One document matched: draft-ietf-mipshop-handover-key-03.txt
Differences from draft-ietf-mipshop-handover-key-02.txt
James Kempf
Internet Draft DoCoMo Labs USA
Document: draft-ietf-mipshop-handover-key-03.txt Rajeev Koodli
Intended Status: Proposed Standard Nokia-Siemens
Research
Center
Expires: May, 2008 November, 2007
Distributing a Symmetric FMIPv6 Handover Key using SEND
(draft-ietf-mipshop-handover-key-03.txt)
Status of this Memo
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Abstract
Fast Mobile IPv6 requires that a Fast Binding Update is secured
using a security association shared between an Access Router and a
Mobile Node in order to avoid certain attacks. In this document, a
method for provisioning a shared key from the Access Router to the
Mobile Node is defined to protect this signaling. The Mobile Node
generates a public/private key pair using the same public key
algorithm as for SEND (RFC 3971). The Mobile Node sends the public
key to the Access Router. The Access Router encrypts a shared
handover key using the public key and sends it back to the Mobile
Node. The Mobile Node decrypts the shared handover key using the
matching private key, and the handover key is then available for
generating an authenticator on a Fast Binding Update. The Mobile
Node and Access Router use the Router Solicitation for Proxy
Advertisement and Proxy Router Advertisement from Fast Mobile IPv6
for the key exchange. The key exchange messages are required to
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have SEND security; that is, the source address is a
Cryptographically Generated Address and the messages are signed
using the CGA private key of the sending node. This allows the
Access Router, prior to providing the shared handover key, to
verify the authorization of the Mobile Node to claim the address
so that the previous care-of CGA in the Fast Binding Update can
act as the name of the key.
Table of Contents
1.0 Introduction.............................................2
2.0 Overview of the Protocol.................................3
3.0 Handover Key Provisioning and Use........................4
4.0 Message Formats..........................................7
5.0 Security Considerations.................................10
6.0 IANA Considerations.....................................10
7.0 Normative References....................................10
8.0 Informative References..................................11
9.0 Author Information......................................11
10.0 IPR Statements.........................................11
11.0 Disclaimer of Validity.................................12
12.0 Copyright Statement....................................12
13.0 Acknowledgment.........................................12
1.0 Introduction
In Fast Mobile IPv6 (FMIPv6) [FMIP], a Fast Binding Update (FBU)
is sent from a Mobile Node (MN), undergoing IP handover, to the
previous Access Router (AR). The FBU causes a routing change so
traffic sent to the MN's previous care-of address on the previous
AR's link is tunneled to the new care-of address on the new AR's
link. Only a MN authorized to claim the address should be able to
change the routing for the previous care-of address. If such
authorization is not established, an attacker can redirect a
victim MN's traffic at will.
In this document, a lightweight mechanism is defined by which a
shared handover key for securing FMIP can be provisioned on the MN
by the AR. The mechanism utilizes SEND [SEND] and an additional
public/private key pair, generated on the MN using the same public
key algorithm as SEND, to encrypt/decrypt a shared handover key
sent from the AR to the MN. The key provisioning occurs at some
arbitrary time prior to handover, thereby relieving any
performance overhead on the handover process. The message exchange
between the MN and AR to provision the handover key is required to
be protected by SEND; that is, the source address for the key
provisioning messages must be a CGA and the messages must be signed
with the CGA private key. This allows the AR to establish the MN's
authorization to operate on the CGA. The AR uses the CGA to name
the handover key. The SEND key pair is, however, independent from
the handover encryption/decryption key pair and from the actual
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handover key. Once the shared handover key has been established,
when the MN undergoes IP handover, the MN generates an
authorization MAC on the FBU. The previous care-of CGA included in
the FBU is used by the AR to find the right handover key for
checking the authorization.
Handover keys are an instantiation of the purpose built key
architectural principle [PBK].
1.1 Terminology
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
RFC 2119 [RFC2119].
In addition, the following terminology is used:
CGA public key
Public key used to generate the CGA according to RFC 3972
[CGA].
CGA private key
Private key corresponding to the CGA public key.
Handover key encryption public key
Public key generated by the MN and sent to the current AR to
encrypt the shared handover key
Handover key encryption private key
Private key corresponding to handover key encryption public
key, held by the MN
2.0 Overview of the Protocol
2.1 Brief Review of SEND
SEND protects against a variety of threats to local link address
resolution (also known as Neighbor Discovery) and last hop router
(AR) discovery in IPv6 [RFC3756]. These threats are not exclusive
to wireless networks, but they generally are easier to mount on
certain wireless networks because the link between the access
point and MN can't be physically secured.
SEND utilizes CGAs in order to secure Neighbor Discovery signaling
[CGA]. Briefly, a CGA is formed by hashing together the IPv6
subnet prefix for a node's subnet, a random nonce, and an RSA
public key, called the CGA public key. The CGA private key is used
to sign a Neighbor Advertisement (NA) message sent to resolve the
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link layer address to the IPv6 address. The combination of the CGA
and the signature on the NA proves to a receiving node the
sender's authorization to claim the address. The node may
opportunistically generate one or several keys specifically for
SEND, or it may use a certified key that it distributes more
widely.
2.2 Protocol Overview
The protocol utilizes the SEND secured Router Solicitation for
Proxy Advertisement (RtSolPr)/Proxy Router Advertisement (PrRtAdv)
[FMIP] exchange between the MN and the AR to transport an
encrypted, shared handover key from the AR to the MN. First, the
MN generates the necessary key pair and associated CGA addresses
so that the MN can employ SEND. Then the MN generates a
public/private key pair for encrypting/decrypting the shared
handover key, using the same public key algorithm as was used for
SEND. The MN then sends a RtSolPr message with a Handover Key
Request Option containing the handover key encryption public key.
The source address of the RtSolPr message is the MN's care-of CGA
on the AR's link, the RtSolPr message is signed with the MN's CGA
key, and contains the CGA Parameters option, in accordance with
RFC 3971 [SEND]. The AR verifies the message using SEND, then
utilizes the handover key encryption public key to encrypt a
shared handover key, which is included with the PrRtAdv in the
Handover Key Reply Option. The MN decrypts the shared handover key
and uses it to establish an authorization MAC when it sends an FBU
to the previous AR.
3.0 Handover Key Provisioning and Use
3.1 Sending Router Solicitations for Proxy Advertisement
At some time prior to handover, the MN MUST generate a handover
key encryption public/private key pair, using exactly the same
public key algorithm with exactly the same parameters (key size,
etc.) as for SEND [SEND]. The MN can reuse the key pair on
different access routers but MUST NOT use the key pair for any
other encryption or for signature operation. In order to prevent
cryptanalysis, the key pair SHOULD be discarded after either a
duration of HKEPK-LIFETIME or HKEPK-HANDOVERS number of handovers,
whichever occurs first. See Section 3.7 for definitions of
protocol constants.
The MN MUST send a Router Solicitation for Proxy Advertisement
(RtSolPr) containing a Handover Key Request Option with the
handover encryption public key. A CGA for the MN MUST be the
source address on the packet, and the MN MUST include the SEND CGA
Option and SEND Signature Option with the packet, as specified in
[SEND]. The SEND signature covers all fields in the RtSolPr,
including the 128 bit source and destination addresses and ICMP
checksum as described in RFC 3971, except for the Signature Option
itself. The MN also sets the handover authentication Algorithm
Type (AT) extension field in the Handover Key Request Option to
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the MN's preferred FBU authentication algorithm. The SEND Nonce
MUST also be included for anti-replay protection.
3.2 Receiving Router Solicitations for Proxy Advertisement and Sending
Proxy Router Advertisements
When an FMIPv6 capable AR with SEND receives a RtSolPr from a MN
protected with SEND and including a Handover Key Request Option,
the AR MUST first validate the RtSolPr using SEND as described in
RFC 3971. If the RtSolPr can not be validated, the AR MUST NOT
include a Handover Key Reply Option in the reply. The AR also MUST
NOT change any existing key record for the address, since the
message may be an attempt by an attacker to disrupt communications
for a legitimate MN. The AR SHOULD respond to the RtSolPr but MUST
NOT perform handover key provisioning.
If the RtSolPr can be validated, the AR MUST then determine
whether the CGA is already associated with a shared handover key.
If the CGA is associated with an existing handover key, the AR
MUST return the existing handover key to the MN. If the CGA does
not have a shared handover key, the AR MUST construct a shared
handover key as described in Section 3.6. The AR MUST encrypt the
handover key with the handover key encryption public key included
in the Handover Key Request Option. The AR MUST insert the
encrypted handover key into a Handover Key Reply Option and MUST
attach the Handover Key Reply Option to the PrRtAdv. The lifetime
of the key, HK-LIFETIME, MUST also be included in the Handover Key
Reply Option. The AR SHOULD set the AT field of the Handover Key
Option to the MN's preferred algorithm type indicated in the AT
field of the Handover Key Request Option, if it is supported;
otherwise, the AR MUST select an authentication algorithm which is
of equivalent strength or stronger and set the field to that. The
AR MUST also include the SEND nonce from the RtSolPr for anti-
replay protection. The AR MUST use the CGA constructed from its
certified key as the source address for the PrRtAdv and include a
SEND CGA Option and a SEND Signature Option with the SEND
signature of the message. The SEND signature covers all fields in
the PrRtAdv, including the 128 bit source and destination
addresses and ICMP checksum as described in RFC 3971, except for
the Signature Option itself. The PrRtAdv is then unicast back to
the MN at the MN's care-of CGA that was the source address on the
RtSolPr. The handover key MUST be stored by the AR for future use,
indexed by the CGA, and the authentication algorithm type (i.e.,
the resolution of the AT field processing) and HK-LIFETIME MUST be
recorded with the key.
3.3 Receiving Proxy Router Advertisements
Upon receipt of one or more PrRtAdvs secured with SEND and having
the Handover Key Reply Option, the MN MUST first validate the
PrRtAdvs as described in RFC 3971. Normally the MN will have
obtained the router's certification path to validate an RA prior
to sending the PrRtSol and the MN MUST check to ensure that the
key used to sign the PrRtAdv is the router's certified public key.
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If the MN does not have the router's certification path cached, it
MUST use the SEND CPS/CPA messages to obtain the certification
path to validate the key. If a certified key from the router was
not used to sign the message, the message MUST be dropped.
From the messages that validate, the MN SHOULD choose one with an
AT flag in the Handover Key Reply Option indicating an
authentication algorithm that the MN supports. From that message,
the MN MUST determine which handover key encryption public key to
use in the event the MN has more than one. The MN finds the right
public key to use by matching the SEND nonce from the RtSolPr. If
no such match occurs, the MN MUST drop the PrRtAdv. The MN MUST
use the matching private key to decrypt the handover key using its
handover key encryption private key, and store the handover key
for later use, named with the AR's CGA, along with the algorithm
type and HK-LIFETIME. The MN MUST use the returned algorithm type
indicated in the PrRtAdv. The MN MUST index the handover keys with
the AR's IPv6 address, to which the MN later sends the FBU, and
the MN's CGA to which the handover key applies. This allows the MN
to select the proper key when communicating with a previous AR.
Prior to HK-LIFETIME expiring, the MN MUST request a new key from
the AR if FMIPv6 service is still required from the router.
If more than one router responds to the RtSolPr, the MN MAY keep
track of all such keys. If none of the PrRtAdvs contains an
algorithm type indicator corresponding to an algorithm the MN
supports, the MN MAY re-send the RtSolPr requesting a different
algorithm, but to prevent bidding down attacks from compromised
routers, the MN SHOULD NOT request an algorithm that is weaker
than its original request.
3.4 Sending FBUs
When the MN needs to signal the Previous AR (PAR) using an FMIPv6
FBU, the MN MUST utilize the handover key and the corresponding
authentication algorithm to generate an authenticator for the
message. The MN MUST select the appropriate key for the PAR using
the PAR's CGA and the MN's previous care-of CGA on the PAR's link.
As defined by the FMIPv6 [FMIP], the MN MUST generate the
authentication MAC using the handover key and the appropriate
algorithm and MUST include the MAC in the FBU message. As
specified by FMIPv6, the MN MUST include the old care-of CGA in a
Home Address Option. The FMIPv6 document provides more detail
about the construction of the authenticator on the FBU.
3.5 Receiving FBUs
When the PAR receives an FBU message containing an authenticator,
the PAR MUST find the corresponding handover key using the MN's
care-of CGA in the Home Address Option as the index. If a handover
key is found, the PAR MUST utilize the handover key and the
appropriate algorithm to verify the authenticator. If the handover
key is not found, the PAR MUST NOT change forwarding for the care-
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of CGA. The FMIPv6 document [FMIP] provides more detail on how the
AR processes an FBU containing an authenticator.
3.6 Key Generation and Lifetime
The AR MUST randomly generate a key having sufficient strength to
match the authentication algorithm. Some authentication algorithms
specify a required key size. The AR MUST generate a unique key for
each CGA public key, and SHOULD take care that the key generation
is uncorrelated between handover keys, and between handover keys
and CGA keys. The actual algorithm used to generate the key is not
important for interoperability since only the AR generates the
key; the MN simply uses it.
A PAR SHOULD NOT discard the handover key immediately after use if
it is still valid. It is possible that the MN may undergo rapid
movement to another AR prior to the completion of Mobile IPv6
binding update on the PAR, and the MN MAY as a consequence
initialize another, subsequent handover optimization to move
traffic from the PAR to another new AR. The default time for
keeping the key valid corresponds to the default time during which
forwarding from the PAR to the new AR is performed for FMIP. The
FMIPv6 document [FMIP] provides more detail about the FMIP
forwarding time default.
If the MN returns to a PAR prior to the expiration of the handover
key, the PAR MAY send and the MN MAY receive the same handover key
as was previously returned, if the MN generates the same CGA for
its care-of address. However, the MN MUST NOT assume that it can
continue to use the old key without actually receiving the
handover key again from the PAR. The MN SHOULD discard the
handover key after MIPv6 binding update is complete on the new AR.
The PAR MUST discard the key after FMIPv6 forwarding for the
previous care-of address times out or when HK-LIFETIME expires.
3.7 Protocol Constants
The following are protocol constants with suggested defaults:
HKEPK-LIFETIME: The maximum lifetime for the handover key
encryption public key. Default is 12 hours.
HKEPK-HANDOVERS: The maximum number of handovers for which the
handover key encryption public key should be
reused. Default is 10.
HK-LIFETIME: The maximum lifetime for the handover key.
Default is 12 hours (43200 seconds).
4.0 Message Formats
4.1 Handover Key Request Option
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The Handover Key Request Option is a standard IPv6 Neighbor
Discovery [RFC2461] option in TLV format. The Handover Key Request
Option is included in the RtSolPr message along with the SEND CGA
Option, RSA Signature Option, and Nonce 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Pad Length | AT |Resrvd.|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Handover Key Encryption Public Key .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type: To be assigned by IANA.
Length: The length of the option in units of 8 octets,
including the Type and Length fields. The value 0
is invalid. The receiver MUST discard a message
that contains this value.
Pad Length: The number of padding octets beyond the end of the
Handover Key Encryption Public Key field but
within the length specified by the Length field.
Padding octets MUST be set to zero by senders and
ignored by receivers.
AT: A 4-bit algorithm type field describing the
algorithm used by FMIPv6 to calculate the
authenticator. See [FMIP] for details.
Resrvd.: A 4-bit field reserved for future use. The value
MUST be initialized to zero by the sender and MUST
be ignored by the receiver.
Handover Key Encryption Public Key:
The handover key encryption public key. The key
MUST be formatted according to the same
specification as the CGA key in the CGA Parameters
Option [CGA] of the message, and MUST have the
same parameters as the CGA key.
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Padding: A variable-length field making the option length a
multiple of 8, containing as many octets as
specified in the Pad Length field.
4.2 Handover Key Reply Option
The Handover Key Reply Option is a standard IPv6 Neighbor
Discovery [RFC2461] option in TLV format. The Handover Key Reply
Option is included in the PrRtAdv message along with the SEND CGA
Option, RSA Signature Option, and Nonce 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Pad Length | AT |Resrvd.|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Lifetime | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
. .
. Encrypted Handover Key .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type: To be assigned by IANA.
Length: The length of the option in units of 8 octets,
including the Type and Length fields. The value 0
is invalid. The receiver MUST discard a message
that contains this value.
Pad Length: The number of padding octets beyond the end of the
Encrypted Handover Key field but within the length
specified by the Length field. Padding octets MUST
be set to zero by senders and ignored by
receivers.
AT: A 4-bit algorithm type field describing the
algorithm used by FMIPv6 to calculate the
authenticator. See [FMIP] for details.
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Resrvd.: A 4-bit field reserved for future use. The value
MUST be initialized to zero by the sender and MUST
be ignored by the receiver.
Key Lifetime: Lifetime of the handover key, HK-LIFETIME, in
seconds.
Encrypted Handover Key:
The shared handover key, encrypted with the MN's
handover key encryption public key, using the
RSAES-PKCS1-v1_5 format [RFC3447].
Padding: A variable-length field making the option length a
multiple of 8, containing as many octets as
specified in the Pad Length field.
5.0 Security Considerations
This document describes a shared key provisioning protocol for the
FMIPv6 handover optimization protocol. The key provisioning
protocol utilizes a public key generated with the same public key
algorithm as SEND to bootstrap a shared key for authorizing
changes due to handover associated with the MN's former address on
the PAR. General security considerations involving CGAs apply to
the protocol described in this document, see [CGA] for a
discussion of security considerations around CGAs. This protocol
is subject to the same risks from replay attacks and DoS attacks
using the RtSolPr as the SEND protocol [SEND] for RS. The measures
recommended in RFC 3971 for mitigating replay attacks and DoS
attacks apply here as well. An additional consideration involves
when to generate the handover key on the AR. To avoid state
depletion attacks, the handover key SHOULD NOT be generated prior
to SEND processing that verifies the originator of RtSolPr. State
depletion attacks can be addressed by techniques such as rate
limiting RtSolPr, restricting the amount of state reserved for
unresolved solicitations, and clever cache management. These
techniques are the same as used in implementing Neighbor
Discovery.
For other FMIPv6 security considerations, please see the FMIPv6
document [FMIP].
6.0 IANA Considerations
Two new IPv6 Neighbor Discovery options, the Handover Key Request
Option and Handover Key Reply Option, are defined, and require a
IPv6 Neighbor Discovery option type code from IANA.
7.0 Normative References
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[FMIP] Koodli, R., editor, "Fast Handovers for Mobile IPv6",
Internet Draft, Work in Progress.
[SEND] Arkko, J., editor, Kempf, J., Zill, B., and Nikander, P.,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[CGA] Aura, T., "Cryptographically Generated Addresses", RFC 3972,
March 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2461] Narten, T., and Nordmark, E., "Neighbor Discovery for IP
version 6 (IPv6)", RFC 2461, December 1998.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
8.0 Informative References
[RFC3756] Nikander, P., editor, Kempf, J., and Nordmark, E., "
IPv6 Neighbor Discovery (ND) Trust Models and Threats",
RFC 3756, May 2004.
[PBK] Bradner, S., Mankin, A., and Schiller, J., "A Framework for
Purpose-Built Keys (PBK)", Internet Draft, work in
progress.
9.0 Author Information
James Kempf Phone: +1 650 496 4711
DoCoMo Labs USA Email: kempf@docomolabs-usa.com
3240 Hillview Avenue
Palo Alto, CA
94303
USA
Rajeev Koodli Phone: +1 650 625 2359
Nokia-Siemens Research Center Fax: +1 650 625 2502
313 Fairchild Drive Email: Rajeev.Koodli@nokia.com
Mountain View, CA
94043
USA
10.0 IPR Statements
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
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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.
11.0 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, THE
IETF TRUST 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.
12.0 Copyright Statement
Copyright (C) The IETF Trust (2007).
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.
13.0 Acknowledgments
Funding for the RFC Editor function is currently provided by the
Internet Society.
The authors would like to thank John C. Mitchell and Arnab Roy, of
Stanford University, for their review of the design and suggestions
for improving it.
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