An IKEv2 Extension for Supporting ERP

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Document Type Active Internet-Draft (individual in sec area)
Authors Yoav Nir  , Qin Wu 
Last updated 2012-11-27 (latest revision 2012-08-01)
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Network Working Group                                             Y. Nir
Internet-Draft                                               Check Point
Updates: 5996 (if approved)                                        Q. Wu
Intended status: Experimental                                     Huawei
Expires: February 2, 2013                                 August 1, 2012

                 An IKEv2 Extension for Supporting ERP


   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.

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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.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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
      NYC.  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), 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

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      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.

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 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,
   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 RFC
   5996.  The responder replies similarly, and the IKE_AUTH exchange is

   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.

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   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

   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

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
   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,

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   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.

4.  ERX_SUPPORTED Notification

   The Notify payload is as described in RFC 5996:

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                            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 1, 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.  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

   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.

6.  IANA Considerations

   IANA is requested to assign a notify message type from the status

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   types range (16418-40959) of the "IKEv2 Notify Message Types"
   registry with name "ERX_SUPPORTED".

7.  Acknowledgements

   The authors would like to thank Yaron Sheffer for comments and
   suggested text that have contributed to this document.

8.  References

8.1.  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.

   [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.

8.2.  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.

              Sheffer, Y. and Y. Nir, "Secure Beacon: Securely Detecting
              a Trusted Network", draft-sheffer-ipsecme-secure-beacon

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              (work in progress), June 2009.

Authors' Addresses

   Yoav Nir
   Check Point Software Technologies Ltd.
   5 Hasolelim st.
   Tel Aviv  67897


   Qin Wu
   Huawei Technologies Co., Ltd.
   101 Software Avenue, Yuhua District
   Nanjing, JiangSu  210012


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