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Versions: (draft-yeung-g-ikev2) 00 01

Network Working Group                                         V. Smyslov
Internet-Draft                                                ELVIS-PLUS
Obsoletes: 6407 (if approved)                                    B. Weis
Intended status: Standards Track                             Independent
Expires: January 14, 2021                                  July 13, 2020


                    Group Key Management using IKEv2
                     draft-ietf-ipsecme-g-ikev2-01

Abstract

   This document presents an extension to the Internet Key Exchange
   version 2 (IKEv2) protocol for the purpose of a group key management.
   The protocol is in conformance with the Multicast Security (MSEC) key
   management architecture, which contains two components: member
   registration and group rekeying.  Both components 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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 14, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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  . . . . . . . . . . . . .   6
       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  . . . . . . . . . . . .  12
       1.4.5.  Group Maintenance Channel . . . . . . . . . . . . . .  13
       1.4.6.  Counter-based modes of operation  . . . . . . . . . .  20
   2.  Group Key Management and Access Control . . . . . . . . . . .  22
     2.1.  Key Wrap Keys . . . . . . . . . . . . . . . . . . . . . .  23
       2.1.1.  Default Key Wrap Key  . . . . . . . . . . . . . . . .  23
     2.2.  GCKS Key Management Semantics . . . . . . . . . . . . . .  23
       2.2.1.  Forward Access Control Requirements . . . . . . . . .  24
     2.3.  GM Key Management Semantics . . . . . . . . . . . . . . .  25
     2.4.  Group SA Keys . . . . . . . . . . . . . . . . . . . . . .  26
   3.  Header and Payload Formats  . . . . . . . . . . . . . . . . .  27
     3.1.  G-IKEv2 Header  . . . . . . . . . . . . . . . . . . . . .  27
     3.2.  Group Identification Payload  . . . . . . . . . . . . . .  27
     3.3.  Security Association - GM Supported Transforms Payload  .  27
     3.4.  Group Security Association Payload  . . . . . . . . . . .  28
       3.4.1.  Group Policies  . . . . . . . . . . . . . . . . . . .  28
       3.4.2.  Group Security Association Policy Substructure  . . .  29
       3.4.3.  Group Associated Policy Substructure  . . . . . . . .  35
     3.5.  Key Download Payload  . . . . . . . . . . . . . . . . . .  37
       3.5.1.  Wrapped Key Format  . . . . . . . . . . . . . . . . .  37
       3.5.2.  Group Key Packet Substructure . . . . . . . . . . . .  39
       3.5.3.  Member Key Packet Substructure  . . . . . . . . . . .  40
     3.6.  Delete Payload  . . . . . . . . . . . . . . . . . . . . .  43
     3.7.  Notify Payload  . . . . . . . . . . . . . . . . . . . . .  43
       3.7.1.  USE_TRANSPORT_MODE Notification . . . . . . . . . . .  44
     3.8.  Authentication Payload  . . . . . . . . . . . . . . . . .  45
   4.  Interaction with other IKEv2 Protocol Extensions  . . . . . .  45
     4.1.  Mixing Preshared Keys in IKEv2 for Post-quantum Security   45



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   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  47
     5.1.  GSA Registration and Secure Channel . . . . . . . . . . .  47
     5.2.  GSA Maintenance Channel . . . . . . . . . . . . . . . . .  47
       5.2.1.  Authentication/Authorization  . . . . . . . . . . . .  47
       5.2.2.  Confidentiality . . . . . . . . . . . . . . . . . . .  47
       5.2.3.  Man-in-the-Middle Attack Protection . . . . . . . . .  48
       5.2.4.  Replay/Reflection Attack Protection . . . . . . . . .  48
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  48
     6.1.  New Registries  . . . . . . . . . . . . . . . . . . . . .  48
     6.2.  Changes in the Existing IKEv2 Registries  . . . . . . . .  50
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  51
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  51
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  52
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  52
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  53
   Appendix A.  Use of LKH in G-IKEv2  . . . . . . . . . . . . . . .  56
     A.1.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .  56
     A.2.  Group Creation  . . . . . . . . . . . . . . . . . . . . .  56
     A.3.  Simple Group SA Rekey . . . . . . . . . . . . . . . . . .  57
     A.4.  Group Member Exclusion  . . . . . . . . . . . . . . . . .  58
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  59

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 an extension to
   IKEv2 [RFC7296] called G-IKEv2, that allows to perform a group key
   management.

   G-IKEv2 conforms to the Multicast Group Security Architecture
   [RFC3740], Multicast Extensions to the Security Architecture for the
   Internet Protocol [RFC5374] and the Multicast Security (MSEC) Group
   Key Management Architecture [RFC4046].  G-IKEv2 replaces GDOI
   [RFC6407], which defines a similar group key management protocol
   using IKEv1 [RFC2409] (since deprecated by IKEv2).  When G-IKEv2 is
   used, group key management use cases can benefit from the simplicity,
   increased robustness and cryptographic improvements of IKEv2 (see
   Appendix A of [RFC7296].

   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



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   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 pseudo-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.)

                                +--------+
                 +------------->|  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.)









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                          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

   IKEv2 message semantics are preserved in that all communications
   consists of message request-response pairs.  The exception to this
   rule is the GSA_REKEY pseudo-exchange, which is a single message
   delivering group updates to the GMs.

1.1.  Requirements 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 4 for more
   details.

   It is assumed that readers are familiar with the IKEv2 protocol, so
   this document skips many details that are described in [RFC7296].








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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].

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
        D             Delete
        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
        N             Notify
        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 in
   G-IKEv2 messages will be shown in brackets, such as [CERTREQ].

   G-IKEv2 defines several new payloads not used in IKEv2:



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   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 keys and the security
      parameters to the GMs using the KD payload.

   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 3.

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



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   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.

    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 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,] [N,] [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 3.6.)

   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 3.7, 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.





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    Initiator (Member)               Responder (GCKS)
   --------------------             ------------------
                              <--   HDR, SK{IDr, [CERT,] AUTH, N}

                     Figure 5: GSA_AUTH Error Response

   If the group member finds the policy sent by the GCKS is
   unacceptable, the member SHOULD initiate GSA_REGISTRATION exchange
   sending IDg and the Notify NO_PROPOSAL_CHOSEN (see Section 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,] [N,] [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.






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    Initiator (Member)                 Responder (GCKS)
   --------------------               ------------------
    HDR, SK{IDg, N}      -->
                            <--        HDR, SK{}

        Figure 8: GM Reporting Errors in GSA_REGISTRATION Exchange

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.

   A GM 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 it is willing to accept for different security protocols.
   Proposals for Rekey SA (with protocol GIKE_REKEY) and for data
   security (AH and/or ESP) SAs may be included into SAg.  Each Proposal
   contains a list of Transforms that the GM is able to support for that
   protocol.  Valid transform types depend on the protocol and are
   defined in Figure 15.  Other transform types SHOULD NOT be included.
   The SPI length of each Proposal in an SAg is set to zero, and thus
   the SPI field is empty.  The GCKS MUST ignore SPI 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.  In particular, the restriction
   from Section 3.3 of [RFC7296] that AEAD and non-AEAD transforms must
   not be combined in a single proposal doesn't hold when the SAg
   payload is being formed.  However if the GM has restrictions on
   combination of algorithms, this can be expressed by sending several
   proposals.






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   Although the SAg payload is optional, it is RECOMMENDED for the GM to
   include this payload into the GSA_AUTH request to allow the GCKS to
   select an appropriate policy.

   A GM may also indicate the support for IPcomp by inclusion one or
   more the IPCOMP_SUPPORTED notifications along with the SAg payload.
   The CPI in these notifications is set to zero and MUST be ignored by
   the GCKS.

   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), 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
   are 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.  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 the attribute GSA_INITIAL_MESSAGE_ID
   with a first Message ID the GM should expect to receive if it is non-
   zero.  The value of the attribute MUST be checked by a GM against any
   previously received Message ID for this group.  If it is less than
   the previously received number, it should be considered stale and
   ignored.  This could happen if two GSA_AUTH exchanges happened in
   parallel, and the Message ID changed.  This attribute is used by the
   GM to prevent GSA_REKEY message replay attacks.  The first GSA_REKEY
   message that the GM receives from the GCKS must have a Message ID
   greater or equal to the Message ID received in the
   GSA_INITIAL_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.





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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
   GSA_INITIAL_MESSAGE_ID attribute, specifying the starting Message ID
   the GCKS will use when sending the GSA_REKEY message to the group
   member if this Message ID is non-zero.  This Message ID is used to
   prevent GSA_REKEY message replay attacks and will be increased each
   time a GSA_REKEY message is sent to the group.  The GCKS data traffic
   policy is included in the GSA TEK and keys are included in the KD
   TEK.  The GAP MAY also be included to provide the ATD and/or DTD
   (Section 3.4.3.1) specifying activation and deactivation delays for
   SAs generated from the TEKs.  If the group member has indicated that
   it is a sender of data traffic and one or more Data Security SAs
   distributed in the GSA payload included a counter mode of operation,
   the GCKS responds with one or more 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.






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   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.

   GSA_REKEY  The GSA_REKEY is a pseudo-exchange initiated by the GCKS,
      where the rekey policy is usually delivered to group members using
      IP multicast as a transport.  This is not a real IKEv2 exchange,
      since no response messages are sent.  This method is valuable for
      large and dynamic groups, and where policy may change frequently
      and a scalable rekeying method is required.  When the GSA_REKEY is
      used, the IKEv2 SA protecting the member registration exchanges is
      usually terminated, and group members await policy changes from
      the GCKS via the GSA_REKEY messages.

   GSA_INBAND_REKEY  The GSA_INBAND_REKEY is a normal IKEv2 exchange
      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 pseudo-exchange.  The
      GSA_INBAND_REKEY exchange provides a reliable policy delivery and
      is useful when G-IKEv2 is used with a small group of cooperating
      devices.

   Depending on the policy the GCKS may combine these two methods.  For
   example, it may use the GSA_INBAND_REKEY to deliver key to the GMs in




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   the group acting as senders (as this would provide reliable keys
   delivery), and the GSA_REKEY for the rest GMs.

1.4.5.1.  GSA_REKEY

   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 3.5.3.2) MUST NOT be
   part of the Rekey Exchange as this is sender specific information and
   the Rekey Exchange is group specific.  The GCKS initiates the
   GSA_REKEY pseudo-exchange as following:

    Members (Responder)           GCKS (Initiator)
   --------------------          ------------------
                             <--  HDR, SK{GSA, KD, [N,] [D,] [AUTH]}

                    Figure 9: GSA_REKEY Pseudo-Exchange

   HDR is defined in Section 3.1.  The Message ID in this message will
   start with the value the GCKS sent to the group members in the KEK
   attribute GSA_INITIAL_MESSAGE_ID or from zero if this attribute
   wasn't sent.  The Message ID will be incremented each time a new
   GSA_REKEY message is sent to the group members.

   The GSA payload contains the current rekey and data security SAs.
   The GSA may contain a new rekey SA and/or a new data security SA
   Section 3.4.

   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
   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 or a dedicated shared secret and MUST NOT be included if
   authentication is implicit.  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 and implicit
   authentication don't provide source origin authentication.  For this



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   reason using them as authentication methods for GSA_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 NOT be NULL Authentication.

   During group member registration, the GCKS sends the authentication
   key in the GSA KEK payload, AUTH_KEY attribute, which the group
   member uses to authenticate the key server.  Before the current
   Authentication Key expires, the GCKS will send a new AUTH_KEY to the
   group members in a GSA_REKEY message.  The AUTH key that is used in
   the rekey message may be not the same as the authentication key used
   in GSA_AUTH.  If implicit authentication is used, then AUTH_KEY MUST
   NOT be sent to GMs.

1.4.5.1.1.  GSA_REKEY Messages Authentication

   The content of the AUTH payload depends on the authentication method
   and is either a digital signature or a result of prf applied to the
   content of the not yet encrypted GSA_REKEY message.

   The authentication algorithm (prf or digital signing) is applied to
   the concatenation of two chunks: A and P.  The chunk A lasts from the
   first octet of the G-IKEv2 Header (not including prepended four
   octets of zeros, if port 4500 is used) to the last octet of the
   Encrypted Payload header.  The chunk P consists of the not yet
   encrypted content of the Encrypted payload, excluding the
   Initialization Vector, the Padding, the Pad Length and the Integrity
   Checksum Data fields (see 3.14 of [RFC7296] for description of the
   Encrypted payload).  In other words, the P chunk is the inner
   payloads of the Encrypted payload in plaintext form.  These inner
   payloads must be fully formed and ready for encryption except for the
   AUTH payload.  Figure 10 illustrates the layout of the P and A chunks
   in the GSA_REKEY message.

   The AUTH payload must have correct values in the Payload Header, the
   Auth Method and the RESERVED fields.  The Authentication Data field
   is zeroed, but if Digital Signature authentication method is in use,
   then the ASN.1 Length and the AlgorithmIdentifier fields must be
   properly filled in, see [RFC7427].

   For the purpose of the AUTH payload calculation the Length field in
   the IKE header and the Payload Length field in the Encrypted Payload
   header are adjusted so that they don't count the lengths of
   Initialization Vector, Integrity Checksum Data and Padding (along
   with Pad Length field).  In other words, the Length field in the IKE
   header (denoted as AdjustedLen in Figure 10 ) is set to the sum of
   the lengths of A and P, and the Payload Length field in the Encrypted




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   Payload header (denoted as AdjustedPldLen in Figure 10) is set to the
   length of P plus the size of the Payload header (four octets).

   DataToAuthenticate = A | P
   GsaRekeyMessage = GenIKEHDR | EncPayload
   GenIKEHDR = [ four octets 0 if using port 4500 ] | AdjustedIKEHDR
   AdjustedIKEHDR =  SPIi | SPIr |  . . . | AdjustedLen
   EncPayload = AdjustedEncPldHdr | IV | InnerPlds | Pad | PadLen | ICV
   AdjustedEncPldHdr = NextPld | C | RESERVED | AdjustedPldLen
   A = AdjustedIKEHDR | AdjustedEncPldHdr
   P = InnerPlds

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ^ ^
   |                     G-IKEv2 SA Initiator's SPI                | | |
   |                                                               | | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ I |
   |                     G-IKEv2 SA Responder's SPI                | K |
   |                                                               | E |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   |  Next Payload | MjVer | MnVer | Exchange Type |     Flags     | H A
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ d |
   |                           Message ID                          | r |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
   |                          AdjustedLeng                         | | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ v |
   | Next Payload  |C|  RESERVED   |         AdjustedPldLen        | | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ E v
   |                     Initialization Vector                     | n
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ c ^
   |                                                               | r |
   ~             Inner payloads (not yet encrypted)                ~   P
   |                                                               | P |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ l v
   |              Padding (0-255 octets)           |  Pad Length   | d
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   ~                    Integrity Checksum Data                    ~ |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ v

         Figure 10: Data to Authenticate in the GSA_REKEY Messages

   The authentication data is calculated using the authentication
   algorithm from the Authentication Method transform and the key
   provided before in the AUTH_KEY attribute.  Depending on the
   authentication method the authentication data is either a digital
   signature or a result of applying prf from the Pseudorandom Function
   transform.  The calculated authentication data is placed into the



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   AUTH payload, the Length fields in the IKE Header and the Encryption
   Payload header are restored, the content of the Encrypted payload is
   encrypted and the ICV is computed using the current SKe/SKa keys.

   The calculation of authentication data MUST be applied to whole
   messages only, before possible IKE Fragmentation.  If the message was
   received in fragmented form, it should be reconstructed before
   verifying its authenticity as if it were received unfragmented.  The
   RESERVED field in the reconstructed Encrypted Payload header MUST be
   set to the value of the RESERVED field in the Encrypted Fragment
   payload header from the first fragment (that with Fragment Number
   equal to 1).

1.4.5.1.2.  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 0 in
   this message.  The GSA, KD, N and D payloads follow with the same
   characteristics as in the GSA Registration exchange.

   The AUTH payload (if present) is created as defined in
   Section 1.4.5.1.1.

   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 be substantially skewed for the GMs that would
   receive different copies of the messages.

   GCKS may also include one or several GSA_NEXT_SPI attributes
   specifying SPIs for the prospected rekeys, so that listening GMs are
   able to detect lost rekey messages and recover from this situation.
   See Sections Section 3.4.2.2.3 for more detail.

1.4.5.1.3.  GSA_REKEY GM Operations

   When a group member receives the Rekey Message from the GCKS it
   decrypts the message using the current KEK, validates its
   authenticity using the 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.




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   Replay protection is achieved by a group member rejecting a GSA_REKEY
   message which has a Message ID smaller than the current Message ID
   that the GM is expecting.  The GM expects the Message ID in the first
   GSA_REKEY message it receives to be equal or greater than the Message
   ID it receives in the GSA_INITIAL_MESSAGE_ID attribute.  Note, that
   if no this attribute was received for the Rekey SA, the GM MUST
   assume zero as the first expected Message ID.  The GM expects the
   Message ID in subsequent GSA_REKEY messages to be greater than the
   last valid GSA_REKEY message ID it received.

   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
   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
   GSA_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.

1.4.5.1.4.  IKE Fragmentation

   IKE fragmentation [RFC7383] can be used to perform fragmentation of
   large GSA_REKEY messages, however when the GSA_REKEY message is
   emitted as an IP multicast packet there is a lack of response from
   the GMs.  This has the following implications.

   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 messages.




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   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.

   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, [N,] [D]}
      HDR, SK{}            -->

                   Figure 11: GSA_INBAND_REKEY Exchange

   Because this is a normal IKEv2 exchange, the HDR is treated as
   defined in [RFC7296].

1.4.5.2.1.  GSA_INBAND_REKEY GCKS Operations

   The GSA, KD, N and D payloads are built in the same manner as in a
   registration exchange.

1.4.5.2.2.  GSA_INBAND_REKEY GM Operations

   The GM processes the GSA, KD, N and D payloads in the same manner as
   if they were received in a registration exchange.

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
   pseudo-exchange as shown below.

    Members (Responder)        GCKS (Initiator)
   --------------------       ------------------
                         <--   HDR, SK{[GSA,] [KD,], [N] [D,] [AUTH]}

                    Figure 12: SA Deletion in GSA_REKEY



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   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
   to start over with a clean state.  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
   Protocol ID of AH or ESP, followed by another Delete payload with a
   SPI of zero and Protocol ID of GIKE_REKEY, 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],
   ChaCha20-Poly1305 [RFC7634], AES-GMAC [RFC4543]) and AH (e.g., AES-
   GMAC [RFC4543]).  These counter-based modes require that no two
   senders in the group ever send a packet with the same Initialization
   Vector (IV) using the same cipher key and mode.  This requirement is
   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



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   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).

   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



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       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 message 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 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.

   o  The most significant bits NUMBER_OF_SID_BITS of the IV are taken
      to be the SID field of the IV.

   o  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.

2.  Group Key Management and Access Control

   Through the G-IKEv2 rekey, G-IKEv2 supports algorithms such as
   Logical Key Hierarchy (LKH) that have the property of denying access
   to a new group key by a member removed from the group (forward access
   control) and to an old group key by a member added to the group
   (backward access control).  An unrelated notion to PFS, "forward
   access control" and "backward access control" have been called
   "perfect forward security" and "perfect backward security" in the
   literature [RFC2627].

   Group management algorithms providing forward and backward access
   control other than LKH have been proposed in the literature,
   including OFT [OFT] and Subset Difference [NNL].  These algorithms
   could be used with G-IKEv2, but are not specified as a part of this
   document.

   The Group Key Management Method transform from the GSA policy
   specifies how members of the group obtain group keys.  This document
   specifies a single method for the group key management - Wrapped Key
   Download.  This method assumes that all group keys are sent to the
   GMs by the GCKS encrypted with other keys, called Key Wrap Keys
   (KWK).







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2.1.  Key Wrap Keys

   Every GM always knows at least one KWK - the KWK that is associated
   with the IKE SA or multicast rekey SA the wrapped keys are sent over.
   In this document it is called default KWK and is denoted as SK_w.

   The GCKS may also send other keys to GMs that will be used as Key
   Wrap Keys for the purpose of building key hierarchy.  Each such key
   is associated with an encryption algorithm from the Encryption
   Algorithm transform used for the SA the key is sent in.  The size of
   such key MUST be of the size of the key size of this Encryption
   Algorithm transform (taking into consideration the Key Length
   attribute for this transform if present).  This association persists
   even if the key is used later in the context of another SA with
   possibly different Encryption Algorithm transform.

   To have an ability to provide forward access control the GCKS
   provides each GM with a personal key at the time of registration.
   Besides several intermediate keys that form a key hierarchy and are
   shared among several GMs are provided by the GCKS.

2.1.1.  Default Key Wrap Key

   The default KWK (SK_w) is only used in the context of a single IKE
   SA.  Every IKE SA (unicast or group rekey) will have its own SK_w.
   The SK_w is used with the algorithm from the Encryption Algorithm
   transform used for the SA the SK_w is used in.  The size of SK_w MUST
   be of the key size of this Encryption Algorithm transform (taking
   into consideration the Key Length attribute for this transform if
   present).

   For the unicast IKE SA (used for the GM registration and optionally
   for GSA_INBAND_REKEY exchanges) the SK_w is computed as follows:

   SK_w = prf+(SK_d, "Key Wrap for G-IKEv2")

   where the string "Key Wrap for G-IKEv2" is 20 ASCII characters
   without null termination.

   For the multicast rekey SA the SK_w is provided along with other SA
   keys as defined in Section 2.4.

2.2.  GCKS Key Management Semantics

   Wrapped Key Download method allows the GCKS to employ various key
   management policies.





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   o  A simple key management policy - when the GCKS always sends group
      SA keys encrypted with the SK_w.

   o  An LKH key management policy - when the GCKS provides each GM with
      an individual key at the time of GM registration (encrypted with
      SK_w).  Then the GCKS forms an hierarchy of keys so that the group
      SA keys are encrypted with other keys which are encrypted with
      other keys and so on, tracing back to the individual GMs' keys.

   Other key policies may also be employed by the GCKS.

2.2.1.  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.
   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.







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2.3.  GM Key Management Semantics

   This specification defines a GM Key Management semantics in such a
   way, that it doesn't depend on the key management policy employed by
   the GCKS.  This allows having all the complexity of key management in
   the GCKS, which is free to implement various key management policies,
   such as direct transmitting of group SA keys or using some kind of
   key hierarchy (e.g.  LKH).  For all these policies the GMs' behavior
   is the same.

   Each key is identified by a 32-bit number called Key ID.  Zero Key ID
   has a special meaning - it always contains keying material from which
   the group SA keys are taken.

   All keys in G-IKEv2 are transmitted in encrypted form, which format
   is defined in Section 3.5.1.  This format specifies a Key ID (ID of a
   key that is encrypted in this attribute) and a KWK ID (ID of a key
   that was used to encrypt this attribute).  Keys may be encrypted
   either with default KWK (SK_w) or with other keys, which the GM has
   received in the KEY_WRAP_KEY attributes.  If a key was encrypted with
   SK_w, then the KWK ID field is set to zero, otherwise the KWK ID
   field identifies the key used for encryption.

   When a GM receives a message from the GCKS installing new data
   security or rekey SA, it will contain a KD payload with a SA_KEY
   attribute containing keying material for this SA.  For a data
   security SA exactly one SA_KEY attribute will be present with both
   Key ID and KWK ID fields set to zero.  This means that the default
   KWK (SK_w) should be used to extract this keying material.

   For a multicast rekey SA multiple SA_KEY attributes may be present
   depending on the key management policy employed by the GCKS.  If
   multiple SA_KEY attributes are present then all of them MUST contain
   the same keying material encrypted using different keys.  The GM in
   general is unaware of the GCKS's key management policy and can always
   use the same procedure to get the keys.  In particular, the GM's task
   is to find a way to decrypt at least one of the SA_KEY attributes
   using either the SK_w or the keys from the KEY_WRAP_KEY attributes
   that are present in the same message or were receives in previous
   messages.

   We will use the term "Key Path" to describe an ordered sequence of
   keys where each subsequent key was used to encrypt the previous one.
   The GM keeps its own Key Path (called working Key Path) in the memory
   associated with each group it is registered to and update it when
   needed.  When the GSA_REKEY message is received the GM processes the
   received SA_KEY attributes one by one trying to construct a new key




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   path that starts from this attributes and ends with any key in the
   working Key Path or with the default KWK (SK_w).

   In the simplest case the SA_KEY attribute is encrypted with SK_w so
   that the new Key Path is empty.  If more complex key management
   policies are used then the Key Path will contain intermediate keys,
   which will be from the KEY_WRAP_KEY attributes received in the same
   messages.  If the GM is able to construct a new Key Path, then it is
   able to decrypt the SA_KEY attribute and use its content to form the
   SA keys.  If it is unable to build a new Key Path, then in means that
   the GM is excluded from the group.

   Depending on the new Key Path the GM should do the following actions
   to be prepared for future key updates:

   o  If the new Key Path is empty then no actions are needed.  This may
      happen if no KEY_WRAP_KEY attributes from the received message
      were used.

   o  If the new Key Path is non-empty and it ends up with the default
      KWK (SK_w), then the whole new Key Path is stored by the GM as the
      GM's working Key Path.  This situation may only happen at the time
      the GM is registering to the group, when the GCKS is providing it
      with its personal key and the other keys from the key tree that
      are needed for this GM.  These keys form an initial working Key
      Path.

   o  In all other cases the new Key Path will end up where some key
      from the GM's working Key Path was used.  In this case the new Key
      Path replaces the part of the GM's working Key Path from the
      beginning and up to (but not including) the key that the GM has
      used to decrypt the last key in the new Key Path.

   Appendix A contains an example of how this algorithm works in case of
   LKH key management policy.

2.4.  Group SA Keys

   Group SA keys are downloaded to GMs in the form of keying material.
   The keys are taken from this keying material as if they were
   concatenated to form it.

   For a data security SA the keys are taken in accordance to the third
   bullet from Section 2.17 of [RFC7296].  In particular, for the ESP
   and AH SAs the encryption key (if any) MUST be taken from the first
   bits of the keying material and the integrity key (if any) MUST be
   taken from the remaining bits.




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   For a group rekey SA the following keys are taken from the keying
   material:

   SK_e | SK_a | SK_w = KEYMAT

   where SK_e and SK_a are the keys used for the Encryption Algorithm
   and the Integrity Algorithm transforms for the corresponding SA and
   SK_w is a default KWK for this SA.  Note, that SK_w is also used with
   the Encryption Algorithm transform as well as SK_e.  Note also, that
   if AEAD algorithm is used for encryption, then SK_a key will not be
   used (GM can use the formula above assuming the length of SK_a is
   zero).

3.  Header and Payload Formats

   The G-IKEv2 is an IKEv2 extension and thus inherits its wire format
   for data structures.  However, the processing of some payloads are
   different and several new payloads are defined: Group Identification
   (IDg), Group Security Association (GSA) Key Download (KD).  New
   exchange types GSA_AUTH, GSA_REGISTRATION, GSA_REKEY and
   GSA_INBAND_REKEY are also added.

   This section describes new payloads and the differences in processing
   of existing IKEv2 payloads.

3.1.  G-IKEv2 Header

   G-IKEv2 uses the same IKE header format as specified in [RFC7296]
   section 3.1.  Major Version is 2 and Minor Version is 0 as in IKEv2.
   IKE SA Initiator's SPI, IKE SA Responder's SPI, Flags, Message ID,
   and Length are as specified in [RFC7296].

3.2.  Group Identification Payload

   The Group Identification (IDg) payload allows the group member to
   indicate which group it wants to join.  The payload is constructed by
   using the IKEv2 Identification Payload (section 3.5 of [RFC7296]).
   ID type ID_KEY_ID MUST be supported.  ID types ID_IPV4_ADDR, ID_FQDN,
   ID_RFC822_ADDR, ID_IPV6_ADDR SHOULD be supported.  ID types
   ID_DER_ASN1_DN and ID_DER_ASN1_GN are not expected to be used.  The
   Payload Type for the Group Identification payload is fifty (50).

3.3.  Security Association - GM Supported Transforms Payload

   The Security Association - GM Supported Transforms Payload (SAg)
   payload declares which Transforms a GM is willing to accept.  The
   payload is constructed using the format of the IKEv2 Security




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   Association payload (section 3.3 of [RFC7296]).  The Payload Type for
   SAg is identical to the SA Payload Type - thirty-three (33).

3.4.  Group Security Association Payload

   The Group Security Association (GSA) payload is used by the GCKS to
   assert security attributes for both Rekey and Data-security SAs.  The
   Payload Type for the Group Security Association payload is fifty-one
   (51).

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|   RESERVED  |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                       <Group Policies>                        ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                       Figure 13: GSA Payload Format

   The Security Association Payload fields are defined as follows:

   o  Next Payload, C, RESERVED, Payload Length fields comprise the
      IKEv2 Generic Payload Header and are defined in Section 3.2. of
      [RFC7296].

   o  Group Policies (variable) - A set of group policies for the group.

3.4.1.  Group Policies

   Croup policies are comprised of two types of policy - Group SA (GSA)
   policy and Group Associated (GA) policy.  GSA policy defines
   parameters for the Security Association for the group.  Depending on
   the employed security protocol GSA policies may further be classified
   as rekeying SA policy (GSA KEK) and data traffic SA policy (GSA TEK).
   GSA payload may contain zero or one GSA KEK policy, zero or more GSA
   TEK policies, and zero or one GA policy, where either one GSA KEK or
   GSA TEK policy MUST be present.

   This latitude allows various group policies to be accommodated.  For
   example if the group policy does not require the use of a Rekey SA,
   the GCKS would not need to send a GSA KEK policy to the group member
   since all SA updates would be performed using the 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



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   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 allows for the distribution of group-wise policy, such as
   instructions for when to activate and de-activate SAs.

   Policies are distributed in substructures to the GSA payload.  The
   format of the substructures is defined below in Section 3.4.2 (for
   GSA policy) and in Section 3.4.3 (for GA policy).  The first octet of
   the substructure unambiguously determines its type - it is zero for
   GAP and non-zero (actually, it is the security protocol ID) for GSA
   policies.

3.4.2.  Group Security Association Policy Substructure

   The GSA policy substructure contains parameters for the SA used with
   this group.  Depending on the security protocol the SA is either a
   rekey SA or a data security SA (ESP and AH).  It is NOT RECOMMENDED
   that the GCKS distribute both ESP and AH policies for the same set of
   Traffic Selectors.



























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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Protocol   |   SPI Size    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                              SPI                              ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                  Source Traffic Selector                      ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                Destination Traffic Selector                   ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                       <GSA Transforms>                        ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                       <GSA Attributes>                        ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 14: GSA Policy Substructure Format

   The GSA policy fields are defined as follows:

   o  Protocol (1 octet) - Identifies the security protocol for this
      group SA.  The values are defined in the IKEv2 Security Protocol
      Identifiers in [IKEV2-IANA].  The valid values for this field are:
      <TBA> (GIKE_REKEY) for GSA KEK policy and 2 (AH) or 3 (ESP) for
      GSA TEK policy.

   o  SPI Size (1 octet) - Size of Security Parameter Index (SPI) for
      the group SA.  SPI size depends on the SA protocol.  For
      GIKE_REKEY it is 16 octets, while for AH and ESP it is 4 octets.

   o  Length (2 octets, unsigned integer) - Length of this substructure
      including the header.

   o  SPI (variable) - Security Parameter Index for the group SA.  The
      size of this field is determined by the SPI Size field.  As
      described above, these SPIs are assigned by the GCKS.  In case of
      GIKE_REKEY the SPI must be the IKEv2 Header SPI pair where the
      first 8 octets become the "Initiator's SPI" field in the G-IKEv2



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      rekey message IKEv2 HDR, and the second 8 octets become the
      "Responder's SPI" in the same HDR.  When selecting SPI the GCKS
      MUST make sure that the sole first 8 octets (corresponding to
      "Initiator's SPI" field in the IKEv2 header) uniquely identify the
      Rekey SA.

   o  Source & Destination Traffic Selectors - (variable) -
      Substructures describing the source and destination of the network
      identities.  The format for these substructures is defined in
      IKEv2 [RFC7296], section 3.13.1.  For the group rekey SA (protocol
      GIKE_REKEY) the destination traffic selectors MUST define a single
      IP address, IP protocol and port the GSA_REKEY messages will be
      destined to.  The source traffic selector in this case MUST either
      define a single IP address, IP protocol and port the GSA_REKEY
      messages will be originated from or be a wildcard selector.  For
      the data security (AH and ESP) SAs the traffic selectors instead
      specify characteristics of the traffic to be protected by the
      corresponding SA.

   o  GSA Transforms (variable) - A list of Transform Substructures
      specifies the policy information for the group SA.  The format is
      defined in IKEv2 [RFC7296], section 3.3.2.  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.  Section 3.4.2.1
      describes using IKEv2 transforms in GSA policy substructure.

   o  GSA Attributes (variable) - Contains policy attributes associated
      with the group SA.  The following sections describe the possible
      attributes.  Any or all attributes may be optional, depending on
      the group SA protocol and the group policy.  Section 3.4.2.2
      defines attributes used in GSA policy.

3.4.2.1.  GSA Transforms

   GSA policy is defined by means of transforms in GSA policy
   substructure.  For this purpose the transforms defined in [RFC7296]
   are used.  In addition, new transform types are defined for using in
   G-IKEv2: Authentication Method (AUTH) and Group Key Management Method
   (GKM), see Section 6.

   Valid Transform Types depend on group SA protocol and are summarized
   in the table below.









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   Protocol    Mandatory Types                 Optional Types
   ----------------------------------------------------------
   GIKE_REKEY  ENCR, INTEG*, PRF, AUTH, GKM
   ESP         ENCR                             INTEG
   AH          INTEG

                     Figure 15: Valid Transform Types

   (*) If AEAD encryption algorithm is used, then INTEG transform MUST
   NOT be specified, otherwise it MUST be specified.

3.4.2.1.1.  Authentication Method Transform

   The Authentication Method (AUTH) transform is used in the GIKE_REKEY
   policy to convey information of how GCKS will authenticate the
   GSA_REKEY messages.  This values are from the IKEv2 Authentication
   Method registry [IKEV2-IANA].  Note, that this registry defines only
   256 possible values, so even that Transform ID field in the Transform
   substructure allows for 65536 possible values, in case of the
   Authentication Method transform the values 257-65535 MUST NOT be
   used.

   Among the currently defined authentication methods in the IKEv2
   Authentication Method registry, only the following are allowed to be
   used in the Authentication Method transform: Shared Key Message
   Integrity Code, NULL Authentication and Digital Signature.  Other
   currently defined authentication methods MUST NOT be used.  The
   following semantics is associated with each of the allowed methods.

      Shared Key Message Integrity Code - GCKS will authenticates the
      GSA_REKEY messages by means of shared secret.  In this case the
      GCKS MUST include the AUTH_KEY attribute containing the shared key
      into the KD payload at the time the GM is registered to the group.

      NULL Authentication - No additional authentication of the
      GSA_REKEY messages will be provided by the GCKS (besides the
      ability for the GMs to correctly decrypt them and verify their
      ICV).  In this case the GCKS MUST NOT include the AUTH_KEY
      attribute into the KD payload.

      Digital Signature - Digital signatures will be used by the GCKS to
      authenticate the GSA_REKEY messages.  In this case the GCKS MUST
      include the AUTH_KEY attribute containing the public key into the
      KD payload at the time the GM is registered to the group.  To
      specify the details of the signature algorithm a new attribute
      Algorithm Identifier (<TBA by IANA>) is defined.  This attribute
      contains DER-encoded ASN.1 object AlgorithmIdentifier, which would
      specify the signature algorithm and the hash function that the



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      GCKS will use for authentication.  The AlgorithmIdentifier object
      is defined in section 4.1.1.2 of [RFC5280], see also [RFC7427] for
      the list of common AlgorithmIdentifier values used in IKEv2.  In
      case of using digital signature the GCKS MUST include the
      Algorithm Identifier attribute in the Authentication Method
      transform.

   The type of the Authentication Method Transform is <TBA by IANA>.

3.4.2.1.2.  Group Key Management Method Transform

   The Group Key Management Method (GKM) transform is used in the
   GIKE_REKEY policy to convey information of how GCKS will manage the
   group keys to provide forward and backward access control (i.e., used
   to exclude group members).  Possible key management methods are
   defined in a new IKEv2 registry "Transform Type <TBA> - Group Key
   Management Methods" (see Section 6).  This document defines one
   values for this registry:

      Wrapped Key Download (<TBA by IANA>) - Keys are downloaded by GCKS
      to the GMs in encrypted form.  This algorithm may provide forward
      and backward access control if some form of key hierarchy is used
      and each GM is provided with a personal key at the time of
      registration.  Otherwise no access control is provided.

   The type of the Group Key Management Method transform is <TBA by
   IANA>.

3.4.2.2.  GSA Attributes

   GSA attributes are generally used to provide GMs with additional
   parameters for the GSA policy.  Unlike security parameters
   distributed via transforms, which are expected not to change over
   time (unless policy changes), the parameters distributed via GSA
   attributes may depend on the time the distribution takes place, on
   the existence of others group SAs or on other conditions.

   This document creates a new IKEv2 IANA registry for the types of the
   GSA attributes which is initially filled as described in Section 6.
   In particular, the following attributes are initially added.

   GSA Attributes          Value  Type   Multiple  Used In
   ---------------------------------------------------------------------
   Reserved                0
   GSA_KEY_LIFETIME        1      V      N         (GIKE_REKEY, AH, ESP)
   GSA_INITIAL_MESSAGE_ID  2      V      N         (GIKE_REKEY)
   GSA_NEXT_SPI            3      V      Y         (GIKE_REKEY, AH, ESP)




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   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).

3.4.2.2.1.  GSA_KEY_LIFETIME Attribute

   The GSA_KEY_LIFETIME attribute specifies the maximum time for which
   the group SA is valid.  The value is a 4 octet number defining a
   valid time period in seconds.  A single attribute of this type MUST
   be included into any GSA policy substructure.

   When the lifetime expires, the group security association and all
   associated keys MUST be deleted.  The GCKS may delete the SA at any
   time before the end of the valid period.

3.4.2.2.2.  GSA_INITIAL_MESSAGE_ID Attribute

   The GSA_INITIAL_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.

   A single attribute of this type MUST be included into the GSA KEK
   policy substructure if the initial Message ID is non-zero.  Note,
   that it is always the case if GMs join the group after some multicast
   rekey operations have already taken place, so in these cases this
   attribute will be included into the GSA policy at the time of GMs'
   registration.

3.4.2.2.3.  GSA_NEXT_SPI Attribute

   The optional GSA_NEXT_SPI attribute contains SPI that the GCKS
   reserved for the next group SA replacing this group SA.  The length
   of the attribute data is determined by the SPI Size field in the GSA
   Policy substructure the attribute resides in (see Section 3.4.2), and
   the attribute data contains SPI as it would appear on the network.
   Multiple attributes of this type MAY be included, meaning that any of
   the supplied SPIs can be used in the replacement group SA.

   The GM may store these values and if later the GM starts receiving
   group SA messages with one of these SPIs without seeing a rekey
   message over the current rekey SA, this may be used as an indication,
   that the rekey message got lost on its way to this GM.  In this case
   the GM SHOULD re-register to the group.

   Note, that this method of detecting lost rekey messages can only be
   used by passive GMs, i.e. those, that only listen and don't send
   data.  There is also no point to include this attribute in the



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   GSA_INBAND_REKEY messages, since they use reliable transport.  Note
   also, that the GCKS is free to forget its promises and not to use the
   SPIs it sent in the GSA_NEXT_SPI attributes before (e.g. in case of
   the GCKS reboot), so the GM must only treat these information as a
   "best effort" made by GCKS to prepare for future rekeys.

3.4.3.  Group Associated Policy Substructure

   Group specific policy that does not belong to any SA policy can be
   distributed to all group member using Group Associated Policy (GAP)
   substructure.

   The GAP substructure is defined as follows:

                        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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            ZERO               |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                        <GAP Attributes>                       ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 16: GAP Substructure Format

   The GAP substructure fields are defined as follows:

   o  ZERO (2 octets) - MUST be zero.

   o  Length (2 octets, unsigned integer) - Length of this substructure
      including the header.

   o  GAP Attributes (variable) - Contains policy attributes associated
      with no specific SA.  The following sections describe the possible
      attributes.  Any or all attributes may be optional, depending on
      the group policy.

   This document creates a new IKEv2 IANA registry for the types of the
   GAP attributes which is initially filled as described in Section 6.
   In particular, the following attributes are initially added.

           GAP Attributes              Value   Type    Multiple
           ----------------------------------------------------
           Reserved                    0
           GAP_ATD                     1       B       N
           GAP_DTD                     2       B       N
           GAP_SID_BITS                3       B       N



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   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).

3.4.3.1.  GAP_ATD And GAP_DTD Attributes

   Section 4.2.1 of [RFC5374] specifies a key rollover method that
   requires two values be provided to group members - Activation Time
   Delay (ATD) and Deactivation Time Delay (DTD).

   The GAP_ATD attribute allows a GCKS to set the Activation Time Delay
   for data security SAs of the group.  The ATD defines how long active
   members of the group (those who sends traffic) should wait after
   receiving new SAs before staring sending traffic over them.  Note,
   that to achieve smooth rollover passive members of the group should
   activate the SAs immediately once they receive them.

   The GAP_DTD attribute allows the GCKS to set the Deactivation Time
   Delay for previously distributed SAs.  The DTD defines how long after
   receiving a request to delete data security SAs passive group members
   should wait before actually deleting them.  Note that active members
   of the group should stop sending traffic over these old SAs once new
   replacement SAs are activated (after time specified in the GAP_ATD
   attribute).

   The GAP_ATD and GAP_DTD attributes contain 16 bit unsigned integer in
   a network byte order, specifying the delay in seconds.  These
   attributes are OPTIONAL.  If one of them or both are not sent by the
   GCKS, the GMs should use default values for activation and
   deactivation time delays.

3.4.3.2.  GAP_SID_BITS Attribute

   The GAP_SID_BITS attribute declares how many bits of the cipher nonce
   are taken 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 KD payload.

   The GCKS MUST include this attribute if there are more than one
   sender in the group and any of the data security SAs use counter-
   based cipher mode.  The number of SID bits is represented as 16 bit
   unsigned integer in network byte order.






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3.5.  Key Download Payload

   The Key Download (KD) payload contains the group keys for the group
   specified in the GSA Payload.  The Payload Type for the Key Download
   payload is fifty-two (52).

                        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 17: Key Download Payload Format

   The Key Download payload fields are defined as follows:

   o  Next Payload, C, RESERVED, Payload Length fields comprise the
      IKEv2 Generic Payload Header and are defined in Section 3.2. of
      [RFC7296].

   o  Key Packets (variable) - Contains Group Key Packet and Member Key
      Packet substructures.  Each Key Packet contains keys for a single
      group rekey or data security SA or a keys and security parameters
      for a GM.

   Two types of Key Packets are used - Group Key Packet and Member Key
   Packet.

3.5.1.  Wrapped Key Format

   The symmetric keys in G-IKEv2 are never sent in clear.  They are
   always encrypted with other keys using the format called Wrapped Key
   that is shown below (Figure 18).

   The keys are encrypted using algorithm that is used to encrypt the
   message the keys are sent in.  It means, that in case of unicast IKE
   SA (used for GMs registration and rekeying using GSA_INBAND_REKEY)
   the encryption algorithm will be the one negotiated during the SA
   establishment, while for the GSA_REKEY messages the algorithm will be
   provided by the GCKS in the Encryption Algorithm transform in the GSA
   payload when this multicast SA was being established (not in the same
   GSA_REKEY message).





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   If AEAD mode is used for encryption, then for the purpose of key
   encryption the authentication tag MUST NOT be used (both not
   calculated and not verified), since the G-IKEv2 provides
   authentication of all its messages.  In addition there is no AAD in
   this case.  If encryption algorithm requires padding, then the
   encrypted key MUST be padded before encryption to have the required
   size.  If the encryption algorithm doesn't define the padding
   content, then the following scheme SHOULD be used: the Padding bytes
   are initialized with a series of (unsigned, 1-byte) integer values.
   The first padding byte appended to the plaintext is numbered 1, with
   subsequent padding bytes making up a monotonically increasing
   sequence: 1, 2, 3, ....  The length of the padding is not transmitted
   and is implicitly determined, since the length of the key is known.

                            1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              Key ID                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              KWK ID                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~                               IV                              ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~                          Encrypted Key                        ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 18: Wrapped Key Format

   The Wrapped Key fields are defined as follows:

   o  Key ID (4 octets) - ID of the encrypted key.  The value zero means
      that the encrypted key contains keying material for the group SA,
      otherwise it contains some intermediate key.

   o  Key Wrap Key (KWK) ID (4 octets) - ID of the key that was used to
      encrypt this key.  The value zero means that the default KWK was
      used to encrypt the key, otherwise some other key was used.

   o  IV (variable) - Initialization Vector used for encryption.  The
      size and the content of IV is defined by the encryption algorithm
      employed.






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   o  Encrypted Key (variable) - The encrypted key bits.  These bits may
      comprise either a single encrypted key or a result of encryption
      of a concatenation of keys (key material) for several algorithms.

3.5.2.  Group Key Packet Substructure

   Group Key Packet substructure contains SA key information.  This key
   information is associated with some group SAs: either with data
   security SAs or with group rekey SA.

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Protocol   |   SPI Size    |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~                              SPI                              ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~               <Group Key Download Attributes>                 ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 19: Group Key Packet Substructure Format

   o  Protocol (1 octet) - Identifies the security protocol for this key
      packet.  The values are defined in the IKEv2 Security Protocol
      Identifiers in [IKEV2-IANA].  The valid values for this field are:
      <TBA> (GIKE_REKEY) for KEK Key packet and 2 (AH) or 3 (ESP) for
      TEK key packet.

   o  SPI Size (1 octet) - Size of Security Parameter Index (SPI) for
      the corresponding SA.  SPI size depends on the security protocol.
      For GIKE_REKEY it is 16 octets, while for AH and ESP it is 4
      octets.

   o  Length (2 octets, unsigned integer) - Length of this substructure
      including the header.

   o  SPI (variable) - Security Parameter Index for the corresponding
      SA.  The size of this field is determined by the SPI Size field.
      In case of GIKE_REKEY the SPI 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.  When selecting SPI the
      GCKS MUST make sure that the sole first 8 octets (corresponding to




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      "Initiator's SPI" field in the IKEv2 header) uniquely identify the
      Rekey SA.

   o  Group Key Download Attributes (variable length) - Contains Key
      information for the corresponding SA.

   This document creates a new IKEv2 IANA registry for the types of the
   Group Key Download attributes which is initially filled as described
   in Section 6.  In particular, the following attributes are initially
   added.

       GKD Attributes      Value   Type    Multiple    Used In
       ------------------------------------------------------------
       Reserved            0
       SA_KEY              1       V       Y           (GIKE_REKEY)
                                           N           (AH, ESP)

   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).

3.5.2.1.  SA_KEY Attribute

   The SA_KEY attribute contains a keying material for the corresponding
   SA.  The content of the attribute is formatted according to
   Section 3.5.1 with a precondition that the Key ID field MUST be zero.
   The size of the keying material MUST be equal to the total size of
   the keys needed to be taken from this keying material (see
   Section 2.4) for the corresponding SA.

   If the Key Packet is for a data security SA (AH or ESP protocols),
   then exactly one SA_KEY attribute MUST be present with both Key ID
   and KWK ID fields set to zero.

   If the Key Packet is for a rekey SA (GIKE_REKEY protocol), then at
   least one SA_KEY attribute with zero Key ID MUST be present.
   Depending on GCKS key management policy more SA_KEY attributes MAY be
   present.

3.5.3.  Member Key Packet Substructure

   The Member Key Packet substructure contains keys and other parameters
   that are specific for the member of the group and are not associated
   with any particular group SA.






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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ZERO              |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                 <Member Key Download Attributes>              ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 20: Member Key Packet Substructure Format

   The Member Key Packet substructure fields are defined as follows:

   o  ZERO (2 octets) - MUST be zero.

   o  Length (2 octets, unsigned integer) - Length of this substructure
      including the header.

   o  Member Key Download Attributes (variable length) - Contains Key
      information and other parameters exclusively for a particular
      member of the group.

   Member Key Packet substructure contains sensitive information for a
   single GM, for this reason it MUST NOT be sent in GSA_REKEY messages
   and MUST only be sent via unicast SA at the time the GM registers to
   the group (in either GSA_AUTH or GSA_REGISTRATION exchanges).

   This document creates a new IKEv2 IANA registry for the types of the
   Member Key Download attributes which is initially filled as described
   in Section 6.  In particular, the following attributes are initially
   added.

             MKD Attributes          Value   Type    Multiple
             ------------------------------------------------
             Reserved                0
             KEY_WRAP_KEY            1       V       Y
             GM_SID                  2       V       Y
             AUTH_KEY                3       V       N

   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).







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3.5.3.1.  KEY_WRAP_KEY Attribute

   The KEY_WRAP_KEY attribute contains a key that is used to encrypt
   other keys.  One or more the these attributes are sent to GMs if the
   GCKS key management policy relies on some key hierarchy (e.g.  LKH).

   The content of the attribute has a format defined in Section 3.5.1
   with a precondition that the Key ID field MUST NOT be zero.  The
   algorithm associated with the key is from the Encryption Transform
   for the SA the KEY_WRAP_KEY attributes was sent in.  The size of the
   key MUST be equal to the key size for this algorithm.

   Multiple instances of the KEY_WRAP_KEY attributes MAY be present in
   the key packet.

3.5.3.2.  GM_SID Attribute

   The GM_SID attribute is used to download one or more Sender-ID (SID)
   values for the exclusive use of a group member.  One or more of this
   attributes MUST be sent by the GCKS if the GM informed the GCKS that
   it would be a sender (by inclusion the SENDER notification to the
   request) and at least one of the data security SAs included in the
   GSA payload uses counter-based mode of encryption.

   If the GMs has requested multiple SID values in the SENDER
   notification, then the GCKS SHOULD provide it with the requested
   number of SIDs by sending multiple instances of the GM_SID attribute.
   The GCKS MAY send fewer SIDs than requested by the GM (e.g. if it is
   running out of SIDs), but it MUST NOT send more than requested.

3.5.3.3.  AUTH_KEY Attribute

   The AUTH_KEY attribute contains the key that is used to authenticate
   the GSA_REKEY messages.  The content of the attribute depends on the
   authentication method the GCKS specified in the Authentication Method
   transform in the GSA payload.

   o  If a shared secret is used for the GSA_REKEY messages
      authentication then the content of the AUTH_KEY attribute is the
      shared secret that MUST be represented in the form of Wrapped Key
      (see Section 3.5.1) with zero KWK ID.  The Key ID in this case is
      arbitrary and MUST be ignored by the GM.

   o  If digital signatures are used for the GSA_REKEY messages
      authentication then the content of the AUTH_KEY attribute is a
      public key used for digital signature authentication.  The public
      key MUST be represented as DER-encoded ASN.1 object
      SubjectPublicKeyInfo, defined in section 4.1.2.7 of [RFC5280].



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      The signature algorithm that will use this key was specified in
      the Algorithm Identifier attribute of the Authentication Method
      transform.  The key MUST be compatible with this algorithm.  An
      RSA public key format is defined in [RFC3447], Section A.1.  DSS
      public key format is defined in [RFC3279] Section 2.3.2.  For
      ECDSA Public keys, use format described in [RFC5480] Section 2.
      Other algorithms added to the IKEv2 Authentication Method registry
      are also expected to include a format of the SubjectPublicKeyInfo
      object included in the algorithm specification.

   Multiple instances of the AUTH_KEY attributes MUST NOT be sent.

3.6.  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 GIKE_REKEY (<TBA>) for GSA_REKEY pseudo-
   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 pseudo-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.

3.7.  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 (see Section 6).

   o  INVALID_GROUP_ID (45) - error type notification that indicates
      that the group id sent during the registration process is invalid.
      The Protocol ID and SPI Size fields in the Notify payload MUST be
      zero.  There is no data associated with this notification and the
      content of the Notification Data field MUST be ignored on receipt.

   o  AUTHORIZATION_FAILED (46) - error type notification that is sent
      in the response to a GSA_AUTH message when authorization failed.
      The Protocol ID and SPI Size fields in the Notify payload MUST be
      zero.  There is no data associated with this notification and the
      content of the Notification Data field MUST be ignored on receipt.

   o  REGISTRATION_FAILED (<TBA>) - error type notification that is sent
      by the GCKS when the GM registration request cannot be satisfied.
      The Protocol ID and SPI Size fields in the Notify payload MUST be
      zero.  There is no data associated with this notification and the
      content of the Notification Data field MUST be ignored on receipt.

   o  SENDER (16429) - status type notification that is sent in the
      GSA_AUTH or the GSA_REGISTRATION exchanges to indicate that the GM
      intends to be sender of data traffic.  The data includes a count
      of how many SID values the GM desires.  The count MUST be 4 octets
      long and contain the big endian representation of the number of
      requested SIDs.  The Protocol ID and SPI Size fields in the Notify
      payload MUST be zero.

   o  REKEY_IS_NEEDED (<TBA>) - status type notification that is sent in
      the 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.  The
      Protocol ID and SPI Size fields in the Notify payload MUST be
      zero.  There is no data associated with this notification and the
      content of the Notification Data field MUST be ignored on receipt.

3.7.1.  USE_TRANSPORT_MODE Notification

   This specification uses USE_TRANSPORT_MODE notification defined in
   section 3.10.1 of [RFC7296] to specify which mode data security SAs
   should be created in.  The GCKS MUST include one USE_TRANSPORT_MODE
   notification in a message containing the GSA payload for every data
   security SAs specified in this payload that is to be created in
   transport mode.  In other words, there must be as many these
   notifications included in the message as many SAs are created in
   transport mode.  The Protocol ID, SPI Size and SPI fields of the
   Notify Payload MUST correctly specify each such SA.



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3.8.  Authentication Payload

   G-IKEv2 uses the same Authentication payload as specified in
   [RFC7296], section 3.8, to authenticate the rekey message.  However,
   if it is used in the GSA_REKEY messages the content of the payload is
   computed differently, as described in Section 1.4.5.1.1.

4.  Interaction with other IKEv2 Protocol Extensions

   A number of IKEv2 extensions is defined that can be used to extend
   protocol functionality.  G-IKEv2 is compatible with most of them.  In
   particular, EAP authentication defined in [RFC7296] can be used to
   establish registration IKE SA, as well as 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 Multiple Key Exchanges in
   IKEv2 framework, defined in [I-D.ietf-ipsecme-ikev2-multiple-ke].

   Some IKEv2 extensions however require special handling if used in
   G-IKEv2.

4.1.  Mixing Preshared Keys in IKEv2 for Post-quantum Security

   G-IKEv2 can take advantage of the protection provided by Postquantum
   Preshared Keys (PPK) for IKEv2 [RFC8784].  However, the use of PPK
   leaves the initial IKE SA susceptible to quantum computer (QC)
   attacks.  For this reason an alternative approach for using PPK in
   IKEv2 defined in [I-D.smyslov-ipsecme-ikev2-qr-alt] SHOULD be used.

   If the alternative approach is not supported by the peers, then 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.

   The GM starts the IKE_SA_INIT exchange requesting using PPK, and the
   GCKS responds with agreement to do it, or aborts according to its
   "mandatory_or_not" flag:










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    Initiator (Member)                Responder (GCKS)
   --------------------              ------------------
    HDR, SAi1, KEi, Ni, N(USE_PPK)  -->
                                 <--  DR, SAr1, KEr, Nr, [CERTREQ],
                                      N(USE_PPK)

           Figure 21: IKE_SA_INIT Exchange requesting using PPK

   The GM then starts the GSA_AUTH exchange with the PPK_ID; if using
   PPK is not mandatory for the GM, the NO_PPK_AUTH notification is
   included in the request:

    Initiator (Member)                Responder (GCKS)
   --------------------              ------------------
    HDR, SK{IDi, AUTH, IDg,
    N(PPK_IDENTITY), N(NO_PPK_AUTH)}  -->

                   Figure 22: GSA_AUTH Request using PPK

   If the GCKS has no such PPK and using PPK is not mandatory for it and
   the NO_PPK_AUTH is included, then the GCKS continues without PPK; in
   this case no rekey is needed:

    Initiator (Member)              Responder (GCKS)
   --------------------            ------------------
                               <--  HDR, SK{IDr, AUTH, GSA, KD}

                 Figure 23: GSA_AUTH Response using no PPK

   If the GCKS has no such PPK and either the NO_PPK_AUTH is missing or
   using PPK is mandatory for the GCKS, the GCKS aborts the exchange:

    Initiator (Member)                Responder (GCKS)
   --------------------              ------------------
                                 <--  HDR, SK{N(AUTHENTICATION_FAILED)}

                    Figure 24: GSA_AUTH Error Response

   Assuming the GCKS has the proper PPK it continues with a request to
   the GM to immediately perform a rekey by sending the REKEY_IS_NEEDED
   notification:

    Initiator (Member)               Responder (GCKS)
   --------------------             ------------------
                                <--  HDR, SK{IDr, AUTH, N(PPK_IDENTITY),
                                     N(REKEY_IS_NEEDED) }

                  Figure 25: GSA_AUTH Response using PPK



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   The GM initiates the CREATE_CHILD_SA exchange to rekey the initial
   IKE SA and then makes a new registration request for the same group
   over the new IKE SA:

    Initiator (Member)                Responder (GCKS)
   --------------------              ------------------
    HDR, SK{SA, Ni, KEi}  -->
                                 <--  HDR, SK{SA, Nr, KEr}
    HDR, SK{IDg} --->
                                 <--  HDR, SK{GSA, KD}

     Figure 26: Rekeying IKE SA followed by GSA_REGISTRATION Exchange

5.  Security Considerations

5.1.  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
   those protections.  In addition, G-IKEv2 brings in the capability to
   authorize a particular group member regardless of whether they have
   the IKEv2 credentials.

5.2.  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.

5.2.1.  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.

5.2.2.  Confidentiality

   Confidentiality is provided by distributing a confidentiality key as
   part of the GSA member registration exchange.







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5.2.3.  Man-in-the-Middle Attack Protection

   GSA maintenance channel is integrity protected by using a digital
   signature.

5.2.4.  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.

6.  IANA Considerations

6.1.  New Registries

   A new set of registries is created for G-IKEv2 on IKEv2 parameters
   page [IKEV2-IANA].  The terms Reserved, Expert Review and Private Use
   are to be applied as defined in [RFC8126].

   This document creates a new IANA registry "Transform Type <TBA> -
   Group Key Management Methods".  The initial values of the new
   registry are:

   Value                       Group Key Management Method
   -------------------------------------------------------
   Reserved                    0
   Wrapped Key Download        1
   Unassigned                 2-1023
   Private Use             1024-65535

   Changes and additions to the unassigned range of this registry are by
   the Expert Review Policy [RFC8126].

   This document creates a new IANA registry "GSA Attributes".  The
   initial values of the new registry are:

   GSA Attributes          Value  Type   Multiple  Used In
   ---------------------------------------------------------------------
   Reserved                0
   GSA_KEY_LIFETIME        1      V      N         (GIKE_REKEY, AH, ESP)
   GSA_INITIAL_MESSAGE_ID  2      V      N         (GIKE_REKEY)
   GSA_NEXT_SPI            3      V      Y         (GIKE_REKEY, AH, ESP)
   Unassigned             5-16383
   Private Use        16384-32767



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   Changes and additions to the unassigned range of this registry are by
   the Expert Review Policy [RFC8126].

   This document creates a new IANA registry "GAP Attributes".  The
   initial values of the new registry are:

   GAP Attributes              Value   Type    Multiple
   ----------------------------------------------------
   Reserved                    0
   GAP_ATD                     1       B       N
   GAP_DTD                     2       B       N
   GAP_SID_BITS                3       B       N
   Unassigned                 4-16383
   Private Use            16384-32767

   Changes and additions to the unassigned range of this registry are by
   the Expert Review Policy [RFC8126].

   This document creates a new IANA registry "Group Key Download
   Attributes".  The initial values of the new registry are:

   GKD Attributes      Value   Type    Multiple    Used In
   ------------------------------------------------------------
   Reserved            0
   SA_KEY              1       V       Y           (GIKE_REKEY)
                                       N           (AH, ESP)
   Unassigned         2-16383
   Private Use    16384-32767

   Changes and additions to the unassigned range of this registry are by
   the Expert Review Policy [RFC8126].

   This document creates a new IANA registry "Member Key Download
   Attributes".  The initial values of the new registry are:

   MKD Attributes          Value   Type    Multiple
   ------------------------------------------------
   Reserved                0
   KEY_WRAP_KEY            1       V       Y
   GM_SID                  2       V       Y
   AUTH_KEY                3       V       N
   Unassigned             4-16383
   Private Use        16384-32767

   Changes and additions to the unassigned range of this registry are by
   the Expert Review Policy [RFC8126].





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6.2.  Changes in the Existing IKEv2 Registries

   This document defines new Exchange Types in the "IKEv2 Exchange
   Types" registry:

   Value       Exchange Type
   ----------------------------
   39          GSA_AUTH
   40          GSA_REGISTRATION
   41          GSA_REKEY
   <TBA>       GSA_INBAND_REKEY

   This document defines new Payload Types in the "IKEv2 Payload Types"
   registry:

   Value       Next Payload Type               Notation
   ----------------------------------------------------
   50          Group Identification            IDg
   51          Group Security Association      GSA
   52          Key Download                    KD

   This document defines a new Security Protocol Identifier in the
   "IKEv2 Security Protocol Identifiers" registry:

   <TBA>       GIKE_REKEY

   This document defines new Transform Types in the "Transform Type
   Values" registry and changes the "Used In" column for the existing
   allocations:

   Type  Description                          Used In
   ---------------------------------------------------------------------
   1     Encryption Algorithm (ENCR)          (IKE, GIKE_REKEY and ESP)
   2     Pseudo-random Function (PRF)         (IKE, GIKE_REKEY)
   3     Integrity Algorithm (INTEG)          (IKE, GIKE_REKEY, AH,
                                               optional in ESP)
   4     Diffie-Hellman Group (D-H)           (IKE, optional in AH, ESP)
   5     Extended Sequence Numbers (ESN)      (AH and ESP)
   <TBA> Authentication Method (AUTH)         (GIKE_REKEY)
   <TBA> Group Key Management Method (GKM)    (GIKE_REKEY)

   This document defines a new Attribute Type in the "IKEv2 Transform
   Attribute Types" registry:

   Value       Attribute Type              Format
   ----------------------------------------------
   <TBA>       Algorithm Identifier        TLV




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   This document defines new Notify Message Types in the "Notify Message
   Types - Status Types" registry:

   Value       Notify Messages - Status Types
   ------------------------------------------
   16429       SENDER

   The Notify type with the value 16429 was allocated earlier in the
   development of G-IKEv2 document with the name SENDER_REQUEST_ID.
   This specification changes its name to SENDER.

   This document defines new Notify Message Types in the "Notify Message
   Types - Error Types" registry:

   Value       Notify Messages - Error Types
   -----------------------------------------
   45          INVALID_GROUP_ID
   46          AUTHORIZATION_FAILED
   <TBA>       REGISTRATION_FAILED

7.  Acknowledgements

   The authors thank Lakshminath Dondeti and Jing Xiang for first
   exploring the use of IKEv2 for group key management and providing the
   basis behind the protocol.  Mike Sullenberger and Amjad Inamdar were
   instrumental in helping resolve many issues in several versions of
   the document.

8.  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










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      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

9.  References

9.1.  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>.



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   [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>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [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>.

9.2.  Informative References

   [I-D.ietf-ipsecme-ikev2-multiple-ke]
              Tjhai, C., Tomlinson, M., grbartle@cisco.com, g., Fluhrer,
              S., Geest, D., Garcia-Morchon, O., and V. Smyslov,
              "Multiple Key Exchanges in IKEv2", draft-ietf-ipsecme-
              ikev2-multiple-ke-00 (work in progress), January 2020.

   [I-D.smyslov-ipsecme-ikev2-qr-alt]
              Smyslov, V., "Alternative Approach for Mixing Preshared
              Keys in IKEv2 for Post-quantum Security", draft-smyslov-
              ipsecme-ikev2-qr-alt-01 (work in progress), February 2020.

   [IKEV2-IANA]
              IANA, "Internet Key Exchange Version 2 (IKEv2)
              Parameters", <http://www.iana.org/assignments/ikev2-
              parameters/ikev2-parameters.xhtml#ikev2-parameters-7>.




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   [NNL]      Naor, D., Noal, M., and J. Lotspiech, "Revocation and
              Tracing Schemes for Stateless Receivers", Advances in
              Cryptology, Crypto '01,  Springer-Verlag LNCS 2139, 2001,
              pp. 41-62, 2001,
              <http://www.wisdom.weizmann.ac.il/~naor/PAPERS/2nl.pdf>.

   [OFT]      McGrew, D. and A. Sherman, "Key Establishment in Large
              Dynamic Groups Using One-Way Function Trees", Manuscript,
               submitted to IEEE Transactions on Software Engineering,
              1998, <https://pdfs.semanticscholar.org/
              d24c/7b41f7bcc2b6690e1b4d80eaf8c3e1cc5ee5.pdf>.

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,
              <https://www.rfc-editor.org/info/rfc2409>.

   [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>.

   [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>.





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   [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>.

   [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>.

   [RFC7634]  Nir, Y., "ChaCha20, Poly1305, and Their Use in the
              Internet Key Exchange Protocol (IKE) and IPsec", RFC 7634,
              DOI 10.17487/RFC7634, August 2015,
              <https://www.rfc-editor.org/info/rfc7634>.

   [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>.

   [RFC8784]  Fluhrer, S., Kampanakis, P., McGrew, D., and V. Smyslov,
              "Mixing Preshared Keys in the Internet Key Exchange
              Protocol Version 2 (IKEv2) for Post-quantum Security",
              RFC 8784, DOI 10.17487/RFC8784, June 2020,
              <https://www.rfc-editor.org/info/rfc8784>.



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Appendix A.  Use of LKH in G-IKEv2

   Section 5.4 of [RFC2627] describes the LKH architecture, and how a
   GCKS uses LKH to exclude group members.  This section clarifies how
   the LKH architecture is used with G-IKEv2.

A.1.  Notation

   In this section we will use the notation X{Y} where a key with ID Y
   is encrypted with the key with ID X.  The notation 0{Y} means that
   the default wrap key (SK_w) is used to encrypt key Y, and the
   notation X{0} means key X is used to encrypt the group SA key.  Note,
   that 0{0} means that the group SA key is encrypted with default wrap
   key.

   The content of the KD payload will be shown as a sequence of Key
   Packets.  The Group Key Packet substructure will be denoted as SAn(),
   when n is an SPI for the SA, and The Member Key Packet substructure
   will be denoted as GM().  The content of the Key Packets is shown as
   SA_KEY and KEY_WRAP_KEY attributes with the notation described above.
   Here is the example of KD payload.

                      KD(SA1(X{0}),GM(Y{X},Z{Y},0{Z})

   For simplicity any other attributes in the KD payload are omitted.

   We will also use the notation X->Y->Z to describe the Key Path, i.e.
   the relation between the keys.  In this case the keys had the
   following relation: Z{Y}, Y{X}.

A.2.  Group Creation

   When a GCKS forms a group, it creates a key tree as shown in the
   figure below.  The key tree contains logical keys (which are
   represented as the values of their Key IDs in the figure) and a
   private key shared with only a single GM (the GMs are represented as
   letters followed by the corresponding key ID in parentheses in the
   figure).  The root of the tree contains the multicast rekey SA key
   (which is represented as SAn(0), showing that its Key ID is always
   zero).  The figure below assumes that the Key IDs are assigned
   sequentially; this is not a requirement and only used for
   illustrative purposes.  The GCKS may create a complete tree as shown,
   or a partial tree which is created on demand as members join the
   group.







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                                 SA1(0)
                    +------------------------------+
                    1                              2
            +---------------+              +---------------+
            3               4              5               6
        +-------+       +-------+      +--------+      +--------+
       A(7)    B(8)    C(9)   D(10)  E(11)    F(12)  G(13)    H(14)

                        Figure 27: Initial LKH tree

   When GM A joins the group, the GCKS provides it with the keys in the
   KEY_WRAP_KEY attributes in the KD payload of the GSA_AUTH or
   GSA_REGISTRATION exchange.  Given the tree shown in figure above, the
   KD payload will be:

                      KD(SA1(1{0}),GM(3{1},7{3},0{7})

                     KD Payload for the Group Member A

   From these attributes the GM A will construct the Key Path
   0->1->3->7->0 and since it ends up with SK_w, it will use all the
   KEY_WRAP_KEY attributes present in the path as its working Key Path:
   1->3->7.

   Similarly, when other GMs will be joining the group they will be
   provided with the corresponding keys, so after all the GMs will have
   the following working Key Paths:

   A: 1->3->7      B: 1->3->8      C: 1->4->9,     D: 1->4->10
   E: 2->5->11     F: 2->5->12     G: 2->6->13     H: 2->6->14

A.3.  Simple Group SA Rekey

   If the GCKS performs a simple SA rekey without changing group
   membership, it will only send Group Key Packet in the KD payload with
   a new SA key encrypted with the default KWK.

                               KD(SA2(0{0}))

                     KD Payload for the Group Member F

   All the GMs will be able to decrypt it and no changes in their
   working Key Paths will take place.








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A.4.  Group Member Exclusion

   If the GKCS has reason to believe that a GM should be excluded, then
   it can do so by sending a GSA_REKEY message that includes a set of
   GM_KEY attributes which would allow all GMs except for the excluded
   one to get a new SA key.

   In the example below the GCKS excludes GM F.  For this purpose it
   changes the key tree as follows, replacing the key 2 with the key 15
   and the key 5 with the key 16.  It also a new SA key for a new SA3.

                                 SA3(0)
                    +------------------------------+
                    1                             15
            +---------------+              +---------------+
            3               4             16               6
        +-------+       +-------+      +----           +--------+
       A(7)    B(8)    C(9)   D(10)  E(11)    F(12)  G(13)    H(14)

               Figure 28: LKH tree after F has been excluded

   Then it sends the following KD payload for the new rekey SA3:

              KD(SA3(1{0},SA3(15{0})),GM(6{15},16{15},11{16})

                     KD Payload for the Group Member F

   While processing this KD payload:

   o  GMs A, B, C and D will be able to decrypt the SA_KEY attribute
      1{0} by using the "1" key from their key path.  Since no new
      GM_KEY attributes are in the new Key Path, they won't update their
      working Key Paths.

   o  GMs G and H will construct new Key Path 15->0 and will be able to
      decrypt the new GM_KEY 15 using the key 6 from their working Key
      Paths.  So, they will update their working Key Paths replacing
      their beginnings up to the key 6 with the new Key Path (thus
      replacing the key 2 with the key 15).

   o  GM E will construct new Key Path 16->15->0 and will be able to
      decrypt the new GM_KEY 16 using the key 11 from its working Key
      Path.  So, it will update its working Key Path replacing its
      beginnings up to the key 11 with the new Key Path (thus replacing
      the key 2 with the key 15 and the key 5 with the key 16).

   o  GM F won't be able to construct any Key Path leading to any key he
      possesses, so it will be unable to decrypt the new SA key for the



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      SA3 and thus it will be excluded from the group once the GCKS
      starts sending TEK keys using SA3.

   Finally, the GMs will have the following working Key Paths:

   A: 1->3->7      B: 1->3->8      C: 1->4->9,     D: 1->4->10
   E: 15->16->11   F: excluded     G: 15->6->13    H: 15->6->14

Authors' Addresses

   Valery Smyslov
   ELVIS-PLUS
   PO Box 81
   Moscow (Zelenograd)  124460
   Russian Federation

   Phone: +7 495 276 0211
   Email: svan@elvis.ru


   Brian Weis
   Independent
   USA

   Email: bew.stds@gmail.com


























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