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Internet Engineering Task Force (IETF)                           B. WeisRequest for Comments: 8263                                 Cisco SystemsCategory: Standards Track                                      U. ManglaISSN: 2070-1721                                    Juniper Networks Inc.                                                                 T. Karl                                                        Deutsche Telekom                                                           N. Maheshwari                                                           November 2017Group Domain of Interpretation (GDOI) GROUPKEY-PUSHAcknowledgement MessageAbstract   The Group Domain of Interpretation (GDOI) includes the ability of a   Group Controller/Key Server (GCKS) to provide a set of current Group   Member (GM) devices with additional security associations (e.g., to   rekey expiring security associations).  This memo adds the ability of   a GCKS to request that the GM devices return an acknowledgement of   receipt of its rekey message and specifies the acknowledgement   method.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 inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8263.Weis, et al.                 Standards Track                    [Page 1]

RFC 8263                    GROUPKEY-PUSH ACK              November 2017Copyright Notice   Copyright (c) 2017 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (https://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1. Introduction ....................................................31.1. Requirements Notation ......................................41.2. Acronyms and Abbreviations .................................42. Acknowledgement Message Request .................................52.1. REKEY_ACK_KEK_SHA256 Type ..................................52.2. REKEY_ACK_LKH_SHA256 Type ..................................62.3. REKEY_ACK_KEK_SHA512 Type ..................................62.4. REKEY_ACK_LKH_SHA512 Type ..................................63. GROUPKEY-PUSH Acknowledgement Message ...........................63.1. HDR ........................................................73.2. HASH .......................................................83.3. SEQ ........................................................93.4. ID .........................................................94. Group Member Operations .........................................95. GCKS Operations ................................................106. Management Considerations ......................................107. Security Considerations ........................................127.1. Protection of the GROUPKEY-PUSH ACK .......................127.2. Transmitting a GROUPKEY-PUSH ACK ..........................137.3. Receiving a GROUPKEY-PUSH ACK .............................138. IANA Considerations ............................................149. References .....................................................159.1. Normative References ......................................159.2. Informative References ....................................16   Acknowledgements ..................................................17   Authors' Addresses ................................................17Weis, et al.                 Standards Track                    [Page 2]

RFC 8263                    GROUPKEY-PUSH ACK              November 20171.  Introduction   The Group Domain of Interpretation (GDOI) [RFC6407] is a group key   management method by which a Group Controller/Key Server (GCKS)   distributes security associations (i.e., cryptographic policy and   keying material) to a set of Group Member (GM) devices.  The GDOI   meets the requirements set forth in [RFC4046] ("Multicast Security   (MSEC) Group Key Management Architecture"), including a Registration   Protocol and a Rekey Protocol.  The GDOI describes the Rekey Protocol   as a GROUPKEY-PUSH message.   A GDOI GCKS uses a GROUPKEY-PUSH message (Section 4 of [RFC6407]) to   alert GMs to updates in policy for the group, including new policy   and keying material, replacement policy and keying material, and   indications of deleted policy and keying material.  Usually, the GCKS   does not require a notification that the GM actually received the   policy.  However, in some cases it is beneficial for a GCKS to be   told by each receiving GM that it received the rekey message and, by   implication, has reacted to the policy contained within.  For   example, a GCKS policy can use the acknowledgements to determine   which GMs are receiving the current group policy and which GMs are no   longer participating in the group.   This memo introduces a method by which a GM returns an   Acknowledgement Message to the GCKS.  Initially, a GCKS requests that   a GM acknowledge GROUPKEY-PUSH messages as part of a distributed   group policy.  Then, as shown in Figure 1, when the GCKS delivers a   GROUPKEY-PUSH message, each GM that honors the GCKS request returns a   GROUPKEY-PUSH Acknowledgement Message.  The rest of this memo   describes this method in detail.                GCKS                          GM1       GM2                 |                             |         |                 |                 +---------->|         |                 |   GROUPKEY-PUSH |           |         |                 |-----------------+           |         |                 |                 |           |         |                 |                 +-------------------->|                 |                             |         |                 |<----------------------------|         |                 |      GROUPKEY-PUSH ACK      |         |                 |                             |         |                 |<--------------------------------------|                 |      GROUPKEY-PUSH ACK      |         |                    Figure 1: GROUPKEY-PUSH Rekey EventWeis, et al.                 Standards Track                    [Page 3]

RFC 8263                    GROUPKEY-PUSH ACK              November 2017   Implementation of the GROUPKEY-PUSH Acknowledgement Message is   OPTIONAL.1.1.  Requirements Notation   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.1.2.  Acronyms and Abbreviations   The following acronyms and abbreviations are used throughout this   document.   ACK   Acknowledgement Message   D     Delete   GCKS  Group Controller/Key Server   GDOI  Group Domain of Interpretation   GM    Group Member   HDR   Header   HMAC  Hashed Message Authentication Code   IV    Initialization Vector   KD    Key Download   KDF   Key Derivation Function   KEK   Key Encryption Key   LKH   Logical Key Hierarchy   MSEC  Multicast Security   PRF   Pseudorandom Function   SA    Security AssociationWeis, et al.                 Standards Track                    [Page 4]

RFC 8263                    GROUPKEY-PUSH ACK              November 2017   SEQ   Sequence Number   SIG   Signature   SPI   Security Parameter Index2.  Acknowledgement Message Request   When a GM is ready to join a group, it contacts the GCKS with a   GROUPKEY-PULL Registration Protocol.  When the GCKS has authenticated   and verified that the GM is an authorized member of the group, it   downloads several sets of policy in a Security Association (SA)   payload.  If the group includes the use of a GROUPKEY-PUSH Rekey   Protocol, the SA payload includes an SA Key Encryption Key (KEK)   payload (Section 5.3 of [RFC6407]).  When necessary, the   GROUPKEY-PUSH Rekey Protocol also contains an SA payload that   includes the SA KEK policy.  The SA KEK policy indicates how the GM   will be receiving and handling the GROUPKEY-PUSH Rekey Protocol.   When the GCKS policy includes the use of the GROUPKEY-PUSH   Acknowledgement Message, the GCKS reports this policy to the GM   within the SA KEK policy.  The GCKS includes a new KEK attribute with   the name KEK_ACK_REQUESTED (9), which indicates that the GM is   requested to return a GROUPKEY-PUSH Acknowledgement Message.   As part of the SA KEK policy, the GCKS specifies information on the   keying material that is used to protect the GROUPKEY-PUSH Rekey   Protocol (e.g., the presence of a KEK management algorithm).  Parts   of this information are used by a GM to derive the ack_key (defined   inSection 3.2), which protects the GROUPKEY-PUSH Acknowledgement   Message.  There are different types of Rekey Acknowledgement   Messages; they share an identical message format but differ in the   keying material used.   The following values of the KEK_ACK_REQUESTED attribute are defined   in this memo.2.1.  REKEY_ACK_KEK_SHA256 Type   This type of Rekey ACK is used when the KEK Download Type   (Section 5.6.2 of [RFC6407]) is part of the group policy.  The prf   (defined inSection 3.2) is PRF-HMAC-SHA-256 [RFC4868].  The base_key   (also defined inSection 3.2) is the KEK_ALGORITHM_KEY used to   decrypt the GROUPKEY-PUSH message.  Note that for some algorithms the   KEK_ALGORITHM_KEY will include an explicit Initialization Vector (IV)   before the actual key (Section 5.6.2.1 of [RFC6407]), but it is not   used in the definition of the base_key.Weis, et al.                 Standards Track                    [Page 5]

RFC 8263                    GROUPKEY-PUSH ACK              November 20172.2.  REKEY_ACK_LKH_SHA256 Type   This type of Rekey ACK can be used when the KEK_MANAGEMENT_ALGORITHM   KEK attribute with a value representing the Logical Key Hierarchy   (LKH) is part of the group policy (Section 5.3.1.1 of [RFC6407]).   The prf is PRF-HMAC-SHA-256.  The base_key is the Key Data field   value taken from the first LKH Key structure in an LKH_DOWNLOAD_ARRAY   attribute (seeSection 5.6.3.1 of [RFC6407]).  This is a secret   symmetric key that the GCKS shares with the GM.  Note that for some   algorithms the LKH Key structure will include an explicit IV before   the actual key (Section 5.6.3.1 of [RFC6407]), but it is not used in   the definition of the base_key.2.3.  REKEY_ACK_KEK_SHA512 Type   This type of Rekey ACK is identical to the REKEY_ACK_KEK_SHA256 Type,   except that the prf is PRF-HMAC-SHA-512 (defined in [RFC4868]).2.4.  REKEY_ACK_LKH_SHA512 Type   This type of Rekey ACK is identical to the REKEY_ACK_LKH_SHA256 Type,   except that the prf is PRF-HMAC-SHA-512 (defined in [RFC4868]).3.  GROUPKEY-PUSH Acknowledgement Message   The GROUPKEY-PUSH message defined in [RFC6407] is reproduced in   Figure 2.  The SA and Key Download (KD) payloads contain the actual   policy and keying material being distributed to the GM.  The Sequence   Number (SEQ) payload contains a sequence number that is used by the   GM for replay protection.  This sequence number defines a unique   rekey message delivered to that GM.  One or more Delete (D) payloads   optionally specify the deletion of the existing group policy.  The   Signature (SIG) payload includes a signature of a hash of the entire   GROUPKEY-PUSH message (excepting the SIG payload octets) before it   has been encrypted.         GM                  GCKS         --                  ----                             <---- HDR*, SEQ, [D,] SA, KD, SIG         * Protected by the Rekey SA KEK; encryption occurs after HDR              Figure 2: GROUPKEY-PUSH Message (fromRFC 6407)Weis, et al.                 Standards Track                    [Page 6]

RFC 8263                    GROUPKEY-PUSH ACK              November 2017   When the GM has received a KEK_ACK_REQUESTED attribute in an SA KEK   and it chooses to respond, it returns the value of the Sequence   Number taken from the GROUPKEY-PUSH message to the GCKS along with   its identity.  This tuple alerts the GCKS that the GM has received   the GROUPKEY-PUSH message and implemented the policy contained   therein.  The GROUPKEY-PUSH Acknowledgement Message is shown in   Figure 3.                      GM                              GCKS                      --                              ----                         HDR, HASH, SEQ, ID   ---->              Figure 3: GROUPKEY-PUSH Acknowledgement Message   The IP header for the GROUPKEY-PUSH Acknowledgement Message is   constructed as if it were a reply to the GROUPKEY-PUSH message.  That   is, the source address of the GROUPKEY-PUSH message becomes the   destination address of the GROUPKEY-PUSH Acknowledgement Message, and   the GM includes its own IP address as the source address of the   GROUPKEY-PUSH Acknowledgement Message.  The source port in the   GROUPKEY-PUSH message UDP header becomes the destination port of the   GROUPKEY-PUSH Acknowledgement Message UDP header, and the destination   port of the GROUPKEY-PUSH message UDP header becomes the source port   of the GROUPKEY-PUSH Acknowledgement Message UDP header.   The following sections describe the payloads in the GROUPKEY-PUSH   Acknowledgement Message.3.1.  HDR   The message begins with a header as defined for the GDOI   GROUPKEY-PUSH message inSection 4.2 of [RFC6407].  The fields in the   HDR MUST be initialized as follows.  The cookies of a GROUPKEY-PUSH   message act as a Security Parameter Index (SPI) and are copied to the   Acknowledgement Message.  "Next Payload" identifies a "Hash (HASH)"   payload (value 8) [ISAKMP-NP].  Major Version is 1 and Minor Version   is 0.  The Exchange Type has value 35 for the GDOI GROUPKEY-PUSH   Acknowledgement Message.  Flags are set to 0.  Message ID MUST be set   to 0.  Length is according toSection 4.2 of [RFC6407].Weis, et al.                 Standards Track                    [Page 7]

RFC 8263                    GROUPKEY-PUSH ACK              November 20173.2.  HASH   The HASH payload is the same one used in the GDOI GROUPKEY-PULL   exchange defined inSection 3.2 of [RFC6407].  The hash data in the   HASH payload is created as follows:      HASH = prf(ack_key, SEQ | ID)   where:   o  "prf" is specific to the KEK_ACK_REQUESTED value and is described      as part of that description.   o  "|" indicates concatenation.   o  "SEQ" and "ID" represent the bytes comprising the Sequence Number      and Identification payloads.   The ack_key is computed from a Key Derivation Function (KDF) that   conforms to KDF in feedback mode as defined in NIST SP800-108   [SP800-108], where the length of the derived keying material is the   same as the output of the prf, there is no IV, and the optional   counter is not used.  Note: When the derived ack_key is smaller than   the prf block size (i.e., 512 bits for PRF-HMAC-SHA-256), it is   zero-filled to the right, as specified inSection 2.1.2 of [RFC4868].      ack_key = prf(base_key, "GROUPKEY-PUSH ACK" | SPI | L)   where:   o  "prf" is specific to the KEK_ACK_REQUESTED value and is described      as part of that description.   o  "base_key" is specific to the KEK_ACK_REQUESTED value and is      described as part of that description.  If the base_key is smaller      than the prf block size (i.e., 512 bits for PRF-HMAC-SHA-256),      then it is zero-filled to the right, as specified inSection 2.1.2      of [RFC4868].   o  "|" indicates concatenation.   o  "GROUPKEY-PUSH ACK" is a label encoded as a null-terminated ASCII      string.   o  "SPI" (per [RFC6407]) is the Initiator Cookie followed by the      Responder Cookie taken from the GROUPKEY-PUSH message HDR, which      describes the context of the key usage.Weis, et al.                 Standards Track                    [Page 8]

RFC 8263                    GROUPKEY-PUSH ACK              November 2017   o  "L" is a length field matching the number of bits in the ack_key.      L MUST match the length of the base_key (i.e., 512 bits for      PRF-HMAC-SHA-256).  The value L is represented as two octets in      network byte order (that is, most significant byte first).3.3.  SEQ   The Sequence Number payload is defined inSection 5.7 of [RFC6407].   The value in the GROUPKEY-PUSH SEQ payload is copied to the   GROUPKEY-PUSH ACK SEQ payload.3.4.  ID   The Identification payload is used as defined inSection 5.1 of   [RFC6407].  The ID payload contains an ID Type of ID_IPV4_ADDR,   ID_IPV6_ADDR, or ID_OID as defined in [RFC8052] for GDOI exchanges.   The Protocol ID and Port fields MUST be set to 0.  The address   provided in the ID payload represents the IP address of the GM and   MUST match the source IP address used for the most recent   GROUPKEY-PULL exchange.4.  Group Member Operations   When a GM receives an SA KEK payload (in a GROUPKEY-PULL exchange or   GROUPKEY-PUSH message) including a KEK_ACK_REQUESTED attribute, it   records in its group state some indication that it is expected to   return a GROUPKEY-PUSH ACK.  A GM recognizing the attribute MUST   honor the KEK_ACK_REQUESTED attribute by returning Acknowledgements,   because it can be expected that the GCKS is likely to take some   policy-specific action regarding unresponsive GMs, including ceasing   to deliver GROUPKEY-PUSH messages to it.   If a GM cannot respond with the requested type of Acknowledgement, it   continues with protocol exchange and participates in the group.  In   any case, if a GM stops receiving GROUPKEY-PUSH messages from a GCKS,   it will re-register before existing SAs expire, so omitting the   sending of Acknowledgements should not be critical.   When a GM receives a GROUPKEY-PUSH message that contains a   KEK_ACK_REQUESTED attribute in the SA KEK payload, it processes the   message according toRFC 6407.  When it concludes successful   processing of the message, it formulates the GROUPKEY-PUSH ACKs as   described inSection 3 and delivers the message to the GCKS from   which the GROUPKEY-PUSH message was received.  A GROUPKEY-PUSH ACK is   sent even if the GROUPKEY-PUSH message contains a Delete payload for   the KEK used to protect the GROUPKEY-PUSH message.Weis, et al.                 Standards Track                    [Page 9]

RFC 8263                    GROUPKEY-PUSH ACK              November 20175.  GCKS Operations   When a GCKS policy includes requesting a GROUPKEY-PUSH ACK from GMs,   it includes the KEK_ACK_REQUESTED attribute in the SA KEK payload.   It does this each time the SA KEK is delivered, in both GROUPKEY-PULL   exchanges and GROUPKEY-PUSH messages.  The value of the   KEK_ACK_REQUESTED attribute will depend upon the type of SA KEK   policy, as described inSection 2.   When a GCKS receives a GROUPKEY-PUSH ACK (identified by an Exchange   Type of GROUPKEY-PUSH-ACK), it first verifies that the group policy   includes receiving GROUPKEY-PUSH ACKs.  If not, the message is   discarded.  GCKS implementations SHOULD keep a record (e.g., a hash   value) of recently received GROUPKEY-PUSH Acknowledgement Messages   and reject duplicate messages prior to performing cryptographic   operations.  This enables an early discard of the replayed messages.   If the message is expected, the GCKS validates the format of the   message and verifies that the HASH has been properly constructed as   described inSection 3.2.  If validation fails, the message is   discarded.  The GCKS extracts the sequence number and identity of the   GM from the SEQ and ID payloads, respectively, and records the fact   that the GM received the GROUPKEY-PUSH message represented by its   sequence number.6.  Management Considerations   The GCKS manages group policy as well as determining which GM devices   are presently "live" members of the group (i.e., members either   sending or receiving messages).  Group policy includes a strategy to   ensure that rekey messages with current group policy reach all live   GMs.  This is discussed briefly inSection 5.3 of [RFC4046].  The   GROUPKEY-PUSH Acknowledgement Message specified in this memo provides   the GCKS with an additional method to assess if a GM is live and has   received the current group policy.  But it is possible for a rekey   message or GROUPKEY-PUSH Acknowledgement Message to be discarded in   the network, resulting in a live GM appearing to be unresponsive.   Also, a GM might not be able to respond with a GROUPKEY-PUSH ACK, so   the GCKS should use caution in using a lack of an Acknowledgement   Message as the only factor in determining whether a GM is live.  In   particular, a GCKS SHOULD NOT consider a GM to have left the group   until it has received at least one ACK from the GM.Weis, et al.                 Standards Track                   [Page 10]

RFC 8263                    GROUPKEY-PUSH ACK              November 2017   Some management considerations for determining how a GM handles   Acknowledgement Messages are as follows:   o  A GM MUST respond with Acknowledgement Messages when requested, as      a GCKS can subsequently determine when a GM unexpectedly becomes      unresponsive.   o  A GM receiving a GROUPKEY-PUSH message as a multicast message MAY      introduce jitter to the timing of its Acknowledgement Message to      help the GCKS better manage replies from GMs.  A GM MUST NOT delay      sending an Acknowledgement Message for more than 5 seconds. a GCKS      SHOULD NOT declare an Acknowledgement Message as missing until it      has waited at least 10 seconds.  Implementations SHOULD make these      timers configurable.   Some management considerations for determining how the GCKS handles   Acknowledgement Messages are as follows:   o  Non-receipt of an Acknowledgement Message is an indication that a      GM is unable to respond.  A GCKS SHOULD wait at least several      seconds before determining non-receipt, as GMs could add jitter to      the response time before sending an Acknowledgement Message.   o  If the GCKS is aware that GMs are expected to respond, then      non-receipt of an Acknowledgement Message SHOULD trigger a logging      event.  The GCKS MAY be configured with such additional policy      actions as transmitting the GROUPKEY-PUSH message several times in      a short period of time (as suggested in [RFC4046]), thereby      mitigating loss of either the GROUPKEY-PUSH message or an      Acknowledgement Message.  Another policy action could be to alert      GCKS administrators of GMs that do not return several consecutive      Acknowledgement Messages or even removing unresponsive GMs from      the group.  However, a GCKS with a policy of removing GMs from the      group needs to be aware that a GM that has not responded will not      receive a newer group policy until it initiates contact with the      GCKS again.   o  When a GROUPKEY-PUSH message includes a Delete payload for the KEK      used to protect the GROUPKEY-PUSH message, the GCKS SHOULD NOT      itself delete the KEK until it has given GMs the opportunity to      acknowledge receipt of the GROUPKEY-PUSH message.  This could be      several seconds, as GMs could add jitter to the response time      before sending an Acknowledgement Message.   o  A GCKS SHOULD log failure events, such as receiving      Acknowledgement Messages for a group in which the GCKS has not      requested Acknowledgements, receiving malformed Acknowledgements,      and Acknowledgements that fail validation.Weis, et al.                 Standards Track                   [Page 11]

RFC 8263                    GROUPKEY-PUSH ACK              November 20177.  Security Considerations   There are three areas of security considerations to consider: the   protection of the GROUPKEY-PUSH ACK, whether the GM should transmit a   GROUPKEY-PUSH ACK, and whether a GCKS should accept a GROUPKEY-PUSH   ACK.  These are addressed in the following subsections.   The construction of the HASH defined in this memo uses   PRF-HMAC-SHA-256 or PRF-HMAC-SHA-512.  The strengths of   PRF-HMAC-SHA-256 and PRF-HMAC-SHA-512 were unquestioned at the time   this memo was developed.  When a HASH construction using a different   prf becomes necessary, a new KEK_ACK_REQUESTED value will be defined   in a new specification.7.1.  Protection of the GROUPKEY-PUSH ACK   The GROUPKEY-PUSH ACK is an Internet Security Association and Key   Management Protocol (ISAKMP) message as discussed in [RFC2408].   (Note:RFC 2408 has been obsoleted byRFC 7296, but onlyRFC 2408   applies in this context.)  Message authentication and protection   against man-in-the-middle attacks are provided by the inclusion of a   HASH payload that includes the output of an HMAC computation over the   bytes of the message.   Because the KEK is a group secret, when the value of REKEY_ACK_KEK is   specified, impersonation of a victim GM by another authorized GM is   possible.  However, security considerations regarding such an   impersonation are limited to a false claim that a victim GM has   received a GROUPKEY-PUSH when the victim GM has in fact not received   it (e.g., because an active attacker has discarded the   GROUPKEY-PUSH).  If a GCKS policy includes sending retransmissions of   the GROUPKEY-PUSH message to that victim GM, then the victim GM might   not receive replacement SAs.  However, this does not introduce any   additional threats over a use case where the GROUPKEY-PUSH ACK is not   deployed and GROUPKEY-PUSH messages are withheld from a victim GM by   an active attacker.  These threats can be mitigated by using a value   of REKEY_ACK_LKH, due to the use of a secret pairwise key shared   between the GCKS and an individual GM.   Confidentiality is not provided for the GROUPKEY-PUSH ACK.  The   contents of the message, including the hash value, the sequence   number from the GROUPKEY-PUSH message to which it is acknowledging   receipt, and the identity of the GM, can be observed by a passive   attacker.  Observation of a hash value or set of hash values will not   compromise the hash key.  The identity of the GM is also available to   the passive attacker as the source IP address of the packet.  Note   that the sequence number in the GROUPKEY-PUSH ACK does reveal the   sequence number (previously not available to the attacker) that wasWeis, et al.                 Standards Track                   [Page 12]

RFC 8263                    GROUPKEY-PUSH ACK              November 2017   included in the GROUPKEY-PUSH message.  However, the attacker is   assumed to not be in possession of the key used to encrypt the   message and thus cannot create a spoofed GROUPKEY-PUSH message.   Therefore, the attacker does not derive any direct value from   learning the sequence number.7.2.  Transmitting a GROUPKEY-PUSH ACK   A GM transmits an ACK only when the policy of the most recently   received SA KEK includes a request by the GCKS for ACKs, and the ACK   is only returned after processing the GROUPKEY-PUSH message according   toSection 4.4 of [RFC6407].  In other words, the form of the   GROUPKEY-PUSH message will have been validated, replay protection   completed, and the digital signature verified as being genuine.   Therefore, the threat of a GM responding to a spoofed or resent   GROUPKEY-PUSH message, and the possibility of the GM being used to   propagate a Distributed Denial of Service (DDoS) attack on a GCKS,   are mitigated.  For more information, see the security considerations   for a GROUPKEY-PUSH message as described inSection 7.3 of [RFC6407].7.3.  Receiving a GROUPKEY-PUSH ACK   A GCKS receiving ACKs will follow the validation steps described inSection 5 before interpreting the contents of the message.  The GCKS   will then be sure to operate only on messages that have been sent by   an authorized GM.   A GCKS SHOULD be prepared to receive GROUPKEY-PUSH ACKs from each GM   to which it was sent.  That is, it needs to ensure that it has   sufficient resources (e.g., receive queue size) so that it does not   unnecessarily drop ACKs.  A GCKS should be aware that a large number   of replayed or invalid GROUPKEY-PUSH messages could be addressed to   it.  However, this is no worse a threat than if it received a large   number of other types of replayed or invalid GDOI or other messages   containing a HASH payload.   How a GCKS processes the sequence number and identity included in an   ACK is a matter of local policy and is outside the scope of this   memo.Weis, et al.                 Standards Track                   [Page 13]

RFC 8263                    GROUPKEY-PUSH ACK              November 20178.  IANA Considerations   The following additions have been made to the "Group Domain of   Interpretation (GDOI) Payloads" [GDOI-REG] registry.   A new attribute has been added to the "SA KEK Payload Values - KEK   Attributes" registry.  The ID Class name is KEK_ACK_REQUESTED with a   value of 9 and is a Basic attribute.   A new registry defining values for KEK_ACK_REQUESTED, "SA KEK Payload   Values - KEK_ACK_REQUESTED", has been added; the initial   registrations are shown in the following table.  The terms   "Reserved", "Unassigned", and "Private Use" are to be applied as   defined in [RFC8126].  The registration procedure is Specification   Required.                   Value            Type                  -------           --------------------                     0              Reserved                     1              REKEY_ACK_KEK_SHA256                     2              REKEY_ACK_LKH_SHA256                     3              REKEY_ACK_KEK_SHA512                     4              REKEY_ACK_LKH_SHA512                    5-128           Unassigned                  129-255           Private Use   A new registry describing ISAKMP Exchange Types for the GDOI, "GDOI   DOI Exchange Types", has been added under the "Group Domain of   Interpretation (GDOI) Payloads" registry [GDOI-REG].  This new   registry defines DOI Specific Use values [ISAKMP-EXCH], which are   Exchange Type values used with the ISAKMP GDOI DOI.  The registration   procedure is Specification Required.  The terms "Known Unregistered   Use" and "Unassigned" are to be applied as defined in [RFC8126].             Value                      Phase        Reference             ----------------------     ------       ---------             GROUPKEY-PULL                32RFC 6407             GROUPKEY-PUSH                33RFC 6407             Known Unregistered Use       34             GROUPKEY-PUSH-ACK            35RFC 8263             Unassigned                 36-239Weis, et al.                 Standards Track                   [Page 14]

RFC 8263                    GROUPKEY-PUSH ACK              November 20179.  References9.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <https://www.rfc-editor.org/info/rfc2119>.   [RFC4868]  Kelly, S. and S. Frankel, "Using HMAC-SHA-256,              HMAC-SHA-384, and HMAC-SHA-512 with IPsec",RFC 4868,              DOI 10.17487/RFC4868, May 2007,              <https://www.rfc-editor.org/info/rfc4868>.   [RFC6407]  Weis, B., Rowles, S., and T. Hardjono, "The Group Domain              of Interpretation",RFC 6407, DOI 10.17487/RFC6407,              October 2011, <https://www.rfc-editor.org/info/rfc6407>.   [RFC8052]  Weis, B., Seewald, M., and H. Falk, "Group Domain of              Interpretation (GDOI) Protocol Support for IEC 62351              Security Services",RFC 8052, DOI 10.17487/RFC8052,              June 2017, <https://www.rfc-editor.org/info/rfc8052>.   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for              Writing an IANA Considerations Section in RFCs",BCP 26,RFC 8126, DOI 10.17487/RFC8126, June 2017,              <https://www.rfc-editor.org/info/rfc8126>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC 2119 Key Words",BCP 14,RFC 8174,              DOI 10.17487/RFC8174, May 2017,              <https://www.rfc-editor.org/info/rfc8174>.Weis, et al.                 Standards Track                   [Page 15]

RFC 8263                    GROUPKEY-PUSH ACK              November 20179.2.  Informative References   [GDOI-REG]              Internet Assigned Numbers Authority, "Group Domain of              Interpretation (GDOI) Payload Type Values", IANA Registry,              September 2017, <https://www.iana.org/assignments/gdoi-payloads/>.   [ISAKMP-EXCH]              Internet Assigned Numbers Authority, "Internet Key              Exchange (IKE) Attributes Exchange Type Values",              IANA Registry, May 2013,              <https://www.iana.org/assignments/ipsec-registry/>.   [ISAKMP-NP]              Internet Assigned Numbers Authority, "Internet Key              Exchange (IKE) Attributes Next Protocol Types",              IANA Registry, May 2013,              <https://www.iana.org/assignments/ipsec-registry/>.   [RFC2408]  Maughan, D., Schertler, M., Schneider, M., and J. Turner,              "Internet Security Association and Key Management Protocol              (ISAKMP)",RFC 2408, DOI 10.17487/RFC2408, November 1998,              <https://www.rfc-editor.org/info/rfc2408>.   [RFC4046]  Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,              "Multicast Security (MSEC) Group Key Management              Architecture",RFC 4046, DOI 10.17487/RFC4046, April 2005,              <https://www.rfc-editor.org/info/rfc4046>.   [SP800-108]              Chen, L., "Recommendation for Key Derivation Using              Pseudorandom Functions (Revised)", National Institute of              Science and Technology, NIST Special Publication 800-108,              DOI 10.6028/NIST.SP.800-108, October 2009,              <http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-108.pdf>.Weis, et al.                 Standards Track                   [Page 16]

RFC 8263                    GROUPKEY-PUSH ACK              November 2017Acknowledgements   Mike Hamada, Adrian Farrel, and Yaron Sheffer provided many useful   technical and editorial comments and suggestions for improvement.Authors' Addresses   Brian Weis   Cisco Systems   170 W. Tasman Drive   San Jose, California  95134-1706   United States of America   Phone: +1-408-526-4796   Email: bew@cisco.com   Umesh Mangla   Juniper Networks Inc.   1133 Innovation Way   Sunnyvale, California  94089   United States of America   Phone: +1-408-936-1022   Email: umangla@juniper.net   Thomas Karl   Deutsche Telekom   Landgrabenweg 151   Bonn  53227   Germany   Phone: +49-228-18138122   Email: thomas.karl@telekom.de   Nilesh Maheshwari   Email: nileshm@gmail.comWeis, et al.                 Standards Track                   [Page 17]

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