Negotiation for Keying Pairwise Routing
Protocols in IKEv2CaliforniaUSAmjethanandani@gmail.comCisco Systems170 W. Tasman DriveSan JoseCalifornia95134USA+1 (408) 526-4796bew@cisco.comArrcusCaliforniaUSAkeyur@arrcus.comHuaweiBeijingChinazhangdacheng@huawei.comPainless Securityhartmans@painless-security.comEricsson Inc.300 Holger WaySan JoseCalifornia95134USAuma.chunduri@ericsson.comEricsson Inc.300 Holger WaySan JoseCalifornia95134USAalbert.tian@ericsson.comUSC/ISI4676 Admiralty WayMarina del ReyCalifornia90292-6695USAtouch@isi.eduThis document describes a mechanism to secure the routing protocols
which use unicast to transport their signaling messages. Most of such
routing protocols are TCP-based (e.g., BGP and LDP), and the TCP
Authentication Option (TCP-AO) is primarily employed for securing the
signaling messages of these routing protocols. There are also two
exceptions: BFD which is over UDP or MPLS, and RSVP-TE which is over IP
(but employs an integrated approach to protecting the signaling messages
instead of using IPsec). The proposed mechanism secures pairwise
TCP-based Routing Protocol (RP) associations, BFD associations and
RSVP-TE associations using the IKEv2 Key Management Protocol (KMP)
integrated with TCP-AO, BFD, and RSVP-TE respectively. Included are
extensions to IKEv2 and its Security Associations to enable its key
negotiation to support TCP-AO, BFD, and RSVP-TE.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 RFC 2119.Existing routing protocols using unicast pairwise communication model
(e.g., BGP, LDP, RSVP-TE, and BFD) have cryptographic authentication
mechanisms that use a key shared between the network devices (devices
for short) on the both sides of the model to protect routing message
exchanges between endpoints. The unicast key management for these
protocols today is limited to statically configured master keys in
individual network devices. This document defines a mechanism to secure
such pairwise Routing Protocol (RP) associations using IKEv2, allowing network devices to automatically
exchange keying material related information between the network
devices. To benefit the discussion, it is implied that the routing
protocols mentioned in the remainder of this memo use unicast pair-wise
communication model, unless otherwise mentioned.This memo assumes that network devices need to be provisioned with
some credentials for a one-to-one authentication protocol. Any method
for a pairwise security protocol specified for use with IKEv2 is
applicable.When two network devices running a routing protocol have not yet
established a secure association, the two endpoints need to select a KMP
solution that meets their mutual requirements and use that KMP solution
to establish the required security before sending out any routing
protocol packets. The KMP solution typically enables the network devices
to perform mutual authentication using their provisioned credentials and
to agree upon certain keying material as the result of an successful
authentication. The keying material then can be applied to secure the
routing protocol.This section lists the key terminologies used throughout the
memo.Network Device: In this memo, a router or any other type of device
participating in routing protocols is referred to as a network
device.Key Management Database (KDMB): A KDMB is a conceptual database
which locates in the middle of a key management protocol and a routing
protocol to provide the long-term key management service. Therefore,
the RP and the KMP need not to cooperate directly.The following acronyms and abbreviations are used throughout this
memo.Internet Key Exchange Protocol Version 2Routing ProtocolSecurity AssociationKey Management ProtocolAs illustrated in Figure 1, this work makes use the state machine of
IKEv2. Assume a network device and its peer device are in State 1. That
is, the device has not authenticated its peer device and does not have
the keys to secure the routing protocol packets which it would like to
exchange with the peer. Before sending any routing protocol packets, the
two devices need to perform a IKE_SA_INIT exchange. If the IKE_SA_INIT
exchange succeeds, both network devices are transferred to State 2 where
they have agreed upon certain keying material but have decided how to
use the material to derive keys to secure routing protocols. To achieve
this objective, the two network devices perform an IKE_AUTH exchange, in
which both endpoints try to authenticate each other and generate
security associations for the routing protocol they intend to support.
If the IKE_AUTH exchange succeeds, the network devices transfer their
state to State 3 where both endpoints are authenticated and keys for
securing the routing protocols are generated. If the endpoints intend to
generate new SAs for routing protocols by using the keying material
already generated, they can just perform an CREATE_CHILD_SA exchange. A
discussion in more details can be found in Section 4.Three types of keys mentioned the discussion of this memo are
listed as follows:PSK (Pre-Shared Key) : a PSK is a pair-wise unique key, which
can be used for securing the routing protocol exchanges or be used
for authenticating a network device by a KMP. These keys are
configured by some mechanism such as manual configuration or a
management application outside of the scope of KMP.Protocol master key: A protocol master key is a key exported by
a KMP for use by a routing protocol. This is the key that is
shared in the KMDB between the routing protocol and KMP. A routing
protocol may use a protocol master key directly or derive traffic
keys from it.Traffic key: A traffic key is the key actually used to protect
the integrity of the routing messages exchanged in a routing
protocol. In existing cryptographic authentication mechanisms for
routing protocols, the traffic key can be the same as or derived
from the protocol master key. If there is no KMP provided, a
traffic key can be the same as or derived from a pre-shared
key.The KARP analysis in BGP, LDP, PCEP, and MSDP indicates that all of
these routing protocols need a dedicated key management protocol to confidentially exchange keying material
between endpoints. There is no need to define an entirely new protocol
for this purpose, when existing mature protocol exchanges and methods
have been vetted. This draft makes use of the IKEv2 protocol exchanges,
state machine, and policy definitions to define a dedicated key
management protocol.The notations contained in the IKEv2 message are defined as
follows.NotationPayloadAUTHAuthenticationCERTCertificateCERTREQCertificate RequestDDeleteHDRIKEv2 Header (not a payload)IDiIdentification - InitiatorIDrIdentification - ResponderKEKey ExchangeNi, NrNonceNNotifySASecurity AssociationSKEncrypted and AuthenticatedTSiTraffic Selector - InitiatorTSrTraffic Selector - ResponderA network device desiring to negotiate a key and other associated
parameters for a pair-wise routing protocol to a peer initiates an
IKE_SA_INIT exchange defined in IKEv2 .
The IKE_SA_INIT exchange is a two-message exchange that allows the
network devices to negotiate cryptographic algorithms, exchange nonce
information, and do a Diffie-Hellman (DH)
exchange, for their routing protocols, after which protocols on these
network devices can communicate privately. Note that at the end of a
IKE_SA_INIT exchange the endpoints on the both sides have not
authenticated each other yet. For the details of this exchange, refer
to IKE_SA_INIT in IKEv2 .Up to this step, this work introduces no change to IKEv2.Next, the network devices perform an IKE_AUTH exchange defined in
IKEv2. The SA payloads contain the
security policies for a key and the associated parameters (as defined
in Header and Payload Formats),
and the TS payloads contains traffic selectors as defined in IKEv2. For the details of the exchange please
refer to IKE_AUTH in IKEv2.In the IKE_AUTH exchange, the Initiator proposes one or
more sets of policies for the key used for securing a routing protocol
in the SAi2. The SA payload indicates that the supported policies
associated with the key are being proposed. The Responder returns the
one policy contained in SAr2 that it accepts. Based on this policy,
appropriate keying material is derived from the existing shared keying
material. At the successful conclusion of the IKE_AUTH exchange, the
initiator and responder have agreed upon a single set of policy and
keying material for a particular routing protocol.The network devices may then destroy the state associated with the
IKEv2 SA, continuing to use the RP policy and keying material, or they
may choose to retain them for further usages. Note that this policy
differs from IKEv2/IPsec, where the deletion of the IKEv2 SA
necessitates the deletion of the IPsec SAs. If both the network
devices choose to retain them, they may use the IKEv2 SA to
subsequently agree upon replacement policy for the same RP, or agree
upon the policy and keying material for another routing protocol.
Either case will require the use of the IKEv2 CREATE_CHILD_SA exchange
as defined in IKEv2.A CREATE_CHILD_SA exchange therefore can be triggered in order
toRekey an antique RP master key and establish a new equivalent
one,Generate needed keying material for a newly executed routing
protocol based on an existing SA, orRekey an IKEv2 SA and establish a new equivalent IKEv2 SA.A CREATE_CHILD_SA exchange MAY be initiated by either end of the SA
after the initial exchanges are completed. All messages in a
CREATE_CHILD_SA exchange are cryptographically protected using the
cryptographic algorithms and keys negotiated in the initial
exchange.For details on the exchange, refer to the CREATE_CHILD_SA exchange
as defined in IKEv2.The IKEv2 INFORMATIONAL exchange is also useful for deleting
specific IKEv2 SAs or sending status information. The Notify (N) and
Delete (D) payloads are as those defined by IKEv2. For example, if the Responder
refused to accept one of Proposals sent by the Initiator, it would
return an INFORMATIONAL exchange of type NO_PROPOSAL_CHOSEN instead of
the response to CREATE_CHILD_SA.IKEv2 is used to dynamically derive keying material information
between the two network devices trying to establish or maintain a
routing protocol neighbor adjacency. Typically network devices running
the routing protocols establish neighbor adjacencies at the routing
protocol level. These routing protocols may run different security
algorithms that provide transport level security for the protocol
neighbor adjacencies. Depending on the security algorithm used, the
routing protocols are configured with security algorithm specific keys
that are either long term keys or short term session keys. These keys
are specific to the security algorithms used to enforce transport
level security for the routing protocols.A routing protocol causes IKEv2 to execute when it needs keying
material to establish neighbor adjacency. This can be as a result of
the routing protocol neighbor being configured, neighbor changed or
updated, a local rekey policy decision, or some other event dictated
by the implementation. The keying material would allow the network
devices to then independently generate the same key and establish an
IKEv2 session between them. This is typically done by the Initiator
(IKEv2 speaker) initiating an IKEv2 IKE_SA_INIT exchange mentioned in
the section 2.1 towards its IKEv2 peer. As part of IKEv2_INIT
exchange, IKEv2 will send a message to the peer's IKEv2 port. The
format of the message is explained in . The procedure to exchange key information
is explained in . Once the keying
material information is successfully exchanged by both of the IKEv2
speakers, the IKEv2 neighbor adjacency may be torn down or kept around
as explained in .The master key data received from IKEv2 peers is stored in the
separate Key Management Database known as KMDB. KMDB follows the
guidelines in Database of Long Lived Symmetric
Cryptographic Keys , and each entry consists of Key specific
information, Security algorithm to which the Key is applicable to,
Routing Protocol Clients of interest, and the announcing KMP Peer.
KMDB is also used to notify the routing protocols about the key
updates. Typically keying material information is exchanged whenever a
routing protocol is about to create a new neighbor adjacency. This is
considered as an Initial Key exchange mode. Keying material
information is also exchanged to refresh existing key data on an
already existing neighbor adjacency. This is considered as Key
rollover exchange mode. The following sections describes their detail
behavior.Routing protocols informs IKEv2 of its new neighbor adjacency. It
does so by creating a local entry in KMDB which consists of a Security
algorithm, Key specific information, routing protocol client and the
routing protocol neighbor. Upon a successful creation of such an entry
IKEv2 initiates KMP peering with the neighbor and starts an initial
IKE_SA_INIT exchange explained in
followed by the RP_AUTH exchanged explained in . Once the key related information is successfully
exchanged, KMDB may invoke the routing protocol client to provide key
specific information updates if any.A routing protocol may need to perform the key selection and
rollover in cooperation with KMDB. Such a procedure is described in
Section 3 of Database of Long-Lived Symmetric
Cryptographic Keys . Details of how RP interact with KMDB and
deals with multiple keys during rollover are also described in that
section. When a routing protocol uses TCP-AO to secure its message
exchanges, conditions could be a little more complex. Typically, a
TCP-AO implementation has its own key tables. TCP-AO may only carry
out key management operations on the key tables if the key information
maintained in KDMB needs not to be updated. In , a Gatekeeper
(GK) mechanism is provided to orchestrate the key management
operations on the TCP-AO key tables and KMDB.Protocol interaction between KMP and its client routing protocols is
typically done using KMDB. Routing protocols may be able to update KMDB
by performing key selection and rollover operations. During a key
selection, if there is no appropriate key found in the conceptual
database, as a part of the KMDB update, IKEv2 is initiated to connect
with its appropriate IKEv2 peer so as to generate a new key. When a key
needs to be revoked, it is also the responsibility of IKEv2 to inform
its peer to guarantee the synchronization of the databases on the both
sides. In addition, when a key is obsoleted for some reasons when it is
being used by a client routing protocol, the routing protocol may need
to be informed of this update. For the routing protocols which using
TCP-AO to secure their message exchanges, a Gatekeeper mechanism is
provided to trigger the update of keys and manage the key revocation
.The protocol defined in this memo uses IKEv2 payload definitions.
However, new security policy definitions are described to support
security transforms and policy defined by routing protocol
documents.The TCP Authentication Option (TCP-AO)
is primarily intended for BGP and other TCP-based routing
protocols. In order for IKEv2 to negotiate TCP-AO policy, a new
Security Protocol Identifier needs to be defined in the IANA
registry for "IKEv2 Security Protocol Identifiers" Magic Numbers' for ISAKMP
Protocol. This memo proposes adding a new Protocol Identifier
to the table, with a Protocol Name of "TCP_AO" and a value of 6.The Security Association (SA) payload contains a list of
Proposals, which describe one or more sets of policies that a
network device is willing to use to protect a routing protocol. In
the Initiator's message, the SAi2 payload contains a list of
Proposal payloads (as defined in the next sections), each of which
contains a single set of policy that can be applied to the packets
described in the Traffic Selector (TS) payloads in the same
exchange. Each set of policy is given a particular "Proposal Number"
uniquely identifying this set of policy.The responder includes a single Proposal payload in it's SA
policy, which denotes the choice it has made amongst the initiator's
list of Proposals. Any attributes of a selected transform MUST be
returned unmodified as explained in IKEv2 section 3.3.6. The initiator of an
exchange MUST check that the accepted offer is consistent with one
of its proposals, and if not MUST terminate the exchange.Each Proposal has a list of Transform (T) substructures, each
of which describe a particular set of cryptographic policy
choices. A TCP-AO proposal uses the INTEG transform to negotiate
the MKT Message Authentication Code (MAC) algorithm. Cryptographic Algorithms for TCP-AO
describes HMAC-SHA-1-96, AES-128-CMAC-96, which map to the
existing INTEG transform IDs of AUTH_HMAC_SHA1_96 and
AUTH_AES_CMAC_96 respectively. The use of each INTEG algorithm
implies the use of a specific KDF (deriving session keys from a
master key), and so the choice of a particular INTEG transform ID
also specifies the required KDF transform. This will be true for
every transform ID used with TCP-AO, as required in RFC 5926 (see
Section 3.2 where the "KDF_Alg" is a fixed element of a MAC
algorithm definition for TCP-AO).A TCP-AO proposal also requires a new type of transform, which
describes whether TCP options are to be protected by the integrity
algorithm. This memo proposes adding a new Transform Type in the
IANA registry for "Transform Type Values" The TCP-AO KeyID is sent in the SPI field of an IKEv2
proposal. A KeyID for TCP-AO has the same purpose as an IPsec SPI
value, so it is natural to place it in this portion of the
proposal. If the KeyID values in a responder's Proposal does not
mach the KeyID values initiator's Proposal, then they have chosen
to use different KeyID values to represent the same master key and
associated proposal policy. This is consistent with how IPsec uses
the SPI value, and the semantic of initiator and responder using
different SendIDs is supported by RFC 5925.The following table shows the Transforms that can be negotiated
for a TCP-AO protocol. shows an example of IKEv2 SA
Payload including a single Proposal sent in the first message of
an IKE_AUTH or CREATE_CHILD_SA exchange. It indicates a
willingness to use either of the two MAC algorithms defined in RFC
5926, and is willing to either protect TCP options or not. The SPI
value represents the new SendID it is associating with the TCP-AO
Master Key Tuple (MKT) policy being negotiated.The responder will record the SPI value to be the
RecvID of the MKT. It chooses its own SendID value, one of each
Transform type, and returns this policy in the response message.
For example, if the responder chose HMAC-SHA-1-96 and chose to
protect the TCP options, the corresponding SA payload would
be:In this example, the Proposal responder chose to use a
different SPI value (0x11) as its SendID. This is possible because
Section 2.2 of declares that "KeyID
values MAY be the same in both directions of a connection, but do
not have to be and there is no special meaning when they are."Each TCP-AO MAC algorithm specification in Section 3.2 of Crypto for TCP-AO defines the Key_Length as
a number of bits <n> needed as keying material for the MAC
algorithm.In order for IKEv2 to negotiate BFD authentication policy, a new
Security Protocol Identifier needs to be defined in the IANA registry
for "IKEv2 Security Protocol Identifiers" Magic Numbers' for ISAKMP Protocol.
This memo proposes adding a new Protocol Identifier to the table, with
a Protocol Name of "BFD" and a value of 7.The base BFD specification defines
five authentication mechanisms: Password, Keyed MD5, Meticulous
Keyed MD5, Keyed SHA1, and Meticulous Keyed SHA1. Because Password
does not use keys, the support of this mechanism is out of the scope
of this work. In the other four mechanisms, Keyed MD5 and Meticulous
Keyed MD5 use MD5 as the Message Authentication Code (MAC)
algorithm, while Keyed SHA1 and Meticulous Keyed SHA1 use SHA1. In
, a generic
authentication mechanism and a generic meticulous authentication
mechanism which can support various MAC algorithms is proposed.Therefore, a BFD proposal also requires a new type of transform
to identify the type of BFD authentication. This memo proposes
adding a new Transform Type in the IANA registry for "Transform Type
Values"Base Authentication in indicates
the keyed (MD5 or SHA-1) authentication mechanism defined in the base BFD specification. Base Meticulous
Authentication indicates the meticulous keyed (MD5 or SHA-1)
authentication mechanism defined in the base BFD specification.
Generic Authentication and Generic Meticulous Authentication
indicate the generic keyed authentication and the generic keyed
meticulous authentication mechanisms defined in respectively.A BFD proposal uses INTEG transforms to negotiate Message
Authentication Code (MAC) algorithms. In the base BFD , keyed MD5 and keyed SHA-1 are adopted. The two
algorithms can be identified using existing INTEG transform IDs of
AUTH_HMAC_MD5_96 and AUTH_HMAC_SHA1_96 respectively. In , it is specified that a BFD using
the authentication mechanisms defined in MUST support
HMAC-SHA-256 which can be identified using existing INTEG transform
IDs of AUTH_HMAC_SHA2_256_128 .The BFD KeyID is sent in the SPI field of an IKEv2 proposal. Note
that according to , the length of KeyID is 8
bits.Because in BFD the transport key is the same as the protocol
master key, no KDF needs to be negotiated.The following figure shows the Transforms that can be negotiated
for a BFD implementation.In order for IKEv2 to negotiate RSVP-TE authentication policy, a
new Security Protocol Identifier needs to be defined in the IANA
registry for "IKEv2 Security Protocol Identifiers" Magic Numbers' for ISAKMP Protocol.
This memo proposes adding a new Protocol Identifier to the table, with
a Protocol Name of "RSVP-TE" and a value of 8.In the authentication mechanism for RSVP-TE , only HMAC-MD5 is mandated. Therefore, no INTG
transform needs to be included in a RSVP-TE proposal.A RSVP-TE proposal requires a new type of transform, which
indicates whether the integrity handshake (which is used to collect
the latest sequence number associated with a key ID) is permitted.
This memo proposes adding a new Transform Type in the IANA registry
for "Transform Type Values" The RSVP-TE KeyID is sent in the SPI field of an IKEv2
proposal.The following figure shows the Transforms that can be negotiated
for a RSVP-TE implementation.A Notify Payload (IKEv2 Section
3.10) or Delete Payload ( IKEv2 Section
3.11) contains a Protocol ID field. The Protocol ID is set to TCP_AO
(6) when a notify message is relevant to the TCP-AO KeyID value
contained in the SPI field. Similarly, the Protocol ID is set to BFD
(7) when a notify message is relevant to the BFD KeyID value contained
in the SPI field, and the Protocol ID is set to RSVP-TE (8) when a
notify message is relevant to the RSVP-TE KeyID value contained in the
SPI field.In order for IKEv2 to negotiate TCP-AO authentication policies, a new
Security Protocol Identifier needs to be defined in the IANA registry
for "IKEv2 Security Protocol Identifiers" Magic Numbers' for ISAKMP Protocol.
IANA is requested to add a new Protocol Identifier to the table, with a
Protocol Name of "TCP-AO" and a value of 6. A TCP-AO proposal also
requires a new type of transform, which describes whether TCP options
are to be protected by the integrity algorithm. This memo proposes
adding a new Transform Type 6 for this transform in the IANA registry
for "Transform Type Values".In order for IKEv2 to negotiate BFD authentication policies, a new
Security Protocol Identifier needs to be defined in the IANA registry
for "IKEv2 Security Protocol Identifiers" Magic Numbers' for ISAKMP Protocol.
IANA is requested to add a new Protocol Identifier to the table, with a
Protocol Name of "BFD" and a value of 7. A BFD proposal also requires a
new type of transform, which identifies the type of BFD authentication
mechanism. This memo proposes adding a new Transform Type 7 in the IANA
registry for "Transform Type Values".In order for IKEv2 to negotiate RSVP-TE authentication policies, a
new Security Protocol Identifier needs to be defined in the IANA
registry for "IKEv2 Security Protocol Identifiers" Magic Numbers' for ISAKMP Protocol.
IANA is requested to add a new Protocol Identifier to the table, with a
Protocol Name of "RSVP-TE" and a value of 8. A RSVP-TE proposal requires
a new type of transform, which indicates whether the integrity handshake
(which is used to collect the latest sequence number associated with a
key ID) is permitted. This memo proposes adding a new Transform Type 8
in the IANA registry for "Transform Type Values".TBDDuring the development of TCP-AO, Gregory Lebovitz noted that a
protocol based on an IKEv2 exchange would be a good automated key
management method for deriving a TCP-AO master key.Internet Key Exchange Version 2 (IKEv2) ParametersNew Directions in CryptographyD'Magic Numbers' for ISAKMP Protocol'Magic Numbers' for ISAKMP Protocol