PANA Working Group
   Internet Draft                                    <M. Parthasarathy>
   Document: draft-ietf-pana-ipsec-00.txt                  October 2003
   Expires: March 2004



                 PANA enabling IPsec based Access Control



Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [i].

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 except that the right to
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Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.


Abstract

   The PANA (Protocol for carrying Authentication for Network Access)
   working group is developing protocol for authenticating clients to
   the access network using IP based protocols.  The PANA protocol
   authenticates the client and also establishes a PANA security
   association between the PANA client and PANA authentication agent at
   the end of a successful authentication. This document discusses the
   details for establishing an IPsec security association using the PANA
   security association for enabling IPsec based access control.


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Table of Contents

   1.0 Introduction..................................................2
   2.0 Keywords......................................................3
   3.0 Pre-requisites for IPsec SA establisment......................3
   4.0 IKE Pre-shared key derivation.................................3
   5.0 IKE and IPsec details.........................................4
   6.0 Packet Formats................................................4
   7.0 IPsec SPD entries.............................................5
   8.0 Double IPsec..................................................8
   9.0 Security considerations.......................................9
   10.0 Normative References.........................................9
   12.0 Acknowledgments.............................................10
   13.0 Revision log................................................10
   14.0 Author's Addresses..........................................10
   15.0 Full Copyright Statement....................................10


1.0 Introduction

   The PANA (Protocol for carrying Authentication for Network Access)
   working group is developing protocol for authenticating clients to
   the access network using IP based protocols.  The PANA protocol
   authenticates the client and also establishes a PANA security
   association between the PANA client and PANA authentication agent at
   the end of successful authentication. The PANA authentication agent
   (PAA) indicates the results of the authentication using the PANA-
   Bind-Request message wherein it can indicate the access control
   method enforced by the access network. The PANA protocol [PANA-PROT]
   does not discuss any details of IPsec [IPSEC] SA establishment, when
   IPsec is used for access control. This document discusses the details
   of establishing an IPsec security association between PANA client and
   the enforcement point. When the IPsec SA is successfully established,
   it can be used for access control and specifically used to prevent
   the service theft mentioned in [PANA-THREATS].

   Please refer to [PANAREQ] for terminology and definitions of terms
   used in this document. The following picture illustrates what is
   being protected with IPsec. In Figure 1, it is assumed that PAA and
   EP are co-located. It is also possible that they are not co-located.
   The IPsec security association protects the traffic between PaC and
   EP. In IPsec terms, EP is a security gateway (therefore a router) and
   forwards packets coming from the PaC to other nodes.







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                      PaC ---------------EP/PAA-+
                      [D1]                      |
                                                +- ----- AR
                                                |
                      PaC ---------------EP/PAA-+
                      [D2]
                      |------IPsec------|

                          Figure 1

   First, this document discusses some of the pre-requisites for IPsec
   SA establishment. Next, it gives details on what should be
   communicated between PAA and EP. Then, it gives the details of
   IKE/IPsec exchange with packet formats and SPD entries. Finally, it
   discusses the issues when IPsec is used for remote access together
   with local access.

2.0 Keywords

   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 [KEYWORDS].


3.0 Pre-requisites for IPsec SA establisment

   This document assumes that the following have already happened before
   the IPSEC SA is established.

     1) PANA client (PaC) learns the IP address of the Enforcement point
        (EP) during the PANA exchange.

     2) PaC learns that the network uses IPsec [IPSEC] for securing the
        link between PaC and EP during the PANA exchange.

     3) PaC has already acquired an IP address and EP knows about the IP
        address of the PaC, before the IKE exchange starts. If IPv6 is
        being used, the EP needs to know both the global address and the
        link-local address of the PaC.

4.0 IKE Pre-shared key derivation

   If the network chooses IPsec to secure the link between PaC and EP,
   PAA should communicate the IKE pre-shared key, the IP address of the
   PaC and the PANA session ID to EP before the IKE exchange begins.
   This might be just an API call, if PAA and EP are co-located. It is


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   assumed that the communication between PAA and EP is already secured
   [PANA-REQ].

   The IKE exchange between PaC and PAA is equivalent to the 4-way
   handshake in [IEEE80211i] following the EAP exchange. The IKE
   exchange establishes the IPsec SA similar to the pair-wise transient
   keys (PTK) established in [IEEE80211i]. The IKE exchange provides
   both key confirmation and protected cipher-suite negotiation.

   IKE pre-shared key is derived as follows.

   IKE Pre-shared Key = HMAC-SHA-1 (MSK, "IKE-preshared key" |
                           Session ID)

   The values have the following meaning:

   MSK: The Master Session Key (MSK) is provided by the EAP method as
   part of the PANA/EAP protocol execution. Please refer to [EAP-KEY]
   for details.

   Session ID: This value is a 128-bit value as defined in the PANA
   protocol [PANA-PROT], which identifies a particular session of a
   client.

   The character "|" denotes concatenation as defined in [IKE].


5.0 IKE and IPsec details

   IKE [IKE] MUST be used for establishing the IPsec SA. Manual keying
   may not be possible, as the network does not know all the PaCs that
   will be authenticating to the network, a priori. Main mode with pre-
   shared key SHOULD be supported. Aggressive mode with pre-shared key
   MUST be supported. PaC and EP SHOULD use its IP address as the phase
   I identifier in main mode and PANA session ID [PANA-PROT] as the
   payload of ID_KEY_ID in aggressive mode for establishing the phase I
   SA. An IP address would also work well as an identifier in aggressive
   mode. But session ID was chosen to avoid potential problems with
   link-local addresses in IPv6, which are guaranteed to be unique only
   within the scope of a link.

   After Phase I SA is established, quick mode exchange is performed to
   establish an ESP tunnel mode IPsec SA for protecting the traffic
   between PaC and EP. The next few sections discusses the packet
   formats and SPD entries.

6.0 Packet Formats

   Following acronyms are used in this section.


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   EP's address is denoted by EP-ADDR.
   PaC's address is denoted by PAC-ADDR.
   The node with which the PaC is communicating is denoted by END-ADDR.

   Following is the packet format on the wire for packets sent from PaC
   to EP:

         IPv4/IPv6 header (source = PAC-ADDR,
                           destination = EP-ADDR)
         ESP header
         IPv4/IPv6 header (source = PAC-ADDR,
                           destination = END-ADDR)

   In case of IPv6, the outer IP header's addresses SHOULD be the link-
   local address of PaC and EP.

   Following is the packet format on the wire for packets sent from EP
   to PaC:


         IPv4/IPv6 header (source = EP-ADDR,
                           destination = PAC-ADDR)
         ESP header
         IPv4/IPv6 header (source = END-ADDR,
                           destination = PAC-ADDR)

   In case of IPv6, the outer IP header's addresses SHOULD be the link-
   local address of PaC and EP.

7.0 IPsec SPD entries

   Following acronyms are used in this section.

   EP's address is denoted by EP-ADDR.
   PaC's address is denoted by PAC-ADDR.
   PaC's link-local address is denoted by PAC-LINK-LOCAL
   PaC's global address is denoted by PAC-GLOBAL-ADDR
   EP's link-local address is denoted by EP-LINK-LOCAL

   The SPD entries given below affect the traffic destined to EP-ADDR.
   If PAA and EP share the same IP address, then the traffic destined to
   PAA will also be affected. This implies that some of the control
   traffic, which is already protected using PANA SA will be protected
   with IPsec also. This can be avoided (if needed) by configuring
   bypass IPsec policy for packets, which are not shown below.

7.1 IPv4 SPD entries



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   PaC's SPD OUT:
             IF source = PAC-ADDR & destination = any
              THEN USE ESP TUNNEL MODE SA:
              outer source = PAC-ADDR
              outer destination = EP-ADDR

   PaC's SPD IN:
            IF source = any & destination = PAC-ADDR
             THEN USE ESP TUNNEL MODE SA:
             outer source = EP-ADDR
             outer destination = PAC-ADDR

   EP's SPD OUT:
            IF source = any & destination = PAC-ADDR
             THEN USE ESP TUNEL MODE SA:
             outer source = EP-ADDR
             outer destination = PAC-ADDR

   EP's SPD IN:
            IF source = PAC-ADDR & destination = any
             THEN USE ESP TUNNEL MODE SA:
              outer source = PAC-ADDR
              outer destination = EP-ADDR

   During the IPsec SA setup, PaC uses PAC-ADDR as its phase 2 identity
   (IDci) and EP uses ID_IPV4_ADDR_RANGE or ID_IPV4_ADDR_SUBNET as its
   phase 2 identity. The starting address is zero IP address and the end
   address is all ones for ID_IPV4_ADDR_RANGE. The starting address is
   zero IP address and the end address is all zeroes for
   ID_IPV4_ADDR_SUBNET.

7.2 IPv6 SPD entries

   The IPv6 SPD entries are slightly different from IPv4 to prevent the
   neighbor/router discovery [IPV6-ND] packets from being protected with
   IPsec. Due to the current limitation in specifying the proper
   selectors for neighbor discovery packets, separate set of selectors
   are added for bypassing IPsec for link-local traffic. All traffic
   destined to global address is always sent to the default router i.e,
   the global prefix is not considered to be on-link. In the future,
   when the IPsec [IPSEC] allows selectors to be based on ICMPv6 types,
   we just need an entry to bypass IPsec for neighbor/router discovery
   packets and the rest of the entries will be similar to IPv4 SPD
   entries.

   Pac's SPD OUT:

             IF source = ::/128  & destination = any
              THEN BYPASS


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             IF source = fe80::/10 & destination = any
             THEN BYPASS

             IF source = any & destination = fe80::/10
              THEN BYPASS

             IF source = PAC-GLOBAL-ADDR & destination = any
              THEN USE ESP TUNNEL MODE SA:
                 outer source = PAC-LINK-LOCAL
                 outer destination = EP-LINK-LOCAL

   PaC's SPD IN:

             IF source = ::/128 & destination = any
              THEN BYPASS

             IF source = fe80::/10 & destination = any
             THEN BYPASS

             IF source = any & destination = fe80::/10
              THEN BYPASS

             IF source = any & destination = PAC-GLOBAL-ADDR
                 THEN USE ESP TUNNEL MODE SA:
                    outer source = EP-LINK-LOCAL
                    outer destination = PAC-LINK-LOCAL

   EP's SPD OUT:

             IF source = ::/128 & destination = any
              THEN BYPASS

             IF source = fe80::/10 & destination = any
             THEN BYPASS

             IF source = any & destination = fe80::/10
              THEN BYPASS

             IF source = any & destination = PAC-GLOBAL-ADDR
                 THEN USE ESP TUNNEL MODE SA:
                    outer source = EP-LINK-LOCAL
                    outer destination = PAC-LINK-LOCAL



   EP's SPD IN:

             IF source = ::/128 & destination = any


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              THEN BYPASS

             IF source = fe80::/10 & destination = any
             THEN BYPASS

             IF source = any & destination = fe80::/10
              THEN BYPASS

             IF source = PAC-GLOBAL-ADDR & destination = any
              THEN USE ESP TUNNEL MODE SA:
                 outer source = PAC-LINK-LOCAL
                 outer destination = EP-LINK-LOCAL


   Following the conceptual model in section 5.1 of [IPV6-ND], PaC would
   maintain the following.

   1) Neighbor Cache: This contains the entry for the link-local
      address of EP.
   2) Destination Cache: This contains the entry for all on-link and
      off-link destinations.
   3) Prefix List: This list contains the link-local prefix alone.
   4) Default Router List: This list contains the EP alone.

   Note that there are no entries for link-local addresses of other PaCs
   as it is assumed that communications with other PaCs use global
   addresses. All packets that are not destined to a link-local address
   are sent to the default router (EP). This can be achieved by turning
   off the "L" bit in the router advertisement.

   During the IPsec SA setup, PaC uses PAC-GLOBAL-ADDR as its phase 2
   identity (IDci) and EP uses ID_IPV6_ADDR_RANGE or ID_IPV6_ADDR_SUBNET
   as its phase 2 identity. The starting address is zero IP address and
   the end address is all ones for ID_IPV6_ADDR_RANGE. The starting
   address is zero IP address and the end address is all zeroes for
   ID_IPV6_ADDR_SUBNET.

8.0 Double IPsec

   If the PaC uses IPsec for secure remote access e.g., Corporate VPN
   access, there will be separate SPD entries protecting the traffic
   to/from remote network. In this case, IPsec may need to be applied
   twice, once for protecting the remote access and once for protecting
   the local access. This is the same as the iterative tunneling
   discussed in [IPSEC].

   When the IPsec SA is established with the remote security gateway,
   the IKE packets from the PaC to the remote security gateway may or
   may not need IPsec protection on the local link depending on the


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   configuration at the EP. If EP requires IPsec protection for all
   packets, then the PaC should configure SPD entries appropriately so
   that IKE packets destined to EP are bypassed whereas IKE packets to
   the remote SG are protected. If EP does not require IPsec protection
   for IKE packets destined to remote security gateway, it needs to
   configure SPD entries that would bypass them. This issue of
   configuring SPD entries for IKE packets is being currently discussed
   in the IPsec mailing list [IPSEC-ML].


9.0 Security considerations

   This document discusses the use of IPsec for access control when PANA
   is used for authenticating the clients to the access network.

   If the PAA does not verify whether PaC is authorized to use an IP
   address, it is possible for the PaC to steal the traffic destined to
   some other PaC. The use of IPsec does not prevent this attack. PAA
   may use other mechanisms to prevent this attack.

   When IPv6 is used, the SPD entries bypass all link-local traffic
   without applying IPsec. This should not be a limitation as the link-
   local address is used only by link-local services e.g.
   neighbor/router discovery, which uses a different mechanism to
   protect their traffic. Moreover, this limitation may not be there in
   the future if IPsec extends the SPD selectors to specify ICMP types.

10.0 Normative References


   Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9,
      RFC 2026, October 1996.

   [IPSEC] S. Kent et al., "Security Architecture for the Internet
      Protocol", RFC 2401, November 1998

11.0 Informative References


   [PANAREQ] A. Yegin et al., "Protocol for Carrying Authentication for
      Network Access (PANA) Requirements and Terminology", draft-ietf-
      pana-requirements-04.txt

   [PANA-PROT] D.Fosberg et al., "Protocol for Carrying Authentication
      for Network Access", draft-ietf-pana-01.txt

   [PANA-THREATS] M.Parthasarathy, "PANA Threat analysis and security
      requirements", draft-ietf-pana-threats-eval-04.txt



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   [KEYWORDS] S. Bradner, "Key words for use in RFCS to indicate
      requirement levels", RFC 2119, March 1997

   [IKE] D. Harkins et al., "Internet Key Exchange", RFC 2409, November
      1998

   [IPV6-ND] T. Narten et al., "Neighbor Discovery for IP version 6
      (IPv6) ", RFC 2461, December 1998

   [EAP-KEY] D.Simon et al., "EAP Key Management Framework", draft-
      aboba-ppext-key-problem-07.txt

   [IPSEC-ML] https://roundup.machshav.com/ipsec/, RFC2401bis, Issue 67.

   [IEEE80211i] IEEE Draft 802.11I/D5.0, "Draft Supplement to STANDARD
      FOR Telecommunications and Information Exchange between Systems –
      LAN/MAN Specific Requirements - Part 11: Wireless Medium Access
      Control (MAC) and physical layer specifications: Specification for
      Enhanced Security", August 2003.

12.0 Acknowledgments

   The author would like to thank Francis Dupont, Pasi Eronen and other
   PANA WG members for their valuable comments and discussions.

13.0 Revision log

   Changes between revision 00 and 01

   -Specified the use of ESP tunnel mode SA instead of IP-IP transport
   mode SA after working group discussion.
   -Specified the IKE pre-shared key derivation.


14.0 Author's Addresses

   Mohan Parthasarathy

   Phone: 408-734-8820
   Email: mohanp@sbcglobal.net

15.0 Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any


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   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
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   The limited permissions granted above are perpetual and will not be
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   Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.


























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