PANA Working Group
Internet Draft M. Parthasarathy
Document: draft-ietf-pana-ipsec-02.txt Nokia
Expires: August 2004 February 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].
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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 IP Address Configuration......................................3
5.0 IKE Pre-shared key derivation.................................4
6.0 IKE and IPsec details.........................................5
7.0 Packet Formats................................................6
8.0 IPsec SPD entries.............................................7
9.0 Double IPsec..................................................9
10.0 Security considerations.....................................10
11.0 Normative References........................................10
12.0 Informative References......................................11
13.0 Acknowledgments.............................................12
14.0 Revision log................................................12
15.0 Author's Addresses..........................................12
16.0 Full Copyright Statement....................................12
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. As shown in Figure 1, Enforcement Point
(EP) and the Access Router (AR) are co-located. PAA is not shown in
the figure. It may or may not be co-located with EP. 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 ----------------------+
[D1] |
+------EP/AR
|
PaC ----------------------+
[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 IKE exchange starts.
1) PANA client (PaC) and PAA mutually authenticate each other using
EAP methods that derive AAA-key [EAP-KEY].
2) PaC learns the IP address of the Enforcement point (EP) during
the PANA exchange.
3) PaC learns that the network uses IPsec [IPSEC] for securing the
link between PaC and EP during the PANA exchange.
4) PaC configures a routable or global address as discussed in
section 4 of this document.
4.0 IP Address Configuration
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PaC configures a link-local address [IPV4-LINK] [IPV6-CONF] before
the PANA protocol begins. If IPv4 is being used, it may even
configure a private address [IPV4-PRIV] using a DHCP server provided
by the Network Access provider. See [PANA-FRAME] for more details.
After a successful authentication, the client configures a routable
or global address using [DHCP][DHCPV6] before running [IKE][IKEv2] or
running address auto-configuration methods available within [IKE] or
[IKEv2] by using a configuration payload or running DHCP over a
special IPsec tunnel mode SA [RFC3456] or auto-configures an address
using stateless auto-configuration [IPv6-ND] before running [IKE] or
[IKEv2] if IPv6 is being used.
In the case of IPV4, the link-local address or private address SHOULD
be un-configured when the global address is configured, to prevent
using the link-local address or private address as the source address
for communicating with the external nodes [IPV4-LINK]. Some
implementations may be able to choose the right address, where the
IPsec tunnel mode SAs are modeled as interfaces. But this document
does not make any such assumptions. In IPv4, all packets are tunneled
using IPsec tunnel mode SA with the inner and outer source address
same as the routable address. In the case of IPv6, such restrictions
don't exist. The link-local address is used for the outer header and
global address is used for the inner header for the tunnel.
5.0 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 link-local address
of the PaC (in IPv6 only), routable address of the PaC and the PANA
session ID to EP before the IKE exchange begins.
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 (AAA-key, "IKE-preshared key" |
Session ID | Key-ID | EP-address)
The values have the following meaning:
AAA-key: A key derived by the peer and EAP server and transported to
the authenticator [EAP-KEY].
Session ID: The value as defined in the PANA protocol [PANA-PROT],
identifies a particular session of a client.
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Key-ID: This identifies the AAA-key within a given session [PANA-
PROT]. During the lifetime of the PANA session, there could be
multiple EAP re-authentications. As EAP re-authentication changes the
AAA-key, key-ID is used to identify the right AAA-key.
EP-address: This is the address of the enforcement point with which
the IKE exchange is being performed. When PAA is controlling multiple
EPs, this provides a different pre-shared key for each of the EPs.
The character "|" denotes concatenation as defined in [IKE].
During EAP re-authentication, the AAA-key changes. Whenever the AAA-
key changes, a new value of Key-ID is established between the PaC and
PAA/EP as defined in [PANA-PROT]. If there is already an IKE SA or
IPsec SA established, it MUST continue to be used till it expires. A
change in the value of AAA-key MUST NOT result in re-negotiating a
new IKE SA or IPsec SA immediately. But any new negotiation of IKE SA
or IPsec SA MUST use the new pre-shared key derived from the latest
AAA-key and is indicated by the Key-ID in the above equation.
6.0 IKE and IPsec details
IKE [IKE] MUST be used for establishing the IPsec SA. The details
specified in this document would work with IKEv2 [IKEV2] also. Any
difference between them would be explicitly noted. PANA authenticates
the client and derives the keys to protect the traffic. Hence, manual
keying cannot be used. Aggressive mode with pre-shared key MUST be
supported. PaC and EP SHOULD use its PANA session ID [PANA-PROT] as
the payload of ID_KEY_ID in aggressive mode for establishing the
phase I SA. IP addresses cannot be used as identifier as the PaC may
be re-authenticated multiple times and hence may not uniquely
identify the pre-shared key. For the same reason, main mode of IKE
cannot be used as it requires addresses to be used as identifiers.
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 identities used during Phase II are explained
in the next section.
As mentioned in section 4, there are multiple ways by which the PaC
may configure the address before the IKE exchange starts. Most of the
IKE implementations assume that they can consult the SPD during the
IKE exchange for policy checks. In the case of address configuration
using [RFC3456] or [IKE] [IKEV2] or [DHCP] [DHCPV6], EP can learn the
address allocated to the client and hence setup the SPD before the
IKE exchange starts. In the case of auto-configuration (which
includes global address or addresses configured as in [PRIV]), EP may
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not know the address assigned to the PaC. Thus, it may not be able to
setup the SPD entries appropriately before IKE exchange starts. As
most of the IKE implementations assume that the SPD can be consulted
during the SA negotiation, it may require slightly a different
behavior from IKE in the auto-configuration case. In the case of
auto-configuration, IKE should be able to setup the SAs for the
traffic selectors (which contains the PaC auto-configured address)
specified by the PaC without requiring a corresponding entry in the
SPD. If there is already an SA for the same address used by a
different session as specified in the ID_KEY_ID payload, then the SA
request MUST be rejected with INVALID-ID-INFORMATION [IKE]. If PaC
establishes the IKE and IPsec SA successfully, EP should add the SPD
entry for protecting the subsequent data packets.
7.0 Packet Formats
Following acronyms are used throughout this document.
PaC's link-local address is denoted by PAC-LINK-LOCAL.
PaC's routable or global address is denoted by PAC-GLOBAL-ADDR.
EP's link-local address is denoted by EP-LINK-LOCAL.
The node with which the PaC is communicating is denoted by END-ADDR.
In IPv4, the global address is used as both inner and outer source
address of the tunneled packet. In IPv6, the link-local address is
used as the outer header and the global address is used as the inner
header of the tunneled packet.
Following is the IPv4 packet format on the wire for packets sent from
PaC to EP:
IPv4 header (source = PAC-GLOBAL-ADDR,
destination = EP-LINK-LOCAL)
ESP header
IPv4 header (source = PAC-GLOBAL-ADDR,
destination = END-ADDR)
Following is the IPv6 packet format on the wire for packets sent from
PaC to EP:
IPv6 header (source = PAC-LINK-LOCAL,
destination = EP-LINK-LOCAL)
ESP header
IPv6 header (source = PAC-GLOBAL-ADDR,
destination = END-ADDR)
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Following is the IPv4 packet format on the wire for packets sent from
EP to PaC:
IPv4 header (source = EP-LINK-LOCAL,
destination = PAC-GLOBAL-ADDR)
ESP header
IPv4 header (source = END-ADDR,
destination = PAC-GLOBAL-ADDR)
Following is the IPv6 packet format on the wire for packets sent from
EP to PaC:
IPv6 header (source = EP-LINK-LOCAL,
destination = PAC-LINK-LOCAL)
ESP header
IPv6 header (source = END-ADDR,
destination = PAC-GLOBAL-ADDR)
8.0 IPsec SPD entries
The SPD entries for IPv4 and IPv6 are specified separately as they
are different.
8.1 IPv4 SPD entries
PaC's SPD OUT:
IF source = PAC-GLOBAL-ADDR & destination = any
THEN USE ESP TUNNEL MODE SA:
outer source = PAC-GLOBAL-ADDR
outer destination = EP-LINK-LOCAL
PaC's SPD IN:
IF source = any & destination = PAC-GLOBAL-ADDR
THEN USE ESP TUNNEL MODE SA:
outer source = EP-LINK-LOCAL
outer destination = PAC-GLOBAL-ADDR
EP's SPD OUT:
IF source = any & destination = PAC-GLOBAL-ADDR
THEN USE ESP TUNEL MODE SA:
outer source = EP-LINK-LOCAL
outer destination = PAC-GLOBAL-ADDR
EP's SPD IN:
IF source = PAC-GLOBAL-ADDR & destination = any
THEN USE ESP TUNNEL MODE SA:
outer source = PAC-GLOBAL-ADDR
outer destination = EP-LINK-LOCAL
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During the IPsec SA setup, PaC uses PAC-GLOBAL-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.
8.2 IPv6 SPD entries
The IPv6 SPD entries are slightly different from IPv4 to prevent the
neighbor and router discovery [IPV6-ND] packets from being protected
with IPsec. The first three entries of the following SPD tables
bypass IPsec protection for neighbor and router discovery packets.
The latest version of the IPsec [IPSEC-BIS] document allows traffic
selectors to be based on ICMPv6 type and code values. In that case,
the first three entries can be based on ICMPv6 type and code values.
All traffic destined to global address is always sent to the default
router (EP) i.e, the global prefix is not considered to be on-link.
This can be achieved by turning off the "L" bit in the router
advertisement.
Pac'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 = 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
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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
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
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.
9.0 Double IPsec
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If the PaC uses IPsec for secure remote access e.g., Corporate VPN
access, there will be separate SPD entries protecting the traffic to
or from the 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
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.
10.0 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. Although section 6 describes an inner address
verification method based on SPD consulting, it is still possible for
an authenticated PaC to launch this attack. PAA may use other
mechanisms to prevent this attack [SEND].
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.
11.0 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
[PANA-PROT] D. Fosberg et al., "Protocol for Carrying Authentication
for Network Access", draft-ietf-pana-03.txt
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[PANA-THREATS] M. Parthasarathy, "PANA Threat analysis and security
requirements", draft-ietf-pana-threats-eval-04.txt
12.0 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-FRAME] P. Jayaraman et al., "PANA Framework", draft-ohba-pana-
framework-00.txt
[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
[IKEV2] C. Kauffman et al., "Internet Key Exchange(IKEv2) Protocol",
draft-ietf-ipsec-ikev2-11.txt
[IPSEC-BIS] S. Kent, "Security Architecture for the Internet
Protocol", draft-ietf-ipsec-rfc2401bis-00.txt
[DHCP] R. Droms, "Dynamic Host Configuration Protocol", RFC 2131,
March 1997
[RFC3456] B. Patel et al., "Dynamic Host Configuration Protocol
(DHCPv4) Configuration of IPsec Tunnel Mode", RFC 3456, January
2003
[DHCPV6] R. Droms et. al, "Dynamic Host Configuration Protocol for
IPv6", RFC 3315, July 2003
[IPV6-ND] T. Narten et al., "Neighbor Discovery for IP version 6
(IPv6) ", RFC 2461, December 1998
[IPV6-CONF] S. Thomson et. al, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998
[PRIV] T. Narten et al., "Privacy Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 3041, January 2001
[EAP-KEY] D. Simon et al., "EAP Key Management Framework", draft-
ietf-eap-keying-01.txt
[SEND] J. Arkko et al., "Secure Neighbor Discovery", draft-ietf-send-
ndopt-03.txt
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[IPV4-LINK] B. Aboba et al., "Dynamic configuration of Link-local
IPv4 addresses", draft-ietf-zeroconf-ipv4-linklocal-12.txt
[IPV4-PRIV] Y. Rekhter et al., "Address Allocation for Private
Internets", BCP 5, RFC 1918, February 1996
[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.
13.0 Acknowledgments
The author would like to thank Francis Dupont, Pasi Eronen, Yoshihiro
Ohba, Jari Arkko, Hannes Tschofenig and other PANA WG members for
their valuable comments and discussions.
14.0 Revision log
Changes between revision 01 and 02
-Updated the draft with the fixes for all open issues
-Added the IP configuration section
-Modified the IKE pre-shared key derivation to handle PAA controlling
multiple EPs
-Clarification regarding DHCP usage and RFC3456 usage.
-Only aggressive mode to be supported. Main mode not needed anymore.
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.
15.0 Author's Addresses
Mohan Parthasarathy
313 Fairchild Drive
Mountain View CA-94043
Phone: 408-734-8820
Email: mohanp@sbcglobal.net
16.0 Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
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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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