Network Working Group A. Patel
Internet-Draft K. Leung
Expires: July 19, 2005 Cisco Systems
M. Khalil
H. Akhtar
Nortel Networks
K. Chowdhury
Starent Networks
January 18, 2005
Authentication Protocol for Mobile IPv6
draft-ietf-mip6-auth-protocol-03.txt
Status of this Memo
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This Internet-Draft will expire on July 19, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract
IPsec is specified as the sole means of securing all signaling
messages between the Mobile Node and Home agent for Mobile IPv6. A
flexible model for security between the Mobile Node and Home Agent is
required from the perspective of deployment of the Mobile IPv6
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protocol. One instance of such deployment need comes from networks
that are built on 3GPP2 standards. This document proposes an
alternate method for securing the signaling messages that are
responsible for performing Registration of a Mobile Node at a home
agent.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 General Terms . . . . . . . . . . . . . . . . . . . . . . 5
4. Operational flow . . . . . . . . . . . . . . . . . . . . . . . 6
5. Mobility message authentication option . . . . . . . . . . . . 7
5.1 MN-HA authentication mobility option . . . . . . . . . . . 8
5.1.1 Processing Considerations . . . . . . . . . . . . . . 9
5.2 MN-AAA authentication mobility option . . . . . . . . . . 9
5.2.1 Processing Considerations . . . . . . . . . . . . . . 10
5.3 Authentication Failure Detection at the Mobile Node . . . 10
6. Mobility message replay protection option . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
10. Normative References . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17
A. Rationale for mobility message replay protection option . . . 19
Intellectual Property and Copyright Statements . . . . . . . . 20
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1. Introduction
The base Mobile IPv6 specification [RFC3775] specifies the signaling
messages, Binding Update (BU) and Binding Acknowledgement (BA),
between the Mobile Node and Home agent to be secured by the IPsec
Security Associations (IPsec SAs) that are established between these
two entities. This security model for Mobile IPv6 does not fit in
very well for deployment scenarios which:
1. rely on the use of a Authentication, Authorization and Accounting
(AAA) infrastructure for authenticating the subscriber
2. require dynamic assignment of Home Agent and home addresses
3. have constraints on the number of messages involved in setting up
IPsec SAs
4. include Mobile Nodes that do not support IKEv1
This indicates the need for a solution that does not necessarily
require an IPsec SA for securing the signaling messages that deal
with the Registration process of a Mobile Node with a home agent.
This document proposes a solution for securing the Binding Update and
Binding Acknowledgment messages between the Mobile Node and Home
agent using an authentication option which is included in these
messages. Such a mechanism enables IPv6 mobility in a host without
having to establish an IPsec SA with its Home Agent. A Mobile Node
can implement Mobile IPv6 without having to integrate it with the
IPsec module, in which case the Binding Update and Binding
Acknowldegement messages (between MN-HA) are secured with the
authentication option. It does not imply that the availability of
such a solution deprecates the use of IPsec for securing Mobile IPv6
signaling between Mobile Nodes and Home Agents. Home agents still
have to implement and support registrations from Mobile Nodes that
are secured via IPsec as well as with the authentication option.
The authentication mechanism proposed here is similar to the
authentication mechanism used in Mobile IPv4 [RFC3344].
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2. Overview
This document presents a lightweight mechanism to authenticate the
Mobile Node at the Home Agent or at the Authentication, Authorization
and Accounting (AAA) server in Home network (AAAH) based on a shared
key based security association between the Mobile Node and the
respective authenticating entity. This shared key based security
association (shared-key based SA) may be statically provisioned or
dynamically created. The term "security association" referred to in
this document is understood to be a "shared-key based Mobile IPv6
authentication" security association. The Mobile Node MUST use only
one means of authentication, based on either the shared key based
authentication or IPsec security association. Home agents still have
to implement and support registrations from Mobile Nodes that are
secured via IPsec as well as with the authentication option.
This document introduces new mobility options to aid in
authentication of the Mobile Node to the Home Agent or AAAH server.
The confidentiality protection of Return Routability messages and
authentication/integrity protection of Mobile Prefix Discovery (MPD)
is outside the scope of this document.
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3. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119.
3.1 General Terms
First (size, input)
Some formulas in this specification use a functional form "First
(size, input)" to indicate truncation of the "input" data so that
only the first "size" bits remain to be used.
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4. Operational flow
MN HA/AAAH
| BU to HA |
(a) |----------------------------------------------------->|
| (including MN-ID option [optional], |
| Message ID option [optional], authentication option)|
| |
| |
| HA/AAAH authenticates MN
| |
| |
| BA to MN |
(b) |<-----------------------------------------------------|
| (including MN-ID option [optional], |
| Message ID option [optional], authentication option)|
| |
Figure 1: Home Registration with Authentication Protocol
Mobile Node MAY use Mobile Node Identifier Option as defined in
[MN_Ident] or Home Address to identify itself while authenticating
with the Home Agent. The mobile node uses the Mobile Node Identifier
option as defined in [MN_Ident] to identify itself as may be required
for use with some existing AAA infrastructure designs.
Mobile Node MAY use Message Identifier option as defined in Section 6
for additional replay protection.
The authentication option in this document Section 5 may be used by
the mobile node to transfer authentication data when the mobile node
and the home agent are utilizing an SPI to index between multiple
security associations. For the case when there is only one such
security association, and no SPI is needed, the Mobile Node and Home
Agent can use the Binding Authorization Data option as defined in the
base Mobile IPv6 specification [RFC3775] for this same purpose.
Since that option does not have any SPI, the Mobile Node and the Home
Agent implicitly agree that the security association to be used is
the only mobility security association that is defined for their
mutual authentication needs.
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5. Mobility message authentication option
This section defines a message authentication mobility option that
may be used to secure Binding Update and Binding Acknowledgement
messages. This option can be used along with IPsec or preferably as
an alternate mechanism to authenticate Binding Update and Binding
Acknowledgement messages in absence of IPsec.
This document also defines subtype numbers, which identify the mode
of authentication and the peer entity to authenticate the message.
Two subtype numbers are specified in this document. It is expected
that other subtypes will be defined by other documents in the future.
Only one instance of an authentication option of a particular subtype
can be present in the message. One message may contain multiple
instances of authentication options with different subtype values.
When a Binding Update or Binding Acknowledgement is received without
an authentication option and the entity receiving it is configured to
use authentication option or has the shared-key based security
association for authentication option, the entity should silently
discard the received message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Subtype |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication Data ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
Option Type:
AUTH-OPTION-TYPE to be defined by IANA. An 8-bit identifier of
the type mobility option.
Option Length:
8-bit unsigned integer, representing the length in octets of
the Sub-type, Security Parameter Index (SPI) and Authentication
Data fields.
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Subtype:
A number assigned to identify the entity and/or mechanism to be
used to authenticate the message.
SPI:
Security Parameter Index
Authentication Data:
This field has the information to authenticate the relevant
mobility entity. This protects the message beginning at the
Mobility Header upto and including the SPI field.
Alignment requirements :
The alignment requirement for this option is 4n + 1.
5.1 MN-HA authentication mobility option
The format of the MN-HA authentication mobility option is as defined
in Figure 2. This option uses the subtype value of 1. The MN-HA
authentication mobility option is used to authenticate the Binding
Update and Binding Acknowledgement messages based on the shared-key
based security association between the Mobile Node and the Home
Agent.
The shared-key based security association between Mobile Node and
Home Agent used within this specification consists of a SPI, a key,
an authentication algorithm and the replay protection mechanism in
use. The SPI is a number in range [0-4294967296], where the range
[0-255] is reserved. The key consists of an arbitrary value and is
16 octets in length. The authentication algorithm is HMAC_SHA1. The
replay protection mechanism may use the Sequence number as specified
in [RFC3775] or the option as defined in Section 6. If the Timestamp
option is used for replay protection as defined in Section 6, the
security association includes a "close enough" field to account for
clock drift. A default value of 7 seconds MAY be used. This value
SHOULD be greater than 3 seconds.
This MUST be the last option in a message with mobility header if it
is the only authentication option in the message. It must occur
before the MN-AAA Section 5.2 authentication option if both options
are present in the message.
The authentication data is calculated on the message starting from
the mobility header upto and including the SPI value of this option.
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Authentication Data = First (96, HMAC_SHA1(MN-HA Shared key, Mobility
Data))
Mobility Data = care-of address | home address | Mobility Header(MH)
Data
MH Data is the content of the Mobility Header upto and including the
SPI field of this option. The Checksum field in Mobility Header MUST
be set to 0 to calculate the Mobility Data.
The first 96 bits from the MAC result are used as the Authentication
Data field.
5.1.1 Processing Considerations
The assumption is that Mobile Node has a shared-key based security
association with the Home Agent. The Mobile Node MUST include this
option in a BU if it has a shared-key based security association with
the Home Agent. The Home Agent MUST include this option in the BA if
it received this option in the corresponding BU and Home Agent has a
shared-key based security association with the Mobile Node.
The Mobile Node or Home Agent receiving this option MUST verify the
authentication data in the option. If authentication fails, the Home
Agent MUST send BA with Status Code MIPV6-AUTH-FAIL. If the Home
Agent does not have shared-key based SA, Home Agent MUST discard the
BU. The Home Agent MAY log such events.
5.2 MN-AAA authentication mobility option
The format of the MN-AAA authentication mobility option is as defined
in Figure 2. This option uses the subtype value of 2. The MN-AAA
authentication mobility option is used to authenticate the Binding
Update message based on the shared security association between
Mobile Node and AAA server in Home network (AAAH). It is not used in
Binding Acknowledgement messages. The corresponding Binding
Acknowledgement messages must be authenticated using the MN-HA
authentication option Section 5.1.
This must be the last option in a message with mobility header. If
both Mobile-Home and Mobile-AAA authentication mobility options are
present, the Mobile-Home Authentication option MUST appear prior to
the Mobile-AAA Authentication option. The corresponding response
MUST include the Mobile-Home Authentication option, and MUST NOT
include the Mobile-AAA Authentication option.
The Mobile Node MAY use Mobile Node Identifier option [MN_Ident] to
enable the Home Agent to make use of available AAA infrastructure.
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The authentication data is calculated on the message starting from
the mobility header upto and including the SPI value of this option.
The authentication data shall be calculated as follows:
Authentication data = hash_fn(MN-AAA Shared key, MAC_Mobility Data)
hash_fn() is decided by the value of SPI field in the authentication
option.
SPI = HMAC_SHA1_SPI:
If SPI has the well-known value HMAC_SHA1_SPI, then hash_fn() is
HMAC_SHA1. When HMAC_SHA1_SPI is used, the BU is authenticated by
AAA using HMAC_SHA1 authentication. In that case, MAC_Mobility Data
is calculated as follows:
MAC_Mobility Data = SHA1(care-of address | home address | MH Data)
MH Data is the content of the Mobility Header upto and including the
SPI field of this option.
5.2.1 Processing Considerations
When the Home Agent receives a Binding Update with the Mobile-AAA
authentication option, the Binding Update is authenticated by an
entity external to the Home Agent, typically a AAA server.
5.3 Authentication Failure Detection at the Mobile Node
In case of authentication failure, the Home Agent MUST send a Binding
Acknowledgement with status code MIPV6-AUTH-FAIL to the Mobile Node,
if an SA to be used between Mobile Node and Home Agent for
authentication exists.
Upon receiving a Binding Acknowledgement with status code
MIPV6-AUTH-FAIL, the Mobile Node SHOULD stop sending new Binding
Updates to the Home Agent.
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6. Mobility message replay protection option
The Mobility message replay protection option MAY be used in Binding
Update/Binding Acknowledgement messages when authenticated using the
mobility message authentication option as described in Section 5.
The mobility message replay protection option is used to let the Home
Agent verify that a Binding Update has been freshly generated by the
Mobile Node and not replayed by an attacker from some previous
Binding Update. This is especially useful for cases where the Home
Agent does not maintain stateful information about the Mobile Node
after the binding entry has been removed. The Home Agent does the
replay protection check after the Binding Update has been
authenticated. The mobility message replay protection option when
included is used by the Mobile Node for matching BA with BU.
If the policy at Home Agent mandates replay protection using this
option (as opposed to the sequence number in Mobility Header in
Binding Update) and the Binding Update from Mobile Node does not
include this option, Home Agent discards the BU and sets the Status
Code in BA to MIPV6-MESG-ID-REQD.
When the Home Agent receives the mobility message replay protection
option in Binding Update, it SHOULD include the mobility message
replay protection option in Binding Acknowledgement. Appendix A
provides details regarding why the mobility message replay protection
option MAY be used when using the authentication option.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3
Option Type:
MESG-ID-OPTION-TYPE to be defined by IANA. An 8-bit identifier
of the type mobility option.
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Option Length:
8-bit unsigned integer, representing the length in octets of
the Timestamp field.
Timestamp:
This field carries the 64 bit timestamp.
Alignment requirements :
The alignment requirement for this option is 8n + 2.
The basic principle of timestamp replay protection is that the node
generating a message inserts the current time of day, and the node
receiving the message checks that this timestamp is sufficiently
close to its own time of day. Unless specified differently in the
shared-key based security association between the nodes, a default
value of 7 seconds MAY be used to limit the time difference. This
value SHOULD be greater than 3 seconds. The two nodes must have
adequately synchronized time-of-day clocks.
The Mobile Node MUST set the Timestamp field to a 64-bit value
formatted as specified by the Network Time Protocol [RFC1305]. The
low-order 32 bits of the NTP format represent fractional seconds, and
those bits which are not available from a time source SHOULD be
generated from a good source of randomness. Note, however, that when
using timestamps, the 64-bit Timestamp used in a Binding Update from
the Mobile Node MUST be greater than that used in any previous
successful Binding Update.
After successful authentication of Binding Update (either locally at
the Home Agent or when a success indication is received from the AAA
server), the Home Agent MUST check the Timestamp field for validity.
In order to be valid, the timestamp contained in the Timestamp field
MUST be close enough to the Home Agent's time of day clock and the
timestamp MUST be greater than all previously accepted timestamps for
the requesting Mobile Node.
If the timestamp is valid, the Home Agent copies the entire Timestamp
field into the Timestamp field in the BA it returns to the Mobile
Node. If the timestamp is not valid, the Home Agent copies only the
low-order 32 bits into the BA, and supplies the high-order 32 bits
from its own time of day.
If the timestamp field is not valid but the authentication of the BU
succeeds, Home Agent MUST send a Binding Acknowledgement with status
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code MIPV6-ID-MISMATCH. The Home Agent does not create a binding
cache entry if the timestamp check fails.
If the Mobile Node receives a Binding Acknowledgement with the code
MIPV6-ID-MISMATCH, the Mobile Node MUST authenticate the BA by
processing the MN-HA authentication mobility option.
If authentication succeeds, the Mobile Node MUST adjust its timestamp
and send subsequent Binding Update using the updated value.
Upon receiving a BA that does not contain the MIPV6-ID-MISMATCH
status code, the Mobile Node MUST compare the Timestamp value in the
BA to the Timestamp value it sent in the corresponding BU. If the
values match, the Mobile Node proceeds to process the MN-HA
authentication data in the BA. If the values do not match, the
Mobile Node silently discards the BA.
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7. Security Considerations
This document proposes new authentication options to authenticate the
control message between Mobile Node, Home Agent and/or home AAA (as
an alternative to IPsec). The new options provide for authentication
of Binding Update and Binding Acknowledgement messages. The MN-AAA
authentication options provides for authentication with AAA
infrastructure. It can be used to generate a per session key between
Mobile Node and Home Agent for subsequent authentication of BU/BA
between Mobile Node and Home Agent via the MN-HA authentication
option.
This memo also introduces an optional replay protection mechanism
Section 6, to prevent replay attacks. The sequence number field in
the Binding Update is not used if this mechanism is used. This memo
defines the timestamp option to be used for mobility message replay
protection.
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8. IANA Considerations
IANA services are required for this specification. The values for
new mobility options and status codes must be assigned from the
Mobile IPv6 [RFC3775] numbering space.
The values for Mobility Option types AUTH-OPTION-TYPE and
MESG-ID-OPTION-TYPE, as defined in Section 5 and Section 6 need to be
assigned. The suggested values are 8 for the AUTH-OPTION-TYPE and 9
for the MESG-ID-OPTION-TYPE Mobility Option.
The values for status codes MIPV6-ID-MISMATCH, MIPv6-AUTH-FAIL and
MIPV6-MESG-ID-REQD as defined in Section 6, Section 6 and Section 5.3
also need to be assigned. The suggested values are 144 for
MIPV6-ID-MISMATCH 145 for MIPV6-MESG-ID-REQD and 146 for
MIPV6-AUTH-FAIL.
IANA should record values for these new Mobility Options and the new
Status Codes.
A new section for enumerating algorithms identified by specific SPIs
within the range 0-255 is to be added to
http://www.isi.edu/in-notes/iana/assignments/mobility-parameters
The currently defined values are as follows:
The value 0 should not be assigned.
The value 3 is suggested for HMAC_SHA1_SPI as defined in Section 5.2.
The value 5 is reserved for use by 3GPP2.
New values for this namespace can be allocated using Standards Action
[RFC2434].
In addition, IANA needs to create a new namespace for the subtype
field of the MN-HA and MN-AAA authentication mobility options under
http://www.isi.edu/in-notes/iana/assignments/mobility-parameters
The currently allocated values are as follows:
1 MN-HA authentication mobility option Section 5.1
2 MN-AAA authentication mobility option Section 5.2
New values for this namespace can be allocated using Standards Action
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[RFC2434].
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9. Acknowledgements
The authors would like to thank Basavaraj Patil, Charlie Perkins
Vijay Devarapalli and Jari Arkko for their thorough review and
suggestions on the document. The authors would like to acknowledge
the fact that a similar authentication method was considered in base
protocol [RFC3775] at one time.
10 Normative References
[MN_Ident]
Patel et. al., A., "Mobile Node Identifier Option for
Mobile IPv6", draft-ietf-mip6-mn-ident-option-01.txt (work
in progress), December 2004.
[RFC1305] Mills, D., "Network Time Protocol (Version 3)
Specification, Implementation", RFC 1305, March 1992.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[RFC3775] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
Authors' Addresses
Alpesh Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
US
Phone: +1 408-853-9580
EMail: alpesh@cisco.com
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Kent Leung
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
US
Phone: +1 408-526-5030
EMail: kleung@cisco.com
Mohamed Khalil
Nortel Networks
2221 Lakeside Blvd.
Richardson, TX 75082
US
Phone: +1 972-685-0574
EMail: mkhalil@nortelnetworks.com
Haseeb Akhtar
Nortel Networks
2221 Lakeside Blvd.
Richardson, TX 75082
US
Phone: +1 972-684-4732
EMail: haseebak@nortelnetworks.com
Kuntal Chowdhury
Starent Networks
2540 Coolwater Dr.
Plano, TX 75025
US
Phone: +1 214 550 1416
EMail: kchowdury@starentnetworks.com
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Appendix A. Rationale for mobility message replay protection option
Mobile IPv6 [RFC3775] defines a Sequence Number in the mobility
header to prevent replay attacks. There are two aspects that stand
out in regards to using the Sequence Number to prevent replay
attacks.
Firstly, the specification states that Home Agent should accept a BU
with a Sequence Number greater than the Sequence Number from previous
Binding Update. This implicitly assumes that the Home Agent has some
information regarding the Sequence Number from previous BU (even when
the binding cache entry is not present). Secondly, the specification
states that if the Home Agent has no binding cache entry for the
indicated home address, it MUST accept any Sequence Number value in a
received Binding Update from this Mobile Node.
With the mechanism defined in this draft, it is possible for the
Mobile Node to register with a different Home Agent during each
mobility session. Thus, it is unreasonable to expect each Home Agent
in the network to maintain state about the Mobile Node. Also, if the
Home Agent does not cache information regarding sequence number, as
per the second point above, a replayed BU can cause a Home Agent to
create a binding cache entry for the Mobile Node. Thus, when
authentication option is used, Sequence Number does not provide
protection against replay attack.
One solution to this problem (when Home Agent does not save state
information for every Mobile Node) would be for the Home Agent to
reject the first BU and assign a (randomly generated) starting
sequence number for the session and force the Mobile Node to send a
fresh BU with the suggested sequence number. While this would work
in most cases, it would require an additional round trip and this
extra signalling and latency is not acceptable in certain deployments
(3GPP2). Also, this rejection and using sequence number as a nonce
in rejection is a new behavior that is not specified in [RFC3775].
Thus, this specification uses the mobility message replay protection
option to prevent replay attacks. Specifically, timestamps are used
to prevent replay attacks as described in Section 6.
It is important to note that as per Mobile IPv6 [RFC3775] this
problem with sequence number exists. Since the base specification
mandates the use of IPsec (and naturally that goes with IKE in most
cases), the real replay protection is provided by IPsec/IKE. In case
of BU/BA between Mobile Node and CN, the liveness proof is provided
by the use of nonces which the CN generates.
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Acknowledgment
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Patel, et al. Expires July 19, 2005 [Page 20]
