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Group Key Management using IKEv2
draft-ietf-ipsecme-g-ikev2-06

Document Type Active Internet-Draft (ipsecme WG)
Authors Valery Smyslov , Brian Weis
Last updated 2022-04-06
Replaces draft-yeung-g-ikev2
Stream Internet Engineering Task Force (IETF)
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draft-ietf-ipsecme-g-ikev2-06
Network Working Group                                         V. Smyslov
Internet-Draft                                                ELVIS-PLUS
Obsoletes: 6407 (if approved)                                    B. Weis
Updates: 7296 (if approved)                                  Independent
Intended status: Standards Track                           April 6, 2022
Expires: October 8, 2022

                    Group Key Management using IKEv2
                     draft-ietf-ipsecme-g-ikev2-06

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.  This documents also updates RFC 7296 by renaming
   one of transform types defined there.

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 October 8, 2022.

Copyright Notice

   Copyright (c) 2022 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

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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include 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 Notation . . . . . . . . . . . . . . . . . .   5
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  G-IKEv2 Protocol  . . . . . . . . . . . . . . . . . . . . . .   7
     2.1.  G-IKEv2 Integration into IKEv2 Protocol . . . . . . . . .   7
       2.1.1.  G-IKEv2 Transport and Port  . . . . . . . . . . . . .   7
     2.2.  G-IKEv2 Payloads  . . . . . . . . . . . . . . . . . . . .   8
     2.3.  G-IKEv2 Member Registration and Secure Channel
           Establishment . . . . . . . . . . . . . . . . . . . . . .   9
       2.3.1.  GSA_AUTH exchange . . . . . . . . . . . . . . . . . .   9
       2.3.2.  GSA_REGISTRATION Exchange . . . . . . . . . . . . . .  11
       2.3.3.  GM Registration Operations  . . . . . . . . . . . . .  12
       2.3.4.  GCKS Registration Operations  . . . . . . . . . . . .  14
     2.4.  Group Maintenance Channel . . . . . . . . . . . . . . . .  15
       2.4.1.  GSA_REKEY . . . . . . . . . . . . . . . . . . . . . .  16
       2.4.2.  GSA_INBAND_REKEY Exchange . . . . . . . . . . . . . .  22
       2.4.3.  Deletion of SAs . . . . . . . . . . . . . . . . . . .  22
     2.5.  Counter-based modes of operation  . . . . . . . . . . . .  23
       2.5.1.  Allocation of SIDs  . . . . . . . . . . . . . . . . .  24
       2.5.2.  GM Usage of SIDs  . . . . . . . . . . . . . . . . . .  25
     2.6.  Replay Protection for Multicast Data-Security SAs . . . .  25
   3.  Group Key Management and Access Control . . . . . . . . . . .  26
     3.1.  Key Wrap Keys . . . . . . . . . . . . . . . . . . . . . .  26
       3.1.1.  Default Key Wrap Key  . . . . . . . . . . . . . . . .  27
     3.2.  GCKS Key Management Semantics . . . . . . . . . . . . . .  27
       3.2.1.  Forward Access Control Requirements . . . . . . . . .  28
     3.3.  GM Key Management Semantics . . . . . . . . . . . . . . .  28
     3.4.  SA Keys . . . . . . . . . . . . . . . . . . . . . . . . .  30
   4.  Header and Payload Formats  . . . . . . . . . . . . . . . . .  31
     4.1.  G-IKEv2 Header  . . . . . . . . . . . . . . . . . . . . .  31
     4.2.  Group Identification Payload  . . . . . . . . . . . . . .  31
     4.3.  Security Association - GM Supported Transforms Payload  .  31
     4.4.  Group Security Association Payload  . . . . . . . . . . .  32
       4.4.1.  Group Policies  . . . . . . . . . . . . . . . . . . .  32
       4.4.2.  Group Security Association Policy Substructure  . . .  33
       4.4.3.  Group Associated Policy Substructure  . . . . . . . .  40
     4.5.  Key Download Payload  . . . . . . . . . . . . . . . . . .  42
       4.5.1.  Wrapped Key Format  . . . . . . . . . . . . . . . . .  42

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       4.5.2.  Group Key Packet Substructure . . . . . . . . . . . .  44
       4.5.3.  Member Key Packet Substructure  . . . . . . . . . . .  46
     4.6.  Delete Payload  . . . . . . . . . . . . . . . . . . . . .  48
     4.7.  Notify Payload  . . . . . . . . . . . . . . . . . . . . .  48
       4.7.1.  USE_TRANSPORT_MODE Notification . . . . . . . . . . .  49
     4.8.  Authentication Payload  . . . . . . . . . . . . . . . . .  50
   5.  Usigng G-IKEv2 Attributes . . . . . . . . . . . . . . . . . .  50
   6.  Interaction with other IKEv2 Protocol Extensions  . . . . . .  52
     6.1.  Mixing Preshared Keys in IKEv2 for Post-quantum Security   53
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  55
     7.1.  GSA Registration and Secure Channel . . . . . . . . . . .  55
     7.2.  GSA Maintenance Channel . . . . . . . . . . . . . . . . .  55
       7.2.1.  Authentication/Authorization  . . . . . . . . . . . .  55
       7.2.2.  Confidentiality . . . . . . . . . . . . . . . . . . .  55
       7.2.3.  Man-in-the-Middle Attack Protection . . . . . . . . .  55
       7.2.4.  Replay/Reflection Attack Protection . . . . . . . . .  55
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  56
     8.1.  New Registries  . . . . . . . . . . . . . . . . . . . . .  56
     8.2.  Changes in the Existing IKEv2 Registries  . . . . . . . .  57
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  59
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  60
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  60
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  60
     11.2.  Informative References . . . . . . . . . . . . . . . . .  61
   Appendix A.  Use of LKH in G-IKEv2  . . . . . . . . . . . . . . .  65
     A.1.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .  65
     A.2.  Group Creation  . . . . . . . . . . . . . . . . . . . . .  65
     A.3.  Simple Group SA Rekey . . . . . . . . . . . . . . . . . .  66
     A.4.  Group Member Exclusion  . . . . . . . . . . . . . . . . .  66
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  68

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

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   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 2.3.1), which is used when a GM first conatcts a GCKS.  The
   second is the GSA_REGISTRATION exchange (Section 2.3.2), 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

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   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 IKE SA.  The GCKS is also likely to
   be a GM in a small group (as shown in Figure 2.)

                          GSA_AUTH, GSA_INBAND_REKEY
            +-----------------------------------------------+
            |                                               |
            |         GSA_AUTH, GSA_INBAND_REKEY            |
            |   +-----------------------------+             |
            |   |                             |             |
            |   | GSA_AUTH, GSA_INBAND_REKEY  |             |
            |   |   +--------+                |             |
            v   v   v        v                v             v
           +---------+    +----+           +----+        +----+
           | GCKS/GM |    | GM |           | GM |        | GM |
           +---------+    +----+           +----+        +----+
                ^            ^                ^             ^
                |            |                |             |
                +----ESP-----+------ESP-------+-----ESP-----+

                  Figure 2: G-IKEv2 used in small groups

   A combination of these approaches is also possible.  For example, the
   GCKS may use more robust GSA_INBAND_REKEY to provide keys for some
   GMs (for example, those acting as senders in the group) and GSA_REKEY
   for the rest.

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

1.1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

1.2.  Terminology

   It is assumed that readers are familiar with the IPsec architecture
   [RFC4301], its extension for multicast [RFC5374].  This document
   defines an extension to the IKEv2 protocol [RFC7296], so it is
   assumed that readers have good understanding of this protocol.

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   The following key terms are used throughout this document (mostly
   borrowed from [RFC5374] and [RFC6407]).

   Group
         A set of devices that work together to protect group
         communications.

   Group Member (GM)
         An IPsec device that belongs to a group.  A Group Member is
         authorized to be a Group Sender and/or a Group Receiver.

   Group Receiver
         A Group Member that is authorized to receive packets sent to a
         group by a Group Sender.

   Group Sender
         A Group Member that is authorized to send packets to a group.

   Group Key Management (GKM) Protocol
         A key management protocol used by a GCKS to distribute IPsec
         Security Association policy and keying material.  A GKM
         protocol is used when a group of IPsec devices require the same
         SAs.  For example, when an IPsec SA describes an IP multicast
         destination, the sender and all receivers need to have the
         group SA.

   Group Controller Key Server (GCKS)
         A Group Key Management (GKM) protocol server that manages IPsec
         state for a group.  A GCKS authenticates and provides the IPsec
         SA policy and keying material to GKM Group Members.

   Data-Security SA
         The security policy distributed by a GDOI GCKS describing
         traffic that is expected to be protected by group members.
         This document described the distribution of IPsec AH and ESP
         Data-Security SAs.

   Rekey SA
         The security policy protecting Group Key Management Protocol.

   Group Security Association (GSA)
         A collection of Data-Security Associations (SAs) and Rekey SAs
         necessary for a Group Member to receive key updates.  A GSA
         describes the working policy for a group.  Refer to [RFC4046]
         for additional information.

   Traffic Encryption Key (TEK)

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         The symmetric cipher key used in a Data-Security SA (e.g.,
         IPsec ESP) to protect trafic.

   Key Encryption Key (KEK)
         The symmetric cipher key used in a Rekey SA to protect
         distribution of new keys.

   Key Wrap Key (KWK)
         The symmetric cipher key used to protect another key.

   Group Associated Policy (GAP)
         Group-wide policy not related to a particular SA.

   Sender-ID (SID)
         A unigue identifier of a Group Sender in the context of an
         active GSA, used to form Initialization Vector (IV) in counter-
         based cipher modes.

   Logical Key Hierarchy (LKH)
         A group management method defined in Section 5.4 of [RFC2627].

2.  G-IKEv2 Protocol

2.1.  G-IKEv2 Integration into IKEv2 Protocol

   G-IKEv2 is an extension to IKEv2 and uses its security mechanisms
   (peer authentication, confidentiality, message integrity) to ensure
   that only authenticated devices have access to the group policy and
   keys.  G-IKEv2 further provides group authorization, and secure
   policy and key download from the GCKS to GMs.

   G-IKEv2 is compatible with most IKEv2 extensions defined so far and
   it is believed that future IKEv2 extensions will also be possible to
   use with G-IKEv2.  However some IKEv2 extensions require special
   handling if used with G-IKEv2.  See Section 6 for more details.

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

2.1.1.  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

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   TCP transport for registration (unicast) IKE SA, as defined in
   [RFC8229].

   Section 2.23 of [RFC7296] describes how IKEv2 deals with NATs.
   Despite the fact, that with G-IKEv2 the registration SA doesn't
   create any unicast IPsec SAs and thus there is no unicast ESP traffic
   between the GM and the GCKS to encapsulate in UDP if NAT is present,
   the actions described in this section concerned with the IKE SA MUST
   be honored.  If the GM and the GCKS used UDP port 848 for the
   IKE_SA_INIT exchange, they MUST behave as if they used UDP port 500.

2.2.  G-IKEv2 Payloads

   In the following descriptions, the payloads contained in the G-IKEv2
   messages are indicated by names as listed below.

      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:

   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.

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   o  SAg (Security Association -- GM Supported Transforms) -- the GM
      sends supported transforms, so that GCKS may select a policy
      appropriate for all members of the group.

   The details of the contents of each payload are described in
   Section 4.

2.3.  G-IKEv2 Member Registration and Secure Channel Establishment

   The registration protocol consists of a minimum of two exchanges,
   IKE_SA_INIT and GSA_AUTH; member registration may have a few more
   messages exchanged if the EAP method, cookie challenge (for DoS
   protection), negotiation of Diffie-Hellman group or IKEv2 extensions
   based on [I-D.ietf-ipsecme-ikev2-intermediate] are used.  Each
   exchange consists of request/response pairs.  The first exchange
   IKE_SA_INIT is defined in IKEv2 [RFC7296].  This exchange negotiates
   cryptographic algorithms, exchanges nonces and computes a shared key
   between the GM and the GCKS.

   The second exchange GSA_AUTH authenticates the previously exchanged
   messages, exchanges identities and certificates.  The GSA_AUTH
   messages are encrypted and integrity protected with keys established
   through the previous exchanges, so the identities are hidden from
   eavesdroppers and all fields in all the messages are authenticated.
   The GCKS 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) as part of the GSA_AUTH
   response message.

2.3.1.  GSA_AUTH exchange

   After the group member and GCKS negotiate cryptographic algorithms,
   exchange nonces, and compute shared keys as defined in IKEv2
   [RFC7296], the GSA_AUTH exchange MUST complete before any other
   exchanges defined in this document can be done.  GSA_AUTH is used to
   authenticate the previous exchanges, exchange identities and
   certificates.  G-IKEv2 also uses this exchange for group member
   registration and authorization.

   The GSA_AUTH exchange is identical to the IKE_AUTH exchange with the
   difference that its goal is to establish multicast Data-Security SAs
   and optionally provide GM with the keys for Rekey SA.  The set of
   payloads in the GSA_AUTH exchange is slightly different, because
   policy is not negotiated between the group member and the GCKS, but
   instead downloaded from the GCKS to the group member.  Note also,
   that GSA_AUTH has its own exchange type, which is different from the
   IKE_AUTH exchange type.

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   Nevertheless, the security properties of the GSA_AUTH exchange are
   the same as the properties of the IKE_AUTH exchange and most IKEv2
   extensions to the IKE_AUTH exchange (like [RFC6467]) can also be used
   with the GSA_AUTH exchange.

    Initiator (Member)                              Responder (GCKS)
   --------------------                            ------------------
    HDR, SK{IDi, [CERT,] [CERTREQ,] [IDr,]
             AUTH, IDg, [SAg,] [N]}        -->

                        Figure 3: GSA_AUTH Request

   A group member initiates a GSA_AUTH request to join a group indicated
   by the IDg payload.  The GM MAY include an SAg payload declaring
   which Transforms it is willing to accept.  A GM that intends to act
   as Group Sender SHOULD include a Notify payload status type of
   SENDER, which enables the GCKS to provide any additional policy
   necessary by group senders.

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

                    Figure 4: GSA_AUTH Normal Response

   The GCKS responds with IDr, optional CERT, and AUTH payloads 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.

   In addition to the IKEv2 error handling, the GCKS can reject the
   registration request when the IDg is invalid or authorization fails,
   etc.  In these cases, see Section 4.7, the GSA_AUTH response will not
   include the GSA and KD, but will include a Notify payload indicating
   errors.  If a GM included an SAg payload, and the GCKS chooses to
   evaluate it, and the GCKS detects that the group member cannot
   support the security policy defined for the group, then the GCKS
   SHOULD return a NO_PROPOSAL_CHOSEN.  Other types of error
   notifications can be INVALID_GROUP_ID, AUTHORIZATION_FAILED or
   REGISTRATION_FAILED.

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

                     Figure 5: GSA_AUTH Error Response

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   If the group member finds the policy sent by the GCKS is
   unacceptable, the member SHOULD initiate GSA_REGISTRATION exchange
   sending IDg and the Notify NO_PROPOSAL_CHOSEN (see Section 2.3.2)).

2.3.2.  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 2.3.1.

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

                Figure 6: GSA_REGISTRATION Normal Exchange

   As with GSA_AUTH exchange, the GCKS can reject the registration
   request when the IDg is invalid or authorization fails, or GM cannot
   support the security policy defined for the group (which can be
   concluded by GCKS by evaluation of SAg payload).  In this case the
   GCKS returns an appropriate error notification as described in
   Section 2.3.1.

    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.  The group member SHOULD notify the
   GCKS by sending IDg and the Notify type NO_PROPOSAL_CHOSEN, as shown
   below.  The GCKS in this case MUST remove the GM from the group IDg.

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

        Figure 8: GM Reporting Errors in GSA_REGISTRATION Exchange

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2.3.3.  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.  The IKE_SA_INIT exchange may optionally be followed by one
   or more the IKE_INTERMEDIATE exchanges if the GM and the GCKS
   negotiated using IKEv2 extensions based on this exchange.

   Next the GM sends the GSA_AUTH request message with the IKEv2
   payloads from IKE_AUTH (without the SAi2, TSi and TSr payloads) along
   with the Group ID informing the GCKS of the group the initiator
   wishes to join.  An initiator intending to emit data traffic SHOULD
   send a SENDER Notify payload status.  The SENDER notification not
   only signifies that it is a sender, but provides the initiator the
   ability to request Sender-ID (SID) values, in case the Data-Security
   SA supports a counter mode cipher.  Section 2.5) includes guidance on
   requesting Sender-ID values.

   A GM may be limited in the 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
   by including the SAg payload into the request message.  Proposals for
   Rekey SA (with protocol GIKE_REKEY) and for Data-Security (AH
   [RFC4302] and/or ESP [RFC4303]) SAs may be included into SAg.  Each
   Proposal contains a list of Transforms that the GM is able and
   willing to support for that protocol.  Valid transform types depend
   on the protocol and are defined in Figure 16.  Other transform types
   SHOULD NOT be included.  The SPI length of each Proposal in an SAg is
   set to zero, and thus the SPI field is empty.  The GCKS MUST ignore
   SPI length and SPI fields in the SAg payload.

   Generally, a single Proposal 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.

   Proposal Num field in Proposal substructure is treated specially in
   SAg payload: it allows a GM to indicate that algorithms used in Rekey
   SA and in Data-Security (AH and/or ESP) SAs are dependent.  In
   particular, Proposals of different types having the same value in
   Proposal Num field are treated as a set, so that if GCKS uses
   transforms from one of such Proposal for one protocol, then it MUST
   only use transforms from one of the Proposals with the same value in

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   Proposal Num field for other protocols.  For example, a GM may
   support algorithms X and Y for both Rekey and Data-Security SAs, but
   with a restriction that if X is used in Rekey SA, then only X can be
   used in Data-Security SAs, and the same for Y.  To indicate this the
   GM sends several Proposals marking those of them that must be used in
   conjunction by putting the same value in their Proposal Num field.
   In the simplest case when no dependency between transforms exists,
   all Proposals in SAg payload will have the same value in Proposal Num
   field.

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

   A GM may also indicate the support for IPcomp by inclusion one or
   more the IPCOMP_SUPPORTED notifications along with the SAg payload.
   The 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 payloads.

   The GSA payload contains the security policy and cryptographic
   protocols used by the group.  This policy describes the optional
   Rekey SA (KEK), Data-security SAs (TEK), and optional Group
   Associated policy (GAP).  If the policy in the GSA payload is not
   acceptable to the GM, it SHOULD notify the GCKS by initiating a
   GSA_REGISTRATION exchange with a NO_PROPOSAL_CHOSEN Notify payload
   (see Section 2.3.2).  Note, that this should normally not happen if
   the GM includes SAg payload in the GSA_AUTH request and the GCKS
   takes it into account.  Finally the KD payload is parsed providing
   the keying material for the TEK and/or KEK.  The 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

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   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 successfully registers to the group it MUST replace any
   information related to this group (policy, keys) that it might have
   as a result of a previous registration with a new one.

   Once a GM has received GIKE_REKEY policy during a registration the
   IKE SA may be closed.  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.  If inband rekeying is used, then the initial IKE
   SA is rekeyed (when necessary) via standard IKEv2 mechanism described
   in Section 1.3.2 of [RFC7296].  If for some reason this SA is teared
   down and no GIKE_REKEY policy was received during the registration
   process, the GM MUST consider itself excluded from the group.  To
   continue participating in the group the GM should re-register.

2.3.4.  GCKS Registration Operations

   A G-IKEv2 GCKS passively listens for incoming requests from group
   members.  When the GCKS receives an IKE_SA_INIT request, it selects
   an IKE proposal and generates a nonce and DH to include them in the
   IKE_SA_INIT response.

   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 GCKS may also respond with an INVALID_GROUP_ID notify
   message if the requested group is unknown to the GCKS or with an
   REGISTRATION_FAILED notify message if there is a problem with the
   requested group (for example the capacity of the group is exceeded).

   The GSA_AUTH response will include the group policy in the GSA
   payload and keys in the KD payload.  If the GCKS policy includes a
   group rekey option, it MUST include the GSA_INITIAL_MESSAGE_ID
   attribute, specifying the starting Message ID the GCKS will use when
   sending the GSA_REKEY message to the group members if this Message ID
   is non-zero.  This Message ID is used to prevent GSA_REKEY message
   replay attacks and will be increased each time a GSA_REKEY message is
   sent to the group.  The GCKS data traffic policy is included in the
   GSA TEK and keys are included in the KD TEK.  The GAP MAY also be
   included to provide the ATD and/or DTD (Section 4.4.3.1) 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

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   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 2.5).

   [RFC5374] defines two modes of operation for multicast Data-Securirt
   SAs: transport mode and tunnel mode with address preservation.  In
   the latter case outer source and destination addresses are taken from
   the inner IP packet.

   If the GCKS receives a GSA_REGISTRATION exchange with a request to
   register a GM to a group, the GCKS will need to authorize the GM with
   the new group (IDg) and respond with the corresponding group policy
   and keys.  If the GCKS fails to authorize the GM, it will respond
   with the AUTHORIZATION_FAILED notification.  The GCKS may also
   respond with an INVALID_GROUP_ID or REGISTRATION_FAILED notify
   messages for the reasons described above.

   If a group member includes an SAg in its GSA_AUTH or GSA_REGISTRATION
   request, the GCKS may evaluate it according to an implementation
   specific policy.

   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 that match the current
      group policy, then the GCKS SHOULD return a NO_PROPOSAL_CHOSEN
      Notification.

   o  The GCKS could store the list of Transforms, with the goal of
      migrating the group policy to a different Transforms when all of
      the group members indicate that they can support that Transforms.

   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 IKE SA.

2.4.  Group Maintenance Channel

   The GCKS is responsible for rekeying the secure group per the group
   policy.  Rekeying is an operation whereby the GCKS provides
   replacement TEKs and KEK, deleting TEKs, and/or excluding group
   members.  The GCKS may initiate a rekey message if group membership

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   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 IKE 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 IKE SA that was setup to protecting the member
         registration exchange.  This exchange allows the GCKS to rekey
         without using an independent GSA_REKEY pseudo-exchange.  The
         GSA_INBAND_REKEY exchange provides a reliable policy delivery
         and is useful when G-IKEv2 is used with a small group of
         cooperating devices.

   Depending on its policy the GCKS MAY combine these two methods.  For
   example, it may use the GSA_INBAND_REKEY to deliver key to the GMs in
   the group acting as senders (as this would provide reliable keys
   delivery), and the GSA_REKEY for the rest GMs.

2.4.1.  GSA_REKEY

   The GCKS initiates the G-IKEv2 Rekey securely, usually using IP
   multicast.  Since this rekey does not require a response and it sends
   to multiple GMs, G-IKEv2 rekeying MUST NOT use IKE SA windowing
   mechanism, described in Section 2.3 of [RFC7296].  The GCKS rekey
   message replaces the rekey GSA KEK or KEK array, and/or creates a new
   Data-Security GSA TEK.  The GM_SID attribute in the Key Download
   payload (defined in Section 4.5.3.3) MUST NOT be part of the Rekey
   Exchange as this is sender specific information and the Rekey
   Exchange is group specific.  The GCKS initiates the GSA_REKEY pseudo-
   exchange as following:

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

                    Figure 9: GSA_REKEY Pseudo-Exchange

   HDR is defined in Section 4.1.  The Message ID in this message will
   start with the value the GCKS sent to the group members in the

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   attribute GSA_INITIAL_MESSAGE_ID or from zero if this attribute
   wasn't sent.  The Message ID will be incremented each time a new
   GSA_REKEY message is sent to the group members.

   The GSA payload contains the current policy for rekey and Data-
   Security SAs.  The GSA may contain a new Rekey SA and/or a new Data-
   Security SAs Section 4.4.

   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.  See Section 4.6 for more detail.

   The AUTH payload MUST be included to authenticate the GSA_REKEY
   message if the authentication method is based on public key
   signatures and MUST NOT be included if authentication is implicit.
   In the latter case, the fact that a GM can decrypt the GSA_REKEY
   message and verify its ICV proves that the sender of this message
   knows the current KEK, thus authenticating the sender as a member of
   the group.  Note, that implicit authentication doesn't provide source
   origin authentication.  For this reason using implicit authentication
   for GSA_REKEY is NOT RECOMMENDED unless source origin authentication
   is not required (for example, in a small group of highly trusted
   GMs).  The value of the Auth Method field in the AUTH payload in the
   GSA_REKEY message MUST NOT be NULL Authentication.

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

2.4.1.1.  GSA_REKEY Messages Authentication

   The content of the AUTH payload 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

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   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.  Figure 10
   illustrates the layout of the P and A chunks in the GSA_REKEY
   message.

   Before the AUTH payload calculation the inner payloads of Encrypted
   payload must be fully formed and ready for encryption except for the
   AUTH payload.  The AUTH payload must have correct values in the
   Payload Header, the Auth Method and the RESERVED fields.  The
   Authentication Data field is zeroed, but 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
   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

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

         Figure 10: Data to Authenticate in the GSA_REKEY Messages

   The authentication data is calculated using the authentication
   algorithm from the Authentication Method transform and the current
   authentication key provided in the AUTH_KEY attribute.  Depending on
   the authentication method the authentication data is a digital
   signature or a result of applying prf from the Pseudorandom Function
   transform.  The calculated authentication data is placed into the
   AUTH payload, the Length fields in the IKE Header and the Encryption
   Payload header are restored, the content of the Encrypted payload is
   encrypted and the ICV is computed using the current KEK keys.

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2.4.1.2.  IKE Fragmentation

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

   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.

   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.

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

2.4.1.3.  GSA_REKEY GCKS Operations

   The GCKS builds the rekey message with a Message ID value that is one
   greater than the value included in the previous rekey message.  The
   first message sent over a new Rekey SA must have the Message ID 0.
   The GSA, KD, N and D payloads follow with the same characteristics as
   in the GSA Registration exchange.  The AUTH payload (if present) is
   created as defined in Section 2.4.1.1.

   Because GSA_REKEY messages are not acknowledged and could be
   discarded by the network, one or more GMs may not receive the new
   policy.  To mitigate such lost messages, during a rekey event the
   GCKS may transmit several 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.

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   GCKS may also include one or several GSA_NEXT_SPI attributes
   specifying SPIs for the prospected rekeys, so that listening GMs are
   able to detect lost rekey messages and recover from this situation.
   See Sections Section 4.4.2.2.3 for more detail.

2.4.1.4.  GSA_REKEY GM Operations

   When a group member receives the Rekey Message from the GCKS it
   decrypts the message 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.

   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 using cipher in a
   counter-modes of operation and the receiving group member is a sender
   for that SA, the group member uses its current 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 the current group
   policy).

   Once a new Rekey SA is installed as a result of GSA_REKEY message,
   the current Rekey SA (over which the message was received) MUST be
   silently deleted after waiting DEACTIVATION_TIME_DELAY interval
   regardless of its expiration time.  If the message includes Delete
   payload for existing Data-security SA, then after installing a new
   Data-Security SA the old one, identified by the Protocol and SPI
   fields in the Delete payload, MUST be silently deleted after waiting
   DEACTIVATION_TIME_DELAY interval regardless of its expiration time.

   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

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   them.  A GM SHOULD also initiate a registration request if a Rekey SA
   is about to expire and not yet replaced with a new one.

2.4.2.  GSA_INBAND_REKEY Exchange

   When the IKE SA protecting the member registration exchange is
   maintained while group member participates in the group, the GCKS can
   use the GSA_INBAND_REKEY exchange to individually provide policy
   updates to the group member.

   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].

2.4.2.1.  GSA_INBAND_REKEY GCKS Operations

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

2.4.2.2.  GSA_INBAND_REKEY GM Operations

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

2.4.3.  Deletion of SAs

   There are occasions when the GCKS may want to signal to group members
   to delete policy at the end of a broadcast, or if group policy has
   changed.  Deletion of SAs is accomplished by sending the G-IKEv2
   Delete Payload [RFC7296], section 3.11 as part of the GSA_REKEY
   pseudo-exchange as shown below.

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

                    Figure 12: SA Deletion in GSA_REKEY

   If GCKS has a unicast SA with group member then it can use the
   GSA_INBAND_REKEY exchange to delete SAs.

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

                Figure 13: SA Deletion in GSA_INBAND_REKEY

   The GCKS MAY specify the remaining active time of the policy by using
   the GAP_DTD attribute in the GSA GAP substructure.  If a GCKS has no
   further SAs to send to group members, the GSA and KD payloads MUST be
   omitted from the message.

   There may be circumstances where the GCKS may want to start over with
   a clean state, for example in case it runs out of available SIDs.
   The GCKS can signal deletion of all the Data-security SAs by sending
   a Delete payload with an SPI value equal to zero.  For example, if
   the GCKS wishes to remove the Rekey SA and all the Data-security SAs,
   the GCKS sends a Delete payload with an SPI of zero and Protocol ID
   of AH or ESP, followed by another Delete payload with a SPI of zero
   and Protocol ID of GIKE_REKEY.

   If a group member receives a Delete payload with zero SPI and
   protocol ID of GIKE_REKEY either via multicast Rekey SA or via
   unicast SA using the GSA_INBAND_REKEY exchange, it means that the
   group member is excluded from the group.  The group member MUST re-
   register if it wants to continue participating in this group.  The
   registration is performed as described in Section 2.3.  Note, that if
   the GSA_INBAND_REKEY exchange is used to exclude a group member from
   the group, and thus the unicast SA between the group member and the
   GCKS exists, then this SA persists after this exchange and the group
   member may use the GSA_REGISTRATION exchange to re-register.

2.5.  Counter-based modes of operation

   Several counter-based modes of operation have been specified for ESP
   (e.g., AES-CTR [RFC3686], AES-GCM [RFC4106], AES-CCM [RFC4309],
   ChaCha20-Poly1305 [RFC7634], AES-GMAC [RFC4543]) and AH (e.g., AES-
   GMAC [RFC4543]).  These counter-based modes require that no two
   senders in the group ever send a packet with the same Initialization
   Vector (IV) using the same cipher key and mode.  This requirement is
   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.

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2.5.1.  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 sender to which it was allocated.  The group
   sender 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 sender 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 sender.  A
   group sender 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 sender MAY request more
   than one SID and use them serially.  This could be useful when it is
   anticipated that the group sender will exhaust their range of Data-
   Security SA nonces using a single 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 sender.

   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 sender.  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 sender 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 sender.  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 registration operation
       by a group sender, regardless of whether the group sender had
       previously contacted the GCKS.  In this way, the GCKS is not
       required to maintaining a record of which SID values it had

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       previously allocated to each group sender.  More importantly,
       since the GCKS cannot reliably detect whether the group sender
       had sent data on the current group Data-Security SAs it does not
       know what Data-Security counter-mode nonce values that a group
       sender has used.  By distributing new SID values, the key server
       ensures that each time a conforming group sender installs a Data-
       Security SA it will use a unique set of counter-based mode
       nonces.

   5.  When the 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 exclude all group
       members from the group as described in Section 2.4.3.  This will
       result in the group members performing re-registration, during
       which they will receive new Data-Security SAs and group senders
       will additionally receive new SID values.  The new SID values can
       safely be used because they are only used with the new Data-
       Security SAs.

2.5.2.  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.

2.6.  Replay Protection for Multicast Data-Security SAs

   IPsec provides replay protection as part of its security services.
   With multicast extension for IPsec replay protection is not always
   possible to acieve (see Section 6.1 of [RFC3740]).  In particular, if
   there are many group senders for a Data-Security SA, then each of
   them will independently incement the Sequence Number field in the ESP
   header (see Section 2 of [RFC4303]) thus making impossible for the
   group receivers to filter out replayed packets.  However, if there is
   only one group sender for a a Data-Security SA, then it is possible
   to acieve replay protection with some restrictions (see
   Section 4.4.2.1.3).  The GCKS may create several Data-Security SAs
   with the same traffic selectors allowing only a single group sender
   in each SA if it is desirable to get replay protection with multiple
   (but still limited number) of group senders.

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   In IPsec architecture assumes that it is a local matter for an IPsec
   receiver whether replay protection is active or not.  In other words,
   an IPsec sender always increments the Sequence Number field in the
   ESP header and a receiver decides whether to check for replayed
   packets or not.  With multicast extension for IPsec this approach
   generally isn't applicable, since group members don't know how many
   group senders exist for a particular Data-Security SA.  For this
   reason the status or replay protection must be part of the policy
   downloaded to GMs by GCKS.

   For this purpose this specification re-uses the Extended Sequence
   Numbers transform, defined in Section 3.3.2 [RFC7296].  This
   specification renames this transform to "Replay Protection" and adds
   a new value for possible Transform IDs: "Not Used" (<TBA by IANA>).
   The GCKS MUST include this transform in the GSA payload for every
   Data-Security SA.  Note, that this specification prohibits using
   Extended Sequence Numbers (see Section 4.4.2.1.3).

3.  Group Key Management and Access Control

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

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

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

3.1.  Key Wrap Keys

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

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

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

3.1.1.  Default Key Wrap Key

   The default KWK (GSK_w) is only used in the context of a single IKE
   SA.  Every IKE SA (unicast IKE SA or multicast Rekey SA) will have
   its own GSK_w.  The GSK_w is used with the algorithm from the
   Encryption Algorithm transform for the SA the GSK_w is used in the
   context of.  The size of GSK_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 for the
   GSA_INBAND_REKEY exchanges, if they are take place) the GSK_w is
   computed as follows:

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

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

   For the multicast Rekey SA the GSK_w is provided along with other SA
   keys as defined in Section 3.4.

3.2.  GCKS Key Management Semantics

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

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

   o  An LKH key management method -- when the GCKS provides each GM
      with an individual key at the time of the GM registration
      (encrypted with GSK_w).  Then the GCKS forms an hierarchy of keys

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      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.

3.2.1.  Forward Access Control Requirements

   When group membership is altered using a group management algorithm
   new Data-Security SAs and their associated keys are usually also
   needed.  New Data-Security SAs and keys ensure that members who were
   denied access can no longer participate in the group.

   If forward access control is a desired property of the group, new TEK
   policy and the associated keys MUST NOT be included in a G-IKEv2
   rekey message which changes group membership.  This is required
   because the GSA TEK policy and the associated keys are not protected
   with the new KEK.  A second G-IKEv2 rekey message can deliver the new
   GSA TEKS and their associated keys because it will be protected with
   the new KEK, and thus will not be visible to the members who were
   denied access.

   If forward access control policy for the group includes keeping group
   policy changes from members that are denied access to the group, then
   two sequential G-IKEv2 rekey messages changing the group KEK MUST be
   sent by the GCKS.  The first G-IKEv2 rekey message creates a new KEK
   for the group.  Group members, which are denied access, will not be
   able to access the new KEK, but will see the group policy since the
   G-IKEv2 rekey message is protected under the current KEK.  A
   subsequent G-IKEv2 rekey message containing the changed group policy
   and again changing the KEK allows complete forward access control.  A
   G-IKEv2 rekey message MUST NOT change the policy without creating a
   new KEK.

   If other methods of using LKH or other group management algorithms
   are added to G-IKEv2, those methods MAY remove the above restrictions
   requiring multiple G-IKEv2 rekey messages, providing those methods
   specify how the forward access control policy is maintained within a
   single G-IKEv2 rekey message.

3.3.  GM Key Management Semantics

   This specification defines a GM Key Management semantics in such a
   way, that it doesn't depend on the key management method employed by
   the GCKS.  This allows having all the complexity of key management in
   the GCKS, which is free to implement various key management methods,
   such as direct transmitting of group SA keys or using some kind of

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   key hierarchy (e.g.  LKH).  For all these policies the GM behavior is
   the same.

   Each key that a GM receives in G-IKEv2 is identified by a 32-bit
   number called Key ID.  Zero Key ID has a special meaning -- it always
   contains keying material from which the keys for protecting Data-
   Security SAs and Rekey SA are taken.

   All keys in G-IKEv2 are transmitted in encrypted form, as specified
   in Section 4.5.1.  This format includes a Key ID (ID of a key that is
   encrypted) and a KWK ID (ID of a key that was used to encrypt this
   key).  Keys may be encrypted either with default KWK (GSK_w) or with
   other keys, which the GM has received in the WRAP_KEY attributes.  If
   a key was encrypted with GSK_w, then the KWK ID field is set to zero,
   otherwise the KWK ID field identifies the key used for encryption.

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

   For a multicast Rekey SA multiple SA_KEY attributes may be present
   depending on the key management method employed by the GCKS.  If
   multiple SA_KEY attributes are present then all of them MUST contain
   the same keying material encrypted using different KWKs.  The GM in
   general is unaware of the GCKS's key management method 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 GSK_w or the keys from the WRAP_KEY attributes that
   are present in the same message or were receives in previous
   messages.

   We will use the term "Key Path" to describe an ordered sequence of
   keys where each subsequent key was used to encrypt the previous one.
   The GM keeps its own Key Path (called Working Key Path) in the memory
   associated with each group it is registered to and updates it when
   needed.  When the GSA_REKEY message is received the GM processes the
   received SA_KEY attributes one by one trying to construct a new key
   path that starts from this attributes and ends with any key in the
   Working Key Path or with the default KWK (GSK_w).

   In the simplest case the SA_KEY attribute is encrypted with GSK_w so
   that the new Key Path is empty.  If more complex key management
   methods are used then a Key Path will contain intermediate keys from
   the WRAP_KEY attributes received by a GM so far starting from its
   registration to the group.  If the GM is able to construct a new Key

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   Path using intermediate keys it has, then it is able to decrypt the
   SA_KEY attribute and use its content to form new SA keys.  If it is
   unable to build a new Key Path, then in means that the GM is excluded
   from the group.

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

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

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

   o  In all other cases the new Key Path will end at some intermediate
      key from the GM's current Working Key Path.  In this case the new
      Key Path is constructed by replacing a part of the GM's current
      Working Key Path from the beginning and up to (but not including)
      the key that the GM has used to decrypt the last key in the new
      Key Path.

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

3.4.  SA Keys

   Keys used for Data-Security SAs or Rekey SA (called here SA keys) are
   downloaded to GMs in the form of keying material.  The keys for each
   algorithm employed in an SA are taken from this keying material as if
   they were concatenated to form it.

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

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

   GSK_e | GSK_a | GSK_w = KEYMAT

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

4.  Header and Payload Formats

   The G-IKEv2 is an IKEv2 extension and thus inherits its wire format
   for data structures.  However, the processing of some payloads are
   different 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.

4.1.  G-IKEv2 Header

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

4.2.  Group Identification Payload

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

4.3.  Security Association - GM Supported Transforms Payload

   The Security Association - GM Supported Transforms Payload (SAg)
   payload declares which Transforms a GM is willing to accept.  The
   payload is constructed using the format of the IKEv2 Security
   Association payload (section 3.3 of [RFC7296]).  The Payload Type for
   SAg is identical to the SA Payload Type -- thirty-three (33).

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4.4.  Group Security Association Payload

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

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

                       Figure 14: GSA Payload Format

   The Security Association Payload fields are defined as follows:

   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.

4.4.1.  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 Rekey SA policy (GSA KEK) and Data-Security SA policy (GSA TEK).
   GSA payload may contain zero or one GSA KEK policy, zero or more GSA
   TEK policies, and zero or one 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 GSA_INBAND_REKEY
   exchange via the unicast IKE SA.  Alternatively, group policy might
   use a Rekey SA but choose to download a KEK to the group member only
   as part of the unicast IKE SA.  Therefore, the GSA KEK policy would
   not be necessary as part of the GSA_REKEY message.

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   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 4.4.2 (for
   GSA policy) and in Section 4.4.3 (for GA policy).  The first octet of
   the substructure unambiguously determines its type -- it is zero for
   GAP and non-zero (actually, it is a security protocol ID) for GSA
   policies.

4.4.2.  Group Security Association Policy Substructure

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

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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 15: 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 Rekey SA and 2 (AH) or 3 (ESP) for Data-
      Security SAs.

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

   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 Rekey SA (with the
      GIKE_REKEY protocol) the destination traffic selectors MUST define
      a single multicast IP address, an IP protocol (assumed to be UDP)
      and a single port the GSA_REKEY messages will be destined to.  The
      source traffic selector in this case MUST either define a single
      IP address, an IP protocol (assumed to be UDP) and a single port
      the GSA_REKEY messages will be originated from or be a wildcard
      selector.  For the Data-Security (AH and ESP) SAs the destination
      traffic selectors SHOULD define a single multicast IP address.
      The source traffic selector in this case SHOULD define a single IP
      address or be a wildcard selector.  IP protocol and ports define
      the characteristics of traffic protected by this Data-Security SA.
      If the Data-Security SAs are created in tunnel mode, then it MUST
      BE tunnel mode with address preservation (see [RFC5374].  UDP
      encapsulation [RFC3948] is not used for the multicast Data-
      Security SAs.

   o  GSA Transforms (variable) -- A list of Transform Substructures
      specifies the policy information for the SA.  The format is
      defined in IKEv2 [RFC7296], section 3.3.2.  The Last Substruc
      value in each Transform Substructure will be set to 3 except for
      the last one in the list, which is set to 0.  Section 4.4.2.1
      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 protocol and the group policy.  Section 4.4.2.2 defines
      attributes used in GSA policy substructure.

4.4.2.1.  GSA Transforms

   GSA policy is defined by means of transforms in the GSA policy
   substructure.  For this purpose the transforms defined in [RFC7296]
   are used.  In addition, new transform types are defined for using in
   G-IKEv2: Authentication Method (AUTH) and Group Key Management Method
   (GKM), see Section 8.

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

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

                     Figure 16: Valid Transform Types

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

   (**) May only appear at the time of a GM registration, (in the
   GSA_aUTH and GSA_REGISTRATION exchanges).

4.4.2.1.1.  Authentication Method Transform

   The Authentication Method (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
   values in a range 0-255, so even that Transform ID field in the
   Transform substructure allows for 65536 possible values, in case of
   the Authentication Method transform the values 256-65535 MUST NOT
   appear.

   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: 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.

   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.  Additionally, the AUTH payload MUST NOT be
         included in the GIKE_REKEY messages.

   Digital Signature  -- Digital signatures will be used by the GCKS to
         authenticate the GSA_REKEY messages.  In this case the GCKS
         MUST include the AUTH_KEY attribute containing the public key
         into the KD payload at the time the GM is registered to the
         group.  To specify the details of the signature algorithm a new
         attribute Algorithm Identifier (<TBA by IANA>) is defined.

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         This attribute contains DER-encoded ASN.1 object
         AlgorithmIdentifier, which would specify the signature
         algorithm and the hash function that the GCKS will use for
         authentication.  The AlgorithmIdentifier object is defined in
         section 4.1.1.2 of [RFC5280], see also [RFC7427] for the list
         of common AlgorithmIdentifier values used in IKEv2.  In case of
         using digital signature the GCKS MUST include the Algorithm
         Identifier attribute in the Authentication Method transform.

   The authentication method MUST NOT change as a result of rekey
   operations.  This means that the Authentication Method transform may
   not appear in the rekey messages, it may only appear in the
   registration exchange (either GSA_AUTH or GSA_REGISTRATION).

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

4.4.2.1.2.  Group Key Management Method Transform

   The Group Key Management Method (GKM) transform is used in the
   GIKE_REKEY policy to convey information of how GCKS will manage the
   group keys to provide forward and backward access control (i.e., used
   to exclude group members).  Possible key management methods are
   defined in a new IKEv2 registry "Transform Type <TBA> -- Group Key
   Management Methods" (see Section 8).  This document defines one
   values for this registry:

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

   The group key management method MUST NOT change as a result of rekey
   operations.  This means that the Group Key Management Method
   transform may not appear in the rekey messages, it may only appear in
   the registration exchange (either GSA_AUTH or GSA_REGISTRATION).

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

4.4.2.1.3.  Replay Protection Transform

   The "Extended Sequence Number (ESN)" Transform is defined in
   [RFC7296].  This specification renames this transform to "Replay
   Protection (RP)".  This transform allows to specify whether the
   64-bit Extended Sequence Numbers (ESN) are to be used in ESP and AH.

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   Since both AH [RFC4302] and ESP [RFC4303] are defined in such a way,
   that high-order 32 bits of extended sequence numbers are never
   transmitted, it makes using ESN in multicast Data-Security SAs
   problematic, because GMs that join group long after it is created
   will have to somehow learn the current high order 32 bits of ESN for
   each sender in the group.  The algorithm for doing this described in
   [RFC4302] and [RFC4303] is resource-consuming and is only suitable
   when a receiver is able to guess the high-order 32 bits close enough
   to its real value, which is not the case for multicast SAs.  For this
   reason extended sequence numbers MUST NOT be used for multicast Data-
   Security SAs and thus the value "Extended Sequence Numbers" (1) for
   the Replay Protection transform type MUST NOT be used in the GSA
   Payload.  The GCKS MUST estimate the data rate and rekey Data-
   Security SAs freuently enough so that Sequence Numbers (SN) don't
   wrap.

4.4.2.2.  GSA Attributes

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

   This document creates a new IKEv2 IANA registry for the types of the
   GSA attributes which is initially filled as described in Section 8.
   In particular, the following attributes are initially added.

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

   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).

4.4.2.2.1.  GSA_KEY_LIFETIME Attribute

   The GSA_KEY_LIFETIME attribute (1) specifies the maximum time for
   which the SA is valid.  The value is a 4 octet unsigned integer in a
   network byte order, specifying a valid time period in seconds.  A
   single attribute of this type MUST be included into any GSA policy
   substructure.

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

   This attribute SHOULD NOT be used if inband rekeying (via the
   GSA_INBAND_REKEY exchange) is employed by the GCKS for the GM.

4.4.2.2.2.  GSA_INITIAL_MESSAGE_ID Attribute

   The GSA_INITIAL_MESSAGE_ID attribute (2) defines the initial Message
   ID to be used by the GCKS in the GSA_REKEY messages.  The Message ID
   is a 4 octet unsigned integer in network byte order.

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

   This attribute MUST NOT be used if inband rekeying (via the
   GSA_INBAND_REKEY exchange) is employed by the GCKS for the GM.

4.4.2.2.3.  GSA_NEXT_SPI Attribute

   The optional GSA_NEXT_SPI attribute (3) contains SPI that the GCKS
   reserved for the next Rekey SA or Data-Security SAs replacing the
   current ones.  The length of the attribute data is determined by the
   SPI Size field in the GSA Policy substructure the attribute resides
   in (see Section 4.4.2), and the attribute data contains SPI as it
   would appear on the network.  Multiple attributes of this type MAY be
   included, meaning that any of the supplied SPIs can be used in the
   replacement group SA.

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

   Note, that this method of detecting lost rekey messages can only be
   used by group receivers.  Additionally there is no point to include
   this attribute in the GSA_INBAND_REKEY messages, since they use
   reliable transport.  Note also, that the GCKS is free to forget its
   promises and not to use the SPIs it sent in the GSA_NEXT_SPI
   attributes before (e.g. in case of the GCKS is rebooted), so the GM
   must only treat these information as a "best effort" made by the GCKS
   to prepare for future rekeys.

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   This attribute MUST NOT be used if inband rekeying (via the
   GSA_INBAND_REKEY exchange) is employed by the GCKS for the GM.

4.4.3.  Group Associated Policy Substructure

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

   The GAP substructure is defined as follows:

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Protocol   |   RESERVED    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                        <GAP Attributes>                       ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 17: GAP Substructure Format

   The GAP substructure fields are defined as follows:

   o  Protocol (1 octet) -- MUST be zero.  This value is reserved in
      Section 8 and is never used for any security protocol, so it is
      used here to indicate that this substructure contains policy not
      related to any specific protocol.

   o  RESERVED ( octet) -- MUST be zero on transmission, MUST be ignored
      on receipt.

   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 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 8.
   In particular, the following attributes are initially added.

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

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

   The GAP_DTD attribute (2) allows the GCKS to set the Deactivation
   Time Delay for previously distributed SAs.  The DTD defines how long
   after receiving a request to delete Data-Security SAs passive group
   members should wait before actually deleting them.  Note that active
   members of the group should stop sending traffic over these old SAs
   once new replacement SAs are activated (after time specified in the
   GAP_ATD attribute).

   The GAP_ATD and GAP_DTD attributes contain 16 bit unsigned integer in
   a network byte order, specifying the delay in seconds.  These
   attributes are OPTIONAL.  If one of them or both are not sent by the
   GCKS, then no corresponding delay should be employed.

4.4.3.2.  GAP_SID_BITS Attribute

   The GAP_SID_BITS attribute (3) 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 2.5.2.  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.

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   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.

4.5.  Key Download Payload

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

                        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 18: 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.

4.5.1.  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 19).

   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 IKE SA
   establishment, while for a GSA_REKEY message the algorithm will be

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   provided by the GCKS in the Encryption Algorithm transform in the GSA
   payload when this multicast SA was being established.

   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 19: 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 SA keys (in the form of
      keying material, see Section 3.4)), otherwise it contains some
      intermediate key.

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

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

   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.

4.5.2.  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 Packet Attributes>                  ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 20: 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

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

   o  Group Key Packet 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 Packet attributes which is initially filled as described in
   Section 8.  In particular, the following attributes are initially
   added.

        Group Key Packet
        Attributes          Value   Type    Multiple    Protocol
        ----------------------------------------------------------
        Reserved            0
        SA_KEY              1       V       N/Y*        GIKE_REKEY,
                                            N           AH, ESP

   (*) Multiple SA_KEY attributes may only appear for the GIKE_REKEY
   protocol in the GSA_REKEY exchange if the GCKS uses the Group Key
   Management method that allows excluding GMs from the group (like
   LKH).

   The attributes 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).

4.5.2.1.  SA_KEY Attribute

   The SA_KEY attribute (1) contains a keying material for the
   corresponding SA.  The content of the attribute is formatted
   according to Section 4.5.1 with a precondition that the Key ID field
   MUST always be zero.  The size of the keying material MUST be equal
   to the total size of the keys needed to be taken from this keying
   material (see Section 3.4) for the corresponding SA.

   If the Key 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 in
   the GSA_AUTH, GSA_REGISTRATION and GSA_INBAND_REKEY exchanges exactly
   one SA_KEY attribute MUST be present.  In the GSA_REKEY exchange at

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   least one SA_KEY attribute MUST be present, and more attributes MAY
   be present (depending on the key management method employed by the
   GCKS).

4.5.3.  Member Key Packet Substructure

   The Member Key Packet substructure contains keys and other parameters
   that are specific for a member of the group and are not associated
   with any particular group 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   |   RESERVED    |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                  <Member Key Packet Attributes>               ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 21: Member Key Packet Substructure Format

   The Member Key Packet substructure fields are defined as follows:

   o  Protocol (1 octet) -- MUST be zero.  This value is reserved in
      Section 8 and is never used for any security protocol, so it is
      used here to indicate that this Key Packet is not associated with
      any particular SA.

   o  RESERVED ( octet) -- MUST be zero on transmission, MUST be ignored
      on receipt.

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

   o  Member Key Packet 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 Packet attributes which is initially filled as described
   in Section 8.  In particular, the following attributes are initially
   added.

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             Member Key Packet
             Attributes              Value   Type    Multiple
             ------------------------------------------------
             Reserved                0
             WRAP_KEY                1       V       Y
             AUTH_KEY                2       V       N
             GM_SID                  3       V       Y

   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).

4.5.3.1.  WRAP_KEY Attribute

   The WRAP_KEY attribute (1) contains a key that is used to encrypt
   other keys.  One or more these attributes are sent to GMs if the GCKS
   key management method relies on some key hierarchy (e.g.  LKH).  This
   attribute MUST NOT be used if inband rekeying (via the
   GSA_INBAND_REKEY exchange) is employed by the GCKS for the GM.

   The content of the attribute has a format defined in Section 4.5.1
   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 WRAP_KEY attributes was sent in.  The size of the key
   MUST be equal to the key size for this algorithm.

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

4.5.3.2.  AUTH_KEY Attribute

   The AUTH_KEY attribute (2) contains the key that is used to
   authenticate the GSA_REKEY messages.  The content of the attribute
   depends on the authentication method the GCKS specified in the
   Authentication Method transform in the GSA payload.

   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].
      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 [RFC8017], Section A.1.  DSS
      public key format is defined in [RFC3279] Section 2.3.2.  For
      ECDSA Public keys, use format described in [RFC5480] Section 2.

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      Other algorithms added to the IKEv2 Authentication Method registry
      are also expected to include a format of the SubjectPublicKeyInfo
      object included in the algorithm specification.

   Multiple instances of the AUTH_KEY attributes MUST NOT be sent.  This
   attribute MUST NOT appear in the rekey operations (in the GSA_REKEY
   or GSA_INBAND_REKEY exchanges).

4.5.3.3.  GM_SID Attribute

   The GM_SID attribute (3) is used to download one or more Sender-ID
   values for the exclusive use of a group member.  One or more of this
   attributes MUST be sent by the GCKS if the GM informed the GCKS that
   it would be a sender (by inclusion the SENDER notification to the
   request) and at least one of the Data-Security SAs included in the
   GSA payload uses counter-based mode of encryption.

   If the GMs has requested multiple 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.

   This attribute MUST NOT appear in the rekey operations (in the
   GSA_REKEY or GSA_INBAND_REKEY exchanges).

4.6.  Delete Payload

   Delete payload is used in G-IKEv2 when the GCKS wants to delete Data-
   Security and Rekey SAs.  The interpretation of the Protocol field in
   the Delete payload is extended, so that zero protocol indicates
   deletion of whole Group SA (i.e. all Data-Security SAs and Rekey SA).
   See Section 2.4.3 for detail.

4.7.  Notify Payload

   G-IKEv2 uses the same Notify payload as specified in [RFC7296],
   section 3.10.

   There are additional Notify Message types introduced by G-IKEv2 to
   communicate error conditions and status (see Section 8).

   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.

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

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

   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.

4.7.1.  USE_TRANSPORT_MODE Notification

   This specification uses the USE_TRANSPORT_MODE notification defined
   in section 3.10.1 of [RFC7296] to specify the mode Data-Security SAs
   should be created in.  The GCKS MUST include the USE_TRANSPORT_MODE
   notification in a message containing the GSA payload if Data-Security
   SAs are to be created in transport mode and MUST NOT include if they
   are to be created in tunnel mode.

   Note, that it is not possible with this specification to create a
   group where some Data-Security SAs use transport mode and the others
   use tunnel mode.  If such a configuration is needed two different
   groups must be defined.

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4.8.  Authentication Payload

   G-IKEv2 uses the same Authentication payload as specified in
   [RFC7296], section 3.8, to authenticate the rekey message.  However,
   if it is used in the GSA_REKEY messages the content of the payload is
   computed differently, as described in Section 2.4.1.1.

5.  Usigng G-IKEv2 Attributes

   G-IKEv2 defines a number of attributes, that are used to convey
   information from GCKS to GMs.  There are some restrictions on where
   and when these attributes can appear in G-IKEv2 messages, which are
   defined when the attributes are introduced.  For convenience these
   restrictions are summarized in Table 1 (for multicast rekey
   operations) and Table 2 (for inband rekey operations) below.

   The following notation is used:

   S     A single attribute of this type must be present

   M     Multiple attributes of this type may be present

   []    Attribute is optional

   -     Attribute must not be present

   Note, that the restrictions are defined per a substructure
   corresponding attributes are defined for and not per whole G-IKEv2
   message.

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   +-------------------------+--------------------+--------------------+
   | Attributes              |      GSA_AUTH      |     GSA_REKEY      |
   |                         |  GSA_REGISTRATION  |                    |
   +-------------------------+--------------------+--------------------+
   | GSA_KEY_LIFETIME        |         S          |         S          |
   |                         |                    |                    |
   | GSA_INITIAL_MESSAGE_ID  |        [S]         |        [S]         |
   |                         |                    |                    |
   | GSA_NEXT_SPI            |        [M]         |        [M]         |
   |                         |                    |                    |
   | GAP_ATD                 |        [S]         |        [S]         |
   |                         |                    |                    |
   | GAP_DTD                 |        [S]         |        [S]         |
   |                         |                    |                    |
   | GAP_SID_BITS            |         S*         |         -          |
   |                         |                    |                    |
   | SA_KEY                  |         S          |      S/[M]**       |
   |                         |                    |                    |
   | WRAP_KEY                |       [M]**        |       [M]**        |
   |                         |                    |                    |
   | AUTH_KEY                |        S***        |      [S]****       |
   |                         |                    |                    |
   | GM_SID                  |      S*/[M]*       |         -          |
   +-------------------------+--------------------+--------------------+

    Table 1: Using attributes in G-IKEv2 exchanges when multicast rekey
                                  is used

   *     The GAP_SID_BITS attribute must be present if the GCKS policy
         includes at least one cipher in counter mode of operation and
         the GM included the SENDER notify into the registration
         request.  Otherwise it must not be present.  At least one
         GM_SID attribute must be present in the former case (and more
         may be present if the GM requested more SIDs) and no GM_SID
         attributes must be present in the latter case.

   **    The WRAP_KEY attributes may be present if the GCKS employs key
         management method that relies on key tree (like LKH).

   ***   The AUTH_KEY attribute must be present if the GCKS employs
         authentication method other than NULL Authentication.

   ***   The AUTH_KEY attribute may be present if the GCKS employs
         authentication method based on digital signatures and wants to
         change the public key for the following multicast rekey
         operations.

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   +-------------------------+--------------------+--------------------+
   | Attributes              |      GSA_AUTH      |  GSA_INBAND_REKEY  |
   |                         |  GSA_REGISTRATION  |                    |
   +-------------------------+--------------------+--------------------+
   | GSA_KEY_LIFETIME        |        [S]         |        [S]         |
   |                         |                    |                    |
   | GSA_INITIAL_MESSAGE_ID  |         -          |         -          |
   |                         |                    |                    |
   | GSA_NEXT_SPI            |         -          |         -          |
   |                         |                    |                    |
   | GAP_ATD                 |        [S]         |        [S]         |
   |                         |                    |                    |
   | GAP_DTD                 |        [S]         |        [S]         |
   |                         |                    |                    |
   | GAP_SID_BITS            |         S*         |         -          |
   |                         |                    |                    |
   | SA_KEY                  |         S          |         S          |
   |                         |                    |                    |
   | WRAP_KEY                |         -          |         -          |
   |                         |                    |                    |
   | AUTH_KEY                |         -          |         -          |
   |                         |                    |                    |
   | GM_SID                  |      S*/[M]*       |         -          |
   +-------------------------+--------------------+--------------------+

    Table 2: Using attributes in G-IKEv2 exchanges when inband rekey is
                                   used

   *     The GAP_SID_BITS attribute must be present if the GCKS policy
         includes at least one cipher in counter mode of operation and
         the GM included the SENDER notify into the registration
         request.  Otherwise it must not be present.  At least one
         GM_SID attribute must be present in the former case (and more
         may be present if the GM requested more SIDs) and no GM_SID
         attributes must be present in the latter case.

6.  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 EAP-only authentication
   [RFC5998] and Secure Password authentication [RFC6467].  G-IKEv2 is
   compatible with and can use IKEv2 Redirect Mechanism [RFC5685] and
   IKEv2 Session Resumption [RFC5723].  G-IKEv2 is also compatible with
   Multiple Key Exchanges in IKEv2 framework, defined in
   [I-D.ietf-ipsecme-ikev2-multiple-ke].

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   The above list of compatible IKEv2 extensions is not exhaustive,
   however some IKEv2 extensions require special handling if used in
   G-IKEv2.

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

   G-IKEv2 can take advantage of the protection provided by Postquantum
   Preshared Keys (PPK) for IKEv2 [RFC8784].  However, the use of PPK
   leaves the initial IKE SA susceptible to quantum computer (QC)
   attacks.  While group SA keys are protected with the default KWK
   (GSK_w), which is derived from SK_d and thus cannot be broken even by
   attacker equipped with a QC, authentication of these keys relies on
   authentication of IKE SA messages, which is not secure against QC
   until the initial IKE SA is rekeyed.  In additional, the other
   content of IKE SA messages may also be visible to an attacker with a
   QC.  See Section 6 of [RFC8784] for details.

   For these reasons the GCKS MUST NOT send GSA and KD payloads in the
   GSA_AUTH response message and MUST return a new notification
   REKEY_IS_NEEDED instead.  Upon receiving this notification in the
   GSA_AUTH response the GM MUST perform an IKE SA rekey and then
   initiate a new GSA_REGISTRATION request for the same group.  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:

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

           Figure 22: IKE_SA_INIT Exchange requesting using PPK

   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 23: GSA_AUTH Request using PPK

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   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 24: 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 25: 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 26: GSA_AUTH Response using PPK

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

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

     Figure 27: Rekeying IKE SA followed by GSA_REGISTRATION Exchange

   Note, that [I-D.smyslov-ipsecme-ikev2-qr-alt] MAY be used to make the
   initial IKE SA secure against QC.

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7.  Security Considerations

7.1.  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.

7.2.  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.

7.2.1.  Authentication/Authorization

   The authentication key is distributed during the GM registration, and
   the receiver of the rekey message uses that key to verify the message
   came from the authorized GCKS.  An implicit authentication can also
   be used, in which case the ability of the GM to decrypt and to verify
   ICV of the received message proved taht a sender of the message is a
   member of the group.  However, implicit authentication doesn't
   provide source origin authentication, so the GM cannot be sure that
   the message came from the GCKS.  For this reason using implicit
   authentication is NOT RECOMMENDED unless in a small group of trusted
   parties.

7.2.2.  Confidentiality

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

7.2.3.  Man-in-the-Middle Attack Protection

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

7.2.4.  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

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   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.

8.  IANA Considerations

8.1.  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  Protocol
   ---------------------------------------------------------------------
   Reserved                0
   GSA_KEY_LIFETIME        1      V      N         GIKE_REKEY, AH, ESP
   GSA_INITIAL_MESSAGE_ID  2      V      N         GIKE_REKEY
   GSA_NEXT_SPI            3      V      Y         GIKE_REKEY, AH, ESP
   Unassigned             5-16383
   Private Use        16384-32767

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

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

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   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 Packet
   Attributes".  The initial values of the new registry are:

   Group Key Packet
   Attributes          Value   Type    Multiple    Protocol
   ------------------------------------------------------------
   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 Packet
   Attributes".  The initial values of the new registry are:

   Member Key Packet
   Attributes              Value   Type    Multiple
   ------------------------------------------------
   Reserved                0
   WRAP_KEY                1       V       Y
   AUTH_KEY                2       V       N
   GM_SID                  3       V       Y
   Unassigned             4-16383
   Private Use        16384-32767

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

8.2.  Changes in the Existing IKEv2 Registries

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

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

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

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

   This document makes the following changes to the "Transform Type
   Values" registry:

   o  Defines two new transform types -- "Authentication Method (AUTH)"
      and "Group Key Management Method (GKM)";

   o  Renames existing transform type "Extended Sequence Numbers (ESN)"
      to "Replay Protection (RP)";

   o  Changes the "Used In" column for the existing allocations as
      follows;

   Type  Description                          Used In
   ---------------------------------------------------------------------
   1     Encryption Algorithm (ENCR)          IKE, GIKE_REKEY and ESP
   2     Pseudo-random Function (PRF)         IKE, GIKE_REKEY
   3     Integrity Algorithm (INTEG)          IKE, GIKE_REKEY, AH,
                                              optional in ESP
   4     Diffie-Hellman Group (D-H)           IKE, optional in AH, ESP
   5     Replay Protection (RP)               AH and ESP
   <TBA> Authentication Method (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

   This document renames the "Transform Type 5 - Extended Sequence
   Numbers Transform IDs" registry to "Transform Type 5 - Replay

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   Protection Transform IDs" and also adds a new value into this
   registry:

   Number       Name
   ---------------------
   <TBA>        Not Used

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

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

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

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

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

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

   Protocol ID       Protocol
   --------------------------
   <TBA>             GIKE_REKEY

9.  Acknowledgements

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

   The authors are grateful to Tero Kivinen for his careful review and
   valuable proposals how to improve the document.

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10.  Contributors

   The following individuals made substantial contributions to early
   versions of this memo.

      Sheela Rowles
      Cisco Systems
      170 W. Tasman Drive
      San Jose, California  95134-1706
      USA

      Phone: +1-408-527-7677
      Email: sheela@cisco.com

      Aldous Yeung
      Cisco Systems
      170 W. Tasman Drive
      San Jose, California  95134-1706
      USA

      Phone: +1-408-853-2032
      Email: cyyeung@cisco.com

      Paulina Tran
      Cisco Systems
      170 W. Tasman Drive
      San Jose, California  95134-1706
      USA

      Phone: +1-408-526-8902
      Email: ptran@cisco.com

      Yoav Nir
      Dell EMC
      9 Andrei Sakharov St
      Haifa  3190500
      Israel

      Email: ynir.ietf@gmail.com

11.  References

11.1.  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>.

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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>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,
              <https://www.rfc-editor.org/info/rfc4302>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

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

   [RFC6054]  McGrew, D. and B. Weis, "Using Counter Modes with
              Encapsulating Security Payload (ESP) and Authentication
              Header (AH) to Protect Group Traffic", RFC 6054,
              DOI 10.17487/RFC6054, November 2010,
              <https://www.rfc-editor.org/info/rfc6054>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <https://www.rfc-editor.org/info/rfc7296>.

   [RFC7427]  Kivinen, T. and J. Snyder, "Signature Authentication in
              the Internet Key Exchange Version 2 (IKEv2)", RFC 7427,
              DOI 10.17487/RFC7427, January 2015,
              <https://www.rfc-editor.org/info/rfc7427>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

11.2.  Informative References

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   [I-D.ietf-ipsecme-ikev2-intermediate]
              Smyslov, V., "Intermediate Exchange in the IKEv2
              Protocol", draft-ietf-ipsecme-ikev2-intermediate-10 (work
              in progress), March 2022.

   [I-D.ietf-ipsecme-ikev2-multiple-ke]
              Tjhai, C., Tomlinson, M., Bartlett, G., Fluhrer, S.,
              Geest, D. V., Garcia-Morchon, O., and V. Smyslov,
              "Multiple Key Exchanges in IKEv2", draft-ietf-ipsecme-
              ikev2-multiple-ke-05 (work in progress), March 2022.

   [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-04 (work in progress), August 2021.

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

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

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

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

   [RFC2627]  Wallner, D., Harder, E., and R. Agee, "Key Management for
              Multicast: Issues and Architectures", RFC 2627,
              DOI 10.17487/RFC2627, June 1999,
              <https://www.rfc-editor.org/info/rfc2627>.

   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
              Identifiers for the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April
              2002, <https://www.rfc-editor.org/info/rfc3279>.

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   [RFC3686]  Housley, R., "Using Advanced Encryption Standard (AES)
              Counter Mode With IPsec Encapsulating Security Payload
              (ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004,
              <https://www.rfc-editor.org/info/rfc3686>.

   [RFC3740]  Hardjono, T. and B. Weis, "The Multicast Group Security
              Architecture", RFC 3740, DOI 10.17487/RFC3740, March 2004,
              <https://www.rfc-editor.org/info/rfc3740>.

   [RFC3948]  Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
              Stenberg, "UDP Encapsulation of IPsec ESP Packets",
              RFC 3948, DOI 10.17487/RFC3948, January 2005,
              <https://www.rfc-editor.org/info/rfc3948>.

   [RFC4046]  Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,
              "Multicast Security (MSEC) Group Key Management
              Architecture", RFC 4046, DOI 10.17487/RFC4046, April 2005,
              <https://www.rfc-editor.org/info/rfc4046>.

   [RFC4106]  Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
              (GCM) in IPsec Encapsulating Security Payload (ESP)",
              RFC 4106, DOI 10.17487/RFC4106, June 2005,
              <https://www.rfc-editor.org/info/rfc4106>.

   [RFC4309]  Housley, R., "Using Advanced Encryption Standard (AES) CCM
              Mode with IPsec Encapsulating Security Payload (ESP)",
              RFC 4309, DOI 10.17487/RFC4309, December 2005,
              <https://www.rfc-editor.org/info/rfc4309>.

   [RFC4543]  McGrew, D. and J. Viega, "The Use of Galois Message
              Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543,
              DOI 10.17487/RFC4543, May 2006,
              <https://www.rfc-editor.org/info/rfc4543>.

   [RFC5374]  Weis, B., Gross, G., and D. Ignjatic, "Multicast
              Extensions to the Security Architecture for the Internet
              Protocol", RFC 5374, DOI 10.17487/RFC5374, November 2008,
              <https://www.rfc-editor.org/info/rfc5374>.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
              <https://www.rfc-editor.org/info/rfc5480>.

   [RFC5685]  Devarapalli, V. and K. Weniger, "Redirect Mechanism for
              the Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 5685, DOI 10.17487/RFC5685, November 2009,
              <https://www.rfc-editor.org/info/rfc5685>.

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   [RFC5723]  Sheffer, Y. and H. Tschofenig, "Internet Key Exchange
              Protocol Version 2 (IKEv2) Session Resumption", RFC 5723,
              DOI 10.17487/RFC5723, January 2010,
              <https://www.rfc-editor.org/info/rfc5723>.

   [RFC5998]  Eronen, P., Tschofenig, H., and Y. Sheffer, "An Extension
              for EAP-Only Authentication in IKEv2", RFC 5998,
              DOI 10.17487/RFC5998, September 2010,
              <https://www.rfc-editor.org/info/rfc5998>.

   [RFC6407]  Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
              of Interpretation", RFC 6407, DOI 10.17487/RFC6407,
              October 2011, <https://www.rfc-editor.org/info/rfc6407>.

   [RFC6467]  Kivinen, T., "Secure Password Framework for Internet Key
              Exchange Version 2 (IKEv2)", RFC 6467,
              DOI 10.17487/RFC6467, December 2011,
              <https://www.rfc-editor.org/info/rfc6467>.

   [RFC7383]  Smyslov, V., "Internet Key Exchange Protocol Version 2
              (IKEv2) Message Fragmentation", RFC 7383,
              DOI 10.17487/RFC7383, November 2014,
              <https://www.rfc-editor.org/info/rfc7383>.

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

   [RFC8017]  Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
              "PKCS #1: RSA Cryptography Specifications Version 2.2",
              RFC 8017, DOI 10.17487/RFC8017, November 2016,
              <https://www.rfc-editor.org/info/rfc8017>.

   [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 GSK_w{Y} means
   that the default wrap key GSK_w (with zero KWK ID)is used to encrypt
   key Y, and the notation X{K_sa} means key X is used to encrypt the SA
   key K_sa (wich always has zero Key ID).  Note, that GSK_w{K_sa} means
   that the SA key is encrypted with the default wrap key, in which case
   both KWK ID and Key ID are zero.  For simplicity we will assume that

   The content of the KD payload will be shown as a sequence of Key
   Packets.  The Group Key Packet substructure will be denoted as
   GP(SAn)(), when n is an SPI for the SA, and the Member Key Packet
   substructure will be denoted as MP().  The content of the Key Packets
   is shown as SA_KEY and WRAP_KEY attributes with the notation
   described above.  For simplicity the type of the attribute will not
   be shown, because it is implicitly defined by the type of Key Packet.

   Here is the example of KD payload.

                  KD(GP1(X{K_sa}),MP(Y{X},Z{Y},GSK_w{Z})

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

   We will also use the notation X->Y->Z to describe the Key Path.  In
   this case key Y is needed to dectypt key X and key Z is needed to
   decrypt key Y.  In the example above the keys had the following
   relation: K_sa->X->Y->Z->GSK_w.

A.2.  Group Creation

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

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                                 SA1(K_sa1)
                    +------------------------------+
                    1                              2
            +---------------+              +---------------+
            3               4              5               6
        +-------+       +-------+      +--------+      +--------+
       A(7)    B(8)    C(9)   D(10)  E(11)    F(12)  G(13)    H(14)

                        Figure 28: Initial LKH tree

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

                KD(GP(SA1)(1{K_sa1}),MP(3{1},7{3},GSK_w{7})

                     KD Payload for the Group Member A

   From these attributes the GM A will construct the Key Path
   K_sa1->1->3->7->GSK_w and since it ends up with GSK_w, it will use
   all the WRAP_KEY attributes present in the path as its Working Key
   Path: 1->3->7.

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

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

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(GP(SA2)(GSK_w{K_sa2}))

                 KD Payload for the Simple Group SA Rekey

   All the GMs will be able to decrypt it and no changes in their
   Working Key Paths will happen.

A.4.  Group Member Exclusion

   If the GKCS has reason to believe that a GM should be excluded, then
   it can do so by sending a GSA_REKEY message that includes a set of

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   GM_KEY attributes which would allow all GMs except for the excluded
   one to get a new SA key.

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

                                 SA3(K_sa3)
                    +------------------------------+
                    1                             15
            +---------------+              +---------------+
            3               4             16               6
        +-------+       +-------+      +----           +--------+
       A(7)    B(8)    C(9)   D(10)  E(11)    F(12)  G(13)    H(14)

               Figure 29: LKH tree after F has been excluded

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

          KD(GP(SA3)(1{K_sa3},15{K_sa3}),MP(6{15},16{15},11{16})

                     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{K_sa3} by using the "1" key from their key path.  Since no new
      GM_KEY attributes are in the new Key Path, they won't update their
      Working Key Paths.

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

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

   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
      SA3 and thus it will be excluded from the group once the SA3 is
      used.

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   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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