One document matched: draft-ietf-pana-ipsec-00.txt
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].
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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
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
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English.
The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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