wdiff rfc9276xml2.original.xml rfc9276.xml

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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-dnsop-nsec3-guidance-10" number="9276" submissionType="IETF" category="bcp" consensus="true" updates="5155"> updates="5155" obsoletes="" tocInclude="true" sortRefs="true" symRefs="true" xml:lang="en" version="3">

 <front>
   <title abbrev="title">Guidance abbrev="NSEC3 Parameter Settings">Guidance for NSEC3 parameter settings</title> Parameter Settings</title>
   <seriesInfo name="RFC" value="9276"/>

   <seriesInfo name="BCP" value="236"/>
   <author initials="W." surname="Hardaker" fullname="Wes Hardaker">
     <organization>USC/ISI</organization>
     <address>
       <email>ietf@hardakers.net</email>
     </address>
   </author>
   <author initials="V." surname="Dukhovni" fullname="Viktor Dukhovni">
     <organization>Bloomberg, L.P.</organization>
     <address>
       <email>ietf-dane@dukhovni.org</email>
     </address>
   </author>
   <date year="2022" month="May" day="25"/> month="August"/>

   <area>ops</area>
   <workgroup>dnsop</workgroup>

<keyword>DNSSEC</keyword>
<keyword>DNS</keyword>
<keyword>NSEC3</keyword>
<keyword>NSEC</keyword>
<keyword>Denial of Existence</keyword>

   <abstract>
     <t>NSEC3 is a DNSSEC mechanism providing proof of non-existence nonexistence by
asserting that there are no names that exist between two domain names
within a zone.  Unlike its counterpart NSEC, NSEC3 avoids directly
disclosing the bounding domain name pairs.  This document provides
guidance on setting NSEC3 parameters based on recent operational
deployment experience.  This document updates <xref target="RFC5155"/> RFC 5155 with
guidance about selecting NSEC3 iteration and salt parameters.</t>
   </abstract>
 </front>
 <middle>
   <section anchor="introduction" title="Introduction"> anchor="introduction">
     <name>Introduction</name>
     <t>As with NSEC <xref target="RFC4035"/>, NSEC3
<xref target="RFC5155"/> provides proof of
non-existence
nonexistence that consists of signed DNS records establishing the
non-existence
nonexistence of a given name or associated Resource Record Type
(RRTYPE) in a DNSSEC DNSSEC-signed zone <xref target="RFC4035"/> signed zone.  In target="RFC4035"/>.  However, in the case of NSEC3,
however, the names of valid nodes in the zone are obfuscated through
(possibly multiple iterations of) hashing (currently only
SHA-1 is in use on the Internet).</t>

<t>NSEC3
<t>
  NSEC3 also provides “opt-out support”, "opt-out support", allowing for blocks of
  unsigned delegations to be covered by a single NSEC3 record.  Use of
  the opt-out feature allows large registries to only sign as many
  NSEC3 records as there are signed DS or other RRsets Resource Record sets
  (RRsets) in the zone; with opt-out, unsigned delegations don’t don't
  require additional NSEC3 records.  This sacrifices the tamper-resistance tamper-
  resistance of the proof of non-existence nonexistence offered by NSEC3 in order to
  reduce memory and CPU overheads.</t> overheads.
</t>

     <t>NSEC3 records have a number of tunable parameters that are specified
via an NSEC3PARAM record at the zone apex.  These parameters are the
hash algorithm, the processing flags, the number of hash iterations iterations, and
the salt.  Each of these has security and operational considerations
that impact both zone owners and validating resolvers.  This document
provides some best-practice recommendations for setting the NSEC3
parameters.</t>
     <section anchor="requirements-notation" title="Requirements Notation">

<t>The anchor="requirements-notation">
       <name>Requirements Notation</name>
       <t>
   The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”,
   “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
   NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
   "<bcp14>MAY</bcp14>", and “OPTIONAL” "<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as
   described in BCP 14 BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
   when, and only when, they appear in all capitals, as shown here.</t> here.
       </t>
     </section>
   </section>
   <section anchor="nsec3-parameter-value-discussions" title="NSEC3 anchor="nsec3-parameter-value-discussions">
     <name>NSEC3 Parameter Value Discussions"> Discussions</name>

     <t>The following sections describes describe the background of the parameters for
the NSEC3 and NSEC3PARAM resource record types.</t> RRTYPEs.</t>
     <section anchor="algorithms" title="Algorithms"> anchor="algorithms">
       <name>Algorithms</name>
       <t>The algorithm field is not discussed by this document.  Readers are
encouraged to read <xref target="RFC8624"/> for guidance about DNSSEC algorithm
usage.</t>
     </section>
     <section anchor="flags" title="Flags"> anchor="flags">
       <name>Flags</name>
       <t>The NSEC3PARAM flags field currently contains only reserved and
unassigned flags.  Individual  However, individual NSEC3 records, however, records contain the
“Opt-Out”
"Opt-Out" flag <xref target="RFC5155"/>, which target="RFC5155"/> that specifies whether that NSEC3 record
provides proof of non-existence. nonexistence.  In general, NSEC3 with the Opt-Out
flag enabled should only be used in large, highly dynamic zones with a
small percentage of signed delegations.  Operationally, this allows
for fewer signature creations when new delegations are inserted into a
zone.  This is typically only necessary for extremely large
registration points providing zone updates faster than real-time
signing allows or when using memory-constrained hardware.

  Operators considering the use of NSEC3 are advised to fully test their
zones deployment architectures and authoritative servers under both
regular operational loads to determine carefully
  weigh the tradeoffs using NSEC3
instead costs and benefits of choosing NSEC3 over NSEC.  Smaller
  zones, or large but relatively static zones, are encouraged to not
  use a the opt-opt flag and to take advantage of
DNSSEC’s proof-of-non-existence support.</t> DNSSEC's
  authenticated denial of existence.
</t>
     </section>
     <section anchor="iterations" title="Iterations"> anchor="iterations">
       <name>Iterations</name>

       <t>NSEC3 records are created by first hashing the input domain and then
repeating that hashing using the same algorithm a number of times based on the
iteration parameter in the NSEC3PARM NSEC3PARAM and NSEC3 records.

The first hash with NSEC3 is typically sufficient to discourage zone
enumeration performed by “zone walking” "zone walking" an unhashed NSEC chain.</t>
       <t>Note that <xref target="RFC5155"/> describes the Iterations field to be “The as follows</t>
<blockquote>The
Iterations field defines the number of additional times the hash
function has been performed.”  This performed.</blockquote>
<t>This means that an NSEC3 record with an
Iterations field of 0 actually requires one hash iteration.</t>
       <t>Only determined parties
with significant resources are likely to try and uncover hashed
values, regardless of the number of additional iterations performed.
If an adversary really wants to expend significant CPU resources to
mount an offline dictionary attack on a zone’s zone's NSEC3 chain, they’ll they'll
likely be able to find most of the “guessable” "guessable" names despite any
level of additional hashing iterations.</t>
       <t>Most names published in the DNS are rarely secret or unpredictable.
They are published to be memorable, used and consumed by humans.  They
are often recorded in many other network logs such as email logs,
certificate transparency logs, web page links, intrusion detection intrusion-detection
systems, malware scanners, email archives, etc.  Many times a simple
dictionary of commonly used domain names prefixes (www, mail,
imap, login, database, etc.) can be used to quickly reveal a large
number of labels within a zone.  Because of this, there are increasing
performance costs yet diminishing returns associated with applying
additional hash iterations beyond the first.</t>
       <t>Although Section 10.3 of <xref target="RFC5155"/> target="RFC5155" sectionFormat="of" section="10.3"/> specifies the upper bounds for the
number of hash iterations to use, there is no published guidance for
zone owners about good values to select.  Recent academic studies
have shown that NSEC3 hashing provides only moderate
protection <xref target="GPUNSEC3"/><xref target="GPUNSEC3"/> <xref target="ZONEENUM"/>.</t>
     </section>
     <section anchor="salt" title="Salt"> anchor="salt">
       <name>Salt</name>
       <t>NSEC3 records provide an additional salt value, which can be
combined with an FQDN a Fully Qualified Domain Name (FQDN) to influence the resulting hash, but properties
of this extra salt are complicated.</t>
       <t>In cryptography, salts generally add a layer of protection against
offline, stored dictionary attacks by combining the value to be hashed
with a unique “salt” "salt" value. This prevents adversaries from building up
and remembering a single dictionary of values that can translate a
hash output back to the value that it was derived from.</t>
       <t>In the case of DNS, the situation is different because the hashed
names placed in NSEC3 records are always implicitly “salted” "salted" by
hashing the fully-qualified domain name FQDN from each zone. Thus, no
single pre-computed table works to speed up dictionary attacks
against multiple target zones. An attacker is always required to
compute a complete dictionary per zone, which is expensive in both
storage and CPU time.</t>
       <t>To understand the role of the additional NSEC3 salt field, we have to
consider how a typical zone walking attack works. Typically, the attack
has two phases - phases: online and offline. In the online phase, an attacker
“walks
"walks the zone” zone" by enumerating (almost) all hashes listed in NSEC3
records and storing them for the offline phase. Then, in the offline
cracking phase, the attacker attempts to crack the underlying hash. In
this phase, the additional salt value raises the cost of the attack
only if the salt value changes during the online phase of the
attack. In other words, an additional, constant salt value does not
change the cost of the attack.</t>
       <t>Changing a zone’s zone's salt value requires the construction of a complete
new NSEC3 chain.  This is true both when re-signing the entire zone at
once,
once and when incrementally signing it in the background where the new
salt is only activated once every name in the chain has been
completed. As a result, re-salting is a very complex operation, with
significant CPU time, memory, and bandwidth consumption. This makes
very frequent re-salting impractical, impractical and renders the additional salt
field functionally useless.</t>
     </section>
   </section>
   <section anchor="recommendations-for-deploying-and-validating-nsec3-records" title="Recommendations anchor="recommendations-for-deploying-and-validating-nsec3-records">
     <name>Recommendations for Deploying and Validating NSEC3 Records"> Records</name>
     <t>The following subsections describe recommendations for the different
operating realms within the DNS.</t>
     <section anchor="best-practice-for-zone-publishers" title="Best-practice anchor="best-practice-for-zone-publishers">
       <name>Best Practice for Zone Publishers"> Publishers</name>
       <t>First, if the operational or security features of NSEC3 are not
needed, then NSEC SHOULD <bcp14>SHOULD</bcp14> be used in preference to NSEC3. NSEC3
requires greater computational power (see <xref target="computationalburdens"/>)
for both authoritative servers and validating clients.  Specifically,
there is a nontrivial complexity in finding matching NSEC3 records to
randomly generated prefixes within a DNS zone.  NSEC mitigates this
concern.  If NSEC3 must be used, then an iterations count of 0 MUST <bcp14>MUST</bcp14> be
used to alleviate computational burdens.  Note that extra iteration
counts other than 0 increase the impact of CPU-exhausting DoS attacks,
and also increase the risk of interoperability problems.</t>
       <t>Note that deploying NSEC with minimally covering NSEC records
<xref target="RFC4470"></xref> target="RFC4470"/> also incurs a cost, and zone owners should measure the
computational difference in deploying either RFC4470 <xref target="RFC4470"/> or NSEC3.</t>
       <t>In short, for all zones, the recommended NSEC3 parameters are as shown
below:</t>

<figure><artwork><![CDATA[

       <artwork><![CDATA[
; SHA-1, no extra iterations, empty salt:
;
bcp.example. IN NSEC3PARAM 1 0 0 -
]]></artwork></figure>
]]></artwork>
       <t>For small zones, the use of opt-out based opt-out-based NSEC3 records is NOT
RECOMMENDED.</t> <bcp14>NOT
RECOMMENDED</bcp14>.</t>
       <t>For very large and sparsely signed zones, where the majority of the
records are insecure delegations, opt-out MAY <bcp14>MAY</bcp14> be used.</t>
       <t>Operators SHOULD NOT <bcp14>SHOULD NOT</bcp14> use a salt by indicating a zero-length salt value
instead (represented as a “-“ "-" in the presentation format).</t>
       <t>If salts are used, note that since the NSEC3PARAM RR is not used by
validating resolvers (see <xref target="RFC5155"></xref> section 4), target="RFC5155" sectionFormat="of" section="4"/>), the iterations and
salt parameters can be changed without the need to wait for RRsets to
expire from caches.  A complete new NSEC3 chain needs to be
constructed and the full zone needs to be re-signed.</t>
     </section>
     <section anchor="recommendation-for-validating-resolvers" title="Recommendation anchor="recommendation-for-validating-resolvers">
       <name>Recommendation for Validating Resolvers"> Resolvers</name>
       <t>Because there has been a large growth of open (public) DNSSEC
validating resolvers that are subject to compute resource constraints
when handling requests from anonymous clients, this document
recommends that validating resolvers change reduce their behavior with
respect to large iteration values. count
limits over time.

Specifically, validating
resolver operators and validating resolver software implementers are
encouraged to continue evaluating NSEC3 iteration count deployments
but deployment
trends and lower their default acceptable iteration limits over time.  Similarly, because
Because
treating a high iterations count as insecure leaves zones subject to
attack, validating resolver operators and validating resolver software
implementers are further encouraged to lower their default and acceptable
limit for returning SERVFAIL when processing NSEC3 parameters
containing large iteration count values.
See
<xref target="deploymentmeasurements"/> for measurements taken near the time of
publication of this document and potential starting points.</t>
       <t>Validating resolvers MAY <bcp14>MAY</bcp14> return an insecure response to their clients
when processing NSEC3 records with iterations larger
than 0.
Note also that a validating resolver returning an insecure response
MUST
<bcp14>MUST</bcp14> still validate the signature over the NSEC3 record to ensure
the iteration count was not altered since record publication (see
<xref target="RFC5155"/> section 10.3).</t> target="RFC5155" sectionFormat="of" section="10.3"/>).</t>
       <t>Validating resolvers MAY <bcp14>MAY</bcp14> also return a SERVFAIL response when
processing NSEC3 records with iterations larger than 0.  Validating
resolvers MAY <bcp14>MAY</bcp14> choose to ignore authoritative server responses with
iteration counts greater than 0, which will likely result in
returning a SERVFAIL to the client when no acceptable responses are
received from authoritative servers.</t>
       <t>Validating resolvers returning an insecure or SERVFAIL answer to their
client after receiving and validating an unsupported NSEC3 parameter
from the authoritative server(s) SHOULD <bcp14>SHOULD</bcp14> return an Extended DNS
Error (EDE) <xref target="RFC8914"/> EDNS0 option of value (RFC EDITOR: TBD). 27.
Validating resolvers that choose to ignore a response with an
unsupported iteration count (and that do not validate the signature) MUST
NOT <bcp14>MUST
NOT</bcp14> return this EDE option.</t>

       <t>Note that this specification updates <xref target="RFC5155"></xref> target="RFC5155"/> by significantly
decreasing the requirements originally specified in Section 10.3 of <xref target="RFC5155"></xref>.
target="RFC5155" sectionFormat="of" section="10.3"/>. See the Security
Considerations (<xref target="security-considerations"/>) for arguments on how to
handle responses with non-zero iteration count.</t>
     </section>
     <section anchor="recommendation-for-primary-secondary-relationships" title="Recommendation anchor="recommendation-for-primary-secondary-relationships">
       <name>Recommendation for Primary / and Secondary Relationships"> Relationships</name>

       <t>Primary and secondary authoritative servers for a zone that are not
being run by the same operational staff and/or using the same software
and configuration must take into account the potential differences in
NSEC3 iteration support.</t>
       <t>Operators of secondary services should advertise the parameter limits
that their servers support. Correspondingly, operators of primary
servers need to ensure that their secondaries support the NSEC3
parameters they expect to use in their zones.  To ensure reliability,
after primaries change their iteration counts, they should query their
secondaries with known non-existent nonexistent labels to verify the secondary
servers are responding as expected.</t>
     </section>
   </section>
   <section anchor="security-considerations" title="Security Considerations"> anchor="security-considerations">
     <name>Security Considerations</name>

     <t>This entire document discusses security considerations with various
parameters
parameter selections of NSEC3 and NSEC3PARAM fields.</t>
     <t>The point where a validating resolver returns insecure vs versus the point
where it returns SERVFAIL must be considered carefully.  Specifically,
when a validating resolver treats a zone as insecure above a
particular value (say 100) and returns SERVFAIL above a higher point
(say 500), it leaves the zone subject to attacker-in-the-middle
attacks as if it was were unsigned between these values.

  Thus, validating resolver operators and software implementers SHOULD
  <bcp14>SHOULD</bcp14> set the point above which a zone is treated as
  insecure for certain values of NSEC3 iterations counts to the same as the
  point where a validating resolver begins returning SERVFAIL.</t> SERVFAIL.

     </t>
   </section>
   <section anchor="operational-considerations" title="Operational Considerations"> anchor="operational-considerations">
     <name>Operational Considerations</name>
     <t>This entire document discusses operational considerations with various
parameters
parameter selections of NSEC3 and NSEC3PARAM fields.</t>
   </section>
   <section anchor="iana-considerations" title="IANA Considerations">

<t>This document requests a new allocation anchor="iana-considerations">
     <name>IANA Considerations</name>

     <t>IANA has allocated the following code in the First Come First Served
     range <xref target="RFC8126"/> of the “Extended "Extended DNS Error Codes” of Codes" registry within the “Domain "Domain Name System
(DNS) Parameters” registration table with the following
characteristics:</t>

<t><list style="symbols">
  <t>INFO-CODE: (RFC EDITOR: TBD)</t>
  <t>Purpose: Unsupported Parameters" registry:</t>
    <dl spacing="compact">
       <dt>INFO-CODE:</dt> <dd>27</dd>
       <dt>Purpose:</dt> <dd>Unsupported NSEC3 iterations value</t>
  <t>Reference: (RFC EDITOR: this document)</t>
</list></t> value</dd>
       <dt>Reference:</dt> <dd>RFC 9276</dd>
     </dl>
   </section>
 </middle>
 <back>

    <references title='Normative References'>

<reference  anchor="RFC2119" target='https://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='S. Bradner'><organization /></author>
<date year='1997' month='March' />
<abstract><t>In many standards track documents several words are used to signify the requirements in the specification.  These words are often capitalized. This document defines these words as they should be interpreted in IETF documents.  This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</reference>

<reference  anchor="RFC5155" target='https://www.rfc-editor.org/info/rfc5155'>
<front>
<title>DNS Security (DNSSEC) Hashed Authenticated Denial of Existence</title>
<author initials='B.' surname='Laurie' fullname='B. Laurie'><organization /></author>
<author initials='G.' surname='Sisson' fullname='G. Sisson'><organization /></author>
<author initials='R.' surname='Arends' fullname='R. Arends'><organization /></author>
<author initials='D.' surname='Blacka' fullname='D. Blacka'><organization /></author>
<date year='2008' month='March' />
<abstract><t>The Domain Name System Security (DNSSEC) Extensions introduced the NSEC resource record (RR) for authenticated denial of existence. This document introduces an alternative resource record, NSEC3, which similarly provides authenticated denial of existence.  However, it also provides measures against zone enumeration and permits gradual expansion of delegation-centric zones.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5155'/>
<seriesInfo name='DOI' value='10.17487/RFC5155'/>
</reference>

<reference  anchor="RFC4035" target='https://www.rfc-editor.org/info/rfc4035'>
<front>
<title>Protocol Modifications for the DNS Security Extensions</title>
<author initials='R.' surname='Arends' fullname='R. Arends'><organization /></author>
<author initials='R.' surname='Austein' fullname='R. Austein'><organization /></author>
<author initials='M.' surname='Larson' fullname='M. Larson'><organization /></author>
<author initials='D.' surname='Massey' fullname='D. Massey'><organization /></author>
<author initials='S.' surname='Rose' fullname='S. Rose'><organization /></author>
<date year='2005' month='March' />
<abstract><t>This document is part of a family of documents that describe the DNS Security Extensions (DNSSEC).  The DNS Security Extensions are a collection of new resource records and protocol modifications that add data origin authentication and data integrity to the DNS.  This document describes the DNSSEC protocol modifications.  This document defines the concept of a signed zone, along with the requirements for serving and resolving by using DNSSEC.  These techniques allow a security-aware resolver to authenticate both DNS resource records and authoritative DNS error indications. </t><t> This document obsoletes RFC 2535 and incorporates changes from all updates to RFC 2535.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4035'/>
<seriesInfo name='DOI' value='10.17487/RFC4035'/>
</reference>

<reference  anchor="RFC4470" target='https://www.rfc-editor.org/info/rfc4470'>
<front>
<title>Minimally Covering NSEC Records and DNSSEC On-line Signing</title>
<author initials='S.' surname='Weiler' fullname='S. Weiler'><organization /></author>
<author initials='J.' surname='Ihren' fullname='J. Ihren'><organization /></author>
<date year='2006' month='April' />
<abstract><t>This document describes how to construct DNSSEC NSEC resource records that cover a smaller range of names than called for by RFC 4034.  By generating and signing these records on demand, authoritative name servers can effectively stop the disclosure of zone contents otherwise made possible by walking the chain of NSEC records in a signed zone.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4470'/>
<seriesInfo name='DOI' value='10.17487/RFC4470'/>
</reference>

<reference  anchor="RFC8174" target='https://www.rfc-editor.org/info/rfc8174'>
<front>
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
<author initials='B.' surname='Leiba' fullname='B. Leiba'><organization /></author>
<date year='2017' month='May' />
<abstract><t>RFC 2119 specifies common key words that may be used in protocol  specifications.  This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the  defined special meanings.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='8174'/>
<seriesInfo name='DOI' value='10.17487/RFC8174'/>
</reference>

<reference  anchor="RFC8914" target='https://www.rfc-editor.org/info/rfc8914'>
<front>
<title>Extended DNS Errors</title>
<author initials='W.' surname='Kumari' fullname='W. Kumari'><organization /></author>
<author initials='E.' surname='Hunt' fullname='E. Hunt'><organization /></author>
<author initials='R.' surname='Arends' fullname='R. Arends'><organization /></author>
<author initials='W.' surname='Hardaker' fullname='W. Hardaker'><organization /></author>
<author initials='D.' surname='Lawrence' fullname='D. Lawrence'><organization /></author>
<date year='2020' month='October' />
<abstract><t>This document defines an extensible method to return additional information about the cause of DNS errors. Though created primarily to extend SERVFAIL to provide additional information about the cause of DNS and DNSSEC failures, the Extended DNS Errors option defined in this document allows all response types to contain extended error information. Extended DNS Error information does not change the processing of RCODEs.</t></abstract>
</front>
<seriesInfo name='RFC' value='8914'/>
<seriesInfo name='DOI' value='10.17487/RFC8914'/>
</reference>
   <references>
     <name>References</name>
     <references>
       <name>Normative References</name>
       <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
       <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5155.xml"/>
       <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4035.xml"/>
       <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4470.xml"/>
       <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
       <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8914.xml"/>
     </references>

    <references title='Informative References'>
     <references>
       <name>Informative References</name>

	<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/>

       <reference anchor="GPUNSEC3" > anchor="GPUNSEC3">
         <front>
           <title>GPU-Based NSEC3 Hash Breaking</title>
           <author initials="M." surname="Wander" fullname="M. fullname="Mätthaus Wander">
      <organization></organization>
             <organization/>
           </author>
           <author initials="L." surname="Schwittmann" fullname="L. fullname="Lorenz Schwittmann">
      <organization></organization>
             <organization/>
           </author>
           <author initials="C." surname="Boelmann" fullname="C. fullname="Christopher Boelmann">
      <organization></organization>
             <organization/>
           </author>
           <author initials="T." surname="Weis" fullname="T. fullname="Torben Weis">
      <organization></organization>
             <organization/>
           </author>
           <date month="August" year="2014"/>
         </front>
         <seriesInfo name="DOI" value="10.1109/NCA.2014.27"/>
       </reference>

       <reference anchor="ZONEENUM" > anchor="ZONEENUM">
         <front>
           <title>An efficient DNSSEC zone enumeration algorithm</title>
           <author initials="Z." surname="Wang" fullname="Zheng Wang">
      <organization></organization>
             <organization/>
           </author>
           <author initials="L." surname="Xiao" fullname="Liyuan Xiao">
      <organization></organization>
             <organization/>
           </author>
           <author initials="R." surname="Wang" fullname="Rui Wang">
      <organization></organization>
             <organization/>
           </author>
	    <date year="n.d."/>
  </front>
</reference>

<reference  anchor="RFC8624" target='https://www.rfc-editor.org/info/rfc8624'>
<front>
<title>Algorithm Implementation Requirements and Usage Guidance for DNSSEC</title>
<author initials='P.' surname='Wouters' fullname='P. Wouters'><organization /></author>
<author initials='O.' surname='Sury' fullname='O. Sury'><organization /></author>
<date year='2019' month='June' />
<abstract><t>The DNSSEC protocol makes use of various cryptographic algorithms in order to provide authentication of DNS data and proof of nonexistence.  To ensure interoperability between DNS resolvers and DNS authoritative servers, it is necessary to specify a set of algorithm implementation requirements and usage guidelines to ensure that there is at least one algorithm that all implementations support.  This document defines the current algorithm implementation requirements and usage guidance for DNSSEC.  This document obsoletes RFC 6944.</t></abstract> month="April" year="2014"/>
         </front>
         <seriesInfo name='RFC' value='8624'/>
<seriesInfo name='DOI' value='10.17487/RFC8624'/> name="DOI" value="10.2495/MIIT130591"/>
       </reference>

       <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8624.xml"/>
     </references>
   </references>
   <section anchor="deploymentmeasurements" title="Deployment measurements numbered="true" toc="default">
     <name>Deployment Measurements at time Time of publication"> Publication</name>
     <t>At the time of publication, setting an upper limit of 100 iterations
for treating a zone as insecure is interoperable without significant
problems, but at the same time still enables CPU-exhausting DoS
attacks.</t>
     <t>At the time of publication, returning SERVFAIL beyond 500 iterations
appears to be interoperable without significant problems.</t>
   </section>
   <section anchor="computationalburdens" title="Computational burdens numbered="true" toc="default">
     <name>Computational Burdens of processing Processing NSEC3 iterations"> Iterations</name>
     <t>The queries per second (QPS) of authoritative servers will decrease due
to computational overhead when processing DNS requests for zones
containing higher NSEC3 iteration counts.  The table below
shows the drop in QPS for various iteration counts.</t>

<figure><artwork><![CDATA[
| Iterations |

<table anchor="iteration-counts-table" align="center">
<name>Drop in QPS for Various Iteration Counts</name>
<thead>
<tr>
<th rowspan="1" colspan="1">Iterations</th>
<th rowspan="1" colspan="1">QPS [% of 0 iterations QPS] |
|------------+-----------------------------|
|          0 | 100 %                       |
|         10 | 89 %                        |
|         20 | 82 %                        |
|         50 | 64 %                        |
|        100 | 47 %                        |
|        150 | 38 %                        |
]]></artwork></figure>

</section>
<section title="Acknowledgments" anchor="qps"> Iterations QPS]</th>
</tr>
</thead>
<tbody>
<tr>
<td>0</td>
<td>100%</td>
</tr>

<tr>
<td>10</td>
<td>89%</td>
</tr>

<tr>
<td>20</td>
<td>82%</td>
</tr>

<tr>
<td>50</td>
<td>64%</td>
</tr>

<tr>
<td>100</td>
<td>47%</td>
</tr>

<tr>
<td>150</td>
<td>38%</td>
</tr>

</tbody>
</table>

   </section>
   <section anchor="qps" numbered="false" toc="default">
     <name>Acknowledgments</name>
     <t>The authors would like to thank the participants in the dns-operations discussion
participants, discussion, which took place on mattermost hosted by DNS-OARC.</t>
     <t>Additionally, the following people contributed text or review comments
to the draft:</t>

<t><list style="symbols">
  <t>Vladimir Cunat</t>
  <t>Tony Finch</t>
  <t>Paul Hoffman</t>
  <t>Warren Kumari</t>
  <t>Alexander Mayrhofer</t>
  <t>Matthijs Mekking</t>
  <t>Florian Obser</t>
  <t>Petr Spacek</t>
  <t>Paul Vixie</t>
  <t>Tim Wicinski</t>
</list></t>

</section>
<section anchor="github-version-of-this-document" title="GitHub Version of This Document">

<t>(RFCEditor: remove this section)</t>

<t>While this document is under development, it can be viewed, tracked,
issued, pushed with PRs, … here:</t>

<t>https://github.com/hardaker/draft-hardaker-dnsop-nsec3-guidance</t>

</section>
<section anchor="implementation-notes" title="Implementation Notes">

<t>(RFCEditor: remove this section)</t>

<t>The following implementations have implemented the guidance in this
document.  They have graciously provided notes about the details of
their implementation below.</t>

<section anchor="opendnssec" title="OpenDNSSEC">

<t>The OpenDNSSEC configuration checking utility will alert the user
about nsec3 iteration values larger than 100.</t>

</section>
<section anchor="powerdns" title="PowerDNS">

<t>PowerDNS 4.5.2 changed the default value of nsec3-max-iterations to 150.</t>

</section>
<section anchor="knot-dns-and-knot-resolver" title="Knot DNS and Knot Resolver">

<t>Knot DNS 3.0.6 warns when signing with more than 20 NSEC3 iterations.
Knot Resolver 5.3.1 treats NSEC3 iterations above 150 as insecure.</t>

</section>
<section anchor="google-public-dns-resolver" title="Google Public DNS Resolver">

<t>Google Public DNS treats NSEC3 iterations above 100 as insecure since
September 2021.</t>

</section>
<section anchor="google-cloud-dns" title="Google Cloud DNS">

<t>Google Cloud DNS uses 1 iteration and 64-bits of fixed random salt for
all zones using NSEC3. These parameters cannot be adjusted by users.</t>

</section> document:</t>
     <ul spacing="normal">
       <li><t><contact fullname="Vladimir Cunat"/></t></li>
       <li><t><contact fullname="Tony Finch"/></t></li>
       <li><t><contact fullname="Paul Hoffman"/></t></li>
       <li><t><contact fullname="Warren Kumari"/></t></li>
       <li><t><contact fullname="Alexander Mayrhofer"/></t></li>
       <li><t><contact fullname="Matthijs Mekking"/></t></li>
       <li><t><contact fullname="Florian Obser"/></t></li>
       <li><t><contact fullname="Petr Spacek"/></t></li>
       <li><t><contact fullname="Paul Vixie"/></t></li>
       <li><t><contact fullname="Tim Wicinski"/></t></li>
     </ul>
   </section>

 </back>

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