PANA Working Group
Internet Draft M. Parthasarathy
Document: draft-ietf-pana-ipsec-03.txt Nokia
Expires: November 2004 May 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
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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 a 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 Dual Stack Operation.........................................10
10.0 Security considerations.....................................10
11.0 Normative References........................................11
12.0 Informative References......................................11
13.0 Acknowledgments.............................................12
14.0 Revision log................................................12
15.0 Appendix A..................................................13
16.0 Author's Addresses..........................................14
17.0 Full Copyright Statement....................................14
1.0 Introduction
The PANA (Protocol for carrying Authentication for Network Access)
working group is developing a 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.
4.0 IP Address Configuration
The IP address configuration is explained in [PANA-FRAME]. Some of
the details relevant to IPsec are briefly repeated here for clarity.
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PaC configures an IP address before the PANA protocol exchange
begins. This address is called a pre-PANA address (PRPA). After a
successful authentication, the client may have to configure a post-
PANA address (POPA) for communication with other nodes, if PRPA is a
local-use (e.g., link-local or private address) or a temporarily
allocated IP address.
The PRPA of the PaC may be a link-local address [IPV4-LINK] or a
private address [IPv4-PRIV] or a routable address. Please refer to
[PANA-FRAME] for more details on how these addresses may be
configured. PaC would use the PRPA as the outer address of IPsec
tunnel mode SA (IPsec-TOA). PaC also needs to configure an inner
address (IPsec-TIA). There are different ways to configure IPsec-TIA.
1) Some IPv4 IPsec implementations are known to work properly when
the same address is configured as both the IPsec-TIA and IPsec-
TOA. When PRPA is a routable address, PRPA may be used as both
IPsec-TIA and IPsec-TOA and POPA may not be configured.
2) In IPv4, an IPsec-TIA can be obtained via the configuration
method available within [RFC3456]. The minor difference from the
original usage of RFC 3456 is that the IPsec-TOA does not need
to be a routable address when [RFC3456] is used between PaC and
EP.
3) When [IKEV2] is used for security association negotiation, the
address configuration method available in [IKEV2] can be used
for configuring the IPsec-TIA for both IPv4 and IPv6.
There are other address configuration methods possible. They have
some implementation issues, which are described in the Appendix A.
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, Key-Id, PRPA of the
PaC, and the session-Id to EP before the IKE exchange begins.
Whenever the IKE pre-shared key changes due to re-authentication as
described below, the new value is computed by the PAA and
communicated to the EP with all the other parameters.
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.
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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.
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. This is
contained in the Key-Id AVP [PANA-PROT].
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 the following value in the payload
of the ID_KEY_ID to identify the pre-shared key.
ID_KEY_ID data = (Session-Id | Key-Id)
The Session-Id and Key-Id are the values contained in the data
portion of the Session-Id and Key-Id AVP respectively [PANA-PROT].
They are concatenated to form the content of ID_KEY_ID data. IP
addresses cannot be used as identifier as the PaC may be re-
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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 4.0, and address (POPA)
may also have to be configured. The address configuration method to
be used by the PaC is indicated in the PANA-Bind-Request message at
the end of the successful PANA authentication. The PaC chooses the
appropriate method and replies back in PANA-Bind-Answer message.
7.0 Packet Formats
Following acronyms are used throughout this document.
PAC-TIA denotes the IPsec-TIA used by the PaC. PAC-TIA may be set to
a PRPA when the same PRPA is used as IPsec-TIA and IPsec-TOA on the
PaC. Otherwise, PAC-TIA is set to POPA.
PAC-TOA denotes the IPsec-TOA used by the PaC.
EP-ADDR denotes the address of the EP.
The node with which the PaC is communicating is denoted by END-ADDR.
Following is the IPv4 packet format on the wire for packets sent from
PaC to EP:
IPv4 header (source = PAC-TOA,
destination = EP-ADDR)
ESP header
IPv4 header (source = PAC-TIA,
destination = END-ADDR)
Following is the IPv6 packet format on the wire for packets sent from
PaC to EP:
IPv6 header (source = PAC-TOA,
destination = EP-ADDR)
ESP header
IPv6 header (source = PAC-TIA,
destination = END-ADDR)
Following is the IPv4 packet format on the wire for packets sent from
EP to PaC:
IPv4 header (source = EP-ADDR,
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destination = PAC-TOA)
ESP header
IPv4 header (source = END-ADDR,
destination = PAC-TIA)
Following is the IPv6 packet format on the wire for packets sent from
EP to PaC:
IPv6 header (source = EP-ADDR,
destination = PAC-TOA)
ESP header
IPv6 header (source = END-ADDR,
destination = PAC-TIA)
8.0 IPsec SPD entries
The SPD entries for IPv4 and IPv6 are specified separately as they
are different. All the SPD entries are dynamically created. When the
same address is used as IPsec-TIA and IPsec-TOA, EP can add the entry
to the SPD before the IKE exchange starts, as it knows the address a
priori. When [IKEV2] or [RFC3456] is used for address configuration,
the SPD entry cannot be created until the IPsec SA is successfully
negotiated as the address is not known a priori. This is very similar
to the road warrior case described in [IPSEC-BIS]. In this case, an
SPD entry with a name selector is used to start with and later
changed with the appropriate addresses. The name used here could be
the contents of ID_KEY_ID payload. The entries shown below are the
entries that are added after the successful IPsec SA negotiation.
The SPD entries shown here affect the flow of data traffic, which
includes neighbor discovery messages for IPv6. When PAA and EP are
not co-located, any traffic destined to PAA is forwarded to PAA after
decrementing the TTL in the IP header. PAA would drop the packet if
the TTL is not 255. PaC also would drop the packets coming from PAA
if the TTL is not 255. Hence, we need the following SPD entry on PaC
and EP for bypassing IPsec protection for PANA traffic.
If source_port = PANA_PORT OR dest_port = PANA_PORT
THEN BYPASS
PANA_PORT is the IANA assigned (TBD) PANA protocol number [PANA-
PROT]. There may be other protocols that expect the TTL to be 255
whose SPD entries are not shown here. Also, when the PaC is using
IPsec for remote access, there may be additional SPD entries and
IPsec security associations, which are not discussed in this
document.
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8.1 IPv4 SPD entries
PaC's SPD OUT:
IF source = PAC-TIA & destination = any
THEN USE ESP TUNNEL MODE SA:
outer source = PAC-TOA
outer destination = EP-ADDR
PaC's SPD IN:
IF source = any & destination = PAC-TIA
THEN USE ESP TUNNEL MODE SA:
outer source = EP-ADDR
outer destination = PAC-TOA
EP's SPD OUT:
IF source = any & destination = PAC-TIA
THEN USE ESP TUNEL MODE SA:
outer source = EP-ADDR
outer destination = PAC-TOA
EP's SPD IN:
IF source = PAC-TIA & destination = any
THEN USE ESP TUNNEL MODE SA:
outer source = PAC-TOA
outer destination = EP-ADDR
During the IPsec SA setup, PaC uses PAC-TIA 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 entries
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.
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-TIA & destination = any
THEN USE ESP TUNNEL MODE SA:
outer source = PAC-TOA
outer destination = EP-ADDR
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-TIA
THEN USE ESP TUNNEL MODE SA:
outer source = EP-ADDR
outer destination = PAC-TOA
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-TIA
THEN USE ESP TUNNEL MODE SA:
outer source = EP-ADDR
outer destination = PAC-TOA
EP's SPD IN:
IF source = ::/128 & destination = any
THEN BYPASS
IF source = fe80::/10 & destination = any
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THEN BYPASS
IF source = any & destination = fe80::/10
THEN BYPASS
IF source = PAC-TIA & destination = any
THEN USE ESP TUNNEL MODE SA:
outer source = PAC-TOA
outer destination = EP-ADDR
During the IPsec SA setup, PaC uses PAC-TIA 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 Dual Stack Operation
[IKEV2] can enable configuration of IPsec-TIA for both IPv4 and IPv6
TIAs by sending both IPv4 and IPv6 configuration attributes in the
configuration request (CFG-REQUEST). This enables use of single IPsec
tunnel mode SA for sending both IPv4 and IPv6 traffic. Therefore,
IKEv2 is recommended for handling dual-stack PaCs where single
execution of IKE is desired.
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 EP 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. When [IKEV2] and [RFC3456] is used for address
configuration, the address is assigned by the EP and hence this
attack is not present in such cases. When the same address is used as
both IPsec-TIA and IPsec-TOA, EP creates the SPD entry with the
appropriate address for the PaC and hence the address is verified
implicitly by the virtue of successful IPsec SA negotiation.
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 [SEND] to protect their
traffic. Moreover, this limitation may not be there in the future if
IPsec extends the SPD selectors to specify ICMP types.
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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
[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
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[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
[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, Alper Yegin and other PANA WG
members for their valuable comments and discussions.
14.0 Revision log
Changes between revision 02 and 03
-Clarified the use of key-Id in ID_KEY_ID payload
-Clarified the address configuration issues.
-Added an Appendix to clarify implementation issues.
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
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-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 Appendix A
This section describes the alternate address configuration methods
for Post-PANA address (POPA) and the issues associated with it. As
mentioned in section 4, there are multiple ways by which the PaC may
configure the POPA address. Only [IKEV2] and [RFC3456] address
configuration methods were described in section 4. Other
possibilities and the issues are as follows.
1) Some IKEv1 implementations support IKEv1 MODECFG for configuring
IP address. There is no RFC describing MODECFG feature of IKEv1.
Also, there is not much information on its widespread support
among the implementations. Hence, this document does not
recommend it.
2) The address may also be obtained using [DHCP] [DHCPV6] before
the IKE exchange starts. Normally the implementations associate
the address and other configuration information (e.g. default
router) with the interface on which the DHCP is performed. This
can cause problems with implementations if they attempt to use
an IP address that is configured via [DHCP] [DHCPV6] on the
physical interface and use it as IPsec-TIA on the IPsec tunnel
interface. This may work without problems when IPsec-TIA and
IPsec-TOA are same as the IPv4 PRPA that was obtained using
DHCP, as the source address selection has to deal with just one
address. But using an IPv4 IPsec-TOA different than IPsec-TIA on
a single interface may cause source address selection problem,
as there is more than one address to be dealt with. Similarly,
an IPv6 address obtained and maintained through a physical link
but used on a tunnel interface requires additional
implementation considerations. Therefore, this document does not
handle the case where DHCP is used to acquire an address for
IPsec-TIA that is different from IPsec-TOA.
3) The address may also be obtained using auto-configuration [IPV6-
ND] including the privacy addresses described in [PRIV]. The
problem described above for DHCP applies to this also. The
implementations would associate the auto-configured addresses
and the default router with the interface on which the router
advertisement was received. As we configure the SPD to bypass
IPsec for router discovery and neighbor discovery messages, the
address would be associated with the physical interface and not
with the IPsec interface. There is also an additional issue, as
the address configured by the PaC is not known to the EP. It
needs to trust whatever PaC provides in its traffic selector
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during the IPsec SA negotiation. This leads to DoS attack where
the PaC can steal some other PaC's address, which cannot be
prevented unless [SEND] is deployed.
16.0 Author's Addresses
Mohan Parthasarathy
313 Fairchild Drive
Mountain View CA-94043
Phone: 408-734-8820
Email: mohanp@sbcglobal.net
17.0 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
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
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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