| Network Working Group | Y. Nir |
| Internet-Draft | Check Point |
| Intended status: Standards Track | Q. Wu |
| Expires: October 15, 2012 | Huawei |
| April 15, 2012 |
An IKEv2 Extension for Supporting ERP
draft-nir-ipsecme-erx-03
This document describes an extension to the IKEv2 protocol that allows an IKE Security Association (SA) to be created and authenticated using the EAP Re-authentication Protocol extension as described in RFC 5296bis.
NOTE TO RFC EDITOR: Replace 5296bis in the previous paragraph with the RFC number assigned to that document.
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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 [RFC5296bis], 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.
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].
This work is motivated by the following several scenarios.
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 replaces the EAP-Initiate/Re-auth-Start message of ERX, and therefore contains the domain name, as specified in section 5.3.1.1 of [RFC5296bis].
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, and receives the rMSK and an EAP-Finish/Re-auth message. It 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 [RFC5996]. The responder replies similarly, and the IKE_AUTH exchange is finished.
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 replaces the IDi payload.
init request --> SA, KE, Ni,
init response <-- SA, KE, Nr,
N[ERX_SUPPORTED]
first request --> EAP(EAP_Initiate/Re-auth),
[[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+],
[IDr],
[CP(CFG_REQUEST)],
SA, TSi, TSr,
[V+][N+]
first response <-- IDr, [CERT+], AUTH,
EAP(EAP-Finish/Re-auth),
[V+][N+]
last request --> AUTH
last response <-- AUTH,
[CP(CFG_REPLY)],
SA, TSi, TSr,
[V+][N+]
Section 3.16 of [RFC5996] 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 supporting this specification MUST accept and transmit EAP messages with at least the codes for Initiate and Finish (5 and 6), in addition to the four codes enumerated in RFC 5996.
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 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 [RFC5296bis] 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 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:
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.
The Notify payload is as described in [RFC5996]
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 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
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.
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".
| [1] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [2] | Kaufman, C, Hoffman, P, Nir, Y and P Eronen, "Internet Key Exchange Protocol: IKEv2", RFC 5996, September 2010. |
| [3] | Wu, W, Cao, Z, Zorn, G, Shi, Y and B He, "EAP Extensions for EAP Re-authentication Protocol (ERP)", Internet-Draft draft-ietf-hokey-rfc5296bis-06, May 2011. |
| [1] | Sheffer, Y. and Y. Nir, "Secure Beacon: Securely Detecting a Trusted Network", Internet-Draft draft-sheffer-ipsecme-secure-beacon, June 2009. |