Internet DRAFT - draft-nir-ipsecme-erx
draft-nir-ipsecme-erx
Network Working Group Y. Nir
Internet-Draft Check Point
Intended status: Experimental Q. Wu
Expires: June 23, 2013 Huawei
December 20, 2012
An IKEv2 Extension for Supporting ERP
draft-nir-ipsecme-erx-11
Abstract
This document updates the IKEv2 protocol, described in RFC 5996.
This extension allows an IKE Security Association (SA) to be created
and authenticated using the EAP Re-authentication Protocol extension
as described in RFC 6696.
Status of this Memo
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1. Introduction
IKEv2, as specified in section 2.16 of [RFC5996], allows
authentication of the initiator using an EAP method. Using EAP
significantly increases the count of round-trips required to
establish the IPsec SA, and also may require user interaction. This
makes it inconvenient to allow a single remote access client to
create multiple IPsec tunnels with multiple IPsec gateways that
belong to the same domain.
The EAP Re-authentication Protocol (ERP), as described in [RFC6696],
allows an EAP peer to authenticate to multiple authenticators, while
performing the full EAP method only once. Subsequent authentications
require fewer round-trips and no user interaction.
Bringing these two technologies together allows a remote access IPsec
client to create multiple tunnels with different gateways that belong
to a single domain, as well as using the keys from other contexts of
using EAP, such as network access within the same domain, to
transparently connect to VPN gateways within this domain.
Additionally, it allows for faster setting up of new tunnels when
previous tunnels have been torn down due to things like network
outage, device suspension, or temporarily moving out of range. This
is similar to the session resumption mechanism described in
[RFC5723], except that instead of a ticket stored by the client, the
re-authentication MSK (rMSK - see section 4.6 of RFC 6696) is used as
the session key stored on both the client and the AAA server.
1.1. Conventions Used in This Document
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].
2. Usage Scenarios
This work is motivated by the following scenarios:
o Multiple tunnels for a single remote access VPN client. Suppose a
company has offices in New York City, Paris, and Shanghai. For
historical reasons, the email server is located in the Paris
office, while most of the servers hosting the company's intranet
are located in Shanghai, and the finance department servers are in
New York City. An employee using remote access VPN may need to
connect to servers from all three locations. While it is possible
to connect to a single gateway, and have that gateway route the
requests to the other gateways (perhaps through site to site VPN),
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this is not efficient, and it is more desirable to have the client
initiate three different tunnels. It is, however, not desirable
to have the user type in a password three times.
o Roaming. In these days of mobile phones and tablets, users often
move from the wireless LAN in their office, where access may be
granted through 802.1x, to a cellular network where VPN is
necessary and back again. Both the VPN server and the 802.1x
access point are authenticators that connect to the same
Authentication, Authorization and Accounting (AAA) servers. So it
makes sense to make the transition smooth, without requiring user
interaction. The device still needs to detect whether it is
within the protected network, in which case it should not use VPN,
but this process is beyond the scope of this document.
[SecureBeacon] is a now-abandoned attempt at this.
o Resumption. If a device gets disconnected from an IKE peer, ERP
can be used to reconnect to the same gateway without user
intervention.
3. Protocol Outline
Supporting ERX requires an EAP payload in the first IKE_AUTH request.
This is a deviation from the rules in RFC 5996, so support needs to
be indicated through a Notify payload in the IKE_SA_INIT response.
This Notify serves the same purpose as the EAP-Initiate/Re-auth-Start
message of ERX, as specified in section 5.3.1 of RFC 6696. The
domain name included in the Domain-Name TLV as specified in section
5.3.1.1 of the same document.
A supporting initiator that has unexpired keys for this domain will
send the EAP_Initiate/Re-auth message in an EAP payload in the first
IKE_AUTH request.
The responder sends the EAP payload content to a backend AAA server.
If that server has a valid rMSK for that session, it sends those
along with an EAP-Finish/Re-auth message. The responder then
forwards the EAP-Finish/Re-auth message to the Initiator in an EAP
payload within the first IKE_AUTH response.
The initiator then sends an additional IKE_AUTH request, that
includes the AUTH payload which has been calculated using the rMSK in
the role of the MSK as described in sections 2.15 and 2.16 of RFC
5996. The responder replies similarly, and the IKE_AUTH exchange is
finished.
If the backend AAA server does not have valid keys for the Re-auth-
Start message, it sends back a normal EAP request, and no rMSK key.
EAP flow continues as in RFC 5996.
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The following figure is adapted from appendixes C.1 and C.3 of RFC
5996, with most of the optional payloads removed. Note that the
EAP_Initiate/Re-auth message is added.
IKE_SA_INIT Exchange:
| init request --> SA, KE, Ni,
|
| init response <-- SA, KE, Nr,
| N[ERX_SUPPORTED]
IKE_AUTH Exchanges:
| first request --> EAP(EAP_Initiate/Re-auth),
| IDi,
| SA, TSi, TSr
|
| first response <-- IDr, [CERT+], AUTH,
| EAP(EAP-Finish/Re-auth)
|
| last request --> AUTH
|
| last response <-- AUTH,
| SA, TSi, TSr
The IDi payload MUST have ID Type ID_RFC822_ADDR and the data field
MUST contain the same value as the KeyName-NAI TLV in the
EAP_Initiate/Re-auth message. See Section 3.2 for details.
3.1. Clarification About EAP Codes
Section 3.16 of RFC 5996 enumerates the EAP codes in EAP messages
which are carried in EAP payloads. The enumeration goes only to 4.
It is not clear whether that list is supposed to be exhaustive or
not.
To clarify, an implementation conforming to this specification MUST
accept and transmit EAP messages with at least the codes for Initiate
and Finish (5 and 6) from RFC 6696, in addition to the four codes
enumerated in RFC 5996. This document is intentionally silent about
other EAP codes that are neither enumerated in RFC 5996 nor in that
document.
3.2. User Name in the Protocol
The authors, as well as participants of the HOKEY and IPsecME working
groups believe that all use cases for this extension to IKE have a
single backend AAA server doing both the authentication and the re-
authentication. The reasoning behind this is that IKE runs over the
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Internet, and would naturally connect to the user's home network.
This section addresses instances where this is not the case.
Section 5.3.2 of RFC 6696 describes the EAP-Initiate/Re-auth packet,
which in the case of IKEv2 is carried in the first IKE_AUTH request.
This packet contains the KeyName-NAI TLV. This TLV contains the
username used in authentication. It is relayed to the AAA server in
the AccessRequest message, and is returned from the AAA server in the
AccessAccept message.
The username part of the NAI within the TLV is the EMSKName
([RFC5295]) encoded in hexadecimal digits. The domain part is the
domain name of the home domain of the user. The username part is
ephemeral in the sense that a new one is generated for each full
authentication. This ephemeral value is not a good basis for making
policy decisions, and they are also a poor source of user
identification for the purposes of logging.
Instead, it is up to the implementation in the IPsec gateway to make
policy decisions based on other factors. The following list is by no
means exhaustive:
o In some cases the home domain name may be enough to make policy
decisions. If all users with a particular home domain get the
same authorization, then policy does not depend on the real user
name. Meaningful logs can still be issued by correlating VPN
gateway IKE events with AAA servers access records.
o Sometimes users receive different authorizations based on groups
they belong to. The AAA server can communicate such information
to the VPN gateway, for example using the CLASS attribute
([RFC2865]) in RADIUS and Diameter ([RFC3588]). Logging again
depends on correlation with AAA servers.
o AAA servers may support extensions that allow them to communicate
with their clients (in our case - the VPN gateway) to push user
information. For example, a certain product integrates a RADIUS
server with the Lightweight Directory Access Protocol (LDAP -
[RFC4511]), so a client could query the server using LDAP and
receive the real record for this user. Others may provide this
data through vendor-specific extensions to RADIUS or DIAMETER.
In any case authorization is a major issue in deployments, if the
backend AAA server supporting the re-authentication is different from
the AAA server that had supported the original authentication. It is
up to the re-authenticating AAA server to provide the necessary
information for authorization. A conforming implementation of this
protocol MAY reject initiators for which it is unable to make policy
decisions because of these reasons.
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4. ERX_SUPPORTED Notification
The Notify payload is as described in RFC 5996:
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 !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Protocol ID ! SPI Size ! ERX Notify Message Type !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Domain Name !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Protocol ID (1 octet) MUST be zero, as this message is related to
an IKE SA.
o SPI Size (1 octet) MUST be zero, in conformance with section 3.10
of RFC 5996.
o ERX Notify Message Type (2 octets) - MUST be xxxxx, the value
assigned for ERX. TBA by IANA.
o Domain Name (variable) - contains the domain name or realm, as
these terms are used in RFC 6696, and encoded as ASCII, as
specified in [RFC4282].
5. Operational Considerations
This specification changes the behavior of IKE peers, both initiators
and responders. The behavior of back-end AAA servers is not changed
by this specification, but they are required to support RFC 6696.
The same goes for the EAP client, if it's not integrated into the IKE
Initiator (for example, if the EAP client is an operating system
component).
This specification is silent about key storage and key lifetimes on
either EAP client or EAP server. These issues are covered in
sections 3, 4, and 5 of RFC 6696. The key lifetime may be
communicated from the AAA server to the EAP client via the Lifetime
attribute in the EAP-Finish/Re-auth message. If the server does not
have a valid key, while the client does have one, regular EAP is used
(see Section 3). This should not happen if lifetimes are
communicated. In such a case, the IKEv2 initiator / EAP client MAY
alert the user and MAY log the event. Note that this does not
necessarily indicate an attack. It could simply be a loss of state
on the AAA server.
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6. Security Considerations
The protocol extension described in this document extends the
authentication from one EAP context, which may or may not be part of
IKEv2, to an IKEv2 context. Successful completion of the protocol
proves to the authenticator, which in our case is a VPN gateway, that
the supplicant, or VPN client, has authenticated in some other EAP
context.
The protocol supplies the authenticator with the domain name with
which the supplicant has authenticated, but does not supply it with a
specific identity. Instead, the gateway receives an EMSKName, which
is an ephemeral ID. With this variant of the IKEv2 protocol, the
initiator never sends its real identity on the wire, while the server
does. This is different from the usual IKEv2 practice of the
initiator revealing its identity first.
If the domain name is sufficient to make access control decisions,
this is enough. If not, then the gateway needs to find out either
the real name or authorization information for that particular user.
This may be done using the AAA protocol or by some other federation
protocol, which is out of scope for this specification.
7. IANA Considerations
IANA is requested to assign a notify message type from the status
types range (16418-40959) of the "IKEv2 Notify Message Types"
registry with name "ERX_SUPPORTED".
8. Acknowledgements
The authors would like to thank Yaron Sheffer for comments and
suggested text that have contributed to this document.
Thanks also to Juergen Schoenwaelder for his OPS-DIR review comments.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
Network Access Identifier", RFC 4282, December 2005.
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[RFC5295] Salowey, J., Dondeti, L., Narayanan, V., and M. Nakhjiri,
"Specification for the Derivation of Root Keys from an
Extended Master Session Key (EMSK)", RFC 5295,
August 2008.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol: IKEv2", RFC 5996,
September 2010.
[RFC6696] Cao, Z., He, B., Shi, Y., Wu, Q., and G. Zorn, "EAP
Extensions for the EAP Re-authentication Protocol (ERP)",
RFC 6696, July 2012.
9.2. Informative References
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol
(LDAP): The Protocol", RFC 4511, June 2006.
[RFC5723] Sheffer, Y. and H. Tschofenig, "Internet Key Exchange
Protocol Version 2 (IKEv2) Session Resumption", RFC 5273,
January 2010.
[SecureBeacon]
Sheffer, Y. and Y. Nir, "Secure Beacon: Securely Detecting
a Trusted Network", draft-sheffer-ipsecme-secure-beacon
(work in progress), June 2009.
Authors' Addresses
Yoav Nir
Check Point Software Technologies Ltd.
5 Hasolelim st.
Tel Aviv 67897
Israel
Email: ynir@checkpoint.com
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Qin Wu
Huawei Technologies Co., Ltd.
101 Software Avenue, Yuhua District
Nanjing, JiangSu 210012
China
Email: sunseawq@huawei.com
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