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Network Working Group R. Arends
Internet-Draft Nominum, Inc.
Expires: May 2, 2002 M. Kosters
D. Blacka
Verisign, Inc.
November 1, 2001
DNSSEC Opt-In
draft-ietf-dnsext-dnssec-opt-in-01
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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 May 2, 2002.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
RFC 2535 defines a secure zone as completely signed. There are cases
where there is no need, it is not practical, or simply not possible
to maintain a completely signed zone. To allow administrators to
gradually adopt DNSSEC, a model, "Opt-In", is proposed that
generalizes the inclusion of unsigned records within a secure zone.
Arends, et al. Expires May 2, 2002 [Page 1]
Internet-Draft DNSSEC Opt-In November 2001
Table of Contents
1. Definitions and Terminology . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Additions . . . . . . . . . . . . . . . . . . . . . . 5
4. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12
A. Implementing Opt-In using "Views" . . . . . . . . . . . . . . 14
Full Copyright Statement . . . . . . . . . . . . . . . . . . . 16
Arends, et al. Expires May 2, 2002 [Page 2]
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1. Definitions and Terminology
Throughout this document, familiarity with the DNS system, RFC 1035
[1], DNS security extensions, RFC 2535 [4], and DNSSEC terminology
RFC 3090 [5] is assumed.
The following abbreviations and terms are used in this document:
RR: is used to refer to a DNS resource record.
RRset: refers to a Resource Record Set, as defined by [3].
Delegation RRset: refers to a RRset of type NS that forms a zone cut.
That is, any NS RRsets except those residing at the zone apex.
node: describes the set all RRsets for a single owner name. In other
words, all records in the zone with the same name (but possibly
differing types).
secure node: refers to a node where all RRsets within the node are
signed, minus delegation RRsets. All signed nodes contain a
single NXT record.
insecure node: refers to a node where none of the RRsets within the
node are signed.
name: refers to the owner name of a node.
The key words "MUST, "MUST NO", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY, and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2].
Arends, et al. Expires May 2, 2002 [Page 3]
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2. Overview
In order to ease deployment of DNSSEC, it is desirable to have a
mechanism that generally allows for unsigned records to exist within
an otherwise secure zone.
In the current definition of DNSSEC, RFC 2535 [4], there are already
two types of unsigned RRsets: delegation point NS RRsets and glue
RRsets. This document proposes a model, Opt-In, that generalizes the
capability to have unsigned records within a secure zone. This is
accomplished by extending the semantics of the NXT record using a
redundant bit in the type bit map.
Arends, et al. Expires May 2, 2002 [Page 4]
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3. Protocol Additions
In RFC 2535, a secured zone consists of a series of secured nodes,
where each node contains a signed NXT RR. The (non)existence of a
node is proven using the intervals defined by the NXT RR's owner
names and next values. The (non)existence of a RRset within a node
is proven using the type bit map in the NXT RR.
Opt-In expands this definition by allowing insecure nodes to be
interleaved between secure nodes. Since this represents a change of
the interpretation of NXT records, resolvers must be able to
distinguish between RFC 2535 NXT records and Opt-In NXT records.
This is accomplished by tagging the NXT records that span (or
potentially span) insecure nodes. This tag is indicated by the
absence of the NXT bit in the type bit map. Since the NXT bit in the
type map merely indicates the existence of the record itself, this
bit is redundant and open for use as a tag.
Using Opt-In, the existence or non-existence of insecure nodes is not
asserted by the tagged NXT records. This allows for the addition or
removal of insecure RRsets without recalculating and resigning the
NXT chain. However, Opt-In NXT records still assert the
(non)existence of secure nodes, and the existence of individual
RRsets within the secure nodes.
Zones using Opt-In MAY contain a mixture of Opt-In tagged NXT records
and RFC 2535 NXT records. At each secure node, the NXT record within
that node MUST either be RFC 2535 or Opt-In compliant. If it is not
Opt-In, there MUST NOT be any insecure nodes between it and the next
node.
In summary,
o An Opt-In NXT type is identified by a zero-valued (or not-
specified) NXT bit in the type bit map of the NXT record.
o A RFC2535 NXT type is identified by a one-valued NXT bit in the
type bit map of the NXT record.
and
o In RFC 2535, NXT records indicate the existence or non-existence
of all nodes in the zone.
o In Opt-In, tagged NXT records indicate the existence or non-
existence of all SECURE nodes in the zone.
Arends, et al. Expires May 2, 2002 [Page 5]
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4. Benefits
Using Opt-In allows administrators of large or rapidly changing zones
to minimize the overhead involved in maintaining the security of the
zone. One particular way that Opt-In accomplishes this is by
eliminating the need for "no-key" KEY records for insecure subzone
delegations. In RFC 2535, insecure delegations are required to have
an associated signed "no-key" KEY RR. Instead, under Opt-In,
insecure subzone delegation records are stored in insecure nodes.
For large, delegation-centric zones (like TLDs) this can lead to
substantial reductions in overhead.
In addition, because the NXT chain for the zone does not have to be
changed when adding or removing insecure RRs, zones that may be
constantly adding and/or removing RRs can do so without incurring the
overhead associated with modifying and resigning the NXT chain.
Arends, et al. Expires May 2, 2002 [Page 6]
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5. Examples
Consider the zone EXAMPLE, shown below. This is a zone where all of
the NXT records are tagged as Opt-In. It consists of 5 nodes: 3
secure nodes (EXAMPLE., FIRST-SECURE.EXAMPLE., and SECOND-
SECURE.EXAMPLE.) and 2 insecure nodes (NOT-SECURE.EXAMPLE., and
UNSIGNED.EXAMPLE.).
Example A: Fully Opt-In Zone.
EXAMPLE. SOA ...
EXAMPLE. SIG SOA ...
EXAMPLE. NS FIRST-SECURE.EXAMPLE.
EXAMPLE. SIG NS ...
EXAMPLE. KEY ...
EXAMPLE. SIG KEY ...
EXAMPLE. NXT FIRST-SECURE.EXAMPLE. SOA NS SIG KEY
EXAMPLE. SIG NXT ...
FIRST-SECURE.EXAMPLE. A ...
FIRST-SECURE.EXAMPLE. SIG A ...
FIRST-SECURE.EXAMPLE. NXT SECOND-SECURE.EXAMPLE. A SIG
FIRST-SECURE.EXAMPLE. SIG NXT ...
NOT-SECURE.EXAMPLE. NS NS.NOT-SECURE.EXAMPLE.
NS.NOT-SECURE.EXAMPLE. A ...
SECOND-SECURE.EXAMPLE. NS NS.ELSEWHERE.
SECOND-SECURE.EXAMPLE. KEY ...
SECOND-SECURE.EXAMPLE. SIG KEY ...
SECOND-SECURE.EXAMPLE. NXT EXAMPLE. NS SIG KEY
SECOND-SECURE.EXAMPLE. SIG NXT ...
UNSIGNED.EXAMPLE. MX ...
In this example, a query for a signed RRset (e.g., "FIRST-
SECURE.EXAMPLE A"), or a secure delegation ("WWW.SECOND-
SECURE.EXAMPLE A") will result in a standard RFC 2535 response. A
query for a nonexistent RRset will result in a response that differs
from RFC 2535 only in the fact that the NXT record will be tagged as
Opt-In.
A query for an insecure RR will return both the answer (in the Answer
or Authority section, as appropriate) and the corresponding Opt-In
NXT record to prove that it is not secure.
Arends, et al. Expires May 2, 2002 [Page 7]
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Example A.1: Response to query for UNSECURE.EXAMPLE. MX
RCODE=NOERROR
Answer Section:
UNSECURE.EXAMPLE. MX ...
Authority Section:
SECOND-SECURE.EXAMPLE. NXT EXAMPLE. NS SIG KEY
SECOND-SECURE.EXAMPLE. SIG NXT ...
Additional Section:
EXAMPLE. KEY ...
EXAMPLE. SIG KEY ...
Similarly, a query for an RR that is delegated to an insecure subzone
will return both the referral and the corresponding Opt-In NXT record
to prove that it is not secure.
Example A.2: Response to query for WWW.NOT-SECURE.EXAMPLE. A
RCODE=NOERROR
Authority Section:
NOT-SECURE.EXAMPLE. NS NS.NOT-SECURE.EXAMPLE.
FIRST-SECURE.EXAMPLE. NXT SECOND-SECURE.EXAMPLE. A SIG
FIRST-SECURE.EXAMPLE. SIG NXT ...
Additional Section:
NS.NOT-SECURE.EXAMPLE. A ...
EXAMPLE. KEY ...
EXAMPLE. SIG KEY ...
In Example A, the EXAMPLE. node MAY use either style of NXT record,
because there are no insecure nodes that occur between it and the
next node, FIRST-SECURE.EXAMPLE. In other words, Example A would
still be a valid zone if the NXT record for EXAMPLE. was changed to
the following RR:
EXAMPLE. NXT FIRST-SECURE.EXAMPLE. SOA NS SIG KEY NXT
However, the other secure nodes (FIRST-SECURE.EXAMPLE. and SECOND-
SECURE.EXAMPLE.) MUST use Opt-In NXT records, because there are
insecure nodes in the range they define. (NOT-SECURE.EXAMPLE and
UNSECURE.EXAMPLE, respectively).
Arends, et al. Expires May 2, 2002 [Page 8]
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6. Security Considerations
Opt-In allows for unsigned names. All unsigned names are insecure,
and their validity can not be cryptographically proven. With Opt-In,
a malicious entity is able to insert, modify or delete unsigned names
in a secured zone. Thus, it is recommended to use RFC 2535 [4] where
possible and to use Opt-In where necessary.
Arends, et al. Expires May 2, 2002 [Page 9]
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7. IANA Considerations
None.
Arends, et al. Expires May 2, 2002 [Page 10]
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8. Acknowledgments
The contributions, suggestions and remarks of the following persons
(in alphabetic order) to this draft are acknowledged:
Mats Dufberg, Miek Gieben, Olafur Gudmundsson, Bob Halley, Olaf
Kolkman, Ted Lindgreen, Bill Manning, Dan Massey, Scott Rose, Mike
Schiraldi, Jakob Schlyter, Brian Wellington.
Arends, et al. Expires May 2, 2002 [Page 11]
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References
[1] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Elz, R. and R. Bush, "Clarifications to the DNS Specification",
RFC 2181, July 1997.
[4] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[5] Lewis, E., "DNS Security Extension Clarification on Zone
Status", RFC 3090, March 2001.
[6] R. Conrad, D., "Indicating Resolver Support of DNSSEC", draft-
ietf-dnsext-dnssec-okbit-03 (work in progress), October 2001.
Authors' Addresses
Roy Arends
Nominum, Inc.
950 Charter Street
Redwood City, CA 94063
US
Phone: +1 650 381 6000
EMail: Roy.Arends@nominum.com
URI: http://www.nominum.com
Mark Kosters
Verisign, Inc.
21355 Ridgetop Circle
Dulles, VA 20166
US
Phone: +1 703 948 3200
EMail: markk@verisign.com
URI: http://www.verisignlabs.com
Arends, et al. Expires May 2, 2002 [Page 12]
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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
Arends, et al. Expires May 2, 2002 [Page 13]
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Appendix A. Implementing Opt-In using "Views"
In many cases, it may be convenient to implement an opt-in zone by
combining two separately maintained "views" of a zone at request
time. In this context, "view" refers to a particular version of a
zone, not to any specific DNS implementation feature.
In this scenario, one view is the secure view, the other is the
insecure (or legacy) view. The secure view consists of an entirely
signed zone using opt-in tagged NXT records. The insecure view
contains no DNSSEC information. It is helpful, although not
necessary, for the secure view to be a subset (minus DNSSEC records)
of the insecure view.
In addition, the secure view must contain entire nodes. That is, if
any of the RRsets with a given name are signed in the combined opt-in
zone, all RRsets must be signed (and thus in the secure view).
These two views may be combined at request time to provide a virtual,
single opt-in zone. The following algorithm is used when responding
to each query:
V_A is the secure view as described above.
V_B is the insecure view as described above.
R_A is a response generated from V_A, following RFC 2535 [4].
R_B is a response generated from V_B, following DNS resolution as
per RFC 1035 [1].
R_C is the response generated by combining R_A with R_B, as
described below.
A query is DNSSEC-aware if it either has the DO bit [6] turned on,
or is for a DNSSEC-specific record type.
1. If V_A is a subset of V_B and the query is not DNSSEC-aware,
generate and return R_B, otherwise
2. Generate R_A.
3. If R_A's RCODE != NXDOMAIN, return R_A, otherwise
4. Generate R_B and combine it with R_A to form R_C:
Arends, et al. Expires May 2, 2002 [Page 14]
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For each section (ANSWER, AUTHORITY, ADDITIONAL), copy the
records from R_A into R_B, EXCEPT the AUTHORITY section SOA
record, if R_B's RCODE = NOERROR.
5. Return R_C.
Arends, et al. Expires May 2, 2002 [Page 15]
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Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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