Internet DRAFT - draft-ietf-mip6-precfgKbm
draft-ietf-mip6-precfgKbm
IETF Mobile IP Working Group Charles E. Perkins
INTERNET-DRAFT Nokia Research Center
5 April 2004
Preconfigured Binding Management Keys for Mobile IPv6
<draft-ietf-mip6-precfgKbm-00.txt>
Status of This Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
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Abstract
A mobile node and a correspondent node may preconfigure a Binding
Management Key for authorizing Binding Updates.
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1. Preconfiguring a Binding Management Key (Kbm)
A mobile node and a correspondent node may preconfigure a Binding
Management Key (Kbm) for authorizing binding management messages,
especially Binding Update and Binding Acknowledgement messages. The
key MUST be the same length as that configured using inputs from
Mobile IPv6 [1] return routability. The key is associated to the
mobile node's home address.
Replay protection for Binding Update messages using the preconfigured
Kbm 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 preconfigured Kbm also MUST keep track of the most recent
value of the Sequence Number field of Binding Update messages using
the preconfigured Kbm value.
When a Binding Update is to be authenticated using such a
preconfigured 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 keys 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
- 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 preconfigured Kbm with a
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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 preconfigured
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 binding management key (Kbm)
for each node in its Binding Update List. 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 a key 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),
or if the sequence numbers are not protected against reboots. If
the mobile node were to move every hour, 24 hours a day, every day
of the year, this would require changing keys every 7 years. Even
if the mobile node were to move 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 expected to use methods other than manual configuration for
Kbm anyway. When the sequence number field rolls over, the parties
SHOULD configure another value for Kbm.
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.
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There is no upper bound on the lifetime defined for the preconfigured
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.
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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
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