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<title>NSEC5, DNSSEC Authenticated Denial of Existence</title>
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<link href="#rfc.toc" rel="Contents"/>
<link href="#rfc.section.1" rel="Chapter" title="1 Introduction"/>
<link href="#rfc.section.1.1" rel="Chapter" title="1.1 Rationale"/>
<link href="#rfc.section.1.2" rel="Chapter" title="1.2 Requirements"/>
<link href="#rfc.section.1.3" rel="Chapter" title="1.3 Terminology"/>
<link href="#rfc.section.2" rel="Chapter" title="2 Backward Compatibility"/>
<link href="#rfc.section.3" rel="Chapter" title="3 How NSEC5 Works"/>
<link href="#rfc.section.4" rel="Chapter" title="4 NSEC5 Algorithms"/>
<link href="#rfc.section.5" rel="Chapter" title="5 The NSEC5KEY Resource Record"/>
<link href="#rfc.section.5.1" rel="Chapter" title="5.1 NSEC5KEY RDATA Wire Format"/>
<link href="#rfc.section.5.2" rel="Chapter" title="5.2 NSEC5KEY RDATA Presentation Format"/>
<link href="#rfc.section.6" rel="Chapter" title="6 The NSEC5 Resource Record"/>
<link href="#rfc.section.6.1" rel="Chapter" title="6.1 NSEC5 RDATA Wire Format"/>
<link href="#rfc.section.6.2" rel="Chapter" title="6.2 NSEC5 Flags Field"/>
<link href="#rfc.section.6.3" rel="Chapter" title="6.3 NSEC5 RDATA Presentation Format"/>
<link href="#rfc.section.7" rel="Chapter" title="7 The NSEC5PROOF Resource Record"/>
<link href="#rfc.section.7.1" rel="Chapter" title="7.1 NSEC5PROOF RDATA Wire Format"/>
<link href="#rfc.section.7.2" rel="Chapter" title="7.2 NSEC5PROOF RDATA Presentation Format"/>
<link href="#rfc.section.8" rel="Chapter" title="8 Types of Authenticated Denial of Existence with NSEC5"/>
<link href="#rfc.section.8.1" rel="Chapter" title="8.1 Name Error Responses"/>
<link href="#rfc.section.8.2" rel="Chapter" title="8.2 No Data Responses"/>
<link href="#rfc.section.8.2.1" rel="Chapter" title="8.2.1 No Data Response, Opt-Out Not In Effect"/>
<link href="#rfc.section.8.2.2" rel="Chapter" title="8.2.2 No Data Response, Opt-Out In Effect"/>
<link href="#rfc.section.8.3" rel="Chapter" title="8.3 Wildcard Responses"/>
<link href="#rfc.section.8.4" rel="Chapter" title="8.4 Wildcard No Data Responses"/>
<link href="#rfc.section.9" rel="Chapter" title="9 Authoritative Server Considerations"/>
<link href="#rfc.section.9.1" rel="Chapter" title="9.1 Zone Signing"/>
<link href="#rfc.section.9.1.1" rel="Chapter" title="9.1.1 Precomputing Closest Provable Encloser Proofs"/>
<link href="#rfc.section.9.2" rel="Chapter" title="9.2 Zone Serving"/>
<link href="#rfc.section.9.3" rel="Chapter" title="9.3 NSEC5KEY Rollover Mechanism"/>
<link href="#rfc.section.9.4" rel="Chapter" title="9.4 Secondary Servers"/>
<link href="#rfc.section.9.5" rel="Chapter" title="9.5 Zones Using Unknown NSEC5 Algorithms"/>
<link href="#rfc.section.9.6" rel="Chapter" title="9.6 Dynamic Updates"/>
<link href="#rfc.section.10" rel="Chapter" title="10 Resolver Considerations"/>
<link href="#rfc.section.11" rel="Chapter" title="11 Validator Considerations"/>
<link href="#rfc.section.11.1" rel="Chapter" title="11.1 Validating Responses"/>
<link href="#rfc.section.11.2" rel="Chapter" title="11.2 Validating Referrals to Unsigned Subzones"/>
<link href="#rfc.section.11.3" rel="Chapter" title="11.3 Responses With Unknown NSEC5 Algorithms"/>
<link href="#rfc.section.12" rel="Chapter" title="12 Special Considerations"/>
<link href="#rfc.section.12.1" rel="Chapter" title="12.1 Transition Mechanism"/>
<link href="#rfc.section.12.2" rel="Chapter" title="12.2 Private NSEC5 keys"/>
<link href="#rfc.section.12.3" rel="Chapter" title="12.3 Domain Name Length Restrictions"/>
<link href="#rfc.section.13" rel="Chapter" title="13 Implementation Status"/>
<link href="#rfc.section.14" rel="Chapter" title="14 Performance Considerations"/>
<link href="#rfc.section.15" rel="Chapter" title="15 Security Considerations"/>
<link href="#rfc.section.15.1" rel="Chapter" title="15.1 Zone Enumeration Attacks"/>
<link href="#rfc.section.15.2" rel="Chapter" title="15.2 Compromise of the Private NSEC5 Key"/>
<link href="#rfc.section.15.3" rel="Chapter" title="15.3 Key Length Considerations"/>
<link href="#rfc.section.15.4" rel="Chapter" title="15.4 NSEC5 Hash Collisions"/>
<link href="#rfc.section.16" rel="Chapter" title="16 IANA Considerations"/>
<link href="#rfc.section.17" rel="Chapter" title="17 Contributors"/>
<link href="#rfc.references" rel="Chapter" title="18 References"/>
<link href="#rfc.references.1" rel="Chapter" title="18.1 Normative References"/>
<link href="#rfc.references.2" rel="Chapter" title="18.2 Informative References"/>
<link href="#rfc.appendix.A" rel="Chapter" title="A Examples"/>
<link href="#rfc.appendix.A.1" rel="Chapter" title="A.1 Name Error Example"/>
<link href="#rfc.appendix.A.2" rel="Chapter" title="A.2 No Data Example"/>
<link href="#rfc.appendix.A.3" rel="Chapter" title="A.3 Delegation to an Unsigned Zone in an Opt-Out span Example"/>
<link href="#rfc.appendix.A.4" rel="Chapter" title="A.4 Wildcard Example"/>
<link href="#rfc.appendix.A.5" rel="Chapter" title="A.5 Wildcard No Data Example"/>
<link href="#rfc.appendix.B" rel="Chapter" title="B Change Log"/>
<link href="#rfc.authors" rel="Chapter"/>
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<link rel="schema.dct" href="http://purl.org/dc/terms/" />
<meta name="dct.creator" content="Vcelak, J., Goldberg, S., Papadopoulos, D., Huque, S., and D. Lawrence" />
<meta name="dct.identifier" content="urn:ietf:id:draft-vcelak-nsec5-07" />
<meta name="dct.issued" scheme="ISO8601" content="2019-2-8" />
<meta name="dct.abstract" content="The Domain Name System Security Extensions (DNSSEC) introduced two resource records (RR) for authenticated denial of existence: the NSEC RR and the NSEC3 RR. This document introduces NSEC5 as an alternative mechanism for DNSSEC authenticated denial of existence. NSEC5 uses verifiable random functions (VRFs) to prevent offline enumeration of zone contents. NSEC5 also protects the integrity of the zone contents even if an adversary compromises one of the authoritative servers for the zone. Integrity is preserved because NSEC5 does not require private zone-signing keys to be present on all authoritative servers for the zone, in contrast to DNSSEC online signing schemes like NSEC3 White Lies." />
<meta name="description" content="The Domain Name System Security Extensions (DNSSEC) introduced two resource records (RR) for authenticated denial of existence: the NSEC RR and the NSEC3 RR. This document introduces NSEC5 as an alternative mechanism for DNSSEC authenticated denial of existence. NSEC5 uses verifiable random functions (VRFs) to prevent offline enumeration of zone contents. NSEC5 also protects the integrity of the zone contents even if an adversary compromises one of the authoritative servers for the zone. Integrity is preserved because NSEC5 does not require private zone-signing keys to be present on all authoritative servers for the zone, in contrast to DNSSEC online signing schemes like NSEC3 White Lies." />
</head>
<body>
<table class="header">
<tbody>
<tr>
<td class="left">Network Working Group</td>
<td class="right">J. Vcelak</td>
</tr>
<tr>
<td class="left">Internet-Draft</td>
<td class="right">CZ.NIC</td>
</tr>
<tr>
<td class="left">Intended status: Standards Track</td>
<td class="right">S. Goldberg</td>
</tr>
<tr>
<td class="left">Expires: August 12, 2019</td>
<td class="right">Boston University</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">D. Papadopoulos</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">HKUST</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">S. Huque</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">Salesforce</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">D. Lawrence</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">Akamai Technologies</td>
</tr>
<tr>
<td class="left"></td>
<td class="right">February 8, 2019</td>
</tr>
</tbody>
</table>
<p class="title">NSEC5, DNSSEC Authenticated Denial of Existence<br />
<span class="filename">draft-vcelak-nsec5-07</span></p>
<h1 id="rfc.abstract">
<a href="#rfc.abstract">Abstract</a>
</h1>
<p>The Domain Name System Security Extensions (DNSSEC) introduced two resource records (RR) for authenticated denial of existence: the NSEC RR and the NSEC3 RR. This document introduces NSEC5 as an alternative mechanism for DNSSEC authenticated denial of existence. NSEC5 uses verifiable random functions (VRFs) to prevent offline enumeration of zone contents. NSEC5 also protects the integrity of the zone contents even if an adversary compromises one of the authoritative servers for the zone. Integrity is preserved because NSEC5 does not require private zone-signing keys to be present on all authoritative servers for the zone, in contrast to DNSSEC online signing schemes like NSEC3 White Lies.</p>
<h1>
<a>Ed note</a>
</h1>
<p>Text inside square brackets ([]) is additional background information, answers to frequently asked questions, general musings, etc. They will be removed before publication. This document is being collaborated on in GitHub at <https://github.com/fcelda/nsec5-draft>. The most recent version of the document, open issues, etc should all be available there. The authors gratefully accept pull requests.</p>
<h1 id="rfc.status">
<a href="#rfc.status">Status of This Memo</a>
</h1>
<p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p>
<p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.</p>
<p>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."</p>
<p>This Internet-Draft will expire on August 12, 2019.</p>
<h1 id="rfc.copyrightnotice">
<a href="#rfc.copyrightnotice">Copyright Notice</a>
</h1>
<p>Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
<p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.</p>
<hr class="noprint" />
<h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
<ul class="toc">
<li>1. <a href="#rfc.section.1">Introduction</a></li>
<ul><li>1.1. <a href="#rfc.section.1.1">Rationale</a></li>
<li>1.2. <a href="#rfc.section.1.2">Requirements</a></li>
<li>1.3. <a href="#rfc.section.1.3">Terminology</a></li>
</ul><li>2. <a href="#rfc.section.2">Backward Compatibility</a></li>
<li>3. <a href="#rfc.section.3">How NSEC5 Works</a></li>
<li>4. <a href="#rfc.section.4">NSEC5 Algorithms</a></li>
<li>5. <a href="#rfc.section.5">The NSEC5KEY Resource Record</a></li>
<ul><li>5.1. <a href="#rfc.section.5.1">NSEC5KEY RDATA Wire Format</a></li>
<li>5.2. <a href="#rfc.section.5.2">NSEC5KEY RDATA Presentation Format</a></li>
</ul><li>6. <a href="#rfc.section.6">The NSEC5 Resource Record</a></li>
<ul><li>6.1. <a href="#rfc.section.6.1">NSEC5 RDATA Wire Format</a></li>
<li>6.2. <a href="#rfc.section.6.2">NSEC5 Flags Field</a></li>
<li>6.3. <a href="#rfc.section.6.3">NSEC5 RDATA Presentation Format</a></li>
</ul><li>7. <a href="#rfc.section.7">The NSEC5PROOF Resource Record</a></li>
<ul><li>7.1. <a href="#rfc.section.7.1">NSEC5PROOF RDATA Wire Format</a></li>
<li>7.2. <a href="#rfc.section.7.2">NSEC5PROOF RDATA Presentation Format</a></li>
</ul><li>8. <a href="#rfc.section.8">Types of Authenticated Denial of Existence with NSEC5</a></li>
<ul><li>8.1. <a href="#rfc.section.8.1">Name Error Responses</a></li>
<li>8.2. <a href="#rfc.section.8.2">No Data Responses</a></li>
<ul><li>8.2.1. <a href="#rfc.section.8.2.1">No Data Response, Opt-Out Not In Effect</a></li>
<li>8.2.2. <a href="#rfc.section.8.2.2">No Data Response, Opt-Out In Effect</a></li>
</ul><li>8.3. <a href="#rfc.section.8.3">Wildcard Responses</a></li>
<li>8.4. <a href="#rfc.section.8.4">Wildcard No Data Responses</a></li>
</ul><li>9. <a href="#rfc.section.9">Authoritative Server Considerations</a></li>
<ul><li>9.1. <a href="#rfc.section.9.1">Zone Signing</a></li>
<ul><li>9.1.1. <a href="#rfc.section.9.1.1">Precomputing Closest Provable Encloser Proofs</a></li>
</ul><li>9.2. <a href="#rfc.section.9.2">Zone Serving</a></li>
<li>9.3. <a href="#rfc.section.9.3">NSEC5KEY Rollover Mechanism</a></li>
<li>9.4. <a href="#rfc.section.9.4">Secondary Servers</a></li>
<li>9.5. <a href="#rfc.section.9.5">Zones Using Unknown NSEC5 Algorithms</a></li>
<li>9.6. <a href="#rfc.section.9.6">Dynamic Updates</a></li>
</ul><li>10. <a href="#rfc.section.10">Resolver Considerations</a></li>
<li>11. <a href="#rfc.section.11">Validator Considerations</a></li>
<ul><li>11.1. <a href="#rfc.section.11.1">Validating Responses</a></li>
<li>11.2. <a href="#rfc.section.11.2">Validating Referrals to Unsigned Subzones</a></li>
<li>11.3. <a href="#rfc.section.11.3">Responses With Unknown NSEC5 Algorithms</a></li>
</ul><li>12. <a href="#rfc.section.12">Special Considerations</a></li>
<ul><li>12.1. <a href="#rfc.section.12.1">Transition Mechanism</a></li>
<li>12.2. <a href="#rfc.section.12.2">Private NSEC5 keys</a></li>
<li>12.3. <a href="#rfc.section.12.3">Domain Name Length Restrictions</a></li>
</ul><li>13. <a href="#rfc.section.13">Implementation Status</a></li>
<li>14. <a href="#rfc.section.14">Performance Considerations</a></li>
<li>15. <a href="#rfc.section.15">Security Considerations</a></li>
<ul><li>15.1. <a href="#rfc.section.15.1">Zone Enumeration Attacks</a></li>
<li>15.2. <a href="#rfc.section.15.2">Compromise of the Private NSEC5 Key</a></li>
<li>15.3. <a href="#rfc.section.15.3">Key Length Considerations</a></li>
<li>15.4. <a href="#rfc.section.15.4">NSEC5 Hash Collisions</a></li>
</ul><li>16. <a href="#rfc.section.16">IANA Considerations</a></li>
<li>17. <a href="#rfc.section.17">Contributors</a></li>
<li>18. <a href="#rfc.references">References</a></li>
<ul><li>18.1. <a href="#rfc.references.1">Normative References</a></li>
<li>18.2. <a href="#rfc.references.2">Informative References</a></li>
</ul><li>Appendix A. <a href="#rfc.appendix.A">Examples</a></li>
<ul><li>A.1. <a href="#rfc.appendix.A.1">Name Error Example</a></li>
<li>A.2. <a href="#rfc.appendix.A.2">No Data Example</a></li>
<li>A.3. <a href="#rfc.appendix.A.3">Delegation to an Unsigned Zone in an Opt-Out span Example</a></li>
<li>A.4. <a href="#rfc.appendix.A.4">Wildcard Example</a></li>
<li>A.5. <a href="#rfc.appendix.A.5">Wildcard No Data Example</a></li>
</ul><li>Appendix B. <a href="#rfc.appendix.B">Change Log</a></li>
<li><a href="#rfc.authors">Authors' Addresses</a></li>
</ul>
<h1 id="rfc.section.1"><a href="#rfc.section.1">1.</a> <a href="#introduction" id="introduction">Introduction</a></h1>
<h1 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1.</a> <a href="#rationale" id="rationale">Rationale</a></h1>
<p id="rfc.section.1.1.p.1">NSEC5 provides an alternative mechanism for authenticated denial of existence for the DNS Security Extensions (DNSSEC). NSEC5 has two key security properties. First, NSEC5 protects the integrity of the zone contents even if an adversary compromises one of the authoritative servers for the zone. Second, NSEC5 prevents offline zone enumeration, where an adversary makes a small number of online DNS queries and then processes them offline in order to learn all of the names in a zone. Zone enumeration can be used to identify routers, servers or other "things" that could then be targeted in more complex attacks. An enumerated zone can also be a source of probable email addresses for spam, or as a "key for multiple WHOIS queries to reveal registrant data that many registries may have legal obligations to protect" <a href="#RFC5155">[RFC5155]</a>.</p>
<p id="rfc.section.1.1.p.2">All other DNSSEC mechanisms for authenticated denial of existence either fail to preserve integrity against a compromised server, or fail to prevent offline zone enumeration.</p>
<p id="rfc.section.1.1.p.3">When offline signing with NSEC is used <a href="#RFC4034">[RFC4034]</a>, an NSEC chain of all existing domain names in the zone is constructed and signed offline. The chain is made of resource records (RRs), where each RR represents two consecutive domain names in canonical order present in the zone. The authoritative server proves the non-existence of a name by presenting a signed NSEC RR which covers the name. Because the authoritative server does not need not to know the private zone-signing key, the integrity of the zone is protected even if the server is compromised. However, the NSEC chain allows for easy zone enumeration: N queries to the server suffice to learn all N names in the zone (see e.g., <a href="#nmap-nsec-enum">[nmap-nsec-enum]</a>, <a href="#nsec3map">[nsec3map]</a>, and <a href="#ldns-walk">[ldns-walk]</a>).</p>
<p id="rfc.section.1.1.p.4">When offline signing with NSEC3 is used <a href="#RFC5155">[RFC5155]</a>, the original names in the NSEC chain are replaced by their cryptographic hashes. Offline signing ensures that NSEC3 preserves integrity even if an authoritative server is compromised. However, offline zone enumeration is still possible with NSEC3 (see e.g., <a href="#nsec3walker">[nsec3walker]</a>, <a href="#nsec3gpu">[nsec3gpu]</a>), and is part of standard network reconnaissance tools (e.g., <a href="#nmap-nsec3-enum">[nmap-nsec3-enum]</a>, <a href="#nsec3map">[nsec3map]</a>).</p>
<p id="rfc.section.1.1.p.5">When online signing is used, the authoritative server holds the private zone-signing key and uses this key to synthesize NSEC or NSEC3 responses on the fly (e.g. NSEC3 White Lies (NSEC3-WL) or Minimally-Covering NSEC, both described in <a href="#RFC7129">[RFC7129]</a>). Because the synthesized response only contains information about the queried name (but not about any other name in the zone), offline zone enumeration is not possible. However, because the authoritative server holds the private zone-signing key, integrity is lost if the authoritative server is compromised.</p>
<table cellpadding="3" cellspacing="0" class="tt full center">
<thead>
<tr>
<th class="left">Scheme</th>
<th class="right">Integrity vs network attacks?</th>
<th class="right">Integrity vs compromised auth. server?</th>
<th class="right">Prevents offline zone enumeration?</th>
<th class="right">Online crypto?</th>
</tr>
</thead>
<tbody>
<tr>
<td class="left">Unsigned</td>
<td class="right">NO</td>
<td class="right">NO</td>
<td class="right">YES</td>
<td class="right">NO</td>
</tr>
<tr>
<td class="left">NSEC</td>
<td class="right">YES</td>
<td class="right">YES</td>
<td class="right">NO</td>
<td class="right">NO</td>
</tr>
<tr>
<td class="left">NSEC3</td>
<td class="right">YES</td>
<td class="right">YES</td>
<td class="right">NO</td>
<td class="right">NO</td>
</tr>
<tr>
<td class="left">NSEC3-WL</td>
<td class="right">YES</td>
<td class="right">NO</td>
<td class="right">YES</td>
<td class="right">YES</td>
</tr>
<tr>
<td class="left">NSEC5</td>
<td class="right">YES</td>
<td class="right">YES</td>
<td class="right">YES</td>
<td class="right">YES</td>
</tr>
</tbody>
</table>
<p id="rfc.section.1.1.p.6">NSEC5 prevents offline zone enumeration and also protects integrity even if a zone's authoritative server is compromised. To do this, NSEC5 replaces the unkeyed cryptographic hash function used in NSEC3 with a verifiable random function (VRF) <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a> <a href="#MRV99">[MRV99]</a>. A VRF is the public-key version of a keyed cryptographic hash. Only the holder of the private VRF key can compute the hash, but anyone with public VRF key can verify the correctness of the hash.</p>
<p id="rfc.section.1.1.p.7">The public VRF key is distributed in an NSEC5KEY RR, similar to a DNSKEY RR, and is used to verify NSEC5 hash values. The private VRF key is present on all authoritative servers for the zone, and is used to compute hash values. For every query that elicits a negative response, the authoritative server hashes the query on the fly using the private VRF key, and also returns the corresponding precomputed NSEC5 record(s). In contrast to the online signing approach <a href="#RFC7129">[RFC7129]</a>, the private key that is present on all authoritative servers for NSEC5 cannot be used to modify the zone contents.</p>
<p id="rfc.section.1.1.p.8">Like online signing approaches, NSEC5 requires the authoritative server to perform online public key cryptographic operations for every query eliciting a denying response. This is necessary; <a href="#nsec5">[nsec5]</a> proved that online cryptography is required to prevent offline zone enumeration while still protecting the integrity of zone contents against network attacks.</p>
<p id="rfc.section.1.1.p.9">NSEC5 is not intended to replace NSEC or NSEC3. It is an alternative mechanism for authenticated denial of existence. This document specifies NSEC5 based on the VRFs in <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a> over the FIPS 186-3 P-256 elliptic curve and over the the Ed25519 elliptic curve. A formal cryptographic proof of security for NSEC5 is in <a href="#nsec5ecc">[nsec5ecc]</a>.</p>
<h1 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2.</a> <a href="#requirements" id="requirements">Requirements</a></h1>
<p id="rfc.section.1.2.p.1">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 <a href="#RFC2119">[RFC2119]</a>.</p>
<h1 id="rfc.section.1.3"><a href="#rfc.section.1.3">1.3.</a> <a href="#terminology" id="terminology">Terminology</a></h1>
<p id="rfc.section.1.3.p.1">The reader is assumed to be familiar with the basic DNS and DNSSEC concepts described in <a href="#RFC1034">[RFC1034]</a>, <a href="#RFC1035">[RFC1035]</a>, <a href="#RFC4033">[RFC4033]</a>, <a href="#RFC4034">[RFC4034]</a>, and <a href="#RFC4035">[RFC4035]</a>; subsequent RFCs that update them in <a href="#RFC2136">[RFC2136]</a>, <a href="#RFC2181">[RFC2181]</a>, <a href="#RFC2308">[RFC2308]</a>, <a href="#RFC5155">[RFC5155]</a>, and <a href="#RFC7129">[RFC7129]</a>; and DNS terms in <a href="#RFC7719">[RFC7719]</a>.</p>
<p id="rfc.section.1.3.p.2">The reader should also be familiar with verifiable random functions (VRFs) as defined in <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a>.</p>
<p id="rfc.section.1.3.p.3">The following terminology is used through this document:</p>
<p/>
<dl>
<dt>Base32hex:</dt>
<dd style="margin-left: 8">The "Base 32 Encoding with Extended Hex Alphabet" as specified in <a href="#RFC4648">[RFC4648]</a>. The padding characters ("=") are not used in the NSEC5 specification.</dd>
<dt>Base64:</dt>
<dd style="margin-left: 8">The "Base 64 Encoding" as specified in <a href="#RFC4648">[RFC4648]</a>.</dd>
<dt>QNAME:</dt>
<dd style="margin-left: 8">The domain name being queried (query name).</dd>
<dt>Private NSEC5 key:</dt>
<dd style="margin-left: 8">The private key for the verifiable random function (VRF).</dd>
<dt>Public NSEC5 key:</dt>
<dd style="margin-left: 8">The public key for the VRF.</dd>
<dt>NSEC5 proof:</dt>
<dd style="margin-left: 8">A VRF proof. The holder of the private NSEC5 key (e.g., authoritative server) can compute the NSEC5 proof for an input domain name. Anyone who knows the public VRF key can verify that the NSEC5 proof corresponds to the input domain name.</dd>
<dt>NSEC5 hash:</dt>
<dd style="margin-left: 8">A cryptographic digest of an NSEC5 proof. If the NSEC5 proof is known, anyone can compute its corresponding NSEC5 hash.</dd>
<dt>NSEC5 algorithm:</dt>
<dd style="margin-left: 8">A triple of VRF algorithms that compute an NSEC5 proof (VRF_prove), verify an NSEC5 proof (VRF_verify), and process an NSEC5 proof to obtain its NSEC5 hash (VRF_proof_to_hash).</dd>
</dl>
<h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a href="#backward-compatibility" id="backward-compatibility">Backward Compatibility</a></h1>
<p id="rfc.section.2.p.1">The specification describes a protocol change that is not backward compatible with <a href="#RFC4035">[RFC4035]</a> and <a href="#RFC5155">[RFC5155]</a>. An NSEC5-unaware resolver will fail to validate responses introduced by this document.</p>
<p id="rfc.section.2.p.2">To prevent NSEC5-unaware resolvers from attempting to validate the responses, new DNSSEC algorithms identifiers are introduced in <a href="#iana_considerations">Section 16</a> which alias existing algorithm numbers. The zones signed according to this specification MUST use only these algorithm identifiers, thus NSEC5-unaware resolvers will treat the zone as insecure.</p>
<h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a href="#how-nsec5-works" id="how-nsec5-works">How NSEC5 Works</a></h1>
<p id="rfc.section.3.p.1">With NSEC5, the original domain name is hashed using a VRF <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a> using the following steps:</p>
<p/>
<ol>
<li>The domain name is processed using a VRF keyed with the private NSEC5 key to obtain the NSEC5 proof. Anyone who knows the public NSEC5 key, normally acquired via an NSEC5KEY RR, can verify that a given NSEC5 proof corresponds to a given domain name.</li>
<li>The NSEC5 proof is then processed using a publicly-computable VRF VRF_proof_to_hash function to obtain the NSEC5 hash. The NSEC5 hash can be computed by anyone who knows the input NSEC5 proof.</li>
</ol>
<p id="rfc.section.3.p.3">The NSEC5 hash determines the position of a domain name in an NSEC5 chain.</p>
<p id="rfc.section.3.p.4">To sign a zone, the private NSEC5 key is used to compute the NSEC5 hashes for each name in the zone. These NSEC5 hashes are sorted in canonical order <a href="#RFC4034">[RFC4034]</a>, and each consecutive pair forms an NSEC5 RR. Each NSEC5 RR is signed offline using the private zone-signing key. The resulting signed chain of NSEC5 RRs is provided to all authoritative servers for the zone, along with the private NSEC5 key.</p>
<p id="rfc.section.3.p.5">To prove non-existence of a particular domain name in response to a query, the server uses the private NSEC5 key to compute the NSEC5 proof and NSEC5 hash corresponding to the queried name. The server then identifies the NSEC5 RR that covers the NSEC5 hash, and responds with this NSEC5 RR and its corresponding RRSIG signature RRset, as well as a synthesized NSEC5PROOF RR that contains the NSEC5 proof corresponding to the queried name.</p>
<p id="rfc.section.3.p.6">To validate the response, the client verifies the following items:</p>
<p/>
<ul>
<li>The client uses the public NSEC5 key, normally acquired from the NSEC5KEY RR, to verify that the NSEC5 proof in the NSEC5PROOF RR corresponds to the queried name.</li>
<li>The client uses the VRF_proof_to_hash function to compute the NSEC5 hash from the NSEC5 proof in the NSEC5PROOF RR. The client verifies that the NSEC5 hash is covered by the NSEC5 RR.</li>
<li>The client verifies that the NSEC5 RR is validly signed by the RRSIG RRset.</li>
</ul>
<h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a href="#nsec5-algorithms" id="nsec5-algorithms">NSEC5 Algorithms</a></h1>
<p id="rfc.section.4.p.1">The algorithms used for NSEC5 authenticated denial are independent of the algorithms used for DNSSEC signing. An NSEC5 algorithm defines how the NSEC5 proof and the NSEC5 hash are computed and validated.</p>
<p id="rfc.section.4.p.2">The NSEC5 proof corresponding to a name is computed using ECVRF_prove(), as specified in <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a>. The input to ECVRF_prove() is a private NSEC5 key and the RR owner name in <a href="#RFC4034">[RFC4034]</a> canonical wire format. The output of ECVRF_prove() is an octet string.</p>
<p id="rfc.section.4.p.3">An NSEC5 hash corresponding to a name is computed from its NSEC5 proof using ECVRF_proof_to_hash(), as specified in <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a>. The input to ECVRF_proof_to_hash() is an NSEC5 proof as an octet string. The output NSEC5 hash is either an octet string, or INVALID.</p>
<p id="rfc.section.4.p.4">An NSEC5 proof for a name is verified using ECVRF_verify(), as specified in <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a>. The input is the NSEC5 public key, followed by an NSEC5 proof as an octet string, followed by an RR owner name in <a href="#RFC4034">[RFC4034]</a> canonical wire format. The output is either VALID or INVALID.</p>
<p id="rfc.section.4.p.5">This document defines the EC-P256-SHA256 NSEC5 algorithm as follows:</p>
<p/>
<ul>
<li>The VRF is the ECVRF algorithm using the ECVRF-P256-SHA256 ciphersuite specified in <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a>.</li>
<li>The public key format to be used in the NSEC5KEY RR is defined in Section 4 of <a href="#RFC6605">[RFC6605]</a> and thus is the same as the format used to store ECDSA public keys in DNSKEY RRs. <br/> [NOTE: This specification does not compress the elliptic curve point used for the public key, but we do compress curve points in every other place we use them. The NSEC5KEY record can be shrunk by 31 additional octets by encoding the public key with point compression.]</li>
</ul>
<p id="rfc.section.4.p.7">This document defines the EC-ED25519-SHA512 NSEC5 algorithm as follows:</p>
<p/>
<ul>
<li>The VRF is the EC-VRF algorithm using the ECVRF-ED25519-SHA512 ciphersuite specified in <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a>.</li>
<li>The public key format to be used in the NSEC5KEY RR is defined in Section 3 of <a href="#RFC8080">[RFC8080]</a> and thus is the same as the format used to store Ed25519 public keys in DNSKEY RRs.</li>
</ul>
<p id="rfc.section.4.p.9">[NOTE: Could alternatively have the EC-ED25519-SHA512 NSEC5 ciphersuite use the EC-VRF-ED25519-SHA512-ELLIGATOR2 ciphersuite specified in <a href="#I-D.irtf-cfrg-vrf">[I-D.irtf-cfrg-vrf]</a>.]</p>
<h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a href="#the-nsec5key-resource-record" id="the-nsec5key-resource-record">The NSEC5KEY Resource Record</a></h1>
<p id="rfc.section.5.p.1">The NSEC5KEY RR stores a public NSEC5 key. The key allows clients to validate an NSEC5 proof sent by a server.</p>
<h1 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1.</a> <a href="#nsec5key-rdata-wire-format" id="nsec5key-rdata-wire-format">NSEC5KEY RDATA Wire Format</a></h1>
<p id="rfc.section.5.1.p.1">The RDATA for the NSEC5KEY RR is as shown below:</p>
<pre>
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm | Public Key /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</pre>
<p id="rfc.section.5.1.p.2">Algorithm is a single octet identifying the NSEC5 algorithm.</p>
<p id="rfc.section.5.1.p.3">Public Key is a variable-sized field holding public key material for NSEC5 proof verification.</p>
<h1 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2.</a> <a href="#nsec5key-rdata-presentation-format" id="nsec5key-rdata-presentation-format">NSEC5KEY RDATA Presentation Format</a></h1>
<p id="rfc.section.5.2.p.1">The presentation format of the NSEC5KEY RDATA is as follows:</p>
<p id="rfc.section.5.2.p.2">The Algorithm field is represented as an unsigned decimal integer.</p>
<p id="rfc.section.5.2.p.3">The Public Key field is represented in Base64 encoding. Whitespace is allowed within the Base64 text.</p>
<h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a href="#the-nsec5-resource-record" id="the-nsec5-resource-record">The NSEC5 Resource Record</a></h1>
<p id="rfc.section.6.p.1">The NSEC5 RR provides authenticated denial of existence for an RRset or domain name. One NSEC5 RR represents one piece of an NSEC5 chain, proving existence of the owner name and non-existence of other domain names in the part of the hashed domain space that is covered until the next owner name hashed in the RDATA.</p>
<h1 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1.</a> <a href="#nsec5-rdata-wire-format" id="nsec5-rdata-wire-format">NSEC5 RDATA Wire Format</a></h1>
<p id="rfc.section.6.1.p.1">The RDATA for the NSEC5 RR is as shown below:</p>
<pre>
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Tag | Flags | Next Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Hashed Owner Name /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Type Bit Maps /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</pre>
<p id="rfc.section.6.1.p.2">The Key Tag field contains the key tag value of the NSEC5KEY RR that validates the NSEC5 RR, in network byte order. The value is computed from the NSEC5KEY RDATA using the same algorithm used to compute key tag values for DNSKEY RRs. This algorithm is defined in <a href="#RFC4034">[RFC4034]</a>.</p>
<p id="rfc.section.6.1.p.3">The Flags field is a single octet. The meaning of individual bits of the field is defined in <a href="#nsec5_flags">Section 6.2</a>.</p>
<p id="rfc.section.6.1.p.4">The Next Length field is an unsigned single octet specifying the length of the Next Hashed Owner Name field in octets.</p>
<p id="rfc.section.6.1.p.5">The Next Hashed Owner Name field is a sequence of binary octets. It contains an NSEC5 hash of the next domain name in the NSEC5 chain.</p>
<p id="rfc.section.6.1.p.6">Type Bit Maps is a variable-sized field encoding RR types present at the original owner name matching the NSEC5 RR. The format of the field is equivalent to the format used in the NSEC3 RR, described in <a href="#RFC5155">[RFC5155]</a>.</p>
<h1 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2.</a> <a href="#nsec5_flags" id="nsec5_flags">NSEC5 Flags Field</a></h1>
<p id="rfc.section.6.2.p.1">The following one-bit NSEC5 flags are defined:</p>
<pre>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| |W|O|
+-+-+-+-+-+-+-+-+
</pre>
<p/>
<ul class="empty">
<li>O - Opt-Out flag</li>
</ul>
<p/>
<ul class="empty">
<li>W - Wildcard flag</li>
</ul>
<p id="rfc.section.6.2.p.4">All the other flags are reserved for future use and MUST be zero.</p>
<p id="rfc.section.6.2.p.5">The Opt-Out flag has the same semantics as in NSEC3. The definition and considerations in <a href="#RFC5155">[RFC5155]</a> are valid, except that NSEC3 is replaced by NSEC5.</p>
<p id="rfc.section.6.2.p.6">The Wildcard flag indicates that a wildcard synthesis is possible at the original domain name level (i.e., there is a wildcard node immediately descending from the immediate ancestor of the original domain name). The purpose of the Wildcard flag is to reduce the maximum number of RRs required for an authenticated denial of existence proof from (at most) three to (at most) two, as originally described in <a href="#I-D.gieben-nsec4">[I-D.gieben-nsec4]</a> Section 7.2.1.</p>
<h1 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3.</a> <a href="#nsec5-rdata-presentation-format" id="nsec5-rdata-presentation-format">NSEC5 RDATA Presentation Format</a></h1>
<p id="rfc.section.6.3.p.1">The presentation format of the NSEC5 RDATA is as follows:</p>
<p id="rfc.section.6.3.p.2">The Key Tag field is represented as an unsigned decimal integer.</p>
<p id="rfc.section.6.3.p.3">The Flags field is represented as an unsigned decimal integer.</p>
<p id="rfc.section.6.3.p.4">The Next Length field is not represented.</p>
<p id="rfc.section.6.3.p.5">The Next Hashed Owner Name field is represented as a sequence of case-insensitive Base32hex digits without any whitespace and without padding.</p>
<p id="rfc.section.6.3.p.6">The Type Bit Maps representation is equivalent to the representation used in NSEC3 RR, described in <a href="#RFC5155">[RFC5155]</a>.</p>
<h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a href="#the-nsec5proof-resource-record" id="the-nsec5proof-resource-record">The NSEC5PROOF Resource Record</a></h1>
<p id="rfc.section.7.p.1">The NSEC5PROOF record is not to be included in the zone file. The NSEC5PROOF record contains the NSEC5 proof, proving the position of the owner name in an NSEC5 chain.</p>
<h1 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1.</a> <a href="#nsec5proof_rdata" id="nsec5proof_rdata">NSEC5PROOF RDATA Wire Format</a></h1>
<p id="rfc.section.7.1.p.1">The RDATA for the NSEC5PROOF RR is shown below:</p>
<pre>
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Tag | Owner Name Hash /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</pre>
<p id="rfc.section.7.1.p.2">Key Tag field contains the key tag value of the NSEC5KEY RR that validates the NSEC5PROOF RR, in network byte order.</p>
<p id="rfc.section.7.1.p.3">Owner Name Hash is a variable-sized sequence of binary octets encoding the NSEC5 proof of the owner name of the RR.</p>
<h1 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2.</a> <a href="#nsec5proof-rdata-presentation-format" id="nsec5proof-rdata-presentation-format">NSEC5PROOF RDATA Presentation Format</a></h1>
<p id="rfc.section.7.2.p.1">The presentation format of the NSEC5PROOF RDATA is as follows:</p>
<p id="rfc.section.7.2.p.2">The Key Tag field is represented as an unsigned decimal integer.</p>
<p id="rfc.section.7.2.p.3">The Owner Name Hash is represented in Base64 encoding. Whitespace is allowed within the Base64 text.</p>
<h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a> <a href="#nsec5_proofs" id="nsec5_proofs">Types of Authenticated Denial of Existence with NSEC5</a></h1>
<p id="rfc.section.8.p.1">This section summarizes all possible types of authenticated denial of existence. For each type the following lists are included:</p>
<p/>
<ol>
<li>Facts to prove: the minimum amount of information that an authoritative server must provide to a client to assure the client that the response content is valid.</li>
<li>Authoritative server proofs: the names for which the NSEC5PROOF RRs are synthesized and added into the response along with the NSEC5 RRs matching or covering each such name. These records together prove the listed facts.</li>
<li>Validator checks: the individual checks that a validating server is required to perform on a response. The response content is considered valid only if all of the checks pass.</li>
</ol>
<p id="rfc.section.8.p.3">If NSEC5 is said to match a domain name, the owner name of the NSEC5 RR has to be equivalent to an NSEC5 hash of that domain name. If an NSEC5 RR is said to cover a domain name, the NSEC5 hash of the domain name must sort in canonical order between that NSEC5 RR's Owner Name and Next Hashed Owner Name.</p>
<h1 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1.</a> <a href="#name-error-responses" id="name-error-responses">Name Error Responses</a></h1>
<p id="rfc.section.8.1.p.1">Facts to prove:</p>
<p/>
<ul class="empty">
<li>Non-existence of the domain name that explictly matches the QNAME.</li>
</ul>
<p/>
<ul class="empty">
<li>Non-existence of the wildcard that matches the QNAME.</li>
</ul>
<p id="rfc.section.8.1.p.4">Authoritative server proofs:</p>
<p/>
<ul class="empty">
<li>NSEC5PROOF for closest encloser and matching NSEC5 RR.</li>
</ul>
<p/>
<ul class="empty">
<li>NSEC5PROOF for next closer name and covering NSEC5 RR.</li>
</ul>
<p id="rfc.section.8.1.p.7">Validator checks:</p>
<p/>
<ul class="empty">
<li>Closest encloser is in the zone.</li>
</ul>
<p/>
<ul class="empty">
<li>The NSEC5 RR matching the closest encloser has its Wildcard flag cleared.</li>
</ul>
<p/>
<ul class="empty">
<li>The NSEC5 RR matching the closest encloser does not have NS without SOA in the Type Bit Map.</li>
</ul>
<p/>
<ul class="empty">
<li>The NSEC5 RR matching the closest encloser does not have DNAME in the Type Bit Map.</li>
</ul>
<p/>
<ul class="empty">
<li>Next closer name is not in the zone.</li>
</ul>
<h1 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2.</a> <a href="#no-data-responses" id="no-data-responses">No Data Responses</a></h1>
<p id="rfc.section.8.2.p.1">The processing of a No Data response for DS QTYPE differs if the Opt-Out is in effect. For DS QTYPE queries, the validator has two possible checking paths. The correct path can be simply decided by inspecting if the NSEC5 RR in the response matches the QNAME.</p>
<p id="rfc.section.8.2.p.2">Note that the Opt-Out is valid only for DS QTYPE queries.</p>
<h1 id="rfc.section.8.2.1"><a href="#rfc.section.8.2.1">8.2.1.</a> <a href="#no-data-response-opt-out-not-in-effect" id="no-data-response-opt-out-not-in-effect">No Data Response, Opt-Out Not In Effect</a></h1>
<p id="rfc.section.8.2.1.p.1">Facts to prove:</p>
<p/>
<ul class="empty">
<li>Existence of an RRset explicitly matching the QNAME.</li>
</ul>
<p/>
<ul class="empty">
<li>Non-existence of QTYPE RRset matching the QNAME.</li>
</ul>
<p/>
<ul class="empty">
<li>Non-existence of CNAME RRset matching the QNAME.</li>
</ul>
<p id="rfc.section.8.2.1.p.5">Authoritative server proofs:</p>
<p/>
<ul class="empty">
<li>NSEC5PROOF for the QNAME and matching NSEC5 RR.</li>
</ul>
<p id="rfc.section.8.2.1.p.7">Validator checks:</p>
<p/>
<ul class="empty">
<li>QNAME is in the zone.</li>
</ul>
<p/>
<ul class="empty">
<li>NSEC5 RR matching the QNAME does not have QTYPE in Type Bit Map.</li>
</ul>
<p/>
<ul class="empty">
<li>NSEC5 RR matching the QNAME does not have CNAME in Type Bit Map.</li>
</ul>
<h1 id="rfc.section.8.2.2"><a href="#rfc.section.8.2.2">8.2.2.</a> <a href="#no-data-response-opt-out-in-effect" id="no-data-response-opt-out-in-effect">No Data Response, Opt-Out In Effect</a></h1>
<p id="rfc.section.8.2.2.p.1">Facts to prove:</p>
<p/>
<ul class="empty">
<li>The delegation is not covered by the NSEC5 chain.</li>
</ul>
<p id="rfc.section.8.2.2.p.3">Authoritative server proofs:</p>
<p/>
<ul class="empty">
<li>NSEC5PROOF for closest provable encloser and matching NSEC5 RR.</li>
</ul>
<p id="rfc.section.8.2.2.p.5">Validator checks:</p>
<p/>
<ul class="empty">
<li>Closest provable encloser is in zone.</li>
</ul>
<p/>
<ul class="empty">
<li>Closest provable encloser covers (not matches) the QNAME.</li>
</ul>
<p/>
<ul class="empty">
<li>NSEC5 RR matching the closest provable encloser has Opt-Out flag set.</li>
</ul>
<h1 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3.</a> <a href="#wildcard-responses" id="wildcard-responses">Wildcard Responses</a></h1>
<p id="rfc.section.8.3.p.1">Facts to prove:</p>
<p/>
<ul class="empty">
<li>A signed positive response to the QNAME demonstrating the existence of the wildcard (label count in RRSIG is less than in QNAME), and also providing closest encloser name.</li>
</ul>
<p/>
<ul class="empty">
<li>Non-existence of the domain name matching the QNAME.</li>
</ul>
<p id="rfc.section.8.3.p.4">Authoritative server proofs:</p>
<p/>
<ul class="empty">
<li>A signed positive response for the wildcard expansion of the QNAME.</li>
</ul>
<p/>
<ul class="empty">
<li>NSEC5PROOF for next closer name and covering NSEC5 RR.</li>
</ul>
<p id="rfc.section.8.3.p.7">Validator checks:</p>
<p/>
<ul class="empty">
<li>Next closer name is not in the zone.</li>
</ul>
<h1 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4.</a> <a href="#wildcard-no-data-responses" id="wildcard-no-data-responses">Wildcard No Data Responses</a></h1>
<p id="rfc.section.8.4.p.1">Facts to prove:</p>
<p/>
<ul class="empty">
<li>The existence of the wildcard at the closest encloser to the QNAME.</li>
</ul>
<p/>
<ul class="empty">
<li>Non-existence of both the QTYPE and of the CNAME type that matches QNAME via wildcard expansion.</li>
</ul>
<p id="rfc.section.8.4.p.4">Authoritative server proofs:</p>
<p/>
<ul class="empty">
<li>NSEC5PROOF for source of synthesis (i.e., wildcard at closest encloser) and matching NSEC5 RR.</li>
</ul>
<p/>
<ul class="empty">
<li>NSEC5PROOF for next closer name and covering NSEC5 RR.</li>
</ul>
<p id="rfc.section.8.4.p.7">Validator checks:</p>
<p/>
<ul class="empty">
<li>Closest encloser to the QNAME exists.</li>
</ul>
<p/>
<ul class="empty">
<li>NSEC5 RR matching the wildcard label prepended to the closest encloser, and which does not have the bits corresponding to the QTYPE and CNAME types set it the type bitmap.</li>
</ul>