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Network Working Group D. Atkins
draft-ietf-dnsext-dns-threats-01.txt IHTFP Consulting
draft-ietf-dnsext-dns-threats-02.txt IHTFP Consulting
R. Austein
InterNetShare, Incorporated
February 2002
Bourgeois Dilettant
November 2002
Threat Analysis Of The Domain Name System
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1. Introduction
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This note assumes that the reader is familiar with both the DNS and
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be prohibitively high. Even more important, however, is that the
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most likely to be successful when the victim is in a known state,
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- Attacker's response includes one or more RRs with DNS names in
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furnished by the user's ISP and advertised to the client via DHCP or
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amplifiers, since DNS response packets tend to be significantly
@@ -418,6 +418,46 @@ draft-ietf-dnsext-dns-threats-01.txt February 2002
if we cannot conceive of a plausible scenario involving this attack
today. This implies that some mitigation of this risk is required.
Note that it's necessary to prove the non-existance of applicable
wildcard RRs as part of the authenticated denial mechanism, and that,
in a zone that is more than one label deep, such a proof may require
proving the non-existance of multiple discrete sets of wildcard RRs.
2.7. Wildcards
Much discussion has taken place over whether and how to provide data
integrity and data origin authentication for "wildcard" DNS names.
Conceptually, RRs with wildcard names are patterns for synthesizing
RRs on the fly according to the matching rules described in section
4.3.2 of RFC 1034. While the rules that control the behavior of
wildcard names have a few quirks that can make them a trap for the
unwary zone administrator, it's clear that a number of sites make
heavy use of wildcard RRs, particularly wildcard MX RRs.
In order to provide the desired services for wildcard RRs, we need to
prove two things:
- We need to prove the existance of the wildcard RR itself (that is,
we need to prove that the synthesis rule exists), and
- We need to prove the non-existance of any RRs which, if they
existed, would make the wildcard RR irrelevant according to the
synthesis rules the way in which wildcards are used (that is, we
need to prove that the synthesis rule is applicable).
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Note that this makes the wildcard proof mechanism dependent upon the
authenticated denial mechanism described in the previous section.
DNSSEC does include mechanisms by which it is possible to furnish
wildcard proofs along the lines described above.
3. Weaknesses of DNSSEC
DNSSEC has some problems of its own:
@@ -444,14 +484,6 @@ draft-ietf-dnsext-dns-threats-01.txt February 2002
topic for another document....)
- Like DNS itself, DNSSEC's trust model is almost totally
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hierarchical. While DNSSEC does allow resolvers to have special
additional knowledge of public keys beyond those for the root, in
the general case the root key is the one that matters. Thus any
@@ -468,6 +500,14 @@ draft-ietf-dnsext-dns-threats-01.txt February 2002
- DNSSEC creates a requirement of loose time synchronization between
the resolver and the host creating the DNSSEC signatures. Prior to
DNSSEC, all time-related actions in DNS could be performed by a
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machine that only knew about "elapsed" or "relative" time. Because
the validity period of a DNSSEC signature is based on "absolute"
time, a resolver must have the same concept of absolute time in
@@ -479,6 +519,20 @@ draft-ietf-dnsext-dns-threats-01.txt February 2002
generating signatures whose validity period does not match what the
signer intended.
- The mechanism for wildcard proofs in DNSSEC is fairly painful. At
various times there have been questions as to whether the proof
mechanism is completely airtight and whether it would be worthwhile
to optimize the wildcard proof mechanism for the common case in
which wildcards do not exist, but the main problem is just the
inherent complexity of the wildcard mechanism itself. This
complexity probably makes the code for generating and checking
wildcard proofs somewhat fragile, but since the alternative of
giving up wildcards entirely is not practical due to widespread
use, we are going to have to live with wildcards, and the question
just becomes one of whether or not the proposed optimizations would
make DNSSEC's wildcard proof mechanisms more or less fragile.
4. Other issues
[Odds and ends that don't yet fit anywhere else, to be revised...]
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limited or closed environment such as a DHCP server updating a local
DNS name server.
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Major issues arise when trying to use dynamic update on a secure
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zone. TSIG can similarly be used in a limited fashion to
authenticate the client to the server, but TSIG only protects DNS
transactions, not the actual data, and the TSIG is not inserted into
@@ -537,12 +592,45 @@ draft-ietf-dnsext-dns-threats-01.txt February 2002
to multiple entities, each of whom may require different kinds of
access. For example, Alice may need to be able to add new nodes to
the zone or change existing nodes, but not remove them; Bob may need
to be able to remove zones but not add them; Charlie may need to be
to be able to remove zones but not add them; Carol may need to be
able to add, remove, or modify nodes, but only A records.
NOTE: Scaling properties of the key management problem here is a
particular concern that needs more study.
4.3. Securing DNS Zone Replication
As discussed in previous sections, DNSSEC per se attempts to provide
data integrity and data origin authentication services on top of the
normal DNS query protocol. Using the terminology discussed in [SEC-
CONS], DNSSEC provides "object security" for the normal DNS query
protocol. For purposes of replicating entire DNS zones, however,
DNSSEC does not provide object security, because zones include
unsigned NS RRs and glue at delegation points. Use of TSIG to
protect zone transfer (AXFR or IXFR) operations provides "channel
security", but still does not provide object security for complete
zones, so the trust relationships involved in zone transfer are still
very much a hop-by-hop matter of name server operators trusting other
name server operators, rather than an end-to-end matter of name
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server operators trusting zone administrators.
Zone object security was not an explicit design goal of DNSSEC, so
failure to provide this service should not be a surprise.
Nevertheless, there are some zone replication scenarios for which
this would be a very useful additional service, so this seems like a
useful area for future work. In theory it should not be difficult to
zone object security as a backwards compatible enhancement to the
existing DNSSEC model, but the DNSEXT WG has not yet discussed either
the desirability of or the requirements for such an enhancement.
5. Conclusion
Based on the above analysis, the DNSSEC extensions do appear to solve
@@ -550,19 +638,9 @@ draft-ietf-dnsext-dns-threats-01.txt February 2002
Security Considerations
This entire document is about security considerations of the DNS. We
believe that deploying DNSSEC will help to address some, but not all,
of the known threats to with DNS.
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This entire document is about security considerations of the DNS.
The authors believe that deploying DNSSEC will help to address some,
but not all, of the known threats to with DNS.
IANA Considerations
@@ -570,12 +648,18 @@ IANA Considerations
Acknowledgments
This note is based both previous published works by others and on on
a number of discussions both public and private over a period of many
This note is based both previous published works by others and on a
number of discussions both public and private over a period of many
years, but particular thanks go to Steve Bellovin, Dan Bernstein,
Randy Bush, Olafur Gudmundsson, Allison Mankin, Paul Vixie, and our
libel lawyers at the firm of Dewey, Chetham, & Howe, none of whom are
responsible for what the authors did with their ideas.
Randy Bush, Olafur Gudmundsson, Allison Mankin, Paul Vixie, and any
other members of the DNS, DNSSEC, DNSIND, and DNSEXT working groups
whose names and contributions the authors have forgotten, none of
whom are responsible for what the authors did with their ideas.
The authors would also like to thank Paul Mockapetris and Xunhua
Wang, both of whom sent useful information to the authors, about
which the authors have, as yet, done absolutely nothing. We were
listening, really, we just ran out of time before the draft deadline.
References
@@ -583,6 +667,15 @@ References
Break-Ins", Proceedings of the Fifth Usenix Unix Security
Symposium, June 1995.
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[Galvin93] Design team meeting summary message posted to dns-
security@tis.com mailing list by Jim Galvin on 19 November 1993.
@@ -611,15 +704,6 @@ References
[DNSSEC] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
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[EDNS0] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
August 1999.
@@ -639,6 +723,20 @@ draft-ietf-dnsext-dns-threats-01.txt February 2002
[DNSSEC-ZONE-STATUS] Lewis, E., "DNS Security Extension Clarification
on Zone Status" RFC 3090, March 2001.
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[SEC-CONS] Rescorla, E., Korver, B., and the Internet Architecture
Board, "Guidelines for Writing RFC Text on Security
Considerations", work in progress (draft-iab-sec-cons-01.txt),
October 2002.
Author's addresses:
Derek Atkins
@@ -646,14 +744,12 @@ Author's addresses:
6 Farragut Ave
Somerville, MA 02144
USA
Email: derek@ihtfp.com
Rob Austein
InterNetShare, Incorporated
325M Sharon Park Drive, Suite 308
Menlo Park, CA 94025
USA
sra@hactrn.net
Email: sra@hactrn.net
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DNSEXT (Independent submission) O. Kolkman
Internet-Draft RIPE NCC
Expires: March 2, 2003 J. Ihren
Autonomica
R. Arends
A.R.E.N.D.S.
September 2002
DNSSEC Wildcard Optimization
draft-olaf-dnsext-dnssec-wildcard-optimization-01.txt
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 March 2, 2003.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
Secure denial of the existence of wildcards may lead to a large
number of NXT RRs and associated SIG RRs in DNS responses, even in
the common case when wildcards are not present in the zone. This
optimization uses one bit from the NXT type array to signal that
there is no closer wildcard in the zone for a given query name. This
reduces the packet size and the need for executing slow, and
complicated, code paths in common queries. In cases where there are
no wildcard RRs in the zone (i.e. the root zone) only one NXT RR and
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corresponding SIG is needed for denial of existence of the wildcard.
The key words "MAY","MAY NOT", "MUST", "MUST NOT", "REQUIRED",
"RECOMMENDED", "SHOULD", and "SHOULD NOT" in this document are to be
interpreted as described in RFC2119.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 RFC2535 Wildcard Processing . . . . . . . . . . . . . . . . 3
1.2 Signalling the Existence of a Wildcard . . . . . . . . . . . 3
2. DNSSEC Protocol Changes . . . . . . . . . . . . . . . . . . 4
2.1 Server Side . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1 Zone Signing . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.2 Server Responses . . . . . . . . . . . . . . . . . . . . . . 4
2.1.3 Dynamic DNS . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Resolver Side . . . . . . . . . . . . . . . . . . . . . . . 5
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . 6
5. Internationalization Considerations . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. Document Changes . . . . . . . . . . . . . . . . . . . . . . 6
7.1 draft 00->01 . . . . . . . . . . . . . . . . . . . . . . . . 6
Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 7
A. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8
A.1 Zone without wildcards . . . . . . . . . . . . . . . . . . . 8
A.1.1 Optimized proof . . . . . . . . . . . . . . . . . . . . . . 8
A.1.2 RFC2535 proof . . . . . . . . . . . . . . . . . . . . . . . 8
A.2 Zone with wildcards . . . . . . . . . . . . . . . . . . . . 9
A.2.1 Optimized proof . . . . . . . . . . . . . . . . . . . . . . 10
A.2.2 NXDOMAIN with additional proof for no wildcard . . . . . . . 10
A.2.3 Another Optimized Proof . . . . . . . . . . . . . . . . . . 11
A.2.4 Denial of Existence of Closer Match . . . . . . . . . . . . 11
A.2.5 The NXT 'next name' Proving Existence of a Wildcard . . . . 12
Full Copyright Statement . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Wildcards make authenticated denial of existence complex. Many zones
do not contain wildcards but still incur a penalty. If the NXT RR
contains an indication that a wildcard match can not exist then less
DNSSEC related RRs and less computation are needed to authoritatively
deny the existence of a name in the zone.
1.1 RFC2535 Wildcard Processing
RFC2535 [1] specifies that the non-existence of a match against a
wildcard is proven by a set of relevant NXT records. In practice
this will result to at least 2 NXT RRs and corresponding SIGs being
returned. There are cases where the denial of the existence of
wildcards will need many more than 2 NXT RRs. Even in zones that do
not use wildcards this will lead to complex answers for which the
resolvers will need to follow NXT chains and which are hard to
troubleshoot by operators.
1.2 Signalling the Existence of a Wildcard
The NXT RR, used to the prove the non-existence of data, uses a type
bit-map to track which types are available for a given name. We
propose to use one bit (see section Section 3) in the type bitmap to
signal if a wildcard is available in a zone. We refer to this bit as
the "NOWILD-bit".
If the NOWILD-bit is set to 1 then the NXT RR signals that there is
no wildcard match possible against the query name, only if the bit is
set to 0 further processing needs to be done. For zones without
wildcards the NOWILD-bit MAY always be set to 1.
The following optimizations are realized:
o Servers and resolvers will only have to execute a slow and
somewhat complicated code paths if wildcard are present in the
zone.
o Packet size of answers reduce in most common cases; for the root
zone the authority section only contains one NXT RR with
associated SIGs instead of two NXT RRs with associated SIGs.
o In case of absence of wildcards-matches answers will be easier to
interpret by human operators troubleshooting responses;
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2. DNSSEC Protocol Changes
This is an update to the RFC2535 protocol. Resolvers MUST implement
these changes. Servers MAY implement these changes.
2.1 Server Side
2.1.1 Zone Signing
Servers that implement the optimization MAY perform the following
actions at zone signing time.
At zone signing time, when the NXT RRs are generated, the NOWILD-bit
MUST be set to 0 if for an ownername 'label(j).label(j-1).label(j-2)
... label(0).' there is no wildcard name '*.label(i).label(i-1) ...
label(0).' in the zone for all i < j. In other words the label is
set to 0 if there exists a wildcard that would match QNAME=ownername
while ignoring the possible existence of a domain name between the
ownername and the wildcard domain. For all other ownernames the bit
MUST be set to 1.
If, because of implementation or policy issues, the algorithm in the
previous paragraph is not applied then the bit MUST be set to 0 for
all NXT RRs in the zone. Servers that do do not implement the
optimization have already set their NOWILD bit to 0 by virtue of the
requirements of RFC2535 section 5.2.
When the algorithm is applied a NXT RR that proves the non-existence
of a full match of the QNAME will also prove, when it's NOWILD-bit is
set to 1, that there is no match of the QNAME to any wildcard that
may exist in the zone
2.1.2 Server Responses
When queried for a name for which there is no match, i.e. no full
and no wildcard match, in the zone:
o Servers MUST return the NXT RR that proves the non-existence of
the query name in the NXDOMAIN response. If there is no match for
a wildcard and the NOWILD-bit is set to 1 at signing time and the
one NXT RR is sufficient. If the NOWILD-bit for the NXT RR that
proves non-existence of the query name is set to 0 then NXT RRs
that prove the non-existence of possible wildcard matches MUST be
returned as well.
When queried for a name for which there is a match in the zone:
o If the match is an exact match than no NXT RRs are returned in the
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additional section.
o Servers for zones that contain one or more wildcards MUST return
the NXT RRs that prove the non-existence of the exact match. They
must also provide proof that there is no closer match for the
QNAME than the match returned in the answer section.
The proof algorithm for non-existence of wildcards, an exact match or
closer matches conforms to RFC2535.
2.1.3 Dynamic DNS
When dynamically adding or removing a name that does not contains
wildcards, the 'next name' for the name immediately above the
inserted, or deleted name needs to be updated. The NOWILD bit of the
inserted name is to be set according to the procedure as described in
Section 2.1.1. Except for setting the NOWILD bit this is similar to
the RFC2535 procedure.
If a name containing a wildcard is deleted from a zone one has to
verify if, for all names in the zone with the bit set to 0, the
NOWILD bit can be toggled. If a name containing a wildcard is added
one has to verify if, for all the names in the zone, the bit needs to
be set to 0.
The NOWILD bit is not to be modified during an update of a name that
already exists in the zone.
Dynamic updates of names that contain wildcards may lead to
performance penalties for large dynamic zones and one MAY therefore
choose not to perform the NOWILD optimization for dynamic zones.
2.2 Resolver Side
When receiving an answer to a query a resolver MUST assess if the
answer is a result of a wildcard match. If the result is an exact
match then there will be no NXT RRs in the authority section.
If the answer is a wildcard match then the resolver will need to
verify that the exact name does not exist. The NXT RRs in the
additional section, which per definition have their NOWILD-bit set to
0, will need to prove that there is no closer match. ( conforming to
RFC2535).
If the response is NXDOMAIN (i.e. no match at all) then the resolver
MUST verify if the NXT RR proves the non-existence of the exact match
in the zone. No further NXT RRs are needed if the NXT RR has it's
NOWILD-bit set to 1. A DNS packet containing an NXDOMAIN response
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accompanied by a NXT RR that has it's NOWILD-bit set to 0 will need
to contain proof that there are no wildcard matches against the QNAME
(conforming to RFC2535 ).
The NXT data and the NOWILD-bit together supply the proof on the non-
existence of a wildcard. There is one situation where the NOWILD-bit
is set to 1 but the NXT's 'next name' proves that there is a
wildcard. This is when the 'next name' itself contains a wildcard.
Resolvers that verify NXDOMAIN replies MUST verify the NXT 'next
name' first before the NOWILD-bit. Also see example Appendix A.2.5.
The fact that resolvers that obtain an answer with a NXT RR's NOWILD
set to 1 do not receive additional proof for the non-existence of
wildcards is incompatible with RFC2535.
3. IANA Considerations
Although there is no RR record associated the NOWILD-bit. The value
of the bit must be registered as a DNS RR-type. To not cause the NXT
type bitmap to grow beyond 4 octets unnecessary we propose to reuse
type code 31 (the EID type code is undocumented).
4. Security Considerations
The draft provides an optimization for wildcard handling. Resolvers
MUST verify for the denial of existence of matches or the denial of
existence of closer matches when an answer is returned and the
NOWILD-bit is set to 0.
5. Internationalization Considerations
There are no internationalization considerations.
6. Acknowledgements
Olafur Gudmundsson, Daniel Karrenberg and Ed Lewis for providing
critique and input on earlier versions of this document.
7. Document Changes
7.1 draft 00->01
Reordered and reworded the 'protocol changes' section. We tried
to make the fact that resolvers must and servers may implement
this optimization more explicit.
Change from using the SIG bit to another bit in the NXT type-
bitmap, changed the name of the bit and added IANA considerations.
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Note that the meaning of the bit being set and unset are changed
because of the default setting. Because of the fact that we want
to maintain backward compatibility with servers that do not
implement this bit and the bit in the typemap is currently set to
0 the default behaviour should be follow old-style NXT proof.
Corrected mistakes in the examples.
Various style and spelling corrections.
Normative References
[1] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
Authors' Addresses
Olaf M. Kolkman
RIPE NCC
Singel 256
1016 AB Amsterdam
NL
Phone: +31 20 535 4444
EMail: olaf@ripe.net
URI: http://www.ripe.net/
Johan Ihren
Autonomica
Bellmansgatan 30
SE-118 47 Stockholm
SE
EMail: johani@autonomica.se
Roy Arends
A.R.E.N.D.S.
Bankastraat 41-e
1094 EB Amsterdam
NL
Phone: +31206931681
EMail: Roy@logmess.com
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Appendix A. Examples
A.1 Zone without wildcards
In the following example zone file there are no wildcards. All
NOWILD bits are set to 1. The actual SIG RRs and the KEY RRs are
left out from the zone data and type bitmaps for clarity only.
$ORIGIN example.
@ IN SOA
@ NXT a SOA NXT NOWILD ; NOWILD-bit set to 1
a A 10.0.0.1
a NXT a.b A NXT NOWILD ; NOWILD-bit set to 1
a.b A 10.0.0.2
a.b NXT a.c A NXT NOWILD ; NOWILD-bit set to 1
a.c A 10.0.0.4
a.c NXT a.b.c A NXT NOWILD ; NOWILD-bit set to 1
a.b.c A 10.0.0.5
a.b.c NXT f A NXT NOWILD ; NOWILD-bit set to 1
f A 10.0.0.6
f NXT @ A NXT NOWILD ; NOWILD-bit set to 1
A.1.1 Optimized proof
A query for any existing name will return a signed answer without NXT
RRs in the authority section. A query for any non existing name will
only return 1 NXT RR proving the non-existence of the QNAME in the
zone and, by virtue of the NOWILD-bit being 1, this is sufficient
proof there is no wildcard.
QNAME= d.b.c.example. QTYPE=A
RCODE=NXDOMAIN
;; Authority
example. SOA
SIG SOA
a.b.c.example. NXT f.example. A NXT NOWILD
SIG NXT
;; Additional
(... skipped ... )
A.1.2 RFC2535 proof
For comparison we supply the same answer without the optimization
applied i.e. NOWILD set to 0 for all NXT RRs in the zone. The
answer needs to contain prove that *.b.c.example, *.c.example and
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*.example do not exist, unless a name that exists in the zone
terminates the possible match of those wildcards against the QNAME.
QNAME= d.b.c.example. QTYPE=A
RCODE=NXDOMAIN
;; Authority
example. SOA
SIG SOA
a.b.c.example. NXT f.example. A NXT
SIG NXT
; proofs non-existence of exact match.
a.c.example. NXT a.b.c.example. A NXT
SIG NXT
; proofs non-existence of *.b.c.example.
;; Additional
(... skipped ... )
Note that the existence of 'a.b.c.example NXT' RR terminates a
wildcard match of QNAME against *.c.example. and *.example. So the
answer packet does not need to contain further proof for the non-
existence of those wildcards. However, a resolver will have to
execute logic to verify that the existence of 'a.b.c.example.'
terminates the possible match of the QNAME against the possible
wildcards and that the answer is therefore complete.
A.2 Zone with wildcards
In the following example zone file there is a wildcard. Some NOWILD
bits are set to 1, others for which there is no wildcard in the zone
if the leftmost labels are chopped off, have there NOWILD-bit set to
0. The actual SIG RRs and the KEY RRs at the apex are left out for
clarity. The queries for which a wildcard match is returned will
have the NOWILD-bit set to 0, there proof for the non-existing closer
match is to be supplied and checked by the resolver.
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$ORIGIN example.
@ IN SOA
@ NXT a SOA NXT NOWILD ; NOWILD-bit set to 1
a A 10.0.0.1
a NXT a.b A NXT NOWILD ; NOWILD-bit set to 1
a.b A 10.0.0.2
a.b NXT *.c A NXT NOWILD ; NOWILD-bit set to 1
*.c A 10.0.0.3
*.c NXT a.c A NXT SIG ; NOWILD-bit set to 0
a.c A 10.0.0.4
a.c NXT a.b.c A NXT SIG ; NOWILD-bit set to 0
a.b.c A 10.0.0.5
a.b.c NXT f A NXT SIG ; NOWILD-bit set to 0
f A 10.0.0.6
f NXT @ A NXT NOWILD ; NOWILD-bit set to 1
A.2.1 Optimized proof
QNAME= c.a.a.example. QTYPE=A
RCODE=NXDOMAIN
;; Authority
example. SOA
SIG SOA
a.example. NXT a.b.example. A NXT SIG NOWILD
; NOWILD-bit set to 1 proves no full
; match and no wildcards that match
; QNAME
SIG NXT
;; Additional
(... skipped ... )
A.2.2 NXDOMAIN with additional proof for no wildcard
The following example contains a NXDOMAIN answer and the proof that
there is no wildcard match.
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QNAME= e.example. QTYPE=A
RCODE=NXDOMAIN
;; Authority
example.example SOA
SIG SOA
a.b.c.example. NXT f.example. A NXT SIG ; NOWILD-bit set to 0,
; proves no full match
SIG NXT
example. NXT a.example A NXT SIG NOWILD ; NOWILD-bit set to 1,
; proves no *.example.
;; Additional
(... skipped ... )
A.2.3 Another Optimized Proof
The following example contains a NXDOMAIN answer and the proof that
there is no wildcard match. In this particular case the proof is
optimized because of the NOWILD-bit on the f NXT RR being set to
zero.
QNAME= g.example. QTYPE=A
RCODE=NXDOMAIN
;; Authority
example.example SOA
SIG SOA
f.example. NXT example. A NXT NOWILD ; NOWILD-bit set to 1
; proves no full match
;; Additional
(... skipped ... )
A.2.4 Denial of Existence of Closer Match
The following example contains an answer with wildcard expansion and
the proof that there is no closer match. This is similar to a
RFC2535 proof of non-existence.
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QNAME= d.b.c.example. QTYPE=A
RCODE=ANSWER
;; Answer
d.b.c.example. A 10.0.0.3 ; expansion of *.c
SIG A (labelcount=2) ; labelcount proofs wildcard
; example
;; Authority
example.example. SOA
SIG SOA
a.b.c.example. NXT f.example. A NXT SIG ; NOWILD-bit set to 0,
; proves no exact match,
SIG NXT
a.c.example. NXT a.b.c.example. A NXT SIG ; NOWILD-bit set to 0
; proves non-existence of
; *.b.c.example.
; No further proofs needed
;; Additional
(... skipped ... )
A.2.5 The NXT 'next name' Proving Existence of a Wildcard
In the zone above the a.b NXT RR has it's NOWILD-bit set to 1. If
one would query for '#.c' which canonically orders between a.b and
*.c one would get back "a.b NXT *.c". A attacker can use the this
NXT RR in a malformed NXDOMAIN response.
QNAME= #.c.example. QTYPE=A
RCODE=NXDOMAIN ; Black hat answer !!!!
;; Authority
example.example SOA
SIG SOA
a.b.example. NXT *.c.example. A NXT NOWILD ; NOWILD-bit set to 1
; but *.c exists
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