wdiff rfc8263.original rfc8263.txt

Network Working Group
Internet Engineering Task Force (IETF) B. Weis
Internet-Draft
Request for Comments: 8263 Cisco Systems
Intended status:
Category: Standards Track U. Mangla
Expires: March 12, 2018
ISSN: 2070-1721 Juniper Networks Inc.
T. Karl
Deutsche Telekom
N. Maheshwari
September 8,
November 2017

GDOI

Group Domain of Interpretation (GDOI) GROUPKEY-PUSH
Acknowledgement Message
draft-weis-gdoi-rekey-ack-07

Abstract

The Group Domain of Interpretation (GDOI) includes the ability for 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 to return an acknowledgement of
receipt of its rekey message, message and specifies the acknowledgement
method.

Status of This Memo

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

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of six months this document, any errata,
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This Internet-Draft will expire on March 12, 2018.
https://www.rfc-editor.org/info/rfc8263.

This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements notation Notation . . . . . . . . . . . . . . . . . . 3
1.2. Acronyms and Abbreviations . . . . . . . . . . . . . . . 4 3
2. Acknowledgement Message Request . . . . . . . . . . . . . . . 4
2.1. REKEY_ACK_KEK_SHA256 Type . . . . . . . . . . . . . . . . 5
2.2. REKEY_ACK_LKH_SHA256 Type . . . . . . . . . . . . . . . . 5
2.3. REKEY_ACK_KEK_SHA512 Type . . . . . . . . . . . . . . . . 5
2.4. REKEY_ACK_LKH_SHA512 Type . . . . . . . . . . . . . . . . 6
3. GROUPKEY-PUSH Acknowledgement Message . . . . . . . . . . . . 6
3.1. HDR . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. HASH . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. SEQ . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4. ID . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Group Member Operations . . . . . . . . . . . . . . . . . . . 8
5. GCKS Operations . . . . . . . . . . . . . . . . . . . . . . . 9
6. Management Considerations . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7.1. Protection of the GROUPKEY-PUSH ACK . . . . . . . . . . . 11
7.2. Transmitting a GROUPKEY-PUSH ACK . . . . . . . . . . . . 12
7.3. Receiving a GROUPKEY-PUSH ACK . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgements References . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . 14
10.1. Normative References . . . . . . . . . . . . . 14
Acknowledgements . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 14 . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15

1. 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 requirement of the Multicast requirements set forth in [RFC4046] ("Multicast Security
(MSEC) Group Key Management
Architecture [RFC4046], and defines both 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 group members 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 Usually, the GCKS
does not require a notification that the group member 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 and, by implication
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 acknowledgment
message
Acknowledgement Message to the GCKS. Initially Initially, a GCKS requests that
a GM to acknowledge GROUPKEY-PUSH messages as part of a distributed
group policy. Then
(shown Then, as shown in Figure 1) 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 Event

Implementation of the GROUPKEY-PUSH Acknowledgement Message is
OPTIONAL.

1.1. Requirements notation Notation

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

GCKS Group Controller/Key Server

GDOI Group Domain of Interpretation

GM Group Member

HDR Header Payload

IV Initialization Vector

KD Key Download Payload

KDF Key Derivation Function

KEK Key Encryption Key

LKH Logical Key Hierarchy

MSEC Multicast Security

SA Security Association

SEQ Sequence Number Payload

SIG Signature Payload

SPI Security Parameter Index

2. 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 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 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 attribute with
the name KEK_ACK_REQUESTED (value TBD-1), (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, material that is used to protect the GROUPKEY-PUSH Rekey
Protocol (e.g., the presence of a KEK Management Algorithm). management algorithm). Parts
of
these this information are used by a GM to derive the ack_key (defined
in Section 3.2), which protects the GROUPKEY-PUSH Acknowledgement
Message. There are different types of Rekey Acknowledgement
messages, which
Messages; they share an identical message format but differ in the
used
keying material. 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 KD Download Type
(Section 5.6.2 of [RFC6407]) is part of the group policy. The prf
(defined in Section 3.2) is PRF-HMAC-SHA-256 [RFC4868]. The base_key
(also defined in Section 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.

2.2. 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 (see Section 5.6.3.1 of [RFC6407]). This is a secret
symmetric key that the GCKS shares with the group member. 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 encrypted.

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

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

Figure 2: GROUPKEY-PUSH from Message (from RFC 6407 6407)

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 source address of the GROUPKEY-PUSH message becomes the
Destination Address
destination address of the GROUPKEY-PUSH Acknowledgement Message Message, and
the GM includes its own IP address as the Source Address source address of the
GROUPKEY-PUSH Acknowledgement Message. The Source source port in the
GROUPKEY-PUSH message UDP header becomes the Destination destination port of the
GROUPKEY-PUSH Acknowledgement Message UDP header, and the Destination destination
port of the GROUPKEY-PUSH message UDP header becomes the Source 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
GROUPKEY-PUSH message in Section 4.1 4.2 of [RFC6407]. The fields in the
HDR MUST be initialized as follows. The Cookies cookies of a GROUPKEY-PUSH
message act as a Security Parameter Index (SPI) and are copied to the
Acknowledgement Message. Next Payload "Next Payload" identifies a Hash "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
Acknowledgment
Acknowledgement Message. Flags are set to 0. Message ID MUST be set
to zero. 0. Length is according to Section 4.1 4.2 of [RFC6407]). [RFC6407].

3.2. HASH

The HASH payload is the same one used in the GDOI GROUPKEY-PULL
exchange defined in Section 3.2 of [RFC6407]. The hash data in the
HASH payload is created as follows:

HASH = prf(ack_key, SEQ | ID)

where:

o prf "prf" is specific to the KEK_ACK_REQUESTED value, value and is described
as part of that description.

o "|" indicates concatenation.

o SEQ "SEQ" and ID "ID" represent the bytes comprising the Sequence Number
and Identification Payloads payloads.

The ack_key is computed from a Key Derivation Function (KDF) that
conforms to KDF in Feedback Mode feedback mode as defined in NIST SP800-108
[SP800-108]
[SP800-108], where the length of the derived keying material is the
same as the output of the prf, there is no initialization vector, 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), PRF-HMAC-SHA-256), it is zero filled
zero-filled to the right, as specified in Section 2.1.2 of [RFC4868].

ack_key = prf(base_key, "GROUPKEY-PUSH ACK" | SPI | L)

where:

o prf "prf" is specific to the KEK_ACK_REQUESTED value, value and is described
as part of that description.

o base_key "base_key" is specific to the KEK_ACK_REQUESTED value, 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 zero-filled to the right, as specified in Section 2.1.2
of [RFC4868].

o "|" indicates concatenation.

o "GROUPKEY-PUSH ACK" is a label encoded as a null terminated null-terminated ASCII
string.

o SPI "SPI" (per [RFC6407]) is the Initiator Cookie followed by the
Responder Cookie taken from the GROUPKEY-PUSH message HDR, which
describes the Context context of the key usage.

o L "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).
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 payload is defined in Section 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 in Section 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 [RFC8052]. 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, 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 message. ACK. A GM recognizing the attribute MUST
honor the KEK_ACK_REQUESTED attribute by returning
Acknowledgments, Acknowledgements,
because it can be expected that the GCKS is likely to take some
policy-specific action regarding non-responsive 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 GCKS,
it will re-register before existing security associations 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 to RFC 6407. When it concludes successful
processing of the message, it formulates the GROUPKEY-PUSH ACK
messages ACKs as
described in Section 3 and delivers the message to the GCKS from
which the GROUPKEY-PUSH message was received. A GROUPKEY-
PUSH GROUPKEY-PUSH ACK message is
sent even if the GROUPKEY-PUSH message contains a Delete payload for
the KEK used to protect the GROUPKEY-PUSH message.

5. GCKS Operations

When a GCKS policy includes requesting a GROUPKEY-PUSH ACK message from Group Members, 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, KEK
policy, as described in Section 2.

When a GCKS receives a GROUPKEY-PUSH ACK message (identified by an Exchange type
Type of GROUPKEY-PUSH-ACK), it first verifies that the group policy
includes receiving GROUPKEY-PUSH ACK messages. ACKs. If not, the message is
discarded. GCKS implementations SHOULD keep a record (e.g., a hash
value) of recently received GROUPKEY-PUSH
Acknowledgment messages 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,
message and verifies that the HASH has been properly constructed as
described in Section 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 payloads, respectively, and records the fact
that the GM received the GROUPKEY-PUSH message represented by its
serial
sequence number.

6. Management Considerations

The GCKS manages both group policy and group membership as well as determining which GM devices
are presently "live" members of a group. the group (i.e., members either
sending or receiving messages). Group membership policy includes a strategy to
ensure that rekey messages with current group policy reach all live group members.
GMs. This is discussed briefly in Section 5.3 of the MSEC Group Key
Management Architecture [RFC4046]. The
GROUPKEY-PUSH Acknowledgement
message Message specified in this memo provides
the GCKS with an additional method to assess if a group member GM is live and has
received the current group policy. But it is possible for a rekey
message or GROUPKEY-
PUSH GROUPKEY-PUSH Acknowledgement message Message to be discarded in
the network, which
results resulting in a live GM appearing to appear be unresponsive. Also
Also, a GM might not be able to respond with an a GROUPKEY-PUSH ACK. So ACK, so
the GCKS should use caution in using a lack of Acknowledgment 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.

Some management considerations for determining how a Group Member handle GM handles
Acknowledgement messages is Messages are as follows:

o A GM MUST respond with Acknowledgement messages Messages when requested, as
a GCKS can subsequently determine when a GM becomes unexpectedly
non-responsive. becomes
unresponsive.

o A GM receiving a GROUPKEY-PUSH message as a multicast message MAY
introduce a jitter to the timing of its Acknowledgement message Message to
help the GCKS better manage replies from group members. GMs. A GM MUST NOT delay
sending an Acknowledgment Acknowledgement Message for more than 5 seconds. a GCKS
SHOULD NOT declare an Acknowledgment 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 is Messages are as follows:

o A non-receipt 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. Acknowledgement Message.

o If the GCKS is aware that GMs are expected to respond, then a non-
receipt
non-receipt of an Acknowledgement Message SHOULD trigger a logging
event. The GCKS MAY be configured with such additional policy
actions such as transmitting the GROUPKEY-PUSH message several times in
a short period of time (as suggested in [RFC4046]), which mitigates a
packet thereby
mitigating loss of either the GROUPKEY-PUSH message or an
Acknowledgement message. Message. Another policy action could be to
alerting alert
GCKS administrators of GMs that do not return several consecutive acknowledgement messages
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. Acknowledgement Message.

o A GCKS SHOULD log failure events, such as receiving
Acknowledgement messages Messages for a group in which the GCKS has not
requested Acknowledgements, receiving malformed Acknowledgement, Acknowledgements,
and Acknowledgements that fail validation.

7. Security Considerations

There are three areas of security considerations to consider: the
protection of the GROUPKEY-PUSH ACK message, 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
PRF-HMAC-SHA-256 or PRF-HMAC-SHA-512. The strength strengths of these PRFs
PRF-HMAC-SHA-256 and PRF-HMAC-SHA-512 were unquestioned at the time
this memo was developed. When a HASH construction is necessary using a different prf,
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 message is an ISAKMP [RFC2408] message. Internet Security Association and Key
Management Protocol (ISAKMP) message as discussed in [RFC2408].
(Note: RFC 2408 has been obsoleted by RFC 7296, but only RFC 2408
applies in this context.) Message authentication and Man-in-the-Middle Attack Protection is protection
against man-in-the-middle attacks are provided by the inclusion of a
HASH payload, which payload that includes the output of an HMAC computation over the
bytes of the message.

When

Because the KEK is a group secret, when the value of REKEY_ACK_KEK is
specified, because the KEK is a
group secret impersonation of a victim GM by another authorized GM is
possible. However, security considerations of the regarding such an
impersonation are limited to a false claim that a victim GM has
received a GROUPKEY-
PUSH 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 security
associations. SAs. However, this adds no 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 message. ACK. The
contents of the message can be observed by a passive attacker,
which includes message, including the hash value, the sequence
number of in from the GROUPKEY-PUSH message to which it is acknowledging
receipt, and the identity of the GM. 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. The Note
that the sequence number in the GROUPKEY-PUSH ACK does reveal the
sequence number (previously not available to the attacker) that was
included in the GROUPKEY-PUSH, which was previously not available
to the attacker. GROUPKEY-PUSH message. However, the attacker is
assumed to not be in possession of the key used to encrypt the message,
message and thus cannot create a spoofed GROUPKEY-PUSH message.
Therefore, there is no
direct value that the attacker derives does not derive any direct value from the knowledge of
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 only the ACK
is only returned after processing the GROUPKEY-PUSH message according
to Section 4.4 of [RFC6407]. In other words, the form of the GROUPKEY-
PUSH
GROUPKEY-PUSH message will have been validated, replay protection
completed, and the digital signature verified as being genuine.
Therefore, the
threats 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 GCKS,
are mitigated. For more information, see the security considerations of
for a GROUPKEY-
PUSH GROUPKEY-PUSH message as described in Section 7.3 of [RFC6407].

7.3. Receiving a GROUPKEY-PUSH ACK

A GCKS receiving ACK messages ACKs will follow the validation steps described in
Section 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 ACK messages 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 ACK messages. An 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 serial sequence number and identity included in an
ACK message is a matter of local policy and is outside the scope of this
memo.

8. IANA Considerations

The following additions are have been made to the GDOI Payloads "Group Domain of
Interpretation (GDOI) Payloads" [GDOI-REG] registry.

A new attribute is has been added to the SA "SA KEK Payload Values - KEK
Attributes
Attributes" registry. The ID Class name is KEK_ACK_REQUESTED with a
value of TBD-1, 9 and is a Basic attribute.

A new registry defining values for KEK_ACK_REQUESTED is needed, and
these values 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,
"Reserved", "Unassigned", and Private Use "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 GDOI is the GDOI, "GDOI
DOI Exchange Types", has been added to
GDOI Payloads 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 Type values used with the ISAKMP GDOI DOI. Its name is "GDOI DOI Exchange Types". The registration
procedure is Specification Required. The terms Known "Known Unregistered Use
Use" and Unassigned "Unassigned" are to be applied as defined in [RFC8126].

Value Phase Reference
---- -----
---------------------- ------ ---------
GROUPKEY-PULL 32 RFC 6407
GROUPKEY-PUSH 33 RFC 6407
Known Unregistered Use 34
GROUPKEY-PUSH-ACK 35 RFC XXXX 8263
Unassigned 36-239

[Note to RFC Editor: Please replace XXXX with the number of the RFC
resulting from this memo, and delete this note.]

9. Acknowledgements

Mike Hamada, Adrian Farrel, and Yaron Sheffer provided many useful
technical and editorial comments and suggestions for improvement.

10. References

10.1.

9.1. 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>.
<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>.
<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>.

10.2.

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

9.2. Informative References

[GDOI-REG]
Internet Assigned Numbers Authority, "Group Domain of
Interpretation (GDOI) Payload Type Values", IANA Registry,
November 2016, <http://www.iana.org/assignments/gdoi-
payloads/gdoi-payloads.xml>.
<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, <http://www.iana.org/assignments/
ipsec-registry/ipsec-registry.xhtml#ipsec-registry-17>.
<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, <http://www.iana.org/assignments/
ipsec-registry/ipsec-registry.xhtml#ipsec-registry-21>.
<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", United States of America, Functions (Revised)", National Institute of
Science and Technology, NIST Special Publication 800-108,
DOI 10.6028/NIST.SP.800-108, October 2009,
<http://dx.doi.org/10.6028/NIST.SP.800-108>.
<http://nvlpubs.nist.gov/nistpubs/Legacy/SP/
nistspecialpublication800-108.pdf>.

Acknowledgements

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
USA
United States of America

Phone: +1-408-526-4796
Email: bew@cisco.com
Umesh Mangla
Juniper Networks Inc.
1133 Innovation Way
Sunnyvale, California 94089
USA
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 +49-228-18138122
Email: thomas.karl@telekom.de

Nilesh Maheshwari

Email: nileshm@gmail.com