Internet Engineering Task Force Wassim Haddad
Internet Draft Ericsson Research Canada
Expires in July 2004 Helsinki University of Technology
Francis Dupont
ENST Bretagne
Lila Madour
Alan Kavanagh
Suresh Krishnan
Ericsson Research Canada
Soohong Daniel Park
Samsung Electronics
Hannu Kari
Helsinki University of Technology
February 2004
BUB: Binding Update Backhauling
<draft-haddad-mipv6-bub-01.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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Distribution of this memo is unlimited
Abstract
Mobile IPv6 protocol defines two different modes to address the
mobility problem. This document describes a new mode, called
Binding Update Backhauling (BUB), which has been especially
designed for highly mobile environment, i.e, the two mobile
nodes are mobile. The BUB mode offers a more secure and
optimized exchange of binding updates (BUs) between the two
mobile endoints.
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Table of Contents
1. Introduction...............................................2
2. Terminology................................................3
3. Motivation.................................................3
4. Proposed solution..........................................4
5. Defining BUB...............................................5
5.1 The BUB test...........................................5
5.2 The BUB Option format..................................7
5.3 The BUB Complete Message Structure.....................8
6. The Diffie Hellman Exchange...............................10
7. Impact on BU/BA Messages..................................10
8. Security Considerations...................................12
9. Acknowledgments...........................................12
10. Normative References.....................................12
11. Informative References...................................13
12. Author's Addresses.......................................13
13. Full Copyright Statement.................................14
Appendix A...................................................16
1. Introduction
The mobility problem has been described in most cases, as a
scenario involving one mobile endpoint referred to as MN and
another static endpoint referred to as CN.
Mobile IPv6 defines two different modes to handle the mobility
problem. These modes are the bidirectional tunneling (BT) and
route optimization (RO). The two modes represent a trade-off
between security and efficiency. For instance, the BT mode
enables a secure exchange but is not optimized at all, while
the RO mode offers better efficiency but raises many security
concerns.
This draft describes a new mode called Binding Update
Backhauling (BUB), which has been especially designed to be
used in scenarios involving two mobile endpoints. This mode
enables a more secure and reliable way for exchanging mobility
signaling messages, while preserving at the same time the
efficiency of the routing optimization mode.
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2. Terminology
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", "MAY"
in this document are to be interpreted as described in RFC 2219
[3].
3. Motivation
The route optimization (RO) mode allows two endpoints to
exchange data traffic by using the direct path between them.
This is achieved by using new mobility headers and relies on
exchanging mobility signaling messages each time the MN
switches to a new network (i.e., changes its IP address).
Each time a MN gets a new IP address (i.e., care-of address),
it needs, according to [1], to run a return routability (RR)
test in order to test the reachability of its new care-of
address and home address by the CN, prior to sending any
binding update (BU) message to the CN.
Such test is performed by exchanging two signaling messages
(CoTI/CoT) on the new direct path (i.e., the path used to
exchange data traffic), and two signaling messages (HoTI/HoT)
using the path going through the MNs'HA. The result of the test
creates a new state at the CN to be used to check the
authenticity of the BU sent by the MN. Only a successful test
allows the MN to send a BU to the CN to update its binding
cache entry (BCE). The CN should acknowledge the BU by sending
a binding acknowledgment (BA) to the MN.
In total, 6 messages are needed to update the CN with the new
MN's IP address.
If the CN becomes mobile, it needs to go through the same
procedure (i.e., exchange 6 messages) each time it gets a new
IP address, in order to keep the session alive.
Note that, for security reasons, it is stated in [1] and
explained in [4] that the lifetime of the state created at the
correspondent node is deliberately restricted to a few minutes,
in order to limit the potential ability of time shifting attack.
From the above scenario it appears that when the RO mode is
used between two mobile endpoints, it may create additional and
undesirable traffic, due to a high redundancy of unprotected
mobility signaling messages, thus more vulnerabilities.
Actually, when the CN becomes mobile, the frequency, as well as
the redundancy, of mobility signaling messages will increase,
thus making them more visible for a malicious node moving
nearby the two endpoints.
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Note that when the CN is mobile, it is highly probable that a
malicious node may be positioned nearby, thus creating a
vulnerability on both sides (since another one may probably be
located nearby the MN). Such scenario makes the exchange of
signaling messages between the two endpoints more challenging
with regards to the security requirements.
If MN2 moves at the same time than MN1, mobility signaling
messages may get lost due to the fact that MN1's care-of address
and MN2's care-of address have changed at the same time. Such
scenario will probably increase the latency of the handover
process, which is not desired especially for time sensitive
applications.
To address all issues described above, any possible solution
should offer an efficient optimization with regards to security
requirements, the number of signaling messages and the handover
latency.
This document describes one such optimization which meets all
these requirements.
4. Proposed solution:
The Binding Update Backhauling (BUB) is a new mode designed to
be used between two mobile endpoints. The suggested mode should
be considered as an enhancement to the route optimization mode
since it uses the same direct path between the MN and CN for the
data traffic exchange.
The main objectives of the BUB mode are to reduce the number of
mobility signaling messages exchanged between the two MNs and
increase the security of what will remain. This is achieved by
eliminating the HoTI/HoT and CoTI/CoT messages, diverting the
BU messages to a more secure and reliable path going through
the two HAs and keep using the direct path for the data traffic
exchange.
The design of the proposed solution is based on the following:
a) The paths between the MNs and their HAs are protected by an
ESP tunnel [2].
b) The path between the two HAs, being part of the backbone, is
assumed to be more secure and more stable than the dynamic
path between the two MNs.
c) A malicious node cannot be at the same time near the MNs
and near the path going between the two HAs.
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By diverting the signaling messages to a more reliable path, BUB
addresses the following issues:
- Security of BUs
By sending the BUs through the link between the two HAs
and by establishing a bidirectional security association
(SA) between the two MNs.
- Double Jumping Problem
By avoiding the loss of mobility signaling messages, BUB
reduces the latency caused by such loss.
- Excessive Signaling
BUB reduces the number of signaling messages, exchanged
between the two MNs, by eliminating the need for the
HoTI/HoT and CoTI/CoT messages.
The mobile nodes should be able to switch to the BUB mode once
both nodes have moved outside their home networks. The BUB mode
can be applied at any time during the ongoing session.
5. Defining BUB
5.1 The BUB Test
When both endoints are mobile, the following four entities become
involved:
MN1 CN(MN2)
| |
| |
| |
| |
| |
HA1------------------HA2
In the above scenario, switching to BUB mode should not occur
before running a successful BUB test. The BUB test makes both
endpoints agree on using the link going through the two HAs for
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exchanging the BU messages. The BUB test consists on exchanging
four messages and MUST be run in parallel with the RR test.
In the following scheme, MN1 is asking MN2 to switch to BUB
mode:
MN1 MN2
| |
_ | Do BUB |
| | -----------------------> |
| | |
HoTI/HoT | | BUB ACK |
messages |_ | <----------------------- |
| |
| |
| Do BUB | _
| -----------------------> | |
| | | CoTI/CoT
| BUB ACK | | messages
| <---------------------- | _|
| |
| |
A successful completion of a BUB test consists of sending two
messages "Do BUB" and receiving two messages "BUB ACK". Each
request is incorporated into a HoTI and a CoTI message and each
reply is incorporated into a HoT and a CoT message. Using these
two messages enables MN1 to use two different paths to test the
willingness of MN2, without adding new ones.
If the sender gets two different responses in the CoT and the
HoT messages, it SHOULD re-run the RR test procedure and the BUB
test. In the latter case, if the sender gets again two different
responses, it MUST abandon switching to the BUB mode.
A BUB test fails if both of the "BUB ACK" messages are not
received after two successive tries. In this case, MN1 MUST send
the BUs according to the RO mode.
Note that in case of test failure, the endpoint, which has
launched the BUB test procedure MUST NOT run it again during
the same session. However, the other endpoint MUST always be
able to start a BUB test at any time during the same ongoing
session.
If one mobile node launchs a BUB test and the other endpoint
does not wish to switch to the BUB mode, it MUST reply to the
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BUB test by sending two negative acknowledgments (NACK). Such
scenario may occur in case the other endpoint is static or it
has became static (i.e., it has not sent any BUs since a
predefined time).
If the two mobile endpoints agree to switch to the BUB mode,
they SHOULD NOT switch back at any time to the RO mode in the
ongoing session.
A positive BUB test will generate an additional message called
BUB Complete (BUBC) message, which will be sent by the responder
to the BUB test. The BUB complete message MUST follow the
following rules:
- The BUBC message is sent on the direct path to the MN's
care-of address used as the source address in the CoTI message
or as the destination address in the CoT message.
- The source address of the BUBC message is the same one used as
the source address in the CoT message.
- The BUBC message MUST contain a HAO including the home address
of the sender and the care-of init cookie sent by the MN in
the CoTI message.
- The BUBC message will contain a cookie called BUB cookie and
MUST be signed by the Kbm. The cookie MUST be used with the
Kbm to sign the DH messages.
- The BUBC message is sent after the CoT message.
If the MN receives the BUBC message before the CoT, it will
stop processing it and wait for the CoT message. If the CoT/BUBC
message is lost, then a new CoTI message is sent and the
responder MUST re-send a new CoT and BUBC messages.
The signature of the DH messages will use the Kbm as pre-shared
secret and the cookie sent in the BUB message. The signature
MUST be equal to:
Signature (DH_Message) =
First(96, HASH_SHA1(Kbm , DH_Message | cookie)
5.2 The BUB Option format
A new BUB option will be defined for carrying BUB messages. This
option MAY be inserted in all Return Routability test messages
(i.e., HoTI, HoT, CoTI, CoT). The format of the new option is
the following:
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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 | Option Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
TBD
Option Length
Length of the option: 1
Option Data
This field can contain one of two possible messages defined
in three different codes as following:
code 0 => "Do BUB"
code 1 => "BUB ACK"
code 2 => "BUB NACK"
- When used in a HoTI message: the field MUST contain the code
"0".
- When used in a HoT message: the field MUST contain either
code "1" or code "2".
- When used in a CoTI message: the field MUST contain the code
"0".
- When used in a CoT message: the field MUST contain either
code "1" or code "2".
5.3 The BUB Complete Message Structure
A mobile node uses the BUBC message to complete a positive BUB
test. The BUBC message adds a cookie to the pre-shared secret
(i.e., Kbm) computed from the RR test. The main goal behind
sending the BUBC message is to force a malicious node to be at
the same time on the path going through the two HAs and on the
new direct path between the two MNs.
The BUB complete message uses the MH Type value 8. When this
value is indicated in the MH Type field, the format of the
Message Data field in the Mobility Header is as follows:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Care-of Init Cookie +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ BUB_Cookie +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
These fields are unused. They MUST be initialized to zero by
the sender and MUST be ignored by the receiver.
Care-of Init Cookie
64-bit field which contains the care-of init cookie.
BUB_Cookie
64 bit field which contains the cookie sent by the responder
to a BUB test.
Mobility Options
Variable-length field of such length that the complete
Mobility Header is an integer multiple of 8 octets long.
This field contains zero or more TLV-encoded mobility
options.
The receiver MUST ignore and skip any options which it does
not understand.
This specification does not define any options valid for the
BUB message.
If no actual options are present in this message, no padding is
necessary and the Header Len field will be set to 2.
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6. The Diffie-Hellman Exchange
After a successful BUB test, the two MNs MUST establish a
bidirectional security association (SA) between them. Such SA
(more details in Appendix 1) MUST use a pre-shared secret
generated from the BUB test, to sign the DH messages.
The DH exchange is launched immediately after a successful BUB
test, by the MN, which has launched the test (e.g., MN1).
In order to mitigate a MiTM attack, MN1 MUST insert its IP home
address in a HAO attached to the first DH message and send it to
the MN2's home address (i.e., via HA2).
After receiving the first DH message, MN2 MUST duplicate the
second DH message and send one copy on the direct path to MN1's
care-of address and another copy to MN1's home address. The
second copy MUST be sent on the path going throught the two HAs.
The third DH message MUST be sent by MN1 to MN2's home address
on the same path than DH1. Upon receiving the third message, MN2
MUST comletes the DH message by sending the fourth message to
MN1's home address.
The different paths taken by the DH messages are shown in the
following:
MN1 HA1 HA2 MN2
| | | |
DH1 |======================================>|##################>|
| | | |
DH2 |<##################|<==================|<##################|
| | | |
DH2 |<==========================================================|
| | | |
DH3 |======================================>|##################>|
| | | |
DH4 |<##################|<======================================|
| | | |
====>: denotes an authenticated message
####>: denotes an encrypted message
7. Impact on BU/BA Messages
As it has been mentioned earlier, the main reasons for
designing BUB are the security concerns around the BU messages
and the high redundancy in mobility signaling messages. The
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establishment of a bidirectional SA between the two MNs enables
them to substantially improve the safety of the BU messages and
eliminates the need for any further HoTI/HoT and CoTI/CoT
messages during the ongoing session. Such optimization leads to
a reduction of 4 messages between the two MNs each time a BU is
sent.
The different paths used to exchange the BU/BA messages appears
in the following scheme:
+------+ +------+
| | BA | |
| MN1 |<================| MN2 |
| | | |
+------+ +------+
# ^
# #
BU# #BU
# #
V #
+------+ +------+
| | | |
| HA1 |================>| HA2 |
| | BU | |
+------+ +------+
====>: denotes an authenticated message
####>: denotes an encrypted message
When MN1 switches to a new network (i.e., gets a new care-of
address), it sends a BU message to MN2 on the path going through
the two HAs. MN1 MAY duplicate the BU message and another copy
on the direct path. The two BU messages MUST have the same
sequence number and MUST be signed with the authenticated
binding management (Kabm) key.
After switching to the BUB mode, the following rules MUST be
applied:
- The MNs MUST NOT use the alternate care-of address option in
the BU messages sent to each other, in order to counter 3rd
party bombing attack [6].
- The MN MUST NOT use the nonce indices option in all new
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binding updates messages sent after a care-of address change.
The MN SHOULD set the Acknowledge (A) bit in the BU message
after switching to OMIPv6.
To avoid replay attacks, the MN, which has launched the BUB test
will keep the sequence number sent in the first BU immediately
after the DH exchange and increment it in all subsequent BU
messages. The same rule MUST be adopted by the other mobile
endpoint.
In case the session starts with one MN and one static node (CN)
and OMIPv6 [7] is applied, then switching to the BUB mode (i.e.,
the static node becomes mobile) can be done seamlessly. In such
scenario, the same Kabm key can be used to sign the BU message
sent by the CN (i.e., MN2) and MN2 MUST send its BU messages on
the path going through the two HAs. MN1 MUST use the same path
for any subsequent BU messages. Both nodes can duplicate their
BU messages and use the direct path to send the second copy.
8. Security considerations
This draft proposes a new mode which makes the exchange of
BUs more secure. It should be considered as an enhancement to
the security of the signaling messages exchange between two
mobile endpoints.
9. Acknowledgments
Authors would like to thank Laurent Marchand for his review and
comments on the draft. Many Thanks to Karim El-Malki and Shinta
Sugimoto for improving the draft.
10. Normative References
[1] D. Johnson and C. Perkins, "Mobility Support in IPv6",
draft-ietf-mobileip-ipv6-24.txt, June 2003.
[2] J.Arkko, V. Devarapalli, F. Dupont, "Using IPsec to Protect
Mobile IPv6 Signaling between Mobile Nodes and Home Agents",
draft-ietf-mobileip-mipv6-ha-ipsec-06.txt.
[3] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119.
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11. Informative References
[4] P. Nikander, T. Aura, J. Arkko, G.Montenegro and E. Nordmark
"Mobile IP version 6 Route Optimization Security Design
Background", draft-nikander-mobileip-v6-ro-sec-01.
[5] Krawczyk, H., "SIGMA: the 'SIGn-and-MAC'Approach to
Authenticated Diffie-Hellman and its use in the IKE
Protocols", in Advanceds in Cryptography - CRYPTO 2003
Proceedings, LNCS 2729, Springer, 2003. Available at:
http://www.ee.technion.ac.il/~hugo/sigma.html.
[6] F. Dupont, "A note about 3rd party bombing in Mobile IPv6",
draft-dupont-mipv6-3bombing-00, February 2004.
[7] W. Haddad, F. Dupont, L. Madour, S. Krishnan, S. D. Park,
"Optimizing Mobile IPv6 (OMIPv6)",
draft-haddad-mipv6-omipv6-01, February 2004.
12. Authors' Addresses
Wassim Haddad
Ericsson Research Canada
8400, Decarie Blvd
Town of Mount Royal
Quebec H4P 2N2
CANADA
Phone: +1 514 345 7900
Fax: +1 514 345 7900
E-Mail: Wassim.Haddad@ericsson.com
Francis Dupont
ENST Bretagne
Campus de Rennes
2, rue de la Chataigneraie
BP 78
35510 Cesson Sevigne Cedex
FRANCE
Fax: +33 2 99 12 70 30
E-Mail: Francis.Dupont@enst-bretagne.fr
Lila Madour
Ericsson Research Canada
8400, Decarie Blvd
Town of Mount Royal
Quebec H4P 2N2
CANADA
Phone: +1 514 345 7900
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Fax: +1 514 345 6195
E-Mail: Lila.Madour@ericsson.com
Alan Kavanagh
Ericsson Research Canada
8400, Decarie Blvd
Town of Mount Royal
Quebec H4P 2N2
CANADA
Phone: +1 514 345 7900
Fax: +1 514 345 6195
E-Mail: Alan.Kavanagh@ericsson.com
Suresh Krishnan
Ericsson Research Canada
8400, Decarie Blvd
Town of Mount Royal
Quebec H4P 2N2
CANADA
Phone: +1 514 345 7900
Fax: +1 514 345 6195
E-Mail: Suresh.Krishnan@ericsson.com
Soohong Daniel Park
Mobile Platform Laboratory, Samsung Electronics
416. Maetan-Dong, Yeongtong-Gu, Suwon
Korea
Phone: +81 31 200 4508
E-Mail: soohong.park@samsung.com
Hannu Kari
Helsinki University of Technology
Laboratory for Theoretical Computer Science
P.O. Box 5400
FIN-02015 HUT
FINLAND
Phone: +358 9 451 2918
E-Mail: Hannu.Kari@hut.fi
13. 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
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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
assignees.
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.
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Appendix A: Establishing the Bidirectional Security Association
As it has been stated in 4.3, after a successful BUB test, the
two MNs MUST establish a bidirectional security association
between them and generate a session key. The session key MUST be
used to authenticate BUs/BAs messages exchanged between the two
MNs via the path going through their two HAs. The session key
MAY also be used to authenticate the CoTI/CoT messages exchanged
via the direct path.
The session key is generated from a Diffie-Hellman (DH) exchange
which MUST be authenticated. Such authentication MAY use the Kbm
key as a pre-shared secret used to sign the DH messages.
Note that the Kbm key MUST be the last key generated from the RR
test (i.e., the RR test during which, the BUB test has been
launched).
The DH messages exchanged between the two MNs are described in
the following (for more details about the messages structure and
how to generate different keys, please refer to [5]):
sid , gX, N , info
MN1 MN1 MN1 MN1 MN2
--------------------------------------------------------------->
sid , sid , gY, N , info
MN1 MN2 MN2 MN2
<---------------------------------------------------------------
sid ,sid ,MN1,SIG (N ,sid ,gX,info ,info ), MAC(MN1)
MN1 MN2 Kbm MN2 MN1 MN1 MN2 Km
--------------------------------------------------------------->
sid ,sid, ,info ,MN2,SIG (N ,sid ,gY,info ,info),MAC(MN2)
MN1 MN2 MN2 Kbm MN1 MN2 MN2 MN1 Km
<---------------------------------------------------------------
In the above scheme, the following abbreviations have been
adopted:
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-gX = shared part of MN1's secret
-gY = shared part of MN2's secret
-sid = session identifier used to specify the ongoing session.
-N = nonce
-info = additional information carried in the protocol
messages
-MN1 = Identity of MN1 (e.g., MN1's Home IP address)
-MN2 = Identity of MN2 (e.g., MN2's Home IP address)
-Kbm = key generated from the RR test
-SIG(msg) = denotes the signature of "msg" using the Kbm.
-Km = key generated from DH (known only by MN1 and MN2)
-MAC(msg) = denotes a message authenticated code computed from
Km "msg" and signed by Km.
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