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Versions: (draft-weis-gdoi-update) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 6407

MSEC Working Group                                               B. Weis
Internet-Draft                                                 S. Rowles
Intended status: Standards Track                           Cisco Systems
Expires: September 15, 2011                                  T. Hardjono
                                                                     MIT
                                                          March 14, 2011


                   The Group Domain of Interpretation
                     draft-ietf-msec-gdoi-update-08

Abstract

   This document describes an updated version of the Group Domain of
   Interpretation (GDOI) protocol specified in RFC 3547.  The GDOI
   provides group key management to support secure group communications
   according to the architecture specified in RFC 4046.  The GDOI
   manages group security associations, which are used by IPsec and
   potentially other data security protocols.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   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 September 15, 2011.

Copyright Notice

   Copyright (c) 2011 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
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   (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
   to this document.  Code Components extracted from this document must



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   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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
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   it for publication as an RFC or to translate it into languages other
   than English.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements notation  . . . . . . . . . . . . . . . . . .  5
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
     1.3.  Acronyms and Abbreviations . . . . . . . . . . . . . . . .  6

   2.  GDOI Phase 1 protocol  . . . . . . . . . . . . . . . . . . . .  8
     2.1.  ISAKMP Phase 1 protocol  . . . . . . . . . . . . . . . . .  8

   3.  GROUPKEY-PULL Exchange . . . . . . . . . . . . . . . . . . . .  9
     3.1.  Authorization  . . . . . . . . . . . . . . . . . . . . . .  9
     3.2.  Messages . . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.3.  Group Member Operations  . . . . . . . . . . . . . . . . . 11
     3.4.  GCKS Operations  . . . . . . . . . . . . . . . . . . . . . 13
     3.5.  Counter-modes of operation . . . . . . . . . . . . . . . . 13

   4.  GROUPKEY-PUSH Message  . . . . . . . . . . . . . . . . . . . . 16
     4.1.  Use of signature keys  . . . . . . . . . . . . . . . . . . 17
     4.2.  ISAKMP Header Initialization . . . . . . . . . . . . . . . 17
     4.3.  GCKS Operations  . . . . . . . . . . . . . . . . . . . . . 17
     4.4.  Group Member Operations  . . . . . . . . . . . . . . . . . 18

   5.  Payloads and Defined Values  . . . . . . . . . . . . . . . . . 20
     5.1.  Identification Payload . . . . . . . . . . . . . . . . . . 20
     5.2.  Security Association Payload . . . . . . . . . . . . . . . 20
     5.3.  SA KEK payload . . . . . . . . . . . . . . . . . . . . . . 22
     5.4.  Group Associated Policy  . . . . . . . . . . . . . . . . . 28
     5.5.  SA TEK Payload . . . . . . . . . . . . . . . . . . . . . . 30
     5.6.  Key Download Payload . . . . . . . . . . . . . . . . . . . 34
     5.7.  Sequence Number Payload  . . . . . . . . . . . . . . . . . 43



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     5.8.  Nonce  . . . . . . . . . . . . . . . . . . . . . . . . . . 44
     5.9.  Delete . . . . . . . . . . . . . . . . . . . . . . . . . . 44

   6.  Algorithm Selection  . . . . . . . . . . . . . . . . . . . . . 46
     6.1.  KEK  . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
     6.2.  TEK  . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 48
     7.1.  ISAKMP Phase 1 . . . . . . . . . . . . . . . . . . . . . . 48
     7.2.  GROUPKEY-PULL Exchange . . . . . . . . . . . . . . . . . . 49
     7.3.  GROUPKEY-PUSH Exchange . . . . . . . . . . . . . . . . . . 51
     7.4.  Forward and Backward Access Control  . . . . . . . . . . . 52
     7.5.  Derivation of keying material  . . . . . . . . . . . . . . 54

   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 55
     8.1.  Additions to current registries  . . . . . . . . . . . . . 55
     8.2.  New registries . . . . . . . . . . . . . . . . . . . . . . 55
     8.3.  Cleanup of existing registries . . . . . . . . . . . . . . 57

   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 59

   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 60
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 60
     10.2. Informative References . . . . . . . . . . . . . . . . . . 60

   Appendix A.  Extending GDOI  . . . . . . . . . . . . . . . . . . . 65
     A.1.  Alternate GDOI Phase 1 protocols . . . . . . . . . . . . . 65
     A.2.  Supporting new SA TEK types  . . . . . . . . . . . . . . . 66

   Appendix B.  GDOI Applications . . . . . . . . . . . . . . . . . . 67

   Appendix C.  Significant Changes from RFC 3547 . . . . . . . . . . 68

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 69

















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1.  Introduction

   Secure group and multicast applications require a method by which
   each group member shares common security policy and keying material.
   This document describes the Group Domain of Interpretation (GDOI),
   which is an ISAMKP [RFC2408] Domain of Interpretation (DOI), a group
   key management system.  The GDOI distributes security associations
   (SAs) for IPsec AH [RFC4302] and ESP [RFC4303] protocols and
   potentially other data security protocols used in group applications.
   The GDOI uses the group key management model defined in [RFC4046],
   and described more generally by the The Multicast Group Security
   Architecture [RFC3740].

   In this group key management model, the GDOI protocol participants
   are a "group controller/key server" (GCKS) and a group member (GM).
   A group member contacts ("registers with") a GCKS to join the group.
   During the registration mutual authentication and authorization are
   achieved, after which the GCKS distributes current group policy and
   keying material to the group member over an authenticated and
   encrypted session.  The GCKS may also initiate contact ("rekeys")
   with group members to provide updates to group policy.

   ISAKMP defines two "phases" of negotiation (p.16 of [RFC2408]).  A
   Phase 1 security association provides mutual authentication and
   authorization, and a security association that is used by the
   protocol participants to execute a phase 2 exchange.  This document
   incorporates (i.e., uses but does not re-define) the Phase 1 security
   association definition from the Internet DOI [RFC2407], [RFC2409].
   Phase 1 security association types other than ISAKMP are possible,
   and are noted in Appendix A.  Requirements of those phase 1 security
   associations are specified in Section 2.  The GDOI includes two new
   phase 2 ISAKMP exchanges (protocols), as well as necessary new
   payload definitions to the ISAKMP standard (p. 14 of [RFC2408]).
   These two new protocols are:

   1.  The GROUPKEY-PULL registration protocol exchange.  This exchange
       uses "pull" behavior since the member initiates the retrieval of
       these SAs from a GCKS.  It is protected by an ISAKMP phase 1
       protocol, as described above.  At the culmination of a GROUPKEY-
       PULL exchange, an authorized group member has received and
       installed a set of SAs that represent group policy, and it is
       ready to participate in secure group communications.

   2.  The GROUPKEY-PUSH rekey protocol exchange.  The rekey protocol is
       a datagram initiated ("pushed") by the GCKS, usually delivered to
       group members using a IP multicast address.  The rekey protocol
       is an ISAKMP protocol, where cryptographic policy and keying
       material ("Re-key SA") is included in the group policy



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       distributed by the GCKS in the GROUPKEY-PULL exchange.  At the
       culmination of a GROUPKEY-PUSH exchange the key server has sent
       group policy to all authorized group members, allowing receiving
       group members to participate in secure group communications.  If
       a group management method is included in group policy (as
       described in Section 7.4), at the conclusion of the GROUPKEY-PUSH
       exchange some members of the group may have been de-authorized
       and no longer able to participate in the secure group
       communications.

      +--------------------------------------------------------------+
      |                                                              |
      |                    +--------------------+                    |
      |            +------>|     GDOI GCKS      |<------+            |
      |            |       +--------------------+       |            |
      |            |                 |                  |            |
      |       GROUPKEY-PULL          |             GROUPKEY-PULL     |
      |         PROTOCOL             |               PROTOCOL        |
      |            |                 |                  |            |
      |            v           GROUPKEY-PUSH            v            |
      |   +-----------------+     PROTOCOL     +-----------------+   |
      |   |                 |        |         |                 |   |
      |   |    GDOI GM(s)   |<-------+-------->|    GDOI GM(S)   |   |
      |   |                 |                  |                 |   |
      |   +-----------------+                  +-----------------+   |
      |            |                                    ^            |
      |            v                                    |            |
      |            +-Data Security Protocol (e.g., ESP)-+            |
      |                                                              |
      +--------------------------------------------------------------+

   Although the GROUPKEY-PUSH protocol specified by this document can be
   used to refresh the Re-key SA protecting the GROUPKEY-PUSH protocol,
   the most common use of GROUPKEY-PUSH is to establish keying material
   and policy for a data security protocol.

   In summary, GDOI is a group security association management protocol:
   all GDOI messages are used to create, maintain, or delete security
   associations for a group.  As described above, these security
   associations protect one or more data security protocol SAs, a Re-key
   SA, and/or other data shared by group members for multicast and
   groups security applications.

1.1.  Requirements notation

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



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1.2.  Terminology

   The following key terms are used throughout this document.

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

   Group Controller/Key Server  A device that defines group policy and
         distributes keys for that policy.[RFC3740]

   Group Member.  An authorized member of a secure group, sending and/or
         receiving IP packets related to the group.

   GROUPKEY-PULL.  A protocol used by a GDOI Group Member to request
         group policy and keying material.

   GROUPKEY-PUSH.  A protocol used by a GDOI GCKS to distribute updates
         of group policy and keying material to authorized group
         members.

   Key Encrypting Key.  The symmetric cipher key used to protect the
         GROUPKEY-PUSH message.

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

   Re-key SA.  The security policy protecting a GROUPKEY-PUSH protocol.

   Traffic Encryption Key.  The symmetric cipher key used to protect a
         data security protocol (e.g., IPsec ESP).

1.3.  Acronyms and Abbreviations

   The following acronyms and abbreviations are used throughout this
   document.

   AH    IP Authentication Header

   ATD   Activation Time Delay

   DOI   Domain of Interpretation

   DTD   Deactivation Time Delay






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   ESP   IP Encapsulating Security Payload

   GCKS  Group Controller/Key Server

   GDOI  Group Domain of Interpretation

   GAP   Group Associated Policy Payload

   GM    Group Member

   IV    Initialization Vector

   KD    Key Download Payload

   KEK   Key Encryption Key

   LKH   Lock Key Hierarchy

   SA    Security Association

   SAK   SA KEK Payload

   SEQ   Sequence Number Payload

   SAT   SA TEK Payload

   SID   Sender-ID

   TEK   Traffic Encryption Key






















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2.  GDOI Phase 1 protocol

   The GDOI GROUPKEY-PULL exchange is a "phase 2" protocol which MUST be
   protected by a "phase 1" protocol.  The "phase 1" protocol can be any
   protocol which provides for the following protections:

   o  Peer Authentication

   o  Confidentiality

   o  Message Integrity

   The following sections describe one such "phase 1" protocol.  Other
   protocols which may be potential "phase 1" protocols are described in
   Appendix A.  However, the use of the protocols listed there are not
   considered part of this document.

2.1.  ISAKMP Phase 1 protocol

   This document defines how the ISAKMP phase 1 exchanges as defined in
   [RFC2409] can be used a "phase 1" protocol for GDOI.  The following
   sections define characteristics of the ISAKMP phase 1 protocols that
   are unique for these exchanges when used for GDOI.

   Section 7.1 describes how the ISAKMP Phase 1 protocols meet the
   requirements of a GDOI "phase 1" protocol.

2.1.1.  DOI value

   The Phase 1 SA payload has a DOI value.  That value MUST be the GDOI
   DOI value as defined later in this document.

2.1.2.  UDP port

   IANA has assigned port 848 for the use of GDOI, which allows for an
   implementation to use separate ISAKMP implementations to service GDOI
   and IKEv1 [RFC2409].  A GCKS SHOULD listen on this port for GROUPKEY-
   PULL exchanges, and the GCKS MAY use this port to distribute
   GROUPKEY-PUSH messages.  An ISAKMP phase 1 exchange implementation
   supporting NAT Traversal [RFC3947] may move to port 4500 to process
   the GROUPKEY-PULL exchange.










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3.  GROUPKEY-PULL Exchange

   The goal of the GROUPKEY-PULL exchange is to establish a Re-key
   and/or Data-security SAs at the member for a particular group.  A
   Phase 1 SA protects the GROUPKEY-PULL; there MAY be multiple
   GROUPKEY-PULL exchanges for a given Phase 1 SA.  The GROUPKEY-PULL
   exchange downloads the data security keys (TEKs) and/or group key
   encrypting key (KEK) or KEK array under the protection of the Phase 1
   SA.

3.1.  Authorization

   The Phase 1 identity SHOULD be used by a GCKS to authorize the Phase
   2 (GROUPKEY-PULL) request for a group key.  A group member MUST
   ensure that the Phase 1 identity of the GCKS is an authorized GCKS.
   When no authorization is performed, it is possible for a rogue GDOI
   participant to perpetrate a man-in-the-middle attack between a group
   member and a GCKS [MP04].

3.2.  Messages

   The GROUPKEY-PULL is a Phase 2 exchange.  Phase 1 computes SKEYID_a
   which is the "key" in the keyed hash used in the GROUPKEY-PULL HASH
   payloads.  When using the Phase 1 defined in this document, SKEYID_a
   is derived according to [RFC2409].  As with the IKEv1 HASH payload
   generation (Section 5.5 of [RFC2409], each GROUPKEY-PULL message
   hashes a uniquely defined set of values (described below).  Nonces
   permute the HASH and provide some protection against replay attacks.
   Replay protection is important to protect the GCKS from attacks that
   a key management server will attract.

   The GROUPKEY-PULL uses nonces to guarantee "liveness" as well as
   against replay of a recent GROUPKEY-PULL message.  The replay attack
   is only possible in the context of the current Phase 1.  If a
   GROUPKEY-PULL message is replayed based on a previous Phase 1, the
   HASH calculation will fail due to a wrong SKEYID_a.  The message will
   fail processing before the nonce is ever evaluated.

   In order for either peer to get the benefit of the replay protection,
   it must postpone as much processing as possible until it receives the
   message in the protocol that proves the peer is live.  For example,
   the GCKS MUST NOT adjust its internal state (e.g., keeping a record
   of the GM) until it receives a message with Nr included properly in
   the HASH payload.  This requirement ensures that replays of GDOI
   messages will not cause the GCKS to change the state of the group
   until it has confirmation that the initiating group member is live.





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              Group Member                      GCKS
              ------------                      ----
              HDR*, HASH(1), Ni, ID     -->
                                        <--     HDR*, HASH(2), Nr, SA
              HDR*, HASH(3) [,GAP]      -->
                                        <--     HDR*, HASH(4), [SEQ,] KD

    * Protected by the Phase 1 SA, encryption occurs after HDR

   HDR is an ISAKMP header payload that uses the Phase 1 cookies and a
   message identifier (M-ID) as in IKEv1.

   Hashes are computed in the manner described within RFC 2409.  Each
   HASH computation (shown below) is a prf over the message id (M-ID)
   from the ISAKMP header concatenated with the entire message that
   follows the hash including all payload headers, but excluding any
   padding added for encryption.  The GM expects to find its nonce, Ni,
   in the HASH of a returned message.  And the GCKS expects to see its
   nonce, Nr, in the HASH of a returned message.  HASH(2), HASH(3), and
   HASH(4) also include nonce values previously passed in the protocol
   (i.e., Ni or Nr minus the payload header).  The nonce passed in Ni is
   represented as Ni_b, and the nonce passed in Nr is represented as
   Nr_b.  The HASH payloads prove that the peer has the Phase 1 secret
   (SKEYID_a) and the nonce for the exchange identified by message id,
   M-ID.


        HASH(1) = prf(SKEYID_a, M-ID | Ni | ID)
        HASH(2) = prf(SKEYID_a, M-ID | Ni_b | Nr | SA)
        HASH(3) = prf(SKEYID_a, M-ID | Ni_b | Nr_b [ | GAP ])
        HASH(4) = prf(SKEYID_a, M-ID | Ni_b | Nr_b [ | SEQ ] | KD)

   In addition to the Nonce and HASH payloads, the GM identifies the
   group it wishes to join through the ISAKMP ID payload.

   The GCKS informs the member of the cryptographic policies of the
   group in the SA payload, which describes the DOI, KEK and/or TEK
   keying material, authentication transforms, and other group policy.
   The SPIs are also determined by the GCKS and downloaded in the SA
   payload chain (see Section 5.2).  The SA KEK attribute contains the
   ISAKMP cookie pair for the Re-key SA, which is not negotiated but
   downloaded.  Each SA TEK attribute contains a SPI as defined in
   Section 5.5 of this document.

   After receiving and parsing the SA payload, the GM responds with an
   acknowledgement message proving its liveness.  It optionally includes
   a GAP payload requesting resources.




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   The GCKS informs the GM of the value of the sequence number in the
   SEQ payload.  This sequence number provides anti-replay state
   associated with a KEK, and its knowledge ensure that the GM will not
   accept GROUPKEY-PULL messages sent prior to the GM joining the group.
   The SEQ payload has no other use, and is omitted from the
   GROUPKEY_PULL exchange when a KEK attribute is not included in the SA
   payload.  When a SEQ payload is included in the GROUPKEY-PULL
   exchange, it includes the most recently used sequence number for the
   group.  At the conclusion of a GROUPKEY-PULL exchange, the initiating
   group member MUST NOT accept any rekey message with both the KEK
   attribute SPI value and a sequence number less than or equal to the
   one received during the GROUPKEY-PULL.  When the first group member
   initiates a GROUPKEY-PULL exchange, the GCKS provides a Sequence
   Number of zero, since no GROUPKEY-PUSH messages have yet been sent.
   Note the sequence number increments only with GROUPKEY-PUSH messages.
   The GROUPKEY-PULL exchange distributes the current sequence number to
   the group member.  The sequence number resets to a value of one with
   the usage of a new KEK attribute.  Thus the first packet sent for a
   given Rekey SA will have a Sequence Number of 1.  The sequence number
   increments with each successive rekey.

   The GCKS always returns a KD payload containing keying material to
   the GM.  If a Re-key SA is defined in the SA payload, then KD will
   contain the KEK; if one or more Data-security SAs are defined in the
   SA payload, KD will contain the TEKs.

3.2.1.  ISAKMP Header Initialization

   Cookies are used in the ISAKMP header to identify a particular GDOI
   session.  The GDOI GROUPKEY-PULL exchange uses cookies according to
   ISAKMP [RFC2408].

   Next Payload identifies an ISAKMP or GDOI payload (see Section 5.0).

   Major Version is 1 and Minor Version is 0 according to ISAKMP
   (Section 3.1 of [RFC2408]).

   The Exchange Type has value 32 for the GDOI GROUPKEY-PULL exchange.

   Flags, Message ID, and Length are according to ISAKMP (Section 3.1 of
   [RFC2408]).

3.3.  Group Member Operations

   Before a GM contacts the GCKS, it must determine the group identifier
   and acceptable Phase 1 policy via an out-of-band method.  Phase 1 is
   initiated using the GDOI DOI in the SA payload.  Once Phase 1 is
   complete, the GM state machine moves to the GDOI protocol.



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   To construct the first GDOI message the GM chooses Ni and creates a
   nonce payload, builds an identity payload including the group
   identifier, and generates HASH(1).

   Upon receipt of the second GDOI message, the GM validates HASH(2),
   extracts the nonce Nr, and interprets the SA payload.  The SA payload
   contains policy describing the security protocol and cryptographic
   protocols used by the group.  This policy describes the Re-key SA (if
   present), Data-security SAs, and other group policy.  If the policy
   in the SA payload is acceptable to the GM, it continues the protocol.
   Otherwise, the GM SHOULD tear down the Phase 1 session after first
   notifying the GCKS that it is doing so.  If a Data-security SA
   describes the use of a counter mode cipher, the GM determines whether
   it requires more than one Sender-ID (SID) (see Section 3.5).  If so,
   it includes a GAP payload indicating how many SID values it requires.

   When constructing the third GDOI message, it first reviews each Data-
   security SA given to it.  If any include a cipher counter mode, it
   needs to request for one or more Sender-IDs for its exclusive use
   within the counter mode nonce.  Do to this, the GM will include a GAP
   payload with its request, as described in the Section 5.4 section of
   this document.  The GM the completes construction of the third GDOI
   message by creating HASH(3).

   Upon receipt of the fourth GDOI message, the GM validates HASH(4).

   If the SEQ payload is present, the sequence number in the SEQ payload
   must be checked against any previously received sequence number for
   this group.  If it is less than the previously received number, it
   should be considered stale and ignored.

   The GM interprets the KD key packets, where each key packet includes
   the keying material for SAs distributed in the SA payload.  Keying
   material is matched by comparing the SPIs in the key packets to SPIs
   previously sent in the SA 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.  If this
   group has a KEK, the KEK policy and keys are marked as ready for use,
   and the GM knows to expect the sequence number reset to 1 with the
   next Rekey SA, which will be encrypted with the new KEK attribute.
   The GM is now ready to receive GROUPKEY-PUSH messages.

   If the KD payload included an LKH array of keys, the GM takes the
   last key in the array as the group KEK.  The array is then stored
   without further processing.






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3.4.  GCKS Operations

   The GCKS passively listens for incoming requests from group members.
   The Phase 1 authenticates the group member and sets up the secure
   session with them.

   Upon receipt of the first GDOI message the GCKS validates HASH(1),
   extracts the Ni and group identifier in the ID payload.  It verifies
   that its database contains the group information for the group
   identifier, and that the GM is authorized to participate in the
   group.

   The GCKS constructs the second GDOI message, including a nonce Nr,
   and the policy for the group in an SA payload, followed by SA KEK,
   GAP, and/or SA TEK payloads according to the GCKS policy.  (See
   Section 5.2.1 for details on how the GCKS chooses which payloads to
   send.)

   Upon receipt of the third GDOI message the GCKS validates HASH(3).
   If the message includes a GAP payload, it caches the requests
   included in that payload for use of constructing the fourth GDOI
   message.

   The GCKS constructs the fourth GDOI message, including the SEQ
   payload (if the GCKS sends rekey messages), and the KD payload
   containing keys corresponding to policy previously sent in the SA TEK
   and SA KEK payloads.  If a group management algorithm is defined as
   part of group policy, the GCKS will first insert the group member
   into the group management structure (e.g., a leaf in the LKH tree),
   and then create an LKH array of keys and include it in the KD
   payload.  The first key in the array is associated with the group
   member leaf node, followed by each LKH node above it in the tree,
   culminating with the root node (which is also the KEK).  If one or
   more Data-Security SAs distributed in the SA payload included a
   counter mode of operation, the GCKS includes at least one SID value
   in the KD payload, and possibly more depending on a request received
   in the third GDOI message.

3.5.  Counter-modes of operation

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




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   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 SAs included in the group policy
   includes a counter-mode, 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 a unique key and nonce usage.

   When a group member receives a Data-Security SA in a SA TEK payload
   for which it is a sender, it 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 sending 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 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 which SIDs that
       have been allocated.  SIDs are allocated sequentially, with the
       first SID allocated to be zero.

   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 distributes an Data-Security SA specifying a
       counter-based mode of operation, and a group member is a sender,
       a group member may request a count of SIDs in a GAP payload.
       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 GROUPKEY-PULL exchange
       originated by a sender, regardless of whether a group member had
       previously contacted the GCKS.  In this way, the GCKS does not
       have a requirement of 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 GROUPKEY-PUSH message deleting all Data-
       Security SAs and the Rekey SA for the group.  This will result in
       the group members initiating a new GROUPKEY-PULL 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
       GROUPKEY-PUSH 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.




















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4.  GROUPKEY-PUSH Message

   GDOI sends control information securely using group communications.
   Typically this will be using IP multicast distribution of a GROUPKEY-
   PUSH message but it can also be "pushed" using unicast delivery if IP
   multicast is not possible.  The GROUPKEY-PUSH message replaces a Re-
   key SA KEK or KEK array, and/or creates a new Data-security SA.

              GM                    GCKS
              --                    ----
                              <---- HDR*, SEQ, [D,] SA, KD, SIG

      * Protected by the Re-key SA KEK; encryption occurs after HDR

   HDR is defined below.  The SEQ payload is defined in the Payloads
   section.  One or more D (Delete) payloads (further described in
   Section 5.9) optionally specify the deletion of existing group
   policy.  The SA defines the group policy for replacement Re-key SA
   and/or Data-security SAs as described in the Payloads section, with
   the KD providing keying material for those SAs.

   The SIG payload includes a signature of a hash of the entire
   GROUPKEY-PUSH message (excepting the SIG payload bytes) before it has
   been encrypted.  The HASH is taken over the string 'rekey', the
   GROUPKEY-PUSH HDR, followed by all payloads preceding the SIG
   payload.  The prefixed string ensures that the signature of the Rekey
   datagram cannot be used for any other purpose in the GDOI protocol.
   The SIG payload is created using the signature of the above hash,
   with the receiver verifying the signature using a public key
   retrieved in a previous GDOI exchange.  The current KEK encryption
   key (also previously distributed in a GROUPKEY-PULL exchange or
   GROUPKEY-PUSH message) encrypts all the payloads following the
   GROUPKEY-PUSH HDR.  Note: The rationale for this order of operations
   is given in Section 7.3.5.

   If the SA defines the use of a single KEK or an LKH KEK array, KD
   MUST contain a corresponding KEK or KEK array for a new Re-key SA,
   which has a new cookie pair.  When the KD payload carries a new SA
   KEK attribute (section 5.3), a Re-key SA is replaced with a new SA
   having the same group identifier (ID specified in message 1 of
   section 3.2) and incrementing the same sequence counter, which is
   initialized in message 4 of section 3.2.  Note the first packet for
   the given Rekey SA encrypted with the new KEK attribute will have a
   Sequence number of 1.  If the SA defines an SA TEK payload, this
   informs the member that a new Data-security SA has been created, with
   keying material carried in KD (Section 5.6).

   If the SA defines a large LKH KEK array (e.g., during group



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   initialization and batched rekeying), parts of the array MAY be sent
   in different unique GROUPKEY-PUSH datagrams.  However, each of the
   GROUPKEY-PUSH datagrams MUST be a fully formed GROUPKEY-PUSH
   datagram.  This results in each datagram containing a sequence number
   and the policy in the SA payload, which corresponds to the KEK array
   portion sent in the KD payload.

4.1.  Use of signature keys

   A signing key should not be used in more than one context (e.g., used
   for host authentication and also for message authentication).  Thus,
   the GCKS SHOULD NOT use the same key to sign the SIG payload in the
   GROUPKEY-PUSH message as was used for authentication in the GROUPKEY-
   PULL exchange.

4.2.  ISAKMP Header Initialization

   Unlike ISAKMP or IKEv1, the cookie pair is completely determined by
   the GCKS.  The cookie pair in the GDOI ISAKMP header identifies the
   Re-key SA to differentiate the secure groups managed by a GCKS.
   Thus, GDOI uses the cookie fields as an SPI.

   Next Payload identifies an ISAKMP or GDOI payload (see Section 5.0).

   Major Version is 1 and Minor Version is 0 according to ISAKMP
   (Section 3.1 of [RFC2408]).

   The Exchange Type has value 33 for the GDOI GROUPKEY-PUSH message.

   Flags MUST have the Encryption bit set according to [RFC2008, Section
   3.1].  All other bits MUST be set to zero.

   Message ID MUST be set to zero.

   Length is according to ISAKMP (Section 3.1 of [RFC2408]).

4.3.  GCKS Operations

   GCKS may initiate a Rekey message for one of several reasons, e.g.,
   the group membership has changed or keys are due to expire.

   To begin the rekey datagram the GCKS builds an ISAKMP HDR with the
   correct cookie pair, and a SEQ payload that includes a sequence
   number which is one greater than the previous rekey datagram.  If the
   message is using the new KEK attribute for the first time, the SEQ is
   reset to 1 in this message.

   An SA payload is then added.  This is identical in structure and



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   meaning to a SA payload sent in a GROUPKEY-PULL exchange.  If there
   are changes to the KEK (including due to group members being
   excluded, in the case of LKH), an SA_KEK attribute is added to the
   SA.  If there are one or more new TEKs then SA_TEK attributes are
   added to describe that policy.

   A KD payload is then added.  This is identical in structure and
   meaning to a KD payload sent in a GROUPKEY-PULL exchange.  If an
   SA_KEK attribute was included in the SA payload then corresponding
   KEK keys (or a KEK update array) is included.  A KEK update array is
   created by first determining which group members have been excluded,
   and then generating new keys as necessary and distribute LKH update
   arrays sufficient to provide the new KEK to remaining group members
   (see Section 5.4.1 of [RFC2627] for details).  TEK keys are also sent
   for each SA_TEK attribute included in the SA payload.

   In the penultimate step, the GCKS creates the SIG payload and adds it
   to the datagram.

   Lastly, the payloads following the HDR are encrypted using the
   current KEK encryption key.  The datagram can now be sent.

4.4.  Group Member Operations

   A group member receiving the GROUPKEY-PUSH datagram matches the
   cookie pair in the ISAKMP HDR to an existing SA.  The message is
   decrypted, and the form of the datagram is validated.  This weeds out
   obvious ill-formed messages (which may be sent as part of a Denial of
   Service attack on the group).

   The sequence number in the SEQ payload is validated to ensure that it
   is greater than the previously received sequence number, and that it
   fits within a window of acceptable values.  The SIG payload is then
   validated.  If the signature fails, the message is discarded.

   The SA and KD payloads are processed which results in a new GDOI
   Rekey-SA (if the SA payload included an SA_KEK attribute) and/or new
   Data-security SAs being added to the system.  If the KD payload
   includes an LKH update array, the group member compares the LKH ID in
   each key update packet to the LKH IDs that it holds.  If it finds a
   match, it decrypts the key using the key prior to it in the key array
   and stores the new key in the LKH key array that it holds.  The final
   decryption yields the new group KEK.

   If the SA payload includes 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



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   hold a current SID value, it MUST NOT install the Data-Security SAs.
   It MAY initiate a GROUPKEY-PULL exchange to the GCKS in order to
   obtain an SID value (along with current group policy).
















































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5.  Payloads and Defined Values

   This document specifies use of several ISAKMP payloads, which are
   defined in accordance with RFC 2408.  The following payloads are
   extended or further specified.


                  Next Payload Type            Value
                  -----------------            -----
                  Security Association (SA)      1
                  Identification (ID)            5
                  Nonce (N)                     10

   Several payload formats specific to the group security exchanges are
   required.


                  Next Payload Type                Value
                  -----------------                -----
                  SA KEK Payload (SAK)              15
                  SA TEK Payload (SAT)              16
                  Key Download (KD)                 17
                  Sequence Number (SEQ)             18
                  Group Associated Policy (GAP)   TBD-1

5.1.  Identification Payload

   The Identification Payload is defined in RFC 2408.  For the GDOI, it
   is used to identify a group identity that will later be associated
   with Security Associations for the group.  A group identity may map
   to a specific IP multicast group, or may specify a more general
   identifier, such as one that represents a set of related multicast
   streams.

   When used with the GDOI, the DOI Specific ID Data field MUST be set
   to 0.

   When used with the GDOI, the ID_KEY_ID ID Type MUST be supported by a
   conforming implementation, and MUST specify a four (4)-octet group
   identifier as its value.  Implementations MAY also support other ID
   Types.

5.2.  Security Association Payload

   The Security Association payload is defined in RFC 2408.  For the
   GDOI, it is used by the GCKS to assert security attributes for both
   Re-key and Data-security SAs.




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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! Next Payload  !   RESERVED    !         Payload Length        !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       !                              DOI                              !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !                           Situation                           !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! SA Attribute Next Payload     !          RESERVED2            !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

   The Security Association Payload fields are defined as follows:

   o Next Payload (1 octet) -- Identifies the next payload for the
   GROUPKEY-PULL or the GROUPKEY-PUSH message as defined above.  The
   next payload MUST NOT be a SAK Payload or SAT Payload type, but the
   next non-Security Association type payload.

   o RESERVED (1 octet) -- 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 payloads.

   o DOI (4 octets) -- Is the GDOI, which is value 2.

   o Situation (4 octets) -- Must be zero.

   o SA Attribute Next Payload (1 octet) -- Must be either a SAK Payload
   or a SAT Payload.  See section 5.2.1 for a description of which
   circumstances are required for each payload type to be present.

   o RESERVED (2 octets) -- Must be zero.

5.2.1.  Payloads following the SA payload

   Payloads that define specific security association attributes for the
   KEK and/or TEKs used by the group MUST follow the SA payload.  How
   many of each payload is dependent upon the group policy.  There may
   be zero or one SAK Payload, zero or one GAP Payload, and zero or more
   SAT Payloads, where either one SAK or SAT payload MUST be present.
   When present, the order of the SA Attributes payloads must be: KEK,
   GAP, and TEKs.

   This latitude regarding SA Attributes payloads allows various group
   policies to be accommodated.  For example if the group policy does
   not require the use of a Re-key SA, the GCKS would not need to send
   an SA KEK attribute to the group member since all SA updates would be



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   performed using the Registration SA.  Alternatively, group policy
   might use a Re-key SA but choose to download a KEK to the group
   member only as part of the Registration SA.  Therefore, the KEK
   policy (in the SA KEK attribute) would not be necessary as part of
   the Re-key SA message SA payload.

   Specifying multiple SATs allows multiple sessions to be part of the
   same group and multiple streams to be associated with a session
   (e.g., video, audio, and text) but each with individual security
   association policy.

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

5.3.  SA KEK payload

   The SA KEK (SAK) payload contains security attributes for the KEK
   method for a group and parameters specific to the GROUPKEY-PULL
   operation.  The source and destination identities describe the
   identities used for the GROUPKEY-PULL datagram.


        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  !   RESERVED    !         Payload Length        !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !    Protocol   !  SRC ID Type  !         SRC ID Port           !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !SRC ID Data Len!          SRC Identification Data              ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! DST ID Type   !         DST ID Port           !DST ID Data Len!
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !                    DST Identification Data                    ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !                                                               !
       ~                              SPI                              ~
       !                                                               !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !                           RESERVED2                           !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ~                        KEK Attributes                         ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

   The SAK Payload fields are defined as follows:

   o Next Payload (1 octet) -- Identifies the next payload for the
   GROUPKEY-PULL or the GROUPKEY-PUSH message.  The only valid next



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   payload types for this message are a GAP Payload, SAT Payload or zero
   to indicate that no SA Attribute payloads follow.

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

   o Payload Length (2 octets) -- Length of this payload, including the
   KEK attributes.

   o Protocol (1 octet) -- Value describing an IP protocol ID (e.g.,
   UDP/TCP) for the rekey datagram.

   o SRC ID Type (1 octet) -- Value describing the identity information
   found in the SRC Identification Data field.  Defined values are
   specified by the IPsec Identification Type section in the IANA
   isakmpd-registry [ISAKMP-REG].

   o SRC ID Port (2 octets) -- Value specifying a port associated with
   the source Id.  A value of zero means that the SRC ID Port field
   should be ignored.

   o SRC ID Data Len (1 octet) -- Value specifying the length of the SRC
   Identification Data field.

   o SRC Identification Data (variable length) -- Value, as indicated by
   the SRC ID Type.

   o DST ID Type (1 octet) -- Value describing the identity information
   found in the DST Identification Data field.  Defined values are
   specified by the IPsec Identification Type section in the IANA
   isakmpd-registry [ISAKMP-REG].

   o DST ID Prot (1 octet) -- Value describing an IP protocol ID (e.g.,
   UDP/TCP).

   o DST ID Port (2 octets) -- Value specifying a port associated with
   the source Id.

   o DST ID Data Len (1 octet) -- Value specifying the length of the DST
   Identification Data field.

   o DST Identification Data (variable length) -- Value, as indicated by
   the DST ID Type.

   o SPI (16 octets) -- Security Parameter Index for the KEK.  The SPI
   must be the ISAKMP Header cookie pair where the first 8 octets become
   the "Initiator Cookie" field of the GROUPKEY-PUSH message ISAKMP HDR,
   and the second 8 octets become the "Responder Cookie" in the same
   HDR.  As described above, these cookies are assigned by the GCKS.



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   o RESERVED2 (4 octets) -- Must be zero.  This bytes represent fields
   previously defined but no longer used by GDOI.

   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.

5.3.1.  KEK Attributes

   The following attributes may be present in a SAK Payload.  The
   attributes must follow the format defined in ISAKMP (Section 3.3 of
   [RFC2408]).  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).


                ID Class                   Value    Type
                --------                   -----    ----
                RESERVED                     0
                KEK_MANAGEMENT_ALGORITHM     1        B
                KEK_ALGORITHM                2        B
                KEK_KEY_LENGTH               3        B
                KEK_KEY_LIFETIME             4        V
                SIG_HASH_ALGORITHM           5        B
                SIG_ALGORITHM                6        B
                SIG_KEY_LENGTH               7        B
                KE_OAKLEY_GROUP              8        B
                Standards Action            9-127
                Private Use               128-255
                Unassigned                256-32767

   The KEK_MANAGEMENT_ALGORITHM attribute may only be included in a
   GROUPKEY-PULL message.

5.3.2.  KEK_MANAGEMENT_ALGORITHM

   The KEK_MANAGEMENT_ALGORITHM class 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.











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                  KEK Management Type               Value
                  -------------------               -----
                  RESERVED                            0
                  LKH                                 1
                  Standards Action                   2-127
                  Private Use                      128-255

5.3.2.1.  LKH

   This type indicates the group management method described in Section
   5.4 of [RFC2627].  A general discussion of LKH operations can also be
   found in Section 6.3 of Multicast and Group Security [HD03]

5.3.3.  KEK_ALGORITHM

   The KEK_ALGORITHM class specifies the encryption algorithm in which
   the KEK is used to provide confidentiality for the GROUPKEY-PUSH
   message.  Defined values are specified in the following table.  A
   GDOI implementation MUST abort if it encounters an attribute or
   capability that it does not understand.


                   Algorithm Type      Value
                   --------------      -----
                   RESERVED               0
                   KEK_ALG_DES            1
                   KEK_ALG_3DES           2
                   KEK_ALG_AES            3
                   Standards Action      4-127
                   Private Use         128-255
                   Unassigned          256-32767

   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
   KEK_ALGORITHM attribute MUST be used for all keys which are included
   as part of the management.

5.3.3.1.  KEK_ALG_DES

   This type specifies DES using the Cipher Block Chaining (CBC) mode as
   described in [FIPS81].

5.3.3.2.  KEK_ALG_3DES

   This type specifies 3DES using three independent keys as described in
   "Keying Option 1" in [FIPS46-3].




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5.3.3.3.  KEK_ALG_AES

   This type specifies AES as described in [FIPS197].  The mode of
   operation for AES is Cipher Block Chaining (CBC) as recommended in
   [SP.800-38A].

5.3.4.  KEK_KEY_LENGTH

   The KEK_KEY_LENGTH class specifies the KEK Algorithm key length (in
   bits).  The Group Controller/Key Server (GCKS) adds the
   KEK_KEY_LENGTH attribute to the SA 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 (e.g., KEK_ALG_3DES), the
   group member can make its decision solely using the KEK_ALGORITHM
   attribute and does not need the KEK_KEY_LENGTH attribute.  Sending
   the KEK_KEY_LENGTH attribute in the SA payload is OPTIONAL if the KEK
   cipher has a fixed key length.  Also, note that the KEK_KEY_LEN
   includes only the actual length of the cipher key (the IV length is
   not included in this attribute).

5.3.5.  KEK_KEY_LIFETIME

   The KEK_KEY_LIFETIME class 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.

5.3.6.  SIG_HASH_ALGORITHM

   SIG_HASH_ALGORITHM specifies the SIG payload hash algorithm.  The
   following table defines the algorithms for SIG_HASH_ALGORITHM.



















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                   Algorithm Type     Value
                   --------------     -----
                   RESERVED             0
                   SIG_HASH_MD5         1
                   SIG_HASH_SHA1        2
                   SIG_HASH_SHA256     TBD-2
                   SIG_HASH_SHA384     TBD-3
                   SIG_HASH_SHA512     TBD-4
                   Standards Action    3-127
                   Private Use       128-255
                   Unassigned        256-32767
   The SHA hash algorithms are defined in the Secure Hash
   Standard[FIPS.180-2.2002].

   If the SIG_ALGORITHM is SIG_ALG_ECDSA-256, SIG_ALG_ECDSA-384, or
   SIG_ALG_ECDSA-521 the hash algorithm is implicit in the definition,
   and SIG_HASH_ALGORITHM is not required to be present in a SAK
   Payload.

5.3.7.  SIG_ALGORITHM

   The SIG_ALGORITHM class specifies the SIG payload signature
   algorithm.  Defined values are specified in the following table.


                   Algorithm Type      Value
                   --------------      -----
                   RESERVED              0
                   SIG_ALG_RSA           1
                   SIG_ALG_DSS           2
                   SIG_ALG_ECDSS         3
                   SIG_ALG_RSA_PSS      TBD-6
                   SIG_ALG_ECDSA-256    TBD-7
                   SIG_ALG_ECDSA-384    TBD-8
                   SIG_ALG_ECDSA-521    TBD-9
                   Standards Action     4-127
                   Private Use        128-255
                   Unassigned         256-32767

5.3.7.1.  SIG_ALG_RSA

   This algorithm specifies the RSA digital signature algorithm using
   the EMSA-PKCS1-v1_5 encoding method, as described in [RFC3447].

5.3.7.2.  SIG_ALG_DSS

   This algorithm specifies the DSS digital signature algorithm as
   described in Section 4 of [FIPS186-3].



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5.3.7.3.  SIG_ALG_ECDSS

   This algorithm specifies the Elliptic Curve digital signature
   algorithm as described in Section 5 of [FIPS186-3].  This definition
   is deprecated in favor of the SIG_ALG_ECDSA family of algorithms.

5.3.7.4.  SIG_ALG_RSA_PSS

   This algorithm specifies the RSA digital signature algorithm using
   the EMSA-PSS encoding method, as described in [RFC3447].

5.3.7.5.  SIG_ALG_ECDSA-256

   This algorithm specifies the 256-bit Random ECP Group, as described
   in [RFC5903].  The format of the signature in the SIG payload MUST be
   as specified in [RFC4754].

5.3.7.6.  SIG_ALG_ECDSA-384

   This algorithm specifies the 384-bit Random ECP Group, as described
   in [RFC5903].  The format of the signature in the SIG payload MUST be
   as specified in [RFC4754].

5.3.7.7.  SIG_ALG_ECDSA-521

   This algorithm specifies the 521-bit Random ECP Group, as described
   in [RFC5903].  The format of the signature in the SIG payload MUST be
   as specified in [RFC4754].

5.3.8.  SIG_KEY_LENGTH

   The SIG_KEY_LENGTH class specifies the length of the SIG payload key
   in bits.

5.4.  Group Associated Policy

   A GCKS may have group-specific policy that is not distributed in an
   SA TEK or SA KEK.  Some of this policy is relevant to all group
   members, and some is sender-specific policy for a particular group
   member.  The former can be distributed in either a GROUPKEY-PULL or
   GROUPKEY-PUSH exchange, whereas the latter MUST only be sent in a
   GROUPKEY-PULL exchange.  Additionally, a group member sometimes has
   the need to make policy requests for resources of the GCKS in a
   GROUPKEY-PULL exchange.  GDOI distributes this associated group
   policy and policy requests in the Group Associated Policy (GAP)
   payload.

   The GAP payload can be distributed by the GCKS as part of the SA



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   payload.  It follows any SA KEK payload, and is placed before any SA
   TEK payloads.  In the case that group policy does not include an SA
   KEK, the SA Attribute Next Payload field in the SA payload MAY
   indicate the SA GAP payload.

   The GAP payload can be optionally included by a group member in
   message 3 of the GROUPKEY-PULL exchange in order to make policy
   requests.

   The SA GAP payload is defined 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! Next Payload  !   RESERVED    !        Payload Length         !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !               Group Associated Policy Attributes              ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

   The SA GAP payload fields are defined as follows:

   o  Next Payload (1 octet) -- Identifies the next payload present in
      the GROUPKEY-PULL or the GROUPKEY-PUSH message.  The only valid
      next payload type for this message is an SA TEK or zero to
      indicate there are no more security association attributes.

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

   o  Payload Length (2 octets) -- Length of this payload, including the
      SA GAP header and Attributes.

   o  Group Associated Policy Attributes (variable) -- Contains
      attributes following the format defined in Section 3.3 of RFC
      2408.

   Several group associated policy attributes are defined in this memo.
   An GDOI implementation MUST abort if it encounters an attribute or
   capability that it does not understand.  The values for these
   attributes are included in the IANA Considerations section of this
   memo.

5.4.1.  ACTIVATION_TIME_DELAY/DEACTIVATION_TIME_DELAY

   Section 4.2.1 of RFC 5374 specifies a key rollover method that
   requires two values be given it from the group key management
   protocol.  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



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   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 that it should deactivate SAs that are
   destroyed by the re-key event.  The value is in seconds.

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

5.4.2.  SENDER_ID_REQUEST

   The SENDER_ID_REQUEST attribute is used by a group member to request
   SIDs during the GROUPKEY-PULL message, and includes a count of how
   many SID values it desires.

5.5.  SA TEK Payload

   The SA TEK (SAT) payload 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! Next Payload  !   RESERVED    !         Payload Length        !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! Protocol-ID   !       TEK Protocol-Specific Payload           ~
       +-+-+-+-+-+-+-+-+                                               ~
       ~                                                               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

   The SAT Payload fields are defined as follows:

   o Next Payload (1 octet) -- Identifies the next payload for the
   GROUPKEY-PULL or the GROUPKEY-PUSH message.  The only valid next
   payload types for this message are another SAT Payload or zero to
   indicate there are no more security association attributes.

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

   o Payload Length (2 octets) -- Length of this payload, 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



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             Protocol ID                       Value
             -----------                       -----
             RESERVED                            0
             GDOI_PROTO_IPSEC_ESP                1
             GDOI_PROTO_IPSEC_AH                TBD-5
             Standards Action                   3-127
             Private Use                      128-255

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

5.5.1.  GDOI_PROTO_IPSEC_ESP/GDOI_PROTO_IPSEC_AH

   The TEK Protocol-Specific payload 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !    Protocol   !  SRC ID Type  !         SRC ID Port           !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !SRC ID Data Len!          SRC Identification Data              ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! DST ID Type   !         DST ID Port           !DST ID Data Len!
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! DST Identification Data                                       ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! Transform ID  !                        SPI                    !
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       !      SPI      !       RFC 2407 SA Attributes                  ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

   The SAT Payload fields are defined as follows:

   o Protocol (1 octet) -- Value describing an IP protocol ID (e.g.,
   UDP/TCP).  A value of zero means that the Protocol field should be
   ignored.

   o SRC ID Type (1 octet) -- Value describing the identity information
   found in the SRC Identification Data field.  Defined values are
   specified by the IPsec Identification Type section in the IANA
   isakmpd-registry [ISAKMP-REG].

   o SRC ID Port (2 octets) -- Value specifying a port associated with
   the source Id.  A value of zero means that the SRC ID Port field
   should be ignored.

   o SRC ID Data Len (1 octet) -- Value specifying the length of the SRC



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   Identification Data field.

   o SRC Identification Data (variable length) -- Value, as indicated by
   the SRC ID Type.  Set to three bytes of zero for multiple-source
   multicast groups that use a common TEK for all senders.

   o DST ID Type (1 octet) -- Value describing the identity information
   found in the DST Identification Data field.  Defined values are
   specified by the IPsec Identification Type section in the IANA
   isakmpd-registry [ISAKMP-REG].

   o DST ID Prot (1 octet) -- Value describing an IP protocol ID (e.g.,
   UDP/TCP).  A value of zero means that the DST Id Prot field should be
   ignored.

   o DST ID Port (2 octets) -- Value specifying a port associated with
   the source Id.  A value of zero means that the DST ID Port field
   should be ignored.

   o DST ID Data Len (1 octet) -- Value specifying the length of the DST
   Identification Data field.

   o DST Identification Data (variable length) -- Value, as indicated by
   the DST ID Type.

   o Transform ID (1 octet) -- Value specifying which ESP or AH
   transform is to be used.  The list of valid values is defined in the
   IPsec ESP or IPsec AH Transform Identifiers section of the IANA
   isakmpd-registry [ISAKMP-REG].

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

   o RFC 2407 Attributes -- ESP and AH Attributes from RFC 2407 Section 
   4.5.  The GDOI supports all IPsec DOI SA Attributes for
   GDOI_PROTO_IPSEC_ESP and GDOI_PROTO_IPSEC_AH excluding the Group
   Description (section 4.5 of [RFC2407], which MUST NOT be sent by a
   GDOI implementation and is ignored by a GDOI implementation if
   received.  The following attributes MUST be supported by an
   implementation supporting ESP and AH: SA Life Type, SA Life Duration,
   Encapsulation Mode.  An implementation supporting ESP must also
   support the Authentication Algorithm attribute if the ESP transform
   includes authentication/ The Authentication Algorithm attribute of
   the IPsec DOI is group authentication in GDOI.

5.5.1.1.  New IPsec Security Association Attributes

   The Multicast Extensions to the Security Architecture for the
   Internet Protocol (RFC 5374) introduces new requirements for a group



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   key management system distributing IPsec policy.  It also defines new
   attributes as part of the Group Security Policy Database (GSPD).
   These attributes describe policy that a group key management system
   must convey to a group member in order to support those extensions.
   The GDOI SA TEK payload distributes IPsec policy using IPsec security
   association attributes defined in [ISAKMP-REG].  This section defines
   how GDOI can convey the new attributes as IPsec Security Association
   Attributes.

5.5.1.1.1.  Address Preservation

   Applications use the extensions in RFC 5374 to copy the IP addresses
   into the outer IP header when encapsulating an IP packet as an IPsec
   tunnel mode packet.  This allows an IP multicast packet to continue
   to be routed as a IP multicast packet.  In order for the GDOI group
   member to appropriately set up the GSPD, the GCKS must provide that
   policy to the group member.

   Depending on group policy, several address preservation methods are
   possible: no address preservation ("None"), preservation of the
   original source address ("Source-Only"), preservation of the original
   destination address ("Destination-Only"), or both addresses ("Source-
   And-Destination").  The IANA Considerations section of this memo adds
   the "Address Preservation" security association attribute.  If this
   attribute is not included in a GDOI SA TEK payload provided by a
   GCKS, then Source-And-Destination address preservation has been
   defined for the SA TEK.

5.5.1.1.2.  SA Direction

   Depending on group policy, an IPsec SA created from an SA TEK payload
   may be required in one or both directions.  SA TEK policy used by
   multiple senders is required to be installed in both the sending and
   receiving direction ("Symmetric"), whereas SA TEK for a single sender
   should only be installed in the receiving direction by receivers
   ("Receiver-Only") and in the sending direction by the sender
   ("Sender-Only").  The IANA Considerations section of this memo adds
   the "SA Direction" security association attribute.

   An SA TEK payload that does not include the SA Direction attribute is
   treated as a Symmetric IPsec SA.  Note that unless Symmetric may be
   the only value that can be meaningfully described for an SA TEK
   distributed in an GROUPKEY-PUSH message.  Alternatively, Receiver-
   Only could be distributed, but group senders would need to be
   configured to not receive GROUPKEY-PUSH messages in order to retain
   their role.





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5.5.2.  Other Security Protocols

   Besides ESP and AH, GDOI should serve to establish SAs for secure
   groups needed by other Security Protocols that operate at the
   transport, application, and internetwork layers.  These other
   Security Protocols, however, are in the process of being developed or
   do not yet exist.

   The following information needs to be provided for a Security
   Protocol to the GDOI.

   o  The Protocol-ID for the particular Security Protocol

   o  The SPI Size

   o  The method of SPI generation

   o  The transforms, attributes and keys needed by the Security
      Protocol

   All Security Protocols must provide the information in the bulleted
   list above to guide the GDOI specification for that protocol.
   Definitions for the support of those Security Protocols in GDOI will
   be specified in separate documents.

   A Security Protocol MAY protect traffic at any level of the network
   stack.  However, in all cases applications of the Security Protocol
   MUST protect traffic which MAY be shared by more than two entities.

5.6.  Key Download Payload

   The Key Download Payload contains group keys for the group specified
   in the SA 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 SA 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
       ! Next Payload  !   RESERVED    !         Payload 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 RESERVED (1 octet) -- 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
   both TEK and Rekey arrays being passed in this data block.

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


        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.











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                          Key Download Type        Value
                          -----------------        -----
                          RESERVED                   0
                          TEK                        1
                          KEK                        2
                          LKH                        3
                          SID                       TBD-7
                          Standards Action          4-127
                          Private Use             128-255

   "KEK" is a single key whereas LKH is an array of key-encrypting keys.

   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 SAK or SAT 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.

5.6.1.  TEK Download Type

   The following attributes may be present in a TEK Download Type.
   Exactly one attribute matching each type sent in the SAT payload MUST
   be present.  The attributes must follow the format defined in ISAKMP
   (Section 3.3 of [RFC2408]).  In the table, attributes defined as TV
   are marked as Basic (B); attributes defined as TLV are marked as
   Variable (V).















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                TEK Class                 Value      Type
                ---------                 -----      ----
                RESERVED                     0
                TEK_ALGORITHM_KEY            1        V
                TEK_INTEGRITY_KEY            2        V
                TEK_SOURCE_AUTH_KEY          3        V
                Standards Action            4-127
                Private Use               128-255
                Unassigned                256-32767

   If no TEK key packets are included in a Registration KD payload, the
   group member can expect to receive the TEK as part of a Re-key SA.
   At least one TEK must be included in each Re-key KD payload.
   Multiple TEKs may be included if multiple streams associated with the
   SA are to be rekeyed.

   When an algorithm specification specifies the format of the keying
   material, the value transported in the KD payload for that key is
   passed according to that specification.  The keying material may
   contain information besides a key.  For example, The Use of Galois/
   Counter Mode (GCM) in IPsec Encapsulating Security Payload (ESP)
   [RFC4106] defines a salt value as part of KEYMAT.

5.6.1.1.  TEK_ALGORITHM_KEY

   The TEK_ALGORITHM_KEY class declares that the encryption key for this
   SPI is contained as the Key Packet Attribute.  The encryption
   algorithm that will use this key was specified in the SAT payload.

   In the case that the algorithm requires multiple keys (e.g., 3DES),
   all keys will be included in one attribute.

   DES keys will consist of 64 bits (the 56 key bits with parity bit).
   Triple DES keys will be specified as a single 192 bit attribute
   (including parity bits) in the order that the keys are to be used for
   encryption (e.g., DES_KEY1, DES_KEY2, DES_KEY3).

5.6.1.2.  TEK_INTEGRITY_KEY

   The TEK_INTEGRITY_KEY class declares that the integrity key for this
   SPI is contained as the Key Packet Attribute.  The integrity
   algorithm that will use this key was specified in the SAT payload.
   Thus, GDOI assumes that both the symmetric encryption and integrity
   keys are pushed to the member.  HMAC-SHA1 keys will consist of 160
   bits[RFC2404], HMAC-MD5 keys will consist of 128 bits[RFC2403].
   HMAC-SHA2 and AES-GMAC keys will have a key length equal to the
   output length of the hash functions [RFC4868][RFC4543].




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5.6.1.3.  TEK_SOURCE_AUTH_KEY

   The TEK_SOURCE_AUTH_KEY class declares that the source authentication
   key for this SPI is contained in the Key Packet Attribute.  The
   source authentication algorithm that will use this key was specified
   in the SAT payload.

5.6.2.  KEK Download Type

   The following attributes may be present in a KEK Download Type.
   Exactly one attribute matching each type sent in the SAK payload MUST
   be present.  The attributes must follow the format defined in ISAKMP
   (Section 3.3 of [RFC2408]).  In the table, attributes defined as TV
   are marked as Basic (B); attributes defined as TLV are marked as
   Variable (V).


                KEK Class                 Value      Type
                ---------                 -----      ----
                RESERVED                     0
                KEK_ALGORITHM_KEY            1        V
                SIG_ALGORITHM_KEY            2        V
                Standards Action            3-127
                Private Use               128-255
                Unassigned                256-32767

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

5.6.2.1.  KEK_ALGORITHM_KEY

   The KEK_ALGORITHM_KEY class declares the encryption key for this SPI
   is contained in the Key Packet Attribute.  The encryption algorithm
   that will use this key was specified in the SAK payload.

   If the mode of operation for the algorithm requires an IV, an
   explicit IV MUST be included in the KEK_ALGORITHM_KEY before the
   actual key.

5.6.2.2.  SIG_ALGORITHM_KEY

   The SIG_ALGORITHM_KEY class declares that the public key for this SPI
   is contained in the Key Packet Attribute, which may be useful when no
   public key infrastructure is available.  The signature algorithm that
   will use this key was specified in the SAK payload.






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5.6.3.  LKH Download Type

   The LKH key packet is comprised of attributes representing different
   nodes 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 ISAKMP
   (Section 3.3 of [RFC2408]).  In the table, attributes defined as TV
   are marked as Basic (B); attributes defined as TLV are marked as
   Variable (V).


                KEK Class                 Value      Type
                ---------                 -----      ----
                RESERVED                     0
                LKH_DOWNLOAD_ARRAY           1        V
                LKH_UPDATE_ARRAY             2        V
                SIG_ALGORITHM_KEY            3        V
                Standards Action            4-127
                Private Use               128-255
                Unassigned                256-32767

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

5.6.3.1.  LKH_DOWNLOAD_ARRAY

   This attribute is used to download a set of keys to a group member.
   It MUST NOT be included in a GROUPKEY-PUSH message KD payload if the
   GROUPKEY-PUSH is sent to more than the 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !  LKH Version  !          # of LKH Keys        !  RESERVED     !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                             LKH Keys                          !
      ~                                                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The KEK_LKH attribute fields are defined as follows:




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   o LKH version (1 octet) -- Version of the LKH data format.  Must be
   one.

   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:


       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            !    Key Type   !    RESERVED   !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        Key Creation Date                      !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                       Key expiration Date                     !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                           Key Handle                          !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                                                               !
      ~                            Key Data                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o LKH ID (2 octets) -- Identity of the LKH node.  A GCKS is free to
   choose the ID in an implementation-specific manner (e.g., the
   position of this key in a binary tree structure used by LKH).

   o Key Type (1 octet) -- Encryption algorithm for which this key data
   is to be used.  This value is specified in Section 5.3.3.

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

   o Key Creation Date (4 octets) -- Time value of when this key data
   was originally generated.  A time value of zero indicates that there
   is no time before which this key is not valid.

   o Key Expiration Date (4 octets) -- Time value of when this key is no
   longer valid for use.  A time value of zero indicates that this key
   does not have an expiration time.

   o Key Handle (4 octets) -- Value assigned by the GCKS to uniquely
   identify a key within an LKH ID.  Each new key distributed by the
   GCKS for this node will have a key handle identity distinct from
   previous or successive key handles specified for this node.

   o Key Data (variable length) -- Key data, which is dependent on the



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   Key Type algorithm for its format.  If the mode of operation for the
   algorithm requires an IV, an explicit IV MUST be included in the Key
   Data field prepended to the actual key.

   The Key Creation Date and Key expiration Dates MAY be zero.  This is
   necessary in the case where time synchronization within the group is
   not possible.

   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 order from the leaf, culminating in the group KEK.

5.6.3.2.  LKH_UPDATE_ARRAY

   This attribute is used to update the keys for a group.  It is most
   likely to be included in a GROUPKEY-PUSH 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 the previous section.

   There may be any number of UPDATE_ARRAY attributes included in a KD
   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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !  LKH Version  !          # of LKH Keys        !  RESERVED     !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !            LKH ID             !           RESERVED2           !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                           Key Handle                          !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                            LKH Keys                           !
      ~                                                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o LKH version (1 octet) -- Version of the LKH data format.  Must be
   one.

   o Number of LKH Keys (2 octets) -- Number of distinct LKH keys in
   this sequence.

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

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




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   o RESERVED2 (2 octets) -- Unused, set to zero.

   o Key Handle (4 octets) -- Value assigned by the GCKS to uniquely
   identify the key within the LKH ID used to encrypt the first LKH Key.

   The LKH Keys are as defined in the previous section.  The LKH Key
   structures contain keys along the path of the key tree in 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.

5.6.3.3.  SIG_ALGORITHM_KEY

   The SIG_ALGORITHM_KEY class declares that the public key for this SPI
   is contained in the Key Packet Attribute, which may be useful when no
   public key infrastructure is available.  The signature algorithm that
   will use this key was specified in the SAK payload.

5.6.4.  SID Download Type

   This attribute is used to download one or more Sender-ID (SID) values
   for the exclusive use of a group member.


                SID Class                 Value      Type
                ---------                 -----      ----
                RESERVED                     0
                NUMBER_OF_SID_BITS           1        B
                SID_VALUE                    2        V
                Standards Action           3-128
                Private Use              129-255
                Unassigned               256-32767

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

5.6.4.1.  NUMBER_OF_SID_BITS

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







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5.6.4.2.  SID_VALUE

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

5.6.4.3.  Group Member 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 no longer 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 NOT process an SID Download Type KD payload
   present in a GROUPKEY-PUSH message.

5.6.4.4.  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
   GROUPKEY-PUSH message, because distributing the same sender-specific
   policy to more than one group member will reduce the security of the
   group.

5.7.  Sequence Number Payload

   The Sequence Number Payload (SEQ) provides an anti-replay protection
   for GROUPKEY-PUSH messages.  Its use is similar to the Sequence
   Number field defined in the IPsec ESP protocol [RFC4303].








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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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ! Next Payload  !   RESERVED    !         Payload Length        !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                      Sequence Number                          !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Sequence Number 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 RESERVED (1 octet) -- Unused, set to zero.

   o Payload Length (2 octets) -- Length in octets of the current
   payload, including the generic payload header.  Must be a value of 8.

   o Sequence Number (4 octets) -- This field contains a monotonically
   increasing counter value for the group.  It is initialized to zero by
   the GCKS, and incremented in each subsequently-transmitted message.
   Thus the first packet sent for a given Rekey SA will have a Sequence
   Number of 1.  The GDOI implementation keeps a sequence counter as an
   attribute for the Rekey SA and increments the counter upon receipt of
   a GROUPKEY-PUSH message.  The current value of the sequence number
   must be transmitted to group members as a part of the Registration SA
   payload.  A group member must keep a sliding receive window.  The
   window must be treated as in the ESP protocol [RFC4303] Section
   3.4.3.

5.8.  Nonce

   The data portion of the Nonce payload (i.e., Ni_b and Nr_b included
   in the HASHs) MUST be a value between 8 and 128 bytes.

5.9.  Delete

   There are times the GCKS may want to signal to receivers to delete
   SAs, for example at the end of a broadcast.  Deletion of keys may be
   accomplished by sending an ISAKMP Delete payload (Section 3.15 of
   [RFC2408]) as part of a GDOI GROUPKEY-PUSH message.

   One or more Delete payloads MAY be placed following the SEQ payload
   in a GROUPKEY-PUSH message.  If a GCKS has no further SAs to send to
   group members, the SA and KD payloads MUST be omitted from the
   message.




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   The following fields of the Delete Payload are further defined as
   follows:

   o The Domain of Interpretation field contains the GDOI DOI.

   o The Protocol-Id field contains TEK protocol id values defined in
   Section 5.5 of this document.  To delete a KEK SA, the value of zero
   MUST be used as the protocol id.  Note that only one protocol id
   value can be defined in a Delete payload.  If a TEK SA and a KEK SA
   must be deleted, they must be sent in different Delete payloads.

   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 policy 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, followed by another delete payload with a spi of
   zero and protocol_id of zero, indicating that the KEK SA should be
   deleted.






























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6.  Algorithm Selection

   For GDOI implementations to interoperate, they must support one or
   more security algorithms in common.  This section specifies the
   security algorithm implementation requirements for standards-
   conformant GDOI implementations.  In all cases the choices are
   intended to maintain at least 112 bits of security [SP.800-131].

   Algorithms not referenced in this section MAY be used.

6.1.  KEK

   These tables list the algorithm selections for values related to the
   KEK.
                Requirement   KEK Management Algorithm
                -----------   ---------------------
                SHOULD        LKH

                Requirement   KEK Algorithm (notes)
                -----------   ---------------------
                MUST          KEK_ALG_AES with 128-bit keys
                SHOULD NOT    KEK_ALG_DES  (1)

                Requirement   KEK Signature Hash Algorithm (notes)
                -----------   ------------------------------------
                MUST          SIG_HASH_SHA256
                SHOULD        SIG_HASH_SHA1 (2)
                SHOULD NOT    SIG_HASH_MD5 (3)

                Requirement   KEK Signature Algorithm (notes)
                -----------   -------------------------------
                MUST          SIG_ALG_RSA with 2048-bit keys

   Notes:

   (1)  DES, with its small key size and corresponding security strength
        is of questionable security for general use

   (2)  The use of SIG_HASH_SHA1 as a signature hash algorithm used with
        GROUPKEY-PUSH messages remains safe at the time of this writing,
        and is a widely deployed signature hash algorithm.

   (3)  Although a real weakness with second preimage resistance with
        MD5 has not been found at the time of this writing, the security
        strength of MD5 has been shown to be rapidly declining over time
        and it's use should be understood and carefully weighed.





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6.2.  TEK

   The following table lists the requirements for Security Protocol
   support for an implementation.

                Requirement   KEK Management Algorithm
                -----------   ---------------------
                MUST          GDOI_PROTO_IPSEC_ESP











































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7.  Security Considerations

   GDOI is a security association (SA) management protocol for groups of
   senders and receivers.  This protocol performs authentication of
   communicating protocol participants (Group Member, Group Controller/
   Key Server).  It provides confidentiality of key management messages,
   and it provides source authentication of those messages.  GDOI
   includes defenses against man-in-middle, connection hijacking,
   replay, reflection, and denial-of-service (DOS) attacks on unsecured
   networks.  GDOI assumes the network is not secure and may be under
   the complete control of an attacker.

   GDOI assumes that the group members and GCKS are secure even though
   the network is insecure.  GDOI ultimately establishes keys among
   members of a group, which MUST be trusted to use those keys in an
   authorized manner according to group policy.  An GDOI entity
   compromised by an attacker may reveal the secrets necessary to
   eavesdrop on group traffic and/or take the identity of a group
   sender, so host security is of the utmost important once.  The latter
   threat could be mitigated by using source origin authentication in
   the Data-Security SAs (e.g., the use of RSA signatures [RFC4359] or
   TESLA [RFC4082]).  The choice of Data-Security SAs is a matter of
   group policy and is not within the scope of this memo.

   There are three phases of GDOI as described in this document: an
   ISAKMP Phase 1 protocol, the GROUPKEY-PULL exchange protected by the
   ISAKMP Phase 1 protocol, and the GROUPKEY-PUSH message.  Each phase
   is considered separately below.

7.1.  ISAKMP Phase 1

   GDOI uses the Phase 1 exchanges defined in [RFC2409] to protect the
   GROUPKEY-PULL exchange.  Therefore all security properties and
   considerations of those exchanges (as noted in [RFC2409]) are
   relevant for GDOI.

   GDOI may inherit the problems of its ancestor protocols [FS00], such
   as identity exposure, absence of unidirectional authentication, or
   stateful cookies [PK01].

7.1.1.  Authentication

   Authentication is provided via the mechanisms defined in [RFC2409],
   namely Pre-Shared Keys or Public Key encryption.







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7.1.2.  Confidentiality

   Confidentiality is achieved in Phase 1 through a Diffie-Hellman
   exchange that provides keying material, and through negotiation of
   encryption transforms.

   The Phase 1 protocol will be protecting encryption and integrity keys
   sent in the GROUPKEY-PULL protocol.  The strength of the encryption
   used for Phase 1 SHOULD exceed that of the keys send in the GROUPKEY-
   PULL protocol.

7.1.3.  Man-in-the-Middle Attack Protection

   A successful man-in-the-middle or connection-hijacking attack foils
   entity authentication of one or more of the communicating entities
   during key establishment.  GDOI relies on Phase 1 authentication to
   defeat man-in-the-middle attacks.

7.1.4.  Replay/Reflection Attack Protection

   In a replay/reflection attack, an attacker captures messages between
   GDOI entities and subsequently forwards them to a GDOI entity.
   Replay and reflection attacks seek to gain information from a
   subsequent GDOI message response or seek to disrupt the operation of
   a GDOI member or GCKS entity.  GDOI relies on the Phase 1 nonce
   mechanism in combination with a hash-based message authentication
   code to protect against the replay or reflection of previous key
   management messages.

7.1.5.  Denial of Service Protection

   A denial of service attacker sends messages to a GDOI entity to cause
   that entity to perform unneeded message authentication operations.
   GDOI uses the Phase 1 cookie mechanism to identify spurious messages
   prior to cryptographic hash processing.  This is a "weak" form of
   denial of service protection in that the GDOI entity must check for
   good cookies, which can be successfully imitated by a sophisticated
   attacker.  The Phase 1 cookie mechanism is stateful, and commits
   memory resources for cookies.

7.2.  GROUPKEY-PULL Exchange

   The GROUPKEY-PULL exchange allows a group member to request SAs and
   keys from a GCKS.  It runs as a "phase 2" protocol under protection
   of the Phase 1 security association.






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7.2.1.  Authentication

   Peer authentication is not required in the GROUPKEY-PULL protocol.
   It is running in the context of the Phase 1 protocol, which has
   previously authenticated the identity of the peer.

   Message authentication is provided by HASH payloads in each message,
   where the HASH is defined to be over SKEYID_a (derived in the Phase 1
   exchange), the ISAKMP Message-ID, and all payloads in the message.
   Because only the two endpoints of the exchange know the SKEYID_a
   value, this provides confidence that the peer sent the message.

7.2.2.  Confidentiality

   Confidentiality is provided by the Phase 1 security association,
   after the manner described in [RFC2409].

7.2.3.  Man-in-the-Middle Attack Protection

   Message authentication (described above) includes a secret known only
   to the group member and GCKS when constructing a HASH payload.  This
   prevents man-in-the-middle and connection-hijacking attacks because
   an attacker would not be able to change the message undetected.

7.2.4.  Replay Protection

   A GROUPKEY-PULL message identifies its messages using a cookie pair
   from the Phase 1 exchange that precedes it.  A GROUPKEY-PULL message
   with invalid cookies will be discarded.  Therefore, GDOI messages
   that are not associated with a current GDOI session will be discarded
   without further processing.

   Replayed GDOI messages that are associated with a current GDOI
   session will be decrypted and authenticated.  The M-ID in the HDR
   identifies a session.  Replayed packets will be processed according
   to the state machine of that session.  Packets not matching that
   state machine will be discarded without processing.

7.2.5.  Denial of Service Protection

   GCKS implementations SHOULD keep a record of recently received
   GROUPKEY-PULL messages (e.g., a hash of the packet) and reject
   messages that have already been processed.  This provides Denial of
   Service and Replay Protection of previously sent messages.  An
   implementation MAY choose to rate-limit the receipt of GDOI messages
   in order to mitigate avoid overloading its computational resources.

   The GCKS SHOULD NOT perform any computationally expensive tasks



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   before receiving a HASH with its own nonce included.  The GCKS MUST
   NOT update the group management state (e.g., LKH key tree, SID-
   counter) until it receives the third message in the exchange with a
   valid HASH payload including its own nonce.

7.2.6.  Authorization

   A GCKS implementation SHOULD maintain an authorization list of
   authorized group members.  Group members MUST specifically list each
   authorized GCKS in its Group Peer Authorization Database (GPAD)
   [RFC5374].

7.3.  GROUPKEY-PUSH Exchange

   The GROUPKEY-PUSH exchange is a single message that allows a GCKS to
   send SAs and keys to group members.  This is likely to be sent to all
   members using an IP multicast group.  This message provides an
   efficient rekey and group membership adjustment capability.

7.3.1.  Authentication

   The GROUPKEY-PULL exchange distributes a public key that is used for
   message authentication.  The GROUPKEY-PUSH message is digitally
   signed using the corresponding private key held by the GCKS.  This
   digital signature provides source authentication for the message.
   Thus, GDOI protects the GCKS from impersonation in group
   environments.

7.3.2.  Confidentiality

   The GCKS encrypts the GROUPKEY-PUSH message with an encryption key
   that was distributed in the GROUPKEY-PULL exchange or a previous
   GROUPKEY-PUSH exchange.  The encryption key may be a simple KEK, or
   the result of a group management method (e.g., LKH) calculation.

7.3.3.  Man-in-the-Middle Attack Protection

   This combination of confidentiality and message authentication
   services protects the GROUPKEY-PUSH message from man-in-middle and
   connection-hijacking attacks.

7.3.4.  Replay/Reflection Attack Protection

   The GROUPKEY-PUSH message includes a monotonically increasing
   sequence number to protect against replay and reflection attacks.  A
   group member will discard sequence numbers associated with the
   current KEK SPI that have the same or lower value as the most
   recently received replay number.



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   Implementations SHOULD keep a record (e.g., a hash value) of recently
   received GROUPKEY-PUSH messages and reject duplicate messages prior
   to performing cryptographic operations.  This enables an early
   discard of the replayed messages.

7.3.5.  Denial of Service Protection

   A cookie pair identifies the security association for the GROUPKEY-
   PUSH message.  The cookies thus serve as a weak form of denial-of-
   service protection for the GROUPKEY-PUSH message.

   The digital signature used for message authentication has a much
   greater computational cost than a message authentication code and
   could amplify the effects of a denial of service attack on GDOI
   members who process GROUPKEY-PUSH messages.  The added cost of
   digital signatures is justified by the need to prevent GCKS
   impersonation: If a shared symmetric key were used for GROUPKEY-PUSH
   message authentication, then GCKS source authentication would be
   impossible and any member would be capable of GCKS impersonation.

   The potential of the digital signature amplifying a denial of service
   attack is mitigated by the order of operations a group member takes,
   where the least expensive cryptographic operation is performed first.
   The group member first decrypts the message using a symmetric cipher.
   If it is a validly formed message then the sequence number is checked
   against the replay window.  Only if the sequence number is valid is
   the digital signature verified.  Thus in order for a denial of
   service attack to be mounted, an attacker would need to know both the
   symmetric encryption key used for confidentiality, and a valid
   sequence number.  Generally speaking this means only current group
   members can effectively deploy a denial of service attack.

7.4.  Forward and Backward Access Control

   Through GROUPKEY-PUSH, the GDOI supports group management methods
   such as LKH (section 5.4 of [RFC2627]) 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).  The concepts "forward access
   control" and "backward access control" have also been described as
   "perfect forward security" and "perfect backward security"
   respectively 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 GDOI, but are not specified as a part of this
   document.



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7.4.1.  Forward Access Control Requirements

   When group membership is altered using a group management algorithm
   new Data-security SAs are usually also needed.  New SAs 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
   Data-security SAs MUST NOT be included in a GROUPKEY-PUSH message
   which changes group membership.  This is required because the new
   Data-security SAs are not protected with the new KEK.  Instead, two
   sequential GROUPKEY-PUSH messages must be sent by the GCKS; the first
   changing the KEK, and the second (protected with the new KEK)
   distributing the new Data-security SAs.

   Note that in the above sequence, although the new KEK can effectively
   deny access to the group to some group members they will be able to
   view the new KEK policy.  If forward access control policy for the
   group includes keeping the KEK policy secret as well as the KEK
   itself secret, then two GROUPKEY-PUSH messages changing the KEK must
   occur before the new Data-security SAs are transmitted.

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

7.4.2.  Backward Access Control Requirements

   If backward access control is a desired property of the group, a new
   member MUST NOT be given Data-security SAs that were used prior to it
   joining the group.  This can be accomplished if the GCKS provides
   only the Rekey SA to the new member in a GROUPKEY-PULL exchange,
   followed by a GROUPKEY-PUSH message that both deletes current Data-
   security SAs, and provides new replacement Data-security SAs.  The
   new group member will effectively join the group at such time as the
   existing members begin sending on the Data-security SAs.

   If there is a possibility that the new group member has stored
   GROUPKEY-PUSH messages delivered prior to joining the group, then the
   above procedure is not sufficient.  In this case, to achieve backward
   access control the GCKS needs to return a new Rekey SA to the group
   member in a GROUPKEY-PULL exchange rather than the existing one.  The
   GCKS would subsequently deliver two GROUPKEY-PUSH messages.  The
   first, intended for existing group members, distributes the new
   Rekey-SA to existing members.  The GCKS would then deliver the second
   GROUPKEY-PUSH message using the new Rekey-SA that both deletes



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   current Data-security SAs, and provides new replacement Data-security
   SAs.  Both preexisting and new members would process the second
   GROUPKEY-PUSH message, and all would be able to communicate using the
   new Data-security SAs.

7.5.  Derivation of keying material

   A GCKS distributes keying material associated with Data-Security SAs
   and the Rekey SA.  Because these security associations are used by a
   set of group members, this keying material is not related to any pair
   wise connection, and there is no requirement in The Multicast Group
   Security Architecture [RFC3740] for group members to permute group
   keying material.  Because the GCKS is solely responsible for the
   generation of the keying material, the GCKS MUST derive the keying
   material using a strong random number generator.  Because there are
   no interoperability concerns with key generation, no method is
   prescribed in GDOI.


































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8.  IANA Considerations

   This memo requests IANA to make several additions to existing
   registries, and to add sever new GDOI registries.  When the new
   registries are added, the following terms are to be applied as
   described in the Guidelines for Writing an IANA Considerations
   Section in RFCs [RFC5226]: Standards Action, and Private Use.

8.1.  Additions to current registries

   The GDOI KEK Attribute named SIG_HASH_ALGORITHM [GDOI-REG] should be
   assigned several new Algorithm Type values from the RESERVED space to
   represent the SHA-256, SHA-384, and SHA-512 hash algorithms as
   defined in [FIPS.180-2.2002].  The new algorithm names should be
   SIG_HASH_SHA256, SIG_HASH_SHA384, and SIG_HASH_SHA512 respectively
   and have the values of TBD-2, TBD-3, and TBD-4 respectively.

   The GDOI KEK Attributed named SIG_ALGORITHM [GDOI-REG] should be
   assigned a new Algorithm Type value from the RESERVED space to
   represent the RSA PSS encoding type.  The new algorithm name should
   be SIG_ALG_RSA_PSS, and has the value of TBD-6.

   A new GDOI SA TEK type Protocol-ID type [GDOI-REG] should be assigned
   from the RESERVED space.  The new algorithm id should be called
   GDOI_PROTO_IPSEC_AH, refers to the IPsec AH encapsulation, and has a
   value of TBD-5.

   A new Next Payload Type [ISAKMP-REG] should be assigned.  The new
   type is called "SA Group Associated Policy (GAP)", and has a value of
   TBD-1.

   A new Key Download Type Section 5.6 should be assigned.  The new type
   is called "SID", and has a value of TBD-7.

8.2.  New registries

   A new namespace should be created in the GDOI Payloads registry
   [GDOI-REG] to describe SA GAP Payload Values.  The following rules
   apply to define the attributes in SA SSA Payload Values:












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              Attribute Type         Value       Type
              ----                   -----       ----
              RESERVED                 0
              ACTIVATION_TIME_DELAY    1          B
              DEACTIVATION_TIME_DELAY  2          B
              SENDER_ID_REQUEST        3          B
              Standards Action        4-127
              Private Use           128-255
              Unassigned            256-32767

   A new IPsec Security Association Attribute [ISAKMP-REG] defining the
   preservation of IP addresses is needed.  The attribute class is
   called "Address Preservation", and it is a Basic type.  The following
   rules apply to define the values of the attribute:

              Name                      Value
              ----                      -----
              Reserved                  0
              None                      1
              Source-Only               2
              Destination-Only          3
              Source-And-Destination    4
              Standards Action         5-61439
              Private Use          61440-65535

   A new IPsec Security Association Attribute [ISAKMP-REG] defining the
   SA direction is needed.  The attribute class is called "SA
   Direction", and it is a Basic type.  The following rules apply to
   define the values of the attribute:

              Name                      Value
              ----                      -----
              Reserved                  0
              Sender-Only               1
              Receiver-Only             2
              Symmetric                 3
              Standards Action         4-61439
              Private Use          61440-65535

   When the SID "Key Download Type" (described in the previous section)
   has a set of attributes.  The attributes must follow the format
   defined in ISAKMP (Section 3.3 of [RFC2408]).  In the table,
   attributes defined as TV are marked as Basic (B); attributes defined
   as TLV are marked as Variable (V).







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                SID Class                 Value      Type
                ---------                 -----      ----
                RESERVED                     0
                NUMBER_OF_SID_BITS           1        B
                SID_VALUE                    2        V
                Standards Action           3-128
                Private Use              129-255
                Unassigned               256-32767

8.3.  Cleanup of existing registries

   Several existing GDOI Payloads registries do not use the terms in RFC
   5226 and/or do not describe the entire range of possible values.  The
   following sections correct these registries.

8.3.1.  Pop Algorithm

   Values 4-127 are to be designated Standards Action.  Values 256-32767
   are to be added and designated Unassigned.

8.3.2.  KEK Attributes

   Values 9-127 are to added and designated Standards Action.  Values
   128-255 are to be added and designated Private Use. Values 256-32767
   are to be added and designated Unassigned.

8.3.3.  KEK_MANAGEMENT_ALGORITHM

   Values 2-127 are to be designated Standards Action.  Values 256-65535
   are to be added and designated Unassigned.

8.3.4.  KEK_ALGORITHM

   Values 4-127 are to be designated Standards Action.  Values 256-65535
   are to be added and designated Unassigned.

8.3.5.  SIG_HASH_ALGORITHM

   Values 3-127 are to be designated Standards Action.  Values 256-65535
   are to be added and designated Unassigned.

8.3.6.  SIG_ALGORITHM

   Values 4-127 are to be designated Standards Action.  Values 256-65535
   are to be added and designated Unassigned.






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8.3.7.  SA TEK Payload Values

   Values 2-127 are to be designated Standards Action.

8.3.8.  Key Download Types

   Values 4-127 are to be designated Standards Action.

8.3.9.  TEK Download Type

   Values 4-127 are to be added and designated Standards Action.  Values
   128-255 are to be added and designated Private Use. Values 256-32767
   are to be added and designated Unassigned.

8.3.10.  KEK Download Type

   Values 3-127 are to be designated Standards Action.  Values 128-255
   are to be added and designated Private Use. Values 256-32767 are to
   be added and designated Unassigned.

8.3.11.  LKH Download Type

   Values 4-127 are to be designated Standards Action.  Values 256-32767
   are to be added and designated Unassigned.



























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9.  Acknowledgements

   This text updates RFC 3547, and the authors wish to thank Mark
   Baugher and Hugh Harney for their extensive contributions that led to
   this updated version of GDOI.

   The authors are grateful to Catherine Meadows for her careful review
   and suggestions for mitigating the man-in-the-middle attack she had
   previously identified.  Yoav Nir and Vincent Roca provided many
   useful technical and editorial comments and suggestions for
   improvement.








































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10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              December 2005.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005.

   [RFC5374]  Weis, B., Gross, G., and D. Ignjatic, "Multicast
              Extensions to the Security Architecture for the Internet
              Protocol", RFC 5374, November 2008.

   [RFC6054]  McGrew, D. and B. Weis, "Using Counter Modes with
              Encapsulating Security Payload (ESP) and Authentication
              Header (AH) to Protect Group Traffic", RFC 6054,
              November 2010.

10.2.  Informative References

   [FIPS.180-2.2002]
              National Institute of Standards and Technology, "Secure
              Hash Standard", FIPS PUB 180-2, August 2002, <http://
              csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf>.

   [FIPS186-3]
              "Digital Signature Standard (DSS)", United States of
              America, National Institute of Science and
              Technology Federal Information Processing Standard (FIPS)
              186-2, June 2009.

   [FIPS197]  "Advanced Encryption Standard (AES)", United States of
              America, National Institute of Science and
              Technology Federal Information Processing Standard (FIPS)
              197, November 2001.

   [FIPS46-3]
              "Data Encryption Standard (DES)", United States of
              America, National Institute of Science and
              Technology Federal Information Processing Standard (FIPS)
              46-3, October 1999.

   [FIPS81]   "DES Modes of Operation", United States of America,
              National Institute of Science and Technology Federal



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              Information Processing Standard (FIPS) 81, December 1980.

   [FS00]     Ferguson, N. and B. Schneier, Counterpane, "A
              Cryptographic Evaluation of IPsec",
              <http://www.counterpane.com/ipsec.html>.

   [GDOI-REG]
              Internet Assigned Numbers Authority, "Group Domain of
              Interpretation (GDOI) Payload Type Values", IANA Registry,
              December 2004,
              <http://www.iana.org/assignments/gdoi-payloads>.

   [HD03]     Hardjono, T. and L. Dondeti, "Multicast and Group
              Security", Artech House Computer Security Series, ISBN
              1-58053-342-6, 2003.

   [I-D.weis-gdoi-mac-tek]
              Weis, B. and S. Rowles, "GDOI Generic Message
              Authentication Code Policy", draft-weis-gdoi-mac-tek-02
              (work in progress), March 2011.

   [ISAKMP-REG]
              "'Magic Numbers' for ISAKMP Protocol",
              <http://www.iana.org/assignments/isakmp-registry>.

   [MP04]     Meadows, C. and D. Pavlovic, "Deriving, Attacking, and
              Defending the GDOI Protocol", ESORICS 2004 pp. 53-72,
              September 2004.

   [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>.

   [PK01]     Perlman, R. and C. Kaufman, "Analysis of the IPsec Key
              Exchange Standard", WET-ICE conference , 2001,
              <http://sec.femto.org/wetice-2001/papers/radia-paper.pdf>.

   [RFC2403]  Madson, C. and R. Glenn, "The Use of HMAC-MD5-96 within
              ESP and AH", RFC 2403, November 1998.




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   [RFC2404]  Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within
              ESP and AH", RFC 2404, November 1998.

   [RFC2407]  Piper, D., "The Internet IP Security Domain of
              Interpretation for ISAKMP", RFC 2407, November 1998.

   [RFC2408]  Maughan, D., Schneider, M., and M. Schertler, "Internet
              Security Association and Key Management Protocol
              (ISAKMP)", RFC 2408, November 1998.

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, November 1998.

   [RFC2627]  Wallner, D., Harder, E., and R. Agee, "Key Management for
              Multicast: Issues and Architectures", RFC 2627, June 1999.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3686]  Housley, R., "Using Advanced Encryption Standard (AES)
              Counter Mode With IPsec Encapsulating Security Payload
              (ESP)", RFC 3686, January 2004.

   [RFC3740]  Hardjono, T. and B. Weis, "The Multicast Group Security
              Architecture", RFC 3740, March 2004.

   [RFC3947]  Kivinen, T., Swander, B., Huttunen, A., and V. Volpe,
              "Negotiation of NAT-Traversal in the IKE", RFC 3947,
              January 2005.

   [RFC4046]  Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,
              "Multicast Security (MSEC) Group Key Management
              Architecture", RFC 4046, April 2005.

   [RFC4082]  Perrig, A., Song, D., Canetti, R., Tygar, J., and B.
              Briscoe, "Timed Efficient Stream Loss-Tolerant
              Authentication (TESLA): Multicast Source Authentication
              Transform Introduction", RFC 4082, June 2005.

   [RFC4106]  Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
              (GCM) in IPsec Encapsulating Security Payload (ESP)",
              RFC 4106, June 2005.




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   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4309]  Housley, R., "Using Advanced Encryption Standard (AES) CCM
              Mode with IPsec Encapsulating Security Payload (ESP)",
              RFC 4309, December 2005.

   [RFC4359]  Weis, B., "The Use of RSA/SHA-1 Signatures within
              Encapsulating Security Payload (ESP) and Authentication
              Header (AH)", RFC 4359, January 2006.

   [RFC4430]  Sakane, S., Kamada, K., Thomas, M., and J. Vilhuber,
              "Kerberized Internet Negotiation of Keys (KINK)",
              RFC 4430, March 2006.

   [RFC4543]  McGrew, D. and J. Viega, "The Use of Galois Message
              Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543,
              May 2006.

   [RFC4754]  Fu, D. and J. Solinas, "IKE and IKEv2 Authentication Using
              the Elliptic Curve Digital Signature Algorithm (ECDSA)",
              RFC 4754, January 2007.

   [RFC4868]  Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
              384, and HMAC-SHA-512 with IPsec", RFC 4868, May 2007.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5903]  Fu, D. and J. Solinas, "Elliptic Curve Groups modulo a
              Prime (ECP Groups) for IKE and IKEv2", RFC 5903,
              June 2010.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 5996, September 2010.

   [SP.800-131]
              Barker, E. and A. Roginsky, "Recommendation for the
              Transitioning of Cryptographic Algorithms and Key
              Lengths", United States of America, National Institute of
              Science and Technology DRAFT NIST Special Publication 800-
              131, June 2010.

   [SP.800-38A]
              Dworkin, M., "Recommendation for Block Cipher Modes of
              Operation", United States of America, National Institute



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              of Science and Technology NIST Special Publication 800-38A
              2001 Edition, December 2001.

















































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Appendix A.  Extending GDOI

A.1.  Alternate GDOI Phase 1 protocols

   This section describes a manner in which other protocols could be
   used as GDOI Phase 1 protocols in place of the ISAKMP Phase 1
   protocol.  However, they are not specified as a part of this
   document.  A separate document MUST be written in order for another
   protocol to be used as a GDOI Phase 1 protocol.

   Other possible phase 1 protocols are also described in [RFC4046].

   Any GDOI phase 1 protocol MUST satisfy the requirements specified in
   Section 2 of this document.

A.1.1.  IKEv2 Exchange

   Version 2 of the IKE protocol (IKEv2) [RFC5996] has been published.
   That protocol simplifies IKE processing, and combines the two phases
   of IKE.  An IKEv2 Phase 1 negotiates an IPsec SA during phase 1,
   which was not possible in IKE.  However, IKEv2 also defines a phase 2
   protocol.  The phase 2 protocol is protected by the Phase 1, similar
   in concept to how IKE Quick Mode is protected by the IKE Phase 1
   protocols in [RFC2409].

   It would be possible to define GDOI as a phase 2 protocol protected
   by an IKEv2 initial exchange.  Alternatively, it would be possible to
   define a new protocol re-using some of the IKEv2 initial exchange
   (e.g., IKE_SA_INIT).

A.1.2.  KINK Protocol

   The Kerberized Internet Negotiation of Keys (KINK) [RFC4430] has
   defined a method of encapsulating an IKEv1 Quick Mode [RFC2409]
   encapsulated in Kerberos KRB_AP_REQ and KRB_AP_REP payloads.  KINK
   provides a low-latency, computationally inexpensive, easily managed,
   and cryptographically sound method of setting up IPsec security
   associations.

   The KINK message format includes a DOI field in the KINK header.  The
   [RFC4430] document defines the DOI for the IPsec DOI.

   A new DOI for KINK could be defined which would encapsulate a
   GROUPKEY-PULL exchange in the Kerberos KRB_AP_REQ and KRB_AP_REP
   payloads.  As such, GDOI would benefit from the computational
   efficiencies of KINK.





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A.2.  Supporting new SA TEK types

   Not all secure multicast or multimedia applications can use IPsec ESP
   or AH.  Many Real Time Transport Protocol applications, for example,
   require security above the IP layer to preserve RTP header
   compression efficiencies and transport-independence [RFC3550].
   Alternatively, GDOI can distribute message authentication code (MAC)
   policy and keys for legacy applications that have defined their own
   security associations [I-D.weis-gdoi-mac-tek].

   In order to add a new data security protocol, a new RFC MUST specify
   the data-security SA parameters conveyed by GDOI for that security
   protocol; these parameters are listed in Section 5.5.2 of this
   document.

   Data security protocol SAs MUST protect group traffic.  GDOI provides
   no restriction on whether that group traffic is transmitted as
   unicast or multicast packets.

































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Appendix B.  GDOI Applications

   GDOI can be used to distribute keys for several secure multicast
   applications, where different applications have different key
   management requirements.  This section outlines two example ways that
   GDOI can be used.  Other examples can be found in Section 10 of
   [HD03].

   A simple application is secure delivery of periodic multicast content
   over an organization's IP network, perhaps a multicast video
   broadcast.  Assuming the content delivery time frame is bounded and
   the group membership is not expected to change over time, there is no
   need for group policy to include a GROUPKEY-PUSH exchange, and
   there's no need for the GCKS to distribute a Re-key SA.  Thus, the
   GDOI GCKS may only need to distribute a single set of Data-Security
   SAs to protect the time-bounded broadcast.

   In contrast, a persistent IP multicast application (e.g., stock-
   ticker delivery service) may have many group members, where the group
   membership changes over time.  A periodic change of Data-security SAs
   may be desirable, and the potential for change in group membership
   requires the use of a group management method enabling de-
   authorization of group members.  The GDOI GCKS will distribute the
   current set of Data-Security SAs and a Re-key SA to registering group
   members.  It will then deliver regularly-scheduled GROUPKEY-PUSH
   protocol delivering the new SAs for the group.  Additionally, the
   group membership on the GCKS may be frequently adjusted, which will
   result in GROUPKEY-PUSH exchange delivering a new Rekey SAs protected
   by a group management method.  Each GROUPKEY-PUSH may include Data-
   security SAs and/or a Rekey SA.

   In each example the relevant policy is defined on the GCKS and
   relayed to group members using the GROUPKEY-PULL and/or GROUPKEY-PUSH
   protocols.  Specific policy choices configured by the GCKS
   administrator depends on each application.
















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Appendix C.  Significant Changes from RFC 3547

   The following significant changes have been made from RFC 3547.

   o  The Proof of Possession (POP) payload was removed from the
      GROUPKEY-PULL exchange.  It provided an alternate form of
      authorization, but its use was underspecified.  Furthermore,
      Meadows and Pavlovic [MP04] discussed a man-in-the-middle attack
      on the POP authorization method, which would require changes to
      its semantics.  No known implementation of RFC 3547 supported the
      POP payload, so it was removed.  Removal of the POP payload
      obviated the need for the CERT payload in that exchange and it was
      removed as well.

   o  The Key Exchange Payloads (KE_I, KE_R) payloads were removed from
      the GROUPKEY-PULL exchange.  However, the specification for
      computing keying material for the additional encryption function
      in RFC 3547 is faulty.  Furthermore, it has been observed that
      because the GDOI registration message uses strong ciphers and
      provides authenticated encryption, additional encryption of the
      keying material in a GDOI registration message provides negligible
      value.  Therefore, the use of KE payloads is deprecated in this
      memo.

   o  The Certificate Payload (CERT) was removed from the GROUPKEY-PUSH
      exchange.  The use of this payload was underspecified.  In all
      known use cases, the public key of used to verify the GROUPKEY-
      PUSH payload is distributed directly from the key server as part
      of the GROUPKEY-PULL exchange.

   o  Supported cryptographic algorithms were changed to meet current
      guidance.  Implementations are required to support AES with 128-
      bit keys to encrypt the rekey message, and SHA-256 for
      cryptographic signatures.  The use of DES is deprecated.

   o  New protocol support for AH.

   o  New protocol definitions were added to conform to the most recent
      Security Architecture for the Internet Protocol [RFC4301] and the
      Multicast Extensions to the Security Architecture for the Internet
      Protocol[RFC5374].  This includes addition of the GAP payload.

   o  New protocol definitions and semantics were added to support Using
      Counter Modes with ESP and AH to Protect Group Traffic[RFC6054].

   o  Specification to IANA to better clarify the use of the GDOI
      Payloads registry.




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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


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

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


   Thomas Hardjono
   MIT
   77 Massachusetts Ave.
   Cambridge, Massachusets  02139
   USA

   Phone: +1-781-729-9559
   Email: hardjono@mit.edu





















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