One document matched: draft-hartman-karp-mrkmp-04.xml
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<rfc category="info" docName="draft-hartman-karp-mrkmp-04" ipr="trust200902">
<front>
<title abbrev="MaRK">Multicast Router Key Management Protocol
(MaRK)</title>
<author fullname="Sam Hartman" initials="S." surname="Hartman">
<organization>Painless Security</organization>
<address>
<email>hartmans-ietf@mit.edu</email>
</address>
</author>
<author fullname="Dacheng Zhang" initials="D." surname="Zhang">
<organization>Huawei Technologies co. ltd</organization>
<address>
<postal>
<street>Huawei Building No.3 Xinxi Rd., Shang-Di Information
Industrial Base Hai-Dian District, Beijing</street>
<country>China</country>
</postal>
<email>zhangdacheng@huawei.com</email>
</address>
</author>
<author fullname="Gregory Lebovitz " initials="G." surname="Lebovitz">
<organization>Juniper Networks, Inc.</organization>
<address>
<postal>
<street>1194 North Mathilda Ave.</street>
<city>Sunnyvale</city>
<region>California</region>
<code>94089-1206</code>
<country>USA</country>
</postal>
<email>gregory.ietf@gmail.com</email>
</address>
</author>
<date />
<area></area>
<workgroup>Network Working Group</workgroup>
<keyword>Internet-Draft</keyword>
<keyword>Intended status: Standards Track</keyword>
<keyword>Draft</keyword>
<abstract>
<t>Several routing protocols engage in one-to-many communication. In
order to authenticate these communications using symmetric cryptography,
a group key needs to be established. This specification defines a group
protocol for establishing and managing such keys.</t>
</abstract>
<note title="Requirements Language">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>Many routing protocols such as OSPF <xref target="RFC2328"></xref>
and IS-IS <xref target="RFC1142"></xref> use a one-to-many or multicast
model of communications. The same message is sent to a number of
recipients.</t>
<t>These protocols have cryptographic authentication mechanisms that use
a key shared among all members of a communicating group in order to
protect messages sent within that group. From a security standpoint, all
routers in a group are considered equal. Protecting against a
misbehaving router that is part of the group is out of scope for this
protocol.</t>
<t>Routers need to be provisioned with some credentials for a one-to-one
authentication protocol. Preshared keys or asymmetric keys and an
authorization list are expected to be common deployments.</t>
<t>The members of a group elect a Group Controller/Key Server (GCKS).
Potentially any member of the group may act as a GCKS. Since protecting
against misbehaving routers is out of scope, there is no need to protect
against an entity that is not currently the GCKS impersonating the
GCKS.</t>
<t>To prove membership in the group, a router authenticates using its
provisioned credentials to the current GCKS. If successful, the router
is given the current key material for the group. Group size is
relatively small and need for forced eviction of members is rare. If a
GCKS needs to evict a member, then it can simply re-authenticate with
the existing members and provide them new key material.</t>
<section title="Terminology">
<t>GCKS (Group Controller/Key Server): a GCKS is a particular group
member which establishes security associations among other authorized
group members which it serves.</t>
<t>group: a group specified in this document is a set of routers,
called group members, which are located on a single broadcast domain/
link/ NBMA segment and use a one-to-many or multicast model of
communication.</t>
</section>
<section title="Relationship to IKEv2">
<t>IKEv2 <xref target="RFC4306"></xref> provides a protocol for
authenticating IPsec security associations between two peers. It
currently provides no group keying. IKEv2 is attractive as a basis for
this protocol because while it is much simpler than IKE <xref
target="RFC2409"></xref>, it provides all the needed flexibility in
one-to-one authentication.</t>
<t>IKev2 is expanded to support authentication of routers in<xref
target="I-D.mahesh-karp-rkmp"></xref>. That dspecification describes how IKEv2 can be used for unicast routing protocols. This specification is part of expanding that work to cover multicast routing.</t>
</section>
<section title="Relationship to GDOI">
<t><xref target="RFC3547"></xref> provides a protocol that is
structurally very similar to this one. As specified, IKE can be used
to provide phase 1 authentication to a GCKS. After that, GDOI provides
phase 2 messages to establish key-encryption keys and traffic keys.
After the phase 2 exchange, additional key management operations can
be accomplished via GDOI messages sent within the group.</t>
<t>In <xref target="I-D.yeung-g-ikev2"/> a group management approach is defined for IKEv2. This approach is extended in
<xref target="I-D.tran-karp-mrmp"></xref> to provide for management of routing messages. This specification ats as a companion to that specification, providing an election protocol and some of the interactions with routing protocols.</t>
</section>
</section>
<section title="Overview">
<t></t>
<section title="Types of Keys">
<t>MaRK manipulates several different types of symmetric keys: <list
style="empty">
<t>PSK (Pre-Shared Key) : PSKs are pair-wise unique keys used for
authenticating one router to another during the initial exchange.
These keys are configured by some mechanism such as manual
configuration or a management application outside of the scope of
MaRK.</t>
<t>Peer key management key: Routers share a key with the GCKS that
is a result of the RP_INIT exchange.</t>
<t>KEK (Key Encryption Key): A KEK is a key used to encrypt group
key management messages to the current members of a group. A KEK
is learned as the product of establishing an MaRK association or
through a group key management message encrypted in a previous
KEK. A KEK has an explicit expiration but may also be retired by a
message encrypted in the KEK sent by the GCKS.</t>
<t>Protocol master key: A protocol master key is the key exported
by MaRK for use by a routing protocol such as OSPF or IS-IS. The
Protocol master key is the key that would be manually configured
if a routing protocol is used without key management. This key is
distinguished from the 'transport key' (see next) in that this
Protocol Master Key may be used in a cryptographic operation in
order to derive a specific transport key.</t>
<t>Transport key: A transport key is the key used to integrity
protect routing messages in a protocol such as IS-IS or OSPF. In
today's routing protocol cryptographic authentication mechanisms
the transport key is the same as the protocol master key. A
disadvantage of this approach is that replay prevention is
challenging with this design. Ideally some key derivation step
would be used to establish a fresh transport key among all the
participants in the group.</t>
</list></t>
<section title="Key Encryption Key">
<t>When a router wishes to join a group, the router performs the
RP_INIT and RP_AUTH exchange with a GCKS. If the exchanges are
successful, the router can establish an association with a specific
group. Part of that association will be delivery of a KEK and
associated parameters.</t>
<t>Group key management messages are sent to a group address rather
than unicast to an individual peer. The authenticity, integrity and
confidentiality of group key management messages need to be
protected with the KEK.</t>
<t>As part of establishing the association, the router joining the
group is given an valid period( which is identified by a start time
point and an expire time point) for the KEK. A group key management
message may establish a new KEK with new parameters.</t>
<t>From time to time, a GCKS may wish to either force early
expiration of a KEK or allow a KEK to expire. Protocol master keys
are permitted to be valid for somewhat longer than the KEK that
created them so as to avoid disrupting routing when this happens.
When a KEK is retired or expires without being replaced by a new KEK
announced in the old KEK, the group members delete that KEK. Unless
local policy configuration dictates otherwise, the group member will
perform a new initial exchange to the GCKS in order to establish a
new KEK. This solution is useful for enforcing "forward security" in
the cases where a router is no longer authorized to be part of the
group. That is, only valid group members can obtain the new KEK
while the ones which have leaven the group will be rejected.</t>
<t>Other mechanisms such as LKH (section 5.4 <xref
target="RFC2627"></xref>) could be used to permit removal of a group
member while avoiding new initial authentications. However these
mechanisms come at a complexity cost that is not justified for a
small number of routers participating in a single multicast
link.</t>
<t></t>
</section>
<section title="Protocol Master Keys">
<t>Current routing protocols directly use the protocol master key to
protect the integrity of messages. One advantage for this approach
is that the initial hello messages used for discovery and capability
exchange can be protected using the same mechanism as other
messages. Typically a sequence number is used for replay detection.
Without changing the key, the existing protocols are vulnerable to a
number of serious denial of service attacks from replays.</t>
<t>The MaRK can solve this replay problem by changing the protocol
master key whenever a peer is about to exhaust its sequence number
space or whenever a peer loses information about what sequence
numbers it used. This could potentially involve changing the
protocol master key whenever a router reboots that was part of the
group using the current protocol master key. Since key changes will
not disrupt active adjacencies and can be accomplished relatively
quickly, this is not expected to be a huge problem. Note that after
one key change, others routers can boot without causing additional
key changes; a flurry of key changes would not be required if
several routers reboot near each other.</t>
<t>Another approach would be to separate the protocol master key
from the transport keys. For example the transport key used by a
given peer could be a fresh key derived from the protocol master key
and nonces announced by that peer. Some secure mechanism would be
provisioned to enable one to confirm that the peer's announcement of
its nonce was fresh and authentic; this mechanism would almost
certainly involve some form of interaction with the router wishing
to guarantee freshness in order to resistant, e.g., replay attacks.
There are two key advantages of this separation between transport
keys and protocol master keys. The first is that the interaction
between the MaRK and routing protocol can be simplified
significantly. The second is that even when manually configured
protocol master keys are used, replay and adequate DOS protection
can be achieved.</t>
<t>A simple compare between the keys described in this section is
provided in the following table.</t>
<t><figure>
<artwork><![CDATA[+-----------+------------+-------------+---------+----------------------+
| Keys |KMP usage |Bootstrapping| Group vs| Other |
| |vs. RP usage|vs. Traffic | Pair-Wis| |
+-----------+------------+-------------+---------+----------------------+
|Pre-Shared |KMP usage |Bootstrapping|Pair-Wise|Distributed in an out-|
|Keys | | | |of-band way |
+-----------+------------+-------------+---------+----------------------+
|Key |KMP usage |Bootstrapping|Group |For GCKS to |
|Encryption | | | |distribute protocol |
|Key | | | |master keys |
+-----------+------------+-------------+---------+----------------------+
|Protocol |KMP usage |Bootstrapping|Group |Used by group |
|Master Key |or Both |or Both | |members to secure |
| | | | |routng packets or |
| | | | |generate traffic keys |
+-----------+------------+-------------+---------+----------------------+
|Transport |RP usage |Traffic |Group |Used by group |
|Key | | | |members to secure |
| | | | |routing packets |
+-----------+------------+-------------+---------+----------------------+ ]]></artwork>
</figure></t>
</section>
</section>
<section title="GCKS Election">
<t>Before a MaRK system actually starts working, the routers in the
multicast group need to elect a GCKS so that they can obtain
cryptographic keys to secure subsequent exchanges of routing
information. MaRK specifies an election protocol that dynamically
assigns the responsibility of key management to one of the group
members. Note that there are already announcer-electing mechanisms
provided in some routing protocols (e.g., OSPF and IS-IS). However,
much involvement between a MaRK system and a routing protocol
implementation will be introduced if the MaRK system reuses the
announcer-electing mechanism for the election of the GCKS. The state
machine of the routing protocol also has to be modified. For instance,
in OSPF, after a DR has been elected, routers need to halt their OSPF
executions, and carry out the initial exchange to authenticate the DR
and collect the keys for subsequent communications. After this step,
the routers need to re-start their OSPF state machines so as to
exchange routing information. As a consequence of such cases, an
individual GCKS electing solution within MaRK is preferable.</t>
<t>Each router has a GCKS priority. Higher priorities are more
preferred GCKSes. As discussed in Section 8, the routing protocol can
influence the GCKS election protocol by manipulating the priority so
that it is likely that the same router will be the announcer for the
routing protocol and the GCKS. Even if two different routers are
elected as the announcer and GCKS, then the routing protocol and MaRK
will function correctly.</t>
<t>A key design goal of the election protocol is to maximize the
chance that some router permitted to take on the role of GCKS will be
elected to that role even when attackers are injecting messages into
the election process. The election process can be attacked to cause a
router other than the most preferred router to be elected.</t>
</section>
<section title="Initial Exchange">
<t>The initial exchange is based on IKEv2's IKE_SA_INIT and
IKE_SA_AUTH exchanges. During this exchange, an initiating router
attempts to authenticate to the router it believes is a GCKS for a
group that the initiating router wants to join. Messages are unicast
from the initiator to the responding GCKS. Unicast MaRK messages form
a request/response protocol; the party sending the messages is
responsible for retransmissions.</t>
<t>The initial exchange provides capability negotiation, specifically
including supported cryptographic suites for the key management
protocol. Identification of the initiator and responder is also
exchanged. A symmetric key is established to protect integrity,
confidentiality and authenticity of the subsequent key management
messages. While routing security does not typically require
confidentiality, the key management protocol does because keys are
exchanged and these must be protected.</t>
<t>Then the identities of each party are cryptographically verified.
This can be done using, e.g., a preshared key, asymmetric keys or
self-signing certificates. Other mechanisms may be added as a future
extension.</t>
<t>The authentication exchange also provides an opportunity to join a
group as part of the initial exchange. In the typical case, a router
can obtain the needed key material for a group in two round-trips.</t>
</section>
<section title="Group Join Exchange">
<t>The primary purpose of the unicast MaRK messages is to get an
initiator the information it needs to join a group and participate in
a routing protocol. The initiator can contact a GCKS to apply to join
a group that the GCKS manages. In the case a GCKS manages multiple
groups concurrently, the initiator can additionally provide a group
identifier to indicate which particular group it intends to join.</t>
<t>The responder performs several checks. First, the responder
confirms that the responder is currently acting as GCKS for the group
in question. Then, the responder confirms that the initiator is
permitted to join the group. If these checks pass, then the responder
provides a key download payload to the initiator encrypted in the peer
key management key. As discussed in Section 2.1.2, the GCKS MUST
change the protocol master key if a router was part of the group under
the current protocol master key and reboots. In this case, the GCKS
SHOULD provide the new and old protocol master key to the initiator,
setting the validity times for the old key to permit reception but not
transmission. The GCKS MUST use the mechanism in the next section to
flood the new key to the rest of the group.</t>
<t>A group association created by this exchange may last beyond the
unicast MaRK association used to create it. Once membership in a group
is established, resources are not required to maintain the unicast
association with the GCKS.</t>
</section>
<section title="Group Key Management ">
<t>After the establishment of a group, a KEK is shared by the GCKS and
all the other group members. Using the KEK, the GCKS can securely send
multicast messages to the group in order to, for example, update the
set of protocol master keys, revoke the KEK, or initiate new group
join exchanges.</t>
<t>Typically, a protocol master key may be changed for the purpose of
replay protection or as a result of KEK update. The KEK needs to be
updated whenever a new GCKS is elected or whenever it is
administratively desirable to change the keys. For example, after an
employee leaves an organization it might not be wise to keep using the
KEKs (and any other keys) that the employee has accessed. A KEK update
is also required whenever forward security is desired: whenever the
authorization of who is permitted to be in a group changes and the
GCKS needs to make sure that the router is no longer participating.
Most authorization changes such as removing a router from service do
not require forward security in practical deployments.</t>
</section>
</section>
<section title="GKCS Election">
<t>After a successful GCKS election process, a single router is selected
to act as the GCKS for a group. Similar with other popular announcer
electing mechanisms (e.g., VRRP, HSRP), in MaRK, only GCKSes use
multicast to periodically send Advertisement messages. Such
advertisements can be used as heart beat packets to indicate the
aliveness of GCKSes. In addition, a state machine with six states
(Initial, Validate, GCKS, GCKS2, Follower, and Member) is specified for
GCKS election. When a router is initially connected to a multicast
network, its state is set as Initial. The router then sends a multicast
initial advertisement. If a GCKS is working on the network, it will
reply to the router with an advertisement. After receiving the
advertisement from the GCKS, the router will try to register with the
GCKS using the initial exchange. Typically this registration will
succeed, and the state of the router is transferred to Member. After a
certain period, if the router still does not receive any advertisement
from a GCKS or other group members, the router then believes there is no
other group member on the network and sets its state as GCKS. If during
the period the router does not receive any advertisement from a GCKS but
receives advertisements from other more preferred routers on the
network, the router believes that the group is involved in a GCKS
election process. The router then puts these routers into its candidate
list. When the timer to end the Initial state expires, the router tries
to authenticate the most preferred router in the candidate list and
validate whether it can be a GCKS. If the validation result is positive,
the router then transfer its state to Member, and the router being
validated transfers its state to GCKS.</t>
<t>In the absence of attacks, this process functions similar to
designated router election protocols in existing routing protocols.
Because the election process happens before group keys are established,
the initial election process is not integrity-protected. An attacker can
inject fake GCKS announcements or initial announcements from fake
routers that are more preferred than any router actually in the group.
Such attacks can create a denial of service situation. If the election
process does not converge within the expected time, or if an
authentication attempt fails, then the group is probably under attack. A
new state called GCKS2 is introduced. A router permitted to be the GCKS
can enter the GCKS2 state after failing to validate a received
announcement in the expected time. GCKS2 is used to increase the
convergence speed while the system is under attack. If an initial router
receives a GCKS2 announcement, the initial router can authenticate and
validate the sender, and transfer its own state to Follower, similar to
how it would respond to a GCKS announcement. GCKS2 routers attempt to
validate each other and to use the resulting security keys to establish
a router to act as GCKS. The GCKS2 state does not generate protocol
master keys: until the election result in a GCKS only keying material
needed for the election is produced. In the subsequent election, the
router will wait for the election results from its GCKS2 router until
its GCKS2 end timer expires. In this way, the authenticated entities
generate a tree structure and avoid generating large amount of KEKs and
protocol master keys when a adversary keeps sending fake GCKS
announcements to disrupt election.</t>
<t>Apart from the initialization of a multicast group, the fail-over of
a GCKS can also trigger an election process. For instance, if a router
does not receive the heart beat advertisement for a certain period, it
will transfer its state to Initial and try to elect a new one. In a GCKS
electing process, a router has to stay in the Initial state until a new
GCKS is allocated. Particularly, the router first sends its initial
advertisement with its priority and waits for a certain period. During
the period, if a router receives an initial advertisement which consists
of a lower priority, the router then sends the advertisement again with
a limited rate. After period, if the router does not find any router
with a higher priority, it announces itself as the GCKS. If two routers
have the same priority, the one with the lowest IP source address used
for messages on the link will be the GCKS. After a router transfers its
state to GCKS, it will reply to the initial advertisements from other
routers with GCKS advertisements, even when the initial advertisements
consist of higher priorities than its priority. This approach guarantees
that a GCKS will not be changed frequently after it has been elected.
After receiving the GCKS advertisement of the new elected GCKS, other
routers transfer their states to Member. However, if a GCKS G1 receives
a GCKS advertisement from another router G2 and G2 is a more preferred
GCKS, G1 follows the procedure in Section 3.2.</t>
<t>If a node in state member fails to perform an initial exchange with
the router it believes to be GCKS, it resets its state to initial but
ignores advertisements from that router. This way an attacker cannot
disrupt communications indefinitely by masquerading as a GCKS.</t>
<section title="A new GCKS is Elected">
<t>This section is a detailed description of the election process.</t>
<t>In the following discussion, the packets are identified by all
upper case characters.</t>
<section title="Parameters, Timers, and Events">
<t>Before going into detailed discussion, several parameters are
introduced: <list style="symbols">
<t>Initial_Anno_Interval, which is the time interval between
INITIAL_ANNOUNCEMENTS ).</t>
<t>Initial_End_Interval, which is the time interval to transfer
the state of a router from Initial to GCKS/Validate if it does
not receive any GCKS or GCKS2 announcement on the link ).</t>
<t>Validate_End_Interval, which is the time interval for a
router to transfer its state from Validate to GCKS2 if it does
not find any other more preferred router ).</t>
<t>GCKS_Down_Interval, which is the time interval for a Member
router to declare a GCKS router is down ).</t>
<t>GCKS2_Down_Interval, which is the time interval for a
Follower router to declare a GCKS2 router is down ).</t>
<t>GCKS2_End_Interval, which is the time interval for a router
to transfer its state from GCKS2 to GCKS if it does not find any
other more preferred router ).</t>
<t>GCKS_Anno_Interval, which is the time interval between
GCKS_ANNOUNCEMENTS ).</t>
<t>GCKS2_Anno_Interval, which is the time interval between
GCKS2_ANNOUNCEMENTS ).</t>
</list>Correspondingly, each router in MaRK has several timers,
Initial_Anno_Timer, Initial_End_Timer, Validate_End_Timer,
GCKS_Down_Timer, GCKS2_Down_Timer, GCKS2_End_Timer, GCKS_Anno_Timer,
GCKS2_Anno_Timer. Initial_Anno_Timer fires to trigger sending of an
INITIAL_ANNOUNCEMENT based on Initial_Announcement_Interval.
Initial_End_Timer fires to trigger the transition of a router state
from Initial to some other state. Validate_End_Timer fires to
trigger the transition of a router state from Validate to GCKS2.
GCKS_Down_Timer fires when no GCKS_ANNOUNCEMENT has been heard for
GCKS_Down_Interval. GCKS2_Down_Timer fires when no
GCKS2_ANNOUNCEMENT has not been heard for GCKS2_Down_Interval.
GCKS2_End_Timer fires to trigger the transition of the state of a
router from GCKS2 to GCKS. GCKS_Anno_Timer fires to trigger sending
of a GCKS_ANNOUNCEMENT based on GCKS_Announcement_Interval.
GCKS2_Anno_Timer fires to trigger sending of a GCKS2_ANNOUNCEMENT
based on GCKS2_Anno_Interval.</t>
<t>During an election process, a MaRK router may have to deal with
following types of events: <list style="symbols">
<t>X_Anno_Received: an X_ANNOUNCEMENT is received.</t>
<t>Requester_Validated: have authenticated and validated against
a some router who believes we should be a GCKS or GCKS2.</t>
<t>GCKS_Validated: a remote entity has been authenticated and
validated to be a GCKS router.</t>
<t>GCKS2_Validated: a remote entity has been authenticated and
validated to be a GCKS2 router.</t>
<t>Referral_Validated: have authenticated and validated against
a candidate who is not a GCKS router but knows one is .</t>
<t>Referral2_Validated: have authenticated and validated against
a candidate who knows a GCKS2 router.</t>
<t>Authentication/Validation_Failed: the remote entity fails in
the authentication or cannot be either a GCKS/GCKS2 or a
referral.</t>
<t>X_Timer_Expired: the timer of type X expired.</t>
<t>KEK_Expired: we have no valid KEK.</t>
</list></t>
</section>
<section title="Initial">
<t>The timers utilized in this state are Initial_Anno_Timer and
Initial_End_Timer.</t>
<t>On entry: <list style="symbols">
<t>Send an INITIAL_ANNOUNCEMENT.</t>
<t>Set the Initial_Anno_Timer with Initial_Anno_Interval.</t>
<t>Set the Initial_End_Timer with Initial_End_Interval.</t>
</list>Events: <list style="symbols">
<t>Initial_Anno_Timer_Expired: send an INITIAL_ANNOUNCEMENT and
reset the Initial_Anno_Timer.</t>
<t>Initial_Anno_Received: if the sender of the announcement is
more preferred, add the entity into the candidate list; if less
preferred, send an INITIAL_ANNOUNCEMENT with a limited rate.</t>
<t>GCKS_Anno_Received: add the sender of the announcement to the
candidate list; set the the Validate_End_Timer with the
remaining period of Initial_End_Interval; transfer to
validate.</t>
<t>GCKS2_Anno_Received: add the sender of the announcement to
candidate list; set the Validate_End_Timer with the remaining
period of Initial_End_Interval; transfer to validate.</t>
<t>Requester_Validated: If the requester is looking for a GCKS
router and the local policy permits, transfer the state to GCKS2
and set GCKS2_End_Interval to time remaining on
Initial_End_timer.</t>
<t>Initial_End_Timer_Expired: if there are candidates, transfer
the state to Validate. If there is no entry in the candidate
list, transfer to GCKS.</t>
</list></t>
</section>
<section title="Validate">
<t>The timer utilized in this state is Validate_End_Timer.</t>
<t>Entering this state means that there is a router which potential
could be a GCKS. The purpose of this state is to confirm that it is
able to establish a security association with that router and that
router's policy permits it to be a GCKS for this group. The two
normal paths through the state machine are Initial leading to GCKS
for the most preferred router and Initial leading to Validate
leading to Member for other routers.</t>
<t>On entry: <list style="symbols">
<t>Authenticate and validate the most preferred entry in the
candidate list.</t>
<t>If Validate_End_timer has more time than
Validate_end_Interval, set Validate_End_timer to
Validate_End_interval.</t>
</list>Events:<list style="symbols">
<t>GCKS_Validated: transfer the state to Member.</t>
<t>GCKS2_Validated: Transfer the state to Follower.</t>
<t>Referral_Validated: perform the authentication/validation on
the recommended node; move the referring from the candidate list
to the black list for Blacklist_Interval.</t>
<t>Referral2_Validated: perform the authentication/validation on
the recommended node; move the referring node from the candidate
list to the black list for Blacklist_Interval.</t>
<t>Requester_Validated: If the requester is looking for a
GCKS/GCKS2 router and the local policy permits, transfer the
state to GCKS2.</t>
<t>Validation_Failed: move the router being validated from the
candidate list to black list for Blacklist_interval.</t>
<t>Initial_Anno_Received: if the sender of the announcement is
more preferred, add the router into the candidate list; if less
preferred, send an INITIAL_ANNOUNCEMENT with a limited rate.</t>
<t>GCKS_Anno_Received: add the router sending the announcement
into the candidate list and perform authentication against that
entity.</t>
<t>GCKS2_Anno_Received: add the router sending the announcement
into the candidate list and start the authentication/validation
against that entity.</t>
<t>Validate_End_Timer_Expired: transfer the state to GCKS2.</t>
</list></t>
</section>
<section title="GCKS2">
<t>The timers utilized in this state include GCKS2_Anno_Timer and
GCKS2_End_Timer.</t>
<t>Whe a router transfers its state from Validate to GCKS2, it is
indicated that there has been some authentication/validation problem
or another node is behaving in a manner inconsistent with the
election state. In this case, the purpose of the GCKS2 state is to
establish sufficient security keys to integrity protect the election
process. In addition, it is possible for a router to enter this
state during normal operations if the router being elected GCKS gets
an authentication request before Initial_End_timer expires. In this
case, the router will transfer its state to GCKS if no more
preferred GCKS candidate is found within a limited period.</t>
<t>On entry: <list style="symbols">
<t>Send an GCSK2_ANNOUNCEMENT.</t>
<t>Set the GCKS2_Anno_Timer with GCKS2_Anno_Interval.</t>
<t>Set the the GCKS2_End_Timer with GCKS2_End_Interval unless it
was set on entry transferring from Initial.</t>
</list></t>
<t>Events: <list style="symbols">
<t>GCKS_Anno_Received: add to candidate list; start
authentication/ validation.</t>
<t>GCKS2_Anno_Received: if more preferred, add to candidate
list, start authentication/validation. If less preferred, send
GCKS2_ANNOUNCEMENT if rate limiting is permitted.</t>
<t>GCKS_Validated: Transfer to member state; flood KEK to the
associated followers.</t>
<t>GCKS2_Validated: Transfer the state to Follower; flood KEK to
the associated followers.</t>
<t>Referral_Validated: Perform authentication and validation on
the recommended node; move the referring node from the candidate
list to the black list for Blacklist_Interval.</t>
<t>Referral2_Validated: if the recommended GCKS2 is more
preferred, perform authentication and validation on the
recommended node; move the referring from the candidate list to
the black list for Blacklist_Interval.</t>
<t>Requester_Validated: if the requester is looking for a GCKS2,
distribute KEK.</t>
<t>Validation_Failed: move the router being validated from the
candidate list to black list for Blacklist_interval.</t>
<t>GCKS2_End_Timer_Expired: transition the state to GCKS.</t>
<t>GCKS2_Anno_Timer_Expired: send a GCKS2_ANNOUNCEMENT.</t>
</list></t>
<t></t>
</section>
<section title="GCKS">
<t>The timer utilized in this state is GCKS_Anno_Timer.</t>
<t>On entry: <list style="symbols">
<t>Senda GCKS_ANNOUNCEMENT.</t>
<t>Set the GCKS_Anno_Timer with GCKS_Anno_Interval.</t>
<t>Generate protocol keys; if needed, generate KEK.</t>
</list>Events: <list style="symbols">
<t>GCKS_Anno_Timer_Expired: send a GCKS_ANNOUNCEMENT.</t>
<t>Initial_Anno_Received: send an GCKS_ANNOUNCEMENT immediately
if the rate limiting is permitted.</t>
<t>GCKS2_Anno_Received: send an GCKS_ANNOUNCEMENT immediately if
the rate limiting is permitted.</t>
<t>GCKS_Anno_Received: if the sender is more preferred, add to
candidate list and start authentication/validation; Otherwise,
send an GCKS_ANNOUNCEMENT immediately if the rate limiting is
permitted.</t>
<t>GCKS_Validated: start network merging operations as what is
illustrated in Section 3.2.</t>
<t>Requester_Validated: If the requester is looking for a GCKS
router, distribute KEK and protocol master keys; if the
requester is another GCKS, start network merging operations as
what is illustrated in Section 3.2.</t>
</list></t>
</section>
<section title="Member">
<t>The timer utilized in this state is GCKS_Down_Timer.</t>
<t>On entry: <list style="symbols">
<t>Set the GCKS_Down_Timer with GCKS_Down_Interval.</t>
</list></t>
<t>Events: <list style="symbols">
<t>GCKS_Down_Timer_Expired: Transfer the state into Initial.</t>
<t>GCKS_Anno_Received: reset GCKS_Down_Timer.</t>
<t>Requester_Validated: if the requester is legal, recommend the
GCKS router to it.</t>
</list></t>
</section>
<section title="Follower">
<t>The timer utilized in this state is GCKS2_Down_Timer.</t>
<t>On entry: <list style="symbols">
<t>Set the GCKS2_Down_Timer with GCKS2_Down_Interval.</t>
</list></t>
<t>Events: <list style="symbols">
<t>GCKS2_Down_Timer_Expired: Transfer the state into
Initial.</t>
<t>GCKS2_Anno_Received: reset GCKS2_Down_Timer.</t>
<t>GCKS_Anno_Received: Add the announcer to the candidate list
and start validation.</t>
<t>Requester_Validated: if the requester is legal, recommend the
GCKS2 router to it.</t>
<t>GCKS_Validated: Transfer the state to member.</t>
</list></t>
<t>The following diagram illustrates the rules of transiting the
states introduced this section.</t>
<t><figure>
<artwork align="center"><![CDATA[
+---------------------------------------------+
| +-----------+ |
| +---->| | |
| | | Follower |--+ |
| | +--| | | |
| | | +-----------+ | |
+----------+ | | +-----------+ | +----------+ |
| |-+ +->| | +->| |<-+
| Validate |<----->| Initial |<----| Member |
| | +->| |<-+ | |<-+
+----------+ | +-----------+ | +----------+ |
| | | +----------+ |
| | +->| | |
| | +-----------+ | GCKS | |
| +->| |---->| | |
| | GCKS2 | +----------+ |
+------------>| |-------------------+
+-----------+
]]></artwork>
</figure></t>
</section>
</section>
<section title="Merging Partitioned Networks">
<t>Whenever a GCKS finds that a more preferred router is also acting
as a GCKS for the same group, then the group is partitioned. Typically
if there is already an active GCKS for a group, even if a more
preferred router joins the group, the GCKS will not change. Two
situations can result in multiple GCKSes active for a group. The first
is that members of the group do not share common authentication
credentials. The second is that the group was previously partitioned
so that some nodes could not see election messages from other nodes.
After the problem resulting in the partition is fixed, then both
active GCKSes will see each others election announcements. The group
needs to merge.</t>
<t>The less preferred GCKS performs a unicast mark_merge_sa unicast
key management message to the more preferred GCKS. In this message the
less preferred GCKS includes its key download payload, so the more
preferred GCKS learns the protocol master keys of the less preferred
GCKS.</t>
<t>The more preferred GCKS generates a new key download payload
including a KEK and the union of all the protocol master keys. The
GCKS SHOULD mark the existing protocol master keys as expiring for
usage in transmitted packets in a relatively short time. The GCKS
SHOULD introduce a new protocol master key. This key download payload
is returned to the less preferred GCKS and is sent out in the current
KEK using a group key management message.</t>
<t>The less preferred GCKS sends the received key download payload
encrypted in its existing KEK and retransmit the message for several
times according to its local policy. After all retransmissions of this
payload the less preferred GCKS sets its state to member.</t>
<t>As a result of this procedure, members learn the protocol master
keys of both GCKSes and converge on a single KEK and GCKS. Changing
the protocol master keys during a merge is important for protocols
that use the protocol master key as a transport key. The new GCKS does
not know which routers have joined the group with the other GCKS.
Therefore, it could not correctly detect one of these routers
rebooting and change the protocol master key at that point. If the key
is changed as part of the merge, replays are handled.</t>
</section>
<section title="Operations on Receiving a Packet ">
<t>When a router attempts to join an election process, it may have a
valid KEK. For instance, when a GCKS cannot work properly, the routers
on the link need to transfer their state to Initial and raise an
election to find a new valid GCKS. If there is still a valid KEK
shared by the router, they can use the KEK to secure the packets
transmitted during the election until a new KEK is distributed by the
new GCKS. A router holding the valid KEK is regarded to be more
preferred than a router which doesn't have the key. By using the KEK,
it is able to prevent an attacker from disturbing the election process
by broadcasting fake announcements. Therefore, after an initial router
does not find any more preferred router holding the valid key, it then
can transfer its state to GCKS directly.</t>
<t>Therefore, the operations on receiving a packet are as follows:
<list style="symbols">
<t>Check the blacklist. If the sender of the packet is on the
blacklist, discard the packet.</t>
<t>If the state is GCKS, accept the packet and generate an event.
GCKS announcements need to be excepted in GCKS state for merges to
work.</t>
<t>If there is a KEK that is not expired, check the packet
integrity against any matching KEK.</t>
<t>If no KEK matches or if the integrity fails to validate,
discard the packet.</t>
<t>If there is no KEK at all or the KEK integrity check passed,
process the packet and generate an event.</t>
</list>It is notable this approach limits the scope of the election
within the routers managed by the failed GCKS. If there are routers
newly accessing the link during the election, no router with a KEK
will process their packets. However these routers can process packets
from routers with the KEK. In many cases one of the routers with a KEK
will be elected GCKS and the other routers can authenticate and join.
In the worst case, two independent GCKSes will be elected and then
merge.</t>
</section>
</section>
<section title="Key Download Payload">
<t>What all is actually in the message you get at the end of phase 1
exchange (the RP_AUTH Exchange) and that is sent out periodically during
group key management.</t>
<t>For the KEK, this needs to include the key itself, the algorithm
(presumably drawn from the IKEv2 symmetric algorithms), key ID, group ID
transmit start time, receive start time, and expire time.</t>
<t>The protocol master keys include the key, an algorithm ID, the key ID
and thelifetimes.</t>
</section>
<section title="Initial Exchanges Details">
<t>Simiilar with <xref target="I-D.tran-karp-mrmp"></xref>, in MRKMP,
when two routers needs to authenticate each other, they need to perform
the initial exchanges defined in <xref
target="I-D.mahesh-karp-rkmp"></xref> . For example, when a router
intends to join a group, it needs to firstly perform a RP Initial
(RP_INIT) Exchange with the GCKS of the group. RP_INIT is identical to
the IKE_SA_INIT exchange defined in Internet Key Exchange Protocol
Version 2 [RFC5996], after which the router and the GCKS can communicate
privately. Note that at this point the network devices have not
identified their peer. For the details of this exchange, refer to
IKE_SA_INIT in Internet Key Exchange Protocol Version 2 [RFC5996].</t>
<t><figure>
<artwork><![CDATA[ Router GCKS
-------------------- ------------------
HDR, SAi1, KEi, Ni -->
<-- HDR, SAr1, KEr, Nr, [CERTREQ,]
RP_INIT
]]></artwork>
</figure>The router and the GCKS then needs to perform an RP_AUTH
exchange defined in <xref target="I-D.mahesh-karp-rkmp"></xref>. At the
successful conclusion of the exchange, the router is adopted as a group
member and obtains keying material (e.g., the KEK and protocol master
key) to securely communicate with other group members.</t>
<t><figure>
<artwork><![CDATA[ Router GCKS
-------------------- ------------------
HDR, SK {IDi, [CERT,] [CERTREQ,]
[IDr,] AUTH, SArpi} -->
<-- HDR, SK {IDr, [CERT,] AUTH,
SArpr}
RP_AUTH
]]></artwork>
</figure></t>
<t></t>
</section>
<section title="Group Management Unicast Exchanges">
<t></t>
<section title="Group Join Exchange">
<t>If a router receives a group join exchange for a group for which it
is not the GCKS, it MUST return a notification. If it knows the GCKS
for the group then it returns MaRK_WRONG_GCKS including the address of
the GCKS or GCKS2 in the notification payload along with an indication
of whether the router is a GCKS or GCKS2. The initiator tries the
group join exchange (probably with a new initial exchange) with the
indicated router. If the responder does not know the GCKS for the
group, either because it is not a member of the group or because its
GCKS election state is initial, it returns the MaRK_GCKS_UNKNOWN
notification.</t>
</section>
</section>
<section title="Group Key Management Operation">
<t></t>
<section title="General operation">
<t>Periodically the GCKS will send out an update message encrypted in
the current KEK including the current group key download payload and
parameters. If a new KEK is about to be valid for receiving messages,
this is included. Any protocol master keys that are valid for sending
or receiving SHOULD be included.</t>
<t>If a previous KEK is still valid for sending, then an update
message is sent encrypted in the old KEK. This message MUST include
the new KEK. This message SHOULD include the protocol master keys.</t>
</section>
<section title="Out of Sequence Space">
<t>A member of a group can also use the unicast exchange to request a
GCKS to change a protocol master key, on the occasions, for example,
where the member is going to exhaust its sequence space of the
associated routing protocol. For protocols where the protocol master
key is the same as the transport key, it is critical that no two
messages be sent by the same router with the same sequence number and
protocol master key. The sequence number space is finite. So if a
router is running low on available sequence space it needs to request
a new protocol master key be generated.</t>
</section>
<section title="Changing the Active GCKS">
<t>When a GCKS finds a more preferred router announcing itself as a
GCKS, it will forward its privilege to another one in the following
conditions. The operations are introduced in Section 3.2.</t>
<t>When a GCKS cannot work properly, it will just stop sending the
GCKS_ANNOUNCEMENT. Then after a certain time period, a new GCKS
election process will be raised.</t>
</section>
<section title="Reboot Cases">
<t>After a reboot, a router in a group will lost the state information
about the group (e.g., protocol master keys, traffic keys, the
sequence numbers used by GCKS). Therefore, the router needs to find
and authenticate the GCKS, and apply to join the group. If the GCKS
finds that the router is already a group member, the GCKS will update
the transport keys (and the protocol master keys if necessary) used in
the group first in order to avoid inter-session replay attacks.</t>
</section>
</section>
<section title="Interface to Routing Protocol">
<t>This section describes signaling between MaRK and the routing
protocol. The primary communication between these protocols is that MaRK
populates rows in the key table making protocol master keys available to
the routing protocol. However additional signaling is also required from
the routing protocol to MaRK. This section discusses that signaling. All
required communication from MaRK to the routing protocol can be
accomplished by manipulating the key table. However an implementation
MAY wish to signal MaRK failures to the routing protocol in order to
provide consistent management feedback.</t>
<section title="Joining a Group">
<t>When a routing protocol instance wishes to begin communicating on a
multicast group, it signals a group join event to MaRK. This event
includes the identity of the group as well as this router's priority
for being a GCKS for the group. When MaRK receives this event, it
starts MaRK for this group and attempts to find a GCKS.</t>
</section>
<section title="Priority Adjustment">
<t>It is desirable that the GCKS function track the functions within a
routing protocol. For example for protocols such as OSPF that
designate a router on a link to manage adjacencies for that link, it
would be desirable for the GCKS role to be assigned to that router.
The routing protocol provides a priority input to the GCKS election
process. Initially the routing protocol should map any priority
mechanism within the routing protocol to the GCKS election procedure
so that routers favored as announcer for a link will also be favored
as a GCKS.</t>
<t>However, the routing protocol SHOULD also dynamically manipulate
the GCKS election priority based on what happens within the routing
protocol. The router actually elected as the announcer SHOULD have a
GCKS election priority higher than any other group member. Typically,
by the time the routing protocol is able to elect an announcer, a GCKS
will already be chosen. However, if a GCKS election is triggered when
the routing protocol is already operational, then the election can
choose the routing protocol's announcer.</t>
</section>
<section title="Leaving a Group">
<t>If a routing protocol terminates on an interface, MaRK
implementation on the router needs to be notified that group is no
longer joined. MaRK MUST stop participating in the GCKS election
process, stop monitoring for key management messages and if the
current router is a GCKS, stop acting in that role.</t>
</section>
<section title="Out of Sequence Space">
<t>If a routing protocol is running out its sequence space, the MaRK
implementation on the router needs to be notified. The MaRK
implementation then needs to contact the GCKS to request the update of
the transport keys (and the protocol master keys if necessary).</t>
</section>
</section>
<section anchor="Security" title="Security Considerations">
<t>This protocol is intended to protect against attackers who are not properly authorized mounting a integrity or availability attack on the system. All parties who are authorized to be part of a given group are equivalent; group members impersonating each other, impacting availability or integrity are all out of scope for this threat model. Protecting confidentiality of key material against parties not authorized for membership in a given group is in scope as it would directly lead to an attack on integrity or availability. Protecting confidentiality of group policy or routing data is not required. Attackers are assumed to be able to insert and observe packets. Even if attackers can modify and suppress packets, integrity should not be impacted. Minimizing the availability impact against attackers who can modify and suppress packets is strongly desirable, although there are limits to this defense. It is important that a member of one group not be able to impact another group. </t>
<t>Significant complexity results from the election protocol. In order to support arbitrary authentication mechanisms including preshared keys, the election protocol itself is not signed. At least before group keys are established, the election protocol is not integrity protected. Later authentication can establish integrity, but managing availability attacks on the election protocol requires significant analysis. </t>
<t>An attacker who can suppress packets sent to the group can create a
denial of service condition. One attack is to suppress GCKS election
packets and cause two routers to believe they are both the GCKS for the
group. If the least preferred router never hears the GCKS advertisement
from the more preferred router, then the group will remain partitioned.
Such an attacker is likely to be able to mount more direct denial of
service, for example suppressing the actual routing protocol
packets.</t>
<t>The election protocol has been designed to try and resist denial of
service conditions. However, the election protocol maintains state in
the form of a candidate list and black list. An attacker can consume
state by generating fake election announcements. An implementation can
discard state if it has insufficient resources. However, if legitimate
routers are discarded from the candidate list, the protocol may take
longer to converge or may not converge. If entries are removed from the
black list, then more resources may be spent on attackers. So the
solution has some residual denial of service possibilities. The election
protocol requires significant analysis to confirm it meets its design
goals.</t>
<t>The security of the election protocol depends on the denial of
service resistance of the authentication protocol. It is important that
an attacker not be able to cause an authentication to fail by injecting
a packet. So, rather than failing an authentication if a bad packet is
received, an implementation needs to wait and see if a good packet
appears in some timeout.</t>
<t>The security of the system as a whole depends on the pair-wise
security between the router currently in the GCKS role and the other
routers in the group. Since any router can potentially act as GCKS, the
pair-wise security between all members of the group is critical to the
security of the system. In practical deployments, information used by
the router acting as GCKS to authorize a member joining the group will
be configured by some management application. In these deployments, the
security of the system depends on the management application correctly
maintaining this information on all routers potentially in the
group.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>The funding for Sam Hartman's work on this document is provided by
Huawei.</t>
<t>XXX add the list of people in the lunch time group unless they are
willing to be listed as authors.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119"?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2409'?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.3547'?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.4306'?>
</references>
<references title="Informative References">
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2328'?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.5996'?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.1142'?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml/reference.RFC.2627'?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.mahesh-karp-rkmp'?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.tran-karp-mrmp'?>
<?rfc include='http://xml.resource.org/public/rfc/bibxml3/reference.I-D.yeung-g-ikev2'?>
</references>
</back>
</rfc>
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