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Network Working Group                                            B. Weis
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                                  Y. Nir
Expires: May 2, 2018                                            Dell EMC
                                                              V. Smyslov
                                                              ELVIS-PLUS
                                                        October 29, 2017


                    Group Key Management using IKEv2
                         draft-yeung-g-ikev2-12

Abstract

   This document presents a new group key distribution protocol.  The
   protocol is in conformance with MSEC key management architecture it
   contains two components: member registration and group rekeying, both
   downloading group security associations from the Group Controller/Key
   Server to a member of the group.  The new protocol is similar to
   IKEv2 in message and payload formats as well as message semantics.

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 http://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 May 2, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (http://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



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction and Overview . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Relationship to GDOI  . . . . . . . . . . . . . . . . . .   4
     1.3.  G-IKEv2 Payloads  . . . . . . . . . . . . . . . . . . . .   4
   2.  G-IKEv2 integration into IKEv2 protocol . . . . . . . . . . .   5
     2.1.  UDP port  . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  G-IKEv2 Protocol  . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  G-IKEv2 member registration and secure channel
           establishment . . . . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  GSA_AUTH exchange . . . . . . . . . . . . . . . . . .   6
       3.1.2.  GSA_REGISTRATION Exchange . . . . . . . . . . . . . .   7
       3.1.3.  IKEv2 Header Initialization . . . . . . . . . . . . .   8
       3.1.4.  GM Registration Operations  . . . . . . . . . . . . .   8
       3.1.5.  GCKS Registration Operations  . . . . . . . . . . . .   9
     3.2.  Counter-based modes of operation  . . . . . . . . . . . .  10
     3.3.  G-IKEv2 group maintenance channel . . . . . . . . . . . .  12
       3.3.1.  G-IKEv2 GSA_REKEY exchange  . . . . . . . . . . . . .  12
       3.3.2.  Forward and Backward Access Control . . . . . . . . .  14
       3.3.3.  Forward Access Control Requirements . . . . . . . . .  14
       3.3.4.  Deletion of SAs . . . . . . . . . . . . . . . . . . .  15
       3.3.5.  GSA_REKEY GCKS Operations . . . . . . . . . . . . . .  15
       3.3.6.  GSA_REKEY GM Operations . . . . . . . . . . . . . . .  16
   4.  Header and Payload Formats  . . . . . . . . . . . . . . . . .  17
     4.1.  The G-IKEv2 Header  . . . . . . . . . . . . . . . . . . .  17
     4.2.  Group Identification (IDg) Payload  . . . . . . . . . . .  17
     4.3.  Security Association - GM Supported Transforms (SAg)  . .  17
     4.4.  Group Security Association Payload  . . . . . . . . . . .  18
       4.4.1.  GSA Policy  . . . . . . . . . . . . . . . . . . . . .  18
     4.5.  KEK Policy  . . . . . . . . . . . . . . . . . . . . . . .  19
       4.5.1.  KEK Attributes  . . . . . . . . . . . . . . . . . . .  20
       4.5.2.  KEK_MANAGEMENT_ALGORITHM  . . . . . . . . . . . . . .  21
       4.5.3.  KEK_ENCR_ALGORITHM  . . . . . . . . . . . . . . . . .  21
       4.5.4.  KEK_KEY_LENGTH  . . . . . . . . . . . . . . . . . . .  22
       4.5.5.  KEK_KEY_LIFETIME  . . . . . . . . . . . . . . . . . .  22
       4.5.6.  KEK_INTEGRITY_ALGORITHM . . . . . . . . . . . . . . .  22
       4.5.7.  KEK_AUTH_METHOD . . . . . . . . . . . . . . . . . . .  22
       4.5.8.  KEK_AUTH_HASH . . . . . . . . . . . . . . . . . . . .  22
       4.5.9.  KEK_MESSAGE_ID  . . . . . . . . . . . . . . . . . . .  23
     4.6.  GSA TEK Policy  . . . . . . . . . . . . . . . . . . . . .  23
       4.6.1.  TEK ESP and AH Protocol-Specific Policy . . . . . . .  24
     4.7.  GSA Group Associated Policy . . . . . . . . . . . . . . .  25



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       4.7.1.  ACTIVATION_TIME_DELAY/DEACTIVATION_TIME_DELAY . . . .  26
     4.8.  Key Download Payload  . . . . . . . . . . . . . . . . . .  27
       4.8.1.  TEK Download Type . . . . . . . . . . . . . . . . . .  28
       4.8.2.  KEK Download Type . . . . . . . . . . . . . . . . . .  29
       4.8.3.  LKH Download Type . . . . . . . . . . . . . . . . . .  30
       4.8.4.  SID Download Type . . . . . . . . . . . . . . . . . .  33
     4.9.  Delete Payload  . . . . . . . . . . . . . . . . . . . . .  34
     4.10. Notify Payload  . . . . . . . . . . . . . . . . . . . . .  35
     4.11. Authentication Payload  . . . . . . . . . . . . . . . . .  36
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  36
     5.1.  GSA registration and secure channel . . . . . . . . . . .  36
     5.2.  GSA maintenance channel . . . . . . . . . . . . . . . . .  36
       5.2.1.  Authentication/Authorization  . . . . . . . . . . . .  36
       5.2.2.  Confidentiality . . . . . . . . . . . . . . . . . . .  36
       5.2.3.  Man-in-the-Middle Attack Protection . . . . . . . . .  36
       5.2.4.  Replay/Reflection Attack Protection . . . . . . . . .  36
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  37
     6.1.  New registries  . . . . . . . . . . . . . . . . . . . . .  37
     6.2.  New payload and exchange types added to the existing
           IKEv2 registry  . . . . . . . . . . . . . . . . . . . . .  37
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  38
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  38
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  38
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  39
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  39
   Appendix A.  Differences between G-IKEv2 and RFC 6407 . . . . . .  41
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  41

1.  Introduction and Overview

   This document presents a group key management protocol protected by
   IKEv2.  The data communications within the group are protected by a
   key pushed to the group members (GMs) by the Group Controller/Key
   Server (GCKS) using IKEv2 [RFC7296].  The GCKS pushes policy and keys
   for the group to the GM after authenticating it using new payloads
   included in a new exchange called GSA_AUTH (similar to the IKE_AUTH
   exchange).  This document references IKEv2 [RFC7296] but it intended
   to be a separate document.  GDOI update document [RFC6407] presented
   GDOI using IKEv1 syntax.  This document uses IKEv2 syntax.  The
   message semantics of IKEv2 are preserved, in that all communications
   consists of message request-response pairs.  The exception to this
   rule are the rekeying messages, which are sent in multicast without a
   response.  A number of payloads were deemed unnecessary since
   [RFC6407] are described in Appendix A







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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

1.2.  Relationship to GDOI

   GDOI protocol specified in [RFC6407] is protected by IKEv1 phase1
   security association defined in [RFC2407], [RFC2408] and [RFC2409];
   these documents are obsoleted and replaced by a new version of the
   IKE protocol defined in RFC 7296.  G-IKEv2 provides group key
   management between the Group Member and GCKS using the new IKEv2
   protocol and inherits the following key advantages over GDOI:

   1.  Provide a simple mechanism for the responder to keep minimal
       state and avoid DoS attack from forged IP address using cookie
       challenge exchange.

   2.  Improve performance and network latency by the reduced number of
       initial messages to complete the G-IKEv2 protocol from (10
       messages in Main mode and Quick mode, 7 messages in Aggressive
       mode and Quick) to 4 messages.

   3.  Fix cryptographic weakness with authentication HASH (IKEv1
       authentication HASH specified in RFC 2409 does not include all
       ISAKMP payloads and does not include ISAKMP header).  This issue
       is documented at [IKE-HASH].

   4.  Improve protocol reliability where all unicast messages are
       acknowledged and sequenced.

   5.  Well defined behavior for error conditions to improve
       interoperability.

1.3.  G-IKEv2 Payloads

   1.  IDg (group ID) - The GM requests the GCKS for membership into the
       group by sending its IDg payload.

   2.  GSA (Group Security Association) - The GCKS sends the group
       policy to the GM using this payload.

   3.  KD (Key Download) - The GCKS sends the control and data keys to
       the GM using the KD payload.





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2.  G-IKEv2 integration into IKEv2 protocol

   The G-IKEv2 protocol uses the security mechanisms of IKEv2 (peer
   authentication, confidentiality, message integrity) to protect the
   group negotiations required for G-IKEv2.  The G-IKEv2 exchange
   further provides group authorization, and secure policy and key
   download from the GCKS to its group members.

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

2.1.  UDP port

   G-IKEv2 SHOULD use 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 IKEv2 header
   distinguishes the G-IKEv2 protocol from GDOI protocol [RFC6407].

3.  G-IKEv2 Protocol

3.1.  G-IKEv2 member registration and secure channel establishment

   The registration protocol consists of a minimum of two message
   exchanges, IKE_SA_INIT and GSA_AUTH; member registration may have a
   few more messages exchanged if the EAP method, cookie challenge (for
   DoS protection) or negotiation of Diffie-Hellman group is included.
   Each exchange consists of request/response pairs.  The first exchange
   IKE_SA_INIT is defined in IKEv2 [RFC7296].  This exchange negotiates
   cryptographic algorithms, exchanges nonces and does a Diffie-Hellman
   exchange between the group member (GM) and the Group Controller/Key
   Server (GCKS).

   The second exchange GSA_AUTH authenticates the previous messages,
   exchanges identities and certificates.  These messages are encrypted
   and integrity protected with keys established through the IKE_SA_INIT
   exchange, so the identities are hidden from eavesdroppers and all
   fields in all the messages are authenticated.  The GCKS SHOULD
   authorize group members to be allowed into the group as part of the
   GSA_AUTH exchange.  Once the GCKS accepts a group member to join a
   group it will download the data security keys (TEKs) and/or group key
   encrypting key (KEK) or KEK array as part of the GSA_AUTH response
   message.  In the following descriptions, the payloads contained in
   the message are indicated by names as listed below.  Payloads defined
   as part of other IKEv2 extensions MAY also be included in these
   exchanges.






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        Notation      Payload
       ------------------------------------------------------------
        AUTH          Authentication
        CERT          Certificate
        CERTREQ       Certificate Request
        GSA           Group Security Association
        HDR           IKEv2 Header
        IDg           Identification - Group
        IDi           Identification - Initiator
        IDr           Identification - Responder
        KD            Key Download
        KE            Key Exchange
        Ni, Nr        Nonce
        SA            Security Association
        SAg           Security Association - GM Supported Transforms

   The details of the contents of each payload are described in
   Section 4.  Payloads that may optionally appear will be shown in
   brackets, such as [ CERTREQ ], to indicate that a certificate request
   payload can optionally be included.

3.1.1.  GSA_AUTH exchange

   After the group member and GCKS use the IKE_SA_INIT exchange to
   negotiate cryptographic algorithms, exchange nonces, and perform a
   Diffie-Hellman exchange as defined in IKEv2 [RFC7296], the GSA_AUTH
   exchange MUST complete before any other exchanges can be done.  The
   security properties of the GSA_AUTH exchange are the same as the
   properties of the IKE_AUTH exchange.  It is used to authenticate the
   IKE_SA_INIT messages, exchange identities and certificates.  G-IKEv2
   also uses this exchange for group member registration and
   authorization.  Even though the IKE_AUTH does contain the SA2, TSi,
   and TSr payload the GSA_AUTH does not.  They are not needed because
   policy is not negotiated between the group member and the GCKS, but
   instead downloaded from the GCKS to the group member.

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

   After the IKE_SA_INIT exchange completes, the group member initiates
   a GSA_AUTH request to join a group indicated by the IDg payload.  The
   GM MAY include an SAg payload declaring which Transforms that it is
   willing to accept, and also MAY include the Notify payload status
   type SENDER_ID_REQUEST to request SIDs for a Counter-based cipher
   from the GCKS.




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                 <-- HDR, SK { IDr, [CERT, ] AUTH, [ GSA, KD, ] [D, ]  }

   The GCKS responds with IDr, optional CERT, and AUTH material as if it
   were an IKE_AUTH.  It also informs the group member of the
   cryptographic policies of the group in the GSA payload and the key
   material in the KD payload.  The GCKS can also include a Delete (D)
   payload instructing the group member to delete existing SAs it might
   have as the result of a previous group member registration.

   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 4.10, the GSA_AUTH response will
   not include the GSA and KD, but will include a Notify payload
   indicating errors.  If the group member included an SAg payload, and
   the GCKS chooses to evaluate it, and it detects that that group
   member cannot support the security policy defined for the group, then
   the GCKS SHOULD return a NO_PROPOSAL_CHOSEN.  When the GCKS indicates
   errors, and the group member cannot resolve the errors, the group
   member MUST delete the registration IKE SA.

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

   If the group member finds the policy sent by the GCKS is
   unacceptable, the member SHOULD notify the GCKS by sending IDg and
   the Notify type NO_PROPOSAL_CHOSEN as shown below.

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

                               <--        HDR, SK {}

3.1.2.  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 by including the desired group ID (IDg) to
   request data security keys (TEKs) and/or group key encrypting keys
   (KEKs) from the GCKS.  If the group member includes an SAg payload,
   and the GCKS chooses to evaluate it, and it detects that group member
   cannot support the security policy defined for the group, then the
   GCKS SHOULD return a NO_PROPOSAL_CHOSEN.  The GM MAY also include the
   Notify payload status type SENDER_ID_REQUEST to request SIDs for a
   Counter-based cipher from the GCKS.  The GCKS response payloads are
   created and processed as in the GSA_AUTH reply.



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

                                   <--  HDR, SK { GSA, KD, [D ] }

   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 MUST unregister the group member.

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

                               <--        HDR, SK {}

3.1.3.  IKEv2 Header Initialization

   The Major Version is (2) and Minor Version is (0) according to IKEv2
   [RFC7296], and maintained in this document.  The G-IKEv2 IKE_SA_INIT,
   GSA_AUTH and GSA_REGISTRATION use the IKE SPI according to IKEv2
   [RFC7296], section 2.6.

3.1.4.  GM Registration Operations

   A G-IKEv2 Initiator (GM) requesting registration contacts the GCKS
   using the IKE_SA_INIT exchange and receives the response from the
   GCKS.  This exchange is unchanged from the IKE_SA_INIT in IKEv2
   protocol.

   Upon completion of parsing and verifying the IKE_SA_INIT response,
   the GM sends the GSA_AUTH message with the IKEv2 payloads from
   IKE_AUTH (without the SAi2, TSi and TSr payloads) along with the
   Group ID informing the GCKS of the group the initiator wishes to
   join.  The initiator MAY specify how many Sender-ID values it would
   like to receive in the Notify payload status type, SENDER_ID_REQUEST,
   in case the Data Security SA supports a counter mode cipher (see
   Section 3.2).

   An initiator may be limited in the types of Transforms that it is
   able or willing to use, and may find it useful to inform the GCKS
   which Transforms that it is willing to accept.  It can OPTIONALLY
   include an SAg payload, which can include ESP and/or AH Proposals.
   Each Proposal contains a list of Transforms that it is willing to
   support for that protocol.  A Proposal of type ESP can include ENCR,
   INTEG, and ESN Transforms.  A Proposal of type AH can include INTEG,
   and ESN Transforms.  The SPI length of each Proposal in an SAg MUST



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   be zero, and the SPI field is null.  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.

   Upon receiving the GSA_AUTH response, the initiator parses the
   response from the GCKS authenticating the exchange using the IKEv2
   method, then processes the GSA and KD.

   The GSA payload contains the security policy and cryptographic
   protocols used by the group.  This policy describes the Rekey SA
   (KEK), if present, Data-security SAs (TEK), and other group policy
   (GAP).  If the policy in the GSA payload is not acceptable to the GM,
   it SHOULD notify the GCKS with a NO_PROPOSAL_CHOSEN Notify payload
   (see Section 3.1.1 and Section 3.1.2).  Finally the KD is parsed
   providing the keying material for the TEK and/or KEK.  The GM
   interprets the KD key packets, where each key packet includes the
   keying material for SAs distributed in the GSA payload.  Keying
   material is matched by comparing the SPIs in the key packets to SPIs
   previously included in the GSA payloads.  Once TEK keys and policy
   are matched, the GM provides them to the data security subsystem, and
   it is ready to send or receive packets matching the TEK policy.

   The GSA KEK policy MUST include KEK attribute KEK_MESSAGE_ID with a
   Message ID.  The Message ID in the KEK_MESSAGE_ID attribute MUST be
   checked against any previously received Message ID for this group.
   If it is less than the previously received number, it should be
   considered stale and ignored.  This could happen if two GSA_AUTH
   exchanges happened in parallel, and the Message ID changed.  This
   KEK_MESSAGE_ID is used by the GM to prevent GSA_REKEY message replay
   attacks.  The first GSA_REKEY message that the GM receives from the
   GCKS must have a Message ID greater or equal to the Message ID
   received in the KEK_MESSAGE_ID attribute.

3.1.5.  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.





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   The GSA_AUTH response will include the group policy in the GSA
   payload and keys in the KD payload.  If the GCKS policy includes a
   group rekey option, this policy is constructed in the GSA KEK and the
   key is constructed in the KD KEK.  The GSA KEK MUST include the
   KEK_MESSAGE_ID attribute, specifying the starting Message ID the GCKS
   will use when sending the GSA_REKEY message to the group member.
   This Message ID is used to prevent GSA_REKEY message replay attacks
   and will be increased each time a GSA_REKEY message is sent to the
   group.  The GCKS data traffic policy is included in the GSA TEK and
   keys are included in the KD TEK.  The GSA GAP MAY also be included to
   provide the ATD and/or DTD (Section 4.7.1) specifying activation and
   deactivation delays for SAs generated from the TEKs.  If one or more
   Data Security SAs distributed in the GSA payload included a counter
   mode of operation, the GCKS includes at least one SID value in the KD
   payload, and possibly more depending on the request received in the
   Notify payload status type SENDER_ID_REQUEST requesting the number of
   SIDs from the group member.

   If the GCKS receives a GSA_REGISTRATION exchange with a request to
   register a GM to a group, the GCKS will need to authorize the GM with
   the new group (IDg) and respond with the corresponding group policy
   and keys.  If the GCKS fails to authorize the GM, it will respond
   with the AUTHORIZATION_FAILED notification.

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

   o  The GCKS could evaluate the list of Transforms and compare it to
      its current policy for the group.  If the group member did not
      include all of the ESP or AH Transforms in its current policy,
      then it could return a NO_PROPOSAL_CHOSEN Notification.

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

   o  The GCKS could store the list of Transforms and adjust the current
      group policy based on the capabilities of the devices as long as
      they fall within the acceptable security policy of the GCKS.

3.2.  Counter-based modes of operation

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



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   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.

   When at least one Data-Security SA included in the group policy
   includes a counter-based mode of operation, the GCKS automatically
   allocates and distributes one SID to each group member acting in the
   role of sender on the Data-Security SA.  The SID value is used
   exclusively by the group member to which it was allocated.  The group
   member uses the same SID for each Data-Security SA specifying the use
   of a counter-based mode of operation.  A GCKS MUST distribute unique
   keys for each Data-Security SA including a counter-based mode of
   operation in order to maintain unique key and nonce usage.

   During registration, the group member can choose to request one or
   more SID values.  Requesting a value of 1 is not necessary since the
   GCKS will automatically allocate exactly one to the group member.  A
   group member MUST request as many SIDs matching the number of
   encryption modules in which it will be installing the TEKs in the
   outbound direction.  Alternatively, a group member MAY request more
   than one SID and use them serially.  This could be useful when it is
   anticipated that the group member will exhaust their range of Data-
   Security SA nonces using a single SID too quickly (e.g., before the
   time-based policy in the TEK expires).

   When the group policy includes a counter-based mode of operation, a
   GCKS SHOULD use the following method to allocate SID values, which
   ensures that each SID will be allocated to just one group member.

   1.  A GCKS maintains an SID-counter, which records the SIDs that have
   been allocated.  SIDs are allocated sequentially, with zero as the
   first allocated SID.

   2.  Each time an SID is allocated, the current value of the counter
   is saved and allocated to the group member.  The SID-counter is then
   incremented in preparation for the next allocation.

   3.  When the GCKS specifies a counter-based mode of operation in the
   Data Security SA a group member may request a count of SIDs during
   registration in a Notify payload information of type SEND_ID_REQUEST.
   When the GCKS receives this request, it increments the SID-counter
   once for each requested SID, and distributes each SID value to the
   group member.



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   4.  A GCKS allocates new SID values for each GSA_REGISTRATION
   exchange originated by a sender, regardless of whether a group member
   had previously contacted the GCKS.  In this way, the GCKS is not
   required to maintaining a record of which SID values it had
   previously allocated to each group member.  More importantly, since
   the GCKS cannot reliably detect whether the group member had sent
   data on the current group Data-Security SAs it does not know what
   Data-Security counter-mode nonce values that a group member has used.
   By distributing new SID values, the key server ensures that each time
   a conforming group member installs a Data-Security SA it will use a
   unique set of counter-based mode nonces.

   5.  When the SID-counter maintained by the GCKS reaches its final SID
   value, no more SID values can be distributed.  Before distributing
   any new SID values, the GCKS MUST delete the Data-Security SAs for
   the group, followed by creation of new Data-Security SAs, and
   resetting the SID-counter to its initial value.

   6.  The GCKS SHOULD send a GSA_REKEY message deleting all Data-
   Security SAs and the Rekey SA for the group.  This will result in the
   group members initiating a new GSA_REGISTRATION exchange, in which
   they will receive both new SID values and new Data-Security SAs.  The
   new SID values can safely be used because they are only used with the
   new Data-Security SAs.  Note that deletion of the Rekey SA is
   necessary to ensure that group members receiving a GSA_REKEY exchange
   before the re-register do not inadvertently use their old SIDs with
   the new Data-Security SAs.  Using the method above, at no time can
   two group members use the same IV values with the same Data-Security
   SA key.

3.3.  G-IKEv2 group maintenance channel

   The GCKS indicates that it will be delivering group rekey messages
   when the KEK policy and keys are present in the G-IKEv2 GSA and KD
   payloads.  Though the G-IKEv2 Rekey is optional, it plays a crucial
   role for large and dynamic groups.  The GCKS is responsible for
   rekeying the secure group per the group policy.  The GCKS uses IP
   multicast to transport the rekey message.  The G-IKEv2 protocol uses
   the GSA_REKEY exchange type in the G-IKEv2 header identifying it as a
   rekey message.  This rekey message is protected by the registration
   exchanges.

3.3.1.  G-IKEv2 GSA_REKEY exchange

   The GCKS initiates the G-IKEv2 Rekey securely using IP multicast.
   Since this multicast rekey does not require a response and it sends
   to multiple GMs, G-IKEv2 rekeying MUST NOT support windowing.  The
   GCKS rekey message replaces the rekey GSA KEK or KEK array, and/or



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   creates a new Data-Security GSA TEK.  The SID Download attribute in
   the Key Download payload (defined in Section 4.8.4) MUST NOT be part
   of the Rekey Exchange as this is sender specific information and the
   Rekey Exchange is group specific.  The GCKS initiates the GSA_REKEY
   exchange as following:

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

   HDR is defined in Section 4.1.  The Message ID in this message will
   start with the same value the GCKS sent to the group members in the
   KEK attribute KEK_MESSAGE_ID during registration; this Message ID
   will be increased each time a new GSA_REKEY message is sent to the
   group members.

   The GSA payload contains the current rekey and data security SAs.
   The GSA may contain a new rekey SA and/or a new data security SA,
   which, optionally contains an LKH rekey SA, Section 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.

   The AUTH payload is included to authenticate the GSA_REKEY message
   using a method defined in the IKEv2 Authentication Method IANA
   registry [IKEV2-IANA].  The method SHOULD be a digital signature
   authentication scheme to ensure that the message was originated from
   an authorized GCKS.  A Shared Key Integrity Code SHOULD NOT be used
   as it doesn't provide source origin authentication (although a small
   group may not require source origin authentication).  During group
   member registration, the GCKS sends the authentication key in the GSA
   KEK payload, KEK_AUTH_KEY attribute, which the group member uses to
   authenticate the key server.  Before the current Authentication Key
   expires, the GCKS will send a new KEK_AUTH_KEY to the group members
   in a GSA_REKEY message.  The AUTH key that is used in the rekey
   message may not be the same as the authentication key used in
   GSA_AUTH.  Typically a rekey message is sent as multicast and
   received by all group members, therefore the same AUTH key is
   distributed to all group members.






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   After adding the AUTH payload to the rekey message, the current KEK
   encryption key is used to encrypt all of the payloads following the
   HDR.

3.3.2.  Forward and Backward Access Control

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

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

   Support for group management algorithms are supported via the
   KEY_MANAGEMENT_ALGORITHM attribute which is sent in the GSA KEK
   policy.  G-IKEv2 specifies one method by which LKH can be used for
   forward and backward access control.  Other methods of using LKH, as
   well as other group management algorithms such as OFT or Subset
   Difference may be added to G-IKEv2 as part of a later document.

3.3.3.  Forward Access Control Requirements

   When group membership is altered using a group management algorithm
   new GSA TEKs (and their associated keys) are usually also needed.
   New GSAs and keys ensure that members who were denied access can no
   longer participate in the group.

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

   If forward access control policy for the group includes keeping group
   policy changes from members that are denied access to the group, then
   two sequential G-IKEv2 rekey messages changing the group KEK MUST be
   sent by the GCKS.  The first G-IKEv2 rekey message creates a new KEK
   for the group.  Group members, which are denied access, will not be



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   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.

3.3.4.  Deletion of SAs

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

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

   The GSA MAY specify the remaining active time of the remaining policy
   by using the DTD attribute in the GSA GAP.  If a GCKS has no further
   SAs to send to group members, the GSA and KD payloads MUST be omitted
   from the message.  There may be circumstances where the GCKS may want
   to start over with a clean slate.  If the administrator is no longer
   confident in the integrity of the group, the GCKS can signal deletion
   of all the policies of a particular TEK protocol by sending a TEK
   with a SPI value equal to zero in the delete payload.  For example,
   if the GCKS wishes to remove all the KEKs and all the TEKs in the
   group, the GCKS SHOULD send a Delete payload with a SPI of zero and a
   protocol_id of a TEK protocol_id value defined in Section 4.6,
   followed by another Delete payload with a SPI of zero and protocol_id
   of zero, indicating that the KEK SA should be deleted.

3.3.5.  GSA_REKEY GCKS Operations

   The GCKS may initiate a rekey message if group membership and/or
   policy has changed, or if the keys are about to expire.  The GCKS
   builds the rekey message with a Message ID value that is one greater
   than the value included in the previous rekey.  If the message is
   using a new KEK attribute, the Message ID is reset to 1 in this
   message.  The GSA and KD follow with the same characteristics as in



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   the GSA Registration exchange.  The AUTH payload is the final payload
   added to the message.  It is created by hashing the string "G-IKEv2"
   and the message created so far, and then is digitally signed.
   Finally, the content of the Encrypted payload is encrypted and
   authenticated using the current KEK keys.

   Because GSA_REKEY messages are not acknowledged and could be
   discarded by the network, one or more GMs may not receive the
   message.  To mitigate such lost messages, during a rekey event the
   GCKS SHOULD transmit several GSA_REKEY messages with the new policy.
   A GCKS MUST NOT re-transmit exactly the same GSA_REKEY message,
   because time-to-live lifetimes in the message will be incorrect,
   resulting in GMs with unsynchronized TEK and KEK lifetimes.

3.3.6.  GSA_REKEY GM Operations

   When a group member receives the Rekey Message from the GCKS it
   decrypts the message using the current KEK, validates the signature
   using the public key retrieved in a previous G-IKEv2 exchange,
   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
   GSA.  The parsing of the payloads is identical to the parsing done in
   the registration exchange.

   Replay protection is achieved by a group member rejecting a GSA_REKEY
   message which has a Message ID smaller than the current Message ID
   that the GM is expecting.  The GM expects the Message ID in the first
   GSA_REKEY message it receives to be equal or greater than the message
   id it receives in the KEK_MESSAGE_ID attribute.  The GM expects the
   message ID in subsequent GSA_REKEY messages to be greater than the
   last valid GSA_REKEY message ID it received.

   If the GSA payload includes a Data-Security SA including a counter-
   modes of operation and the receiving group member is a sender for
   that SA, the group member uses its current SID value with the Data-
   Security SAs to create counter-mode nonces.  If it is a sender and
   does not hold a current SID value, it MUST NOT install the Data-
   Security SAs.  It MAY initiate a GSA_REGISTRATION exchange to the
   GCKS in order to obtain an SID value (along with current group
   policy).

   If the GM receives a notification that a Data-Security SA is about to
   expire (such as a "soft lifetime" expiration as described in
   Section 4.4.2.1 of [RFC4301]), it SHOULD initiate a registration to
   the GCKS.  This registration serves as a request for current SAs, and
   will result in the download of replacement SAs, assuming the GCKS
   policy has created them.




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4.  Header and Payload Formats

   Refer to IKEv2 [RFC7296] for existing payloads.  Some payloads used
   in G-IKEv2 exchanges are not aligned to 4-octet boundaries, which is
   also the case for some IKEv2 payloads (see Section 3.2 of [RFC7296]).

4.1.  The G-IKEv2 Header

   G-IKEv2 uses the same IKE header format as specified in RFC 7296
   section 3.1.

   Several new payload formats are required in the group security
   exchanges.

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

   New exchange types GSA_AUTH, GSA_REGISTRATION and GSA_REKEY are added
   to the IKEv2 [RFC7296] protocol.

              Exchange Type           Value
              --------------          -----
              GSA_AUTH                 39
              GSA_REGISTRATION         40
              GSA_REKEY                41

   Major Version is 2 and Minor Version is 0 as in IKEv2 [RFC7296].  IKE
   SA Initiator's SPI, IKE SA Responder's SPI, Flags, Message ID, and
   Length are as specified in [RFC7296].

4.2.  Group Identification (IDg) Payload

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

4.3.  Security Association - GM Supported Transforms (SAg)

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



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4.4.  Group Security Association Payload

   The Group Security Association payload is used by the GCKS to assert
   security attributes for both Rekey and Data-security SAs.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Next Payload  |C|   RESERVED  |         Payload Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Security Association Payload fields are defined as follows:

   o  Next Payload (1 octet) -- Identifies the next payload type for the
      G-IKEv2 registration or the G-IKEv2 rekey message.

   o  Critical (1 bit) -- Set according to [RFC7296].

   o  RESERVED (7 bits) -- Must be zero.

   o  Payload Length (2 octets) -- Is the octet length of the current
      payload including the generic header and all TEK and KEK policies.

4.4.1.  GSA Policy

   Following the GSA generic payload header are GSA policies for group
   rekeying (KEK), data traffic SAs (TEK) and/or Group Associated Policy
   (GAP).  There may be zero or one GSA KEK policy, zero or one GAP
   policies, and zero or more GSA TEK policies, where either one GSA KEK
   or GSA TEK payload MUST be present.

   This latitude allows various group policies to be accommodated.  For
   example if the group policy does not require the use of a Rekey SA,
   the GCKS would not need to send a GSA KEK attribute to the group
   member since all SA updates would be performed using the Registration
   SA.  Alternatively, group policy might use a Rekey SA but choose to
   download a KEK to the group member only as part of the Registration
   SA.  Therefore, the GSA KEK policy would not be necessary as part of
   the GSA_REKEY message.

   Specifying multiple GSA TEKs allows multiple related data streams
   (e.g., video, audio, and text) to be associated with a session, but
   each protected with an individual security association policy.

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

   Policies following the GSA payload use the following common header.



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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Type       |   RESERVED    |                 Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type is defined as follows:

                          ID Class        Value
                          --------        -----
                          RESERVED          0
                          KEK               1
                          GAP               2
                          TEK               3
                          Expert Review    4-127
                          Private Use    128-255

4.5.  KEK Policy

   The GSA KEK policy contains security attributes for the KEK method
   for a group and parameters specific to the G-IKEv2 registration
   operation.  The source and destination traffic selectors describe the
   network identities used for the rekey messages.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Type = 1   !   RESERVED    !                 Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                              SPI                              ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                 <Source Traffic Selector>                     ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~               <Destination Traffic Selector>                  ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        KEK Attributes                         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The GSA KEK Payload fields are defined as follows:





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   o  Type = 1 (1 octet) -- Identifies the GSA payload type as KEK in
      the G-IKEv2 registration or the G-IKEv2 rekey message.

   o  RESERVED (1 octet) -- Must be zero.

   o  Length (2 octets) -- Length of this structure including KEK
      attributes.

   o  SPI (16 octets) -- Security Parameter Index for the rekey message.
      The SPI must be the IKEv2 Header SPI pair where the first 8 octets
      become the "Initiator's SPI" field in the G-IKEv2 rekey message
      IKEv2 HDR, and the second 8 octets become the "Responder's SPI" in
      the same HDR.  As described above, these SPIs are assigned by the
      GCKS.

   o  Source & Destination Traffic Selectors - Substructures describing
      the source and destination of the network identities.  These
      identities refer to the source and destination of the next KEK
      rekey SA.  Defined format and values are specified by IKEv2
      [RFC7296], section 3.13.1.

   o  KEK Attributes -- Contains KEK policy attributes associated with
      the group.  The following sections describe the possible
      attributes.  Any or all attributes may be optional, depending on
      the group policy.

4.5.1.  KEK Attributes

   The following attributes may be present in a GSA KEK policy.  The
   attributes must follow the format defined in the IKEv2 [RFC7296]
   section 3.3.5.  In the table, attributes that are defined as TV are
   marked as Basic (B); attributes that are defined as TLV are marked as
   Variable (V).  The terms Reserved, Unassigned, and Private Use are to
   be applied as defined in [RFC8126].  The registration procedure is
   Expert Review.
















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                 ID Class                   Value    Type
                 --------                   -----    ----
                 Reserved                     0
                 KEK_MANAGEMENT_ALGORITHM     1        B
                 KEK_ENCR_ALGORITHM           2        B
                 KEK_KEY_LENGTH               3        B
                 KEK_KEY_LIFETIME             4        V
                 KEK_INTEGRITY_ALGORITHM      5        B
                 KEK_AUTH_METHOD              6        B
                 KEK_AUTH_HASH                7        B
                 KEK_MESSAGE_ID               8        V
                 Unassigned                  9-16383
                 Private Use             16384-32767

   The following attributes may only be included in a G-IKEv2
   registration message: KEK_MANAGEMENT_ALGORITHM.

   Minimum attributes that must be sent as part of an GSA KEK:
   KEK_ENCR_ALGORITHM, KEK_KEY_LENGTH (if the cipher definition includes
   a variable length key), KEK_MESSAGE_ID, KEK_KEY_LIFETIME,
   KEK_INTEGRITY_ALGORITHM, KEK_AUTH_METHOD, and KEK_AUTH_HASH (except
   for DSA based algorithms).

4.5.2.  KEK_MANAGEMENT_ALGORITHM

   The KEK_MANAGEMENT_ALGORITHM attribute specifies the group KEK
   management algorithm used to provide forward or backward access
   control (i.e., used to exclude group members).  Defined values are
   specified in the following table.  The terms Reserved, Unassigned,
   and Private Use are to be applied as defined in [RFC8126].  The
   registration procedure is Expert Review.

                  KEK Management Type               Value
                  -------------------               -----
                  Reserved                            0
                  LKH                                 1
                  Unassigned                         2-16383
                  Private Use                    16384-32767

4.5.3.  KEK_ENCR_ALGORITHM

   The KEK_ENCR_ALGORITHM attribute specifies the encryption algorithm
   used with the KEK.  This value is a value from the IKEv2 Transform
   Type 1 - Encryption Algorithm Transform IDs registry[IKEV2-IANA].  If
   a KEK_MANAGEMENT_ALGORITHM is defined which defines multiple keys
   (e.g., LKH), and if the management algorithm does not specify the
   algorithm for those keys, then the algorithm defined by the




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   KEK_ENCR_ALGORITHM attribute MUST be used for all keys which are
   included as part of this KEK management.

4.5.4.  KEK_KEY_LENGTH

   The KEK_KEY_LENGTH attribute specifies the KEK Algorithm key length
   (in bits).

   The Group Controller/Key Server (GCKS) adds the KEK_KEY_LENGTH
   attribute to the GSA payload when distributing KEK policy to group
   members.  The group member verifies whether or not it has the
   capability of using a cipher key of that size.  If the cipher
   definition includes a fixed key length, the group member can make its
   decision solely using the KEK_ENCR_ALGORITHM attribute and does not
   need the KEK_KEY_LENGTH attribute.  Sending the KEK_KEY_LENGTH
   attribute in the GSA payload is OPTIONAL if the KEK cipher has a
   fixed key length.

4.5.5.  KEK_KEY_LIFETIME

   The KEK_KEY_LIFETIME attribute specifies the maximum time for which
   the KEK is valid.  The GCKS may refresh the KEK at any time before
   the end of the valid period.  The value is a four (4) octet number
   defining a valid time period in seconds.

4.5.6.  KEK_INTEGRITY_ALGORITHM

   The KEK_INTEGRITY attribute specifies the integrity algorithm used to
   protect the rekey message.  This integrity algorithm is a value from
   the IKEv2 Transform Type 3 - Integrity Algorithm Transform IDs
   registry [IKEV2-IANA].

4.5.7.  KEK_AUTH_METHOD

   The KEK_AUTH_METHOD attribute specifies the method of authentication
   used.  This value is from the IKEv2 Authentication Method registry
   [IKEV2-IANA].

4.5.8.  KEK_AUTH_HASH

   The KEK_AUTH_HASH attribute specifies the hash algorithm used to
   generate the AUTH key to authenticate GSA_REKEY messages.  Hash
   algorithms are defined in IANA registry IKEv2 Hash Algorithms
   [IKEV2-IANA].  This attribute can be used by a group member to
   determine in advance if it supports the algorithm used in the rekey
   message.





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4.5.9.  KEK_MESSAGE_ID

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

4.6.  GSA TEK Policy

   The GSA TEK policy contains security attributes for a single TEK
   associated with a group.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Type = 3   |   RESERVED    |                 Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Protocol-ID   |       TEK Protocol-Specific Payload           |
      +-+-+-+-+-+-+-+-+                                               ~
      ~                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The GSA TEK Payload fields are defined as follows:

   o  Type = 3 (1 octet) -- Identifies the GSA payload type as TEK in
      the G-IKEv2 registration or the G-IKEv2 rekey message.

   o  RESERVED (1 octet) -- Must be zero.

   o  Length (2 octets) -- Length of this structure, including the TEK
      Protocol-Specific Payload.

   o  Protocol-ID (1 octet) -- Value specifying the Security Protocol.
      The following table defines values for the Security Protocol.
      Support for the GSA_PROTO_IPSEC_AH GSA TEK is OPTIONAL.  The terms
      Reserved, Unassigned, and Private Use are to be applied as defined
      in [RFC8126].  The registration procedure is Expert Review.

             Protocol ID                       Value
             -----------                       -----
             Reserved                            0
             GSA_PROTO_IPSEC_ESP                 1
             GSA_PROTO_IPSEC_AH                  2
             Unassigned                         3-127
             Private Use                      128-255

   o  TEK Protocol-Specific Payload (variable) -- Payload which
      describes the attributes specific for the Protocol-ID.




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4.6.1.  TEK ESP and AH Protocol-Specific Policy

   The TEK Protocol-Specific policy contains two traffic selectors one
   for the source and one for the destination of the protected traffic,
   SPI, Transforms, and Attributes.

   The TEK Protocol-Specific policy for ESP and AH is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             SPI                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                 <Source Traffic Selector>                     ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~               <Destination Traffic Selector>                  ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~               <Transform Substructure List>                   ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        TEK Attributes                         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The GSA TEK Policy fields are defined as follows:

   o  SPI (4 octets) -- Security Parameter Index.

   o  Source & Destination Traffic Selectors - The traffic selectors
      describe the source and the destination of the protected traffic.
      The format and values are defined in IKEv2 [RFC7296], section
      3.13.1.

   o  Transform Substructure List -- A list of Transform Substructures
      specifies the transform information.  The format and values are
      defined in IKEv2 [RFC7296], section 3.3.2.  Valid Transform Types
      for ESP are ENCR, INTEG, and ESN.  Valid Transform Types for AH
      are INTEG and ESN.  As described in the IKEv2 registries
      [IKEV2-IANA].  The Last Substruc value in each Transform
      Substructure will be set to 3 except for the last one in the list,
      which is set to 0.

   o  TEK Attributes -- Contains the TEK policy attributes associated
      with the group, in the format defined in Section 3.3.5 of



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      [RFC7296].  All attributes are optional, depending on the group
      policy.

   Attribute Types are as follows.  The terms Reserved, Unassigned, and
   Private Use are to be applied as defined in [RFC8126].  The
   registration procedure is Expert Review.

                 ID Class                   Value    Type
                 --------                   -----    ----
                 Reserved                     0
                 TEK_KEY_LIFETIME             1        V
                 TEK_MODE                     2        B
                 Unassigned                   3-16383
                 Private Use             16384-32767

   It is NOT RECOMMENDED that the GCKS distribute both ESP and AH
   Protocol-Specific Policies for the same set of Traffic Selectors.

4.6.1.1.  TEK_KEY_LIFETIME

   The TEK_KEY_LIFETIME attribute specifies the maximum time for which
   the TEK is valid.  When the TEK expires, the AH or ESP security
   association and all keys downloaded under the security association
   are discarded.  The GCKS may refresh the TEK at any time before the
   end of the valid period.

   The value is a four (4) octet number defining a valid time period in
   seconds.  If unspecified the default value of 28800 seconds (8 hours)
   shall be assumed.

4.6.1.2.  TEK_MODE

   The value of 0 is used for tunnel mode and 1 for transport mode.  In
   the absence of this attribute tunnel mode will be used.

4.7.  GSA Group Associated Policy

   Group specific policy that does not belong to rekey policy (GSA KEK)
   or traffic encryption policy (GSA TEK) can be distributed to all
   group member using GSA GAP (Group Associated Policy).

   The GSA GAP payload is defined as follows:









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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Type = 2   !   RESERVED    !                 Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~               Group Associated Policy Attributes              ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The GSA GAP payload fields are defined as follows:

   o  Type = 2 (1 octet) -- Identifies the GSA payload type as GAP in
      the G-IKEv2 registration or the G-IKEv2 rekey message.

   o  RESERVED (1 octet) -- Must be zero.

   o  Length (2 octets) -- Length of this structure, including the GSA
      GAP header and Attributes.

   o  Group Associated Policy Attributes (variable) -- Contains
      attributes following the format defined in Section 3.3.5 of
      [RFC7296].

   Attribute Types are as follows.  The terms Reserved, Unassigned, and
   Private Use are to be applied as defined in [RFC8126].  The
   registration procedure is Expert Review.

                 Attribute Type         Value       Type
                 --------------         -----       ----
                 Reserved                 0
                 ACTIVATION_TIME_DELAY    1          B
                 DEACTIVATION_TIME_DELAY  2          B
                 Unassigned              3-16383
                 Private Use         16384-32767

4.7.1.  ACTIVATION_TIME_DELAY/DEACTIVATION_TIME_DELAY

   Section 4.2.1 of RFC 5374 specifies a key rollover method that
   requires two values be provided to group members.  The
   ACTIVATION_TIME_DELAY attribute allows a GCKS to set the Activation
   Time Delay (ATD) for SAs generated from TEKs.  The ATD defines how
   long after receiving new SAs that they are to be activated by the GM.
   The ATD value is in seconds.

   The DEACTIVATION_TIME_DELAY allows the GCKS to set the Deactivation
   Time Delay (DTD) for previously distributed SAs.  The DTD defines how
   long after receiving new SAs it should deactivate SAs that are
   destroyed by the rekey event.  The value is in seconds.




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   The values of ATD and DTD are independent.  However, the DTD value
   should be larger, which allows new SAs to be activated before older
   SAs are deactivated.  Such a policy ensures that protected group
   traffic will always flow without interruption.

4.8.  Key Download Payload

   The Key Download Payload contains the group keys for the group
   specified in the GSA Payload.  These key download payloads can have
   several security attributes applied to them based upon the security
   policy of the group as defined by the associated GSA Payload.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Next Payload  |C|  RESERVED   |                 Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Number of Key Packets         |            RESERVED2          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
      ~                    Key Packets                                ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Key Download Payload fields are defined as follows:

   o  Next Payload (1 octet) -- Identifier for the payload type of the
      next payload in the message.  If the current payload is the last
      in the message, then this field will be zero.

   o  Critical (1 bit) -- Set according to [RFC7296].

   o  RESERVED (7 bits) -- Unused, set to zero.

   o  Payload Length (2 octets) -- Length in octets of the current
      payload, including the generic payload header.

   o  Number of Key Packets (2 octets) -- Contains the total number of
      Key Packets passed in this data block.

   o  Key Packets (variable) -- Contains Key Packets.  Several types of
      key packets are defined.  Each Key Packet has the following
      format.










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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   KD Type     |   RESERVED    |            KD Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    SPI Size   |                   SPI (variable)              ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                    Key Packet Attributes                      ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Key Download (KD) Type (1 octet) -- Identifier for the Key Data
      field of this Key Packet.  In the following table the terms
      Reserved, Unassigned, and Private Use are to be applied as defined
      in [RFC8126].  The registration procedure is Expert Review.

                          Key Download Type        Value
                          -----------------        -----
                          Reserved                   0
                          TEK                        1
                          KEK                        2
                          LKH                        3
                          SID                        4
                          Unassigned                5-127
                          Private Use             128-255

   o  RESERVED (1 octet) -- Unused, set to zero.

   o  Key Download Length (2 octets) -- Length in octets of the Key
      Packet data, including the Key Packet header.

   o  SPI Size (1 octet) -- Value specifying the length in octets of the
      SPI as defined by the Protocol-Id.

   o  SPI (variable length) -- Security Parameter Index which matches a
      SPI previously sent in an GSA KEK or GSA TEK Payload.

   o  Key Packet Attributes (variable length) -- Contains Key
      information.  The format of this field is specific to the value of
      the KD Type field.  The following sections describe the format of
      each KD Type.

4.8.1.  TEK Download Type

   The following attributes may be present in a TEK Download Type.
   Exactly one attribute matching each type sent in the GSA TEK payload
   MUST be present.  The attributes must follow the format defined in
   IKEv2 (Section 3.3.5 of [RFC7296]).  In the table, attributes defined
   as TV are marked as Basic (B); attributes defined as TLV are marked



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   as Variable (V).  The terms Reserved, Unassigned, and Private Use are
   to be applied as defined in [RFC8126].  The registration procedure is
   Expert Review.

                 TEK Class                 Value      Type
                 ---------                 -----      ----
                 Reserved                     0
                 TEK_ALGORITHM_KEY            1        V
                 TEK_INTEGRITY_KEY            2        V
                 Unassigned                  3-16383
                 Private Use             16384-32767

   It is possible that the GCKS will send no TEK key packets in a
   Registration KD payload (as well as no corresponding GSA TEK payloads
   in the GSA payload), after which the TEK payloads will be sent in a
   rekey message.  At least one TEK MUST be included in each Rekey KD
   payload.

4.8.1.1.  TEK_ALGORITHM_KEY

   The TEK_ALGORITHM_KEY class contains encryption keying material for
   the corresponding SPI.  This keying material will be used with the
   encryption algorithm specified in the GSA TEK payload, and according
   to the IPsec transform describing that encryption algorithm.  The
   keying material is treated equivalent to IKEv2 KEYMAT derived for
   that IPsec transform.  If the encryption algorithm requires a nonce
   (e.g., AES-GCM), the nonce is chosen as shown in Section 3.2.

4.8.1.2.  TEK_INTEGRITY_KEY

   The TEK_INTEGRITY_KEY class declares that the integrity key for the
   corresponding SPI is contained in the Key Packet Attribute.  Readers
   should refer to [IKEV2-IANA] for the latest values.

4.8.2.  KEK Download Type

   The following attributes may be present in a KEK Download Type.
   Exactly one attribute matching each type sent in the GSA KEK payload
   MUST be present.  The attributes must follow the format defined in
   IKEv2 (Section 3.3.5 of [RFC7296]).  In the table, attributes defined
   as TV are marked as Basic (B); attributes defined as TLV are marked
   as Variable (V).  The terms Reserved, Unassigned, and Private Use are
   to be applied as defined in [RFC8126].  The registration procedure is
   Expert Review.







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                 KEK Class                 Value      Type
                 ---------                 -----      ----
                 Reserved                     0
                 KEK_ENCR_KEY                 1        V
                 KEK_INTEGRITY_KEY            2        V
                 KEK_AUTH_KEY                 3        V
                 Unassigned                  4-16383
                 Private Use             16384-32767

   If the KEK Key Packet is included, there MUST be only one present in
   the KD payload.

4.8.2.1.  KEK_ENCR_KEY

   The KEK_ENCR_KEY class declares that the encryption key for the
   corresponding SPI is contained in the Key Packet Attribute.  The
   encryption algorithm that will use this key was specified in the GSA
   KEK payload.

   If the mode of operation for the algorithm requires an Initialization
   Vector (IV), an explicit IV MUST be included in the KEK_ENCR_KEY
   before the actual key.

4.8.2.2.  KEK_INTEGRITY_KEY

   The KEK_INTEGRITY_KEY class declares the integrity key for this SPI
   is contained in the Key Packet Attribute.  The integrity algorithm
   that will use this key was specified in the GSA KEK payload.

4.8.2.3.  KEK_AUTH_KEY

   The KEK_AUTH_KEY class declares that the authentication key for this
   SPI is contained in the Key Packet Attribute.  The signature
   algorithm that will use this key was specified in the GSA KEK
   payload.  An RSA public key format is defined in RFC 3447,
   Section A.1.1.  DSS public key format is defined in RFC 3279
   Section 2.3.2.  For ECDSA Public keys, use format described in RFC
   5480 Section 2.2.

4.8.3.  LKH Download Type

   The LKH key packet is comprised of attributes representing different
   leaves in the LKH key tree.

   The following attributes are used to pass an LKH KEK array in the KD
   payload.  The attributes must follow the format defined in IKEv2
   (Section 3.3.5 of [RFC7296]).  In the table, attributes defined as TV
   are marked as Basic (B); attributes defined as TLV are marked as



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   Variable (V).  The terms Reserved, Unassigned, and Private Use are to
   be applied as defined in [RFC8126].  The registration procedure is
   Expert Review.

                 LKH Download Class        Value      Type
                 ------------------        -----      ----
                 Reserved                     0
                 LKH_DOWNLOAD_ARRAY           1        V
                 LKH_UPDATE_ARRAY             2        V
                 Unassigned                  3-16383
                 Private Use             16384-32767

   If an LKH key packet is included in the KD payload, there MUST be
   only one present.

4.8.3.1.  LKH_DOWNLOAD_ARRAY

   The LKH_DOWNLOAD_ARRAY class is used to download a set of LKH keys to
   a group member.  It MUST NOT be included in a IKEv2 rekey message KD
   payload if the IKEv2 rekey is sent to more than one group member.  If
   an LKH_DOWNLOAD_ARRAY attribute is included in a KD payload, there
   MUST be only one present.

   This attribute consists of a header block, followed by one or more
   LKH keys.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         # of LKH Keys        |             RESERVED           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                             LKH Keys                          ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The KEK_LKH attribute fields are defined as follows:

   o  Number of LKH Keys (2 octets) -- This value is the number of
      distinct LKH keys in this sequence.

   o  RESERVED (1 octet) -- Unused, set to zero.

   Each LKH Key is defined as follows:









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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !             LKH ID            |             Encr Alg          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Key Handle                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                            Key Data                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  LKH ID (2 octets) -- This is the position of this key in the
      binary tree structure used by LKH.

   o  Encr Alg (2 octets) -- This is the encryption algorithm for which
      this key data is to be used.  This value is specified in
      Section 4.5.3.

   o  RESERVED (1 octet) -- Unused, set to zero.

   o  Key Handle (4 octets) -- This is a randomly generated value to
      uniquely identify a key within an LKH ID.

   o  Key Data (variable length) -- This is the actual encryption key
      data, which is dependent on the Encr Alg algorithm for its format.
      If the mode of operation for the algorithm requires an
      Initialization Vector (IV), an explicit IV MUST be included in the
      Key Data field before the actual key.

   The first LKH Key structure in an LKH_DOWNLOAD_ARRAY attribute
   contains the Leaf identifier and key for the group member.  The rest
   of the LKH Key structures contain keys along the path of the key tree
   in the order starting from the leaf, culminating in the group KEK.

4.8.3.2.  LKH_UPDATE_ARRAY

   The LKH_UPDATE_ARRAY class is used to update the LKH keys for a
   group.  It is most likely to be included in a G-IKEv2 rekey message
   KD payload to rekey the entire group.  This attribute consists of a
   header block, followed by one or more LKH keys, as defined in
   Section 4.8.3.1.

   There may be any number of LKH_UPDATE_ARRAY attributes included in a
   KD payload.








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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          # of LKH Keys        |             LKH ID            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Key Handle                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                            LKH Keys                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Number of LKH Keys (2 octets) -- This value is the number of
      distinct LKH keys in this sequence.

   o  LKH ID (2 octets) -- This is the node identifier associated with
      the key used to encrypt the first LKH Key.

   o  Key Handle (4 octets) -- This is the value that uniquely
      identifies the key within the LKH ID which was used to encrypt the
      first LKH key.

   The LKH Keys are as defined in Section 4.8.3.1.  The LKH Key
   structures contain keys along the path of the key tree in the order
   from the LKH ID found in the LKH_UPDATE_ARRAY header, culminating in
   the group KEK.  The Key Data field of each LKH Key is encrypted with
   the LKH key preceding it in the LKH_UPDATE_ARRAY attribute.  The
   first LKH Key is encrypted under the key defined by the LKH ID and
   Key Handle found in the LKH_UPDATE_ARRAY header.

4.8.4.  SID Download Type

   The SID attribute is used to download one or more Sender-ID (SID)
   values for the exclusive use of a group member.  The terms Reserved,
   Unassigned, and Private Use are to be applied as defined in
   [RFC8126].  The registration procedure is Expert Review.

                 SID Download Class        Value      Type
                 ------------------        -----      ----
                 Reserved                     0
                 NUMBER_OF_SID_BITS           1        B
                 SID_VALUE                    2        V
                 Unassigned                  3-16383
                 Private Use             16384-32767

   Because a SID value is intended for a single group member, the SID
   Download type MUST NOT be distributed in a GSA_REKEY message
   distributed to multiple group members.





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4.8.4.1.  NUMBER_OF_SID_BITS

   The NUMBER_OF_SID_BITS class declares how many bits of the cipher
   nonce in which to represent an SID value.  This value is applied to
   each SID value distributed in the SID Download.

4.8.4.2.  SID_VALUE

   The SID_VALUE class declares a single SID value for the exclusive use
   of this group member.  Multiple SID_VALUE attributes MAY be included
   in a SID Download.

4.8.4.3.  GM Semantics

   The SID_VALUE attribute value distributed to the group member MUST be
   used by that group member as the SID field portion of the IV for all
   Data-Security SAs including a counter-based mode of operation
   distributed by the GCKS as a part of this group.  When the Sender-
   Specific IV (SSIV) field for any Data-Security SA is exhausted, the
   group member MUST NOT act as a sender on that SA using its active
   SID.  The group member SHOULD re-register, at which time the GCKS
   will issue a new SID to the group member, along with either the same
   Data-Security SAs or replacement ones.  The new SID replaces the
   existing SID used by this group member, and also resets the SSIV
   value to its starting value.  A group member MAY re-register prior to
   the actual exhaustion of the SSIV field to avoid dropping data
   packets due to the exhaustion of available SSIV values combined with
   a particular SID value.

   A group member MUST ignore an SID Download Type KD payload present in
   a GSA-REKEY message, otherwise more than one GM may end up using the
   same SID.

4.8.4.4.  GCKS Semantics

   If any KD payload includes keying material that is associated with a
   counter-mode of operation, an SID Download Type KD payload containing
   at least one SID_VALUE attribute MUST be included.  The GCKS MUST NOT
   send the SID Download Type KD payload as part of a GSA_REKEY message,
   because distributing the same sender-specific policy to more than one
   group member will reduce the security of the group.

4.9.  Delete Payload

   There are occasions when the GCKS may want to signal to group members
   to delete policy at the end of a broadcast, or if policy has changed.
   Deletion of keys MAY be accomplished by sending an IKEv2 Delete
   Payload, section 3.11 of [RFC7296] as part of the GSA_AUTH or



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   GSA_REKEY Exchange.  One or more Delete payloads MAY be placed
   following the HDR payload in the GSA_AUTH or GSA_REKEY Exchange.

   The Protocol ID MUST be 41 for GSA_REKEY Exchange, 2 for AH or 3 for
   ESP.  Note that only one protocol id value can be defined in a Delete
   payload.  If a TEK and a KEK SA for GSA_REKEY Exchange must be
   deleted, they must be sent in different Delete payloads.  Similarly,
   if a TEK specifying ESP and a TEK specifying AH need to be deleted,
   they must be sent in different Delete payloads.

   There may be circumstances where the GCKS may want to reset the
   policy and keying material for the group.  The GCKS can signal
   deletion of all policy of a particular TEK by sending a TEK with a
   SPI value equal to zero in the delete payload.  In the event that the
   administrator is no longer confident in the integrity of the group
   they may wish to remove all KEK and all the TEKs in the group.  This
   is done by having the GCKS send a delete payload with a SPI of zero
   and a Protocol-ID of AH or ESP to delete all TEKs, followed by
   another delete payload with a SPI value of zero and Protocol-ID of
   KEK SA to delete the KEK SA.

4.10.  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.

   NOTIFY messages - error types          Value
   -------------------------------------------------------------------
   INVALID_GROUP_ID -                      45
   Indicates the group id sent during the registration process is
   invalid.

   AUTHORIZATION_FAILED -                  46
   Sent in the response to a GSA_AUTH message when authorization failed.

   NOTIFY messages - status types          Value
   -------------------------------------------------------------------
   SENDER_ID_REQUEST   -                    16429
   Sent in GSA_AUTH or GSA_REGISTRATION to request SIDs from the GCKS.
   The data includes a count of how many SID values it desires.








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4.11.  Authentication Payload

   G-IKEv2 uses the same Authentication payload as specified in
   [RFC7296], section 3.8, to sign the rekey message.

5.  Security Considerations

5.1.  GSA registration and secure channel

   G-IKEv2 registration exchange uses IKEv2 IKE_SA_INIT protocols,
   inheriting all the security considerations documented in [RFC7296]
   section 5 Security Considerations, including authentication,
   confidentiality, protection against man-in-the-middle, protection
   against replay/reflection attacks, and denial of service protection.
   The GSA_AUTH and GSA_REGISTRATION exchanges also take advantage of
   those protections.  In addition, G-IKEv2 brings in the capability to
   authorize a particular group member regardless of whether they have
   the IKEv2 credentials.

5.2.  GSA maintenance channel

   The GSA maintenance channel is cryptographically and integrity
   protected using the cryptographic algorithm and key negotiated in the
   GSA member registration exchanged.

5.2.1.  Authentication/Authorization

   Authentication is implicit, the public key of the identity is
   distributed during the registration, and the receiver of the rekey
   message uses that public key and identity to verify the message came
   from the authorized GCKS.

5.2.2.  Confidentiality

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

5.2.3.  Man-in-the-Middle Attack Protection

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

5.2.4.  Replay/Reflection Attack Protection

   The GSA_REKEY message includes a monotonically increasing sequence
   number to protect against replay and reflection attacks.  A group
   member will recognize a replayed message by comparing the Message ID
   number to that of the last received rekey message, any rekey message



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   containing a Message ID number less than or equal to the last
   received value MUST be discarded.  Implementations should keep a
   record of recently received GSA rekey messages for this comparison.

6.  IANA Considerations

6.1.  New registries

   A new set of registries should be created for G-IKEv2, on a new page
   titled Group Key Management using IKEv2 (G-IKEv2) Parameters.  The
   following registries should be placed on that page.  The terms
   Reserved, Expert Review and Private Use are to be applied as defined
   in [RFC8126].

   GSA Policy Type Registry, see Section 4.4.1

   KEK Attributes Registry, see Section 4.5.1

   KEK Management Algorithm Registry, see Section 4.5.2

   GSA TEK Payload Protocol ID Type Registry, see Section 4.6

   TEK Attributes Registry, see Section 4.6

   Key Download Type Registry, see Section 4.8

   TEK Download Type Attributes Registry, see Section 4.8.1

   KEK Download Type Attributes Registry, see Section 4.8.2

   LKH Download Type Attributes Registry, see Section 4.8.3

   SID Download Type Attributes Registry, see Section 4.8.4

6.2.  New payload and exchange types added to the existing IKEv2
      registry

   The following new payloads and exchange types specified in this memo
   have already been allocated by IANA and require no further action,
   other than replacing the draft name with an RFC number.

   The present document describes new IKEv2 Next Payload types, see
   Section 4.1

   The present document describes new IKEv2 Exchanges types, see
   Section 4.1





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   The present document describes new IKEv2 notification types, see
   Section 4.10

7.  Acknowledgements

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

8.  Contributors

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

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

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

      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

9.  References








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9.1.  Normative References

   [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>.

9.2.  Informative References

   [IKE-HASH]
              Kivinen, T., "Fixing IKE Phase 1 & 2 Authentication
              HASHs", November 2001, <http://tools.ietf.org/html/
              draft-ietf-ipsec-ike-hash-revised-03>.

   [IKEV2-IANA]
              IANA, "Internet Key Exchange Version 2 (IKEv2)
              Parameters", February 2016,
              <http://www.iana.org/assignments/ikev2-parameters/
              ikev2-parameters.xhtml#ikev2-parameters-7>.

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

   [OFT]      McGrew, D. and A. Sherman, "Key Establishment in Large
              Dynamic Groups Using One-Way Function Trees", Manuscript,
               submitted to IEEE Transactions on Software Engineering,
              1998, <http://download.nai.com/products/media/nai/misc/
              oft052098.ps>.

   [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>.

   [RFC2407]  Piper, D., "The Internet IP Security Domain of
              Interpretation for ISAKMP", RFC 2407,
              DOI 10.17487/RFC2407, November 1998, <https://www.rfc-
              editor.org/info/rfc2407>.




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   [RFC2408]  Maughan, D., Schertler, M., Schneider, M., and J. Turner,
              "Internet Security Association and Key Management Protocol
              (ISAKMP)", RFC 2408, DOI 10.17487/RFC2408, November 1998,
              <https://www.rfc-editor.org/info/rfc2408>.

   [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>.

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

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

   [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>.

   [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>.

   [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>.

   [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>.





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Appendix A.  Differences between G-IKEv2 and RFC 6407

   KE Payload - The KE payload is no longer needed with the availability
   of newer algorithms such as AES and GCM which provide adequate
   protection therefore not needing the PFS capability the KE payload
   offers.

   SIG Payload - The AUTH payload is used for the same purpose instead.

   DOI/Situation - The DOI and Situation fields in the SA payload are no
   longer needed in the G-IKEv2 protocol as port 848 will distinguish
   the IKEv2 messages from the G-IKEv2 messages.

   SEQ Payload - The SEQ payload is no longer needed since IKEv2 header
   has message id which is used to prevent message replay attacks.

Authors' Addresses

   Brian Weis
   Cisco Systems
   170 W. Tasman Drive
   San Jose, California  95134-1706
   USA

   Phone: +1-408-526-4796
   Email: bew@cisco.com


   Yoav Nir
   Dell EMC
   9 Andrei Sakharov St
   Haifa  3190500
   Israel

   Email: ynir.ietf@gmail.com


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

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






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