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config.threads.in
+152
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@@ -0,0 +1,152 @@
#
# Begin pthreads checking.
#
# First, decide whether to use multithreading or not.
#
# Enable multithreading by default on systems where it is known
# to work well, and where debugging of multithreaded programs
# is supported.
#
AC_MSG_CHECKING(whether to build with thread support)
case $host in
*-dec-osf*)
use_threads=true ;;
[*-solaris2.[0-6]])
# Thread signals are broken on Solaris 2.6; they are sometimes
# delivered to the wrong thread.
use_threads=false ;;
*-solaris*)
use_threads=true ;;
*-ibm-aix*)
use_threads=true ;;
*-hp-hpux10*)
use_threads=false ;;
*-hp-hpux11*)
use_threads=true ;;
*-sgi-irix*)
use_threads=true ;;
*-sco-sysv*uw*|*-*-sysv*UnixWare*)
# UnixWare
use_threads=false ;;
*-*-sysv*OpenUNIX*)
# UnixWare
use_threads=true ;;
*-netbsd*)
if test -r /usr/lib/libpthread.so ; then
use_threads=true
else
# Socket I/O optimizations introduced in 9.2 expose a
# bug in unproven-pthreads; see PR #12650
use_threads=false
fi
;;
*-openbsd*)
# OpenBSD users have reported that named dumps core on
# startup when built with threads.
use_threads=false ;;
*-freebsd*)
use_threads=false ;;
*-bsdi[234]*)
# Thread signals do not work reliably on some versions of BSD/OS.
use_threads=false ;;
*-bsdi5*)
use_threads=true ;;
*-linux*)
# Threads are disabled on Linux by default because most
# Linux kernels produce unusable core dumps from multithreaded
# programs, and because of limitations in setuid().
use_threads=false ;;
*)
use_threads=false ;;
esac
AC_ARG_ENABLE(threads,
[ --enable-threads enable multithreading])
case "$enable_threads" in
yes)
use_threads=true
;;
no)
use_threads=false
;;
'')
# Use system-dependent default
;;
*)
AC_MSG_ERROR([--enable-threads takes yes or no])
;;
esac
if $use_threads
then
AC_MSG_RESULT(yes)
else
AC_MSG_RESULT(no)
fi
if $use_threads
then
#
# Search for / configure pthreads in a system-dependent fashion.
#
case "$host" in
*-netbsd*)
# NetBSD has multiple pthreads implementations. The
# recommended one to use is "unproven-pthreads". The
# older "mit-pthreads" may also work on some NetBSD
# versions. The PTL2 thread library does not
# currently work with bind9, but can be chosen with
# the --with-ptl2 option for those who wish to
# experiment with it.
CC="gcc"
AC_MSG_CHECKING(which NetBSD thread library to use)
AC_ARG_WITH(ptl2,
[ --with-ptl2 on NetBSD, use the ptl2 thread library (experimental)],
use_ptl2="$withval", use_ptl2="no")
: ${LOCALBASE:=/usr/pkg}
if test "X$use_ptl2" = "Xyes"
then
AC_MSG_RESULT(PTL2)
AC_MSG_WARN(
[linking with PTL2 is highly experimental and not expected to work])
CC=ptlgcc
else
if test -r /usr/lib/libpthread.so
then
AC_MSG_RESULT(native)
LIBS="-lpthread $LIBS"
else
if test ! -d $LOCALBASE/pthreads
then
AC_MSG_RESULT(none)
AC_MSG_ERROR("could not find thread libraries")
fi
if $use_threads
then
AC_MSG_RESULT(mit-pthreads/unproven-pthreads)
pkg="$LOCALBASE/pthreads"
lib1="-L$pkg/lib -Wl,-R$pkg/lib"
lib2="-lpthread -lm -lgcc -lpthread"
LIBS="$lib1 $lib2 $LIBS"
CPPFLAGS="$CPPFLAGS -I$pkg/include"
STD_CINCLUDES="$STD_CINCLUDES -I$pkg/include"
fi
fi
fi
;;
*)
AC_CHECK_LIB(pthread, pthread_create,,
AC_CHECK_LIB(pthread, __pthread_create,,
AC_CHECK_LIB(pthread, __pthread_create_system,,
AC_CHECK_LIB(c_r, pthread_create,,
AC_CHECK_LIB(c, pthread_create,,
AC_MSG_ERROR("could not find thread libraries"))))))
;;
esac
fi
doc/draft/draft-ietf-dnsext-dhcid-rr-09.txt
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DNSEXT M. Stapp
Internet-Draft Cisco Systems, Inc.
Expires: August 13, 2005 T. Lemon
A. Gustafsson
Nominum, Inc.
February 9, 2005
A DNS RR for Encoding DHCP Information (DHCID RR)
<draft-ietf-dnsext-dhcid-rr-09.txt>
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of Section 3 of RFC 3667. By submitting this Internet-Draft, each
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 become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 13, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
It is possible for multiple DHCP clients to attempt to update the
same DNS FQDN as they obtain DHCP leases. Whether the DHCP server or
the clients themselves perform the DNS updates, conflicts can arise.
To resolve such conflicts, "Resolution of DNS Name Conflicts" [1]
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proposes storing client identifiers in the DNS to unambiguously
associate domain names with the DHCP clients to which they refer.
This memo defines a distinct RR type for this purpose for use by DHCP
clients and servers, the "DHCID" RR.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The DHCID RR . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1 DHCID RDATA format . . . . . . . . . . . . . . . . . . . . 4
3.2 DHCID Presentation Format . . . . . . . . . . . . . . . . 4
3.3 The DHCID RR Type Codes . . . . . . . . . . . . . . . . . 4
3.4 Computation of the RDATA . . . . . . . . . . . . . . . . . 4
3.5 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.5.1 Example 1 . . . . . . . . . . . . . . . . . . . . . . 6
3.5.2 Example 2 . . . . . . . . . . . . . . . . . . . . . . 6
4. Use of the DHCID RR . . . . . . . . . . . . . . . . . . . . . 6
5. Updater Behavior . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1 Normative References . . . . . . . . . . . . . . . . . . . 8
9.2 Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . 10
Stapp, et al. Expires August 13, 2005 [Page 2]
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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 [2].
2. Introduction
A set of procedures to allow DHCP [7] clients and servers to
automatically update the DNS (RFC 1034 [3], RFC 1035 [4]) is proposed
in "Resolution of DNS Name Conflicts" [1].
Conflicts can arise if multiple DHCP clients wish to use the same DNS
name. To resolve such conflicts, "Resolution of DNS Name Conflicts"
[1] proposes storing client identifiers in the DNS to unambiguously
associate domain names with the DHCP clients using them. In the
interest of clarity, it is preferable for this DHCP information to
use a distinct RR type. This memo defines a distinct RR for this
purpose for use by DHCP clients or servers, the "DHCID" RR.
In order to avoid exposing potentially sensitive identifying
information, the data stored is the result of a one-way MD5 [5] hash
computation. The hash includes information from the DHCP client's
REQUEST message as well as the domain name itself, so that the data
stored in the DHCID RR will be dependent on both the client
identification used in the DHCP protocol interaction and the domain
name. This means that the DHCID RDATA will vary if a single client
is associated over time with more than one name. This makes it
difficult to 'track' a client as it is associated with various domain
names.
The MD5 hash algorithm has been shown to be weaker than the SHA-1
algorithm; it could therefore be argued that SHA-1 is a better
choice. However, SHA-1 is significantly slower than MD5. A
successful attack of MD5's weakness does not reveal the original data
that was used to generate the signature, but rather provides a new
set of input data that will produce the same signature. Because we
are using the MD5 hash to conceal the original data, the fact that an
attacker could produce a different plaintext resulting in the same
MD5 output is not significant concern.
3. The DHCID RR
The DHCID RR is defined with mnemonic DHCID and type code [TBD]. The
DHCID RR is only defined in the IN class. DHCID RRs cause no
additional section processing. The DHCID RR is not a singleton type.
Stapp, et al. Expires August 13, 2005 [Page 3]
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3.1 DHCID RDATA format
The RDATA section of a DHCID RR in transmission contains RDLENGTH
bytes of binary data. The format of this data and its interpretation
by DHCP servers and clients are described below.
DNS software should consider the RDATA section to be opaque. DHCP
clients or servers use the DHCID RR to associate a DHCP client's
identity with a DNS name, so that multiple DHCP clients and servers
may deterministically perform dynamic DNS updates to the same zone.
From the updater's perspective, the DHCID resource record RDATA
consists of a 16-bit identifier type, in network byte order, followed
by one or more bytes representing the actual identifier:
< 16 bits > DHCP identifier used
< n bytes > MD5 digest
3.2 DHCID Presentation Format
In DNS master files, the RDATA is represented as a single block in
base 64 encoding identical to that used for representing binary data
in RFC 2535 [8]. The data may be divided up into any number of white
space separated substrings, down to single base 64 digits, which are
concatenated to form the complete RDATA. These substrings can span
lines using the standard parentheses.
3.3 The DHCID RR Type Codes
The DHCID RR Type Code specifies what data from the DHCP client's
request was used as input into the hash function. The type codes are
defined in a registry maintained by IANA, as specified in Section 7.
The initial list of assigned values for the type code is:
0x0000 = htype, chaddr from a DHCPv4 client's DHCPREQUEST [7].
0x0001 = The data portion from a DHCPv4 client's Client Identifier
option [9].
0x0002 = The client's DUID (i.e., the data portion of a DHCPv6
client's Client Identifier option [10] or the DUID field from a
DHCPv4 client's Client Identifier option [12]).
0x0003 - 0xfffe = Available to be assigned by IANA.
0xffff = RESERVED
3.4 Computation of the RDATA
The DHCID RDATA is formed by concatenating the two type bytes with
Stapp, et al. Expires August 13, 2005 [Page 4]
Internet-Draft The DHCID RR February 2005
some variable-length identifying data.
< type > < data >
The RDATA for all type codes other than 0xffff, which is reserved for
future expansion, is formed by concatenating the two type bytes and a
16-byte MD5 hash value. The input to the hash function is defined to
be:
data = MD5(< identifier > < FQDN >)
The FQDN is represented in the buffer in unambiguous canonical form
as described in RFC 2535 [8], section 8.1. The type code and the
identifier are related as specified in Section 3.3: the type code
describes the source of the identifier.
When the updater is using the client's link-layer address as the
identifier, the first two bytes of the DHCID RDATA MUST be zero. To
generate the rest of the resource record, the updater computes a
one-way hash using the MD5 algorithm across a buffer containing the
client's network hardware type, link-layer address, and the FQDN
data. Specifically, the first byte of the buffer contains the
network hardware type as it appeared in the DHCP 'htype' field of the
client's DHCPREQUEST message. All of the significant bytes of the
chaddr field in the client's DHCPREQUEST message follow, in the same
order in which the bytes appear in the DHCPREQUEST message. The
number of significant bytes in the 'chaddr' field is specified in the
'hlen' field of the DHCPREQUEST message. The FQDN data, as specified
above, follows.
When the updater is using the DHCPv4 Client Identifier option sent by
the client in its DHCPREQUEST message, the first two bytes of the
DHCID RR MUST be 0x0001, in network byte order. The rest of the
DHCID RR MUST contain the results of computing an MD5 hash across the
payload of the option, followed by the FQDN. The payload of the
option consists of the bytes of the option following the option code
and length.
When the updater is using the DHCPv6 DUID sent by the client in its
REQUEST message, the first two bytes of the DHCID RR MUST be 0x0002,
in network byte order. The rest of the DHCID RR MUST contain the
results of computing an MD5 hash across the payload of the option,
followed by the FQDN. The payload of the option consists of the
bytes of the option following the option code and length.
3.5 Examples
Stapp, et al. Expires August 13, 2005 [Page 5]
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3.5.1 Example 1
A DHCP server allocating the IPv4 address 10.0.0.1 to a client with
Ethernet MAC address 01:02:03:04:05:06 using domain name
"client.example.com" uses the client's link-layer address to identify
the client. The DHCID RDATA is composed by setting the two type
bytes to zero, and performing an MD5 hash computation across a buffer
containing the Ethernet MAC type byte, 0x01, the six bytes of MAC
address, and the domain name (represented as specified in
Section 3.4).
client.example.com. A 10.0.0.1
client.example.com. DHCID AAAUMru0ZM5OK/PdVAJgZ/HU
3.5.2 Example 2
A DHCP server allocates the IPv4 address 10.0.12.99 to a client which
included the DHCP client-identifier option data 01:07:08:09:0a:0b:0c
in its DHCP request. The server updates the name "chi.example.com"
on the client's behalf, and uses the DHCP client identifier option
data as input in forming a DHCID RR. The DHCID RDATA is formed by
setting the two type bytes to the value 0x0001, and performing an MD5
hash computation across a buffer containing the seven bytes from the
client-id option and the FQDN (represented as specified in
Section 3.4).
chi.example.com. A 10.0.12.99
chi.example.com. DHCID AAHdd5jiQ3kEjANDm82cbObk\012
4. Use of the DHCID RR
This RR MUST NOT be used for any purpose other than that detailed in
"Resolution of DNS Name Conflicts" [1]. Although this RR contains
data that is opaque to DNS servers, the data must be consistent
across all entities that update and interpret this record.
Therefore, new data formats may only be defined through actions of
the DHC Working Group, as a result of revising [1].
5. Updater Behavior
The data in the DHCID RR allows updaters to determine whether more
than one DHCP client desires to use a particular FQDN. This allows
site administrators to establish policy about DNS updates. The DHCID
RR does not establish any policy itself.
Updaters use data from a DHCP client's request and the domain name
Stapp, et al. Expires August 13, 2005 [Page 6]
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that the client desires to use to compute a client identity hash, and
then compare that hash to the data in any DHCID RRs on the name that
they wish to associate with the client's IP address. If an updater
discovers DHCID RRs whose RDATA does not match the client identity
that they have computed, the updater SHOULD conclude that a different
client is currently associated with the name in question. The
updater SHOULD then proceed according to the site's administrative
policy. That policy might dictate that a different name be selected,
or it might permit the updater to continue.
6. Security Considerations
The DHCID record as such does not introduce any new security problems
into the DNS. In order to avoid exposing private information about
DHCP clients to public scrutiny, a one-way hash is used to obscure
all client information. In order to make it difficult to 'track' a
client by examining the names associated with a particular hash
value, the FQDN is included in the hash computation. Thus, the RDATA
is dependent on both the DHCP client identification data and on each
FQDN associated with the client.
Administrators should be wary of permitting unsecured DNS updates to
zones which are exposed to the global Internet. Both DHCP clients
and servers SHOULD use some form of update authentication (e.g., TSIG
[11]) when performing DNS updates.
7. IANA Considerations
IANA is requested to allocate an RR type number for the DHCID record
type.
This specification defines a new number-space for the 16-bit type
codes associated with the DHCID RR. IANA is requested to establish a
registry of the values for this number-space.
Three initial values are assigned in Section 3.3, and the value
0xFFFF is reserved for future use. New DHCID RR type codes are
tentatively assigned after the specification for the associated type
code, published as an Internet Draft, has received expert review by a
designated expert. The final assignment of DHCID RR type codes is
through Standards Action, as defined in RFC 2434 [6].
8. Acknowledgements
Many thanks to Josh Littlefield, Olafur Gudmundsson, Bernie Volz, and
Ralph Droms for their review and suggestions.
Stapp, et al. Expires August 13, 2005 [Page 7]
Internet-Draft The DHCID RR February 2005
9. References
9.1 Normative References
[1] Stapp, M. and B. Volz, "Resolution of DNS Name Conflicts Among
DHCP Clients (draft-ietf-dhc-dns-resolution-*)", July 2004.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[4] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April
1992.
[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
9.2 Informative References
[7] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[8] Eastlake, D., "Domain Name System Security Extensions",
RFC 2535, March 1999.
[9] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[10] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[11] Vixie, P., Gudmundsson, O., Eastlake, D. and B. Wellington,
"Secret Key Transaction Authentication for DNS (TSIG)",
RFC 2845, May 2000.
[12] Lemon, T. and B. Sommerfeld, "Node-Specific Client Identifiers
for DHCPv4 (draft-ietf-dhc-3315id-for-v4-*)", February 2004.
Stapp, et al. Expires August 13, 2005 [Page 8]
Internet-Draft The DHCID RR February 2005
Authors' Addresses
Mark Stapp
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
Phone: 978.936.1535
Email: mjs@cisco.com
Ted Lemon
Nominum, Inc.
950 Charter St.
Redwood City, CA 94063
USA
Email: mellon@nominum.com
Andreas Gustafsson
Nominum, Inc.
950 Charter St.
Redwood City, CA 94063
USA
Email: gson@nominum.com
Stapp, et al. Expires August 13, 2005 [Page 9]
Internet-Draft The DHCID RR February 2005
Intellectual Property Statement
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 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.
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 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.
Copyright Statement
Copyright (C) The Internet Society (2005). 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Stapp, et al. Expires August 13, 2005 [Page 10]
doc/draft/draft-ietf-dnsext-dnssec-experiments-00.txt
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Network Working Group D. Blacka
Internet-Draft Verisign, Inc.
Expires: August 3, 2005 February 2, 2005
DNSSEC Experiments
draft-ietf-dnsext-dnssec-experiments-00
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each
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 become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 3, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
In the long history of the development of the DNS security [1]
extensions (DNSSEC), a number of alternate methodologies and
modifications have been proposed and rejected for practical, rather
than strictly technical, reasons. There is a desire to be able to
experiment with these alternate methods in the public DNS. This
document describes a methodology for deploying alternate,
non-backwards-compatible, DNSSEC methodologies in an experimental
fashion without disrupting the deployment of standard DNSSEC.
Blacka Expires August 3, 2005 [Page 1]
Internet-Draft DNSSEC Experiments February 2005
Table of Contents
1. Definitions and Terminology . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Experiments . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Defining an Experiment . . . . . . . . . . . . . . . . . . . 8
6. Considerations . . . . . . . . . . . . . . . . . . . . . . . 9
7. Transitions . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1 Normative References . . . . . . . . . . . . . . . . . . . 13
10.2 Informative References . . . . . . . . . . . . . . . . . . 13
Editorial Comments . . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . 15
Blacka Expires August 3, 2005 [Page 2]
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1. Definitions and Terminology
Throughout this document, familiarity with the DNS system (RFC 1035
[4]) and the DNS security extensions ([1], [2], and [3].
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 [5].
Blacka Expires August 3, 2005 [Page 3]
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2. Overview
Historically, experimentation with DNSSEC alternatives has been a
problematic endeavor. There has typically been a desire to both
introduce non-backwards-compatible changes to DNSSEC, and to try
these changes on real zones in the public DNS. This creates a
problem when the change to DNSSEC would make all or part of the zone
using those changes appear bogus or otherwise broken to existing
DNSSEC-aware resolvers.
This document describes a standard methodology for setting up public
DNSSEC experiments. This methodology addresses the issue of
co-existence with standard DNSSEC and DNS by using unknown algorithm
identifiers to hide the experimental DNSSEC protocol modifications
from standard DNSSEC-aware resolvers.
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3. Experiments
When discussing DNSSEC experiments, it is necessary to classify these
experiments into two broad categories:
Backwards-Compatible: describes experimental changes that, while not
strictly adhering to the DNSSEC standard, are nonetheless
interoperable with clients and server that do implement the DNSSEC
standard.
Non-Backwards-Compatible: describes experiments that would cause a
standard DNSSEC-aware resolver to (incorrectly) determine that all
or part of a zone is bogus, or to otherwise not interoperable with
standard DNSSEC clients and servers.
Not included in these terms are experiments with the core DNS
protocol itself.
The methodology described in this document is not necessary for
backwards-compatible experiments, although it certainly could be used
if desired.
Note that, in essence, this metholodolgy would also be used to
introduce a new DNSSEC algorithm, independently from any DNSSEC
experimental protocol change.
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4. Method
The core of the methodology is the use of only "unknown" algorithms
to sign the experimental zone, and more importantly, having only
unknown algorithm DS records for the delegation to the zone at the
parent.
This technique works because of the way DNSSEC-compliant validators
are expected to work in the presence of a DS set with only unknown
algorithms. From [3], Section 5.2:
If the validator does not support any of the algorithms listed in
an authenticated DS RRset, then the resolver has no supported
authentication path leading from the parent to the child. The
resolver should treat this case as it would the case of an
authenticated NSEC RRset proving that no DS RRset exists, as
described above.
And further:
If the resolver does not support any of the algorithms listed in
an authenticated DS RRset, then the resolver will not be able to
verify the authentication path to the child zone. In this case,
the resolver SHOULD treat the child zone as if it were unsigned.
While this behavior isn't strictly mandatory (as marked by MUST), it
is unlikely that a validator would not implement the behavior, or,
more to the point, it will not violate this behavior in an unsafe way
(see below (Section 6).)
Because we are talking about experiments, it is recommended that
private algorithm numbers be used (see [2], appendix A.1.1
[Comment.1].) Normally, instead of actually inventing new signing
algorithms, the recommended path is to create alternate algorithm
identifiers that are aliases for the existing, known algorithms.
While, strictly speaking, it is only necessary to create an alternate
identifier for the mandatory algorithms (currently, this is only
algorithm 5, RSASHA1), it is RECOMMENDED that all OPTIONAL defined
algorithms be aliased as well.
It is RECOMMENDED that for a particular DNSSEC experiment, a
particular domain name base is chosen for all new algorithms, then
the algorithm number (or name) is prepended to it. For example, for
experiment A, the base name of "dnssec-experiment-a.example.com" is
chosen. Then, aliases for algorithms 3 (DSA) and 5 (RSASHA1) are
defined to be "3.dnssec-experiment-a.example.com" and
"5.dnssec-experiment-a.example.com". However, any unique identifier
will suffice.
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Using this method, resolvers (or, more specificially, DNSSEC
validators) essentially indicate their ability to understand the
DNSSEC experiment's semantics by understanding what the new algorithm
identifiers signify.
This method creates two classes of DNSSEC-aware servers and
resolvers: servers and resolvers that are aware of the experiment
(and thus recognize the experiments algorithm identifiers and
experimental semantics), and servers and resolvers that are unware of
the experiment.
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5. Defining an Experiment
The DNSSEC experiment must define the particular set of (previously
unknown) algorithms that identify the experiment, and define what
each unknown algorithm identifier means. Typically, unless the
experiment is actually experimenting with a new DNSSEC algorithm,
this will be a mapping of private algorithm identifiers to existing,
known algorithms.
Typically, the experiment will choose a DNS name as the algorithm
identifier base. This DNS name SHOULD be under the control of the
authors of the experiment. Then the experiment will define a mapping
between known mandatory and optional algorithms into this private
algorithm identifier space. Alternately, the experiment MAY use the
OID private algorithm space instead (using algorithm number 254), or
may choose non-private algorithm numbers, although this would require
an IANA allocation (see below (Section 9).)
For example, an experiment might specify in its description the DNS
name "dnssec-experiment-a.example.com" as the base name, and provide
the mapping of "3.dnssec-experiment-a.example.com" is an alias of
DNSSEC algorithm 3 (DSA), and "5.dnssec-experiment-a.example.com" is
an alias of DNSSEC algorithm 5 (RSASHA1).
Resolvers MUST then only recognize the experiment's semantics when
present in a zone signed by one or more of these private algorithms.
In general, however, resolvers involved in the experiment are
expected to understand both standard DNSSEC and the defined
experimental DNSSEC protocol, although this isn't, strictly speaking,
required.
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6. Considerations
There are a number of considerations with using this methodology.
1. Under some circumstances, it may be that the experiment will not
be sufficiently masked by this technique and may cause resolution
problem for resolvers not aware of the experiment. For instance,
the resolver may look at the not validatable response and
conclude that the response is bogus, either due to local policy
or implementation details. This is not expected to be the common
case, however.
2. It will, in general, not be possible for DNSSEC-aware resolvers
not aware of the experiment to build a chain of trust through an
experimental zone.
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7. Transitions
If an experiment is successful, there may be a desire to move the
experiment to a standards-track extension. One way to do so would be
to move from private algorithm numbers to IANA allocated algorithm
numbers, with otherwise the same meaning. This would still leave a
divide between resolvers that understood the extension versus
resolvers that did not. It would, in essence, create an additional
version of DNSSEC.
An alternate technique might be to do a typecode rollover, thus
actually creating a definitive new version of DNSSEC. There may be
other transition techniques available, as well.
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8. Security Considerations
Zones using this methodology will be considered insecure by all
resolvers except those aware of the experiment. It is not generally
possible to create a secure delegation from an experimental zone that
will be followed by resolvers unaware of the experiment.
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9. IANA Considerations
IANA may need to allocate new DNSSEC algorithm numbers if that
transition approach is taken, or the experiment decides to use
allocated numbers to begin with. No IANA action is required to
deploy an experiment using private algorithm identifiers.
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10. References
10.1 Normative References
[1] Arends, R., Austein, R., Massey, D., Larson, M. and S. Rose,
"DNS Security Introduction and Requirements",
draft-ietf-dnsext-dnssec-intro-13 (work in progress), October
2004.
[2] Arends, R., "Resource Records for the DNS Security Extensions",
draft-ietf-dnsext-dnssec-records-11 (work in progress), October
2004.
[3] Arends, R., "Protocol Modifications for the DNS Security
Extensions", draft-ietf-dnsext-dnssec-protocol-09 (work in
progress), October 2004.
10.2 Informative References
[4] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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Editorial Comments
[Comment.1] Note: how private algorithms work in DNSSEC is not well
explained in the DNSSECbis RFCs. In particular, how to
validate that the DS records contain only unknown
algorithms is not explained at all.
Author's Address
David Blacka
Verisign, Inc.
21355 Ridgetop Circle
Dulles, VA 20166
US
Phone: +1 703 948 3200
EMail: davidb@verisign.com
URI: http://www.verisignlabs.com
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Acknowledgment
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DNS Extensions Working Group R. Arends
Internet-Draft Telematica Instituut
Expires: August 25, 2005 P. Koch
DENIC eG
J. Schlyter
NIC-SE
February 21, 2005
Evaluating DNSSEC Transition Mechanisms
draft-ietf-dnsext-dnssec-trans-02.txt
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of Section 3 of RFC 3667. By submitting this Internet-Draft, each
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 become aware will be disclosed, in accordance with
RFC 3668.
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Internet-Drafts are draft documents valid for a maximum of six months
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The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on August 25, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document collects and summarizes different proposals for
alternative and additional strategies for authenticated denial in DNS
responses, evaluates these proposals and gives a recommendation for a
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way forward.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Transition Mechanisms . . . . . . . . . . . . . . . . . . . . 3
2.1 Mechanisms With Need of Updating DNSSEC-bis . . . . . . . 4
2.1.1 Dynamic NSEC Synthesis . . . . . . . . . . . . . . . . 4
2.1.2 Add Versioning/Subtyping to Current NSEC . . . . . . . 5
2.1.3 Type Bit Map NSEC Indicator . . . . . . . . . . . . . 6
2.1.4 New Apex Type . . . . . . . . . . . . . . . . . . . . 6
2.1.5 NSEC White Lies . . . . . . . . . . . . . . . . . . . 7
2.1.6 NSEC Optional via DNSSKEY Flag . . . . . . . . . . . . 8
2.1.7 New Answer Pseudo RR Type . . . . . . . . . . . . . . 9
2.1.8 SIG(0) Based Authenticated Denial . . . . . . . . . . 9
2.2 Mechanisms Without Need of Updating DNSSEC-bis . . . . . . 10
2.2.1 Partial Type-code and Signal Rollover . . . . . . . . 10
2.2.2 A Complete Type-code and Signal Rollover . . . . . . . 11
2.2.3 Unknown Algorithm in RRSIG . . . . . . . . . . . . . . 11
3. Recommendation . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1 Normative References . . . . . . . . . . . . . . . . . . . 13
5.2 Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . 15
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1. Introduction
This report shall document the process of dealing with the NSEC
walking problem late in the Last Call for
[I-D.ietf-dnsext-dnssec-intro, I-D.ietf-dnsext-dnssec-protocol,
I-D.ietf-dnsext-dnssec-records]. It preserves some of the discussion
that took place in the DNSEXT WG during the first half of June 2004
as well as some additional ideas that came up subsequently.
This is an edited excerpt of the chairs' mail to the WG:
The working group consents on not including NSEC-alt in the
DNSSEC-bis documents. The working group considers to take up
"prevention of zone enumeration" as a work item.
There may be multiple mechanisms to allow for co-existence with
DNSSEC-bis. The chairs allow the working group a little over a
week (up to June 12, 2004) to come to consensus on a possible
modification to the document to enable gentle rollover. If that
consensus cannot be reached the DNSSEC-bis documents will go out
as-is.
To ease the process of getting consensus, a summary of the proposed
solutions and analysis of the pros and cons were written during the
weekend.
This summary includes:
An inventory of the proposed mechanisms to make a transition to
future work on authenticated denial of existence.
List the known Pros and Cons, possibly provide new arguments, and
possible security considerations of these mechanisms.
Provide a recommendation on a way forward that is least disruptive
to the DNSSEC-bis specifications as they stand and keep an open
path to other methods for authenticated denial of existence.
The descriptions of the proposals in this document are coarse and do
not cover every detail necessary for implementation. In any case,
documentation and further study is needed before implementaion and/or
deployment, including those which seem to be solely operational in
nature.
2. Transition Mechanisms
In the light of recent discussions and past proposals, we have found
several ways to allow for transition to future expansion of
authenticated denial. We tried to illuminate the paths and pitfalls
in these ways forward. Some proposals lead to a versioning of
DNSSEC, where DNSSEC-bis may co-exist with DNSSEC-ter, other
proposals are 'clean' but may cause delay, while again others may be
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plain hacks.
Some paths do not introduce versioning, and might require the current
DNSSEC-bis documents to be fully updated to allow for extensions to
authenticated denial mechanisms. Other paths introduce versioning
and do not (or minimally) require DNSSEC-bis documents to be updated,
allowing DNSSEC-bis to be deployed, while future versions can be
drafted independent from or partially depending on DNSSEC-bis.
2.1 Mechanisms With Need of Updating DNSSEC-bis
Mechanisms in this category demand updates to the DNSSEC-bis document
set.
2.1.1 Dynamic NSEC Synthesis
This proposal assumes that NSEC RRs and the authenticating RRSIG will
be generated dynamically to just cover the (non existent) query name.
The owner name is (the) one preceding the name queried for, the Next
Owner Name Field has the value of the Query Name Field + 1 (first
successor in canonical ordering). A separate key (the normal ZSK or
a separate ZSK per authoritative server) would be used for RRSIGs on
NSEC RRs. This is a defense against enumeration, though it has the
presumption of online signing.
2.1.1.1 Coexistence and Migration
There is no change in interpretation other then that the next owner
name might or might not exist.
2.1.1.2 Limitations
This introduces an unbalanced cost between query and response
generation due to dynamic generation of signatures.
2.1.1.3 Amendments to DNSSEC-bis
The current DNSSEC-bis documents might need to be updated to indicate
that the next owner name might not be an existing name in the zone.
This is not a real change to the spec since implementers have been
warned not to synthesize with previously cached NSEC records. A
specific bit to identify the dynamic signature generating key might
be useful as well, to prevent it from being used to fake positive
data.
2.1.1.4 Cons
Unbalanced cost is a ground for DDoS. Though this protects against
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enumeration, it is not really a path for versioning.
2.1.1.5 Pros
Hardly any amendments to DNSSEC-bis.
2.1.2 Add Versioning/Subtyping to Current NSEC
This proposal introduces versioning for the NSEC RR type (a.k.a.
subtyping) by adding a (one octet) version field to the NSEC RDATA.
Version number 0 is assigned to the current (DNSSEC-bis) meaning,
making this an 'Must Be Zero' (MBZ) for the to be published docset.
2.1.2.1 Coexistence and Migration
Since the versioning is done inside the NSEC RR, different versions
may coexist. However, depending on future methods, that may or may
not be useful inside a single zone. Resolvers cannot ask for
specific NSEC versions but may be able to indicate version support by
means of a to be defined EDNS option bit.
2.1.2.2 Limitations
There are no technical limitations, though it will cause delay to
allow testing of the (currently unknown) new NSEC interpretation.
Since the versioning and signaling is done inside the NSEC RR, future
methods will likely be restricted to a single RR type authenticated
denial (as opposed to e.g. NSEC-alt, which currently proposes three
RR types).
2.1.2.3 Amendments to DNSSEC-bis
Full Update of the current DNSSEC-bis documents to provide for new
fields in NSEC, while specifying behavior in case of unknown field
values.
2.1.2.4 Cons
Though this is a clean and clear path without versioning DNSSEC, it
takes some time to design, gain consensus, update the current
dnssec-bis document, test and implement a new authenticated denial
record.
2.1.2.5 Pros
Does not introduce an iteration to DNSSEC while providing a clear and
clean migration strategy.
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2.1.3 Type Bit Map NSEC Indicator
Bits in the type-bit-map are reused or allocated to signify the
interpretation of NSEC.
This proposal assumes that future extensions make use of the existing
NSEC RDATA syntax, while it may need to change the interpretation of
the RDATA or introduce an alternative denial mechanism, invoked by
the specific type-bit-map-bits.
2.1.3.1 Coexistence and migration
Old and new NSEC meaning could coexist, depending how the signaling
would be defined. The bits for NXT, NSEC, RRSIG or other outdated RR
types are available as well as those covering meta/query types or
types to be specifically allocated.
2.1.3.2 Limitations
This mechanism uses an NSEC field that was not designed for that
purpose. Similar methods were discussed during the Opt-In discussion
and the Silly-State discussion.
2.1.3.3 Amendments to DNSSEC-bis
The specific type-bit-map-bits must be allocated and they need to be
specified as 'Must Be Zero' (MBZ) when used for standard (dnssec-bis)
interpretation. Also, behaviour of the resolver and validator must
be documented in case unknown values are encountered for the MBZ
field. Currently the protocol document specifies that the validator
MUST ignore the setting of the NSEC and the RRSIG bits, while other
bits are only used for the specific purpose of the type-bit-map field
2.1.3.4 Cons
The type-bit-map was not designed for this purpose. It is a
straightforward hack. Text in protocol section 5.4 was put in
specially to defend against this usage.
2.1.3.5 Pros
No change needed to the on-the-wire protocol as specified in the
current docset.
2.1.4 New Apex Type
This introduces a new Apex type (parallel to the zone's SOA)
indicating the DNSSEC version (or authenticated denial) used in or
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for this zone.
2.1.4.1 Coexistence and Migration
Depending on the design of this new RR type multiple denial
mechanisms may coexist in a zone. Old validators will not understand
and thus ignore the new type, so interpretation of the new NSEC
scheme may fail, negative responses may appear 'bogus'.
2.1.4.2 Limitations
A record of this kind is likely to carry additional
feature/versioning indications unrelated to the current question of
authenticated denial.
2.1.4.3 Amendments to DNSSEC-bis
The current DNSSEC-bis documents need to be updated to indicate that
the absence of this type indicates dnssec-bis, and that the (mere)
presence of this type indicated unknown versions.
2.1.4.4 Cons
The only other 'zone' or 'apex' record is the SOA record. Though
this proposal is not new, it is yet unknown how it might fulfill
authenticated denial extensions. This new RR type would only provide
for a generalized signaling mechanism, not the new authenticated
denial scheme. Since it is likely to be general in nature, due to
this generality consensus is not to be reached soon.
2.1.4.5 Pros
This approach would allow for a lot of other per zone information to
be transported or signaled to both (slave) servers and resolvers.
2.1.5 NSEC White Lies
This proposal disables one part of NSEC (the pointer part) by means
of a special target (root, apex, owner, ...), leaving intact only the
ability to authenticate denial of existence of RR sets, not denial of
existence of domain names (NXDOMAIN). It may be necessary to have
one working NSEC to prove the absence of a wildcard.
2.1.5.1 Coexistence and Migration
The NSEC target can be specified per RR, so standard NSEC and 'white
lie' NSEC can coexist in a zone. There is no need for migration
because no versioning is introduced or intended.
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2.1.5.2 Limitations
This proposal breaks the protocol and is applicable to certain types
of zones only (no wildcard, no deep names, delegation only). Most of
the burden is put on the resolver side and operational consequences
are yet to be studied.
2.1.5.3 Amendments to DNSSEC-bis
The current DNSSEC-bis documents need to be updated to indicate that
the NXDOMAIN responses may be insecure.
2.1.5.4 Cons
Strictly speaking this breaks the protocol and doesn't fully fulfill
the requirements for authenticated denial of existence. Security
implications need to be carefully documented: search path problems
(forged denial of existence may lead to wrong expansion of non-FQDNs
[RFC1535]) and replay attacks to deny existence of records.
2.1.5.5 Pros
Hardly any amendments to DNSSEC-bis. Operational "trick" that is
available anyway.
2.1.6 NSEC Optional via DNSSKEY Flag
A new DNSKEY may be defined to declare NSEC optional per zone.
2.1.6.1 Coexistence and Migration
Current resolvers/validators will not understand the Flag bit and
will have to treat negative responses as bogus. Otherwise, no
migration path is needed since NSEC is simply turned off.
2.1.6.2 Limitations
NSEC can only be made completely optional at the cost of being unable
to prove unsecure delegations (absence of a DS RR [RFC3658]). A next
to this approach would just disable authenticated denial for
non-existence of nodes.
2.1.6.3 Amendments to DNSSEC-bis
New DNSKEY Flag to be defined. Resolver/Validator behaviour needs to
be specified in the light of absence of authenticated denial.
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2.1.6.4 Cons
Doesn't fully meet requirements. Operational consequences to be
studied.
2.1.6.5 Pros
Official version of the "trick" presented in (8). Operational
problems can be addressed during future work on validators.
2.1.7 New Answer Pseudo RR Type
A new pseudo RR type may be defined that will be dynamically created
(and signed) by the responding authoritative server. The RR in the
response will cover the QNAME, QCLASS and QTYPE and will authenticate
both denial of existence of name (NXDOMAIN) or RRset.
2.1.7.1 Coexistence and Migration
Current resolvers/validators will not understand the pseudo RR and
will thus not be able to process negative responses so testified. A
signaling or solicitation method would have to be specified.
2.1.7.2 Limitations
This method can only be used with online keys and online signing
capacity.
2.1.7.3 Amendments to DNSSEC-bis
Signaling method needs to be defined.
2.1.7.4 Cons
Keys have to be held and processed online with all security
implications. An additional flag for those keys identifying them as
online or negative answer only keys should be considered.
2.1.7.5 Pros
Expands DNSSEC authentication to the RCODE.
2.1.8 SIG(0) Based Authenticated Denial
2.1.8.1 Coexistence and Migration
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2.1.8.2 Limitations
2.1.8.3 Amendments to DNSSEC-bis
2.1.8.4 Cons
2.1.8.5 Pros
2.2 Mechanisms Without Need of Updating DNSSEC-bis
2.2.1 Partial Type-code and Signal Rollover
Carefully crafted type code/signal rollover to define a new
authenticated denial space that extends/replaces DNSSEC-bis
authenticated denial space. This particular path is illuminated by
Paul Vixie in a Message-Id <20040602070859.0F50913951@sa.vix.com>
posted to <namedroppers@ops.ietf.org> 2004-06-02.
2.2.1.1 Coexistence and Migration
To protect the current resolver for future versions, a new DNSSEC-OK
bit must be allocated to make clear it does or does not understand
the future version. Also, a new DS type needs to be allocated to
allow differentiation between a current signed delegation and a
'future' signed delegation. Also, current NSEC needs to be rolled
into a new authenticated denial type.
2.2.1.2 Limitations
None.
2.2.1.3 Amendments to DNSSEC-bis
None.
2.2.1.4 Cons
It is cumbersome to carefully craft an TCR that 'just fits'. The
DNSSEC-bis protocol has many 'borderline' cases that needs special
consideration. It might be easier to do a full TCR, since a few of
the types and signals need upgrading anyway.
Arends, et al. Expires August 25, 2005 [Page 10]
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2.2.1.5 Pros
Graceful adoption of future versions of NSEC, while there are no
amendments to DNSSEC-bis.
2.2.2 A Complete Type-code and Signal Rollover
A new DNSSEC space is defined which can exist independent of current
DNSSEC-bis space.
This proposal assumes that all current DNSSEC type-codes
(RRSIG/DNSKEY/NSEC/DS) and signals (DNSSEC-OK) are not used in any
future versions of DNSSEC. Any future version of DNSSEC has its own
types to allow for keys, signatures, authenticated denial, etcetera.
2.2.2.1 Coexistence and Migration
Both spaces can co-exist. They can be made completely orthogonal.
2.2.2.2 Limitations
None.
2.2.2.3 Amendments to DNSSEC-bis
None.
2.2.2.4 Cons
With this path we abandon the current DNSSEC-bis. Though it is easy
to role specific well-known and well-tested parts into the re-write,
once deployment has started this path is very expensive for
implementers, registries, registrars and registrants as well as
resolvers/users. A TCR is not to be expected to occur frequently, so
while a next generation authenticated denial may be enabled by a TCR,
it is likely that that TCR will only be agreed upon if it serves a
whole basket of changes or additions. A quick introduction of
NSEC-ng should not be expected from this path.
2.2.2.5 Pros
No amendments/changes to current DNSSEC-bis docset needed. It is
always there as last resort.
2.2.3 Unknown Algorithm in RRSIG
This proposal assumes that future extensions make use of the existing
NSEC RDATA syntax, while it may need to change the interpretation of
Arends, et al. Expires August 25, 2005 [Page 11]
Internet-Draft Evaluating DNSSEC Transition Mechanisms February 2005
the RDATA or introduce an alternative denial mechanism, invoked by
the specific unknown signing algorithm. The different interpretation
would be signaled by use of different signature algorithms in the
RRSIG records covering the NSEC RRs.
When an entire zone is signed with a single unknown algorithm, it
will cause implementations that follow current dnssec-bis documents
to treat individual RRsets as unsigned.
2.2.3.1 Coexistence and migration
Old and new NSEC RDATA interpretation or known and unknown Signatures
can NOT coexist in a zone since signatures cover complete (NSEC)
RRSets.
2.2.3.2 Limitations
Validating resolvers agnostic of new interpretation will treat the
NSEC RRset as "not signed". This affects wildcard and non-existence
proof, as well as proof for (un)secured delegations. Also, all
positive signatures (RRSIGs on RRSets other than DS, NSEC) appear
insecure/bogus to an old validator.
The algorithm version space is split for each future version of
DNSSEC. Violation of the 'modular components' concept. We use the
'validator' to protect the 'resolver' from unknown interpretations.
2.2.3.3 Amendments to DNSSEC-bis
None.
2.2.3.4 Cons
The algorithm field was not designed for this purpose. This is a
straightforward hack.
2.2.3.5 Pros
No amendments/changes to current DNSSEC-bis docset needed.
3. Recommendation
The authors recommend that the working group commits to and starts
work on a partial TCR, allowing graceful transition towards a future
version of NSEC. Meanwhile, to accomodate the need for an
immediately, temporary, solution against zone-traversal, we recommend
On-Demand NSEC synthesis.
Arends, et al. Expires August 25, 2005 [Page 12]
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This approach does not require any mandatory changes to DNSSEC-bis,
does not violate the protocol and fulfills the requirements. As a
side effect, it moves the cost of implementation and deployment to
the users (zone owners) of this mechanism.
4. Acknowledgements
The authors would like to thank Sam Weiler and Mark Andrews for their
input and constructive comments.
5. References
5.1 Normative References
[I-D.ietf-dnsext-dnssec-intro]
Arends, R., Austein, R., Massey, D., Larson, M. and S.
Rose, "DNS Security Introduction and Requirements",
Internet-Draft draft-ietf-dnsext-dnssec-intro-13, October
2004.
[I-D.ietf-dnsext-dnssec-protocol]
Arends, R., "Protocol Modifications for the DNS Security
Extensions",
Internet-Draft draft-ietf-dnsext-dnssec-protocol-09,
October 2004.
[I-D.ietf-dnsext-dnssec-records]
Arends, R., "Resource Records for the DNS Security
Extensions",
Internet-Draft draft-ietf-dnsext-dnssec-records-11,
October 2004.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2931] Eastlake, D., "DNS Request and Transaction Signatures (
SIG(0)s)", RFC 2931, September 2000.
5.2 Informative References
[RFC1535] Gavron, E., "A Security Problem and Proposed Correction
With Widely Deployed DNS Software", RFC 1535, October
1993.
[RFC2535] Eastlake, D., "Domain Name System Security Extensions",
Arends, et al. Expires August 25, 2005 [Page 13]
Internet-Draft Evaluating DNSSEC Transition Mechanisms February 2005
RFC 2535, March 1999.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC3658] Gudmundsson, O., "Delegation Signer (DS) Resource Record
(RR)", RFC 3658, December 2003.
Authors' Addresses
Roy Arends
Telematica Instituut
Brouwerijstraat 1
Enschede 7523 XC
The Netherlands
Phone: +31 53 4850485
Email: roy.arends@telin.nl
Peter Koch
DENIC eG
Wiesenh"uttenplatz 26
Frankfurt 60329
Germany
Phone: +49 69 27235 0
Email: pk@DENIC.DE
Jakob Schlyter
NIC-SE
Box 5774
Stockholm SE-114 87
Sweden
Email: jakob@nic.se
URI: http://www.nic.se/
Arends, et al. Expires August 25, 2005 [Page 14]
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This document and the information contained herein are provided on an
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
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Arends, et al. Expires August 25, 2005 [Page 15]
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+930
View File
@@ -0,0 +1,930 @@
INTERNET-DRAFT ECC Keys in the DNS
Expires: June 2005 December 2004
Elliptic Curve KEYs in the DNS
-------- ----- ---- -- --- ---
<draft-ietf-dnsext-ecc-key-06.txt>
Richard C. Schroeppel
Donald Eastlake 3rd
Status of This Document
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
or will be disclosed, and any of which I become aware will be
disclosed, in accordance with RFC 3668.
This draft is intended to be become a Proposed Standard RFC.
Distribution of this document is unlimited. Comments should be sent
to the DNS mailing list <namedroppers@ops.ietf.org>.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than a "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Abstract
The standard method for storing elliptic curve cryptographic keys and
signatures in the Domain Name System is specified.
Copyright Notice
Copyright (C) The Internet Society. All Rights Reserved.
R. Schroeppel, et al [Page 1]
INTERNET-DRAFT ECC Keys in the DNS
Acknowledgement
The assistance of Hilarie K. Orman in the production of this document
is greatfully acknowledged.
Table of Contents
Status of This Document....................................1
Abstract...................................................1
Copyright Notice...........................................1
Acknowledgement............................................2
Table of Contents..........................................2
1. Introduction............................................3
2. Elliptic Curve Data in Resource Records.................3
3. The Elliptic Curve Equation.............................9
4. How do I Compute Q, G, and Y?..........................10
5. Elliptic Curve SIG Resource Records....................11
6. Performance Considerations.............................13
7. Security Considerations................................13
8. IANA Considerations....................................13
Copyright and Disclaimer..................................14
Informational References..................................15
Normative Refrences.......................................15
Author's Addresses........................................16
Expiration and File Name..................................16
R. Schroeppel, et al [Page 2]
INTERNET-DRAFT ECC Keys in the DNS
1. Introduction
The Domain Name System (DNS) is the global hierarchical replicated
distributed database system for Internet addressing, mail proxy, and
other information. The DNS has been extended to include digital
signatures and cryptographic keys as described in [RFC intro,
protocol, records].
This document describes how to store elliptic curve cryptographic
(ECC) keys and signatures in the DNS so they can be used for a
variety of security purposes. Familiarity with ECC cryptography is
assumed [Menezes].
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].
2. Elliptic Curve Data in Resource Records
Elliptic curve public keys are stored in the DNS within the RDATA
portions of key RRs, such as RRKEY and KEY [RFC records] RRs, with
the structure shown below.
The research world continues to work on the issue of which is the
best elliptic curve system, which finite field to use, and how to
best represent elements in the field. So, representations are
defined for every type of finite field, and every type of elliptic
curve. The reader should be aware that there is a unique finite
field with a particular number of elements, but many possible
representations of that field and its elements. If two different
representations of a field are given, they are interconvertible with
a tedious but practical precomputation, followed by a fast
computation for each field element to be converted. It is perfectly
reasonable for an algorithm to work internally with one field
representation, and convert to and from a different external
representation.
R. Schroeppel, et al [Page 3]
INTERNET-DRAFT ECC Keys in the DNS
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S M -FMT- A B Z|
+-+-+-+-+-+-+-+-+
| LP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| P (length determined from LP) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LF |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| F (length determined from LF) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DEG |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DEGH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DEGI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DEGJ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TRDV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| LH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| H (length determined from LH) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| LK |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| K (length determined from LK) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LQ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Q (length determined from LQ) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| A (length determined from LA) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ALTA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LB |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| B (length determined from LB) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C (length determined from LC) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LG |
R. Schroeppel, et al [Page 4]
INTERNET-DRAFT ECC Keys in the DNS
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G (length determined from LG) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LY |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Y (length determined from LY) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
SMFMTABZ is a flags octet as follows:
S = 1 indicates that the remaining 7 bits of the octet selects
one of 128 predefined choices of finite field, element
representation, elliptic curve, and signature parameters.
MFMTABZ are omitted, as are all parameters from LP through G.
LY and Y are retained.
If S = 0, the remaining parameters are as in the picture and
described below.
M determines the type of field underlying the elliptic curve.
M = 0 if the field is a GF[2^N] field;
M = 1 if the field is a (mod P) or GF[P^D] field with P>2.
FMT is a three bit field describing the format of the field
representation.
FMT = 0 for a (mod P) field.
> 0 for an extension field, either GF[2^D] or GF[P^D].
The degree D of the extension, and the field polynomial
must be specified. The field polynomial is always monic
(leading coefficient 1.)
FMT = 1 The field polynomial is given explicitly; D is implied.
If FMT >=2, the degree D is given explicitly.
= 2 The field polynomial is implicit.
= 3 The field polynomial is a binomial. P>2.
= 4 The field polynomial is a trinomial.
= 5 The field polynomial is the quotient of a trinomial by a
short polynomial. P=2.
= 6 The field polynomial is a pentanomial. P=2.
Flags A and B apply to the elliptic curve parameters.
R. Schroeppel, et al [Page 5]
INTERNET-DRAFT ECC Keys in the DNS
A = 1 When P>=5, the curve parameter A is negated. If P=2, then
A=1 indicates that the A parameter is special. See the
ALTA parameter below, following A. The combination A=1,
P=3 is forbidden.
B = 1 When P>=5, the curve parameter B is negated. If P=2 or 3,
then B=1 indicates an alternate elliptic curve equation is
used. When P=2 and B=1, an additional curve parameter C
is present.
The Z bit SHOULD be set to zero on creation of an RR and MUST be
ignored when processing an RR (when S=0).
Most of the remaining parameters are present in some formats and
absent in others. The presence or absence of a parameter is
determined entirely by the flags. When a parameter occurs, it is in
the order defined by the picture.
Of the remaining parameters, PFHKQABCGY are variable length. When
present, each is preceded by a one-octet length field as shown in the
diagram above. The length field does not include itself. The length
field may have values from 0 through 110. The parameter length in
octets is determined by a conditional formula: If LL<=64, the
parameter length is LL. If LL>64, the parameter length is 16 times
(LL-60). In some cases, a parameter value of 0 is sensible, and MAY
be represented by an LL value of 0, with the data field omitted. A
length value of 0 represents a parameter value of 0, not an absent
parameter. (The data portion occupies 0 space.) There is no
requirement that a parameter be represented in the minimum number of
octets; high-order 0 octets are allowed at the front end. Parameters
are always right adjusted, in a field of length defined by LL. The
octet-order is always most-significant first, least-significant last.
The parameters H and K may have an optional sign bit stored in the
unused high-order bit of their length fields.
LP defines the length of the prime P. P must be an odd prime. The
parameters LP,P are present if and only if the flag M=1. If M=0, the
prime is 2.
LF,F define an explicit field polynomial. This parameter pair is
present only when FMT = 1. The length of a polynomial coefficient is
ceiling(log2 P) bits. Coefficients are in the numerical range
[0,P-1]. The coefficients are packed into fixed-width fields, from
higher order to lower order. All coefficients must be present,
including any 0s and also the leading coefficient (which is required
to be 1). The coefficients are right justified into the octet string
of length specified by LF, with the low-order "constant" coefficient
at the right end. As a concession to storage efficiency, the higher
order bits of the leading coefficient may be elided, discarding high-
order 0 octets and reducing LF. The degree is calculated by
R. Schroeppel, et al [Page 6]
INTERNET-DRAFT ECC Keys in the DNS
determining the bit position of the left most 1-bit in the F data
(counting the right most bit as position 0), and dividing by
ceiling(log2 P). The division must be exact, with no remainder. In
this format, all of the other degree and field parameters are
omitted. The next parameters will be LQ,Q.
If FMT>=2, the degree of the field extension is specified explicitly,
usually along with other parameters to define the field polynomial.
DEG is a two octet field that defines the degree of the field
extension. The finite field will have P^DEG elements. DEG is
present when FMT>=2.
When FMT=2, the field polynomial is specified implicitly. No other
parameters are required to define the field; the next parameters
present will be the LQ,Q pair. The implicit field poynomial is the
lexicographically smallest irreducible (mod P) polynomial of the
correct degree. The ordering of polynomials is by highest-degree
coefficients first -- the leading coefficient 1 is most important,
and the constant term is least important. Coefficients are ordered
by sign-magnitude: 0 < 1 < -1 < 2 < -2 < ... The first polynomial of
degree D is X^D (which is not irreducible). The next is X^D+1, which
is sometimes irreducible, followed by X^D-1, which isn't. Assuming
odd P, this series continues to X^D - (P-1)/2, and then goes to X^D +
X, X^D + X + 1, X^D + X - 1, etc.
When FMT=3, the field polynomial is a binomial, X^DEG + K. P must be
odd. The polynomial is determined by the degree and the low order
term K. Of all the field parameters, only the LK,K parameters are
present. The high-order bit of the LK octet stores on optional sign
for K; if the sign bit is present, the field polynomial is X^DEG - K.
When FMT=4, the field polynomial is a trinomial, X^DEG + H*X^DEGH +
K. When P=2, the H and K parameters are implicitly 1, and are
omitted from the representation. Only DEG and DEGH are present; the
next parameters are LQ,Q. When P>2, then LH,H and LK,K are
specified. Either or both of LH, LK may contain a sign bit for its
parameter.
When FMT=5, then P=2 (only). The field polynomial is the exact
quotient of a trinomial divided by a small polynomial, the trinomial
divisor. The small polynomial is right-adjusted in the two octet
field TRDV. DEG specifies the degree of the field. The degree of
TRDV is calculated from the position of the high-order 1 bit. The
trinomial to be divided is X^(DEG+degree(TRDV)) + X^DEGH + 1. If
DEGH is 0, the middle term is omitted from the trinomial. The
quotient must be exact, with no remainder.
When FMT=6, then P=2 (only). The field polynomial is a pentanomial,
with the degrees of the middle terms given by the three 2-octet
R. Schroeppel, et al [Page 7]
INTERNET-DRAFT ECC Keys in the DNS
values DEGH, DEGI, DEGJ. The polynomial is X^DEG + X^DEGH + X^DEGI +
X^DEGJ + 1. The values must satisfy the inequality DEG > DEGH > DEGI
> DEGJ > 0.
DEGH, DEGI, DEGJ are two-octet fields that define the degree of
a term in a field polynomial. DEGH is present when FMT = 4,
5, or 6. DEGI and DEGJ are present only when FMT = 6.
TRDV is a two-octet right-adjusted binary polynomial of degree <
16. It is present only for FMT=5.
LH and H define the H parameter, present only when FMT=4 and P
is odd. The high bit of LH is an optional sign bit for H.
LK and K define the K parameter, present when FMT = 3 or 4, and
P is odd. The high bit of LK is an optional sign bit for K.
The remaining parameters are concerned with the elliptic curve and
the signature algorithm.
LQ defines the length of the prime Q. Q is a prime > 2^159.
In all 5 of the parameter pairs LA+A,LB+B,LC+C,LG+G,LY+Y, the data
member of the pair is an element from the finite field defined
earlier. The length field defines a long octet string. Field
elements are represented as (mod P) polynomials of degree < DEG, with
DEG or fewer coefficients. The coefficients are stored from left to
right, higher degree to lower, with the constant term last. The
coefficients are represented as integers in the range [0,P-1]. Each
coefficient is allocated an area of ceiling(log2 P) bits. The field
representation is right-justified; the "constant term" of the field
element ends at the right most bit. The coefficients are fitted
adjacently without regard for octet boundaries. (Example: if P=5,
three bits are used for each coefficient. If the field is GF[5^75],
then 225 bits are required for the coefficients, and as many as 29
octets may be needed in the data area. Fewer octets may be used if
some high-order coefficients are 0.) If a flag requires a field
element to be negated, each non-zero coefficient K is replaced with
P-K. To save space, 0 bits may be removed from the left end of the
element representation, and the length field reduced appropriately.
This would normally only happen with A,B,C, because the designer
chose curve parameters with some high-order 0 coefficients or bits.
If the finite field is simply (mod P), then the field elements are
simply numbers (mod P), in the usual right-justified notation. If
the finite field is GF[2^D], the field elements are the usual right-
justified polynomial basis representation.
R. Schroeppel, et al [Page 8]
INTERNET-DRAFT ECC Keys in the DNS
LA,A is the first parameter of the elliptic curve equation.
When P>=5, the flag A = 1 indicates A should be negated (mod
P). When P=2 (indicated by the flag M=0), the flag A = 1
indicates that the parameter pair LA,A is replaced by the two
octet parameter ALTA. In this case, the parameter A in the
curve equation is x^ALTA, where x is the field generator.
Parameter A often has the value 0, which may be indicated by
LA=0 (with no A data field), and sometimes A is 1, which may
be represented with LA=1 and a data field of 1, or by setting
the A flag and using an ALTA value of 0.
LB,B is the second parameter of the elliptic curve equation.
When P>=5, the flag B = 1 indicates B should be negated (mod
P). When P=2 or 3, the flag B selects an alternate curve
equation.
LC,C is the third parameter of the elliptic curve equation,
present only when P=2 (indicated by flag M=0) and flag B=1.
LG,G defines a point on the curve, of order Q. The W-coordinate
of the curve point is given explicitly; the Z-coordinate is
implicit.
LY,Y is the user's public signing key, another curve point of
order Q. The W-coordinate is given explicitly; the Z-
coordinate is implicit. The LY,Y parameter pair is always
present.
3. The Elliptic Curve Equation
(The coordinates of an elliptic curve point are named W,Z instead of
the more usual X,Y to avoid confusion with the Y parameter of the
signing key.)
The elliptic curve equation is determined by the flag octet, together
with information about the prime P. The primes 2 and 3 are special;
all other primes are treated identically.
If M=1, the (mod P) or GF[P^D] case, the curve equation is Z^2 = W^3
+ A*W + B. Z,W,A,B are all numbers (mod P) or elements of GF[P^D].
If A and/or B is negative (i.e., in the range from P/2 to P), and
P>=5, space may be saved by putting the sign bit(s) in the A and B
bits of the flags octet, and the magnitude(s) in the parameter
fields.
If M=1 and P=3, the B flag has a different meaning: it specifies an
alternate curve equation, Z^2 = W^3 + A*W^2 + B. The middle term of
the right-hand-side is different. When P=3, this equation is more
R. Schroeppel, et al [Page 9]
INTERNET-DRAFT ECC Keys in the DNS
commonly used.
If M=0, the GF[2^N] case, the curve equation is Z^2 + W*Z = W^3 +
A*W^2 + B. Z,W,A,B are all elements of the field GF[2^N]. The A
parameter can often be 0 or 1, or be chosen as a single-1-bit value.
The flag B is used to select an alternate curve equation, Z^2 + C*Z =
W^3 + A*W + B. This is the only time that the C parameter is used.
4. How do I Compute Q, G, and Y?
The number of points on the curve is the number of solutions to the
curve equation, + 1 (for the "point at infinity"). The prime Q must
divide the number of points. Usually the curve is chosen first, then
the number of points is determined with Schoof's algorithm. This
number is factored, and if it has a large prime divisor, that number
is taken as Q.
G must be a point of order Q on the curve, satisfying the equation
Q * G = the point at infinity (on the elliptic curve)
G may be chosen by selecting a random [RFC 1750] curve point, and
multiplying it by (number-of-points-on-curve/Q). G must not itself
be the "point at infinity"; in this astronomically unlikely event, a
new random curve point is recalculated.
G is specified by giving its W-coordinate. The Z-coordinate is
calculated from the curve equation. In general, there will be two
possible Z values. The rule is to choose the "positive" value.
In the (mod P) case, the two possible Z values sum to P. The smaller
value is less than P/2; it is used in subsequent calculations. In
GF[P^D] fields, the highest-degree non-zero coefficient of the field
element Z is used; it is chosen to be less than P/2.
In the GF[2^N] case, the two possible Z values xor to W (or to the
parameter C with the alternate curve equation). The numerically
smaller Z value (the one which does not contain the highest-order 1
bit of W (or C)) is used in subsequent calculations.
Y is specified by giving the W-coordinate of the user's public
signature key. The Z-coordinate value is determined from the curve
equation. As with G, there are two possible Z values; the same rule
is followed for choosing which Z to use.
R. Schroeppel, et al [Page 10]
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During the key generation process, a random [RFC 1750] number X must
be generated such that 1 <= X <= Q-1. X is the private key and is
used in the final step of public key generation where Y is computed
as
Y = X * G (as points on the elliptic curve)
If the Z-coordinate of the computed point Y is wrong (i.e., Z > P/2
in the (mod P) case, or the high-order non-zero coefficient of Z >
P/2 in the GF[P^D] case, or Z sharing a high bit with W(C) in the
GF[2^N] case), then X must be replaced with Q-X. This will
correspond to the correct Z-coordinate.
5. Elliptic Curve SIG Resource Records
The signature portion of an RR RDATA area when using the EC
algorithm, for example in the RRSIG and SIG [RFC records] RRs is
shown below.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R, (length determined from LQ) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S, (length determined from LQ) .../
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R and S are integers (mod Q). Their length is specified by the LQ
field of the corresponding KEY RR and can also be calculated from the
SIG RR's RDLENGTH. They are right justified, high-order-octet first.
The same conditional formula for calculating the length from LQ is
used as for all the other length fields above.
The data signed is determined as specified in [RFC 2535]. Then the
following steps are taken where Q, P, G, and Y are as specified in
the public key [Schneier]:
hash = SHA-1 ( data )
Generate random [RFC 1750] K such that 0 < K < Q. (Never sign two
different messages with the same K. K should be chosen from a
very large space: If an opponent learns a K value for a single
signature, the user's signing key is compromised, and a forger
can sign arbitrary messages. There is no harm in signing the
same message multiple times with the same key or different
keys.)
R = (the W-coordinate of ( K*G on the elliptic curve )) interpreted
R. Schroeppel, et al [Page 11]
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as an integer, and reduced (mod Q). (R must not be 0. In
this astronomically unlikely event, generate a new random K
and recalculate R.)
S = ( K^(-1) * (hash + X*R) ) mod Q.
S must not be 0. In this astronomically unlikely event, generate a
new random K and recalculate R and S.
If S > Q/2, set S = Q - S.
The pair (R,S) is the signature.
Another party verifies the signature as follows:
Check that 0 < R < Q and 0 < S < Q/2. If not, it can not be a
valid EC sigature.
hash = SHA-1 ( data )
Sinv = S^(-1) mod Q.
U1 = (hash * Sinv) mod Q.
U2 = (R * Sinv) mod Q.
(U1 * G + U2 * Y) is computed on the elliptic curve.
V = (the W-coordinate of this point) interpreted as an integer
and reduced (mod Q).
The signature is valid if V = R.
The reason for requiring S < Q/2 is that, otherwise, both (R,S) and
(R,Q-S) would be valid signatures for the same data. Note that a
signature that is valid for hash(data) is also valid for
hash(data)+Q or hash(data)-Q, if these happen to fall in the range
[0,2^160-1]. It's believed to be computationally infeasible to
find data that hashes to an assigned value, so this is only a
cosmetic blemish. The blemish can be eliminated by using Q >
2^160, at the cost of having slightly longer signatures, 42 octets
instead of 40.
We must specify how a field-element E ("the W-coordinate") is to be
interpreted as an integer. The field-element E is regarded as a
radix-P integer, with the digits being the coefficients in the
polynomial basis representation of E. The digits are in the ragne
[0,P-1]. In the two most common cases, this reduces to "the
obvious thing". In the (mod P) case, E is simply a residue mod P,
and is taken as an integer in the range [0,P-1]. In the GF[2^D]
R. Schroeppel, et al [Page 12]
INTERNET-DRAFT ECC Keys in the DNS
case, E is in the D-bit polynomial basis representation, and is
simply taken as an integer in the range [0,(2^D)-1]. For other
fields GF[P^D], it's necessary to do some radix conversion
arithmetic.
6. Performance Considerations
Elliptic curve signatures use smaller moduli or field sizes than
RSA and DSA. Creation of a curve is slow, but not done very often.
Key generation is faster than RSA or DSA.
DNS implementations have been optimized for small transfers,
typically less than 512 octets including DNS overhead. Larger
transfers will perform correctly and and extensions have been
standardized to make larger transfers more efficient [RFC 2671].
However, it is still advisable at this time to make reasonable
efforts to minimize the size of RR sets stored within the DNS
consistent with adequate security.
7. Security Considerations
Keys retrieved from the DNS should not be trusted unless (1) they
have been securely obtained from a secure resolver or independently
verified by the user and (2) this secure resolver and secure
obtainment or independent verification conform to security policies
acceptable to the user. As with all cryptographic algorithms,
evaluating the necessary strength of the key is essential and
dependent on local policy.
Some specific key generation considerations are given in the body
of this document.
8. IANA Considerations
The key and signature data structures defined herein correspond to
the value 4 in the Algorithm number field of the IANA registry
Assignment of meaning to the remaining ECC data flag bits or to
values of ECC fields outside the ranges for which meaning in
defined in this document requires an IETF consensus as defined in
[RFC 2434].
R. Schroeppel, et al [Page 13]
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Copyright and Disclaimer
Copyright (C) The Internet Society 2004. 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.
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 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.
R. Schroeppel, et al [Page 14]
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Informational References
[RFC 1034] - P. Mockapetris, "Domain names - concepts and
facilities", 11/01/1987.
[RFC 1035] - P. Mockapetris, "Domain names - implementation and
specification", 11/01/1987.
[RFC 1750] - D. Eastlake, S. Crocker, J. Schiller, "Randomness
Recommendations for Security", 12/29/1994.
[RFC intro] - "DNS Security Introduction and Requirements", R.
Arends, M. Larson, R. Austein, D. Massey, S. Rose, work in
progress, draft-ietf-dnsext-dnssec-intro-*.txt.
[RFC protocol] - "Protocol Modifications for the DNS Security
Extensions", R. Arends, M. Larson, R. Austein, D. Massey, S. Rose,
work in progress, draft-ietf-dnsext-dnssec-protocol-*.txt.
[RFC 2671] - P. Vixie, "Extension Mechanisms for DNS (EDNS0)",
August 1999.
[Schneier] - Bruce Schneier, "Applied Cryptography: Protocols,
Algorithms, and Source Code in C", 1996, John Wiley and Sons
[Menezes] - Alfred Menezes, "Elliptic Curve Public Key
Cryptosystems", 1993 Kluwer.
[Silverman] - Joseph Silverman, "The Arithmetic of Elliptic
Curves", 1986, Springer Graduate Texts in mathematics #106.
Normative Refrences
[RFC 2119] - S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[RFC 2434] - T. Narten, H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", October 1998.
[RFC records] - "Resource Records for the DNS Security Extensions",
R. Arends, R. Austein, M. Larson, D. Massey, S. Rose, work in
progress, draft-ietf-dnsext-dnssec-records- *.txt.
R. Schroeppel, et al [Page 15]
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Author's Addresses
Rich Schroeppel
500 S. Maple Drive
Woodland Hills, UT 84653 USA
Telephone: +1-505-844-9079(w)
+1-801-423-7998(h)
Email: rschroe@sandia.gov
Donald E. Eastlake 3rd
Motorola Laboratories
155 Beaver Street
Milford, MA 01757 USA
Telephone: +1 508-786-7554 (w)
+1 508-634-2066 (h)
EMail: Donald.Eastlake@motorola.com
Expiration and File Name
This draft expires in June 2004.
Its file name is draft-ietf-dnsext-ecc-key-06.txt.
R. Schroeppel, et al [Page 16]
doc/draft/draft-ietf-dnsext-insensitive-05.txt
+697
View File
@@ -0,0 +1,697 @@
INTERNET-DRAFT Donald E. Eastlake 3rd
Updates RFC 1034, 1035 Motorola Laboratories
Expires July 2005 January 2005
Domain Name System (DNS) Case Insensitivity Clarification
------ ---- ------ ----- ---- ------------- -------------
<draft-ietf-dnsext-insensitive-05.txt>
Donald E. Eastlake 3rd
Status of This Document
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
or will be disclosed, and any of which I become aware will be
disclosed, in accordance with RFC 3668.
Distribution of this document is unlimited. Comments should be sent
to the DNSEXT working group at namedroppers@ops.ietf.org.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than a "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright Notice
Copyright (C) The Internet Society. All Rights Reserved.
Abstract
Domain Name System (DNS) names are "case insensitive". This document
explains exactly what that means and provides a clear specification
of the rules. This clarification updates RFCs 1034 and 1035.
D. Eastlake 3rd [Page 1]
INTERNET-DRAFT DNS Case Insensitivity
Acknowledgements
The contributions to this document of Rob Austein, Olafur
Gudmundsson, Daniel J. Anderson, Alan Barrett, Marc Blanchet, Dana,
Andreas Gustafsson, Andrew Main, Thomas Narten, and Scott Seligman
are gratefully acknowledged.
Table of Contents
Status of This Document....................................1
Copyright Notice...........................................1
Abstract...................................................1
Acknowledgements...........................................2
Table of Contents..........................................2
1. Introduction............................................3
2. Case Insensitivity of DNS Labels........................3
2.1 Escaping Unusual DNS Label Octets......................3
2.2 Example Labels with Escapes............................4
3. Name Lookup, Label Types, and CLASS.....................4
3.1 Original DNS Label Types...............................5
3.2 Extended Label Type Case Insensitivity Considerations..5
3.3 CLASS Case Insensitivity Considerations................5
4. Case on Input and Output................................6
4.1 DNS Output Case Preservation...........................6
4.2 DNS Input Case Preservation............................6
5. Internationalized Domain Names..........................7
6. Security Considerations.................................7
Full Copyright Notice and Disclaimer.......................9
Normative References.......................................9
Informative References....................................10
-02 to -03 Changes........................................10
-03 to -04 Changes........................................11
-04 to -05 Changes........................................11
Author's Address..........................................11
Expiration and File Name..................................12
D. Eastlake 3rd [Page 2]
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1. Introduction
The Domain Name System (DNS) is the global hierarchical replicated
distributed database system for Internet addressing, mail proxy, and
other information. Each node in the DNS tree has a name consisting of
zero or more labels [STD 13][RFC 1591, 2606] that are treated in a
case insensitive fashion. This document clarifies the meaning of
"case insensitive" for the DNS. This clarification updates RFCs 1034
and 1035 [STD 13].
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].
2. Case Insensitivity of DNS Labels
DNS was specified in the era of [ASCII]. DNS names were expected to
look like most host names or Internet email address right halves (the
part after the at-sign, "@") or be numeric as in the in-addr.arpa
part of the DNS name space. For example,
foo.example.net.
aol.com.
www.gnu.ai.mit.edu.
or 69.2.0.192.in-addr.arpa.
Case varied alternatives to the above would be DNS names like
Foo.ExamplE.net.
AOL.COM.
WWW.gnu.AI.mit.EDU.
or 69.2.0.192.in-ADDR.ARPA.
However, the individual octets of which DNS names consist are not
limited to valid ASCII character codes. They are 8-bit bytes and all
values are allowed. Many applications, however, interpret them as
ASCII characters.
2.1 Escaping Unusual DNS Label Octets
In Master Files [STD 13] and other human readable and writable ASCII
contexts, an escape is needed for the byte value for period (0x2E,
".") and all octet values outside of the inclusive range of 0x21
("!") to 0x7E ("~"). That is to say, 0x2E and all octet values in
the two inclusive ranges 0x00 to 0x20 and 0x7F to 0xFF.
D. Eastlake 3rd [Page 3]
INTERNET-DRAFT DNS Case Insensitivity
One typographic convention for octets that do not correspond to an
ASCII printing graphic is to use a back-slash followed by the value
of the octet as an unsigned integer represented by exactly three
decimal digits.
The same convention can be used for printing ASCII characters so that
they will be treated as a normal label character. This includes the
back-slash character used in this convention itself which can be
expressed as \092 or \\ and the special label separator period (".")
which can be expressed as and \046 or \. respectively. It is
advisable to avoid using a backslash to quote an immediately
following non-printing ASCII character code to avoid implementation
difficulties.
A back-slash followed by only one or two decimal digits is undefined.
A back-slash followed by four decimal digits produces two octets, the
first octet having the value of the first three digits considered as
a decimal number and the second octet being the character code for
the fourth decimal digit.
2.2 Example Labels with Escapes
The first example below shows embedded spaces and a period (".")
within a label. The second one show a 5-octet label where the second
octet has all bits zero, the third is a backslash, and the fourth
octet has all bits one.
Donald\032E\.\032Eastlake\0323rd.example.
and a\000\\\255z.example.
3. Name Lookup, Label Types, and CLASS
The design decision was made that comparisons on name lookup for all
DNS queries should be case insensitive [STD 13]. That is to say, a
lookup string octet with a value in the inclusive range of 0x41 to
0x5A, the upper case ASCII letters, MUST match the identical value
and also match the corresponding value in the inclusive range 0x61 to
0x7A, the lower case ASCII letters. And a lookup string octet with a
lower case ASCII letter value MUST similarly match the identical
value and also match the corresponding value in the upper case ASCII
letter range.
(Historical Note: the terms "upper case" and "lower case" were
invented after movable type. The terms originally referred to the
two font trays for storing, in partitioned areas, the different
physical type elements. Before movable type, the nearest equivalent
D. Eastlake 3rd [Page 4]
INTERNET-DRAFT DNS Case Insensitivity
terms were "majuscule" and "minuscule".)
One way to implement this rule would be, when comparing octets, to
subtract 0x20 from all octets in the inclusive range 0x61 to 0x7A
before the comparison. Such an operation is commonly known as "case
folding" but implementation via case folding is not required. Note
that the DNS case insensitivity does NOT correspond to the case
folding specified in [iso-8859-1] or [iso-8859-2]. For example, the
octets 0xDD (\221) and 0xFD (\253) do NOT match although in other
contexts, where they are interpreted as the upper and lower case
version of "Y" with an acute accent, they might.
3.1 Original DNS Label Types
DNS labels in wire-encoded names have a type associated with them.
The original DNS standard [RFC 1035] had only two types. ASCII
labels, with a length of from zero to 63 octets, and indirect labels
which consist of an offset pointer to a name location elsewhere in
the wire encoding on a DNS message. (The ASCII label of length zero
is reserved for use as the name of the root node of the name tree.)
ASCII labels follow the ASCII case conventions described herein and,
as stated above, can actually contain arbitrary byte values. Indirect
labels are, in effect, replaced by the name to which they point which
is then treated with the case insensitivity rules in this document.
3.2 Extended Label Type Case Insensitivity Considerations
DNS was extended by [RFC 2671] to have additional label type numbers
available. (The only such type defined so far is the BINARY type [RFC
2673].)
The ASCII case insensitivity conventions only apply to ASCII labels,
that is to say, label type 0x0, whether appearing directly or invoked
by indirect labels.
3.3 CLASS Case Insensitivity Considerations
As described in [STD 13] and [RFC 2929], DNS has an additional axis
for data location called CLASS. The only CLASS in global use at this
time is the "IN" or Internet CLASS.
The handling of DNS label case is not CLASS dependent.
D. Eastlake 3rd [Page 5]
INTERNET-DRAFT DNS Case Insensitivity
4. Case on Input and Output
While ASCII label comparisons are case insensitive, [STD 13] says
case MUST be preserved on output, and preserved when convenient on
input. However, this means less than it would appear since the
preservation of case on output is NOT required when output is
optimized by the use of indirect labels, as explained below.
4.1 DNS Output Case Preservation
[STD 13] views the DNS namespace as a node tree. ASCII output is as
if a name was marshaled by taking the label on the node whose name is
to be output, converting it to a typographically encoded ASCII
string, walking up the tree outputting each label encountered, and
preceding all labels but the first with a period ("."). Wire output
follows the same sequence but each label is wire encoded and no
periods inserted. No "case conversion" or "case folding" is done
during such output operations, thus "preserving" case. However, to
optimize output, indirect labels may be used to point to names
elsewhere in the DNS answer. In determining whether the name to be
pointed to, for example the QNAME, is the "same" as the remainder of
the name being optimized, the case insensitive comparison specified
above is done. Thus such optimization may easily destroy the output
preservation of case. This type of optimization is commonly called
"name compression".
4.2 DNS Input Case Preservation
Originally, DNS input came from an ASCII Master File as defined in
[STD 13] or a zone transfer. DNS Dynamic update and incremental zone
transfers [RFC 1995] have been added as a source of DNS data [RFC
2136, 3007]. When a node in the DNS name tree is created by any of
such inputs, no case conversion is done. Thus the case of ASCII
labels is preserved if they are for nodes being created. However,
when a name label is input for a node that already exist in DNS data
being held, the situation is more complex. Implementations may retain
the case first input for such a label or allow new input to override
the old case or even maintain separate copies preserving the input
case.
For example, if data with owner name "foo.bar.example" is input and
then later data with owner name "xyz.BAR.example" is input, the name
of the label on the "bar.example" node, i.e. "bar", might or might
not be changed to "BAR" or the actual input case could be preserved.
Thus later retrieval of data stored under "xyz.bar.example" in this
case can easily return data with "xyz.BAR.example". The same
D. Eastlake 3rd [Page 6]
INTERNET-DRAFT DNS Case Insensitivity
considerations apply when inputting multiple data records with owner
names differing only in case. For example, if an "A" record is stored
as the first resourced record under owner name "xyz.BAR.example" and
then a second "A" record is stored under "XYZ.BAR.example", the
second MAY be stored with the first (lower case initial label) name
or the second MAY override the first so that only an upper case
initial label is retained or both capitalizations MAY be kept.
Note that the order of insertion into a server database of the DNS
name tree nodes that appear in a Master File is not defined so that
the results of inconsistent capitalization in a Master File are
unpredictable output capitalization.
5. Internationalized Domain Names
A scheme has been adopted for "internationalized domain names" and
"internationalized labels" as described in [RFC 3490, 3454, 3491, and
3492]. It makes most of [UNICODE] available through a separate
application level transformation from internationalized domain name
to DNS domain name and from DNS domain name to internationalized
domain name. Any case insensitivity that internationalized domain
names and labels have varies depending on the script and is handled
entirely as part of the transformation described in [RFC 3454] and
[RFC 3491] which should be seen for further details. This is not a
part of the DNS as standardized in STD 13.
6. Security Considerations
The equivalence of certain DNS label types with case differences, as
clarified in this document, can lead to security problems. For
example, a user could be confused by believing two domain names
differing only in case were actually different names.
Furthermore, a domain name may be used in contexts other than the
DNS. It could be used as a case sensitive index into some data base
system. Or it could be interpreted as binary data by some integrity
or authentication code system. These problems can usually be handled
by using a standardized or "canonical" form of the DNS ASCII type
labels, that is, always mapping the ASCII letter value octets in
ASCII labels to some specific pre-chosen case, either upper case or
lower case. An example of a canonical form for domain names (and also
a canonical ordering for them) appears in Section 8 of [RFC 2535].
See also [RFC 3597].
Finally, a non-DNS name may be stored into DNS with the false
expectation that case will always be preserved. For example, although
D. Eastlake 3rd [Page 7]
INTERNET-DRAFT DNS Case Insensitivity
this would be quite rare, on a system with case sensitive email
address local parts, an attempt to store two "RP" records that
differed only in case would probably produce unexpected results that
might have security implications. That is because the entire email
address, including the possibly case sensitive local or left hand
part, is encoded into a DNS name in a readable fashion where the case
of some letters might be changed on output as described above.
D. Eastlake 3rd [Page 8]
INTERNET-DRAFT DNS Case Insensitivity
Full Copyright Notice and Disclaimer
Copyright (C) The Internet Society 2005. 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.
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 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.
Normative References
[ASCII] - ANSI, "USA Standard Code for Information Interchange",
X3.4, American National Standards Institute: New York, 1968.
[RFC 1034, 1035] - See [STD 13].
[RFC 1995] - M. Ohta, "Incremental Zone Transfer in DNS", August
1996.
[RFC 2119] - S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[RFC 2136] - P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)", April 1997.
[RFC 2535] - D. Eastlake, "Domain Name System Security Extensions",
March 1999.
[RFC 3007] - B. Wellington, "Secure Domain Name System (DNS) Dynamic
Update", November 2000.
[RFC 3597] - Andreas Gustafsson, "Handling of Unknown DNS RR Types",
draft-ietf-dnsext-unknown-rrs-05.txt, March 2003.
[STD 13]
- P. Mockapetris, "Domain names - concepts and facilities", RFC
1034, November 1987.
- P. Mockapetris, "Domain names - implementation and
specification", RFC 1035, November 1987.
D. Eastlake 3rd [Page 9]
INTERNET-DRAFT DNS Case Insensitivity
Informative References
[ISO 8859-1] - International Standards Organization, Standard for
Character Encodings, Latin-1.
[ISO 8859-2] - International Standards Organization, Standard for
Character Encodings, Latin-2.
[RFC 1591] - J. Postel, "Domain Name System Structure and
Delegation", March 1994.
[RFC 2606] - D. Eastlake, A. Panitz, "Reserved Top Level DNS Names",
June 1999.
[RFC 2929] - D. Eastlake, E. Brunner-Williams, B. Manning, "Domain
Name System (DNS) IANA Considerations", September 2000.
[RFC 2671] - P. Vixie, "Extension mechanisms for DNS (EDNS0)", August
1999.
[RFC 2673] - M. Crawford, "Binary Labels in the Domain Name System",
August 1999.
[RFC 3092] - D. Eastlake 3rd, C. Manros, E. Raymond, "Etymology of
Foo", 1 April 2001.
[RFC 3454] - P. Hoffman, M. Blanchet, "Preparation of
Internationalized String ("stringprep")", December 2002.
[RFC 3490] - P. Faltstrom, P. Hoffman, A. Costello,
"Internationalizing Domain Names in Applications (IDNA)", March 2003.
[RFC 3491] - P. Hoffman, M. Blanchet, "Nameprep: A Stringprep Profile
for Internationalized Domain Names (IDN)", March 2003.
[RFC 3492] - A. Costello, "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications (IDNA)", March
2003.
[UNICODE] - The Unicode Consortium, "The Unicode Standard",
<http://www.unicode.org/unicode/standard/standard.html>.
-02 to -03 Changes
The following changes were made between draft version -02 and -03:
1. Add internationalized domain name section and references.
D. Eastlake 3rd [Page 10]
INTERNET-DRAFT DNS Case Insensitivity
2. Change to indicate that later input of a label for an existing DNS
name tree node may or may not be normalized to the earlier input or
override it or both may be preserved.
3. Numerous minor wording changes.
-03 to -04 Changes
The following changes were made between draft versions -03 and -04:
1. Change to conform to the new IPR, Copyright, etc., notice
requirements.
2. Change in some section headers for clarity.
3. Drop section on wildcards.
4. Add emphasis on loss of case preservation due to name compression.
5. Add references to RFCs 1995 and 3092.
-04 to -05 Changes
The following changes were made between draft versions -04 and -05:
1. More clearly state that this draft updates RFCs 1034, 1035 [STD
13].
2. Add informative references to ISO 8859-1 and ISO 8859-2.
3. Fix hyphenation and capitalization nits.
Author's Address
Donald E. Eastlake 3rd
Motorola Laboratories
155 Beaver Street
Milford, MA 01757 USA
Telephone: +1 508-786-7554 (w)
+1 508-634-2066 (h)
EMail: Donald.Eastlake@motorola.com
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Network Working Group S. Josefsson
Internet-Draft January 2005
Expires: July 2, 2005
Storing Certificates in the Domain Name System (DNS)
draft-ietf-dnsext-rfc2538bis-01
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each
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 become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on July 2, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
Cryptographic public key are frequently published and their
authenticity demonstrated by certificates. A CERT resource record
(RR) is defined so that such certificates and related certificate
revocation lists can be stored in the Domain Name System (DNS).
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The CERT Resource Record . . . . . . . . . . . . . . . . . . . 3
2.1 Certificate Type Values . . . . . . . . . . . . . . . . . 4
2.2 Text Representation of CERT RRs . . . . . . . . . . . . . 5
2.3 X.509 OIDs . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Appropriate Owner Names for CERT RRs . . . . . . . . . . . . . 6
3.1 Content-based X.509 CERT RR Names . . . . . . . . . . . . 7
3.2 Purpose-based X.509 CERT RR Names . . . . . . . . . . . . 8
3.3 Content-based OpenPGP CERT RR Names . . . . . . . . . . . 8
3.4 Purpose-based OpenPGP CERT RR Names . . . . . . . . . . . 9
3.5 Owner names for IPKIX, ISPKI, and IPGP . . . . . . . . . . 9
4. Performance Considerations . . . . . . . . . . . . . . . . . . 9
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Changes since RFC 2538 . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1 Normative References . . . . . . . . . . . . . . . . . . . . 11
9.2 Informative References . . . . . . . . . . . . . . . . . . . 12
A. Copying conditions . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . 14
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1. Introduction
Public keys are frequently published in the form of a certificate and
their authenticity is commonly demonstrated by certificates and
related certificate revocation lists (CRLs). A certificate is a
binding, through a cryptographic digital signature, of a public key,
a validity interval and/or conditions, and identity, authorization,
or other information. A certificate revocation list is a list of
certificates that are revoked, and incidental information, all signed
by the signer (issuer) of the revoked certificates. Examples are
X.509 certificates/CRLs in the X.500 directory system or OpenPGP
certificates/revocations used by OpenPGP software.
Section 2 below specifies a CERT resource record (RR) for the storage
of certificates in the Domain Name System.
Section 3 discusses appropriate owner names for CERT RRs.
Sections 4, 5, and 6 below cover performance, IANA, and security
considerations, respectively.
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 [10].
2. The CERT Resource Record
The CERT resource record (RR) has the structure given below. Its RR
type code is 37.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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 | key tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| algorithm | /
+---------------+ certificate or CRL /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
The type field is the certificate type as define in section 2.1
below.
The algorithm field has the same meaning as the algorithm field in
DNSKEY and RRSIG RRs [9] except that a zero algorithm field indicates
the algorithm is unknown to a secure DNS, which may simply be the
result of the algorithm not having been standardized for DNSSEC.
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The key tag field is the 16 bit value computed for the key embedded
in the certificate, using the RRSIG Key Tag Algorithm described in
Appendix B of [9]. This field is used as an efficiency measure to
pick which CERT RRs may be applicable to a particular key. The key
tag can be calculated for the key in question and then only CERT RRs
with the same key tag need be examined. However, the key must always
be transformed to the format it would have as the public key portion
of a DNSKEY RR before the key tag is computed. This is only possible
if the key is applicable to an algorithm (and limits such as key size
limits) defined for DNS security. If it is not, the algorithm field
MUST BE zero and the tag field is meaningless and SHOULD BE zero.
2.1 Certificate Type Values
The following values are defined or reserved:
Value Mnemonic Certificate Type
----- -------- ----------- ----
0 reserved
1 PKIX X.509 as per PKIX
2 SPKI SPKI certificate
3 PGP OpenPGP packet
4 IPKIX The URL of an X.509 data object
5 ISPKI The URL of an SPKI certificate
6 IPGP The URL of an OpenPGP packet
7-252 available for IANA assignment
253 URI URI private
254 OID OID private
255-65534 available for IANA assignment
65535 reserved
The PKIX type is reserved to indicate an X.509 certificate conforming
to the profile being defined by the IETF PKIX working group. The
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
certificate section (see 2.3 below). (NOTE: X.509 certificates do
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
specified by the IETF SPKI working group.
The PGP type indicates an OpenPGP packet as described in [5] and its
extensions and successors. Two uses are to transfer public key
material and revocation signatures. The data is binary, and MUST NOT
be encoded into an ASCII armor. An implementation SHOULD process
transferable public keys as described in section 10.1 of [5], but it
MAY handle additional OpenPGP packets.
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The IPKIX, ISPKI and IPGP types indicate a URL which will serve the
content that would have been in the "certificate, CRL or URL" field
of the corresponding (PKIX, SPKI or PGP) packet types. These types
are known as "indirect". These packet types MUST be used when the
content is too large to fit in the CERT RR, and MAY be used at the
implementations discretion. They SHOULD NOT be used where the entire
UDP packet would have fit in 512 bytes.
The URI private type indicates a certificate format defined by an
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
format certificate itself. The URI SHOULD be such that a retrieval
from it will lead to documentation on the format of the certificate.
Recognition of private certificate types need not be based on URI
equality but can use various forms of pattern matching so that, for
example, subtype or version information can also be encoded into the
URI.
The OID private type indicates a private format certificate specified
by a an ISO OID prefix. The certificate section will start with a
one byte unsigned OID length and then a BER encoded OID indicating
the nature of the remainder of the certificate section. This can be
an X.509 certificate format or some other format. X.509 certificates
that conform to the IETF PKIX profile SHOULD be indicated by the PKIX
type, not the OID private type. Recognition of private certificate
types need not be based on OID equality but can use various forms of
pattern matching such as OID prefix.
2.2 Text Representation of CERT RRs
The RDATA portion of a CERT RR has the type field as an unsigned
decimal integer or as a mnemonic symbol as listed in section 2.1
above.
The key tag field is represented as an unsigned decimal integer.
The algorithm field is represented as an unsigned decimal integer or
a mnemonic symbol as listed in [9].
The certificate / CRL portion is represented in base 64 [11] and may
be divided up into any number of white space separated substrings,
down to single base 64 digits, which are concatenated to obtain the
full signature. These substrings can span lines using the standard
parenthesis.
Note that the certificate / CRL portion may have internal sub-fields
but these do not appear in the master file representation. For
example, with type 254, there will be an OID size, an OID, and then
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the certificate / CRL proper. But only a single logical base 64
string will appear in the text representation.
2.3 X.509 OIDs
OIDs have been defined in connection with the X.500 directory for
user certificates, certification authority certificates, revocations
of certification authority, and revocations of user certificates.
The following table lists the OIDs, their BER encoding, and their
length prefixed hex format for use in CERT RRs:
id-at-userCertificate
= { joint-iso-ccitt(2) ds(5) at(4) 36 }
== 0x 03 55 04 24
id-at-cACertificate
= { joint-iso-ccitt(2) ds(5) at(4) 37 }
== 0x 03 55 04 25
id-at-authorityRevocationList
= { joint-iso-ccitt(2) ds(5) at(4) 38 }
== 0x 03 55 04 26
id-at-certificateRevocationList
= { joint-iso-ccitt(2) ds(5) at(4) 39 }
== 0x 03 55 04 27
3. Appropriate Owner Names for CERT RRs
It is recommended that certificate CERT RRs be stored under a domain
name related to their subject, i.e., the name of the entity intended
to control the private key corresponding to the public key being
certified. It is recommended that certificate revocation list CERT
RRs be stored under a domain name related to their issuer.
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
backslash followed by the octal representation of the ASCII code for
the character such as \000 for NULL.
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 might only know the hostname of a service
that uses X.509 certificates or the Key ID of an OpenPGP key.
This motivates describing two different owner name guidelines. We
call the two rules content-based owner names and purpose-based owner
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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
are expected to know; for example the host name of a X.509 protected
service or a 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.
Implementations SHOULD use the purpose-based owner name guidelines
described in this document, and MAY use CNAMEs at content-based owner
names (or other names), pointing to the purpose-based owner name.
3.1 Content-based X.509 CERT RR Names
Some X.509 versions permit multiple names to be associated with
subjects and issuers under "Subject Alternate Name" and "Issuer
Alternate Name". For example, x.509v3 has such Alternate Names with
an ASN.1 specification as follows:
GeneralName ::= CHOICE {
otherName [0] INSTANCE OF OTHER-NAME,
rfc822Name [1] IA5String,
dNSName [2] IA5String,
x400Address [3] EXPLICIT OR-ADDRESS.&Type,
directoryName [4] EXPLICIT Name,
ediPartyName [5] EDIPartyName,
uniformResourceIdentifier [6] IA5String,
iPAddress [7] OCTET STRING,
registeredID [8] OBJECT IDENTIFIER
}
The recommended locations of CERT storage are as follows, in priority
order:
1. If a domain name is included in the identification in the
certificate or CRL, that should be used.
2. If a domain name is not included but an IP address is included,
then the translation of that IP address into the appropriate
inverse domain name should be used.
3. If neither of the above it used but a URI containing a domain
name is present, that domain name should be used.
4. If none of the above is included but a character string name is
included, then it should be treated as described for OpenPGP
names below.
5. If none of the above apply, then the distinguished name (DN)
should be mapped into a domain name as specified in [3].
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Example 1: Assume that an X.509v3 certificate is issued to /CN=John
Doe/DC=Doe/DC=com/DC=xy/O=Doe Inc/C=XY/ with Subject Alternative
names of (a) string "John (the Man) Doe", (b) domain name john-
doe.com, and (c) uri <https://www.secure.john-doe.com:8080/>. Then
the storage locations recommended, in priority order, would be
1. john-doe.com,
2. www.secure.john-doe.com, and
3. Doe.com.xy.
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
of (a) domain name widget.foo.example, (b) IPv4 address
10.251.13.201, and (c) string "James Hacker
<hacker@mail.widget.foo.example>". Then the storage locations
recommended, in priority order, would be
1. widget.foo.example,
2. 201.13.251.10.in-addr.arpa, and
3. hacker.mail.widget.foo.example.
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.
An alternative approach for IPSEC is to store raw public keys [12].
3.3 Content-based OpenPGP CERT RR Names
OpenPGP signed keys (certificates) use a general character string
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User ID [5]. However, it is recommended by OpenPGP that such names
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
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
RFC 2822 name can be extracted from the string name no specific
domain name is recommended.
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:
$ORIGIN example.org.
smith IN CERT PGP 0 0 <OpenPGP binary>
john.smith IN CNAME smith
js IN CNAME smith
3.4 Purpose-based OpenPGP CERT RR Names
Applications that receive an OpenPGP packet containing encrypted or
signed data but do not know the email address of the sender will have
difficulties constructing the correct owner name and cannot use the
content-based owner name guidelines. However, these clients commonly
know the key fingerprint or the Key ID. The key ID is found in
OpenPGP packets, and the key fingerprint is commonly found in
auxilliary data that may be available. For these situations, it is
recommended to use an owner name identical to the key fingerprint and
key ID expressed in hexadecimal [11]. For example:
$ORIGIN example.org.
0424D4EE81A0E3D119C6F835EDA21E94B565716F IN CERT PGP ...
F835EDA21E94B565716F IN CERT PGP ...
B565716F IN CERT PGP ...
If the same key material is stored at several owner names, the use of
CNAME may be used to avoid data duplication. Note that CNAME is not
always applicable, because it map an owner names to the other for all
purposes, and this may be sub-optimal when two keys with the same Key
ID are stored.
3.5 Owner names for IPKIX, ISPKI, and IPGP
These types are stored under the same owner names, both purpose- and
content-based, as the PKIX, SPKI and PGP types, respectively.
4. Performance Considerations
Current Domain Name System (DNS) implementations are optimized for
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small transfers, typically not more than 512 bytes including
overhead. While larger transfers will perform correctly and work is
underway to make larger transfers more efficient, it is still
advisable at this time to make every reasonable effort to minimize
the size of certificates stored within the DNS. Steps that can be
taken may include using the fewest possible optional or extensions
fields and using short field values for variable length fields that
must be included.
The RDATA field in the DNS protocol may only hold data of size 65535
octets (64kb) or less. This means that each CERT RR cannot contain
more than 64kb worth of payload, even if the corresponding
certificate or certificate revocation list is larger. This document
address this by defining "indirect" data types for each normal type.
5. Acknowledgements
The majority of this document is copied verbatim from RFC 2538, by
Donald Eastlake 3rd and Olafur Gudmundsson.
The author wishes to thank David Shaw and Michael Graff for their
contributions to the earlier work that motivated this revised
document.
This document was improved by suggestions and comments from Olivier
Dubuisson, Ben Laurie, Samuel Weiler, and Florian Weimer. No doubt
the list is incomplete. We apologize to anyone we left out.
6. Security Considerations
By definition, certificates contain their own authenticating
signature. Thus it is reasonable to store certificates in non-secure
DNS zones or to retrieve certificates from DNS with DNS security
checking not implemented or deferred for efficiency. The results MAY
be trusted if the certificate chain is verified back to a known
trusted key and this conforms with the user's security policy.
Alternatively, if certificates are retrieved from a secure DNS zone
with DNS security checking enabled and are verified by DNS security,
the key within the retrieved certificate MAY be trusted without
verifying the certificate chain if this conforms with the user's
security policy.
When the URI type is used, it should be understood that it introduces
an additional indirection that may allow for a new attack vector.
One method to secure that indirection is to include a hash of the
certificate in the URI itself.
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CERT RRs are not used by DNSSEC [8] so there are no security
considerations related to CERT RRs and securing the DNS itself.
If DNSSEC [8] is used then the non-existence of a CERT RR, and
consequently certificates or revocation lists, can be securely
asserted. Without DNSSEC, this is not possible.
7. IANA Considerations
Certificate types 0x0000 through 0x00FF and 0xFF00 through 0xFFFF can
only be assigned by an IETF standards action [6]. This document
assigns 0x0001 through 0x0006 and 0x00FD and 0x00FE. Certificate
types 0x0100 through 0xFEFF are assigned through IETF Consensus [6]
based on RFC documentation of the certificate type. The availability
of private types under 0x00FD and 0x00FE should satisfy most
requirements for proprietary or private types.
8. Changes since RFC 2538
1. Editorial changes to conform with new document requirements,
including splitting reference section into two parts and updating
the references to point at latest versions, and to add some
additional references.
2. Improve terminology. For example replace "PGP" with "OpenPGP",
to align with RFC 2440.
3. In section 2.1, clarify that OpenPGP public key data are binary,
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.
5. Replace KEY/SIG with DNSKEY/RRSIG etc, to align with DNSSECbis
terminology. Improve reference for Key Tag Algorithm
calculations.
6. Add examples that suggest use of CNAME to reduce bandwidth.
7. In section 3, appended the last 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.
8. Added size considerations.
9. Added indirect types IPKIX, ISPKI, and IPGP.
9. References
9.1 Normative References
[1] Mockapetris, P., "Domain names - concepts and facilities", STD
13, RFC 1034, November 1987.
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[2] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[3] Kille, S., Wahl, M., Grimstad, A., Huber, R. and S. Sataluri,
"Using Domains in LDAP/X.500 Distinguished Names", RFC 2247,
January 1998.
[4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
[5] Callas, J., Donnerhacke, L., Finney, H. and R. Thayer, "OpenPGP
Message Format", RFC 2440, November 1998.
[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[7] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[8] Arends, R., Austein, R., Massey, D., Larson, M. and S. Rose,
"DNS Security Introduction and Requirements",
draft-ietf-dnsext-dnssec-intro-13 (work in progress), October
2004.
[9] Arends, R., "Resource Records for the DNS Security Extensions",
draft-ietf-dnsext-dnssec-records-11 (work in progress), October
2004.
9.2 Informative References
[10] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[11] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
RFC 3548, July 2003.
[12] Richardson, M., "A method for storing IPsec keying material in
DNS", draft-ietf-ipseckey-rr-11 (work in progress), July 2004.
Author's Address
Simon Josefsson
EMail: simon@josefsson.org
Appendix A. Copying conditions
Regarding the portion of this document that was written by Simon
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Josefsson ("the author", for the remainder of this section), the
author makes no guarantees and is not responsible for any damage
resulting from its use. The author grants irrevocable permission to
anyone to use, modify, and distribute it in any way that does not
diminish the rights of anyone else to use, modify, and distribute it,
provided that redistributed derivative works do not contain
misleading author or version information. Derivative works need not
be licensed under similar terms.
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Intellectual Property Statement
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
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Copies of IPR disclosures made to the IETF Secretariat and any
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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.
Disclaimer of Validity
This document and the information contained herein are provided on an
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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
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Copyright Statement
Copyright (C) The Internet Society (2005). 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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Network Working Group M. StJohns
Internet-Draft Nominum, Inc.
Expires: April 14, 2005 October 14, 2004
Automated Updates of DNSSEC Trust Anchors
draft-ietf-dnsext-trustupdate-timers-00
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each
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RFC 3668.
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This Internet-Draft will expire on April 14, 2005.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This document describes a means for automated, authenticated and
authorized updating of DNSSEC "trust anchors". The method provides
protection against single key compromise of a key in the trust point
key set. Based on the trust established by the presence of a current
anchor, other anchors may be added at the same place in the
hierarchy, and, ultimately, supplant the existing anchor.
This mechanism, if adopted, will require changes to resolver
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management behavior (but not resolver resolution behavior), and the
addition of a single flag bit to the DNSKEY record.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Compliance Nomenclature . . . . . . . . . . . . . . . . . 3
1.2 Changes since -00 . . . . . . . . . . . . . . . . . . . . 3
2. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 4
2.1 Revocation . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Add Hold-Down . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Remove Hold-down . . . . . . . . . . . . . . . . . . . . . 5
2.4 Active Refresh . . . . . . . . . . . . . . . . . . . . . . 6
2.5 Resolver Parameters . . . . . . . . . . . . . . . . . . . 6
2.5.1 Add Hold-Down Time . . . . . . . . . . . . . . . . . . 6
2.5.2 Remove Hold-Down Time . . . . . . . . . . . . . . . . 6
2.5.3 Minimum Trust Anchors per Trust Point . . . . . . . . 6
3. Changes to DNSKEY RDATA Wire Format . . . . . . . . . . . . . 6
4. State Table . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1 Events . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2 States . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1 Adding A Trust Anchor . . . . . . . . . . . . . . . . . . 8
5.2 Deleting a Trust Anchor . . . . . . . . . . . . . . . . . 9
5.3 Key Roll-Over . . . . . . . . . . . . . . . . . . . . . . 9
5.4 Active Key Compromised . . . . . . . . . . . . . . . . . . 9
5.5 Stand-by Key Compromised . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6.1 Key Ownership vs Acceptance Policy . . . . . . . . . . . . 10
6.2 Multiple Key Compromise . . . . . . . . . . . . . . . . . 10
6.3 Dynamic Updates . . . . . . . . . . . . . . . . . . . . . 10
7. Normative References . . . . . . . . . . . . . . . . . . . . . 10
Editorial Comments . . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . 12
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1. Introduction
As part of the reality of fielding DNSSEC (Domain Name System
Security Extensions) [RFC2535][DSINTRO][DSPROT][DSREC], the community
has come to the realization that there will not be one signed name
space, but rather islands of signed name space each originating from
specific points (i.e. 'trust points') in the DNS tree. Each of
those islands will be identified by the trust point name, and
validated by at least one associated public key. For the purpose of
this document we'll call the association of that name and a
particular key a 'trust anchor'. A particular trust point can have
more than one key designated as a trust anchor.
For a DNSSEC-aware resolver to validate information in a DNSSEC
protected branch of the hierarchy, it must have knowledge of a trust
anchor applicable to that branch. It may also have more than one
trust anchor for any given trust point. Under current rules, a chain
of trust for DNSSEC-protected data that chains its way back to ANY
known trust anchor is considered 'secure'.
Because of the probable balkanization of the DNSSEC tree due to
signing voids at key locations, a resolver may need to know literally
thousands of trust anchors to perform its duties. (e.g. Consider an
unsigned ".COM".) Requiring the owner of the resolver to manually
manage this many relationships is problematic. It's even more
problematic when considering the eventual requirement for key
replacement/update for a given trust anchor. The mechanism described
herein won't help with the initial configuration of the trust anchors
in the resolvers, but should make trust point key
replacement/rollover more viable.
As mentioned above, this document describes a mechanism whereby a
resolver can update the trust anchors for a given trust point, mainly
without human intervention at the resolver. There are some corner
cases discussed (e.g. multiple key compromise) that may require
manual intervention, but they should be few and far between. This
document DOES NOT discuss the general problem of the initial
configuration of trust anchors for the resolver.
1.1 Compliance Nomenclature
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 BCP 14, [RFC2119].
1.2 Changes since -00
Resubmitted draft-stjohns-dnssec-trustupdate as a working group
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draft.
Added the concept of timer triggered resolver queries to refresh the
resolvers view of the trust anchor key RRSet.
2. Theory of Operation
The general concept of this mechanism is that existing trust anchors
can be used to authenticate new trust anchors at the same point in
the DNS hierarchy. When a new SEP key is added to a trust point
DNSKEY RRSet, and when that RRSet is validated by an existing trust
anchor, then the new key can be added to the set of trust anchors.
There are some issues with this approach which need to be mitigated.
For example, a compromise of one of the existing keys could allow an
attacker to add their own 'valid' data. This implies a need for a
method to revoke an existing key regardless of whether or not that
key is compromised. As another example assuming a single key
compromise, an attacker could add a new key and revoke all the other
old keys.
2.1 Revocation
Assume two trust anchor keys A and B. Assume that B has been
compromised. Without a specific revocation bit, B could invalidate A
simply by sending out a signed trust point key set which didn't
contain A. To fix this, we add a mechanism which requires knowledge
of the private key of a DNSKEY to revoke that DNSKEY.
A key is considered revoked when the resolver sees the key in a
self-signed RRSet and the key has the REVOKE bit set to '1'. Once
the resolver sees the REVOKE bit, it MUST NOT use this key as a trust
anchor or for any other purposes except validating the RRSIG over the
DNSKEY RRSet specifically for the purpose of validating the
revocation. Unlike the 'Add' operation below, revocation is
immediate and permanent upon receipt of a valid revocation at the
resolver.
N.B. A DNSKEY with the REVOKE bit set has a different fingerprint
than one without the bit set. This affects the matching of a DNSKEY
to DS records in the parent, or the fingerprint stored at a resolver
used to configure a trust point. [msj3]
In the given example, the attacker could revoke B because it has
knowledge of B's private key, but could not revoke A.
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2.2 Add Hold-Down
Assume two trust point keys A and B. Assume that B has been
compromised. An attacker could generate and add a new trust anchor
key - C (by adding C to the DNSKEY RRSet and signing it with B), and
then invalidate the compromised key. This would result in the both
the attacker and owner being able to sign data in the zone and have
it accepted as valid by resolvers.
To mitigate, but not completely solve, this problem, we add a
hold-down time to the addition of the trust anchor. When the
resolver sees a new SEP key in a validated trust point DNSKEY RRSet,
the resolver starts an acceptance timer, and remembers all the keys
that validated the RRSet. If the resolver ever sees the DNSKEY RRSet
without the new key but validly signed, it stops the acceptance
process and resets the acceptance timer. If all of the keys which
were originally used to validate this key are revoked prior to the
timer expiring, the resolver stops the acceptance process and resets
the timer.
Once the timer expires, the new key will be added as a trust anchor
the next time the validated RRSet with the new key is seen at the
resolver. The resolver MUST NOT treat the new key as a trust anchor
until the hold down time expires AND it has retrieved and validated a
DNSKEY RRSet after the hold down time which contains the new key.
N.B.: Once the resolver has accepted a key as a trust anchor, the key
MUST be considered a valid trust anchor by that resolver until
explictly revoked as described above.
In the given example, the zone owner can recover from a compromise by
revoking B and adding a new key D and signing the DNSKEY RRSet with
both A and B.
The reason this does not completely solve the problem has to do with
the distributed nature of DNS. The resolver only knows what it sees.
A determined attacker who holds one compromised key could keep a
single resolver from realizing that key had been compromised by
intercepting 'real' data from the originating zone and substituting
their own (e.g. using the example, signed only by B). This is no
worse than the current situation assuming a compromised key.
2.3 Remove Hold-down
A new key which has been seen by the resolver, but hasn't reached
it's add hold-down time, MAY be removed from the DNSKEY RRSet by the
zone owner. If the resolver sees a validated DNSKEY RRSet without
this key, it waits for the remove hold-down time and then, if the key
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hasn't reappeared, SHOULD discard any information about the key.
2.4 Active Refresh
A resolver which has been configured for automatic update of keys
from a particular trust point MUST query that trust point (e.g. do a
lookup for the DNSKEY RRSet and related RRSIG records) no less often
than the lesser of 15 days or half the original TTL for the DNSKEY
RRSet or half the RRSIG expiration interval. The expiration interval
is the amount of time from when the RRSIG was last retrieved until
the expiration time in the RRSIG.
If the query fails, the resolver MUST repeat the query until
satisfied no more often than once an hour and no less often than the
lesser of 1 day or 10% of the original TTL or 10% of the original
expiration interval.
2.5 Resolver Parameters
2.5.1 Add Hold-Down Time
The add hold-down time is 30 days or the expiration time of the TTL
of the first trust point DNSKEY RRSet which contained the key,
whichever is greater. This ensures that at least two validated
DNSKEY RRSets which contain the new key MUST be seen by the resolver
prior to the key's acceptance.
2.5.2 Remove Hold-Down Time
The remove hold-down time is 30 days.
2.5.3 Minimum Trust Anchors per Trust Point
A compliant resolver MUST be able to manage at least five SEP keys
per trust point.
3. Changes to DNSKEY RDATA Wire Format
Bit n [msj2] of the DNSKEY Flags field is designated as the 'REVOKE'
flag. If this bit is set to '1', AND the resolver sees an
RRSIG(DNSKEY) signed by the associated key, then the resolver MUST
consider this key permanently invalid for all purposes except for
validing the revocation.
4. State Table
The most important thing to understand is the resolver's view of any
key at a trust point. The following state table describes that view
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at various points in the key's lifetime. The table is a normative
part of this specification. The initial state of the key is 'Start'.
The resolver's view of the state of the key changes as various events
occur.
[msj1] This is the state of a trust point key as seen from the
resolver. The column on the left indicates the current state. The
header at the top shows the next state. The intersection of the two
shows the event that will cause the state to transition from the
current state to the next.
NEXT STATE
--------------------------------------------------
FROM |Start |AddPend |Valid |Missing|Revoked|Removed|
----------------------------------------------------------
Start | |NewKey | | | | |
----------------------------------------------------------
AddPend |KeyRem | |AddTime| | |
----------------------------------------------------------
Valid | | | |KeyRem |Revbit | |
----------------------------------------------------------
Missing | | |KeyPres| |Revbit | |
----------------------------------------------------------
Revoked | | | | | |RemTime|
----------------------------------------------------------
Removed | | | | | | |
----------------------------------------------------------
4.1 Events
NewKey The resolver sees a valid DNSKEY RRSet with a new SEP key.
That key will become a new trust anchor for the named trust point
after its been present in the RRSet for at least 'add time'.
KeyPres The key has returned to the valid DNSKEY RRSet.
KeyRem The resolver sees a valid DNSKEY RRSet that does not contain
this key.
AddTime The key has been in every valid DNSKEY RRSet seen for at
least the 'add time'.
RemTime A revoked key has been missing from the trust point DNSKEY
RRSet for sufficient time to be removed from the trust set.
RevBit The key has appeared in the trust anchor DNSKEY RRSet with its
"REVOKED" bit set, and there is an RRSig over the DNSKEY RRSet
signed by this key.
4.2 States
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Start The key doesn't yet exist as a trust anchor at the resolver.
It may or may not exist at the zone server, but hasn't yet been
seen at the resolver.
AddPend The key has been seen at the resolver, has its 'SEP' bit set,
and has been included in a validated DNSKEY RRSet. There is a
hold-down time for the key before it can be used as a trust
anchor.
Valid The key has been seen at the resolver and has been included in
all validated DNSKEY RRSets from the time it was first seen up
through the hold-down time. It is now valid for verifying RRSets
that arrive after the hold down time. Clarification: The DNSKEY
RRSet does not need to be continuously present at the resolver
(e.g. its TTL might expire). If the RRSet is seen, and is
validated (i.e. verifies against an existing trust anchor), this
key MUST be in the RRSet otherwise a 'KeyRem' event is triggered.
Missing This is an abnormal state. The key remains as a valid trust
point key, but was not seen at the resolver in the last validated
DNSKEY RRSet. This is an abnormal state because the zone operator
should be using the REVOKE bit prior to removal. [Discussion
item: Should a missing key be considered revoked after some
period of time?]
Revoked This is the state a key moves to once the resolver sees an
RRSIG(DNSKEY) signed by this key where that DNSKEY RRSet contains
this key with its REVOKE bit set to '1'. Once in this state, this
key MUST permanently be considered invalid as a trust anchor.
Removed After a fairly long hold-down time, information about this
key may be purged from the resolver. A key in the removed state
MUST NOT be considered a valid trust anchor.
5. Scenarios
The suggested model for operation is to have one active key and one
stand-by key at each trust point. The active key will be used to
sign the DNSKEY RRSet. The stand-by key will not normally sign this
RRSet, but the resolver will accept it as a trust anchor if/when it
sees the signature on the trust point DNSKEY RRSet.
Since the stand-by key is not in active signing use, the associated
private key may (and SHOULD) be provided with additional protections
not normally available to a key that must be used frequently. E.g.
locked in a safe, split among many parties, etc. Notionally, the
stand-by key should be less subject to compromise than an active key,
but that will be dependent on operational concerns not addressed
here.
5.1 Adding A Trust Anchor
Assume an existing trust anchor key 'A'.
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1. Generate a new key pair.
2. Create a DNSKEY record from the key pair and set the SEP and Zone
Key bits.
3. Add the DNSKEY to the RRSet.
4. Sign the DNSKEY RRSet ONLY with the existing trust anchor key -
'A'.
5. Wait a while.
5.2 Deleting a Trust Anchor
Assume existing trust anchors 'A' and 'B' and that you want to revoke
and delete 'A'.
1. Set the revolcation bit on key 'A'.
2. Sign the DNSKEY RRSet with both 'A' and 'B'.
'A' is now revoked. The operator SHOULD include the revoked 'A' in
the RRSet for at least the remove hold-down time, but then may remove
it from the DNSKEY RRSet.
5.3 Key Roll-Over
Assume existing keys A and B. 'A' is actively in use (i.e. has been
signing the DNSKEY RRSet.) 'B' was the stand-by key. (i.e. has
been in the DNSKEY RRSet and is a valid trust anchor, but wasn't
being used to sign the RRSet.)
1. Generate a new key pair 'C'.
2. Add 'C' to the DNSKEY RRSet.
3. Set the revocation bit on key 'A'.
4. Sign the RRSet with 'A' and 'B'.
'A' is now revoked, 'B' is now the active key, and 'C' will be the
stand-by key once the hold-down expires. The operator SHOULD include
the revoked 'A' in the RRSet for at least the remove hold-down time,
but may then remove it from the DNSKEY RRSet.
5.4 Active Key Compromised
This is the same as the mechanism for Key Roll-Over (Section 5.3)
above assuming 'A' is the active key.
5.5 Stand-by Key Compromised
Using the same assumptions and naming conventions as Key Roll-Over
(Section 5.3) above:
1. Generate a new key pair 'C'.
2. Add 'C' to the DNSKEY RRSet.
3. Set the revocation bit on key 'B'.
4. Sign the RRSet with 'A' and 'B'.
'B' is now revoked, 'A' remains the active key, and 'C' will be the
stand-by key once the hold-down expires. 'B' SHOULD continue to be
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included in the RRSet for the remove hold-down time.
6. Security Considerations
6.1 Key Ownership vs Acceptance Policy
The reader should note that, while the zone owner is responsible
creating and distributing keys, it's wholly the decision of the
resolver owner as to whether to accept such keys for the
authentication of the zone information. This implies the decision
update trust anchor keys based on trust for a current trust anchor
key is also the resolver owner's decision.
The resolver owner (and resolver implementers) MAY choose to permit
or prevent key status updates based on this mechanism for specific
trust points. If they choose to prevent the automated updates, they
will need to establish a mechanism for manual or other out-of-band
updates outside the scope of this document.
6.2 Multiple Key Compromise
This scheme permits recovery as long as at least one valid trust
anchor key remains uncompromised. E.g. if there are three keys, you
can recover if two of them are compromised. The zone owner should
determine their own level of comfort with respect to the number of
active valid trust anchors in a zone and should be prepared to
implement recovery procedures once they detect a compromise. A
manual or other out-of-band update of all resolvers will be required
if all trust anchor keys at a trust point are compromised.
6.3 Dynamic Updates
Allowing a resolver to update its trust anchor set based in-band key
information is potentially less secure than a manual process.
However, given the nature of the DNS, the number of resolvers that
would require update if a trust anchor key were compromised, and the
lack of a standard management framework for DNS, this approach is no
worse than the existing situation.
7 Normative References
[DSINTRO] Arends, R., "DNS Security Introduction and Requirements",
ID draft-ietf-dnsext-dnssec-intro-09.txt, October 2004,
<http://www.ietf.org/internet-drafts/draft-ietf-dnsext-dns
sec-intro-13.txt>.
[DSPROT] Arends, R., "Protocol Modifications for the DNS Security
Extensions", ID draft-ietf-dnsext-dnssec-protocol-05.txt,
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October 2004,
<http://www.ietf.org/internet-drafts/draft-ietf-dnsext-dns
sec-protocol-09.txt>.
[DSREC] Arends, R., "Resource Records for the DNS Security
Extensions", ID draft-ietf-dnsext-dnssec-records-07.txt,
October 2004,
<http://www.ietf.org/internet-drafts/draft-ietf-dnsext-dns
sec-records-11.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2535] Eastlake, D., "Domain Name System Security Extensions",
RFC 2535, March 1999.
Editorial Comments
[msj1] msj: N.B. This table is preliminary and will be revised to
match implementation experience. For example, should there
be a state for "Add hold-down expired, but haven't seen the
new RRSet"?
[msj2] msj: To be assigned.
[msj3] msj: For discussion: What's the implementation guidance for
resolvers currently with respect to the non-assigned flag
bits? If they consider the flag bit when doing key matching
at the trust anchor, they won't be able to match.
Author's Address
Michael StJohns
Nominum, Inc.
2385 Bay Road
Redwood City, CA 94063
USA
Phone: +1-301-528-4729
EMail: Mike.StJohns@nominum.com
URI: www.nominum.com
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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INTERNET-DRAFT D. Senie
Category: BCP Amaranth Networks Inc.
Expires in six months February 2005
Encouraging the use of DNS IN-ADDR Mapping
Status of this Memo
By submitting this Internet-Draft, each 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 becomes
aware will be disclosed, in accordance with Section 6 of RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
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The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
<http://www.ietf.org/shadow.html>http://www.ietf.org/shadow.html
Abstract
Mapping of addresses to names has been a feature of DNS. Many sites,
implement it, many others don't. Some applications attempt to use it
as a part of a security strategy. The goal of this document is to
encourage proper deployment of address to name mappings, and provide
guidance for their use.
Copyright Notice
Copyright (C) The Internet Society. (2005)
1. Introduction
The Domain Name Service has provision for providing mapping of IP
addresses to host names. It is common practice to ensure both name to
address, and address to name mappings are provided for networks. This
practice, while documented, has never been required, though it is
generally encouraged. This document both encourages the presence of
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these mappings and discourages reliance on such mappings for security
checks.
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].
2. Discussion
From the early days of the Domain Name Service [RFC883] a special
domain has been set aside for resolving mappings of IP addresses to
domain names. This was refined in [RFC1035], describing the .IN-
ADDR.ARPA in use today. For the in the IPv6 address space, .IP6.ARPA
was added [RFC3152]. This document uses IPv4 CIDR block sizes and
allocation strategy where there are differences and uses IPv4
terminology. Aside from these differences, this document can and
should be applied to both address spaces.
The assignment of blocks of IP address space was delegated to three
regional registries. Guidelines for the registries are specified in
[RFC2050], which requires regional registries to maintain IN-ADDR
records on the large blocks of space issued to ISPs and others.
ARIN's policy requires ISPs to maintain IN-ADDR for /16 or larger
allocations. For smaller allocations, ARIN can provide IN-ADDR for
/24 and shorter prefixes. [ARIN]. APNIC provides methods for ISPs to
update IN-ADDR, however the present version of its policy document
for IPv4 [APNIC] dropped the IN-ADDR requirements that were in draft
copies of this document. As of this writing, it appears APNIC has no
actual policy on IN-ADDR. RIPE appears to have the strongest policy
in this area [RIPE302] indicating Local Internet Registries should
provide IN-ADDR services, and delegate those as appropriate when
address blocks are delegated.
As we can see, the regional registries have their own policies for
recommendations and/or requirements for IN-ADDR maintenance. It
should be noted, however, that many address blocks were allocated
before the creation of the regional registries, and thus it is
unclear whether any of the policies of the registries are binding on
those who hold blocks from that era.
Registries allocate address blocks on CIDR [RFC1519] boundaries.
Unfortunately the IN-ADDR zones are based on classful allocations.
Guidelines [RFC2317] for delegating on non-octet-aligned boundaries
exist, but are not always implemented.
3. Examples of impact of missing IN-ADDR
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These are some examples of problems that may be introduced by
reliance on IN-ADDR.
Some applications use DNS lookups for security checks. To ensure
validity of claimed names, some applications will look up IN-ADDR
records to get names, and then look up the resultant name to see if
it maps back to the address originally known. Failure to resolve
matching names is seen as a potential security concern.
Some FTP sites will flat-out reject users, even for anonymous FTP, if
the IN-ADDR lookup fails or if the result of the IN-ADDR lookup when
itself resolved, does not match. Some Telnet servers also implement
this check.
Web sites are in some cases using IN-ADDR checks to verify whether
the client is located within a certain geopolitical entity. This
approach has been employed for downloads of crypto software, for
example, where export of that software is prohibited to some locales.
Credit card anti-fraud systems also use these methods for geographic
placement purposes.
The popular TCP Wrappers program found on most Unix and Linux systems
has options to enforce IN-ADDR checks and to reject any client that
does not resolve. This program also has a way to check to see that
the name given by a PTR record then resolves back to the same IP
address. This method provdes more comfort but no appreciable
additional security.
Some anti-spam (anti junk email) systems use IN-ADDR to verify the
presence of a PTR record, or validate the PTR value points back to
the same address.
Many web servers look up the IN-ADDR of visitors to be used in log
analysis. This adds to the server load, but in the case of IN-ADDR
unavailability, it can lead to delayed responses for users.
Traceroutes with descriptive IN-ADDR naming proves useful when
debugging problems spanning large areas. When this information is
missing, the traceroutes take longer, and it takes additional steps
to determine that network is the cause of problems.
Wider-scale implementation of IN-ADDR on dialup, wireless access and
other such client-oriented portions of the Internet would result in
lower latency for queries (due to lack of negative caching), and
lower name server load and DNS traffic.
4. Recommendations
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4.1 Delegation Recommendations
Regional Registries and any Local Registries to whom they delegate
should establish and convey a policy to those to whom they delegate
blocks that IN-ADDR mappings are recommended. Policies should
recommend those receiving delegations to provide IN-ADDR service
and/or delegate to downstream customers.
Network operators should define and implement policies and procedures
which delegate IN-ADDR to their clients who wish to run their own IN-
ADDR DNS services, and provide IN-ADDR services for those who do not
have the resources to do it themselves. Delegation mechanisms should
permit the downstream customer to implement and comply with IETF
recommendations application of IN-ADDR to CIDR [RFC2317].
All IP address space assigned and in use should be resolved by IN-
ADDR records. All PTR records must use canonical names.
All IP addresses in use within a block should have an IN-ADDR
mapping. Those addresses not in use, and those that are not valid for
use (zeros or ones broadcast addresses within a CIDR block) need not
have mappings.
It should be noted that due to CIDR, many addresses that appear to be
otherwise valid host addresses may actually be zeroes or ones
broadcast addresses. As such, attempting to audit a site's degree of
compliance may only be done with knowledge of the internal subnet
architecture of the site. It can be assumed, however, any host that
originates an IP packet necessarily will have a valid host address,
and must therefore have an IN-ADDR mapping.
4.2 Application Recommendations
Applications SHOULD NOT rely on IN-ADDR for proper operation. The use
of IN-ADDR, sometimes in conjunction with a lookup of the name
resulting from the PTR record provides no real security, can lead to
erroneous results and generally just increases load on DNS servers.
Further, in cases where address block holders fail to properly
configure IN-ADDR, users of those blocks are penalized.
5. Security Considerations
This document has no negative impact on security. While it could be
argued that lack of PTR record capabilities provides a degree of
anonymity, this is really not valid. Trace routes, whois lookups and
other sources will still provide methods for discovering identity.
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By recommending applications avoid using IN-ADDR as a security
mechanism this document points out that this practice, despite its
use by many applications, is an ineffective form of security.
Applications should use better mechanisms of authentication.
6. IANA Considerations
There are no IANA considerations for this document.
7. References
7.1 Normative References
[RFC883] P.V. Mockapetris, "Domain names: Implementation
specification," RFC883, November 1983.
[RFC1035] P.V. Mockapetris, "Domain Names: Implementation
Specification," RFC 1035, November 1987.
[RFC1519] V. Fuller, et. al., "Classless Inter-Domain Routing (CIDR):
an Address Assignment and Aggregation Strategy," RFC 1519, September
1993.
[RFC2026] S. Bradner, "The Internet Standards Process -- Revision 3",
RFC 2026, BCP 9, October 1996.
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC2050] K. Hubbard, et. al., "Internet Registry IP Allocation
Guidelines", RFC2050, BCP 12, Novebmer 1996.
[RFC2317] H. Eidnes, et. al., "Classless IN-ADDR.ARPA delegation,"
RFC 2317, March 1998.
[RFC3152] R. Bush, "Delegation of IP6.ARPA," RFC 3152, BCP 49, August
2001.
7.2 Informative References
[ARIN] "ISP Guidelines for Requesting Initial IP Address Space," date
unknown,
<http://www.arin.net/regserv/initial-isp.html>http://www.arin.net/regserv/initial-isp.html
[APNIC] "Policies For IPv4 Address Space Management in the Asia
Pacific Region," APNIC-086, 13 January 2003.
[RIPE302] "Policy for Reverse Address Delegation of IPv4 and IPv6
Address Space in the RIPE NCC Service Region", RIPE-302, April 26,
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2004.
<http://www.ripe.net//ripe/docs/rev-del.html>http://www.ripe.net//ripe/docs/rev-del.html
8. Acknowledgements
Thanks to Peter Koch and Gary Miller for their input, and to many
people who encouraged me to write this document.
9. Author's Address
Daniel Senie
Amaranth Networks Inc.
324 Still River Road
Bolton, MA 01740
Phone: (978) 779-5100
EMail: <mailto:dts@senie.com>dts@senie.com
10. Full Copyright Statement
Copyright (C) The Internet Society (2004). 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.
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 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.
Intellectual Property
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 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
Senie [Page 6]
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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>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 <mailto:ietf-ipr@ietf.org>ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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DNSOP G. Guette
Internet-Draft IRISA / INRIA
Expires: July 19, 2005 O. Courtay
Thomson R&D
January 18, 2005
Requirements for Automated Key Rollover in DNSSEC
draft-ietf-dnsop-key-rollover-requirements-02.txt
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on July 19, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract
This document describes problems that appear during an automated
rollover and gives the requirements for the design of communication
between parent zone and child zone during an automated rollover
process. This document is essentially about in-band key rollover.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Key Rollover Process . . . . . . . . . . . . . . . . . . . 3
3. Basic Requirements . . . . . . . . . . . . . . . . . . . . . . 4
4. Messages authentication and information exchanged . . . . . . 5
5. Emergency Rollover . . . . . . . . . . . . . . . . . . . . . . 5
6. Security consideration . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7
A. Documents details and changes . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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1. Introduction
The DNS security extensions (DNSSEC) [4][6][5][7] uses public-key
cryptography and digital signatures. It stores the public part of
keys in DNSKEY Resource Records (RRs). Because old keys and
frequently used keys are vulnerable, they must be renewed
periodically. In DNSSEC, this is the case for Zone Signing Keys
(ZSKs) and Key Signing Keys (KSKs) [1][2]. Automation of key
exchanges between parents and children is necessary for large zones
because there are too many changes to handle.
Let us consider for example a zone with 100000 secure delegations.
If the child zones change their keys once a year on average, that
implies 300 changes per day for the parent zone. This amount of
changes is hard to manage manually.
Automated rollover is optional and resulting from an agreement
between the administrator of the parent zone and the administrator of
the child zone. Of course, key rollover can also be done manually by
administrators.
This document describes the requirements for a protocol to perform
the automated key rollover process and focusses on interaction
between parent and child zone.
2. The Key Rollover Process
Key rollover consists of renewing the DNSSEC keys used to sign
resource records in a given DNS zone file. There are two types of
rollover, ZSK rollovers and KSK rollovers.
During a ZSK rollover, all changes are local to the zone that renews
its key: there is no need to contact other zones administrators to
propagate the performed changes because a ZSK has no associated DS
record in the parent zone.
During a KSK rollover, new DS RR(s) must be created and stored in the
parent zone. In consequence, data must be exchanged between child
and parent zones.
The key rollover is built from two parts of different nature:
o An algorithm that generates new keys and signs the zone file. It
can be local to the zone,
o the interaction between parent and child zones.
One example of manual key rollover [3] is:
o The child zone creates a new KSK,
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o the child zone waits for the creation of the DS RR in its parent
zone,
o the child zone deletes the old key,
o the parent zone deletes the old DS RR.
This document concentrates on defining interactions between entities
present in key rollover process.
3. Basic Requirements
This section provides the requirements for automated key rollover in
case of normal use. Exceptional case like emergency rollover is
specifically described later in this document.
The main condition during a key rollover is that the chain of trust
must be preserved to every validating DNS client. No matter if this
client retrieves some of the RRs from recursive caching name server
or from the authoritative servers for the zone involved in the
rollover.
Automated key rollover solution may be interrupted by a manual
intervention. This manual intervention should not compromise the
security state of the chain of trust. If the chain is safe before
the manual intervention, the chain of trust must remain safe during
and after the manual intervention
Two entities act during a KSK rollover: the child zone and its parent
zone. These zones are generally managed by different administrators.
These administrators should agree on some parameters like
availability of automated rollover, the maximum delay between
notification of changes in the child zone and the resigning of the
parent zone. The child zone needs to know this delay to schedule its
changes and/or to verify that the changes had been taken into account
in the parent zone. Hence, the child zone can also avoid some
critical cases where all child key are changed prior to the DS RR
creation.
By keeping some resource records during a given time, the recursive
cache servers can act on the automated rollover. The existence of
recursive cache servers must be taken into account by automated
rollover solution.
Indeed, during an automated key rollover a name server could have to
retrieve some DNSSEC data. An automated key rollover solution must
ensure that these data are not old DNSSEC material retrieved from a
recursive name server.
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4. Messages authentication and information exchanged
This section addresses in-band rollover, security of out-of-band
mechanisms is out of scope of this document.
The security provided by DNSSEC must not be compromised by the key
rollover, thus every exchanged message must be authenticated to avoid
fake rollover messages from malicious parties.
Once the changes related to a KSK are made in a child zone, there are
two ways for the parent zone to take this changes into account:
o the child zone notify directly or not directly its parent zone in
order to create the new DS RR and store this DS RR in parent zone
file,
o or the parent zone poll the child zone.
In both cases, the parent zone must receive all the child keys that
need the creation of associated DS RRs in the parent zone.
Because errors could occur during the transmission of keys between
child and parent, the key exchange protocol must be fault tolerant.
Should an error occured during the automated key rollover, an
automated key rollover solution must be able to keep the zone files
in a consistent state.
5. Emergency Rollover
Emergency key rollover is a special case of rollover decided by the
zone administrator generally for security reasons. In consequence,
emergency key rollover can break some of the requirement described
above.
A zone key might be compromised and an attacker can use the
compromised key to create and sign fake records. To avoid this, the
zone administrator may change the compromised key or all its keys as
soon as possible, without waiting for the creation of new DS RRs in
its parent zone.
Fast changes may break the chain of trust. The part of DNS tree
having this zone as apex can become unverifiable, but the break of
the chain of trust is necessary if the administrator wants to prevent
the compromised key from being used (to spoof DNS data).
Parent and child zones sharing an automated rollover mechanism,
should have an out-of-band way to re-establish a consistent state at
the delegation point (DS and DNSKEY RRs). This allows to avoid that
a malicious party uses the compromised key to roll the zone keys.
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6. Security consideration
The automated key rollover process in DNSSEC allows automated renewal
of any kind of DNS key (ZSK or KSK). It is essential that parent
side and child side can do mutual authentication. Moreover,
integrity of the material exchanged between the parent and child zone
must be provided to ensure the right DS are created.
As in any application using public key cryptography, in DNSSEC a key
may be compromised. What to do in such a case can be describe in the
zone local policy and can violate some requirements described in this
draft. The emergency rollover can break the chain of trust in order
to protect the zone against the use of the compromised key.
7. Acknowledgments
The authors want to thank members of IDsA project for their
contribution to this document.
8 Normative References
[1] Gudmundsson, O., "Delegation Signer (DS) Resource Record (RR)",
RFC 3658, December 2003.
[2] Kolkman, O., Schlyter, J. and E. Lewis, "Domain Name System KEY
(DNSKEY) Resource Record (RR) Secure Entry Point (SEP) Flag",
RFC 3757, May 2004.
[3] Kolkman, O., "DNSSEC Operational Practices",
draft-ietf-dnsop-dnssec-operational-practice-01 (work in
progress), May 2004.
[4] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[5] Arends, R., Austein, R., Larson, M., Massey, D. and S. Rose,
"Resource Records for the DNS Security Extensions",
draft-ietf-dnsext-dnssec-records-11 (work in progress), October
2004.
[6] Arends, R., Austein, R., Larson, M., Massey, D. and S. Rose,
"DNS Security Introduction and Requirements",
draft-ietf-dnsext-dnssec-intro-13 (work in progress), October
2004.
[7] Arends, R., Austein, R., Larson, M., Massey, D. and S. Rose,
"Protocol Modifications for the DNS Security Extensions",
draft-ietf-dnsext-dnssec-protocol-09 (work in progress), October
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2004.
Authors' Addresses
Gilles Guette
IRISA / INRIA
Campus de Beaulieu
35042 Rennes CEDEX
FR
EMail: gilles.guette@irisa.fr
URI: http://www.irisa.fr
Olivier Courtay
Thomson R&D
1, avenue Belle Fontaine
35510 Cesson S?vign? CEDEX
FR
EMail: olivier.courtay@thomson.net
Appendix A. Documents details and changes
This section is to be removed by the RFC editor if and when the
document is published.
Section about NS RR rollover has been removed
Remarks from Samuel Weiler and Rip Loomis added
Clarification about in-band rollover and in emergency section
Section 3, details about recursive cache servers added
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Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property 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; neither does it represent
that it has made any effort to identify any such rights.
Information on the IETF's procedures with respect to rights in
IETF Documents can be found in BCP 78 and 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 which may cover technology that may be required
to implement this standard. Please address the information to the
IETF at ietf-ipr.org.
Full Copyright Statement
Copyright (C) The Internet Society (2005). 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.
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 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Guette & Courtay Expires July 19, 2005 [Page 8]