IETF Mobile IP Working Group Charles E. Perkins
INTERNET-DRAFT Nokia Research Center
21 October 2004
Precomputable Binding Management Key Kbm for Mobile IPv6
<draft-ietf-mip6-precfgkbm-01.txt>
Status of This Memo
This document is a submission by the IETF MIPv6 Working Group Working
Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the mip6@ietf.org mailing list.
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note
that other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
A mobile node and a correspondent node may preconfigure data useful
for precomputing a Binding Management Key that can subsequently be
used for authorizing Binding Updates.
Perkins Expires 21 April 2005 [Page i]
INTERNET-DRAFT Precomputable Kbm 21 October 2004
1. Precomputing a Binding Management Key (Kbm)
A mobile node and a correspondent node may preconfigure data useful
for creating a Binding Management Key (Kbm), which can then be used
for authorizing binding management messages, especially Binding
Update and Binding Acknowledgement messages. This data is as
follows:
- A shared key (Kcn) used to generate keygen tokens, at least 20
octets long
- A nonce for use when generating the care-of keygen token
- A nonce for use when generating the home keygen token
The keygen tokens MUST be generated from Kcn and the nonces as
specified in Mobile IPv6 [1] return routability. Likewise, the
binding management key Kbm must subsequently be generated from the
keygen tokens in the same way as specified in Mobile IPv6 [1]. The
preconfigured data is associated to the mobile node's home address.
Replay protection for Binding Update messages using Kbm computed from
the preconfigured data depends upon the value of the sequence number
field in the Binding Update. If the correspondent node does not
maintain information about the recently used values of that field,
then there may be an opportunity for a malicious node to replay old
Binding Update messages and fool the correspondent node into routing
towards an old care-of address. For this reason, a correspondent
node that uses a precomputable Kbm also MUST keep track of the most
recent value of the Sequence Number field of Binding Update messages
using the precomputable Kbm value.
When a Binding Update is to be authenticated using such a
precomputable binding key (Kbm), the Binding Authorization Data
suboption MUST be present. The Nonce Indices option SHOULD NOT
be present. If it is present, the nonce indices supplied MAY be
ignored and are not included as part of the calculation for the
authentication data, which is to be carried exactly as specified
in [1].
2. Applicability Statement
Preconfigured shared keys (such as Kcn) between a mobile node and a
correspondent node are useful in several specific scenarios:
- mobile node and correspondent node are administered within the
same domain, and the correspondent node has good reason to trust
the actions of the mobile node
Perkins Expires 21 April 2005 [Page 1]
INTERNET-DRAFT Precomputable Kbm 21 October 2004
- the correspondent node has some guarantee that the mobile node
will behave properly (perhaps by contractual agreement)
- the method of assignment for keys between the correspondent node
and mobile node results in a stronger security association than
what can be provided by the Return Routability procedure.
- diagnostic procedures
- software development and testing
Generally speaking, the required level of trust that the
correspondent node needs for enabling a precomputable Kbm with a
mobile node is more often found within relatively small, closed
groups of users who are personally familiar with each other, or who
have some external basis for establishing trustworthy interactions.
3. Security Considerations
A correspondent node and a mobile node MAY use a precomputable
binding management key (Kbm) to manage the authentication
requirements for binding cache management messages. Such keys must
be handled carefully to avoid inadvertent exposure to the threats
outlined in [2].
A mobile node MUST use a different value for Kcn for each node in
its Binding Update List, and a correspondent node MUST ensure that
every mobile node uses a different value of Kcn. This ensures that
the sender of a Binding Update can always be uniquely determined.
This is necessary, as this authorization method does not provide any
guarantee that the given care-of address is legitimate. For the
same reason, this method SHOULD only be applied between nodes that
are under the same administration. The return routability procedure
is RECOMMENDED for all general use and MUST be the default, unless
the user explicitly overrides this by entering the abovementioned
preconfigured data for a particular peer.
Replay protection for the Binding Authorization Data option
authentication mechanism is provided by the Sequence Number field
of the Binding Update. This method of providing replay protection
fails when the Binding Update sequence numbers cycle through the 16
bit counter (i.e., not more than 65,536 distinct uses of Kbm for
any particular care-of address), or if the sequence numbers are not
protected against reboots. If the mobile node were to send a fresh
Binding Update to its correspondent node every hour, 24 hours a day,
every day of the year, and utilize the same care-of address every
time, this would require changing keys every 7 years. Even if the
mobile node were to do so every minute, this would provide protection
for over a month. Given typical mobility patterns, there is little
danger of replay problems; nodes for which problems might arise are
Perkins Expires 21 April 2005 [Page 2]
INTERNET-DRAFT Precomputable Kbm 21 October 2004
expected to use methods other than manual configuration for Kcn and
the associated nonces. When the sequence number field rolls over,
the parties SHOULD configure a new value for Kcn, so that new Kbm
values will be computed.
If a correspondent node does NOT keep track of the Sequence Number
for Binding Update messages from a particular mobile node, then the
correspondent node could be fooled into accepting an old value for
the mobile node's care-of address. In the unlikely event that this
address was reallocated to another IPv6 node in the meantime, that
IPv6 node would then be vulnerable to unwanted traffic emanating from
the correspondent node. In order to circumvent this possibility,
correspondent nodes are mandated to keep track of the most recent
Sequence Number value in a Binding Update message from the mobile
node.
There is no upper bound on the lifetime defined for the precomputable
Kbm. As noted, the key is very, very likely to be quite secure
over the lifetime of the security association and usefulness of
applications between a mobile node and correspondent node that fit
the terms specified in section 2.
4. IANA Considerations
No new protocol numbers are required.
5. Acknowledgement
Thanks are due to everyone who reviewed the discussion of issue #146.
References
[1] D. Johnson, C. Perkins, and J. Arkko. Mobility support in IPv6
(work in progress). Internet Draft, Internet Engineering Task
Force, May 2003.
[2] P. Nikander, T. Aura, J. Arkko, G. Montenegro, and E. Nordmark.
Mobile IP version 6 Route Optimization Security Design
Background. Internet Draft, Internet Engineering Task Force,
June 2003.
The first citation is normative, and the second citation is
informative only.
Perkins Expires 21 April 2005 [Page 3]
INTERNET-DRAFT Precomputable Kbm 21 October 2004
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the
use of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided
on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM 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.
Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Perkins Expires 21 April 2005 [Page 4]
INTERNET-DRAFT Precomputable Kbm 21 October 2004
Author's Address
Questions about this document can also be directed to the author:
Charles E. Perkins
Nokia Research Center
313 Fairchild Drive
Mountain View, CA 94043
USA
Phone: +1 650 625-2986
Fax: +1 650 625-2502
E-mail: charles.perkins@nokia.com
Perkins Expires 21 April 2005 [Page 5]
