKS)
-------------------- ------------------
HDR, SK {IDg, N } -->
<-- HDR, SK {}
Figure 8: GM Reporting Errors in GSA_REGISTRATION Exchange
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1.4.3. GM Registration Operations
A G-IKEv2 Initiator (GM) requesting registration contacts the GCKS
using the IKE_SA_INIT exchange and receives the response from the
GCKS. This exchange is unchanged from the IKE_SA_INIT in IKEv2
protocol.
Upon completion of parsing and verifying the IKE_SA_INIT response,
the GM sends the GSA_AUTH 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 initiator wishes to
join. An initiator intending to emit data traffic SHOULD send a
SENDER Notify payload status. The SENDER not only signifies that it
is a sender, but provides the initiator the ability to request
Sender-ID values, in case the Data Security SA supports a counter
mode cipher. Section 1.4.6) includes guidance on requesting Sender-
ID values.
An initiator may be limited in the types of Transforms that it is
able or willing to use, and may find it useful to inform the GCKS
which Transforms that it is willing to accept. It can OPTIONALLY
include an SAg payload, which can include ESP and/or AH Proposals.
Each Proposal contains a list of Transforms that it is willing to
support for that protocol. A Proposal of type ESP can include ENCR,
INTEG, and ESN Transforms. A Proposal of type AH can include INTEG,
and ESN Transforms. The SPI length of each Proposal in an SAg is set
to zero, and thus the SPI field is null. The GCKS MUST ignore SPI
field in the SAg payload. Generally, a single Proposal of each type
will suffice, because the group member is not negotiating Transform
sets, simply alerting the GCKS to restrictions it may have, however
if the GM has restrictions on combination of algorithms, this can be
expressed by sending several proposals.
Upon receiving the GSA_AUTH response, the initiator parses the
response from the GCKS authenticating the exchange using the IKEv2
method, then processes the GSA and KD.
The GSA payload contains the security policy and cryptographic
protocols used by the group. This policy describes the Rekey SA
(KEK), if present, Data-security SAs (TEK), and other group policy
(GAP). If the policy in the GSA payload is not acceptable to the GM,
it SHOULD notify the GCKS by initiating a GSA_REGISTRATION exchange
with a NO_PROPOSAL_CHOSEN Notify payload (see Section 1.4.2). 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 is parsed providing the keying material for the TEK and/or
KEK. The GM interprets the KD key packets, where each key packet
includes the keying material for SAs distributed in the GSA payload.
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Keying material is matched by comparing the SPIs in the key packets
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 KEK attribute KEK_MESSAGE_ID with a
Message ID. The Message ID in the KEK_MESSAGE_ID attribute MUST be
checked against any previously received Message ID for this group.
If it is less than the previously received number, it should be
considered stale and ignored. This could happen if two GSA_AUTH
exchanges happened in parallel, and the Message ID changed. This
KEK_MESSAGE_ID is used by the GM to prevent GSA_REKEY message replay
attacks. The first GSA_REKEY message that the GM receives from the
GCKS must have a Message ID greater or equal to the Message ID
received in the KEK_MESSAGE_ID attribute.
Once a GM has received GSA_REKEY policy during a registration the IKE
SA may be closed. However, the GM SHOULD NOT close IKE SA, it is the
GCKS who makes the decision whether to close or keep it, because
depending on the policy the IKE SA may be used for inband rekeying
for small groups.
1.4.4. 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.
Upon receiving the GSA_AUTH request, the GCKS authenticates the group
member using the same procedures as in the IKEv2 IKE_AUTH. 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 will respond with an AUTHORIZATION_FAILED notify
message.
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, this policy is constructed in the GSA KEK and the
key is constructed in the KD KEK. The GSA KEK MUST include the
KEK_MESSAGE_ID attribute, specifying the starting Message ID the GCKS
will use when sending the GSA_REKEY message to the group member.
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 GSA GAP MAY also be included to
provide the ATD and/or DTD (Section 2.4.4.1) specifying activation
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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 SIDs
(see Section 1.4.6).
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.
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.
o 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 or AH Transforms in its current policy,
then it could return a NO_PROPOSAL_CHOSEN Notification.
o The GCKS could store the list of Transforms, with the goal of
migrating the group policy to a different Transform when all of
the group members indicate that they can support that Transform.
o 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 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 IKEv2 SA. The delay before closing
provides for receipt of a GM's error notification in the event of
packet loss.
1.4.5. 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.
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GSA_REKEY The GSA_REKEY exchange is an exchange initiated by the
GCKS, where the rekey policy is usually delivered to group members
using IP multicast as a transport. This is valuable for large and
dynamic groups, and where policy may change frequently and an
scalable rekeying method is required. When the GSA_REKEY exchange
is used, the IKEv2 SA protecting the member registration exchanges
is terminated, and group members await policy changes from the
GCKS via the GSA_REKEY exchange.
GSA_INBAND_REKEY The GSA_INBAND_REKEY exchange is a rekey method
using the IKEv2 SA that was setup to protecting the member
registration exchange. This exchange allows the GCKS to rekey
without using an independent GSA_REKEY exchange. The
GSA_INBAND_REKEY exchange is useful when G-IKEv2 is used with a
small group of cooperating devices.
1.4.5.1. GSA_REKEY Exchange
The GCKS initiates the G-IKEv2 Rekey securely, usually using IP
multicast. Since this rekey does not require a response and it sends
to multiple GMs, G-IKEv2 rekeying MUST NOT support IKE SA windowing.
The GCKS rekey message replaces the rekey GSA KEK or KEK array, and/
or creates a new Data-Security GSA TEK. The SID Download attribute
in the Key Download payload (defined in Section 2.5.4) 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 exchange as following:
Members (Responder) GCKS (Initiator)
-------------------- ------------------
<-- HDR, SK { GSA, KD, [D,] [AUTH] }
Figure 9: GSA_REKEY Exchange
HDR is defined in Section 2.1. The Message ID in this message will
start with the same value the GCKS sent to the group members in the
KEK attribute KEK_MESSAGE_ID during registration; this Message ID
will be increased each time a new GSA_REKEY message is sent to the
group members.
The GSA payload contains the current rekey and data security SAs.
The GSA may contain a new rekey SA and/or a new data security SA,
which, optionally contains an LKH rekey SA, Section 2.4.
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
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refreshed in this rekey message, the rekey Key or the LKH KEK array
is updated in the KD payload.
A Delete payload MAY be included to instruct the GM to delete
existing SAs.
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 it is based on shared secret.
In a 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 that the sender is a
member of the group. Shared secret authentication doesen't provide
source origin authentication. For this reason using it as
authentication method for multicast Rekey is NOT RECOMMENDED unless
source origin authentication is not required (for example, in a small
group of highly trusted GMs). If AUTH payload is included then the
Auth Method field MUST be one specifying using digital signatures.
During group member registration, the GCKS sends the authentication
key in the GSA KEK payload, KEK_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 KEK_AUTH_KEY to
the group members in a GSA_REKEY message. The AUTH key that is used
in the rekey message may be not the same as the authentication key
used in GSA_AUTH.
1.4.5.1.1. 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. If the
message is using a new KEK attribute, the Message ID is reset to 1 in
this message. The GSA, KD, and D payloads follow with the same
characteristics as in the GSA Registration exchange.
If present the AUTH payload is created as follows. First the message
is prepared, all payloads are formed and included in the message, but
the content of the Encrypted payload is not yet encrypted. However,
the Encrypted payload must be fully formed, including correct values
in IV, Padding and Pad Length and fields. The AUTH payload is
included in the message with the correct values in the Payload Header
(including Next Payload, Payload Length and Auth Method fields). The
Authentication Data field is zeroed for the purposes of signature
calculation, but if Digiatal Signature authentication method is in
use, then the ASN.1 Length and the AlgorithmIdentifier fields must be
properly filled in, see [RFC7427]. The signature is computed using
the signature algorithm from the KEK_AUTH_METHOD attribute (along
with the KEK_AUTH_HASH if KEK_AUTH_METHOD is not Digital Signature)
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and the private key corresponding to the public key from the
KEK_AUTH_KEY attribute. It is computed over the block of data
starting from the first octet of IKE Header (but non including non-
ESP marker if it is present) to the last octet of the (not yet
encrypted) Encrypted Payload (i.e. up to and including Pad Length
field). Then the signature is placed into the Signature Value of the
AUTH payload, the content of the Encrypted payload is encrypted and
the ICV is computed using current KEK keys.
Because GSA_REKEY messages are not acknowledged and could be
discarded by the network, one or more GMs may not receive the
message. To mitigate such lost messages, during a rekey event the
GCKS may transmit several GSA_REKEY messages with the new policy.
The 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 not substantially skewed for the GMs that
would receive different copies of the messages.
GCKS may also include one or several KEK_NEXT_SPI/TEK_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 2.4.2.1.6 and Section 2.4.3.1.4
for more detail.
1.4.5.1.2. GSA_REKEY GM Operations
When a group member receives the Rekey Message from the GCKS it
decrypts the message using the current KEK, validates the signature
using the public key retrieved in a previous G-IKEv2 exchange if AUTH
payload is present, 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 KEK_MESSAGE_ID attribute. The GM expects the
message ID in subsequent GSA_REKEY messages to be greater than the
last valid GSA_REKEY message ID it received.
If the GSA payload includes a Data-Security SA including a counter-
modes of operation and the receiving group member is a sender for
that SA, the group member uses its current SID value with the Data-
Security SAs to create counter-mode nonces. If it is a sender and
does not hold a current SID value, it MUST NOT install the Data-
Security SAs. It MAY initiate a GSA_REGISTRATION exchange to the
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GCKS in order to obtain an SID value (along with 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 GSA TEK payload includes
TEK_REKEY_SPI attribute then after installing a new Data-Security SA
the old one, identified by the SPI in this attribute, MUST be
silently deleted after waiting DEACTIVATION_TIME_DELAY interval
regardless of its expiration time.
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.
1.4.5.1.3. Forward and Backward Access Control
Through the G-IKEv2 rekey, G-IKEv2 supports algorithms such as 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.
Support for group management algorithms are supported via the
KEY_MANAGEMENT_ALGORITHM attribute which is sent in the GSA KEK
policy. G-IKEv2 specifies one method by which LKH can be used for
forward and backward access control. Other methods of using LKH, as
well as other group management algorithms such as OFT or Subset
Difference may be added to G-IKEv2 as part of a later document.
1.4.5.1.3.1. Forward Access Control Requirements
When group membership is altered using a group management algorithm
new GSA TEKs (and their associated keys) are usually also needed.
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New GSAs 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 GSA
TEKs and the associated key packets in the KD payload 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 key
packets in the KD payload are not protected with the new KEK. A
second G-IKEv2 rekey message can deliver the new GSA TEKS and their
associated key packets 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.
1.4.5.1.4. 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.
o 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 exchange messages.
o The GCKS must always use IKE fragmentation based on a known
fragmentation threshold (unspecified in this memo), as there is no
way to check if fragmentation is needed by first sending
unfragmented messages and waiting for response.
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o PMTU probing cannot be performed due to lack of GSA_REKEY response
message.
1.4.5.2. GSA_INBAND_REKEY Exchange
When the IKEv2 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.
Member (Responder) GCKS (Initiator)
-------------------- ------------------
<-- HDR, SK { GSA, KD, [D,] }
HDR, SK {} -->
Figure 10: GSA_INBAND_REKEY Exchange
Because this is an IKEv2 exchange, the HDR is treated as defined in
[RFC7296].
1.4.5.2.1. GSA_INBAND_REKEY GCKS Operations
The GSA, KD, and D payloads are built in the same manner as in a
registration exchange.
1.4.5.2.2. GSA_INBAND_REKEY GM Operations
The GM processes the GSA, KD, and D payloads in the same manner as if
they were received in a registration exchange.
1.4.5.3. 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 keys MAY be accomplished by sending the G-IKEv2
Delete Payload [RFC7296], section 3.11 as part of the GSA_REKEY
Exchange as shown below.
Members (Responder) GCKS (Initiator)
-------------------- ------------------
<-- HDR, SK { [GSA ], [KD ], [D, ] [AUTH ] }
Figure 11: SA Deletion in GSA_REKEY
The GSA MAY specify the remaining active time of the remaining policy
by using the DTD attribute in the GSA GAP. 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
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to start over with a clean slate. If the administrator is no longer
confident in the integrity of the group, the GCKS can signal deletion
of all the policies of a particular TEK protocol by sending a TEK
with a SPI value equal to zero in the delete payload. For example,
if the GCKS wishes to remove all the KEKs and all the TEKs in the
group, the GCKS SHOULD send a Delete payload with a SPI of zero and a
protocol_id of a TEK protocol_id value defined in Section 2.4.3,
followed by another Delete payload with a SPI of zero and protocol_id
of zero, indicating that the KEK SA should be deleted.
1.4.6. Counter-based modes of operation
Several new counter-based modes of operation have been specified for
ESP (e.g., AES-CTR [RFC3686], AES-GCM [RFC4106], AES-CCM [RFC4309],
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 met in G-IKEv2 when the
following requirements are met:
o The GCKS distributes a unique key for each Data-Security SA.
o 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 SID values.
1.4.6.1. Allocation of SIDs
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 SID to each group member acting in the
role of sender on the Data-Security SA. The SID value is used
exclusively by the group member to which it was allocated. The group
member uses the same SID 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 member can choose to request one or
more SID values. Requesting a value of 1 is not necessary since the
GCKS will automatically allocate exactly one to the group member. A
group member MUST request as many SIDs matching the number of
encryption modules in which it will be installing the TEKs in the
outbound direction. Alternatively, a group member MAY request more
than one SID and use them serially. This could be useful when it is
anticipated that the group member will exhaust their range of Data-
Security SA nonces using a single SID too quickly (e.g., before the
time-based policy in the TEK expires).
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When the group policy includes a counter-based mode of operation, a
GCKS SHOULD use the following method to allocate SID values, which
ensures that each SID will be allocated to just one group member.
1. A GCKS maintains an SID-counter, which records the SIDs that have
been allocated. SIDs are allocated sequentially, with zero as the
first allocated SID.
2. Each time an SID is allocated, the current value of the counter
is saved and allocated to the group member. The SID-counter is then
incremented in preparation for the next allocation.
3. When the GCKS specifies a counter-based mode of operation in the
Data Security SA a group member may request a count of SIDs during
registration in a Notify payload information of type SENDER. When
the GCKS receives this request, it increments the SID-counter once
for each requested SID, and distributes each SID value to the group
member. The GCKS SHOULD have a policy-defined upper bound for the
number of SIDs that it will return irrespective of the number
requested by the GM.
4. A GCKS allocates new SID values for each GSA_REGISTRATION
exchange originated by a sender, regardless of whether a group member
had previously contacted the GCKS. In this way, the GCKS is not
required to maintaining a record of which SID values it had
previously allocated to each group member. More importantly, since
the GCKS cannot reliably detect whether the group member had sent
data on the current group Data-Security SAs it does not know what
Data-Security counter-mode nonce values that a group member has used.
By distributing new SID values, the key server ensures that each time
a conforming group member installs a Data-Security SA it will use a
unique set of counter-based mode nonces.
5. When the SID-counter maintained by the GCKS reaches its final SID
value, no more SID values can be distributed. Before distributing
any new SID values, the GCKS MUST delete the Data-Security SAs for
the group, followed by creation of new Data-Security SAs, and
resetting the SID-counter to its initial value.
6. The GCKS SHOULD send a GSA_REKEY message deleting all Data-
Security SAs and the Rekey SA for the group. This will result in the
group members initiating a new GSA_REGISTRATION exchange, in which
they will receive both new SID values and new Data-Security SAs. The
new SID values can safely be used because they are only used with the
new Data-Security SAs. Note that deletion of the Rekey SA is
necessary to ensure that group members receiving a GSA_REKEY exchange
before the re-register do not inadvertently use their old SIDs with
the new Data-Security SAs. Using the method above, at no time can
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two group members use the same IV values with the same Data-Security
SA key.
1.4.6.2. GM Usage of SIDs
A GM applies the SID to Data Security SA as follows.
1. The most significant bits NUMBER_OF_SID_BITS of the IV are taken
to be the SID field of the IV.
2. The SID is placed in the least significant bits of the SID field,
where any unused most significant bits are set to zero. If the SID
value doesn't fit into the NUMBER_OF_SID_BITS bits, then the GM MUST
treat this as a fatal error and re-register to the group.
1.5. Interaction with IKEv2 Protocol Extensions
IKEv2 defines a number of extensions that can be used to extend
protocol functionality. G-IKEv2 is compatible with most of such
extensions. In particular, EAP authentication defined in [RFC7296]
can be used to establish registration IKE SA, as well as Secure
Password authentication ([RFC6467]). G-IKEv2 is compatible with and
can use IKEv2 Session Resumption [RFC5723] except that a GM would
include the initial ticket request in a GSA_AUTH exchange instead of
an IKE_AUTH exchange. G-IKEv2 is also compatible with Quantum Safe
Key Exchange framework, defined in
[I-D.tjhai-ipsecme-hybrid-qske-ikev2].
Some IKEv2 extensions however require special handling if used in
G-IKEv2.
1.5.1. Postquantum Preshared Keys for IKEv2
G-IKEv2 can take advantage of the protection provided by Postquantum
Preshared Keys (PPK) for IKEv2 [I-D.ietf-ipsecme-qr-ikev2]. However,
the use of PPK leaves the initial IKE SA susceptible to quantum
computer (QC) attacks. So, if PPK was used for IKE SA setup, the
GCKS MUST NOT send GSA and KD payloads in the GSA_AUTH response
message. Instead, the GCKS MUST return a new notification
REKEY_IS_NEEDED. 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. Below are possible
scenarios involving using PPK.
GM begins IKE_SA_INIT requesting PPK, and GCKS responds with
willingness to do it, or aborts according to its "mandatory_or_not"
flag:
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Initiator (Member) Responder (GCKS)
-------------------- ------------------
HDR, SAi1, KEi, Ni, N(USE_PPK) --->
<--- HDR, SAr1, KEr, Nr, [CERTREQ],
N(USE_PPK)
Figure 12: IKE_SA_INIT Exchange requesting using PPK
GM begins GSA_AUTH with PPK_ID; if using PPK is not mandatory for the
GM, N(NO_PPK_AUTH) is included too:
Initiator (Member) Responder (GCKS)
-------------------- ------------------
HDR, SK {IDi, AUTH, IDg,
N(PPK_IDENTITY), N(NO_PPK_AUTH) } --->
Figure 13: GSA_AUTH Request using PPK
If GCKS has no such PPK and using PPK is not mandatory for it and
N(NO_PPK_AUTH) is included, then the GCKS continues w/o PPK; in this
case no rekey is needed:
Initiator (Member) Responder (GCKS)
-------------------- ------------------
<--- HDR, SK { IDr, AUTH, GSA, KD }
Figure 14: GSA_AUTH Response using no PPK
If GCKS has no such PPK and either N(NO_PPK_AUTH) is missing or using
PPK is mandatory for GCKS, the GCKS aborts the exchange:
Initiator (Member) Responder (GCKS)
-------------------- ------------------
<--- HDR, SK { N(AUTHENTICATION_FAILED) }
Figure 15: GSA_AUTH Error Response
Assuming GCKS has a proper PPK the GCKS continues with request to GM
to immediately perform a rekey:
Initiator (Member) Responder (GCKS)
-------------------- ------------------
<--- HDR, SK{IDr, AUTH, N(PPK_IDENTITY),
N(REKEY_IS_NEEDED) }
Figure 16: GSA_AUTH Response using PPK
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GM initiates CREATE_CHILD_SA to rekey IKE SA and then makes a new
registration request for the same group over the new IKE SA:
Initiator (Member) Responder (GCKS)
-------------------- ------------------
HDR, SK {SA, Ni, KEi } --->
<--- HDR, SK {SA, Nr, KEr }
HDR, SK {IDg } --->
<--- HDR, SK { GSA, KD }
Figure 17: Rekeying IKE SA followed by GSA_REGISTRATION Exchange
2. Header and Payload Formats
Refer to IKEv2 [RFC7296] for existing payloads. Some payloads used
in G-IKEv2 exchanges are not aligned to 4-octet boundaries, which is
also the case for some IKEv2 payloads (see Section 3.2 of [RFC7296]).
2.1. The G-IKEv2 Header
G-IKEv2 uses the same IKE header format as specified in [RFC7296]
section 3.1.
Several new payload formats are required in the group security
exchanges.
Next Payload Type Value
----------------- -----
Group Identification (IDg) 50
Group Security Association (GSA) 51
Key Download (KD) 52
New exchange types GSA_AUTH, GSA_REGISTRATION and GSA_REKEY are added
to the IKEv2 [RFC7296] protocol.
Exchange Type Value
-------------- -----
GSA_AUTH 39
GSA_REGISTRATION 40
GSA_REKEY 41
GSA_INBAND_REKEY TBD
Major Version is 2 and Minor Version is 0 as in IKEv2 [RFC7296]. IKE
SA Initiator's SPI, IKE SA Responder's SPI, Flags, Message ID, and
Length are as specified in [RFC7296].
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2.2. Group Identification (IDg) Payload
The 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.
2.3. Security Association - GM Supported Transforms (SAg)
The 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 (33).
2.4. Group Security Association Payload
The Group Security Association payload is used by the GCKS to assert
security attributes for both Rekey and Data-security SAs.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: GSA Payload Format
The Security Association Payload fields are defined as follows:
o Next Payload (1 octet) -- Identifies the next payload type for the
G-IKEv2 registration or the G-IKEv2 rekey message.
o Critical (1 bit) -- Set according to [RFC7296].
o RESERVED (7 bits) -- Must be zero.
o Payload Length (2 octets) -- Is the octet length of the current
payload including the generic header and all TEK and KEK policies.
2.4.1. GSA Policy
Following the GSA generic payload header are GSA policies for group
rekeying (KEK), data traffic SAs (TEK) and/or Group Associated Policy
(GAP). There may be zero or one GSA KEK policy, zero or one GAP
policies, and zero or more GSA TEK policies, where either one GSA KEK
or GSA TEK payload MUST be present.
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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 attribute to the group
member since all SA updates would be performed using the Registration
SA. Alternatively, group policy might use a Rekey SA but choose to
download a KEK to the group member only as part of the Registration
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.
A GAP payload 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, and
include the following header.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | RESERVED | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: GSA Policy Generic Header Format
The payload fields are defined as follows:
o Type (1 octet) -- Identifies the substructure type. In the
following table the terms Reserved, Unassigned, and Private Use
are to be applied as defined in [RFC8126]. The registration
procedure is Expert Review.
Type Value
-------- -----
Reserved 0
KEK 1
GAP 2
TEK 3
Unassigned 4-127
Private Use 128-255
o RESERVED (1 octet) -- Unused, set to zero.
o Length (2 octets) -- Length in octets of the substructure,
including its header.
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2.4.2. KEK Policy
The GSA KEK policy contains security attributes for the KEK method
for a group and parameters specific to the G-IKEv2 registration
operation. The source and destination traffic selectors describe the
network identities used for the rekey messages.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1 | RESERVED | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ SPI ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Source Traffic Selector> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Destination Traffic Selector> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Transform Substructure List> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ KEK Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: KEK Policy Format
The GSA KEK Payload fields are defined as follows:
o Type = 1 (1 octet) -- Identifies the GSA payload type as KEK in
the G-IKEv2 registration or the G-IKEv2 rekey message.
o RESERVED (1 octet) -- Must be zero.
o Length (2 octets) -- Length of this structure including KEK
attributes.
o SPI (16 octets) -- Security Parameter Index for the rekey message.
The SPI must be 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. As described above, these SPIs are assigned by the
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GCKS. 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.
o Source & Destination Traffic Selectors - Substructures describing
the source and destination of the network identities. These
identities refer to the source and destination of the next KEK
rekey SA. Defined format and values are specified by IKEv2
[RFC7296], section 3.13.1.
o Transform Substructure List -- A list of Transform Substructures
specifies the transform information. The format is defined in
IKEv2 [RFC7296], section 3.3.2, and values are described in the
IKEv2 registries [IKEV2-IANA]. Valid Transform Types are ENCR,
INTEG. The Last Substruc value in each Transform Substructure
will be set to 3 except for the last one in the list, which is set
to 0.
o KEK Attributes -- Contains KEK policy attributes associated with
the group. The following sections describe the possible
attributes. Any or all attributes may be optional, depending on
the group policy.
2.4.2.1. KEK Attributes
The following attributes may be present in a GSA KEK policy. The
attributes must 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). The terms Reserved, Unassigned, and Private Use are to
be applied as defined in [RFC8126]. The registration procedure is
Expert Review.
KEK Attributes Value Type Mandatory
-------------- ----- ---- ---------
Reserved 0
KEK_MANAGEMENT_ALGORITHM 1 B N
Reserved 2
Reserved 3
KEK_KEY_LIFETIME 4 V Y
Reserved 5
KEK_AUTH_METHOD 6 B Y
KEK_AUTH_HASH 7 B N
KEK_MESSAGE_ID 8 V Y (*)
KEK_NEXT_SPI 9 V N
Unassigned 10-16383
Private Use 16384-32767
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(*) the KEK_MESSAGE_ID MUST be included in a G-IKEv2 registration
message and MUST NOT be included in rekey messages.
The following attributes may only be included in a G-IKEv2
registration message: KEK_MANAGEMENT_ALGORITHM, KEK_MESSAGE_ID.
2.4.2.1.1. KEK_MANAGEMENT_ALGORITHM
The KEK_MANAGEMENT_ALGORITHM attribute specifies the group KEK
management algorithm used to provide forward or backward access
control (i.e., used to exclude group members). Defined values are
specified in the following table. The terms Reserved, Unassigned,
and Private Use are to be applied as defined in [RFC8126]. The
registration procedure is Expert Review.
KEK Management Type Value
------------------- -----
Reserved 0
LKH 1
Unassigned 2-16383
Private Use 16384-32767
2.4.2.1.2. KEK_KEY_LIFETIME
The KEK_KEY_LIFETIME attribute specifies the maximum time for which
the KEK is valid. The GCKS may refresh the KEK at any time before
the end of the valid period. The value is a four (4) octet number
defining a valid time period in seconds.
2.4.2.1.3. KEK_AUTH_METHOD
The KEK_AUTH_METHOD attribute specifies the method of authentication
used. This value is from the IKEv2 Authentication Method registry
[IKEV2-IANA]. The method must either specify using some public key
signatures or Shared Key Message Integrity Code. Other
authentication methods MUST NOT be used.
2.4.2.1.4. KEK_AUTH_HASH
The KEK_AUTH_HASH attribute specifies the hash algorithm used to
generate the AUTH key to authenticate GSA_REKEY messages. Hash
algorithms are defined in IANA registry IKEv2 Hash Algorithms
[IKEV2-IANA].
This attribute SHOULD NOT be sent if the KEK_AUTH_METHOD implies a
particular hash algorithm (e.g., for DSA-based algorithms).
Furthermore, it is not necessary for the GCKS to send it if the GM is
known to support the algorithm because it declared it in a
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SIGNATURE_HASH_ALGORITHMS notification during registration (see
[RFC7427]).
2.4.2.1.5. KEK_MESSAGE_ID
The KEK_MESSAGE_ID attribute 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.
2.4.2.1.6. KEK_NEXT_SPI
The KEK_NEXT_SPI attribute may optionally be included by GCKS in
GSA_REKEY message, indicating what IKE SPIs are intended be used for
the next rekey SA. The attribute data MUST be 16 octets in length
specifying the pair of IKE SPIs as they appear in the IKE header.
Multiple attributes of this type MAY be included, meaning that any of
the supplied SPIs can be used for the next rekey.
The GM may save these values and if later the GM starts receiving IKE
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 was lost on its way to this GM. In this case the GM
SHOULD re-register to the group.
Note, that this method of detecting missed rekeys can only be used by
passive GMs, i.e. those, that only listen and don't send data. It's
also 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 KEK_NEXT_SPI attributes before (e.g. in case of GCKS reboot),
so the GM must only treat these information as a "best effort" made
by GCKS to prepare for future rekeys.
2.4.3. GSA TEK Policy
The GSA TEK policy contains security attributes for a single TEK
associated with a group.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 3 | RESERVED | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol-ID | TEK Protocol-Specific Payload |
+-+-+-+-+-+-+-+-+ ~
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: TEK Policy Generic Header Format
The GSA TEK Payload fields are defined as follows:
o Type = 3 (1 octet) -- Identifies the GSA payload type as TEK in
the G-IKEv2 registration or the G-IKEv2 rekey message.
o RESERVED (1 octet) -- Must be zero.
o Length (2 octets) -- Length of this structure, including the TEK
Protocol-Specific Payload.
o Protocol-ID (1 octet) -- Value specifying the Security Protocol.
The following table defines values for the Security Protocol.
Support for the GSA_PROTO_IPSEC_AH GSA TEK is OPTIONAL. The terms
Reserved, Unassigned, and Private Use are to be applied as defined
in [RFC8126]. The registration procedure is Expert Review.
Protocol ID Value
----------- -----
Reserved 0
GSA_PROTO_IPSEC_ESP 1
GSA_PROTO_IPSEC_AH 2
Unassigned 3-127
Private Use 128-255
o TEK Protocol-Specific Payload (variable) -- Payload which
describes the attributes specific for the Protocol-ID.
2.4.3.1. TEK ESP and AH Protocol-Specific Policy
The TEK Protocol-Specific policy contains two traffic selectors one
for the source and one for the destination of the protected traffic,
SPI, Transforms, and Attributes.
The TEK Protocol-Specific policy for ESP and AH is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Source Traffic Selector> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Destination Traffic Selector> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ <Transform Substructure List> ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TEK Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: AH and ESP TEK Policy Format
The GSA TEK Policy fields are defined as follows:
o SPI (4 octets) -- Security Parameter Index.
o Source & Destination Traffic Selectors - The traffic selectors
describe the source and the destination of the protected traffic.
The format and values are defined in IKEv2 [RFC7296], section
3.13.1.
o Transform Substructure List -- A list of Transform Substructures
specifies the transform information. The format is defined in
IKEv2 [RFC7296], section 3.3.2, and values are described in the
IKEv2 registries [IKEV2-IANA]. Valid Transform Types for ESP are
ENCR, INTEG, and ESN. Valid Transform Types for AH are INTEG and
ESN. The Last Substruc value in each Transform Substructure will
be set to 3 except for the last one in the list, which is set to
0. A Transform Substructure with attributes (e.g., the ENCR Key
Length), they are included within the Transform Substructure as
usual.
o TEK Attributes -- Contains the TEK policy attributes associated
with the group, in the format defined in Section 3.3.5 of
[RFC7296]. All attributes are optional, depending on the group
policy.
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Attribute Types are as follows. The terms Reserved, Unassigned, and
Private Use are to be applied as defined in [RFC8126]. The
registration procedure is Expert Review.
TEK Attributes Value Type Mandatory
-------------- ----- ---- ---------
Reserved 0
TEK_KEY_LIFETIME 1 V N
TEK_MODE 2 B Y
TEK_REKEY_SPI 3 V N
TEK_NEXT_SPI 4 V N
Unassigned 5-16383
Private Use 16384-32767
It is NOT RECOMMENDED that the GCKS distribute both ESP and AH
Protocol-Specific Policies for the same set of Traffic Selectors.
2.4.3.1.1. TEK_KEY_LIFETIME
The TEK_KEY_LIFETIME attribute specifies the maximum time for which
the TEK is valid. When the TEK expires, the AH or ESP security
association and all keys downloaded under the security association
are discarded. The GCKS may refresh the TEK at any time before the
end of the valid period.
The value is a four (4) octet number defining a valid time period in
seconds. If unspecified the default value of 28800 seconds (8 hours)
shall be assumed.
2.4.3.1.2. TEK_MODE
The value of 0 is used for tunnel mode and 1 for transport mode. In
the absence of this attribute tunnel mode will be used.
2.4.3.1.3. TEK_REKEY_SPI
This attribute contains an SPI for the SA that is being rekeyed. The
size of SPI depends on the protocol, for ESP and AH it is 4 octets,
so the size of the data MUST be 4 octets for AH and ESP.
If this attribute is included in the rekey message, the GM SHOULD
delete the SA corresponding to this SPI once the new SA is installed
and regardless of the expiration time of the SA to be deleted (but
after waiting DEACTIVATION_TIME_DELAY time period).
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2.4.3.1.4. TEK_NEXT_SPI
This attribute contains an SPI that the GCKS reserved for the next
rekey. The size of SPI depends on the protocol, for ESP and AH it is
4 octets, so the size of the data MUST be 4 octets for AH and ESP.
Multiple attributes of this type MAY be included, which means that
any of the provided SPIs can be used in the next rekey.
The GM may save these values and if later the GM starts receiving
IPsec messages with one of these SPIs without seeing a rekey message
for it, this may be used as an indication, that the rekey message was
lost on its way to this GM. In this case the GM SHOULD re-register
to the group.
Note, that this method of detecting missed rekey messages can only be
used by passive GMs, i.e. those, that only listen and don't send
data. It's also 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 TEK_NEXT_SPI attributes before (e.g. in case of
GCKS reboot), so the GM must only treat these information as a "best
effort" made by GCKS to prepare for future rekeys.
2.4.4. GSA Group Associated Policy
Group specific policy that does not belong to rekey policy (GSA KEK)
or traffic encryption policy (GSA TEK) can be distributed to all
group member using GSA GAP (Group Associated Policy).
The GSA GAP payload is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | RESERVED | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Group Associated Policy Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: GAP Policy Format
The GSA GAP payload fields are defined as follows:
o Type = 2 (1 octet) -- Identifies the GSA payload type as GAP in
the G-IKEv2 registration or the G-IKEv2 rekey message.
o RESERVED (1 octet) -- Must be zero.
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o Length (2 octets) -- Length of this structure, including the GSA
GAP header and Attributes.
o Group Associated Policy Attributes (variable) -- Contains
attributes following the format defined in Section 3.3.5 of
[RFC7296].
Attribute Types are as follows. The terms Reserved, Unassigned, and
Private Use are to be applied as defined in [RFC8126]. The
registration procedure is Expert Review.
Attribute Type Value Type
-------------- ----- ----
Reserved 0
ACTIVATION_TIME_DELAY 1 B
DEACTIVATION_TIME_DELAY 2 B
Unassigned 3-16383
Private Use 16384-32767
2.4.4.1. ACTIVATION_TIME_DELAY/DEACTIVATION_TIME_DELAY
Section 4.2.1 of [RFC5374] specifies a key rollover method that
requires two values be provided to group members. The
ACTIVATION_TIME_DELAY attribute allows a GCKS to set the Activation
Time Delay (ATD) for SAs generated from TEKs. The ATD defines how
long after receiving new SAs that they are to be activated by the GM.
The ATD value is in seconds.
The DEACTIVATION_TIME_DELAY allows the GCKS to set the Deactivation
Time Delay (DTD) for previously distributed SAs. The DTD defines how
long after receiving new SAs it should deactivate SAs that are
destroyed by the rekey event. The value is in seconds.
The values of ATD and DTD are independent. However, the DTD value
should be larger, which allows new SAs to be activated before older
SAs are deactivated. Such a policy ensures that protected group
traffic will always flow without interruption.
2.5. Key Download Payload
The Key Download Payload contains the group keys for the group
specified in the GSA Payload. These key download payloads can have
several security attributes applied to them based upon the security
policy of the group as defined by the associated GSA Payload.
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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 Packets ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: Key Download Payload Format
The Key Download Payload fields are defined as follows:
o Next Payload (1 octet) -- Identifier for the payload type of the
next payload in the message. If the current payload is the last
in the message, then this field will be zero.
o Critical (1 bit) -- Set according to [RFC7296].
o RESERVED (7 bits) -- Unused, set to zero.
o Payload Length (2 octets) -- Length in octets of the current
payload, including the generic payload header.
o Key Packets (variable) -- Contains Key Packets. Several types of
key packets are defined. Each Key Packet has the following
format.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| KD Type | RESERVED | KD Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI Size | SPI (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Key Packet Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25: Key Packet Format
o Key Download (KD) Type (1 octet) -- Identifier for the Key Data
field of this Key Packet. In the following table the terms
Reserved, Unassigned, and Private Use are to be applied as defined
in [RFC8126]. The registration procedure is Expert Review.
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Key Download Type Value
----------------- -----
Reserved 0
TEK 1
KEK 2
LKH 3
SID 4
Unassigned 5-127
Private Use 128-255
o RESERVED (1 octet) -- Unused, set to zero.
o Key Download Length (2 octets) -- Length in octets of the Key
Packet data, including the Key Packet header.
o SPI Size (1 octet) -- Value specifying the length in octets of the
SPI as defined by the Protocol-Id.
o SPI (variable length) -- Security Parameter Index which matches a
SPI previously sent in an GSA KEK or GSA TEK Payload.
o Key Packet Attributes (variable length) -- Contains Key
information. The format of this field is specific to the value of
the KD Type field. The following sections describe the format of
each KD Type.
2.5.1. TEK Download Type
The following attributes may be present in a TEK Download Type.
Exactly one attribute matching each type sent in the GSA TEK payload
MUST be present. The attributes must follow the format defined in
IKEv2 (Section 3.3.5 of [RFC7296]). In the table, attributes defined
as TV are marked as Basic (B); attributes defined as TLV are marked
as Variable (V). The terms Reserved, Unassigned, and Private Use are
to be applied as defined in [RFC8126]. The registration procedure is
Expert Review.
TEK KD Attributes Value Type Mandatory
----------------- ----- ---- ---------
Reserved 0-2
TEK_KEYMAT 3 V Y
Unassigned 4-16383
Private Use 16384-32767
It is possible that the GCKS will send no TEK key packets in a
Registration KD payload (as well as no corresponding GSA TEK payloads
in the GSA payload), after which the TEK payloads will be sent in a
rekey message.
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2.5.1.1. TEK_KEYMAT
The TEK_KEYMAT attribute contains keying material for the
corresponding SPI. This keying material will be used with the
transform specified in the GSA TEK payload. The keying material is
treated equivalent to IKEv2 KEYMAT derived for that IPsec transform.
2.5.2. KEK Download Type
The following attributes may be present in a KEK Download Type.
Exactly one attribute matching each type sent in the GSA KEK payload
MUST be present. The attributes must follow the format defined in
IKEv2 (Section 3.3.5 of [RFC7296]). In the table, attributes defined
as TV are marked as Basic (B); attributes defined as TLV are marked
as Variable (V). The terms Reserved, Unassigned, and Private Use are
to be applied as defined in [RFC8126]. The registration procedure is
Expert Review.
KEK KD Attributes Value Type Mandatory
----------------- ----- ---- ---------
Reserved 0
KEK_ENCR_KEY 1 V Y
KEK_INTEGRITY_KEY 2 V N
KEK_AUTH_KEY 3 V N
Unassigned 4-16383
Private Use 16384-32767
If the KEK Key Packet is included, there MUST be only one present in
the KD payload.
2.5.2.1. KEK_ENCR_KEY
The KEK_ENCR_KEY attribute type declares that the encryption key for
the corresponding SPI is contained in the Key Packet Attribute. The
encryption algorithm that will use this key was specified in the GSA
KEK payload.
2.5.2.2. KEK_INTEGRITY_KEY
The KEK_INTEGRITY_KEY attribute type declares the integrity key for
this SPI is contained in the Key Packet Attribute. The integrity
algorithm that will use this key was specified in the GSA KEK
payload.
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2.5.2.3. KEK_AUTH_KEY
The KEK_AUTH_KEY attribute type declares that the authentication key
for this SPI is contained in the Key Packet Attribute. The signature
algorithm that will use this key was specified in the GSA KEK
payload. An RSA public key format is defined in [RFC3447],
Section A.1.1. DSS public key format is defined in [RFC3279]
Section 2.3.2. For ECDSA Public keys, use format described in
[RFC5480] Section 2.2. Other algorithms added to the IKEv2
Authentication Method registry are also expected to include a format
of the public key included in the algorithm specification.
2.5.3. LKH Download Type
The LKH key packet is comprised of attributes representing different
leaves in the LKH key tree.
The following attributes are used to pass an LKH KEK array in the KD
payload. The attributes must follow the format defined in IKEv2
(Section 3.3.5 of [RFC7296]). In the table, attributes defined as TV
are marked as Basic (B); attributes defined as TLV are marked as
Variable (V). The terms Reserved, Unassigned, and Private Use are to
be applied as defined in [RFC8126]. The registration procedure is
Expert Review.
LKH KD Attributes Value Type
----------------- ----- ----
Reserved 0
LKH_DOWNLOAD_ARRAY 1 V
LKH_UPDATE_ARRAY 2 V
Unassigned 3-16383
Private Use 16384-32767
If an LKH key packet is included in the KD payload, there MUST be
only one present.
2.5.3.1. LKH_DOWNLOAD_ARRAY
The LKH_DOWNLOAD_ARRAY attribute type is used to download a set of
LKH keys to a group member. It MUST NOT be included in a IKEv2 rekey
message KD payload if the IKEv2 rekey is sent to more than one group
member. If an LKH_DOWNLOAD_ARRAY attribute is included in a KD
payload, there MUST be only one present.
This attribute consists of a header block, followed by one or more
LKH keys.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # of LKH Keys | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ LKH Keys ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: LKH_DOWNLOAD_ARRAY Format
The KEK_LKH attribute fields are defined as follows:
o Number of LKH Keys (2 octets) -- This value is the number of
distinct LKH keys in this sequence.
o RESERVED (2 octets) -- Unused, set to zero.
Each LKH Key is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LKH ID | Encr Alg |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Handle |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Key Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: LKH Key Format
o LKH ID (2 octets) -- This is the position of this key in the
binary tree structure used by LKH.
o Encr Alg (2 octets) -- This is the encryption algorithm for which
this key data is to be used. This value is specified in the ENCR
transform in the GSA payload.
o Key Handle (4 octets) -- This is a randomly generated value to
uniquely identify a key within an LKH ID.
o Key Data (variable length) -- This is the actual encryption key
data, which is dependent on the Encr Alg algorithm for its format.
The first LKH Key structure in an LKH_DOWNLOAD_ARRAY attribute
contains the Leaf identifier and key for the group member. The rest
of the LKH Key structures contain keys along the path of the key tree
in the order starting from the leaf, culminating in the group KEK.
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2.5.3.2. LKH_UPDATE_ARRAY
The LKH_UPDATE_ARRAY attribute type is used to update the LKH keys
for a group. It is most likely to be included in a G-IKEv2 rekey
message KD payload to rekey the entire group. This attribute
consists of a header block, followed by one or more LKH keys, as
defined in Section 2.5.3.1.
There may be any number of LKH_UPDATE_ARRAY attributes included in a
KD payload.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # of LKH Keys | LKH ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Handle |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ LKH Keys ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: LKH_UPDATE_ARRAY Format
o Number of LKH Keys (2 octets) -- This value is the number of
distinct LKH keys in this sequence.
o LKH ID (2 octets) -- This is the node identifier associated with
the key used to encrypt the first LKH Key.
o Key Handle (4 octets) -- This is the value that uniquely
identifies the key within the LKH ID which was used to encrypt the
first LKH key.
The LKH Keys are as defined in Section 2.5.3.1. The LKH Key
structures contain keys along the path of the key tree in the order
from the LKH ID found in the LKH_UPDATE_ARRAY header, culminating in
the group KEK. The Key Data field of each LKH Key is encrypted with
the LKH key preceding it in the LKH_UPDATE_ARRAY attribute. The
first LKH Key is encrypted under the key defined by the LKH ID and
Key Handle found in the LKH_UPDATE_ARRAY header.
2.5.4. SID Download Type
The SID attribute is used to download one or more Sender-ID (SID)
values for the exclusive use of a group member. The terms Reserved,
Unassigned, and Private Use are to be applied as defined in
[RFC8126]. The registration procedure is Expert Review.
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SID KD Attributes Value Type
----------------- ----- ----
Reserved 0
NUMBER_OF_SID_BITS 1 B
SID_VALUE 2 V
Unassigned 3-16383
Private Use 16384-32767
Because a SID value is intended for a single group member, the SID
Download type MUST NOT be distributed in a GSA_REKEY message
distributed to multiple group members.
2.5.4.1. NUMBER_OF_SID_BITS
The NUMBER_OF_SID_BITS attribute type declares how many bits of the
cipher nonce in which to represent an SID value. The bits are
applied as the most significant bits of the IV, as shown in Figure 1
of [RFC6054] and specified in Section 1.4.6.2. Guidance for a GCKS
choosing the NUMBER_OF_SID_BITS is provided in Section 3 of
[RFC6054].
This value is applied to each SID value distributed in the SID
Download.
2.5.4.2. SID_VALUE
The SID_VALUE attribute type declares a single SID value for the
exclusive use of this group member. Multiple SID_VALUE attributes
MAY be included in a SID Download.
2.5.4.3. GM Semantics
The SID_VALUE attribute value distributed to the group member MUST be
used by that group member as the SID field portion of the IV for all
Data-Security SAs including a counter-based mode of operation
distributed by the GCKS as a part of this group. When the Sender-
Specific IV (SSIV) field for any Data-Security SA is exhausted, the
group member MUST NOT act as a sender on that SA using its active
SID. The group member SHOULD re-register, at which time the GCKS
will issue a new SID to the group member, along with either the same
Data-Security SAs or replacement ones. The new SID replaces the
existing SID used by this group member, and also resets the SSIV
value to its starting value. A group member MAY re-register prior to
the actual exhaustion of the SSIV field to avoid dropping data
packets due to the exhaustion of available SSIV values combined with
a particular SID value.
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A group member MUST ignore an SID Download Type KD payload present in
a GSA-REKEY message, otherwise more than one GM may end up using the
same SID.
2.5.4.4. GCKS Semantics
If any KD payload includes keying material that is associated with a
counter-mode of operation, an SID Download Type KD payload containing
at least one SID_VALUE attribute MUST be included. The GCKS MUST NOT
send the SID Download Type KD payload as part of a GSA_REKEY message,
because distributing the same sender-specific policy to more than one
group member will reduce the security of the group.
2.6. Delete Payload
There are occasions when the GCKS may want to signal to group members
to delete policy at the end of a broadcast, if group policy has
changed, or the GCKS needs to reset the policy and keying material
for the group due to an emergency. Deletion of keys MAY be
accomplished by sending an IKEv2 Delete Payload, section 3.11 of
[RFC7296] as part of a registration or rekey Exchange. Whenever an
SA is to be deleted, the GKCS SHOULD send the Delete Payload in both
registration and rekey exchanges, because GMs with previous group
policy may contact the GCKS using either exchange.
The Protocol ID MUST be 41 for GSA_REKEY Exchange, 2 for AH or 3 for
ESP. Note that only one protocol id value can be defined in a Delete
payload. If a TEK and a KEK SA for GSA_REKEY Exchange must be
deleted, they must be sent in different Delete payloads. Similarly,
if a TEK specifying ESP and a TEK specifying AH need to be deleted,
they must be sent in different Delete payloads.
There may be circumstances where the GCKS may want to reset the
policy and keying material for the group. The GCKS can signal
deletion of all policy of a particular TEK by sending a TEK with a
SPI value equal to zero in the delete payload. In the event that the
administrator is no longer confident in the integrity of the group
they may wish to remove all KEK and all the TEKs in the group. This
is done by having the GCKS send a delete payload with a SPI of zero
and a Protocol-ID of AH or ESP to delete all TEKs, followed by
another delete payload with a SPI value of zero and Protocol-ID of
KEK SA to delete the KEK SA.
2.7. Notify Payload
G-IKEv2 uses the same Notify payload as specified in [RFC7296],
section 3.10.
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There are additional Notify Message types introduced by G-IKEv2 to
communicate error conditions and status.
NOTIFY messages - error types Value
-------------------------------------------------------------------
INVALID_GROUP_ID - 45
AUTHORIZATION_FAILED - 46
REGISTRATION_FAILED - TBD
INVALID_GROUP_ID indicates the group id sent during the registration
process is invalid.
AUTHORIZATION_FAILED is sent in the response to a GSA_AUTH message
when authorization failed.
REGISTRATION_FAILED is sent by the GCKS when the GM registration
request cannot be satisfied.
NOTIFY messages - status types Value
-------------------------------------------------------------------
SENDER - 16429
REKEY_IS_NEEDED - TBD
SENDER notification is sent in GSA_AUTH or GSA_REGISTRATION to
indicate that the GM intends to be sender of data traffic. The data
includes a count of how many SID values the GM desires. The count
MUST be 4 octets long and contain the big endian representation of
the number of requested SIDs.
REKEY_IS_NEEDED is sent in GSA_AUTH response message to indicate that
the GM must perform an immediate rekey of IKE SA to make it secure
against quantum computers and then start a registration request over.
2.8. Authentication Payload
G-IKEv2 uses the same Authentication payload as specified in
[RFC7296], section 3.8, to sign the rekey message.
3. Security Considerations
3.1. GSA Registration and Secure Channel
G-IKEv2 registration exchange uses IKEv2 IKE_SA_INIT protocols,
inheriting all the security considerations documented in [RFC7296]
section 5 Security Considerations, 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
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those protections. In addition, G-IKEv2 brings in the capability to
authorize a particular group member regardless of whether they have
the IKEv2 credentials.
3.2. GSA Maintenance Channel
The GSA maintenance channel is cryptographically and integrity
protected using the cryptographic algorithm and key negotiated in the
GSA member registration exchanged.
3.2.1. Authentication/Authorization
Authentication is implicit, the public key of the identity is
distributed during the registration, and the receiver of the rekey
message uses that public key and identity to verify the message came
from the authorized GCKS.
3.2.2. Confidentiality
Confidentiality is provided by distributing a confidentiality key as
part of the GSA member registration exchange.
3.2.3. Man-in-the-Middle Attack Protection
GSA maintenance channel is integrity protected by using a digital
signature.
3.2.4. 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.
4. IANA Considerations
4.1. New Registries
A new set of registries should be created for G-IKEv2, on a new page
titled Group Key Management using IKEv2 (G-IKEv2) Parameters. The
following registries should be placed on that page. The terms
Reserved, Expert Review and Private Use are to be applied as defined
in [RFC8126].
GSA Policy Type Registry, see Section 2.4.1
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KEK Attributes Registry, see Section 2.4.2.1
KEK Management Algorithm Registry, see Section 2.4.2.1.1
GSA TEK Payload Protocol ID Type Registry, see Section 2.4.3
TEK Attributes Registry, see Section 2.4.3
Key Download Type Registry, see Section 2.5
TEK Download Type Attributes Registry, see Section 2.5.1
KEK Download Type Attributes Registry, see Section 2.5.2
LKH Download Type Attributes Registry, see Section 2.5.3
SID Download Type Attributes Registry, see Section 2.5.4
4.2. New Payload and Exchange Types Added to the Existing IKEv2
Registry
The following new payloads and exchange types specified in this memo
have already been allocated by IANA and require no further action,
other than replacing the draft name with an RFC number.
The present document describes new IKEv2 Next Payload types, see
Section 2.1
The present document describes new IKEv2 Exchanges types, see
Section 2.1
The present document describes new IKEv2 notification types, see
Section 2.7
4.3. Changes to Previous Allocations
Section 4.7 indicates an allocation in the IKEv2 Notify Message Types
- Status Types registry has been made. This NOTIFY type was
allocated earlier in the development of G-IKEv2. The number is
16429, and was allocated with the name SENDER_REQUEST_ID. The name
should be changed to SENDER.
5. 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
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instrumental in helping resolve many issues in several versions of
the document.
6. 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
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
7. References
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7.1. 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>.
[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>.
[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>.
[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>.
[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>.
[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>.
[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>.
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7.2. Informative References
[I-D.ietf-ipsecme-qr-ikev2]
Fluhrer, S., McGrew, D., Kampanakis, P., and V. Smyslov,
"Postquantum Preshared Keys for IKEv2", draft-ietf-
ipsecme-qr-ikev2-08 (work in progress), March 2019.
[I-D.tjhai-ipsecme-hybrid-qske-ikev2]
Tjhai, C., Tomlinson, M., grbartle@cisco.com, g., Fluhrer,
S., Geest, D., Garcia-Morchon, O., and V. Smyslov,
"Framework to Integrate Post-quantum Key Exchanges into
Internet Key Exchange Protocol Version 2 (IKEv2)", draft-
tjhai-ipsecme-hybrid-qske-ikev2-03 (work in progress),
January 2019.
[IKEV2-IANA]
IANA, "Internet Key Exchange Version 2 (IKEv2)
Parameters", February 2016,
<http://www.iana.org/assignments/ikev2-parameters/
ikev2-parameters.xhtml#ikev2-parameters-7>.
[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/>.
[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, <http://download.nai.com/products/media/nai/misc/
oft052098.ps>.
[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>.
[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>.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, DOI 10.17487/RFC3447, February
2003, <https://www.rfc-editor.org/info/rfc3447>.
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[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>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[RFC8229] Pauly, T., Touati, S., and R. Mantha, "TCP Encapsulation
of IKE and IPsec Packets", RFC 8229, DOI 10.17487/RFC8229,
August 2017, <https://www.rfc-editor.org/info/rfc8229>.
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. 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 (represented as
numbers in the figure) and a private key shared with only a single GM
(represented as letters in the figure). Note that the use of numbers
and letters is used for explanatory purposes; in fact, each key would
have an LKH ID, which is two-octet identifier chosen by the GCKS.
The GCKS may create a complete tree as shown, or a partial tree which
is created on demand as members join the group. The top of the key
tree (i.e., "1" in Figure 29) is used as the KEK for the group.
1
+------------------------------+
2 3
+---------------+ +---------------+
4 5 6 7
+-------+ +-------+ +--------+ +--------+
A B C D E F G H
Figure 29: Initial LKH tree
When GM "A" joins the group, the GCKS provides an LKH_DOWNLOAD_ARRAY
in the KD payload of the GSA_AUTH or GSA_REGISTRATION exchange.
Given the tree shown in figure above, the LKH_DOWNLOAD_ARRAY will
contain four LKH Key payloads, each containing an LKH ID and Key
Data. If the LKH ID values were chosen as shown in the figure, four
LKH Keys would be provided to GM "A", in the following order: A, 4,
2, 1. When GM "B" joins the group, it would also be given four LKH
Keys in the following order: B, 4, 2, 1. And so on, until GM "H"
joins the group and is given H, 7, 3, 1.
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A.2. 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 exchange that includes a set of
LKH_UPDATE_ARRAY attributes in the KD payload. Each LKH_UPDATE_ARRAY
contains a set of LKH Key payloads, in which every GM other than the
excluded GM will be able to determine a set of new logical keys,
which culminate in a new key "1". The excluded GM will observe the
set of LKH_UPDATE_ARRAY attributes, but cannot determine the new
logical keys because each of the "Key Data" fields is encrypted with
a key held by other GMs. The GM will hold no keys to properly
decrypt any of the "Key Data" fields, including key "1" (i.e., the
new KEK). When a subsequent GSA_REKEY exchange is delivered by the
GCKS and protected by the new KEK, the excluded GM will no longer be
able to see the contents of the GSA_REKEY, including new TEKs that
will be delivered to replace existing TEKs. At this point, the GM
will no longer be able to participate in the group.
In the example below, new keys are represented as the number followed
by a "prime" symbol (e.g., "1" becomes "1'"). Each key is encrypted
by another key. This is represented as "{key1}key2", where key2
encrypts key1. For example, "{1'}2' states that a new key "1'" is
encrypted with a new key "2'".
If GM "B" is to be excluded, the GCKS will need to include three
LKH_UPDATE_ARRAY attributes in the GSA_REKEY message. The order of
the attributes does not matter; only the order of the keys within
each attribute.
o One will provide GM "A" with new logical keys that are shared with
B: {4'}A, {2'}4', {1'}2'
o One will provide all GMs holding key "5" with new logical keys:
{2'}5, {1'}2'
o One will provide all GMs holding key "3" with a new KEK: {1'}3
Each GM will look at each LKH_UPDATE_ARRAY attribute and observe an
LKH ID which is present in an LKH Key delivered to them in the
LKH_DOWNLOAD_ARRAY they were given. If they find a matching LKH ID,
then they will decrypt the new key with the logical key immediately
preceding that LKH Key, and so on until they have received the new 1'
key.
The resulting key tree from this rekey event would would be shown in
Figure 30.
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1'
+------------------------------+
2' 3
+---------------+ +---------------+
4' 5 6 7
+---+ +-------+ +--------+ +--------+
A B C D E F G H
Figure 30: LKH tree after B has been excluded
Authors' Addresses
Brian Weis
Independent
USA
Email: bew.stds@gmail.com
Valery Smyslov
ELVIS-PLUS
PO Box 81
Moscow (Zelenograd) 124460
Russian Federation
Phone: +7 495 276 0211
Email: svan@elvis.ru
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