PANA Working Group                                               Y. Ohba
Internet-Draft                                                   Toshiba
Expires: May 21, April 27, 2009                                 October 24, 2008                                  November 18, 2007

                  Pre-authentication Support for PANA
                       draft-ietf-pana-preauth-02
                       draft-ietf-pana-preauth-03

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Copyright Notice

   Copyright (C) The IETF Trust (2007). April 27, 2009.

Abstract

   This document defines an extension to the PANA protocol used Protocol for carrying
   Authentication for Network Access (PANA) for proactively establishing
   a PANA SA (Security Association) between a PaC in an one access network
   and a PAA in another access network to which the PaC may move.  The
   proposed method operates across multiple administrative domains.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Specification of Requirements  . . . . . . . . . . . . . .  3
   2.  Terminogy  . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Pre-authentication Procedure . . . . . . . . . . . . . . . . .  4
   4.  PANA Extensions  . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Authorization and Accounting Considerations  . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  9
   Intellectual Property and Copyright Statements . . . . . . . . . . 10

1.  Introduction

   The PANA protocol [I-D.ietf-pana-pana] Protocol for carrying Authentication for Network Access (PANA)
   [RFC5191] carries EAP messages between a PaC (PANA Client) and a PAA
   (PANA Authentication Agent) in the access network.  If the PaC is a
   mobile device and is capable of moving one access network to another
   while running its applications, it is critical for the PaC to perform
   a handover seamlessly without degrading the performance of the
   applications during the handover period.  When the handover requires
   the PaC to establish a PANA session with the PAA in the new access
   network, the signaling to establish the PANA session should be
   completed as fast as possible.

   This document defines an extension to the PANA protocol
   [I-D.ietf-pana-pana] [RFC5191]
   used for proactively executing EAP authentication and establishing a
   PANA SA (Security Association) between a PaC in an access network and
   a PAA in another access network to which the PaC may move.  The
   proposed method operates across multiple AAA domains.  The extension
   to the PANA protocol is designed to realize direct pre-authentication
   defined in [I-D.ietf-hokey-preauth-ps].

1.1.  Specification of Requirements

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.  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.  Terminogy

   The following terms are used in this document in addition to the
   terms defined in [I-D.ietf-pana-pana]. [RFC5191].

   Serving PAA (SPAA):  A PAA that resides in the serving network and
      provides network access authentication for a particular PaC.  For
      simplicity, this document assumes that there is only one SPAA in
      the serving network while the pre-authentication mechanism
      described in this document is generally applicable to the case
      where there are two or more SPAAs in the serving network.

   Candidate PAA (CPAA):  A PAA that resides in a candidate network to
      which the PaC may move.  A CPAA for a particular PaC may be a SPAA
      for another PaC.

   Pre-authentication:  Pre-authentication refers to EAP pre-
      authentication and defined as the utilization of EAP to pre-
      establish EAP keying material on an authenticator prior to arrival
      of the peer at the access network served by that authenticator
      [I-D.ietf-hokey-preauth-ps].  In this draft, EAP pre-
      authentication is performed between a PaC and a CPAA.

   Pre-authorization:  An authorization for a PaC, made by a CPAA for
      the PaC at the time of pre-authentication.

   Post-authorization:  An authorization for a PaC, made by a CPAA for
      the PaC when the CPAA becomes the SPAA for the PaC.

   Pre-authorization SA:  A PANA SA established between a PaC and its
      CPAA.

   Post-authorization SA:  A PANA SA established between the PaC and its
      SPAA.

3.  Pre-authentication Procedure

   A PaC that supports pre-authentication may establish a PANA session
   for each CPAA.

   There may be several mechanisms for a PaC and a CPAA to discover each
   other.  However, such mechanisms are out of the scope of this
   document.

   There may be a number of criteria for CPAA selection, the timing to
   start pre-authentication and the timing to make a pre-authorization
   SA a post-authorization SA (and hence the CPAA becomes the SPAA).
   Such criteria can be implementation specific and thus are outside the
   scope of this document.

   Pre-authentication may be initiated by both a PaC and a CPAA.  A new
   'E' (prE-authentication) bit is defined in the PANA header.  When
   pre-authentication is performed, the 'E' (prE-authentication) bit of
   PANA messages are set in order to indicate whether this PANA run is
   for pre-authentication.  Use of pre-authentication is negotiated as
   follows.

   o  When a PaC initiates pre-authentication, it sends a PANA-Client-
      Initiation (PCI) message with the 'E' (prE-authentication) bit
      set.  The PCI message MUST be unicast.  The CPAA responds with a
      PANA-Start-Request (PSR) message with the 'S' (Start) and 'E'
      (prE-authentication) bits set only if it supports pre-
      authentication.  Otherwise, it MUST silently discard the message.

   o  When a CPAA initiates pre-authentication, it sends a PSR message
      with the 'S' (Start) and 'E' (prE-authentication) bits set.  The
      PaC responds with a PANA-Start-Answer (PSA) message with the 'S'
      (Start) and 'E' (prE-authentication) bits set only if it supports
      pre-authentication.  Otherwise, it MUST silently discard the
      message.

   o  Once the PaC and CPAA have agreed on performing pre-authentication
      using the 'S' (Start) and 'E' (prE-authentication) bits, the
      subsequent PANA messages exchanged between them MUST have the 'E'
      (prE-authentication) bit set.

   When a CPAA with which the PaC has a pre-authorization SA becomes the
   SPAA due to, e.g., movement of the PaC, the PaC performs an IP
   address update procedure defined in Section 5.6 of
   [I-D.ietf-pana-pana] [RFC5191] in order
   to update the SPAA with the PaC's new address obtained from the new
   serving network.  PANA-Notification-
   Request  PANA-Notification-Request (PNR) and PANA-Notification-Answer PANA-
   Notification-Answer (PNA) messages with 'P' (Ping) bit set are used
   for this purpose.  The completion of the IP address update procedure
   will change the pre-authorization SA to a post-authorization SA.  In
   this case, the 'E' MUST NOT be set in the PNR and PNA messages and
   subsequent PANA messages.

   If there is another CPAA with which the PaC has a pre-authorization
   SA and the PaC wants to keep the pre-authorization SA after the
   change of SPAA, the PaC also performs an IP address update procedure
   defined in Section 5.6 of [I-D.ietf-pana-pana] [RFC5191] in order to update the CPAA with
   the PaC's new address.  PNR and PNA messages with 'P' (Ping) bit set
   is used for this purpose.  In this case, the 'E' (prE-
   authentication) (prE-authentication)
   bit MUST be set in the PNR and PNA messages and subsequent PANA
   messages.  The IP address update procedure with the CPAA will not
   change the pre-authorization SA to a post-authorization SA.

   The pre-authorization SA and the corresponding PANA session between
   the PaC and a CPAA is deleted by entering the termination phase of
   the PANA protocol.

   Example call flows for PaC-initiated pre-authentication and PAA-
   initiated pre-authentication are shown in Figure 1 and Figure 1, 2,
   respectively.

        PaC                                               CPAA
         |                                                 |
   +------------------+                                    |
   |Pre-authentication|                                    |
   |trigger           |                                    |
   +------------------+                                    |
         |                  PCI w/'E' bit set              |
         |------------------------------------------------>|
         |            PAR w/'S' and 'E' bits set           |
         |<------------------------------------------------|
         |            PAN w/'S' and 'E' bits set           |
         |------------------------------------------------>|
         |           PAR-PAN exchange w/'E' bit set        |
         |<----------------------------------------------->|
         |                                        +------------------+
         |                                        |pre-authorization |
         |                                        +------------------+
         |            PAR w/'C' and 'E' bits set           |
         |<------------------------------------------------|
         |            PAN w/'C' and 'E' bits set           |
         |------------------------------------------------>|
         .                        .                        .
         .                        .                        .
   +----------+                                            |
   | Movement |                                            |
   +----------+                                            |
         |        PNR w/ 'P' bit set and w/o 'E' bit set   |
         |------------------------------------------------>|
         |                                        +-------------------+
         |                                        |post-authorization |
         |                                        |(CPAA becomes SPAA)|
         |                                        +-------------------+
         |        PNA w/ 'P' bit set and w/o 'E' bit set   |
         |<------------------------------------------------|
         |                                                 |

           Figure 1: PaC-initiated Pre-authentication Call Flow
        PaC                                               CPAA
         |                                                 |
         |                                        +------------------+
         |                                        |Pre-authentication|
         |                                        |trigger           |
         |                                        +------------------+
         |            PAR w/'S' and 'E' bits set           |
         |<------------------------------------------------|
         |            PAN w/'S' and 'E' bits set           |
         |------------------------------------------------>|
         |           PAR-PAN exchange w/'E' bit set        |
         |<----------------------------------------------->|
         |                                        +------------------+
         |                                        |pre-authorization |
         |                                        +------------------+
         |            PAR w/'C' and 'E' bits set           |
         |<------------------------------------------------|
         |            PAN w/'C' and 'E' bits set           |
         |------------------------------------------------>|
         .                        .                        .
         .                        .                        .
   +----------+                                            |
   | Movement |                                            |
   +----------+                                            |
         |        PNR w/ 'P' bit set and w/o 'E' bit set   |
         |------------------------------------------------>|
         |                                        +-------------------+
         |                                        |post-authorization |
         |                                        |(CPAA becomes SPAA)|
         |                                        +-------------------+
         |        PNA w/ 'P' bit set and w/o 'E' bit set   |
         |<------------------------------------------------|
         |                                                 |

           Figure 2: PAA-initiated Pre-authentication Call Flow

4.  PANA Extensions

   A new 'E' (prE-authentication) bit is defined in Flags field of PANA
   header as follows.

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |R S C A P I E r r r r r r r r r|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   E(PrE-authentication)  When pre-authentication is performed, the 'E'
      (prE-authentication) bit of PANA messages are set in order to
      indicate whether this PANA run is for establishing a pre-
      authorization SA.  The exact usage of this bit is described in
      Section 3.  This bit is to be assigned by IANA.

5.  Authorization and Accounting Considerations

   A pre-authorization and a post-authorization for the PaC may have
   different authorization policies.  For example, the pre-authorization
   policy may not allow the PaC to sent or receive packets through an
   (Enforcement Point)
   Enforcement Point (EP) that is under control of the CPAA, while both
   the pre-authorization and post-authorization policies may allow
   installing credentials to the EP, where the credentials are used for
   establishing a security association for per-packet cryptographic
   filtering.

   In an access network where accounting is performed, accounting starts
   when the pre-authorization SA becomes the post-authorization SA by
   default.  Depending on the pre-authorization policy, accounting may
   start immediately after the pre-authorization SA is established.

6.  Security Considerations

   Since the mechanism described in this document is designed to work
   across multiple access networks, each EP in the serving network
   SHOULD be configured to allow PANA messages to be forwarded between a
   PaC and a CPAA only if the PaC has a post-authorization SA with the
   SPAA in order to avoid an unauthorized PaC to initiate pre-
   authentication.  Also, each access network that supports pre-
   authentication SHOULD block pre-authentication attempts from networks
   from which a handover is not likely to occur.

   When pre-authentication is initiated by a CPAA, it is possible that
   the PaC simultaneously communicates with multiple CPAAs initiating
   pre-authentication.  In order to avoid possible resource consumption
   attacks on the PaC caused by a blind attacker initiating pre-
   authentication for the PaC by changing source addresses, the PaC
   SHOULD limit the maximum number of CPAAs allowed to communicate.

   The pre-authentication mechanism defined in this document does not
   have an issue on context binding in which link-layer independent
   context carried over pre-authentication signaling is bound to the
   link-layer specific context [I-D.ietf-hokey-preauth-ps], because the
   same EAP transport protocol (i.e., PANA) is used for normal
   authentication and pre-authentication in the candidate network.

7.  IANA Considerations

   As described in Section 4, bit 6 of the Flags field of PANA Header
   needs to be assigned by IANA for the 'E' (prE-authentication) bit.

8.  Acknowledgments

   The author would like to thank Alper Yegin, Ashutosh Dutta, Julien
   Bournelle and Sasikanth Bharadwaj for their valuable comments.

9.  References

9.1.  Normative References

   [I-D.ietf-pana-pana]

   [RFC5191]  Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
              Yegin, "Protocol for Carrying Authentication for Network
              Access (PANA)", draft-ietf-pana-pana-18 (work in
              progress), September 2007. RFC 5191, May 2008.

   [I-D.ietf-hokey-preauth-ps]
              Ohba, Y., "EAP Pre-authentication Problem Statement",
              draft-ietf-hokey-preauth-ps-01
              draft-ietf-hokey-preauth-ps-04 (work in progress),
              October 2007.
              September 2008.

9.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

Author's Address

   Yoshihiro Ohba
   Toshiba America Research, Inc.
   1 Telcordia Drive
   Piscateway, NJ  08854
   USA

   Phone: +1 732 699 5365 5305
   Email: yohba@tari.toshiba.com

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