draft-josefsson-rfc2538bis-00.txt   draft-josefsson-rfc2538bis-01.txt 
Network Working Group S. Josefsson Network Working Group S. Josefsson
Expires: April 14, 2005 Expires: July 4, 2005
Storing Certificates in the Domain Name System (DNS) Storing Certificates in the Domain Name System (DNS)
draft-josefsson-rfc2538bis-00 draft-josefsson-rfc2538bis-01
Status of this Memo Status of this Memo
This document is an Internet-Draft and is subject to all provisions This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of 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 is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with which he or she become aware will be disclosed, in accordance with
RFC 3668. RFC 3668.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 14, 2005. This Internet-Draft will expire on July 4, 2005.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). Copyright (C) The Internet Society (2005).
Abstract Abstract
Cryptographic public key are frequently published and their Cryptographic public key are frequently published and their
authenticity demonstrated by certificates. A CERT resource record authenticity demonstrated by certificates. A CERT resource record
(RR) is defined so that such certificates and related certificate (RR) is defined so that such certificates and related certificate
revocation lists can be stored in the Domain Name System (DNS). revocation lists can be stored in the Domain Name System (DNS).
More information on this document, including rfcdiff output, may be More information on this document, including rfcdiff output, may be
found at <http://josefsson.org/rfc2538bis/>. found at <http://josefsson.org/rfc2538bis/>.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The CERT Resource Record . . . . . . . . . . . . . . . . . . . 3 2. The CERT Resource Record . . . . . . . . . . . . . . . . . . . 3
2.1 Certificate Type Values . . . . . . . . . . . . . . . . . 4 2.1 Certificate Type Values . . . . . . . . . . . . . . . . . 4
2.2 Text Representation of CERT RRs . . . . . . . . . . . . . 5 2.2 Text Representation of CERT RRs . . . . . . . . . . . . . 5
2.3 X.509 OIDs . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 X.509 OIDs . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Appropriate Owner Names for CERT RRs . . . . . . . . . . . . . 6 3. Appropriate Owner Names for CERT RRs . . . . . . . . . . . . . 6
3.1 X.509 CERT RR Names . . . . . . . . . . . . . . . . . . . 6 3.1 Content-based X.509 CERT RR Names . . . . . . . . . . . . 7
3.2 PGP CERT RR Names . . . . . . . . . . . . . . . . . . . . 7 3.2 Purpose-based X.509 CERT RR Names . . . . . . . . . . . . 8
4. Performance Considerations . . . . . . . . . . . . . . . . . . 8 3.3 Content-based PGP CERT RR Names . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 3.4 Purpose-based PGP CERT RR Names . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 4. Performance Considerations . . . . . . . . . . . . . . . . . . 9
7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Changes since RFC 2538 . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 10 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8. Changes since RFC 2538 . . . . . . . . . . . . . . . . . . . . 10
9.1 Normative References . . . . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 12
9.2 Informative References . . . . . . . . . . . . . . . . . . . 10 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . 12 9.1 Normative References . . . . . . . . . . . . . . . . . . . . 11
9.2 Informative References . . . . . . . . . . . . . . . . . . . 12
B. Copying conditions . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . 13
1. Introduction 1. Introduction
Public keys are frequently published in the form of a certificate and Public keys are frequently published in the form of a certificate and
their authenticity is commonly demonstrated by certificates and their authenticity is commonly demonstrated by certificates and
related certificate revocation lists (CRLs). A certificate is a related certificate revocation lists (CRLs). A certificate is a
binding, through a cryptographic digital signature, of a public key, binding, through a cryptographic digital signature, of a public key,
a validity interval and/or conditions, and identity, authorization, a validity interval and/or conditions, and identity, authorization,
or other information. A certificate revocation list is a list of or other information. A certificate revocation list is a list of
certificates that are revoked, and incidental information, all signed certificates that are revoked, and incidental information, all signed
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2.1 Certificate Type Values 2.1 Certificate Type Values
The following values are defined or reserved: The following values are defined or reserved:
Value Mnemonic Certificate Type Value Mnemonic Certificate Type
----- -------- ----------- ---- ----- -------- ----------- ----
0 reserved 0 reserved
1 PKIX X.509 as per PKIX 1 PKIX X.509 as per PKIX
2 SPKI SPKI certificate 2 SPKI SPKI certificate
3 PGP OpenPGP data packet 3 PGP OpenPGP packet
4-252 available for IANA assignment 4-252 available for IANA assignment
253 URI URI private 253 URI URI private
254 OID OID private 254 OID OID private
255-65534 available for IANA assignment 255-65534 available for IANA assignment
65535 reserved 65535 reserved
The PKIX type is reserved to indicate an X.509 certificate conforming The PKIX type is reserved to indicate an X.509 certificate conforming
to the profile being defined by the IETF PKIX working group. The to the profile being defined by the IETF PKIX working group. The
certificate section will start with a one byte unsigned OID length certificate section will start with a one byte unsigned OID length
and then an X.500 OID indicating the nature of the remainder of the and then an X.500 OID indicating the nature of the remainder of the
certificate section (see 2.3 below). (NOTE: X.509 certificates do certificate section (see 2.3 below). (NOTE: X.509 certificates do
not include their X.500 directory type designating OID as a prefix.) not include their X.500 directory type designating OID as a prefix.)
The SPKI type is reserved to indicate a certificate formated as to be The SPKI type is reserved to indicate a certificate formated as to be
specified by the IETF SPKI working group. specified by the IETF SPKI working group.
The PGP type indicates an OpenPGP data packet. Two uses are to The PGP type indicates an OpenPGP packet as described in [5] and its
transfer public key material and revocation signatures. The data is extensions and successors. Two uses are to transfer public key
binary, and MUST NOT be encoded into an ASCII armor. Public keys can material and revocation signatures. The data is binary, and MUST NOT
use the OpenPGP public key packet (tag 6) or public subkey packet be encoded into an ASCII armor. An implementation SHOULD process
(tag 14), as described in section 5.5 of [5]. Revocation signatures transferable public keys as described in section 10.1 of [5], but it
can use an OpenPGP signature packet with a revocation signature type, MAY handle additional OpenPGP packets.
i.e., signature type 0x20, 0x28 or 0x30, as described in section 5.2
of [5].
The URI private type indicates a certificate format defined by an The URI private type indicates a certificate format defined by an
absolute URI. The certificate portion of the CERT RR MUST begin with absolute URI. The certificate portion of the CERT RR MUST begin with
a null terminated URI [4] and the data after the null is the private a null terminated URI [4] and the data after the null is the private
format certificate itself. The URI SHOULD be such that a retrieval format certificate itself. The URI SHOULD be such that a retrieval
from it will lead to documentation on the format of the certificate. from it will lead to documentation on the format of the certificate.
Recognition of private certificate types need not be based on URI Recognition of private certificate types need not be based on URI
equality but can use various forms of pattern matching so that, for equality but can use various forms of pattern matching so that, for
example, subtype or version information can also be encoded into the example, subtype or version information can also be encoded into the
URI. URI.
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name related to their subject, i.e., the name of the entity intended name related to their subject, i.e., the name of the entity intended
to control the private key corresponding to the public key being to control the private key corresponding to the public key being
certified. It is recommended that certificate revocation list CERT certified. It is recommended that certificate revocation list CERT
RRs be stored under a domain name related to their issuer. RRs be stored under a domain name related to their issuer.
Following some of the guidelines below may result in the use in DNS Following some of the guidelines below may result in the use in DNS
names of characters that require DNS quoting which is to use a names of characters that require DNS quoting which is to use a
backslash followed by the octal representation of the ASCII code for backslash followed by the octal representation of the ASCII code for
the character such as \000 for NULL. the character such as \000 for NULL.
3.1 X.509 CERT RR Names The choice of name under which CERT RRs are stored is important to
clients that perform CERT queries. In some situations, the client
may not know all information about the CERT RR object it wishes to
retrieve. For example, a client may not know the subject name of an
X.509 certificate, or the e-mail address of the owner of an OpenPGP
key. Further, the client may only know the hostname of a service
that uses X.509 certificates or the OpenPGP key id of an OpenPGP key.
This motivate describing two different owner name guidelines. We
call the two rules content-based owner names and purpose-based owner
names. A content-based owner name is derived from the content of the
CERT RR data; for example the Subject field in an X.509 certificate
or the User ID field in OpenPGP keys. A purpose-based owner name is
selected to be a name that clients that wishes to retrieve CERT RRs
knows; for example the host name of a X.509 protected service or a
OpenPGP key id of an OpenPGP key. Note that in some situations, the
content-based and purpose-based owner name can be the same; for
example when a client look up keys based on e-mail addresses for
incoming e-mail.
[Editorial note: Purpose-based owner name guidelines were introduced
in RFC 2538bis. Earlier, in RFC 2538, only content-based owner name
guidelines were described. Implementation experience suggested that
the content-based owner name guidelines were not generally
applicable. It was realized that purpose-based owner name guidelines
were required to use CERT RRs in some ways.]
3.1 Content-based X.509 CERT RR Names
Some X.509 versions permit multiple names to be associated with Some X.509 versions permit multiple names to be associated with
subjects and issuers under "Subject Alternate Name" and "Issuer subjects and issuers under "Subject Alternate Name" and "Issuer
Alternate Name". For example, x.509v3 has such Alternate Names with Alternate Name". For example, x.509v3 has such Alternate Names with
an ASN.1 specification as follows: an ASN.1 specification as follows:
GeneralName ::= CHOICE { GeneralName ::= CHOICE {
otherName [0] INSTANCE OF OTHER-NAME, otherName [0] INSTANCE OF OTHER-NAME,
rfc822Name [1] IA5String, rfc822Name [1] IA5String,
dNSName [2] IA5String, dNSName [2] IA5String,
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Example 2: Assume that an X.509v3 certificate is issued to /CN=James Example 2: Assume that an X.509v3 certificate is issued to /CN=James
Hacker/L=Basingstoke/O=Widget Inc/C=GB/ with Subject Alternate names Hacker/L=Basingstoke/O=Widget Inc/C=GB/ with Subject Alternate names
of (a) domain name widget.foo.example, (b) IPv4 address of (a) domain name widget.foo.example, (b) IPv4 address
10.251.13.201, and (c) string "James Hacker 10.251.13.201, and (c) string "James Hacker
<hacker@mail.widget.foo.example>". Then the storage locations <hacker@mail.widget.foo.example>". Then the storage locations
recommended, in priority order, would be recommended, in priority order, would be
1. widget.foo.example, 1. widget.foo.example,
2. 201.13.251.10.in-addr.arpa, and 2. 201.13.251.10.in-addr.arpa, and
3. hacker.mail.widget.foo.example. 3. hacker.mail.widget.foo.example.
3.2 PGP CERT RR Names 3.2 Purpose-based X.509 CERT RR Names
It is difficult for clients that do not already posses a certificate
to reconstruct the content-based owner name that should be used to
retrieve the certificate. For this reason, purpose-based owner names
are recommended in this section. Because purpose-based owner names
by nature depend on the specific scenario, or purpose, for which the
certificate will be used, there are more than one recommendation.
The following table summarize the purpose-based X.509 CERT RR owner
name guidelines.
Scenario Owner name
-------------------------------------------------------------------
S/MIME Certificate Standard translation of RFC 822 email address.
Example: A S/MIME certificate for
"postmaster@example.org" will use a standard
hostname translation of the owner name,
i.e. "postmaster.example.org".
SSL Certificate Hostname of the SSL server.
IPSEC Certificate Hostname of the IPSEC machine, and/or
for the in-addr.arpa reverse lookup IP address.
CRLs Hostname of the issuing CA.
3.3 Content-based PGP CERT RR Names
OpenPGP signed keys (certificates) use a general character string OpenPGP signed keys (certificates) use a general character string
User ID [5]. However, it is recommended by PGP that such names User ID [5]. However, it is recommended by PGP that such names
include the RFC 2822 [7] email address of the party, as in "Leslie include the RFC 2822 [7] email address of the party, as in "Leslie
Example <Leslie@host.example>". If such a format is used, the CERT Example <Leslie@host.example>". If such a format is used, the CERT
should be under the standard translation of the email address into a should be under the standard translation of the email address into a
domain name, which would be leslie.host.example in this case. If no domain name, which would be leslie.host.example in this case. If no
RFC 2822 name can be extracted from the string name no specific RFC 2822 name can be extracted from the string name no specific
domain name is recommended. domain name is recommended.
If a user has more than one email address, the CNAME type can be used If a user has more than one email address, the CNAME type can be used
to reduce the amount of data stored in the DNS. For example: to reduce the amount of data stored in the DNS. For example:
$ORIGIN example.org. $ORIGIN example.org.
smith IN CERT PGP 0 0 <OpenPGP binary> smith IN CERT PGP 0 0 <OpenPGP binary>
john.smith IN CNAME smith john.smith IN CNAME smith
js IN CNAME smith js IN CNAME smith
For some applications, the above guidelines are not useful. 3.4 Purpose-based PGP CERT RR Names
Applications that receive an OpenPGP packet but do not know the email Applications that receive an OpenPGP packet but do not know the email
address of the sender will have difficulties guessing the correct address of the sender will have difficulties guessing the correct
owner name. However, the OpenPGP packet typically contain the Key ID owner name, and cannot use the content-based owner name guidelines.
of the key. Such applications can derive the owner name from the Key However, the OpenPGP packet typically contain the Key ID of the key.
ID using an Base 16 encoding [8]. For example: In these situations, it is recommended to use an owner name derived
from the Key ID. For example:
$ORIGIN example.org. $ORIGIN example.org.
F835EDA21E94B565716F IN CERT PGP ... F835EDA21E94B565716F IN CERT PGP ...
B565716F IN CNAME F835EDA21E94B565716F B565716F IN CNAME F835EDA21E94B565716F
Again, if the same key material is stored at several owner names, As before, if the same key material is stored at several owner names,
using CNAME can be used to avoid data duplication. using CNAME can be used to avoid data duplication.
4. Performance Considerations 4. Performance Considerations
Current Domain Name System (DNS) implementations are optimized for Current Domain Name System (DNS) implementations are optimized for
small transfers, typically not more than 512 bytes including small transfers, typically not more than 512 bytes including
overhead. While larger transfers will perform correctly and work is overhead. While larger transfers will perform correctly and work is
underway to make larger transfers more efficient, it is still underway to make larger transfers more efficient, it is still
advisable at this time to make every reasonable effort to minimize advisable at this time to make every reasonable effort to minimize
the size of certificates stored within the DNS. Steps that can be the size of certificates stored within the DNS. Steps that can be
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the key within the retrieved certificate MAY be trusted without the key within the retrieved certificate MAY be trusted without
verifying the certificate chain if this conforms with the user's verifying the certificate chain if this conforms with the user's
security policy. security policy.
CERT RRs are not used in connection with securing the DNS security CERT RRs are not used in connection with securing the DNS security
additions so there are no security considerations related to CERT RRs additions so there are no security considerations related to CERT RRs
and securing the DNS itself. and securing the DNS itself.
7. Open Issues 7. Open Issues
1. Not yet described: New DNSSEC Key Tag algorithm "OpenPGPKeyID" to 1. How to handle PGP certificates larger than 64kb? In
optimize PGP key retreival. Compare section 5 of
draft-josefsson-cert-openpgp. Not clear that it is needed.
2. How to handle PGP certificates larger than 64kb? In
draft-josefsson-cert-openpgp I outline one approach, but it may draft-josefsson-cert-openpgp I outline one approach, but it may
not be the best one. not be the best one.
3. Should the document suggest use of both 8 and 4 byte OpenPGP key 2. Whether to enforce owner name guidelines with SHOULD/MUST. From
id owner names? Perhaps only 8 byte version. David Shaw (on OpenPGP): "One of the things that struck me when
4. Any feedback on the X.509 data format and owner name guidelines reading this draft is that while there are several suggested ways
would be appreciated. Is anyone using this at all? They appear to name keys in DNS, there is no one canonical name as a SHOULD
as unnecessarily complex to me. or MUST. I suggest that the key fingerprint be the canonical
name, and all others be CNAMEs pointing to the fingerprint
name.". From Sean P. Turner (on PKIX): "Should "recommended" be
"RECOMMENDED" in the 1st and 2nd sentences?" referring to the
text in section 3 that recommend appropriate owner names.
3. Should the document suggest use of both full fingerprints, 4/8
byte OpenPGP key id owner names? Perhaps only fingerprint
version.
8. Changes since RFC 2538 8. Changes since RFC 2538
1. Editorial changes to conform with new document requirements, 1. Editorial changes to conform with new document requirements,
including splitting reference section into two parts and updating including splitting reference section into two parts and updating
references to point at latest versions. references to point at latest versions.
2. Improve terminology. For example replace "PGP" with "OpenPGP", 2. Improve terminology. For example replace "PGP" with "OpenPGP",
to align with RFC 2440. to align with RFC 2440.
3. Clarify that OpenPGP public key data are binary, not the ASCII 3. In section 2.1, clarify that OpenPGP public key data are binary,
armored format. not the ASCII armored format, and reference 10.1 in RFC 2440 on
how to deal with OpenPGP keys, and acknowledge that
implementations may handle additional packet types.
4. Clarify that integers in the representation format are decimal. 4. Clarify that integers in the representation format are decimal.
5. Replace KEY/SIG with DNSKEY/RRSIG etc, to align with DNSSECbis 5. Replace KEY/SIG with DNSKEY/RRSIG etc, to align with DNSSECbis
terminology. terminology.
6. Suggest additional OpenPGP owner name guidelines. 6. Add examples that suggest use of CNAME to reduce bandwidth.
7. In section 3, add three paragraphs that discuss "content-based"
vs "purpose-based" owner names. Add section 3.2 for
purpose-based X.509 CERT owner names, and section 3.4 for
purpose-based OpenPGP CERT owner names.
9. References 9. References
9.1 Normative References 9.1 Normative References
[1] Mockapetris, P., "Domain names - concepts and facilities", STD [1] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987. 13, RFC 1034, November 1987.
[2] Mockapetris, P., "Domain names - implementation and [2] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
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Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
Author's Address Author's Address
Simon Josefsson Simon Josefsson
EMail: simon@josefsson.org EMail: simon@josefsson.org
Appendix A. Acknowledgements Appendix A. Acknowledgements
The majority of this document is copied verbatim from RFC 2538, by D. The majority of this document is copied verbatim from RFC 2538, by
Eastlake and O. Gudmundsson. Donald Eastlake 3rd and Olafur Gudmundsson.
The author wishes to thank David Shaw and Michael Graff for their The author wishes to thank David Shaw and Michael Graff for their
contributions to draft-josefsson-cert-openpgp. contributions to the earlier work that motivated this revised
document.
Florian Weimer suggested to clarify wording regarding what data can
be stored in RRDATA portion of OpenPGP CERT RRs. Olivier Dubuisson
confirmed that the X.509 OID were indeed correct.
Appendix B. Copying conditions
In addition to the IETF/ISOC copying conditions, the following
statement grant third parties further rights to the parts of this
document ("the work") that were written by Simon Josefsson.
Copyright (C) 2004, 2005 Simon Josefsson
Copying and distribution of the work, with or without
modification, are permitted in any medium without royalty
provided the copyright notice and this notice are preserved.
Intellectual Property Statement Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights 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 might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
skipping to change at page 12, line 41 skipping to change at page 13, line 41
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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