MSEC Working Group B. Weis
Internet-Draft S. Rowles
Intended status: Standards Track Cisco Systems
Expires: January 13, 2011 T. Hardjono
MIT
July 12, 2010
The Group Domain of Interpretation
draft-ietf-msec-gdoi-update-06
Abstract
This document describes an updated version of the Group Domain of
Interpretation (GDOI) protocol specified in RFC 3547. The GDOI
provides group key management to support secure group communications
according to the architecture specified in RFC 4046. The GDOI
manages group security associations, which are used by IPsec and
potentially other data security protocols.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 5
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.3. GDOI Applications . . . . . . . . . . . . . . . . . . . . 6
1.4. Extending GDOI . . . . . . . . . . . . . . . . . . . . . . 6
1.5. Forward and Backward Access Control . . . . . . . . . . . 7
2. GDOI Phase 1 protocol . . . . . . . . . . . . . . . . . . . . 9
2.1. ISAKMP Phase 1 protocol . . . . . . . . . . . . . . . . . 9
3. GROUPKEY-PULL Exchange . . . . . . . . . . . . . . . . . . . . 10
3.1. Authorization . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Messages . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Initiator Operations . . . . . . . . . . . . . . . . . . . 12
3.4. Receiver Operations . . . . . . . . . . . . . . . . . . . 13
4. GROUPKEY-PUSH Message . . . . . . . . . . . . . . . . . . . . 15
4.1. Use of signature keys . . . . . . . . . . . . . . . . . . 16
4.2. ISAKMP Header Initialization . . . . . . . . . . . . . . . 16
4.3. Deletion of SAs . . . . . . . . . . . . . . . . . . . . . 16
4.4. GCKS Operations . . . . . . . . . . . . . . . . . . . . . 17
4.5. Group Member Operations . . . . . . . . . . . . . . . . . 18
5. Payloads and Defined Values . . . . . . . . . . . . . . . . . 19
5.1. Identification Payload . . . . . . . . . . . . . . . . . . 19
5.2. Security Association Payload . . . . . . . . . . . . . . . 19
5.3. SA KEK payload . . . . . . . . . . . . . . . . . . . . . . 21
5.4. Group Associated Policy . . . . . . . . . . . . . . . . . 27
5.5. SA TEK Payload . . . . . . . . . . . . . . . . . . . . . . 30
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5.6. Key Download Payload . . . . . . . . . . . . . . . . . . . 34
5.7. Sequence Number Payload . . . . . . . . . . . . . . . . . 42
5.8. Nonce . . . . . . . . . . . . . . . . . . . . . . . . . . 43
6. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 44
6.1. KEK . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.2. TEK . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7. Security Considerations . . . . . . . . . . . . . . . . . . . 46
7.1. ISAKMP Phase 1 . . . . . . . . . . . . . . . . . . . . . . 46
7.2. GROUPKEY-PULL Exchange . . . . . . . . . . . . . . . . . . 47
7.3. GROUPKEY-PUSH Exchange . . . . . . . . . . . . . . . . . . 49
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
8.1. Additions to current registries . . . . . . . . . . . . . 51
8.2. New registries . . . . . . . . . . . . . . . . . . . . . . 51
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 53
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 54
10.1. Normative References . . . . . . . . . . . . . . . . . . . 54
10.2. Informative References . . . . . . . . . . . . . . . . . . 54
Appendix A. Alternate GDOI Phase 1 protocols . . . . . . . . . . 58
A.1. IKEv2 Exchange . . . . . . . . . . . . . . . . . . . . . . 58
A.2. KINK Protocol . . . . . . . . . . . . . . . . . . . . . . 58
Appendix B. Significant Changes from RFC 3547 . . . . . . . . . . 59
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 60
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1. Introduction
Secure group and multicast applications require a method by which
each group member shares common security policy and keying material.
This document describes the Group Domain of Interpretation (GDOI),
which is an ISAMKP [RFC2408] Domain of Interpretation (DOI), a group
key management system. The GDOI distributes security associations
(SAs) for IPsec AH and ESP protocols and potentially other data
security protocols used in group applications. The GDOI uses the
group key management model defined in [RFC4046], and described more
generally by the The Multicast Group Security Architecture [RFC3740].
In this group key management model, the GDOI protocol participants
are a "group controller/key server" (GCKS) and a group member (GM).
A group member contacts ("registers with") a GCKS to join the group.
During the registration mutual authentication and authorization are
achieved, after which the GCKS distributes current group policy and
keying material to the group member over an authenticated and
encrypted session. The GCKS may also initiate contact ("rekeys")
group members to provide updates to group policy.
ISAKMP defines two "phases" of negotiation (p.16 of [RFC2408]). A
Phase 1 security association provides mutual authentication and
authorization, and a security association that is used by the
protocol participants to execute a phase 2 exchange. This document
incorporates (i.e., uses but does not re-define) the Phase 1 security
association definition from the Internet DOI [RFC2407], [RFC2409].
Phase 1 security association types other than ISAKMP are possible,
and are noted in Appendix A. Requirements of those phase 1 security
associations are specified in Section 2. The GDOI includes two new
phase 2 ISAKMP exchanges (protocols), as well as necessary new
payload definitions to the ISAKMP standard (p. 14 of [RFC2408]).
These two new protocols are:
1. The GROUPKEY-PULL registration protocol exchange. This exchange
uses "pull" behavior since the member initiates the retrieval of
these SAs from a GCKS. It is protected by an ISAKMP phase 1
protocol, as described above. At the culmination of a GROUPKEY-
PULL exchange, an authorized group member has received and
installed a set of SAs that represent group policy, and it is
ready to participate in secure group communications.
2. The GROUPKEY-PUSH rekey protocol exchange. The rekey protocol is
a datagram initiated ("pushed") by the GCKS, usually delivered to
group members using a IP multicast address. It is treated as a
ISAKMP phase 2 protocol, where the "phase 1" cryptographic policy
and keying material is included in the group policy distributed
by the GCKS in the GROUPKEY-PULL exchange. At the culmination of
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a GROUPKEY-PUSH exchange, all authorized group members have
received and installed updates to group policy, and can continue
to participate in secure group communications. If a group
management method is included in group policy (as described in
Section 1.5.1), at the conclusion of the GROUPKEY-PUSH exchange
some members of the group may have been de-authorized and no
longer able to participate in the secure group communications.
+--------------------------------------------------------------+
| |
| +--------------------+ |
| +------>| GDOI GCKS |<------+ |
| | +--------------------+ | |
| | | | |
| GROUPKEY-PULL | GROUPKEY-PULL |
| PROTOCOL | PROTOCOL |
| | | | |
| v GROUPKEY-PUSH v |
| +-----------------+ PROTOCOL +-----------------+ |
| | | | | | |
| | GDOI GM(s) |<-------+-------->| GDOI GM(S) | |
| | | | | |
| +-----------------+ +-----------------+ |
| | ^ |
| v | |
| +-Data Security Protocol (e.g., ESP)-+ |
| |
+--------------------------------------------------------------+
Although the GROUPKEY-PUSH specified by this document can be used to
refresh a Re-key SA, the most common use of GROUPKEY-PUSH is to
establish a Data-security SA for a data security protocol. In
summary, GDOI is a group security association management protocol:
All GDOI messages are used to create, maintain, or delete security
associations for a group. As described above, these security
associations protect one or more key-encrypting keys, traffic-
encrypting keys, or 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.
Key Encrypting Key (KEK). The symmetric cipher key used to protect
the GROUPKEY-PUSH message.
Logical Key Hierarchy (LKH). A group management method defined in
Section 5.4 of [RFC2627].
Traffic Encryption Key (TEK). The symmetric cipher key used to
protect a data security protocol (e.g., IPsec ESP).
1.3. GDOI Applications
Secure multicast applications include video broadcast and multicast
file transfer. GDOI can also secure group applications that do not
use multicast transport such as video-on-demand where the same
encrypted content is delivered to each group member.
A GDOI application may require Data-security SAs (such as IPsec ESP
SAs), and/or a Rekey-SA (the SA used to protect GROUPKEY-PUSH
messages). For example, a secure multicast video broadcast may only
need to distribute a single set of Data-Security SAs to protect the
time-bounded broadcast. In this case, no Rekey-SA may be necessary
because the initial Data-security SAs will not be cryptographically
overused, and there is no desire to de-authorize group members.
In contrast, an always-on IP multicast application (e.g., stock-
ticker delivery service) with many group members may require a policy
of frequent change of Data-security SAs and regular de-authorization
of group members. In this case, the GCKS policy will regularly
replace Data-security SAs with new SAs defining the same traffic
selectors but new keying material. This will result in a regularly-
scheduled GROUPKEY-PUSH delivering the new SAs. Additionally, the
group membership on the GCKS may be frequently adjusted, which will
result in GROUPKEY-PUSH exchange delivering a new Rekey SAs protected
by a group management method. Each GROUPKEY-PUSH may include Data-
security SAs and/or a Rekey SA. In all cases, the relevant policy is
defined on the GCKS and relayed to group members. Specific policy
choices possible by the GCKS depends on each application and further
discussion of policy is beyond the scope of this memo.
1.4. Extending GDOI
Not all secure multicast or multimedia applications can use IPsec ESP
or AH. Many Real Time Transport Protocol applications, for example,
require security above the IP layer to preserve RTP header
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compression efficiencies and transport-independence [RFC3550]. A
future RTP security protocol may benefit from using GDOI to establish
group SAs. Alternatively, GDOI can distribute message authentication
code (MAC) policy and keys for legacy applications that have defined
their own security associations [I-D.weis-gdoi-mac-tek].
In order to add a new data security protocol, a new RFC MUST specify
the data-security SA parameters conveyed by GDOI for that security
protocol; these parameters are listed in Section 5.5.2 of this
document.
Data security protocol SAs MUST protect group traffic. GDOI provides
no restriction on whether that group traffic is transmitted as
unicast or multicast packets.
1.5. 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). An unrelated notion to PFS,
"forward access control" and "backward access control" have been
called "perfect forward security" and "perfect backward security" in
the literature [RFC2627].
Group management algorithms providing forward and backward access
control other than LKH have been proposed in the literature,
including OFT [OFT] and Subset Difference [NNL]. These algorithms
could be used with GDOI, but are not specified as a part of this
document.
1.5.1. Forward Access Control Requirements
When group membership is altered using a group management algorithm
new Data-security SAs are usually also needed. New SAs ensure that
members who were denied access can no longer participate in the
group.
If forward access control is a desired property of the group, new
Data-security SAs MUST NOT be included in a GROUPKEY-PUSH message
which changes group membership. This is required because the new
Data-security SAs are not protected with the new KEK. Instead, two
sequential GROUPKEY-PUSH messages must be sent by the GCKS; the first
changing the KEK, and the second (protected with the new KEK)
distributing the new Data-security SAs.
Note that in the above sequence, although the new KEK can effectively
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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.
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2. GDOI Phase 1 protocol
The GDOI GROUPKEY-PULL exchange is a "phase 2" protocol which MUST be
protected by a "phase 1" protocol. The "phase 1" protocol can be any
protocol which provides for the following protections:
o Peer Authentication
o Confidentiality
o Message Integrity
The following sections describe one such "phase 1" protocol. Other
protocols which may be potential "phase 1" protocols are described in
Appendix A. However, the use of the protocols listed there are not
considered part of this document.
2.1. ISAKMP Phase 1 protocol
This document defines how the ISAKMP phase 1 exchanges as defined in
[RFC2409] can be used a "phase 1" protocol for GDOI. The following
sections define characteristics of the ISAKMP phase 1 protocols that
are unique for these exchanges when used for GDOI.
Section 7.1 describes how the ISAKMP Phase 1 protocols meet the
requirements of a GDOI "phase 1" protocol.
2.1.1. DOI value
The Phase 1 SA payload has a DOI value. That value MUST be the GDOI
DOI value as defined later in this document.
2.1.2. UDP port
IANA has assigned port 848 for the use of GDOI, which allows for an
implementation to use separate ISAKMP implementations to service GDOI
and IKEv1 [RFC2409]. A GCKS SHOULD listen on this port for GROUPKEY-
PULL exchanges, and the GCKS MAY use this port to distribute
GROUPKEY-PUSH messages. An ISAKMP phase 1 exchange implementation
supporting NAT Traversal [RFC3947] may move to port 4500 to process
the GROUPKEY-PULL exchange.
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3. GROUPKEY-PULL Exchange
The goal of the GROUPKEY-PULL exchange is to establish a Re-key
and/or Data-security SAs at the member for a particular group. A
Phase 1 SA protects the GROUPKEY-PULL; there MAY be multiple
GROUPKEY-PULL exchanges for a given Phase 1 SA. The GROUPKEY-PULL
exchange downloads the data security keys (TEKs) and/or group key
encrypting key (KEK) or KEK array under the protection of the Phase 1
SA.
3.1. Authorization
The Phase 1 identity SHOULD be used by a GCKS to authorize the Phase
2 (GROUPKEY-PULL) request for a group key. Similarly, a group member
SHOULD ensure that the Phase 1 identity of the GCKS is an authorized
GCKS. When no authorization is performed, it is possible for a rogue
GDOI participant to perpetrate a man-in-the-middle attack between a
group member and a GCKS [MP04].
3.2. Messages
The GROUPKEY-PULL is a Phase 2 exchange. Phase 1 computes SKEYID_a
which is the "key" in the keyed hash used in the GROUPKEY-PULL HASH
payloads. When using the Phase 1 defined in this document, SKEYID_a
is derived according to [RFC2409]. As with the IKEv1 HASH payload
generation (Section 5.5 of [RFC2409], each GROUPKEY-PULL message
hashes a uniquely defined set of values. 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", or against
replay of a recent GROUPKEY-PULL message. The replay attack is only
useful in the context of the current Phase 1. If a GROUPKEY-PULL
message is replayed based on a previous Phase 1, the HASH calculation
will fail due to a wrong SKEYID_a. The message will fail processing
before the nonce is ever evaluated. In order for either peer to get
the benefit of the replay protection, it must postpone as much
processing as possible until it receives the message in the protocol
that proves the peer is live. For example, the Responder MUST NOT
adjust its internal state (e.g., keeping a record of the Initiator)
until it receives a message with Nr included properly in the HASH
payload.
Nonces require an additional message in the protocol exchange to
ensure that the GCKS does not add a group member until it proves
liveliness. The GROUPKEY-PULL member-initiator expects to find its
nonce, Ni, in the HASH of a returned message. And the GROUPKEY-PULL
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GCKS responder expects to see its nonce, Nr, in the HASH of a
returned message before providing group-keying material as in the
following exchange.
Initiator (Member) Responder (GCKS)
------------------ ----------------
HDR*, HASH(1), Ni, ID -->
<-- HDR*, HASH(2), Nr, SA
HDR*, HASH(3) -->
<-- HDR*, HASH(4), [SEQ,] KD
Hashes are computed as follows:
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
HASH(4) = prf(SKEYID_a, M-ID | Ni_b | Nr_b [ | SEQ | ] KD)
* Protected by the Phase 1 SA, encryption occurs after HDR
HDR is an ISAKMP header payload that uses the Phase 1 cookies and a
message identifier (M-ID) as in IKEv1. Note that nonces are included
in the first two messages, with the GCKS returning only the SA policy
payload before liveliness is proven. The HASH payloads [RFC2409]
prove that the peer has the Phase 1 secret (SKEYID_a) and the nonce
for the exchange identified by message id, M-ID. Once liveliness is
established, the last message completes the real processing of
downloading the KD payload.
In addition to the Nonce and HASH payloads, the member-initiator
identifies the group it wishes to join through the ISAKMP ID payload.
The GCKS responder informs the member of the current value of the
sequence number in the SEQ payload; the sequence number provides
anti-replay state associated with a KEK. The SEQ payload has no
other use, and is omitted from the GROUPKEY_PULL exchange when a KEK
attribute is not included in the SA payload.
When a SEQ payload is included in the GROUPKEY-PULL exchange, it
includes the most recently used sequence number for the group. At
the conclusion of a GROUPKEY-PULL exchange, the initiating group
member MUST NOT accept any rekey message with both the KEK attribute
SPI value and a sequence number less than or equal to the one
received during the GROUPKEY-PULL. When the first group member
initiates a GROUPKEY-PULL exchange, the GCKS provides a Sequence
Number of zero, since no GROUPKEY-PUSH messages have yet been sent.
Note the sequence number increments only with GROUPKEY-PUSH messages.
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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 responder informs the member of the cryptographic policies
of the group in the SA payload, which describes the DOI, KEK and/or
TEK keying material, and authentication transforms. The SPIs are
also determined by the GCKS and downloaded in the SA payload chain
(see Section 5.2). The SA KEK attribute contains the ISAKMP cookie
pair for the Re-key SA, which is not negotiated but downloaded. The
SA TEK attribute contains a SPI as defined in Section 5.5 of this
document. The second message downloads this SA payload. If a Re-key
SA is defined in the SA payload, then KD will contain the KEK; if one
or more Data-security SAs are defined in the SA payload, KD will
contain the TEKs. This is useful if there is an initial set of TEKs
for the particular group and can obviate the need for future TEK
GROUPKEY-PUSH messages (described in section 4).
3.2.1. ISAKMP Header Initialization
Cookies are used in the ISAKMP header to identify a particular GDOI
session. The GDOI GROUPKEY-PULL exchange uses cookies according to
ISAKMP [RFC2408].
Next Payload identifies an ISAKMP or GDOI payload (see Section 5.0).
Major Version is 1 and Minor Version is 0 according to ISAKMP
(Section 3.1 of [RFC2408]).
The Exchange Type has value 32 for the GDOI GROUPKEY-PULL exchange.
Flags, Message ID, and Length are according to ISAKMP (Section 3.1 of
[RFC2408]).
3.3. Initiator Operations
Before a group member (GDOI initiator) contacts the GCKS, it must
determine the group identifier and acceptable Phase 1 policy via an
out-of-band method. Phase 1 is initiated using the GDOI DOI in the
SA payload. Once Phase 1 is complete, the initiator state machine
moves to the GDOI protocol.
To construct the first GDOI message the initiator chooses Ni and
creates a nonce payload, builds an identity payload including the
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group identifier, and generates HASH(1).
Upon receipt of the second GDOI message, the initiator validates
HASH(2), extracts the nonce Nr, and interprets the SA payload. The
SA payload contains policy describing the security protocol and
cryptographic protocols used by the group. This policy describes the
Re-key SA (if present), Data-security SAs, and other group policy.
If the policy in the SA payload is acceptable to the initiator, it
continues the protocol.
The initiator constructs the third GDOI message by creating HASH(3).
Upon receipt of the fourth GDOI message, the initiator validates
HASH(4).
If SEQ payload is present, the sequence number in the SEQ payload
must be checked against any previously received sequence number for
this group. If it is less than the previously received number, it
should be considered stale and ignored. This could happen if two
GROUPKEY-PULL messages happened in parallel, and the sequence number
changed between the times the results of two GROUPKEY-PULL messages
were returned from the GCKS.
The initiator interprets the KD key packets, where each key packet
includes the keying material for SAs distributed in the SA payload.
Keying material is matched by comparing the SPIs in the key packets
to SPIs previously sent in the SA payloads. Once TEK keys and policy
are matched, the initiator 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 initiator knows to expect the
sequence number reset to 1 with the next Rekey SA, which will be
encrypted with the new KEK attribute. The initiator is now ready to
receive GROUPKEY-PUSH messages.
If the KD payload included an LKH array of keys, the initiator takes
the last key in the array as the group KEK. The array is then stored
without further processing.
3.4. Receiver Operations
The GCKS (responder) passively listens for incoming requests from
group members. The Phase 1 authenticates the group member and sets
up the secure session with them.
Upon receipt of the first GDOI message the GCKS validates HASH(1),
extracts the Ni and group identifier in the ID payload. It verifies
that its database contains the group information for the group
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identifier.
The GCKS constructs the second GDOI message, including a nonce Nr,
and the policy for the group in an SA payload, followed by SA GAP, SA
KEK, 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).
The GCKS constructs the fourth GDOI message, including the SEQ
payload (if the GCKS sends rekey messages), and the KD payload
containing keys corresponding to policy previously sent in the SA TEK
and SA KEK payloads. If a group management algorithm is defined as
part of group policy, the GCKS will first insert the group member
into the group management structure (e.g., a leaf in the LKH tree),
and then create an LKH array of keys and include it in the KD
payload. The first key in the array is associated with the group
member leaf node, followed by each LKH node above it in the tree,
culminating with the root node (which is also the KEK).
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4. GROUPKEY-PUSH Message
GDOI sends control information securely using group communications.
Typically this will be using IP multicast distribution of a GROUPKEY-
PUSH message but it can also be "pushed" using unicast delivery if IP
multicast is not possible. The GROUPKEY-PUSH message replaces a Re-
key SA KEK or KEK array, and/or creates a new Data-security SA.
Member GCKS or Delegate
------ ----------------
<---- HDR*, SEQ, [D,] SA, KD, SIG
* Protected by the Re-key SA KEK; encryption occurs after HDR
HDR is defined below. The SEQ payload is defined in the Payloads
section. One or more D (Delete) payloads optionally specify the
deletion of existing group policy. The SA defines the policy (e.g.,
protection suite) and attributes (e.g., SPI) for a replacement Re-key
SA and/or Data-security SAs. KD is the key download payload as
described in the Payloads section.
The SIG payload includes a signature of a hash of the entire
GROUPKEY-PUSH message (excepting the SIG payload bytes) before it has
been encrypted. The HASH is taken over the string 'rekey', the
GROUPKEY-PUSH HDR, followed by all payloads preceding the SIG
payload. The prefixed string ensures that the signature of the Rekey
datagram cannot be used for any other purpose in the GDOI protocol.
After the SIG payload is created using the signature of the above
hash, with the receiver verifying the signature using a public key
retrieved in policy received by a GROUPKEY-PULL exchange, or
distributed in an earlier GROUPKEY-PUSH message. The current KEK
encryption key (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 an LKH KEK array or single KEK, KD contains a KEK
or KEK array for a new Re-key SA, which has a new cookie pair. When
the KD payload carries a new SA KEK attribute (section 5.3), a Re-key
SA is replaced with a new SA having the same group identifier (ID
specified in message 1 of section 3.2) and incrementing the same
sequence counter, which is initialized in message 4 of section 3.2.
Note the first packet for the given Rekey SA encrypted with the new
KEK attribute will have a Sequence number of 1. If the SA defines an
SA TEK payload, this informs the member that a new Data-security SA
has been created, with keying material carried in KD (Section 5.6).
If the SA defines a large LKH KEK array (e.g., during group
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initialization and batched rekeying), parts of the array MAY be sent
in different unique GROUPKEY-PUSH datagrams. However, each of the
GROUPKEY-PUSH datagrams MUST be a fully formed GROUPKEY-PUSH
datagram. This results in each datagram containing a sequence number
and the policy in the SA payload, which corresponds to the KEK array
portion sent in the KD payload.
4.1. Use of signature keys
In order to avoid overusing its authentication signature key, the
GCKS SHOULD NOT use the same key to sign the SIG payload in the
GROUPKEY-PUSH message as was used for authentication in the GROUPKEY-
PULL exchange.
4.2. ISAKMP Header Initialization
Unlike ISAKMP or IKEv1, the cookie pair is completely determined by
the GCKS. The cookie pair in the GDOI ISAKMP header identifies the
Re- key SA to differentiate the secure groups managed by a GCKS.
Thus, GDOI uses the cookie fields as an SPI.
Next Payload identifies an ISAKMP or GDOI payload (see Section 5.0).
Major Version is 1 and Minor Version is 0 according to ISAKMP
(Section 3.1 of [RFC2408]).
The Exchange Type has value 33 for the GDOI GROUPKEY-PUSH message.
Flags MUST have the Encryption bit set according to [RFC2008, Section
3.1]. All other bits MUST be set to zero.
Message ID MUST be set to zero.
Length is according to ISAKMP (Section 3.1 of [RFC2408]).
4.3. Deletion of SAs
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
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follows:
o The Domain of Interpretation field contains the GDOI DOI.
o The Protocol-Id field contains TEK protocol id values defined in
Section 5.5 of this document. To delete a KEK SA, the value of zero
MUST be used as the protocol id. Note that only one protocol id
value can be defined in a Delete payload. If a TEK SA and a KEK SA
must be deleted, they must be sent in different Delete payloads.
There may be circumstances where the GCKS may want to start over with
a clean slate. If the administrator is no longer confident in the
integrity of the group, the GCKS can signal deletion of all policy of
a particular TEK protocol by sending a TEK with a SPI value equal to
zero in the delete payload. For example, if the GCKS wishes to
remove all the KEKs and all the TEKs in the group, the GCKS SHOULD
send a delete payload with a spi of zero and a protocol_id of a TEK
protocol_id value, followed by another delete payload with a spi of
zero and protocol_id of zero, indicating that the KEK SA should be
deleted.
4.4. GCKS Operations
GCKS or its delegate may initiate a Rekey message for one of several
reasons, e.g., the group membership has changed or keys are due to
expire.
To begin the rekey datagram the GCKS builds an ISAKMP HDR with the
correct cookie pair, and a SEQ payload that includes a sequence
number which is one greater than the previous rekey datagram. If the
message is using the new KEK attribute for the first time, the SEQ is
reset to 1 in this message.
An SA payload is then added. This is identical in structure and
meaning to a SA payload sent in a GROUPKEY-PULL exchange. If there
are changes to the KEK (including due to group members being
excluded, in the case of LKH), an SA_KEK attribute is added to the
SA. If there are one or more new TEKs then SA_TEK attributes are
added to describe that policy.
A KD payload is then added. This is identical in structure and
meaning to a KD payload sent in a GROUPKEY-PULL exchange. If an
SA_KEK attribute was included in the SA payload then corresponding
KEK keys (or a KEK update array) is included. A KEK update array is
created by first determining which group members have been excluded,
and then generating new keys as necessary and distribute LKH update
arrays sufficient to provide the new KEK to remaining group members
(see Section 5.4.1 of [RFC2627] for details). TEK keys are also sent
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for each SA_TEK attribute included in the SA payload.
In the penultimate step, the initiator hashes the string "rekey"
followed by the key management message already formed. The hash is
signed, placed in a SIG payload and added to the datagram.
Lastly, the payloads following the HDR are encrypted using the
current KEK encryption key. The datagram can now be sent.
4.5. Group Member Operations
A group member receiving the GROUPKEY-PUSH datagram matches the
cookie pair in the ISAKMP HDR to an existing SA. The message is
decrypted, and the form of the datagram is validated. This weeds out
obvious ill-formed messages (which may be sent as part of a Denial of
Service attack on the group).
The sequence number in the SEQ payload is validated to ensure that it
is greater than the previously received sequence number, and that it
fits within a window of acceptable values. The SIG payload is then
validated. If the signature fails, the message is discarded.
The SA and KD payloads are processed which results in a new GDOI
Rekey SA (if the SA payload included an SA_KEK attribute) and/or new
IPsec SAs being added to the system. If the KD payload includes an
LKH update array, the group member compares the LKH ID in each key
update packet to the LKH IDs that it holds. If it finds a match, it
decrypts the key using the key prior to it in the key array and
stores the new key in the LKH key array that it holds. The final
decryption yields the new group KEK.
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5. Payloads and Defined Values
This document specifies use of several ISAKMP payloads, which are
defined in accordance with RFC 2408. The following payloads are
extended or further specified.
Next Payload Type Value
----------------- -----
Security Association (SA) 1
Identification (ID) 5
Nonce (N) 10
Several payload formats specific to the group security exchanges are
required.
Next Payload Type Value
----------------- -----
SA KEK Payload (SAK) 15
SA TEK Payload (SAT) 16
Key Download (KD) 17
Sequence Number (SEQ) 18
SA Group Associated Policy (GAP) TBD-1
5.1. Identification Payload
The Identification Payload is defined in RFC 2408. For the GDOI, it
is used to identify a group identity that will later be associated
with Security Associations for the group. A group identity may map
to a specific IP multicast group, or may specify a more general
identifier, such as one that represents a set of related multicast
streams.
When used with the GDOI, the DOI Specific ID Data field MUST be set
to 0.
When used with the GDOI, the ID_KEY_ID ID Type MUST be supported by a
conforming implementation, and MUST specify a four (4)-octet group
identifier as its value. Implementations MAY also support other ID
Types.
5.2. Security Association Payload
The Security Association payload is defined in RFC 2408. For the
GDOI, it is used by the GCKS to assert security attributes for both
Re-key and Data-security SAs.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Next Payload ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! DOI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Situation !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! SA Attribute Next Payload ! RESERVED2 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
The Security Association Payload fields are defined as follows:
o Next Payload (1 octet) -- Identifies the next payload for the
GROUPKEY-PULL or the GROUPKEY-PUSH message as defined above. The
next payload MUST NOT be a SAK Payload or SAT Payload type, but the
next non-Security Association type payload.
o RESERVED (1 octet) -- Must be zero.
o Payload Length (2 octets) -- Is the octet length of the current
payload including the generic header and all TEK and KEK payloads.
o DOI (4 octets) -- Is the GDOI, which is value 2.
o Situation (4 octets) -- Must be zero.
o SA Attribute Next Payload (1 octet) -- Must be either a SAK Payload
or a SAT Payload. See section 5.2.1 for a description of which
circumstances are required for each payload type to be present.
o RESERVED (2 octets) -- Must be zero.
5.2.1. Payloads following the SA payload
Payloads that define specific security association attributes for the
KEK and/or TEKs used by the group MUST follow the SA payload. How
many of each payload is dependent upon the group policy. There may
be zero or one SAK Payloads, zero or more GAP Payloads, and zero or
more SAT Payloads, where either one SAK or SAT payload MUST be
present. When present, the order of the SA Attributes payloads must
be: KEK, GAP, and TEKs.
This latitude allows various group policies to be accommodated. For
example if the group policy does not require the use of a Re-key SA,
the GCKS would not need to send an SA KEK attribute to the group
member since all SA updates would be performed using the Registration
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SA. Alternatively, group policy might use a Re-key SA but choose to
download a KEK to the group member only as part of the Registration
SA. Therefore, the KEK policy (in the SA KEK attribute) would not be
necessary as part of the Re-key SA message SA payload.
Specifying multiple SATs allows multiple sessions to be part of the
same group and multiple streams to be associated with a session
(e.g., video, audio, and text) but each with individual security
association policy.
A GAP payload allows for the distribution of group-wise policy, such
as instructions as to when to activate and de-activate SAs.
5.3. SA KEK payload
The SA KEK (SAK) payload contains security attributes for the KEK
method for a group and parameters specific to the GROUPKEY-PULL
operation. The source and destination identities describe the
identities used for the GROUPKEY-PULL datagram.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Next Payload ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Protocol ! SRC ID Type ! SRC ID Port !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
!SRC ID Data Len! SRC Identification Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! DST ID Type ! DST ID Port !DST ID Data Len!
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! DST Identification Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! !
~ SPI ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! RESERVED2 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
~ KEK Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
The SAK Payload fields are defined as follows:
o Next Payload (1 octet) -- Identifies the next payload for the
GROUPKEY-PULL or the GROUPKEY-PUSH message. The only valid next
payload types for this message are a GAP Payload, SAT Payload or zero
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to indicate that no SA Attribute payloads follow.
o RESERVED (1 octet) -- Must be zero.
o Payload Length (2 octets) -- Length of this payload, including the
KEK attributes.
o Protocol (1 octet) -- Value describing an IP protocol ID (e.g.,
UDP/TCP) for the rekey datagram.
o SRC ID Type (1 octet) -- Value describing the identity information
found in the SRC Identification Data field. Defined values are
specified by the IPsec Identification Type section in the IANA
isakmpd-registry [ISAKMP-REG].
o SRC ID Port (2 octets) -- Value specifying a port associated with
the source Id. A value of zero means that the SRC ID Port field
should be ignored.
o SRC ID Data Len (1 octet) -- Value specifying the length of the SRC
Identification Data field.
o SRC Identification Data (variable length) -- Value, as indicated by
the SRC ID Type.
o DST ID Type (1 octet) -- Value describing the identity information
found in the DST Identification Data field. Defined values are
specified by the IPsec Identification Type section in the IANA
isakmpd-registry [ISAKMP-REG].
o DST ID Prot (1 octet) -- Value describing an IP protocol ID (e.g.,
UDP/TCP).
o DST ID Port (2 octets) -- Value specifying a port associated with
the source Id.
o DST ID Data Len (1 octet) -- Value specifying the length of the DST
Identification Data field.
o DST Identification Data (variable length) -- Value, as indicated by
the DST ID Type.
o SPI (16 octets) -- Security Parameter Index for the KEK. The SPI
must be the ISAKMP Header cookie pair where the first 8 octets become
the "Initiator Cookie" field of the GROUPKEY-PUSH message ISAKMP HDR,
and the second 8 octets become the "Responder Cookie" in the same
HDR. As described above, these cookies are assigned by the GCKS.
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o RESERVED2 (4 octets) -- Must be zero.
o KEK Attributes -- Contains KEK policy attributes associated with
the group. The following sections describe the possible attributes.
Any or all attributes may be optional, depending on the group policy.
5.3.1. KEK Attributes
The following attributes may be present in a SAK Payload. The
attributes must follow the format defined in ISAKMP (Section 3.3 of
[RFC2408]). In the table, attributes that are defined as TV are
marked as Basic (B); attributes that are defined as TLV are marked as
Variable (V).
ID Class Value Type
-------- ----- ----
RESERVED 0
KEK_MANAGEMENT_ALGORITHM 1 B
KEK_ALGORITHM 2 B
KEK_KEY_LENGTH 3 B
KEK_KEY_LIFETIME 4 V
SIG_HASH_ALGORITHM 5 B
SIG_ALGORITHM 6 B
SIG_KEY_LENGTH 7 B
The KEK_MANAGEMENT_ALGORITHM attribute may only be included in a
GROUPKEY-PULL message.
5.3.2. KEK_MANAGEMENT_ALGORITHM
The KEK_MANAGEMENT_ALGORITHM class specifies the group KEK management
algorithm used to provide forward or backward access control (i.e.,
used to exclude group members). Defined values are specified in the
following table.
KEK Management Type Value
------------------- -----
RESERVED 0
LKH 1
RESERVED 2-127
Private Use 128-255
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5.3.2.1. LKH
This type indicates the group management method described in Section
5.4 of [RFC2627].
5.3.3. KEK_ALGORITHM
The KEK_ALGORITHM class specifies the encryption algorithm using with
the KEK. Defined values are specified in the following table. An
GDOI implementation MUST abort if it encounters and attribute or
capability that it does not understand.
Algorithm Type Value
-------------- -----
RESERVED 0
KEK_ALG_DES 1
KEK_ALG_3DES 2
KEK_ALG_AES 3
RESERVED 4-127
Private Use 128-255
If a KEK_MANAGEMENT_ALGORITHM is defined which defines multiple keys
(e.g., LKH), and if the management algorithm does not specify the
algorithm for those keys, then the algorithm defined by the
KEK_ALGORITHM attribute MUST be used for all keys which are included
as part of the management.
5.3.3.1. KEK_ALG_DES
This type specifies DES using the Cipher Block Chaining (CBC) mode as
described in [FIPS81].
5.3.3.2. KEK_ALG_3DES
This type specifies 3DES using three independent keys as described in
"Keying Option 1" in [FIPS46-3].
5.3.3.3. KEK_ALG_AES
This type specifies AES as described in [FIPS197]. The mode of
operation for AES is Cipher Block Chaining (CBC) as recommended in
[SP.800-38A].
5.3.4. KEK_KEY_LENGTH
The KEK_KEY_LENGTH class specifies the KEK Algorithm key length (in
bits). The Group Controller/Key Server (GCKS) adds the KEK_KEY_LEN
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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 KEK_ALGORITHM
attribute and does not need the KEK_KEY_LEN attribute. Sending the
KEK_KEY_LEN attribute in the SA payload is OPTIONAL if the KEK cipher
has a fixed key length. Also, note that the KEK_KEY_LEN includes
only the actual length of the cipher key (the IV length is not
included in this attribute).
5.3.5. KEK_KEY_LIFETIME
The KEK_KEY_LIFETIME class specifies the maximum time for which the
KEK is valid. The GCKS may refresh the KEK at any time before the
end of the valid period. The value is a four (4) octet number
defining a valid time period in seconds.
5.3.6. SIG_HASH_ALGORITHM
SIG_HASH_ALGORITHM specifies the SIG payload hash algorithm. The
following table defines the algorithms for SIG_HASH_ALGORITHM.
Algorithm Type Value
-------------- -----
RESERVED 0
SIG_HASH_MD5 1
SIG_HASH_SHA1 2
SIG_HASH_SHA256 TBD-2
SIG_HASH_SHA384 TBD-3
SIG_HASH_SHA512 TBD-4
RESERVED 6-127
Private Use 128-255
The SHA hash algorithms are defined in the Secure Hash
Standard[FIPS.180-2.2002].
If the SIG_ALGORITHM is SIG_ALG_ECDSA-256, SIG_ALG_ECDSA-384, or
SIG_ALG_ECDSA-521 the hash algorithm is implicit in the definition,
and SIG_HASH_ALGORITHM is not required to be present in a SAK
Payload.
5.3.7. SIG_ALGORITHM
The SIG_ALGORITHM class specifies the SIG payload signature
algorithm. Defined values are specified in the following table.
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Algorithm Type Value
-------------- -----
RESERVED 0
SIG_ALG_RSA 1
SIG_ALG_DSS 2
SIG_ALG_ECDSS 3
SIG_ALG_RSA_PSS TBD-6
SIG_ALG_ECDSA-256 TBD-7
SIG_ALG_ECDSA-384 TBD-8
SIG_ALG_ECDSA-521 TBD-9
RESERVED 8-127
Private Use 128-255
5.3.7.1. SIG_ALG_RSA
This algorithm specifies the RSA digital signature algorithm using
the EMSA-PKCS1-v1_5 encoding method, as described in [RFC3447].
5.3.7.2. SIG_ALG_DSS
This algorithm specifies the DSS digital signature algorithm as
described in Section 4 of [FIPS186-3].
5.3.7.3. SIG_ALG_ECDSS
This algorithm specifies the Elliptic Curve digital signature
algorithm as described in Section 5 of [FIPS186-3]. This definition
is deprecated in favor of the SIG_ALG_ECDSA family of algorithms.
5.3.7.4. SIG_ALG_RSA_PSS
This algorithm specifies the RSA digital signature algorithm using
the EMSA-PSS encoding method, as described in [RFC3447].
5.3.7.5. SIG_ALG_ECDSA-256
This algorithm specifies the 256-bit Random ECP Group, as described
in [RFC5903]. The format of the signature in the SIG payload MUST be
as specified in [RFC4754].
5.3.7.6. SIG_ALG_ECDSA-384
This algorithm specifies the 384-bit Random ECP Group, as described
in [RFC5903]. The format of the signature in the SIG payload MUST be
as specified in [RFC4754].
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5.3.7.7. SIG_ALG_ECDSA-521
This algorithm specifies the 521-bit Random ECP Group, as described
in [RFC5903]. The format of the signature in the SIG payload MUST be
as specified in [RFC4754].
5.3.8. SIG_KEY_LENGTH
The SIG_KEY_LENGTH class specifies the length of the SIG payload key
in bits.
5.4. Group Associated Policy
RFC 3547 provides for the distribution of policy in the GROUPKEY-PULL
exchange in an SA payload. Policy can define GROUPKEY-PUSH policy
(SA KEK) or traffic encryption policy (SA TEK) such as IPsec policy.
There is a need to distribute group policy that fits into neither
category. Some of this policy is generic to the group, and some is
sender-specific policy for a particular group member.
GDOI distributes this associated group policy in a new payload called
the SA Group Associated Policy (SA GAP). The SA GAP payload follows
any SA KEK payload, and is placed before any SA TEK payloads. In the
case that group policy does not include an SA KEK, the SA Attribute
Next Payload field in the SA payload MAY indicate the SA GAP payload.
The SA GAP payload is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Next Payload ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Group Associated Policy Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
The SA GAP payload fields are defined as follows:
o Next Payload (1 octet) -- Identifies the next payload present in
the GROUPKEY-PULL or the GROUPKEY-PUSH message. The only valid
next payload type for this message is an SA TEK or zero to
indicate there are no more security association attributes.
o RESERVED (1 octet) -- Must be zero.
o Payload Length (2 octets) -- Length of this payload, including the
SA GAP header and Attributes.
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o Group Associated Policy Attributes (variable) -- Contains
attributes following the format defined in Section 3.3 of RFC
2408.
Several group associated policy attributes are defined in this memo.
An GDOI implementation MUST abort if it encounters and attribute or
capability that it does not understand.
5.4.1. ACTIVATION_TIME_DELAY
This attribute allows a GCKS to set the Activation Time Delay for SAs
generated from TEKs. The value is in seconds. If a group member
receives a TEK with an ATD value, but discovers that it has no
current SAs matching the policy in the TEK, then it SHOULD create and
install SAs from the TEK immediately.
5.4.2. DEACTIVATION_TIME_DELAY
This attribute allows a GCKS to set the Deactivation Time Delay for
SAs generated from TEKs. The value is in seconds.
5.4.3. SENDER_ID
Several new AES counter-based modes of operation have been specified
for ESP [RFC3686],[RFC4106],[RFC4309],[RFC4543] and AH [RFC4543].
These AES counter-based modes require that no two senders in the
group ever send a packet with the same IV. This requirement can be
met using the method described in
[I-D.ietf-msec-ipsec-group-counter-modes], which requires each sender
to be allocated a unique Sender ID (SID). The SENDER_ID attribute is
used to distribute a SID to a group member during the GROUPKEY-PULL
message. Other algorithms with the same need may be defined in the
future; the sender MUST use the IV construction method described
above with those algorithms as well.
The SENDER_ID attribute value contains the following fields.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! SID Length ! SID Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
o SID Length (1 octet) -- A natural number defining the number of
bits to be used in the SID field of the counter mode transform
nonce.
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o SID Value (variable) -- The Sender ID value allocated to the group
member.
5.4.3.1. GCKS Semantics
The GCKS maintains a SID counter (SIDC). It is incremented each time
a SENDER_ID attribute is distributed to a group member. The first
group member to register is given the SID of 1.
Any group member registering will be given a new SID value, which
allows group members to act as a group sender when an older SID value
becomes unusable (as described in the next section).
A GCKS MAY allocate multiple SID values in one SA GAP payload.
Allocating several SID values at the same time to a group member
expected to send at a high rate would obviate the need for the group
member to re-register as frequently.
If a GCKS allocates all SID values, it can no longer respond to GDOI
registrations and must re-initialize the entire group. This is done
by issuing DELETE notifications for all ESP and AH SAs in a GDOI
rekey message, resetting the SIDC to zero, and creating new ESP and
AH SAs that match the group policy. When group members re-register,
the SIDs are allocated again beginning with the value 1 as described
above. Each re-registering group member will be given a new SID and
the new group policy.
The SENDER_ID attribute MUST NOT be sent as part of a GROUPKEY-PUSH
message, because distributing the same sender-specific policy to more
than one group member may reduce the security of the group.
5.4.3.2. Group Member Semantics
The SENDER_ID attribute value distributed to the group member MUST be
used by that group member as the Sender Identifier (SID) field
portion of the IV. The SID is used for all counter mode SAs
distributed by the GCKS to be used for communications sent as a part
of this group.
When the Sender-Specific IV (SSIV) field for any IPsec SA is
exhausted, the group member MUST no longer act as a sender using its
active SID. The group member SHOULD re-register, during which time
the GCKS will issue a new SID to the group member. The new SID
replaces the existing SID used by this group member, and also resets
the SSIV value to it's 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.
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A group member MUST NOT process SENDER_ID attribute present in a
GROUPKEY-PUSH message.
5.5. SA TEK Payload
The SA TEK (SAT) payload contains security attributes for a single
TEK associated with a group.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Next Payload ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Protocol-ID ! TEK Protocol-Specific Payload ~
+-+-+-+-+-+-+-+-+ ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
The SAT Payload fields are defined as follows:
o Next Payload (1 octet) -- Identifies the next payload for the
GROUPKEY-PULL or the GROUPKEY-PUSH message. The only valid next
payload types for this message are another SAT Payload or zero to
indicate there are no more security association attributes.
o RESERVED (1 octet) -- Must be zero.
o Payload Length (2 octets) -- Length of this payload, including the
TEK Protocol-Specific Payload.
o Protocol-ID (1 octet) -- Value specifying the Security Protocol.
The following table defines values for the Security Protocol
Protocol ID Value
----------- -----
RESERVED 0
GDOI_PROTO_IPSEC_ESP 1
GDOI_PROTO_IPSEC_AH TBD-5
RESERVED 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 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
The SAT Payload fields are defined as follows:
o Protocol (1 octet) -- Value describing an IP protocol ID (e.g.,
UDP/TCP). A value of zero means that the Protocol field should be
ignored.
o SRC ID Type (1 octet) -- Value describing the identity information
found in the SRC Identification Data field. Defined values are
specified by the IPsec Identification Type section in the IANA
isakmpd-registry [ISAKMP-REG].
o SRC ID Port (2 octets) -- Value specifying a port associated with
the source Id. A value of zero means that the SRC ID Port field
should be ignored.
o SRC ID Data Len (1 octet) -- Value specifying the length of the SRC
Identification Data field.
o SRC Identification Data (variable length) -- Value, as indicated by
the SRC ID Type. Set to three bytes of zero for multiple-source
multicast groups that use a common TEK for all senders.
o DST ID Type (1 octet) -- Value describing the identity information
found in the DST Identification Data field. Defined values are
specified by the IPsec Identification Type section in the IANA
isakmpd-registry [ISAKMP-REG].
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o DST ID Prot (1 octet) -- Value describing an IP protocol ID (e.g.,
UDP/TCP). A value of zero means that the DST Id Prot field should be
ignored.
o DST ID Port (2 octets) -- Value specifying a port associated with
the source Id. A value of zero means that the DST ID Port field
should be ignored.
o DST ID Data Len (1 octet) -- Value specifying the length of the DST
Identification Data field.
o DST Identification Data (variable length) -- Value, as indicated by
the DST ID Type.
o Transform ID (1 octet) -- Value specifying which ESP or AH
transform is to be used. The list of valid values is defined in the
IPsec ESP or IPsec AH Transform Identifiers section of the IANA
isakmpd-registry [ISAKMP-REG].
o SPI (4 octets) -- Security Parameter Index for ESP.
o RFC 2407 Attributes -- ESP and AH Attributes from RFC 2407 Section
4.5. The GDOI supports all IPsec DOI SA Attributes for
GDOI_PROTO_IPSEC_ESP and GDOI_PROTO_IPSEC_AH excluding the Group
Description (section 4.5 of [RFC2407], which MUST NOT be sent by a
GDOI implementation and is ignored by a GDOI implementation if
received. The following attributes MUST be supported by an
implementation supporting ESP and AH: SA Life Type, SA Life Duration,
Encapsulation Mode. An implementation supporting ESP must also
support the Authentication Algorithm attribute if the ESP transform
includes authentication/ The Authentication Algorithm attribute of
the IPsec DOI is group authentication in GDOI.
5.5.1.1. Harmonization with RFC 5374
The Multicast Extensions to the Security Architecture for the
Internet Protocol (RFC 5374) introduces new requirements for a group
key management system distributing IPsec policy. The following
sections describe new GDOI requirements that result from harmonizing
with that document.
5.5.1.1.1. Group Security Policy Database Attributes
RFC 5374 describes 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
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[ISAKMP-REG]. This section defines how GDOI can convey the new
attributes as IPsec Security Association Attributes.
5.5.1.1.2. Address Preservation
Applications use the extensions in RFC 5374 create encapsulate IPsec
multicast packets that are IP multicast packets. In order for the
GDOI group member to appropriately setup the GSPD, the GCKS must
provide that policy to the group member.
Depending on group policy, several address preservation methods are
possible: no address preservation ("None"), preservation of the
original source address ("Source-Only"), preservation of the original
destination address ("Destination-Only"), or both addresses ("Source-
And-Destination"). This memo adds the "Address Preservation"
security association attribute. If this attribute is not included in
a GDOI SA TEK payload provided by a GCKS, then Source-And-Destination
address preservation has been defined for the SA TEK.
5.5.1.1.3. SA Direction
Depending on group policy, an IPsec SA created from an SA TEK payload
may be required in one or both directions. SA TEK policy used by
multiple senders is required to be installed in both the sending and
receiving direction ("Symmetric"), whereas SA TEK for a single sender
should only be installed in the receiving direction by receivers
("Receiver-Only") and in the sending direction by the sender
("Sender-Only"). This memo adds the "SA Direction" security
association attribute. If the attribute is not included in a GDOI SA
TEK payload, then the IPsec SA is treated as a Symmetric IPsec SA.
5.5.1.1.4. Re-key rollover
Section 4.2.1 of RFC 5374 specifies a key rollover method that
requires two values be given it from the group key management
protocol. The Activation Time Delay (ATD) attribute allows the GCKS
to specify how long after the start of a re-key event that a group
member is to activate new TEKs. The Deactivation Time Delay (DTD)
attribute allows the GCKS to specify how long after the start of a
re-key event that a group member is to deactivate existing TEKs.
This memo adds new attributes by which a GCKS can relay these values
to group members as part of the Group Associated Policy described in
Section 5.
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5.5.2. Other Security Protocols
Besides ESP and AH, GDOI should serve to establish SAs for secure
groups needed by other Security Protocols that operate at the
transport, application, and internetwork layers. These other
Security Protocols, however, are in the process of being developed or
do not yet exist.
The following information needs to be provided for a Security
Protocol to the GDOI.
o The Protocol-ID for the particular Security Protocol
o The SPI Size
o The method of SPI generation
o The transforms, attributes and keys needed by the Security
Protocol
All Security Protocols must provide the information in the bulleted
list above to guide the GDOI specification for that protocol.
Definitions for the support of those Security Protocols in GDOI will
be specified in separate documents.
A Security Protocol MAY protect traffic at any level of the network
stack. However, in all cases applications of the Security Protocol
MUST protect traffic which MAY be shared by more than two entities.
5.6. Key Download Payload
The Key Download Payload contains group keys for the group specified
in the SA Payload. These key download payloads can have several
security attributes applied to them based upon the security policy of
the group as defined by the associated SA Payload.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Next Payload ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Number of Key Packets ! RESERVED2 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
~ Key Packets ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
The Key Download Payload fields are defined as follows:
o Next Payload (1 octet) -- Identifier for the payload type of the
next payload in the message. If the current payload is the last in
the message, then this field will be zero.
o RESERVED (1 octet) -- Unused, set to zero.
o Payload Length (2 octets) -- Length in octets of the current
payload, including the generic payload header.
o Number of Key Packets (2 octets) -- Contains the total number of
both TEK and Rekey arrays being passed in this data block.
o Key Packets Several types of key packets are defined. Each Key
Packet has the following format.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! KD Type ! RESERVED ! KD Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! SPI Size ! SPI (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
~ Key Packet Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
o Key Download (KD) Type (1 octet) -- Identifier for the Key Data
field of this Key Packet.
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Key Download Type Value
----------------- -----
RESERVED 0
TEK 1
KEK 2
LKH 3
RESERVED 4-127
Private Use 128-255
"KEK" is a single key whereas LKH is an array of key-encrypting keys.
o RESERVED (1 octet) -- Unused, set to zero.
o Key Download Length (2 octets) -- Length in octets of the Key
Packet data, including the Key Packet header.
o SPI Size (1 octet) -- Value specifying the length in octets of the
SPI as defined by the Protocol-Id.
o SPI (variable length) -- Security Parameter Index which matches a
SPI previously sent in an SAK or SAT Payload.
o Key Packet Attributes (variable length) -- Contains Key
information. The format of this field is specific to the value of
the KD Type field. The following sections describe the format of
each KD Type.
5.6.1. TEK Download Type
The following attributes may be present in a TEK Download Type.
Exactly one attribute matching each type sent in the SAT payload MUST
be present. The attributes must follow the format defined in ISAKMP
(Section 3.3 of [RFC2408]). In the table, attributes defined as TV
are marked as Basic (B); attributes defined as TLV are marked as
Variable (V).
TEK Class Value Type
--------- ----- ----
RESERVED 0
TEK_ALGORITHM_KEY 1 V
TEK_INTEGRITY_KEY 2 V
TEK_SOURCE_AUTH_KEY 3 V
If no TEK key packets are included in a Registration KD payload, the
group member can expect to receive the TEK as part of a Re-key SA.
At least one TEK must be included in each Re-key KD payload.
Multiple TEKs may be included if multiple streams associated with the
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SA are to be rekeyed.
5.6.1.1. TEK_ALGORITHM_KEY
The TEK_ALGORITHM_KEY class declares that the encryption key for this
SPI is contained as the Key Packet Attribute. The encryption
algorithm that will use this key was specified in the SAT payload.
In the case that the algorithm requires multiple keys (e.g., 3DES),
all keys will be included in one attribute.
DES keys will consist of 64 bits (the 56 key bits with parity bit).
Triple DES keys will be specified as a single 192 bit attribute
(including parity bits) in the order that the keys are to be used for
encryption (e.g., DES_KEY1, DES_KEY2, DES_KEY3).
5.6.1.2. TEK_INTEGRITY_KEY
The TEK_INTEGRITY_KEY class declares that the integrity key for this
SPI is contained as the Key Packet Attribute. The integrity
algorithm that will use this key was specified in the SAT payload.
Thus, GDOI assumes that both the symmetric encryption and integrity
keys are pushed to the member. HMAC-SHA1 keys will consist of 160
bits[RFC2404], HMAC-MD5 keys will consist of 128 bits[RFC2403].
HMAC-SHA2 and AES-GMAC keys will have a key length equal to the
output length of the hash functions [RFC4868][RFC4543].
5.6.1.3. TEK_SOURCE_AUTH_KEY
The TEK_SOURCE_AUTH_KEY class declares that the source authentication
key for this SPI is contained in the Key Packet Attribute. The
source authentication algorithm that will use this key was specified
in the SAT payload.
5.6.2. KEK Download Type
The following attributes may be present in a KEK Download Type.
Exactly one attribute matching each type sent in the SAK payload MUST
be present. The attributes must follow the format defined in ISAKMP
(Section 3.3 of [RFC2408]). In the table, attributes defined as TV
are marked as Basic (B); attributes defined as TLV are marked as
Variable (V).
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KEK Class Value Type
--------- ----- ----
RESERVED 0
KEK_ALGORITHM_KEY 1 V
SIG_ALGORITHM_KEY 2 V
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 Initialization
Vector (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
RESERVED 4-127
Private Use 128-255
If an LKH key packet is included in the KD payload, there must be
only one present.
5.6.3.1. LKH_DOWNLOAD_ARRAY
This attribute is used to download a set of keys to a group member.
It MUST NOT be included in a GROUPKEY-PUSH message KD payload if the
GROUPKEY-PUSH is sent to more than the group member. If an
LKH_DOWNLOAD_ARRAY attribute is included in a KD payload, there must
be only one present.
This attribute consists of a header block, followed by one or more
LKH keys.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! LKH Version ! # of LKH Keys ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! LKH Keys !
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The KEK_LKH attribute fields are defined as follows:
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 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o LKH ID (2 octets) -- Identity of the LKH node. A GCKS is free to
choose the ID in an implementation-specific manner (e.g., the
position of this key in a binary tree structure used by LKH).
o Key Type (1 octet) -- Encryption algorithm for which this key data
is to be used. This value is specified in Section 5.3.3.
o RESERVED (1 octet) -- Unused, set to zero.
o Key Creation Date (4 octets) -- Time value of when this key data
was originally generated. A time value of zero indicates that there
is no time before which this key is not valid.
o Key Expiration Date (4 octets) -- Time value of when this key is no
longer valid for use. A time value of zero indicates that this key
does not have an expiration time.
o Key Handle (4 octets) -- Value assigned by the GCKS to uniquely
identify a key within an LKH ID. Each new key distributed by the
GCKS for this node will have a key handle identity distinct from
previous or successive key handles specified for this node.
o Key Data (variable length) -- Key data, which is dependent on the
Key Type algorithm for its format. If the mode of operation for the
algorithm requires an Initialization Vector (IV), an explicit IV MUST
be included in the Key Data field 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
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of the LKH Key structures contain keys along the path of the key tree
in order from the leaf, culminating in the group KEK.
5.6.3.2. LKH_UPDATE_ARRAY
This attribute is used to update the keys for a group. It is most
likely to be included in a GROUPKEY-PUSH message KD payload to rekey
the entire group. This attribute consists of a header block,
followed by one or more LKH keys, as defined in the previous section.
There may be any number of UPDATE_ARRAY attributes included in a KD
payload.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! LKH Version ! # of LKH Keys ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! LKH ID ! RESERVED2 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Key Handle !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! LKH Keys !
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o LKH version (1 octet) -- Version of the LKH data format. Must be
one.
o Number of LKH Keys (2 octets) -- Number of distinct LKH keys in
this sequence.
o RESERVED (1 octet) -- Unused, set to zero.
o LKH ID (2 octets) -- Node identifier associated with the key used
to encrypt the first LKH Key.
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
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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.
5.7. Sequence Number Payload
The Sequence Number Payload (SEQ) provides an anti-replay protection
for GROUPKEY-PUSH messages. Its use is similar to the Sequence
Number field defined in the IPsec ESP protocol [RFC4303].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Sequence Number !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Sequence Number Payload fields are defined as follows:
o Next Payload (1 octet) -- Identifier for the payload type of the
next payload in the message. If the current payload is the last in
the message, then this field will be zero.
o RESERVED (1 octet) -- Unused, set to zero.
o Payload Length (2 octets) -- Length in octets of the current
payload, including the generic payload header.
o Sequence Number (4 octets) -- This field contains a monotonically
increasing counter value for the group. It is initialized to zero by
the GCKS, and incremented in each subsequently-transmitted message.
Thus the first packet sent for a given Rekey SA will have a Sequence
Number of 1. The GDOI implementation keeps a sequence counter as an
attribute for the Rekey SA and increments the counter upon receipt of
a GROUPKEY-PUSH message. The current value of the sequence number
must be transmitted to group members as a part of the Registration SA
payload. A group member must keep a sliding receive window. The
window must be treated as in the ESP protocol [RFC4303] Section
3.4.3.
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5.8. Nonce
The data portion of the Nonce payload (i.e., Ni_b and Nr_b included
in the HASHs) MUST be a value between 8 and 128 bytes.
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6. Algorithm Selection
For GDOI implementations to interoperate, they must support one or
more security algorithms in common. This section specifies the
security algorithm implementation requirements for standards-
conformant GDOI implementations. In call cases the choices are
intended to maintain at least 112 bits of security [SP.800-131].
Algorithms not referenced in this section can also be used.
6.1. KEK
These tables list the algorithm selections for values related to the
KEK.
Requirement KEK Management Algorithm
----------- ---------------------
SHOULD LKH
Requirement KEK Algorithm (notes)
----------- ---------------------
MUST KEK_ALG_AES with 128-bit keys
SHOULD NOT KEK_ALG_DES (1)
Requirement KEK Signature Hash Algorithm (notes)
----------- ------------------------------------
MUST SIG_HASH_SHA256
SHOULD SIG_HASH_SHA1 (2)
SHOULD NOT SIG_HASH_MD5 (3)
Requirement KEK Signature Algorithm (notes)
----------- -------------------------------
MUST SIG_ALG_RSA with 2048-bit keys
Notes:
(1) DES, with its small key size and corresponding security strength
is of questionable security for general use
(2) The use of SIG_HASH_SHA1 as a signature hash algorithm used with
GROUPKEY-PUSH messages remains safe at the time of this writing,
and is a widely deployed signature hash algorithm.
(3) Although a real weakness with second preimage resistance with
MD5 has not been found at the time of this writing, the security
strength of MD5 has been shown to be rapidly declining over time
and it's use should be understood and carefully weighed.
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6.2. TEK
The following table lists the requirements for Security Protocol
support for an implementation.
Requirement KEK Management Algorithm
----------- ---------------------
MUST GDOI_PROTO_IPSEC_ESP
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7. Security Considerations
GDOI is a security association (SA) management protocol for groups of
senders and receivers. Unlike a data security protocol, SA
management includes a key establishment protocol to securely
establish keys at communication endpoints. This protocol performs
entity authentication of the GDOI member or Group Controller/Key
Server (GCKS), it provides confidentiality of key management
messages, and it provides source authentication of those messages.
This protocol also uses best-known practices for defense against man-
in-middle, connection hijacking, replay, reflection, and denial-of-
service (DOS) attacks on unsecured networks [STS], [RFC2522],
[SKEME]. GDOI assumes the network is not secure and may be under the
complete control of an attacker.
GDOI assumes that the host computer is 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. The security of GDOI, therefore,
is as good as the degree to which group members can be trusted to
protect authenticators, encryption keys, decryption keys, and message
authentication keys.
There are three phases of GDOI as described in this document: an
ISAKMP Phase 1 protocol, a new exchange called GROUPKEY-PULL which is
protected by the ISAKMP Phase 1 protocol, and a new message called
GROUPKEY-PUSH. Each phase is considered separately below.
7.1. ISAKMP Phase 1
As described in this document, GDOI uses the Phase 1 exchanges
defined in [RFC2409] to protect the GROUPKEY-PULL exchange.
Therefore all security properties and considerations of those
exchanges (as noted in [RFC2409]) are relevant for GDOI.
GDOI may inherit the problems of its ancestor protocols [FS00], such
as identity exposure, absence of unidirectional authentication, or
stateful cookies [PK01]. GDOI could benefit, however, from
improvements to its ancestor protocols just as it benefits from years
of experience and work embodied in those protocols. To reap the
benefits of future IKE improvements, however, GDOI would need to be
revised in a future standards-track RFC, which is beyond the scope of
this specification.
7.1.1. Authentication
Authentication is provided via the mechanisms defined in [RFC2409],
namely Pre-Shared Keys or Public Key encryption.
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7.1.2. Confidentiality
Confidentiality is achieved in Phase 1 through a Diffie-Hellman
exchange that provides keying material, and through negotiation of
encryption transforms.
The Phase 1 protocol will be protecting encryption and integrity keys
sent in the GROUPKEY-PULL protocol. The strength of the encryption
used for Phase 1 SHOULD exceed that of the keys send in the GROUPKEY-
PULL protocol.
7.1.3. Man-in-the-Middle Attack Protection
A successful man-in-the-middle or connection-hijacking attack foils
entity authentication of one or more of the communicating entities
during key establishment. GDOI relies on Phase 1 authentication to
defeat man-in-the-middle attacks.
7.1.4. Replay/Reflection Attack Protection
In a replay/reflection attack, an attacker captures messages between
GDOI entities and subsequently forwards them to a GDOI entity.
Replay and reflection attacks seek to gain information from a
subsequent GDOI message response or seek to disrupt the operation of
a GDOI member or GCKS entity. GDOI relies on the Phase 1 nonce
mechanism in combination with a hash-based message authentication
code to protect against the replay or reflection of previous key
management messages.
7.1.5. Denial of Service Protection
A denial of service attacker sends messages to a GDOI entity to cause
that entity to perform unneeded message authentication operations.
GDOI uses the Phase 1 cookie mechanism to identify spurious messages
prior to cryptographic hash processing. This is a "weak" form of
denial of service protection in that the GDOI entity must check for
good cookies, which can be successfully imitated by a sophisticated
attacker. The Phase 1 cookie mechanism is stateful, and commits
memory resources for cookies, but stateless cookies are a better
defense against denial of service attacks.
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/Reflection Attack Protection
Nonces provide freshness of the GROUPKEY-PULL exchange. The group
member and GCKS exchange nonce values first two messages. These
nonces are included in subsequent HASH payload calculations. The
Group member and GCKS MUST 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) until
it receives the third message in the exchange with a valid HASH
payload including its own nonce.
Implementations SHOULD keep a record of recently received GROUPKEY-
PULL messages and reject messages that have already been processed.
This enables an early discard of the replayed messages.
7.2.5. Denial of Service Protection
A GROUPKEY-PULL message identifies its messages using a cookie pair
from the Phase 1 exchange that precedes it. The cookies provide a
weak form of denial of service protection as described above, in the
sense that a GROUPKEY-PULL message with invalid cookies will be
discarded.
The replay protection mechanisms described above provide the basis
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for denial of service protection.
7.2.6. Authorization
A GCKS implementation should maintain an authorization list of
authorized group members. Group members will 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 provides an efficient
rekey and group membership adjustment capability.
7.3.1. Authentication
The GROUPKEY-PULL exchange identifies 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 or its
delegate. 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 established by the GROUPKEY-PULL exchange.
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 recognize a replayed message by comparing the
sequence number to a sliding window, in the same manner as the ESP
protocol uses sequence numbers.
Implementations SHOULD keep a record of recently received GROUPKEY-
PUSH messages and reject duplicate messages. This enables an early
discard of the replayed messages.
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7.3.5. Denial of Service Protection
A cookie pair identifies the security association for the GROUPKEY-
PUSH message. The cookies thus serve as a weak form of denial-of-
service protection for the GROUPKEY-PUSH message.
The digital signature used for message authentication has a much
greater computational cost than a message authentication code and
could amplify the effects of a denial of service attack on GDOI
members who process GROUPKEY-PUSH messages. The added cost of
digital signatures is justified by the need to prevent GCKS
impersonation: If a shared symmetric key were used for GROUPKEY-PUSH
message authentication, then GCKS source authentication would be
impossible and any member would be capable of GCKS impersonation.
The potential of the digital signature amplifying a denial of service
attack is mitigated by the order of operations a group member takes,
where the least expensive cryptographic operation is performed first.
The group member first decrypts the message using a symmetric cipher.
If it is a validly formed message then the sequence number is checked
against the replay window. Only if the sequence number is valid is
the digital signature verified. Thus in order for a denial of
service attack to be mounted, an attacker would need to know both the
symmetric encryption key used for confidentiality, and a valid
sequence number. Generally speaking this means only current group
members can effectively deploy a denial of service attack.
7.3.6. Forward Access Control
If a group management algorithm (such as LKH) is used, forward access
control may not be ensured in some cases. This can happen if some
group members are denied access to the group in the same GROUPKEY-
PUSH message as new policy and TEKs are delivered to the group. As
discussed in Section 1.5.1, forward access control can be maintained
by sending multiple GROUPKEY-PUSH messages, where the group
membership changes are sent from the GCKS separate from the new
policy and TEKs.
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8. IANA Considerations
This memo requests IANA to make several additions to existing
registries, and to add sever new GDOI registries. When the new
registries are added, the following terms are to be applied as
described in the Guidelines for Writing an IANA Considerations
Section in RFCs [RFC5226]: Standards Action, and Private Use.
8.1. Additions to current registries
The GDOI KEK Attribute named SIG_HASH_ALGORITHM [GDOI-REG] should be
assigned several new Algorithm Type values from the RESERVED space to
represent the SHA-256, SHA-384, and SHA-512 hash algorithms as
defined in [FIPS.180-2.2002]. The new algorithm names should be
SIG_HASH_SHA256, SIG_HASH_SHA384, and SIG_HASH_SHA512 respectively
and have the values of TBD-2, TBD-3, and TBD-4 respectively.
The GDOI KEK Attributed named SIG_ALGORITHM [GDOI-REG] should be
assigned a new Algorithm Type value from the RESERVED space to
represent the RSA PSS encoding type. The new algorithm name should
be SIG_ALG_RSA_PSS, and has the value of TBD-6.
A new GDOI SA TEK type Protocol-ID type [GDOI-REG] should be assigned
from the RESERVED space. The new algorithm id should be called
GDOI_PROTO_IPSEC_AH, refers to the IPsec AH encapsulation, and has a
value of TBD-5.
A new Next Payload Type [ISAKMP-REG] should be assigned. The new
type is called "SA Group Associated Policy (GAP)", and has a value of
TBD-1.
8.2. New registries
A new namespace should be created in the GDOI Payloads registry
[GDOI-REG] to describe SA GAP Payload Values. The following rules
apply to define the attributes in SA SSA Payload Values:
Attribute Type Value Type
---- ----- ----
RESERVED 0
ACTIVATION_TIME_DELAY 1 B
DEACTIVATION_TIME_DELAY 2 B
SENDER_ID 3 V
Standards Action 4-127
Private Use 128-255
A new IPsec Security Association Attribute [ISAKMP-REG] defining the
preservation of IP addresses is needed. The attribute class is
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called "Address Preservation", and it is a Basic type. The following
rules apply to define the values of the attribute:
Name Value
---- -----
Reserved 0
None 1
Source-Only 2
Destination-Only 3
Source-And-Destination 4
Standards Action 5-61439
Private Use 61440-65535
A new IPsec Security Association Attribute [ISAKMP-REG] defining the
SA direction is needed. The attribute class is called "SA
Direction", and it is a Basic type. The following rules apply to
define the values of the attribute:
Name Value
---- -----
Reserved 0
Sender-Only 1
Receiver-Only 2
Symmetric 3
Standards Action 4-61439
Private Use 61440-65535
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9. Acknowledgements
This text updates RFC 3547, and the authors with to thank Mark
Baugher and Hugh Harney for their extensive contributions.
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 provided many useful technical and
editorial comments and suggestions for improvement.
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10. References
10.1. Normative References
[I-D.ietf-msec-ipsec-group-counter-modes]
McGrew, D. and B. Weis, "Using Counter Modes with
Encapsulating Security Payload (ESP) and Authentication
Header (AH) to Protect Group Traffic",
draft-ietf-msec-ipsec-group-counter-modes-05 (work in
progress), March 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC5374] Weis, B., Gross, G., and D. Ignjatic, "Multicast
Extensions to the Security Architecture for the Internet
Protocol", RFC 5374, November 2008.
10.2. Informative References
[FIPS.180-2.2002]
National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-2, August 2002, <http://
csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf>.
[FIPS186-3]
"Digital Signature Standard (DSS)", United States of
America, National Institute of Science and
Technology Federal Information Processing Standard (FIPS)
186-2, June 2009.
[FIPS197] "Advanced Encryption Standard (AES)", United States of
America, National Institute of Science and
Technology Federal Information Processing Standard (FIPS)
197, November 2001.
[FIPS46-3]
"Data Encryption Standard (DES)", United States of
America, National Institute of Science and
Technology Federal Information Processing Standard (FIPS)
46-3, October 1999.
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[FIPS81] "DES Modes of Operation", United States of America,
National Institute of Science and Technology Federal
Information Processing Standard (FIPS) 81, December 1980.
[FS00] Ferguson, N. and B. Schneier, Counterpane, "A
Cryptographic Evaluation of IPsec",
<http://www.counterpane.com/ipsec.html>.
[GDOI-REG]
Internet Assigned Numbers Authority, "Group Domain of
Interpretation (GDOI) Payload Type Values", IANA Registry,
December 2004,
<http://www.iana.org/assignments/gdoi-payloads>.
[I-D.weis-gdoi-mac-tek]
Weis, B. and S. Rowles, "GDOI Generic Message
Authentication Code Policy", draft-weis-gdoi-mac-tek-01
(work in progress), June 2010.
[ISAKMP-REG]
"'Magic Numbers' for ISAKMP Protocol",
<http://www.iana.org/assignments/isakmp-registry>.
[MP04] Meadows, C. and D. Pavlovic, "Deriving, Attacking, and
Defending the GDOI Protocol", ESORICS 2004 pp. 53-72,
September 2004.
[NNL] Naor, D., Noal, M., and J. Lotspiech, "Revocation and
Tracing Schemes for Stateless Receivers", Advances in
Cryptology, Crypto '01, Springer-Verlag LNCS 2139, 2001,
pp. 41-62, 2001,
<http://www.wisdom.weizmann.ac.il/~naor/>.
[OFT] McGrew, D. and A. Sherman, "Key Establishment in Large
Dynamic Groups Using One-Way Function Trees", Manuscript,
submitted to IEEE Transactions on Software Engineering,
1998, <http://download.nai.com/products/media/nai/misc/
oft052098.ps>.
[PK01] Perlman, R. and C. Kaufman, "Analysis of the IPsec Key
Exchange Standard", WET-ICE conference , 2001,
<http://sec.femto.org/wetice-2001/papers/radia-paper.pdf>.
[RFC2403] Madson, C. and R. Glenn, "The Use of HMAC-MD5-96 within
ESP and AH", RFC 2403, November 1998.
[RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within
ESP and AH", RFC 2404, November 1998.
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[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.
[RFC2522] Karn, P. and W. Simpson, "Photuris: Session-Key Management
Protocol", RFC 2522, March 1999.
[RFC2627] Wallner, D., Harder, E., and R. Agee, "Key Management for
Multicast: Issues and Architectures", RFC 2627, June 1999.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode With IPsec Encapsulating Security Payload
(ESP)", RFC 3686, January 2004.
[RFC3740] Hardjono, T. and B. Weis, "The Multicast Group Security
Architecture", RFC 3740, March 2004.
[RFC3947] Kivinen, T., Swander, B., Huttunen, A., and V. Volpe,
"Negotiation of NAT-Traversal in the IKE", RFC 3947,
January 2005.
[RFC4046] Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,
"Multicast Security (MSEC) Group Key Management
Architecture", RFC 4046, April 2005.
[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.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM
Mode with IPsec Encapsulating Security Payload (ESP)",
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RFC 4309, December 2005.
[RFC4430] Sakane, S., Kamada, K., Thomas, M., and J. Vilhuber,
"Kerberized Internet Negotiation of Keys (KINK)",
RFC 4430, March 2006.
[RFC4543] McGrew, D. and J. Viega, "The Use of Galois Message
Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543,
May 2006.
[RFC4754] Fu, D. and J. Solinas, "IKE and IKEv2 Authentication Using
the Elliptic Curve Digital Signature Algorithm (ECDSA)",
RFC 4754, January 2007.
[RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
384, and HMAC-SHA-512 with IPsec", RFC 4868, May 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5903] Fu, D. and J. Solinas, "Elliptic Curve Groups modulo a
Prime (ECP Groups) for IKE and IKEv2", RFC 5903,
June 2010.
[SKEME] Krawczyk, H., "SKEME: A Versatile Secure Key Exchange
Mechanism for Internet", ISOC Secure Networks and
Distributed Systems Symposium San Diego, 1996.
[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.
[STS] Diffie, W., Van Oorschot, P., and M. Wiener,
"Authentication and Authenticated Key Exchanges", Designs,
Codes and Cryptography, 2, 107-125 (1992), Kluwer Academic
Publishers, 1992.
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Appendix A. Alternate GDOI Phase 1 protocols
This section describes a manner in which other protocols could be
used as GDOI Phase 1 protocols in place of the ISAKMP Phase 1
protocol. However, they are not specified as a part of this
document. A separate document MUST be written in order for another
protocol to be used as a GDOI Phase 1 protocol.
Other possible phase 1 protocols are also described in [RFC4046].
Any GDOI phase 1 protocol MUST satisfy the requirements specified in
Section 2 of this document.
A.1. IKEv2 Exchange
Version 2 of the IKE protocol (IKEv2) [RFC4306] has been
published.That protocol simplifies IKE processing, and combines the
two phases of IKE. An IKEv2 Phase 1 negotiates an IPsec SA during
phase 1, which was not possible in IKE. However, IKEv2 also defines
a phase 2 protocol. The phase 2 protocol is protected by the Phase
1, similar in concept to how IKE Quick Mode is protected by the IKE
Phase 1 protocols in [RFC2409].
It would be possible to define GDOI as a phase 2 protocol protected
by an IKEv2 initial exchange. Alternatively, it would be possible to
define a new protocol re-using some of the IKEv2 initial exchange
(e.g., IKE_SA_INIT).
A.2. KINK Protocol
The Kerberized Internet Negotiation of Keys (KINK) [RFC4430] has
defined a method of encapsulating an IKEv1 Quick Mode [RFC2409]
encapsulated in Kerberos KRB_AP_REQ and KRB_AP_REP payloads. KINK
provides a low-latency, computationally inexpensive, easily managed,
and cryptographically sound method of setting up IPsec security
associations.
The KINK message format includes a GDOI field in the KINK header.
The [RFC4430] document defines the DOI for the IPsec DOI.
A new DOI for KINK could be defined which would encapsulate a
GROUPKEY-PULL exchange in the Kerberos KRB_AP_REQ and KRB_AP_REP
payloads. As such, GDOI would benefit from the computational
efficiencies of KINK.
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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
POP payload, so it was removed. Removal of the POP payload
obviated the need for the CERT payload in that exchange and it was
removed as well.
o The Key Exchange Payloads (KE_I, KE_R) payloads were removed from
the GROUPKEY-PULL exchange. However, the specification for
computing keying material for the additional encryption function
in RFC 3547 is faulty. Furthermore, it has been observed that
because the GDOI registration message uses strong ciphers and
provides authenticated encryption, additional encryption of the
keying material in a GDOI registration message provides negligible
value. Therefore, the use of KE payloads is deprecated in this
memo.
o The Certificate Payload (CERT) was removed from the GROUPKEY-PUSH
exchange. The use of this payload was underspecified. In all
known use cases, the public key of used to verify the GROUPKEY-
PUSH payload is distributed directly from the key server as part
of the GROUPKEY-PULL exchange.
o Supported cryptographic algorithms were changed to meet current
guidance. Implementations are required to support AES with 128-
bit keys to encrypt the rekey message, and SHA-256 for
cryptographic signatures. The use of DES is deprecated.
o New protocol support for AH.
o New protocol definitions were added to conform to the most recent
Security Architecture for the Internet Protocol [RFC4301] and the
Multicast Extensions to the Security Architecture for the Internet
Protocol[RFC5374].
o New protocol definitions were added to support Using Counter Modes
with ESP and AH to Protect Group
Traffic[I-D.ietf-msec-ipsec-group-counter-modes].
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Authors' Addresses
Brian Weis
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-526-4796
Email: bew@cisco.com
Sheela Rowles
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-527-7677
Email: sheela@cisco.com
Thomas Hardjono
MIT
77 Massachusetts Ave.
Cambridge, Massachusets 02139
USA
Phone: +1-781-729-9559
Email: hardjono@mit.edu
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