path: root/doc/rfc/rfc6407.txt

Internet Engineering Task Force (IETF)                           B. Weis
Request for Comments: 6407                                     S. Rowles
Obsoletes: 3547                                            Cisco Systems
Category: Standards Track                                    T. Hardjono
ISSN: 2070-1721                                                      MIT
                                                            October 2011


                   The Group Domain of Interpretation

Abstract

   This document describes 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.  This document replaces RFC 3547.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6407.

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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




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RFC 6407                          GDOI                      October 2011


   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
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Notation  . . . . . . . . . . . . . . . . . .  5
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
     1.3.  Acronyms and Abbreviations . . . . . . . . . . . . . . . .  7
   2.  GDOI Phase 1 Protocol  . . . . . . . . . . . . . . . . . . . .  8
     2.1.  DOI value  . . . . . . . . . . . . . . . . . . . . . . . .  8
     2.2.  UDP port . . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  GROUPKEY-PULL Exchange . . . . . . . . . . . . . . . . . . . .  9
     3.1.  Authorization  . . . . . . . . . . . . . . . . . . . . . .  9
     3.2.  Messages . . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.3.  Group Member Operations  . . . . . . . . . . . . . . . . . 12
     3.4.  GCKS Operations  . . . . . . . . . . . . . . . . . . . . . 13
     3.5.  Counter-Modes of Operation . . . . . . . . . . . . . . . . 14
   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  . . . . . . . . . . . . . . . . . 19
     5.1.  Identification Payload . . . . . . . . . . . . . . . . . . 20
     5.2.  Security Association Payload . . . . . . . . . . . . . . . 20
     5.3.  SA KEK Payload . . . . . . . . . . . . . . . . . . . . . . 21
     5.4.  Group Associated Policy  . . . . . . . . . . . . . . . . . 27
     5.5.  SA TEK Payload . . . . . . . . . . . . . . . . . . . . . . 30
     5.6.  Key Download Payload . . . . . . . . . . . . . . . . . . . 34
     5.7.  Sequence Number Payload  . . . . . . . . . . . . . . . . . 44
     5.8.  Nonce  . . . . . . . . . . . . . . . . . . . . . . . . . . 44
     5.9.  Delete . . . . . . . . . . . . . . . . . . . . . . . . . . 45
   6.  Algorithm Selection  . . . . . . . . . . . . . . . . . . . . . 45
     6.1.  KEK  . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
     6.2.  TEK  . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 47
     7.1.  ISAKMP Phase 1 . . . . . . . . . . . . . . . . . . . . . . 47
     7.2.  GROUPKEY-PULL Exchange . . . . . . . . . . . . . . . . . . 48



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RFC 6407                          GDOI                      October 2011


     7.3.  GROUPKEY-PUSH Exchange . . . . . . . . . . . . . . . . . . 50
     7.4.  Forward and Backward Access Control  . . . . . . . . . . . 51
     7.5.  Derivation of Keying Material  . . . . . . . . . . . . . . 53
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 53
     8.1.  Additions to Current Registries  . . . . . . . . . . . . . 53
     8.2.  New Registries . . . . . . . . . . . . . . . . . . . . . . 54
     8.3.  Cleanup of Existing Registries . . . . . . . . . . . . . . 55
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 57
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 57
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 57
     10.2. Informative References . . . . . . . . . . . . . . . . . . 58
   Appendix A.  GDOI Applications . . . . . . . . . . . . . . . . . . 62
   Appendix B.  Significant Changes from RFC 3547 . . . . . . . . . . 62

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 Internet Security Association and Key Management Protocol
   (ISAMKP) [RFC2408] Domain of Interpretation (DOI), a group key
   management system.  The GDOI distributes security associations (SAs)
   for IPsec Authentication Header (AH) [RFC4302] and Encapsulating
   Security Payload (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 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 (Section 2.3 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 redefine) the
   Phase 1 security association definition from the Internet DOI
   [RFC2407], [RFC2409].  Although RFCs 2407, 2408, and 2409 were
   obsoleted by [RFC4306] (and subsequently [RFC5996]), they are used by
   this document because the protocol definitions remain relevant for
   ISAKMP protocols other than IKEv2.




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RFC 6407                          GDOI                      October 2011


   The GDOI includes two new Phase 2 ISAKMP exchanges (protocols), as
   well as necessary new payload definitions to the ISAKMP standard
   (Section 2.1 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 ("Rekey SA") are included in the group policy
       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.

























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RFC 6407                          GDOI                      October 2011


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

                   Figure 1. Group Key Management Model

   Although the GROUPKEY-PUSH protocol specified by this document can be
   used to refresh the Rekey 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.

   GDOI defines several payload types used to distribute policy and
   keying material within the GROUPKEY-PULL and GROUPKEY-PUSH protocols:
   Security Association (SA), SA KEK, SA TEK, Group Associated Policy
   (GAP), Sequence Number (SEQ), and Key Download (KD).  Format and
   usage of these payloads are defined in later sections of this memo.

   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 Rekey
   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].

   Rekey SA.  The security policy protecting a GROUPKEY-PUSH protocol.

   SA Attribute Payload  A payload that follows the Security Association
         payload and that describes group security attributes associated
         with the security association.  SA Attribute payloads include
         the SAK, SAT, and GAP payloads.

   Security Parameter Index  An arbitrary value that is used by a
         receiver to identify a security association such as an IPsec
         ESP Security Association or a Rekey SA.

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










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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

   ESP   IP Encapsulating Security Payload

   GCKS  Group Controller/Key Server

   GDOI  Group Domain of Interpretation

   GAP   Group Associated Policy Payload

   GM    Group Member

   GSPD  Group Security Policy Database

   IV    Initialization Vector

   KD    Key Download Payload

   KEK   Key Encryption Key

   LKH   Logical Key Hierarchy

   SA    Security Association

   SAK   SA KEK Payload

   SEQ   Sequence Number Payload

   SAT   SA TEK Payload

   SID   Sender-ID

   SPI   Security Parameter Index

   SSIV  Sender-Specific IV

   TEK   Traffic Encryption Key



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RFC 6407                          GDOI                      October 2011


   TLV   Type/Length/Value

   TV    Type/Value

2.  GDOI Phase 1 Protocol

   The GDOI GROUPKEY-PULL exchange is a Phase 2 protocol that MUST be
   protected by a Phase 1 protocol.  The Phase 1 protocol can be any
   protocol that 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.

   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.  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.

2.2.  UDP port

   IANA has assigned port 848 for the use of GDOI; this allows for an
   implementation to use separate ISAKMP implementations to service GDOI
   and the Internet Key Exchange Protocol (IKE) [RFC5996].  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 Rekey 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

   It is important that a group member explicitly trust entities that it
   expects to act as a GCKS for a particular group.  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].  A group member MUST specifically list each
   authorized GCKS in its Group Peer Authorization Database (GPAD)
   [RFC5374].  A group member MUST ensure that the Phase 1 identity of
   the GCKS is an authorized GCKS.

   It is important that a GCKS explicitly authorize group members before
   providing them with group policy and keying material.  A GCKS
   implementation SHOULD have a method of authorizing group members
   (e.g., by maintaining an authorization list).  When the GCKS performs
   authorization, it MUST use the Phase 1 identity to authorize the
   GROUPKEY-PULL request for group policy and keying material.

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 ISAKMP HASH payloads
   [RFC2408] included in GROUPKEY-PULL messages.  When using the Phase 1
   defined in this document, SKEYID_a is derived according to [RFC2409].
   Each GROUPKEY-PULL message hashes a uniquely defined set of values
   (described below) and includes the result in the HASH payload.
   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.






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RFC 6407                          GDOI                      October 2011


   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.

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

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

                     Figure 2. GROUPKEY-PULL Exchange

   Figure 2 demonstrates the four messages that are part of a GROUPKEY-
   PULL exchange.  HDR is an ISAKMP header payload that uses the Phase 1
   cookies and a message identifier (M-ID) as in ISAKMP.  Following each
   HDR is a set of payloads conveying requests (messages 1 and 3
   originated by the group member), or group policy and/or keying
   material (messages 2 and 4 originated by the GCKS).

   Hashes are computed in the manner described within [RFC2409].  The
   HASH computation for each message is unique; it is shown in Figure 2
   and below as HASH(n) where (n) represents the GROUPKEY-PULL message
   number.  Each HASH calculation is a pseudo-random function ("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)




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   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.
   Each SPI is 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 Rekey 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.

   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 ensures that the GM will not
   accept GROUPKEY-PUSH 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 exchange.  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 Rekey 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].




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RFC 6407                          GDOI                      October 2011


   Next Payload identifies an ISAKMP or GDOI payload (see Section 5).

   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]).  The Commit flag is not useful because there is no
   synchronization between the GROUPKEY-PULL exchange and the data
   traffic protected by the policy distributed by the GROUPKEY-PULL
   exchange.

3.3.  Group Member Operations

   Before a GM contacts the GCKS, it needs to 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.

   To construct the first GDOI message, the GM chooses Ni, 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 (including its
   SA Attribute payloads) .  The SA payload contains policy describing
   the security protocol and cryptographic protocols used by the group.
   This policy describes the Rekey 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 notifying the GCKS with an
   ISAKMP Informational Exchange containing a Delete payload.

   When constructing the third GDOI message, it first reviews each Data-
   Security SA given to it.  If any describe 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 requests the required number of
   Sender-IDs for its exclusive use within the counter mode nonce as
   described in Section 5.4 of this document.  The GM then 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 included in the
   SEQ payload asserts the lowest acceptable sequence number present in
   a future GROUPKEY-PUSH message.  But if the KEK associated with this
   sequence number had been previously installed, due to the



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   asynchronous processing of GROUPKEY-PULL and GROUPKEY-PUSH messages,
   this sequence number may be lower than the sequence number contained
   in the most recently received GROUPKEY-PUSH message.  In this case,
   the sequence number value in the SEQ payload MUST 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 SPI in each key packet to SPI
   values previously sent in the SA payloads.  Once TEKs 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 a sequence number not less than the one
   distributed in the SEQ payload.  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.

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)
   and 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
   Attribute payloads (i.e, 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 the 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



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   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:

   o  The GCKS distributes a unique key for each Data-Security SA.

   o  The GCKS uses the method described in [RFC6054], which assigns
      each sender a portion of the IV space by provisioning each sender
      with one or more unique SID values.

   When at least one Data-Security SA included in the group policy
   includes a counter-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).



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   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 a SID-counter, which records which SIDs have
       been allocated.  SIDs are allocated sequentially, with the first
       SID allocated to be zero.

   2.  Each time a 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 a 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.

   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 which Data-Security counter-mode nonce values 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.





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   Using the method above, at no time can two group members use the same
   IV values with the same Data-Security SA key.

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 Rekey SA KEK or KEK array, and/or it creates a new Data-
   Security SA.

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

        * Protected by the Rekey SA KEK; encryption occurs after HDR

                      Figure 3. GROUPKEY-PUSH Message

   HDR is defined below.  The SEQ payload is defined in Section 5
   ("Payloads").  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 Rekey SA
   and/or Data-Security SAs as described in Section 5, 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 octets) 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 (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 Rekey SA,
   which has a new cookie pair.  When the KD payload carries a new SA
   KEK attribute (Section 5.3), a Rekey 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



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   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
   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, the cookie pair is completely determined by the GCKS.
   The cookie pair in the GDOI ISAKMP header identifies the Rekey 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).

   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 Section 3.1 of
   [RFC2408].  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.





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   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 that is 1 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
   meaning to an 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
   KEKs (or a KEK update array) are included.  A KEK update array is
   created by first determining which group members have been excluded,
   generating new keys as necessary, and then distributing LKH update
   arrays sufficient to provide the new KEK to remaining group members
   (see Section 5.4.1 of [RFC2627] for details).  TEKs 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.  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.  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




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

5.  Payloads and Defined Values

   This document specifies use of several ISAKMP payloads, which are
   defined in accordance with [RFC2408].  The following payloads are
   used as defined in [RFC2408].

                  Next Payload Type            Value
                  -----------------            -----
                  Hash Payload (HASH)            8
                  Signature (SIG)                9

   The following payloads are extended or further specified.

                  Next Payload Type            Value
                  -----------------            -----
                  Security Association (SA)      1
                  Identification (ID)            5
                  Nonce (N)                     10
                  Delete (D)                    12

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

                  Next Payload Type                Value
                  -----------------                -----
                  SA KEK (SAK)                      15
                  SA TEK (SAT)                      16
                  Key Download (KD)                 17
                  Sequence Number (SEQ)             18
                  Group Associated Policy (GAP)     22

   All multi-octet fields in GDOI payloads representing integers are
   laid out in big endian order (also known as "most significant byte
   first" or "network byte order").




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   All payloads including an ISAKMP Generic Payload Header create a
   Payload Length field that includes the length of the generic payload
   header (Section 3.2 of [RFC2408]).

5.1.  Identification Payload

   The Identification payload is defined in [RFC2408].  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 IPv4 or IPv6 multicast address, 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 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 [RFC2408].  For the
   GDOI, it is used by the GCKS to assert security attributes for both
   Rekey and Data-Security SAs.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
      ! Next Payload  !   RESERVED    !         Payload Length        !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                              DOI                              !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
      !                           Situation                           !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
      ! SA Attribute Next Payload     !          RESERVED2            !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

                  Figure 4. Security Association Payload

   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 an SA Attribute payload; it MUST be the
      next payload following the Security Association type payload.

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



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   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 (2 octets) -- MUST be the code for an SA
      Attribute payload type.  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.  SA Attribute Payloads

   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 Attribute payloads MUST be: SAK,
   GAP, and SATs.

   This latitude regarding SA Attribute payloads allows various group
   policies to be accommodated.  For example, if the group policy does
   not require the use of a Rekey SA, the GCKS would not need to send an
   SA KEK attribute to the group member since all SA updates would be
   performed using the Registration SA.  Alternatively, group policy
   might use a Rekey SA but choose to download a KEK to the group member
   only as part of the Registration SA.  Therefore, the KEK policy (in
   the SA KEK attribute) would not be necessary as part of the Rekey 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-wide policy, such
   as instructions as to when to activate and deactivate 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.



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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        !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
      !    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                         ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

                         Figure 5. SA KEK Payload

   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
      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) [PROT-REG] for the GROUPKEY-PUSH 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
      ISAKMP 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
      MUST be ignored.




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   o  SRC ID Data Len (1 octet) -- Value specifying the length (in
      octets) 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
      ISAKMP registry [ISAKMP-REG].

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

   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 (in
      octets) 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
      is 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.

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

   o  KEK Attributes -- Contains KEK policy attributes associated with
      the group.  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).












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                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
                RESERVED                     8        B
                Unassigned                  9-127
                Private Use               128-255
                Unassigned                256-32767

   The KEK_ALGORITHM and SIG_ALGORITHM attributes MUST be included;
   others are OPTIONAL and are included depending on group policy.  The
   KEK_MANAGEMENT_ALGORITHM attribute MUST NOT be included in a
   GROUPKEY-PULL message, and MUST be ignored if present.

5.3.1.  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.

                  KEK Management Type               Value
                  -------------------               -----
                  Reserved                            0
                  LKH                                 1
                  Unassigned                         2-127
                  Private Use                      128-255
                  Unassigned                       256-65535

5.3.1.1.  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]

5.3.2.  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.



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

   If a KEK_MANAGEMENT_ALGORITHM is defined that specifies 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 that are included
   as part of the management.

5.3.2.1.  KEK_ALG_DES

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

5.3.2.2.  KEK_ALG_3DES

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

5.3.2.3.  KEK_ALG_AES

   This type specifies AES as described in [FIPS197].  The mode of
   operation for AES is CBC as defined in [SP.800-38A].

5.3.3.  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).






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5.3.4.  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 4-octet number defining a
   valid time period in seconds.

5.3.5.  SIG_HASH_ALGORITHM

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

                   Algorithm Type     Value
                   --------------     -----
                   Reserved             0
                   SIG_HASH_MD5         1
                   SIG_HASH_SHA1        2
                   SIG_HASH_SHA256      3
                   SIG_HASH_SHA384      4
                   SIG_HASH_SHA512      5
                   Unassigned          6-127
                   Private Use       128-255
                   Unassigned        256-65535

   The SHA hash algorithms are defined in the Secure Hash Standard
   [FIPS180-3.2008].

   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 OPTIONAL in a SAK payload.

5.3.6.  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_ECDSA-256     4
                   SIG_ALG_ECDSA-384     5
                   SIG_ALG_ECDSA-521     6
                   Unassigned           7-127
                   Private Use        128-255
                   Unassigned         256-65535



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5.3.6.1.  SIG_ALG_RSA

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

5.3.6.2.  SIG_ALG_DSS

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

5.3.6.3.  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.

5.3.6.4.  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].

5.3.6.5.  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].

5.3.6.6.  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].

5.3.7.  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



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   GROUPKEY-PULL exchange.  GDOI distributes this associated group
   policy and the policy requests in the Group Associated Policy (GAP)
   payload.

   The GAP payload can be distributed by the GCKS as part of the SA
   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 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 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              ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

                           Figure 6. GAP Payload

   The 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
      GAP header and Attributes.

   o  Group Associated Policy Attributes (variable) -- Contains
      attributes following the format defined in 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).








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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
              Unassigned              4-127
              Private Use           128-255
              Unassigned            256-32767

   Several group associated policy attributes are defined in this memo.
   A 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 [RFC5374] 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
   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 rekey event.  The value is in seconds.

   The values of ATD and DTD are independent.  However, the most
   effective policy will have the DTD value be the larger value, as this
   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.










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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           ~
      +-+-+-+-+-+-+-+-+                                               ~
      ~                                                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

                         Figure 7. SA TEK 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.

             Protocol ID                       Value
             -----------                       -----
             RESERVED                            0
             GDOI_PROTO_IPSEC_ESP                1
             GDOI_PROTO_IPSEC_AH                 2
             Unassigned                         3-127
             Private Use                      128-255

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









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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                  ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

                       Figure 8. ESP/AH TEK Payload

   The SAT payload fields are defined as follows:

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

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

   o  SRC Identification Data (variable length) -- Value, as indicated
      by the SRC ID Type.  Set to 3 octets or 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
      ISAKMP registry [ISAKMP-REG].



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

   o  DST ID Data Len (1 octet) -- Value specifying the length (in
      octets) 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 ISAKMP registry [ISAKMP-REG].

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

   o  RFC 2407 Attributes -- ESP and AH Attributes from Section 4.5 of
      [RFC2407].  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, and 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

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





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5.5.1.1.1.  Address Preservation

   Applications use the extensions in [RFC5374] 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.  This attribute also provides
   the necessary policy so that the GDOI group member can appropriately
   set up the GSPD.  The following table defines values for the Address
   Preservation attribute.

              Address Preservation Type               Value
              -------------------------               -----
              Reserved                                  0
              None                                      1
              Source-Only                               2
              Destination-Only                          3
              Source-and-Destination                    4
              Unassigned                               5-61439
              Private Use                          61440-65535

   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").  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
   is defined to be in the sending and/or receiving direction.  The
   following table defines values for the SA Direction attribute.

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

   SA TEK policy used by multiple senders MUST be installed in both the
   sending and receiving direction ("Symmetric"), whereas SA TEK for a
   single sender SHOULD be installed in the receiving direction by
   receivers ("Receiver-Only") and in the sending direction by the
   sender ("Sender-Only").



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   An SA TEK payload that does not include the SA Direction attribute is
   treated as a Symmetric IPsec SA.  Note that Symmetric is the only
   value that can be meaningfully described for an SA TEK distributed in
   a 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.

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 that 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                                ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

                      Figure 9. Key Download Payload

   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
      key packets 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                      ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

                            Figure 10. Key Packet

   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                        4
                          Unassigned                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 a 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).

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




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   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 Rekey SA.  At
   least one TEK must be included in each Rekey 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 bits).
   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 GM.  HMAC-SHA1 keys will consist of 160 bits
   [RFC2404], and 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].

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.







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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
                Unassigned                  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.

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).



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                KEK Class                 Value      Type
                ---------                 -----      ----
                RESERVED                     0
                LKH_DOWNLOAD_ARRAY           1        V
                LKH_UPDATE_ARRAY             2        V
                SIG_ALGORITHM_KEY            3        V
                Unassigned                  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                          !
      ~                                                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 11. LKH Download Array

   The KEK_LKH attribute fields are defined as follows:

   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:






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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !             LKH ID            !    Key Type   !    RESERVED   !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                        Key Creation Date                      !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                       Key Expiration Date                     !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                           Key Handle                          !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      !                                                               !
      ~                            Key Data                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                              Figure 12. LKH Key

   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) -- Unsigned time value defining a
      valid time period in seconds representing the number of seconds
      since 0 hours, 0 minutes, 0 seconds, January 1, 1970, Coordinated
      Universal Time (UTC), without including leap seconds.  [RFC5905].
      This is the time 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) -- Unsigned time value defining a
      valid time period in seconds representing the number of seconds
      since 0 hours, 0 minutes, 0 seconds, January 1, 1970, Coordinated
      Universal Time (UTC), without including leap seconds.  [RFC5905].
      This is the time 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.





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

                        Figure 13. LKH Update Array

   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.





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

   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.

   The SID Download Type does not require an SPI.  When the KD Type is
   SID, the SPI Size field MUST be zero, and the SPI field is omitted.

                SID Class                 Value      Type
                ---------                 -----      ----
                RESERVED                     0
                NUMBER_OF_SID_BITS           1        B
                SID_VALUE                    2        V
                Unassigned                 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.







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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.

5.6.4.2.  SID_VALUE

   The SID_VALUE class declares a single SID value for the exclusive use
   of the 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.

   GROUPKEY-PUSH message may include Data-Security SAs that are
   distributed to the group member for the first time.  A SID previously
   issued to the receiving group member is used with counter-based mode
   of operation Data-Security SAs on which the group member acts as a
   sender.  Because this Data-Security SA has not previously been used
   for transmission, the SSIV field should be set to its starting value.

5.6.4.4.  GCKS Semantics

   If any KD payload includes keying material that is associated with a
   counter-mode of operation, a 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.




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5.7.  Sequence Number Payload

   The Sequence Number (SEQ) Payload 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].

       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                          !
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 14. Sequence Number Payload

   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.

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 octets.









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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.

   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.  Thus, if a TEK SA
      and a KEK SA are to be deleted, their SPI values 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 an 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 an SPI of zero and a Protocol-ID of a TEK
   Protocol-ID value, followed by another delete payload with an SPI
   value of zero and Protocol-ID of zero, indicating that the KEK SA
   should be deleted.

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.







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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 it 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 its use should be understood and carefully weighed.

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.  A 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 measures mitigating unauthorized access are
   of the utmost importance.  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, 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 sent 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 DoS 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 DoS
   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 DoS and
   replay protection of previously sent messages.  An implementation MAY
   choose to rate-limit the receipt of GDOI messages in order to
   mitigate overloading its computational resources.





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   The GCKS SHOULD NOT perform any computationally expensive tasks
   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.  A group member 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




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   current KEK SPI that have the same or lower value as the most
   recently received replay number.

   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 DoS
   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 DoS 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 DoS 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 most recently received sequence number.  Only when the
   sequence number is valid (i.e., it is a larger value than previously
   received) is the digital signature verified and the message further
   processed.  Thus, in order for a DoS 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 DoS
   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].




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

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
   that 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
   its 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



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   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
   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.

8.  IANA Considerations

8.1.  Additions to Current Registries

   The GDOI KEK Attribute named SIG_HASH_ALGORITHM [GDOI-REG] has been
   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 [FIPS180-3.2008].  The new algorithm names are
   SIG_HASH_SHA256, SIG_HASH_SHA384, and SIG_HASH_SHA512, respectively,
   and have the values of 3, 4, and 5, respectively.

   The GDOI KEK Attribute named SIG_ALGORITHM [GDOI-REG] has been
   assigned several new Algorithm Type values from the RESERVED space to
   represent the SIG_ALG_ECDSA-256, SIG_ALG_ECDSA-384, and
   SIG_ALG_ECDSA-521 signature algorithms.  The Algorithm Types values
   are 4, 5, and 6, respectively.

   A new GDOI SA TEK type Protocol-ID type [GDOI-REG] has been assigned
   from the RESERVED space.  The new algorithm ID is called
   GDOI_PROTO_IPSEC_AH, refers to the IPsec AH encapsulation, and has a
   value of 2.

   A new Next Payload Type [ISAKMP-REG] has been assigned.  The new type
   is called "SA Group Associated Policy (GAP)" and has a value of 22.



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   A new Key Download Type Section 5.6 has been assigned.  The new type
   is called "SID" and has a value of 4.

8.2.  New Registries

   A new registry identifying the possible values of GAP Payload Policy
   Attributes (of the form described in Section 3.3 of [RFC2408]) has
   been created in the GDOI Payloads registry [GDOI-REG].  This memo
   defines the following values for this registry:

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

   The registration procedure is Standards Action.  The terms Standards
   Action and Private Use are to be applied as defined in [RFC5226].

   A new IPsec Security Association Attribute [ISAKMP-REG] defining the
   preservation of IP addresses has been registered.  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
              Unassigned               5-61439
              Private Use          61440-65535

   The registration procedure is Standards Action.  The terms Standards
   Action and Private Use are to be applied as defined in [RFC5226].

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






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

   The registration procedure is Standards Action. terms Standards
   Action and Private Use are to be applied as defined in [RFC5226].

   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).

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

   The registration procedure is Standards Action. terms Standards
   Action and Private Use are to be applied as defined in [RFC5226].

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.  The terms Standards
   Action, Unassigned, and Private Use are to be applied as defined in
   [RFC5226].

8.3.1.  Pop Algorithm

   The registration procedure is Standards Action.  Values 4-27 are
   designated Unassigned.  Values 256-32767 have been added and are
   designated Unassigned.








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8.3.2.  KEK Attributes

   The registration procedure is Standards Action.  Values 9-127 have
   been added and are designated Unassigned.  Values 128-255 have been
   added and are designated Private Use.  Values 256-32767 have been
   added and are designated Unassigned.

8.3.3.  KEK_MANAGEMENT_ALGORITHM

   The registration procedure is Standards Action.  Values 2-127 are
   designated Unassigned.  Values 128-255 have been added and designated
   Private Use.  Values 256-65535 have been added and are designated
   Unassigned.

8.3.4.  KEK_ALGORITHM

   The registration procedure is Standards Action.  Values 4-127 are
   designated Unassigned.  Values 256-65535 have been added and are
   designated Unassigned.

8.3.5.  SIG_HASH_ALGORITHM

   The registration procedure is Standards Action.  Values 6-127 are
   designated Unassigned.  Values 256-65535 have been added and are
   designated Unassigned.

8.3.6.  SIG_ALGORITHM

   The registration procedure is Standards Action.  Values 7-127 are
   designated Unassigned.  Values 256-65535 have been added and are
   designated Unassigned.

8.3.7.  SA TEK Payload Values

   The registration procedure is Standards Action.  Values 3-127 are
   designated Unassigned.

8.3.8.  Key Download Types

   The registration procedure is Standards Action.  Values 5-127 are
   designated Unassigned.

8.3.9.  TEK Download Type

   The registration procedure is Standards Action.  Values 4-127 have
   been added and are designated Unassigned.  Values 128-255 have been
   added and are designated Private Use.  Values 256-32767 have been
   added and are designated Unassigned.



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8.3.10.  KEK Download Type

   The registration procedure is Standards Action.  Values 3-127 are
   designated Unassigned.  Values 128-255 have been added and are
   designated Private Use.  Values 256-32767 have been added and are
   designated Unassigned.

8.3.11.  LKH Download Type

   The registration procedure is Standards Action.  Values 4-127 are
   designated Unassigned.  Values 256-32767 have been added and are
   designated Unassigned.

9.  Acknowledgements

   This memo replaces RFC 3547, and the authors wish to thank Mark
   Baugher and Hugh Harney for their extensive contributions that led to
   this newer specification 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, Vincent Roca, Sean Turner, and
   Elwyn Davies provided many useful technical and editorial comments
   and suggestions for improvement.

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.

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

   [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.




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   [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.

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

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

   [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.

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

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

   [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

   [FIPS180-3.2008]
                National Institute of Standards and Technology, "Secure
                Hash Standard", FIPS PUB 180-3, October 2008, <http://
                csrc.nist.gov/publications/fips/fips180-3/
                fips180-3_final.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.





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   [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
                Information Processing Standard (FIPS) 81,
                December 1980.

   [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.

   [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", European Symposium on
                Research in Computer Security (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.iacr.org/archive/crypto2001/21390040.pdf>.

   [OFT]        Sherman, A. and D. McGrew, "Key Establishment in Large
                Dynamic Groups Using One-Way Function Trees", IEEE
                Transactions on Software Engineering, Vol. 29, Issue 5,
                pp. 444-458, May 2003,
                <http://ieeexplore.ieee.org/search/
                freesrchabstract.jsp?tp=&arnumber=1199073>.







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   [PK01]       Perlman, R. and C. Kaufman, "Analysis of the IPsec Key
                Exchange Standard", Enabling Technologies:
                Infrastructure for Collaborative Enterprises, WET ICE
                2001, Proceedings. Tenth IEEE International Workshops on
                IEEE Transactions on Software Engineering, pp. 150-156,
                June 2001, <http://ieeexplore.ieee.org/search/
                freesrchabstract.jsp?tp=&arnumber=953405>.

   [PROT-REG]   "Assigned Internet Protocol Numbers",
                <http://www.iana.org/assignments/protocol-numbers/>.

   [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.

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

   [RFC4306]    Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
                RFC 4306, 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.



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

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

   [RFC5905]    Mills, D., Martin, J., Burbank, J., and W. Kasch,
                "Network Time Protocol Version 4: Protocol and
                Algorithms Specification", RFC 5905, 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
                of Science and Technology, NIST Special Publication
                800-38A 2001 Edition, December 2001.

























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Appendix A.  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 examples of 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
   is no need for the GCKS to distribute a Rekey 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 Rekey SA to registering group
   members.  It will then use regularly scheduled GROUPKEY-PUSH
   exchanges to deliver the new SAs for the group.  Additionally, the
   group membership on the GCKS may be frequently adjusted, which will
   result in a GROUPKEY-PUSH exchange that delivers 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 depend on each application.

Appendix B.  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





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      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) 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 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 support 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 Encapsulating Security Payload (ESP) and
      Authentication Header (AH) to Protect Group Traffic" [RFC6054].

   o  Specification to IANA was added 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, Massachusetts  02139
   USA

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





















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