Internet Engineering Task Force                               D. Wessels
Internet-Draft                                                 P. Barber
Intended status: Standards Track                                Verisign
Expires: December 14, 2020                                   M. Weinberg
                                                                  Amazon
                                                               W. Kumari
                                                                  Google
                                                             W. Hardaker
                                                                 USC/ISI
                                                           June 12, 2020


                      Message Digest for DNS Zones
                  draft-ietf-dnsop-dns-zone-digest-08

Abstract

   This document describes a protocol and new DNS Resource Record that
   can be used to provide a cryptographic message digest over DNS zone
   data.  The ZONEMD Resource Record conveys the digest data in the zone
   itself.  When a zone publisher includes an ZONEMD record, recipients
   can verify the zone contents for accuracy and completeness.  This
   provides assurance that received zone data matches published data,
   regardless of how the zone data has been transmitted and received.

   ZONEMD is not designed to replace DNSSEC.  Whereas DNSSEC protects
   individual RRSets (DNS data with fine granularity), ZONEMD protects a
   zone's data as a whole, whether consumed by authoritative name
   servers, recursive name servers, or any other applications.

   As specified at this time, ZONEMD is not designed for use in large,
   dynamic zones due to the time and resources required for digest
   calculation.  The ZONEMD record described in this document is
   designed so that new digest schemes may be developed in the future to
   support large, dynamic zones.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   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 https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any



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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 14, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Design Overview . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . .   6
       1.3.1.  Root Zone . . . . . . . . . . . . . . . . . . . . . .   6
       1.3.2.  Providers, Secondaries, and Anycast . . . . . . . . .   6
       1.3.3.  Response Policy Zones . . . . . . . . . . . . . . . .   7
       1.3.4.  Centralized Zone Data Service . . . . . . . . . . . .   7
       1.3.5.  General Purpose Comparison Check  . . . . . . . . . .   7
     1.4.  Requirements Language . . . . . . . . . . . . . . . . . .   7
   2.  The ZONEMD Resource Record  . . . . . . . . . . . . . . . . .   7
     2.1.  Non-apex ZONEMD Records . . . . . . . . . . . . . . . . .   8
     2.2.  ZONEMD RDATA Wire Format  . . . . . . . . . . . . . . . .   8
       2.2.1.  The Serial Field  . . . . . . . . . . . . . . . . . .   8
       2.2.2.  The Scheme Field  . . . . . . . . . . . . . . . . . .   9
       2.2.3.  The Hash Algorithm Field  . . . . . . . . . . . . . .   9
       2.2.4.  The Digest Field  . . . . . . . . . . . . . . . . . .   9
     2.3.  ZONEMD Presentation Format  . . . . . . . . . . . . . . .   9
     2.4.  ZONEMD Example  . . . . . . . . . . . . . . . . . . . . .  10
   3.  Calculating the Digest  . . . . . . . . . . . . . . . . . . .  10
     3.1.  Add ZONEMD Placeholder  . . . . . . . . . . . . . . . . .  10
     3.2.  Optionally Sign the Zone  . . . . . . . . . . . . . . . .  10
     3.3.  Canonical Format and Ordering . . . . . . . . . . . . . .  11
     3.4.  Inclusion/Exclusion Rules . . . . . . . . . . . . . . . .  11
     3.5.  Scheme-Specific Processing  . . . . . . . . . . . . . . .  12
       3.5.1.  The SIMPLE Scheme . . . . . . . . . . . . . . . . . .  12



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     3.6.  Update ZONEMD RR  . . . . . . . . . . . . . . . . . . . .  12
   4.  Verifying Zone Digest . . . . . . . . . . . . . . . . . . . .  12
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     5.1.  ZONEMD RRtype . . . . . . . . . . . . . . . . . . . . . .  14
     5.2.  ZONEMD Scheme . . . . . . . . . . . . . . . . . . . . . .  14
     5.3.  ZONEMD Hash Algorithm . . . . . . . . . . . . . . . . . .  14
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
     6.1.  Attacks Against the Zone Digest . . . . . . . . . . . . .  15
     6.2.  Attacks Utilizing ZONEMD Queries  . . . . . . . . . . . .  15
     6.3.  Resilience and Fragility  . . . . . . . . . . . . . . . .  16
   7.  Performance Considerations  . . . . . . . . . . . . . . . . .  16
     7.1.  SIMPLE SHA384 . . . . . . . . . . . . . . . . . . . . . .  16
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  17
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   10. Implementation Status . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Authors' Implementation  . . . . . . . . . . . . . . . .  17
     10.2.  Shane Kerr's Implementation  . . . . . . . . . . . . . .  18
     10.3.  NIC Chile Labs Implementation  . . . . . . . . . . . . .  18
   11. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  19
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     12.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Appendix A.  Example Zones With Digests . . . . . . . . . . . . .  26
     A.1.  Simple EXAMPLE Zone . . . . . . . . . . . . . . . . . . .  27
     A.2.  Complex EXAMPLE Zone  . . . . . . . . . . . . . . . . . .  27
     A.3.  EXAMPLE Zone with multiple digests  . . . . . . . . . . .  28
     A.4.  The URI.ARPA Zone . . . . . . . . . . . . . . . . . . . .  29
     A.5.  The ROOT-SERVERS.NET Zone . . . . . . . . . . . . . . . .  32
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

1.  Introduction

   In the DNS, a zone is the collection of authoritative resource
   records (RRs) sharing a common origin ([RFC8499]).  Zones are often
   stored as files on disk in the so-called master file format
   [RFC1034].  Zones are generally distributed among name servers using
   the AXFR [RFC5936], and IXFR [RFC1995] protocols.  Zone files can
   also be distributed outside of the DNS, with such protocols as FTP,
   HTTP, rsync, and even via email.  Currently there is no standard way
   to verify the authenticity of a stand-alone zone.

   This document introduces a new RR type that serves as a cryptographic
   message digest of the data in a zone.  It allows a receiver of the
   zone to verify the zone's authenticity, especially when used in
   combination with DNSSEC.  This technique makes the digest a part of
   the zone itself, allowing verification the zone as a whole, no matter
   how it is transmitted.  Furthermore, the digest is based on the wire




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   format of zone data.  Thus, it is independent of presentation format,
   such as changes in whitespace, capitalization, and comments.

   DNSSEC provides three strong security guarantees relevant to this
   protocol:

   1.  whether or not to expect DNSSEC records in the zone,

   2.  whether or not to expect a ZONEMD record in a signed zone, and

   3.  whether or not the ZONEMD record has been altered since it was
       signed.

   This specification is OPTIONAL to implement by both publishers and
   consumers of zone data.

1.1.  Motivation

   The motivation for this protocol enhancement is the desire for the
   ability to verify the authenticity of a stand-alone zone, regardless
   of how it is transmitted.  A consumer of zone data should be able to
   verify that the data is as-published by the zone operator.

   One approach to preventing data tampering and corruption is to secure
   the distribution channel.  The DNS has a number of features that can
   already be used for channel security.  Perhaps the most widely used
   is DNS transaction signatures (TSIG [RFC2845]).  TSIG uses shared
   secret keys and a message digest to protect individual query and
   response messages.  It is generally used to authenticate and validate
   UPDATE [RFC2136], AXFR [RFC5936], and IXFR [RFC1995] messages.

   DNS Request and Transaction Signatures (SIG(0) [RFC2931]) is another
   protocol extension designed to authenticate individual DNS
   transactions.  Whereas SIG records were originally designed to cover
   specific RR types, SIG(0) is used to sign an entire DNS message.
   Unlike TSIG, SIG(0) uses public key cryptography rather than shared
   secrets.

   The Transport Layer Security protocol suite is also designed to
   provide channel security.  One can easily imagine the distribution of
   zones over HTTPS-enabled web servers, as well as DNS-over-HTTPS
   [RFC8484], and perhaps even a future version of DNS-over-TLS
   ([RFC7858]).

   Unfortunately, the protections provided by these channel security
   techniques are (in practice) ephemeral and are not retained after the
   data transfer is complete.  They can ensure that the client receives
   the data from the expected server, and that the data sent by the



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   server is not modified during transmission.  However, they do not
   guarantee that the server transmits the data as originally published,
   and do not provide any methods to verify data that is read after
   transmission is complete.  For example, a name server loading saved
   zone data upon restart cannot guarantee that the on-disk data has not
   been modified.  For these reasons, it is preferable to secure the
   data itself.

   Why not simply rely on DNSSEC, which provides certain data security
   guarantees?  Certainly for zones that are signed, a recipient could
   validate all of the signed RRSets.  Additionally, denial-of-existence
   records can prove that RRSets have not been added or removed.
   However, not all RRSets in a zone are signed.  The design of DNSSEC
   stipulates that delegations (non-apex NS records) are not signed, and
   neither are any glue records.  ZONEMD protects the integrity of
   delegation, glue, and other records that are not otherwise covered by
   DNSSEC.  Furthermore, zones that employ NSEC3 with opt-out are
   susceptible to the removal or addition of names between the signed
   nodes.  Whereas DNSSEC is primarily designed to protect consumers of
   DNS response messages, this protocol is designed to protect consumers
   of zones.

   There are existing tools and protocols that provide data security,
   such as OpenPGP [RFC4880] and S/MIME [RFC5751].  In fact, the
   internic.net site publishes PGP signatures along side the root zone
   and other files available there.  However, this is a detached
   signature with no strong association to the corresponding zone file
   other than its timestamp.  Non-detached signatures are, of course,
   possible, but these necessarily change the format of the file being
   distributed.  That is, a zone signed with OpenPGP or S/MIME no longer
   looks like a DNS zone and could not directly be loaded into a name
   server.  Once loaded the signature data is lost, so it does not
   survive further propagation.

   It seems the desire for data security in DNS zones was envisioned as
   far back as 1997.  [RFC2065] is an obsoleted specification of the
   first generation DNSSEC Security Extensions.  It describes a zone
   transfer signature, aka AXFR SIG, which is similar to the technique
   proposed by this document.  That is, it proposes ordering all
   (signed) RRSets in a zone, hashing their contents, and then signing
   the zone hash.  The AXFR SIG is described only for use during zone
   transfers.  It did not postulate the need to validate zone data
   distributed outside of the DNS.  Furthermore, its successor,
   [RFC2535], omits the AXFR SIG, while at the same time introducing an
   IXFR SIG.






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1.2.  Design Overview

   This document introduces a new Resource Record type designed to
   convey a message digest of the content of a zone.  The digest is
   calculated at the time of zone publication.  Ideally the zone is
   signed with DNSSEC to guarantee that any modifications of the digest
   can be detected.  The procedures for digest calculation and DNSSEC
   signing are similar.  Both require data to be processed in a well-
   defined order and format.  In some cases it may be possible to
   perform DNSSEC signing and digest calculation in parallel.

   The zone digest is designed to be used on zones that are relatively
   stable and have infrequent updates.  As currently specified, the
   digest is re-calculated over the entire zone content each time.  This
   specification does not provide an efficient mechanism for incremental
   updates of zone data.  It is, however, extensible so that future
   schemes to support incremental zone digest algorithms (e.g. using
   Merkle trees) can be accommodated.

   It is expected that verification of a zone digest would be
   implemented in name server software.  That is, a name server can
   verify the zone data it was given and refuse to serve a zone which
   fails verification.  For signed zones, the name server needs a trust
   anchor to perform DNSSEC validation.  For signed non-root zones, the
   name server may need to send queries to validate a chain-of-trust.
   Digest verification could also be performed externally.

1.3.  Use Cases

1.3.1.  Root Zone

   The root zone [InterNIC] is one of the most widely distributed DNS
   zone on the Internet, served by more than 1000 separate instances
   [RootServers] at the time of this writing.  Additionally, many
   organizations configure their own name servers to serve the root zone
   locally.  Reasons for doing so include privacy and reduced access
   time.  [RFC7706] describes one, but not the only, way to do this.  As
   the root zone spreads beyond its traditional deployment boundaries,
   the need for verification of the completeness of the zone contents
   becomes increasingly important.

1.3.2.  Providers, Secondaries, and Anycast

   Since its very early days, the developers of the DNS recognized the
   importance of secondary name servers and service diversity.  However,
   they may not have anticipated the complexity of modern DNS service
   provisioning which can include multiple third-party providers and
   hundreds of anycast instances.  Instead of a simple primary-to-



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   secondary zone distribution system, today it is possible to have
   multiple levels, multiple parties, and multiple protocols involved in
   the distribution of zone data.  This complexity introduces new places
   for problems to arise.  The zone digest protects the integrity of
   data that flows through such systems.

1.3.3.  Response Policy Zones

   DNS Response Policy Zones is "a method of expressing DNS response
   policy information inside specially constructed DNS zones..." [RPZ].
   A number of companies provide RPZ feeds, which can be consumed by
   name server and firewall products.  Since these are zones, AXFR is
   often, but not necessarily used for transmission.  While RPZ zones
   can certainly be signed with DNSSEC, the data is not queried
   directly, and would not be subject to DNSSEC validation.

1.3.4.  Centralized Zone Data Service

   ICANN operates the Centralized Zone Data Service [CZDS], which is a
   repository of top-level domain zone files.  Users request access to
   the system, and to individual zones, and are then able to download
   zone data for certain uses.  Adding a zone digest to these would
   provide CZDS users with assurances that the data has not been
   modified.  Note that ZONEMD could be added to CZDS zone data
   independently of the zone served by production name servers.

1.3.5.  General Purpose Comparison Check

   Since the zone digest calculation does not depend on presentation
   format, it could be used to compare multiple copies of a zone
   received from different sources, or copies generated by different
   processes.

1.4.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  The ZONEMD Resource Record

   This section describes the ZONEMD Resource Record, including its
   fields, wire format, and presentation format.  The Type value for the
   ZONEMD RR is 63.  The ZONEMD RR is class independent.  The RDATA of
   the resource record consists of four fields: Serial, Scheme, Hash
   Algorithm, and Digest.



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   A zone MAY contain multiple ZONEMD RRs to support algorithm agility
   [RFC7696] and rollovers.  Each ZONEMD RR must specify a unique Scheme
   and Hash Algorithm tuple.  It is recommended that a zone include only
   one ZONEMD RR, unless the zone publisher is in the process of
   transitioning to a new Scheme or Hash Algorithm.

2.1.  Non-apex ZONEMD Records

   This specification utilizes ZONEMD RRs located at the zone apex.
   Non-apex ZONEMD RRs are not forbidden, but have no meaning in this
   specification.  Non-apex ZONEMD RRs MUST NOT be used for
   verification.

   During digest calculation, non-apex ZONEMD RRs are treated like any
   other RRs.  They are digested as-is and the RR is not replaced by a
   placeholder RR.

   Unless explicitly stated otherwise, "ZONEMD" always refers to apex
   records throughout this document.

2.2.  ZONEMD RDATA Wire Format

   The ZONEMD RDATA wire format is encoded as follows:

                        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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Serial                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Scheme     |Hash Algorithm |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                             Digest                            |
   /                                                               /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.2.1.  The Serial Field

   The Serial field is a 32-bit unsigned integer in network order.  It
   is equal to the serial number from the zone's SOA record ([RFC1035]
   section 3.3.13) for which the zone digest was generated.

   The zone's serial number is included here in order to make DNS
   response messages of type ZONEMD meaningful.  Without the serial
   number, a stand-alone ZONEMD digest has no association to any
   particular instance of a zone.





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2.2.2.  The Scheme Field

   The Scheme field is an 8-bit unsigned integer that identifies the
   methods by which data is collated and presented as input to the
   hashing function.

   At the time of this writing, SIMPLE, with value 1, is the only
   standardized Scheme defined for ZONEMD records.  The Scheme registry
   is further described in Section 5.

   Scheme values 240-254 are allocated for Private Use as described in
   [RFC8126].

2.2.3.  The Hash Algorithm Field

   The Hash Algorithm field is an 8-bit unsigned integer that identifies
   the cryptographic hash algorithm used to construct the digest.

   At the time of this writing, SHA384, with value 1, is the only
   standardized Hash Algorithm defined for ZONEMD records.  The Hash
   Algorithm registry is further described in Section 5.

   Hash Algorithm values 240-254 are allocated for Private Use as
   described in [RFC8126].

2.2.4.  The Digest Field

   The Digest field is a variable-length sequence of octets containing
   the output of the hash algorithm.  The Digest field must not be
   empty.  Section 3 describes how to calculate the digest for a zone.
   Section 4 describes how to use the digest to verify the contents of a
   zone.

2.3.  ZONEMD Presentation Format

   The presentation format of the RDATA portion is as follows:

   The Serial field is represented as an unsigned decimal integer.

   The Scheme field is represented as an unsigned decimal integer.

   The Hash Algorithm field is represented as an unsigned decimal
   integer.

   The Digest is represented as a sequence of case-insensitive
   hexadecimal digits.  Whitespace is allowed within the hexadecimal
   text.




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2.4.  ZONEMD Example

   The following example shows a ZONEMD RR.

   example.com. 86400 IN ZONEMD 2018031500 1 1 (
       FEBE3D4CE2EC2FFA4BA99D46CD69D6D29711E55217057BEE
       7EB1A7B641A47BA7FED2DD5B97AE499FAFA4F22C6BD647DE )

3.  Calculating the Digest

3.1.  Add ZONEMD Placeholder

   In preparation for calculating the zone digest, any existing ZONEMD
   records (and covering RRSIGs) at the zone apex are first deleted.

   Prior to calculation of the digest, and prior to signing with DNSSEC,
   one or more placeholder ZONEMD records are added to the zone apex.
   This ensures that denial-of-existence (NSEC, NSEC3) records are
   created correctly if the zone is signed with DNSSEC.  If placeholders
   are not added prior to signing, the later addition of ZONEMD records
   would also require updating the Type Bit Maps field of any apex NSEC/
   NSEC3 RRs, which then invalidates the calculated digest value.

   When multiple ZONEMD RRs are published in the zone, e.g., during an
   algorithm rollover, each must specify a unique Scheme and Hash
   Algorithm tuple.

   It is recommended that the TTL of the ZONEMD record match the TTL of
   the SOA.

   In the placeholder record, the Serial field is set to the current SOA
   Serial.  The Scheme field is set to the value for the chosen
   collation scheme.  The Hash Algorithm field is set to the value for
   the chosen hash algorithm.  Since ZONEMD records are excluded from
   digest calculation, the value of the Digest field does not matter at
   this point in the process.  Implementations MAY want to set the
   Digest field to all zeroes anyway.

3.2.  Optionally Sign the Zone

   Following addition of placeholder records, the zone may be signed
   with DNSSEC.  Note that when the digest calculation is complete, and
   the ZONEMD record is updated, the signature(s) for the ZONEMD RRSet
   MUST be recalculated and updated as well.  Therefore, the signer is
   not required to calculate a signature over the placeholder record at
   this step in the process, but it is harmless to do so.





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3.3.  Canonical Format and Ordering

   Calculation of a zone digest REQUIRES RRs to be processed in a
   consistent format and ordering.  Correct ordering depends on (1)
   ordering of owner names, (2) ordering of RRSets with the same owner
   name, and (3) ordering of RRs within an RRSet.

   This specification adopts DNSSEC's canonical ordering for names
   (Section 6.1 of [RFC4034]), and canonical ordering for RRs within an
   RRSet (Section 6.3 of [RFC4034]).  It also adopts DNSSEC's canonical
   RR form (Section 6.2 of [RFC4034]).

   However, since DNSSEC does not define a canonical ordering for RRSets
   having the same owner name, that ordering is defined here.  For the
   purposes of calculating the zone digest, RRSets having the same owner
   name MUST be numerically ordered, in ascending order, by their
   numeric RR TYPE.

   This specification adopts DNSSEC's canonical on-the-wire RR format
   (without name compression) as specified in [RFC4034]:

   RR(i) = owner | type | class | TTL | RDATA length | RDATA

   where "|" denotes concatenation.

3.4.  Inclusion/Exclusion Rules

   When iterating over records in the zone, the following inclusion/
   exclusion rules apply:

   o  All records in the zone, including glue records, MUST be included.

   o  Occluded data ([RFC5936] Section 3.5) MUST be included.

   o  Only one instance of duplicate RRs with equal owner, class, type
      and RDATA SHALL be included ([RFC4034] Section 6.3).

   o  The placeholder ZONEMD RR(s) MUST NOT be included.

   o  If the zone is signed, DNSSEC RRs MUST be included, except:

   o  The RRSIG covering ZONEMD MUST NOT be included because the RRSIG
      will be updated after all digests have been calculated.








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3.5.  Scheme-Specific Processing

   At this time, only the SIMPLE collation scheme is defined.
   Additional schemes may be defined in future updates to this document.

3.5.1.  The SIMPLE Scheme

   For the SIMPLE scheme, the digest is calculated over the zone as a
   whole.  This means that a change to a single RR in the zone requires
   iterating over all RRs in the zone to recalculate the digest.  SIMPLE
   is a good choice for zones that are small and/or stable, but probably
   not good for zones that are large and/or dynamic.

   A zone digest using the SIMPLE scheme is calculated by concatenating
   the canonical form of all RRs in the zone, in the order described in
   Section 3.3, subject to the inclusion/exclusion rules described in
   Section 3.4, and then applying the SHA-384 algorithm:

   digest = hash( RR(1) | RR(2) | RR(3) | ... )

   where "|" denotes concatenation.

3.6.  Update ZONEMD RR

   Once a zone digest has been calculated, the published ZONEMD record
   is finalised by inserting the digest into the placeholder ZONEMD.
   Repeat for each digest if multiple digests are to be published.

   If the zone is signed with DNSSEC, the RRSIG record(s) covering the
   ZONEMD RRSet MUST then be added or updated.  Because the ZONEMD
   placeholder was added prior to signing, the zone will already have
   the appropriate denial-of-existence (NSEC, NSEC3) records.

   Some DNSSEC implementations (especially "online signing") might be
   designed such that the SOA serial number is updated whenever a new
   signature is made.  To preserve the calculated digest, generation of
   an ZONEMD signature must not also result in a change to the SOA
   serial number.  The ZONEMD RR and the matching SOA MUST be published
   at the same time.

4.  Verifying Zone Digest

   The recipient of a zone that has a ZONEMD RR can verify the zone by
   calculating the digest as follows.  If multiple ZONEMD RRs are
   present in the zone, e.g., during an algorithm rollover, a match
   using any one of the recipient's supported Schemes and Hash
   Algorithms is sufficient to verify the zone.




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   1.  The verifier MUST first determine whether or not to expect DNSSEC
       records in the zone.  This can be done by examining locally
       configured trust anchors, or querying for (and validating) DS RRs
       in the parent zone.  For zones that are provably insecure, or if
       DNSSEC validation can not be performed, digest validation
       continues at step 4 below.

   2.  For zones that are provably secure, the existence of the apex
       ZONEMD record MUST be verified.  If the ZONEMD record provably
       does not exist, digest verification cannot be done.  If the
       ZONEMD record does provably exist, but is not found in the zone,
       digest verification MUST NOT be considered successful.

   3.  For zones that are provably secure, the SOA and ZONEMD RRSets
       MUST have valid signatures, chaining up to a trust anchor.  If
       DNSSEC validation of the SOA or ZONEMD records fails, digest
       verification MUST NOT be considered successful.

   4.  If the ZONEMD RRSet contains more than one RR with the same
       Scheme and Hash Algorithm, digest verification MUST NOT be
       considered successful.

   5.  Loop over all apex ZONEMD RRs and perform the following steps:

       A.  The SOA Serial field MUST exactly match the ZONEMD Serial
           field.  If the fields do not match, digest verification MUST
           NOT be considered successful with this ZONEMD RR.

       B.  The Scheme field MUST be checked.  If the verifier does not
           support the given scheme, it SHOULD report that the RR's
           digest could not be verified due to an unsupported scheme.

       C.  The Hash Algorithm field MUST be checked.  If the verifier
           does not support the given hash algorithm, it SHOULD report
           that the RR's digest could not be verified due to an
           unsupported algorithm.

       D.  The zone digest is computed over the zone data as described
           in Section 3.5, using the Scheme and Hash Algorithm for the
           current ZONEMD RR.

       E.  The computed digest is compared to the received digest.  If
           the two digest values match, verification is considered
           successful.  Otherwise, verification MUST NOT be considered
           successful for this ZONEMD RR.






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5.  IANA Considerations

5.1.  ZONEMD RRtype

   This document defines a new DNS RR type, ZONEMD, whose value 63 has
   been allocated by IANA from the "Resource Record (RR) TYPEs"
   subregistry of the "Domain Name System (DNS) Parameters" registry:

   Type: ZONEMD

   Value: 63

   Meaning: Message Digest Over Zone Data

   Reference: This document

5.2.  ZONEMD Scheme

   This document asks IANA to create a new "ZONEMD Scheme" registry with
   initial contents as follows:

   +---------+--------------------+----------+-----------+-------------+
   | Value   | Description        | Mnemonic | Status    | Reference   |
   +---------+--------------------+----------+-----------+-------------+
   | 0       | Reserved           | RESERVED | N/A       | N/A         |
   | 1       | Simple ZONEMD      | SIMPLE   | Mandatory | This        |
   |         | collation          |          |           | document    |
   | 240-254 | Private Use        | N/A      | N/A       | [RFC8126]   |
   +---------+--------------------+----------+-----------+-------------+

                      Table 1: ZONEMD Scheme Registry

   The IANA policy for assigning new values to the ZONEMD Scheme
   registry shall be Specification Required, as described in [RFC8126].

5.3.  ZONEMD Hash Algorithm

   This document asks IANA to create a new "ZONEMD Hash Algorithm"
   registry with initial contents as follows:












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   +---------+----------------------+----------+-----------+-----------+
   | Value   | Description          | Mnemonic | Status    | Reference |
   +---------+----------------------+----------+-----------+-----------+
   | 0       | Reserved             | RESERVED | N/A       | N/A       |
   | 1       | The SHA-384 hash     | SHA384   | Mandatory | [RFC6234] |
   |         | algorithm            |          |           |           |
   | 240-254 | Private Use          | N/A      | N/A       | [RFC8126] |
   +---------+----------------------+----------+-----------+-----------+

                  Table 2: ZONEMD Hash Algorithm Registry

   The IANA policy for assigning new values to the ZONEMD Hash Algorithm
   registry shall be Specification Required, as described in [RFC8126].

6.  Security Considerations

6.1.  Attacks Against the Zone Digest

   The zone digest allows the receiver to verify that the zone contents
   haven't been modified since the zone was generated/published.
   Verification is strongest when the zone is also signed with DNSSEC.
   An attacker, whose goal is to modify zone content before it is used
   by the victim, may consider a number of different approaches.

   The attacker might perform a downgrade attack to an unsigned zone.
   This is why Section 4 talks about determining whether or not to
   expect DNSSEC signatures for the zone in step 1.

   The attacker might perform a downgrade attack by removing one or more
   ZONEMD records.  Such a removal is detectable only with DNSSEC
   validation and is why Section 4 talks about checking denial-of-
   existence proofs in step 2 and signature validation in step 3.

   The attacker might alter the Scheme, Hash Algorithm, or Digest fields
   of the ZONEMD record.  Such modifications are detectable only with
   DNSSEC validation.

6.2.  Attacks Utilizing ZONEMD Queries

   Nothing in this specification prevents clients from making, and
   servers from responding to, ZONEMD queries.  Servers SHOULD NOT
   calculate zone digests dynamically (for each query) as this can be
   used as a CPU resource exhaustion attack.

   One might consider how well ZONEMD responses could be used in a
   distributed denial-of-service amplification attack.  The ZONEMD RR is
   moderately sized, much like the DS RR.  A single ZONEMD RR
   contributes approximately 40 to 65 octets to a DNS response, for



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   currently defined digest types.  Certainly other RR types result in
   larger amplification effects (i.e., DNSKEY).

6.3.  Resilience and Fragility

   ZONEMD can be used to detect incomplete or corrupted zone data prior
   to its use, thereby increasing resilience, but also introducing some
   fragility.  Publishers and consumers of zones containing ZONEMD
   records should be aware of these tradeoffs.  While the intention is
   to secure the zone data, misconfigurations or implementation bugs are
   generally indistinguishable from intentional tampering, and could
   lead to service failures when verification is performed
   automatically.

   Zone publishers may want to deploy ZONEMD gradually, perhaps by
   utilizing one of the private use hash algorithms listed in
   Section 5.3.  Similarly, recipients may want to initially configure
   verification failures only as a warning, and later as an error after
   gaining experience and confidence with the feature.

7.  Performance Considerations

   This section is provided to make zone publishers aware of the
   performance requirements and implications of including ZONEMD RRs in
   a zone.

7.1.  SIMPLE SHA384

   As mentioned previously, the SIMPLE scheme may not be appropriate for
   use in zones that are either large or highly dynamic.  Zone
   publishers should carefully consider the use of ZONEMD in such zones,
   since it might cause consumers of zone data (e.g., secondary name
   servers) to expend resources on digest calculation.  Furthermore, for
   such use cases, it is recommended that ZONEMD only be used when
   digest calculation time is significantly less than propagation times
   and update intervals.

   The authors' implementation (Section 10.1) includes an option to
   record and report CPU usage of its operation.  The software was used
   to generate digests for more than 800 TLD zones available from
   [CZDS].  The table below summarizes the the results for the SIMPLE
   scheme and SHA384 hash algorithm grouped by zone size.  The Rate
   column is the mean amount of time per RR to calculate the digest,
   running on commodity hardware at the time of this writing.







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                 +---------------------+----------------+
                 |     Zone Size (RRs) | Rate (msec/RR) |
                 +---------------------+----------------+
                 |             10 - 99 |        0.00683 |
                 |           100 - 999 |        0.00551 |
                 |         1000 - 9999 |        0.00505 |
                 |       10000 - 99999 |        0.00602 |
                 |     100000 - 999999 |        0.00845 |
                 |   1000000 - 9999999 |         0.0108 |
                 | 10000000 - 99999999 |         0.0148 |
                 +---------------------+----------------+

   For example, based on the above table, it takes approximately 0.13
   seconds to calculate a SIMPLE SHA384 digest for a zone with 22,000
   RRs, and about 2.5 seconds for a zone with 300,000 RRs.

   These benchmarks attempt to emulate a worst-case scenario and take
   into account the time required to canonicalize the zone for
   processing.  Each of the 800+ zones were measured three times, and
   then averaged, with a different random sorting of the input data
   prior to each measurement.

8.  Privacy Considerations

   This specification has no impact on user privacy.

9.  Acknowledgments

   The authors wish to thank David Blacka, Scott Hollenbeck, and Rick
   Wilhelm for providing feedback on early drafts of this document.
   Additionally, they thank Joe Abley, Mark Andrews, Ralph Dolmans,
   Richard Gibson, Olafur Gudmundsson, Bob Harold, Paul Hoffman, Evan
   Hunt, Shumon Huque, Tatuya Jinmei, Mike St. Johns, Burt Kaliski,
   Shane Kerr, Matt Larson, John Levine, Ed Lewis, Matt Pounsett, Mukund
   Sivaraman, Petr Spacek, Ondrej Sury, Willem Toorop, Florian Weimer,
   Tim Wicinksi, Wouter Wijngarrds, Paul Wouters, and other members of
   the dnsop working group for their input.

10.  Implementation Status

10.1.  Authors' Implementation

   The authors have an open source implementation in C, using the ldns
   library [ldns-zone-digest].  This implementation is able to perform
   the following functions:

   o  Read an input zone and output a zone with the ZONEMD placeholder.




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   o  Compute zone digest over signed zone and update the ZONEMD record.

   o  Re-compute DNSSEC signature over the ZONEMD record.

   o  Verify the zone digest from an input zone.

   This implementation does not:

   o  Perform DNSSEC validation of the ZONEMD record during
      verification.

10.2.  Shane Kerr's Implementation

   Shane Kerr wrote an implementation of this specification during the
   IETF 102 hackathon [ZoneDigestHackathon].  This implementation is in
   Python and is able to perform the following functions:

   o  Read an input zone and output a zone with ZONEMD record.

   o  Verify the zone digest from an input zone.

   o  Output the ZONEMD record in its defined presentation format.

   This implementation does not:

   o  Re-compute DNSSEC signature over the ZONEMD record.

   o  Perform DNSSEC validation of the ZONEMD record.

10.3.  NIC Chile Labs Implementation

   NIC Chile Labs wrote an implementation of this specification as part
   of "dns-tools" suite [DnsTools], which besides digesting, can also
   sign and verify zones.  This implementation is in Go and is able to
   perform the following functions:

   o  Compute zone digest over signed zone and update the ZONEMD record.

   o  Verify the zone digest from an input zone.

   o  Perform DNSSEC validation of the ZONEMD record during
      verification.

   o  Re-compute DNSSEC signature over the ZONEMD record.







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11.  Change Log

   RFC Editor: Please remove this section.

   This section lists substantial changes to the document as it is being
   worked on.

   From -00 to -01:

   o  Removed requirement to sort by RR CLASS.

   o  Added Kumari and Hardaker as coauthors.

   o  Added Change Log section.

   o  Minor clarifications and grammatical edits.

   From -01 to -02:

   o  Emphasize desire for data security over channel security.

   o  Expanded motivation into its own subsection.

   o  Removed discussion topic whether or not to include serial in
      ZONEMD.

   o  Clarified that a zone's NS records always sort before the SOA
      record.

   o  Clarified that all records in the zone must are digested, except
      as specified in the exclusion rules.

   o  Added for discussion out-of-zone and occluded records.

   o  Clarified that update of ZONEMD signature must not cause a serial
      number change.

   o  Added persons to acknowledgments.

   From -02 to -03:

   o  Added recommendation to set ZONEMD TTL to SOA TTL.

   o  Clarified that digest input uses uncompressed names.

   o  Updated Implementations section.





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   o  Changed intended status from Standards Track to Experimental and
      added Scope of Experiment section.

   o  Updated Motivation, Introduction, and Design Overview sections in
      response to working group discussion.

   o  Gave ZONEMD digest types their own status, separate from DS digest
      types.  Request IANA to create a registry.

   o  Added Reserved field for future work supporting dynamic updates.

   o  Be more rigorous about having just ONE ZONEMD record in the zone.

   o  Expanded use cases.

   From -03 to -04:

   o  Added an appendix with example zones and digests.

   o  Clarified that only apex ZONEMD RRs shall be processed.

   From -04 to -05:

   o  Made SHA384 the only supported ZONEMD digest type.

   o  Disassociated ZONEMD digest types from DS digest types.

   o  Updates to Introduction based on list feedback.

   o  Changed "zone file" to "zone" everywhere.

   o  Restored text about why ZONEMD has a Serial field.

   o  Clarified ordering of RRSets having same owner to be numerically
      ascending.

   o  Clarified that all duplicate RRs (not just SOA) must be suppressed
      in digest calculation.

   o  Clarified that the Reserved field must be set to zero and checked
      for zero in verification.

   o  Clarified that occluded data must be included.

   o  Clarified procedure for verification, using temporary location for
      received digest.

   o  Explained why Reserved field is 8-bits.



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   o  IANA Considerations section now more specific.

   o  Added complex zone to examples.

   o

   From -05 to -06:

   o  RR type code 63 was assigned to ZONEMD by IANA.

   From -06 to -07:

   o  Fixed mistakes in ZONEMD examples.

   o  Added private use Digest Type values 240-254.

   o  Clarified that Digest field must not be empty.

   From -07 to draft-ietf-dnsop-dns-zone-digest-00:

   o  Adopted by dnsop.

   o  Clarified further that non-apex ZONEMD RRs have no meaning.

   o  Changed "provably [un]signed" to "provably [in]secure".

   o  Allow multiple ZONEMD RRs to support algorithm agility/rollovers.

   o  Describe verification when there are multiple ZONEMD RRs.

   From -00 to -01:

   o  Simplified requirements around verifying multiple digests.  Any
      one match is sufficient.

   o  Updated implementation notes.

   o  Both implementations produce expected results on examples given in
      this document.

   From -01 to -02:

   o  Changed the name of the Reserved field to Parameter.

   o  Changed the name of Digest Type 1 from SHA384 to SHA384-STABLE.

   o  The meaning of the Parameter field now depends on Digest Type.




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   o  No longer require Parameter field to be zero in verification.

   o  Updated a rule from earlier versions that said multiple ZONEMD RRs
      were not allowed.

   From -02 to -03:

   o  Changed the name of Digest Type 1 from SHA384-STABLE to
      SHA384-SIMPLE.

   o  Changed document status from Experimental to Standards Track.

   o  Removed Scope of Experimentation section.

   From -03 to -04:

   o  Addressing WGLC feedback.

   o  Changed from "Digest Type + Paramter" to "Scheme + Hash
      Algorithm".  This should make it more obvious how ZONEMD can be
      expanded in the future with new schemes and hash algorithms, while
      sacrificing some of the flexibility that the Parameter was
      intended to provide.

   o  Note: old RDATA fields: Serial, Digest Type, Parameter, Digest.

   o  Note: new RDATA fields: Serial, Scheme, Hash Algorithm, Digest.

   o  Add new IANA requirement for a Scheme registry.

   o  Rearranged some sections and separated scheme-specific aspects
      from general aspects of digest calculation.

   o  When discussing multiple ZONEMD RRs, allow for Scheme, as well as
      Hash Algorithm, transition.

   o  Added Performance Considerations section with some benchmarks.

   o  Further clarifications about non-apex ZONEMD RRs.

   o  Clarified inclusion rule for duplicate RRs.

   o  Removed or lowercased some inappropriately used RFC 2119 key
      words.

   o  Clarified that all ZONEMD RRs, even for unsupported hash
      algorithms, must be zeroized during digest calculation.




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   o  Added Resilience and Fragility to security considerations.

   o  Updated examples since changes in this version result in different
      hash values.

   From -04 to -05:

   o  Clarifications about non-apex and multiple ZONEMD RRs.

   o  Clarifications about benchmark results.

   o  Don't compute ZONEMD on-the-fly.

   o  Specifciation Required for updates to ZONEMD protocol registries.

   o  Other rewording based on WGLC feedback.

   o  Updated RFC numbers for some references.

   o  Use documentation IP addresses instead of loopback.

   o  Updated examples in the appendix.

   From -05 to -06:

   o  Per WG suggestion, no longer include any apex ZONEMD record in
      digest calculation.

   o  Updated examples in the appendix.

   o  Clarified verification procedure by describing a loop over all
      ZONEMD RRs.

   From -06 to -07:

   o  Added NIC Chile Labs implementation.

   From -07 to -08:

   o  Update an author's affiliation.

   o  Clarified why placeholder RRs are still important (for NSEC/
      NSEC3).

   o  Moved subsection ("Order of RRSets Having the Same Owner Name")
      with single sentence paragraph up into parent section.





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12.  References

12.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <https://www.rfc-editor.org/info/rfc4034>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <https://www.rfc-editor.org/info/rfc6234>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

12.2.  Informative References

   [CZDS]     Internet Corporation for Assigned Names and Numbers,
              "Centralized Zone Data Service", October 2018,
              <https://czds.icann.org/>.

   [DnsTools]
              NIC Chile Labs, "DNS tools for zone signature (file,
              pkcs11-hsm) and validation, and zone digest (ZONEMD)",
              April 2020, <https://github.com/niclabs/dns-tools>.

   [InterNIC]
              ICANN, "InterNIC FTP site", May 2018,
              <ftp://ftp.internic.net/domain/>.






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   [ldns-zone-digest]
              Verisign, "Implementation of Message Digests for DNS Zones
              using the ldns library", July 2018,
              <https://github.com/verisign/ldns-zone-digest>.

   [RFC1995]  Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
              DOI 10.17487/RFC1995, August 1996,
              <https://www.rfc-editor.org/info/rfc1995>.

   [RFC2065]  Eastlake 3rd, D. and C. Kaufman, "Domain Name System
              Security Extensions", RFC 2065, DOI 10.17487/RFC2065,
              January 1997, <https://www.rfc-editor.org/info/rfc2065>.

   [RFC2136]  Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, DOI 10.17487/RFC2136, April 1997,
              <https://www.rfc-editor.org/info/rfc2136>.

   [RFC2535]  Eastlake 3rd, D., "Domain Name System Security
              Extensions", RFC 2535, DOI 10.17487/RFC2535, March 1999,
              <https://www.rfc-editor.org/info/rfc2535>.

   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
              Wellington, "Secret Key Transaction Authentication for DNS
              (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
              <https://www.rfc-editor.org/info/rfc2845>.

   [RFC2931]  Eastlake 3rd, D., "DNS Request and Transaction Signatures
              ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
              2000, <https://www.rfc-editor.org/info/rfc2931>.

   [RFC4880]  Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
              Thayer, "OpenPGP Message Format", RFC 4880,
              DOI 10.17487/RFC4880, November 2007,
              <https://www.rfc-editor.org/info/rfc4880>.

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, DOI 10.17487/RFC5751, January
              2010, <https://www.rfc-editor.org/info/rfc5751>.

   [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
              <https://www.rfc-editor.org/info/rfc5936>.







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   [RFC7696]  Housley, R., "Guidelines for Cryptographic Algorithm
              Agility and Selecting Mandatory-to-Implement Algorithms",
              BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
              <https://www.rfc-editor.org/info/rfc7696>.

   [RFC7706]  Kumari, W. and P. Hoffman, "Decreasing Access Time to Root
              Servers by Running One on Loopback", RFC 7706,
              DOI 10.17487/RFC7706, November 2015,
              <https://www.rfc-editor.org/info/rfc7706>.

   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/info/rfc7858>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.

   [RootServers]
              Root Server Operators, "Root Server Technical Operations",
              July 2018, <https://www.root-servers.org/>.

   [RPZ]      Vixie, P. and V. Schryver, "DNS Response Policy Zones
              (RPZ)", draft-vixie-dnsop-dns-rpz-00 (work in progress),
              June 2018, <https://tools.ietf.org/html/draft-vixie-dnsop-
              dns-rpz-00>.

   [ZoneDigestHackathon]
              Kerr, S., "Prototype implementation of ZONEMD for the IETF
              102 hackathon in Python", July 2018,
              <https://github.com/shane-kerr/ZoneDigestHackathon>.

Appendix A.  Example Zones With Digests

   This appendix contains example zones with accurate ZONEMD records.
   These can be used to verify an implementation of the zone digest
   protocol.




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A.1.  Simple EXAMPLE Zone

   Here, the EXAMPLE zone contains an SOA record, NS and glue records,
   and a ZONEMD record.

   example.      86400   IN  SOA     ns1 admin 2018031900 (
                                     1800 900 604800 86400 )
                 86400   IN  NS      ns1
                 86400   IN  NS      ns2
                 86400   IN  ZONEMD  2018031900 1 1 (
                                     c68090d90a7aed71
                                     6bc459f9340e3d7c
                                     1370d4d24b7e2fc3
                                     a1ddc0b9a87153b9
                                     a9713b3c9ae5cc27
                                     777f98b8e730044c )
   ns1           3600    IN  A       203.0.113.63
   ns2           3600    IN  AAAA    2001:db8::63

A.2.  Complex EXAMPLE Zone

   Here, the EXAMPLE zone contains duplicate RRs, and an occluded RR,
   and one out-of-zone RR.




























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   example.      86400   IN  SOA     ns1 admin 2018031900 (
                                     1800 900 604800 86400 )
                 86400   IN  NS      ns1
                 86400   IN  NS      ns2
                 86400   IN  ZONEMD  2018031900 1 1 (
                                     31cefb03814f5062
                                     ad12fa951ba0ef5f
                                     8da6ae354a415767
                                     246f7dc932ceb1e7
                                     42a2108f529db6a3
                                     3a11c01493de358d )
   ns1           3600    IN  A       203.0.113.63
   ns2           3600    IN  AAAA    2001:db8::63
   occluded.sub  7200    IN  TXT     "I'm occluded but must be digested"
   sub           7200    IN  NS      ns1
   duplicate     300     IN  TXT     "I must be digested just once"
   duplicate     300     IN  TXT     "I must be digested just once"
   foo.test.     555     IN  TXT     "out-of-zone data must be excluded"
   non-apex      900     IN  ZONEMD  2018031900 1 1 (
                                     616c6c6f77656420
                                     6275742069676e6f
                                     7265642e20616c6c
                                     6f77656420627574
                                     2069676e6f726564
                                     2e20616c6c6f7765 )

A.3.  EXAMPLE Zone with multiple digests

   Here, the EXAMPLE zone contains multiple ZONEMD records.  Since only
   one Scheme (SIMPLE) and one Hash Algorithm (SHA384) is defined at
   this time, this example utilizes additional ZONEMD records with
   Scheme and Hash Algorithm values in the private range (240-254).
   These additional private-range digests are not verifiable.


















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   example.      86400   IN  SOA     ns1 admin 2018031900 (
                                     1800 900 604800 86400 )
   example.      86400   IN  NS      ns1.example.
   example.      86400   IN  NS      ns2.example.
   example.      86400   IN  ZONEMD  2018031900 1 1 (
                                     62e6cf51b02e54b9
                                     b5f967d547ce4313
                                     6792901f9f88e637
                                     493daaf401c92c27
                                     9dd10f0edb1c56f8
                                     080211f8480ee306 )
   example.      86400   IN  ZONEMD  2018031900 1 240 (
                                     e2d523f654b9422a
                                     96c5a8f44607bbee )
   example.      86400   IN  ZONEMD  2018031900 241 1 (
                                     e1846540e33a9e41
                                     89792d18d5d131f6
                                     05fc283e )
   ns1.example.  3600    IN  A       203.0.113.63
   ns2.example.  86400   IN  TXT     "This example has multiple digests"
   ns2.example.  3600    IN  AAAA    2001:db8::63

A.4.  The URI.ARPA Zone

   The URI.ARPA zone retrieved 2018-10-21.  Note this sample zone has
   (expired) signatures, but no signature for the ZONEMD RR.

   ; <<>> DiG 9.9.4 <<>> @lax.xfr.dns.icann.org uri.arpa axfr
   ; (2 servers found)
   ;; global options: +cmd
   uri.arpa.         3600    IN      SOA     sns.dns.icann.org. (
       noc.dns.icann.org. 2018100702 10800 3600 1209600 3600 )
   uri.arpa.         3600    IN      RRSIG   NSEC 8 2 3600 (
       20181028142623 20181007205525 47155 uri.arpa.
       eEC4w/oXLR1Epwgv4MBiDtSBsXhqrJVvJWUpbX8XpetAvD35bxwNCUTi
       /pAJVUXefegWeiriD2rkTgCBCMmn7YQIm3gdR+HjY/+o3BXNQnz97f+e
       HAE9EDDzoNVfL1PyV/2fde9tDeUuAGVVwmD399NGq9jWYMRpyri2kysr q/g= )
   uri.arpa.         86400   IN      RRSIG   NS 8 2 86400 (
       20181028172020 20181007175821 47155 uri.arpa.
       ATyV2A2A8ZoggC+68u4GuP5MOUuR+2rr3eWOkEU55zAHld/7FiBxl4ln
       4byJYy7NudUwlMOEXajqFZE7DVl8PpcvrP3HeeGaVzKqaWj+aus0jbKF
       Bsvs2b1qDZemBfkz/IfAhUTJKnto0vSUicJKfItu0GjyYNJCz2CqEuGD Wxc= )
   uri.arpa.         600     IN      RRSIG   MX 8 2 600 (
       20181028170556 20181007175821 47155 uri.arpa.
       e7/r3KXDohX1lyVavetFFObp8fB8aXT76HnN9KCQDxSnSghNM83UQV0t
       lTtD8JVeN1mCvcNFZpagwIgB7XhTtm6Beur/m5ES+4uSnVeS6Q66HBZK
       A3mR95IpevuVIZvvJ+GcCAQpBo6KRODYvJ/c/ZG6sfYWkZ7qg/Em5/+3 4UI= )
   uri.arpa.         3600    IN      RRSIG   DNSKEY 8 2 3600 (



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       20181028152832 20181007175821 15796 uri.arpa.
       nzpbnh0OqsgBBP8St28pLvPEQ3wZAUdEBuUwil+rtjjWlYYiqjPxZ286
       XF4Rq1usfV5x71jZz5IqswOaQgia91ylodFpLuXD6FTGs2nXGhNKkg1V
       chHgtwj70mXU72GefVgo8TxrFYzxuEFP5ZTP92t97FVWVVyyFd86sbbR
       6DZj3uA2wEvqBVLECgJLrMQ9Yy7MueJl3UA4h4E6zO2JY9Yp0W9woq0B
       dqkkwYTwzogyYffPmGAJG91RJ2h6cHtFjEZe2MnaY2glqniZ0WT9vXXd
       uFPm0KD9U77Ac+ZtctAF9tsZwSdAoL365E2L1usZbA+K0BnPPqGFJRJk
       5R0A1w== )
   uri.arpa.         3600    IN      RRSIG   DNSKEY 8 2 3600 (
       20181028152832 20181007175821 55480 uri.arpa.
       lWtQV/5szQjkXmbcD47/+rOW8kJPksRFHlzxxmzt906+DBYyfrH6uq5X
       nHvrUlQO6M12uhqDeL+bDFVgqSpNy+42/OaZvaK3J8EzPZVBHPJykKMV
       63T83aAiJrAyHzOaEdmzLCpalqcEE2ImzlLHSafManRfJL8Yuv+JDZFj
       2WDWfEcUuwkmIZWX11zxp+DxwzyUlRl7x4+ok5iKZWIg5UnBAf6B8T75
       WnXzlhCw3F2pXI0a5LYg71L3Tp/xhjN6Yy9jGlIRf5BjB59X2zra3a2R
       PkI09SSnuEwHyF1mDaV5BmQrLGRnCjvwXA7ho2m+vv4SP5dUdXf+GTeA
       1HeBfw== )
   uri.arpa.         3600    IN      RRSIG   SOA 8 2 3600 (
       20181029114753 20181008222815 47155 uri.arpa.
       qn8yBNoHDjGdT79U2Wu9IIahoS0YPOgYP8lG+qwPcrZ1BwGiHywuoUa2
       Mx6BWZlg+HDyaxj2iOmox+IIqoUHhXUbO7IUkJFlgrOKCgAR2twDHrXu
       9BUQHy9SoV16wYm3kBTEPyxW5FFm8vcdnKAF7sxSY8BbaYNpRIEjDx4A JUc= )
   uri.arpa.         3600    IN      NSEC    ftp.uri.arpa. NS SOA (
       MX RRSIG NSEC DNSKEY )
   uri.arpa.         86400   IN      NS      a.iana-servers.net.
   uri.arpa.         86400   IN      NS      b.iana-servers.net.
   uri.arpa.         86400   IN      NS      c.iana-servers.net.
   uri.arpa.         86400   IN      NS      ns2.lacnic.net.
   uri.arpa.         86400   IN      NS      sec3.apnic.net.
   uri.arpa.         600     IN      MX      10 pechora.icann.org.
   uri.arpa.         3600    IN      DNSKEY  256 3 8 (
       AwEAAcBi7tSart2J599zbYWspMNGN70IBWb4ziqyQYH9MTB/VCz6WyUK
       uXunwiJJbbQ3bcLqTLWEw134B6cTMHrZpjTAb5WAwg4XcWUu8mdcPTiL
       Bl6qVRlRD0WiFCTzuYUfkwsh1Rbr7rvrxSQhF5rh71zSpwV5jjjp65Wx
       SdJjlH0B )
   uri.arpa.         3600    IN      DNSKEY  257 3 8 (
       AwEAAbNVv6ulgRdO31MtAehz7j3ALRjwZglWesnzvllQl/+hBRZr9QoY
       cO2I+DkO4Q1NKxox4DUIxj8SxPO3GwDuOFR9q2/CFi2O0mZjafbdYtWc
       3zSdBbi3q0cwCIx7GuG9eqlL+pg7mdk9dgdNZfHwB0LnqTD8ebLPsrO/
       Id7kBaiqYOfMlZnh2fp+2h6OOJZHtY0DK1UlssyB5PKsE0tVzo5s6zo9
       iXKe5u+8WTMaGDY49vG80JPAKE7ezMiH/NZcUMiE0PRZ8D3foq2dYuS5
       ym+vA83Z7v8A+Rwh4UGnjxKB8zmr803V0ASAmHz/gwH5Vb0nH+LObwFt
       l3wpbp+Wpm8= )
   uri.arpa.         3600    IN      DNSKEY  257 3 8 (
       AwEAAbwnFTakCvaUKsXji4mgmxZUJi1IygbnGahbkmFEa0L16J+TchKR
       wcgzVfsxUGa2MmeA4hgkAooC3uy+tTmoMsgy8uq/JAj24DjiHzd46LfD
       FK/qMidVqFpYSHeq2Vv5ojkuIsx4oe4KsafGWYNOczKZgH5loGjN2aJG
       mrIm++XCphOskgCsQYl65MIzuXffzJyxlAuts+ecAIiVeqRaqQfr8LRU



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       7wIsLxinXirprtQrbor+EtvlHp9qXE6ARTZDzf4jvsNpKvLFZtmxzFf3
       e/UJz5eHjpwDSiZL7xE8aE1o1nGfPtJx9ZnB3bapltaJ5wY+5XOCKgY0
       xmJVvNQlwdE= )
   ftp.uri.arpa.     3600    IN      RRSIG   NSEC 8 3 3600 (
       20181028080856 20181007175821 47155 uri.arpa.
       HClGAqPxzkYkAT7Q/QNtQeB6YrkP6EPOef+9Qo5/2zngwAewXEAQiyF9
       jD1USJiroM11QqBS3v3aIdW/LXORs4Ez3hLcKNO1cKHsOuWAqzmE+BPP
       Arfh8N95jqh/q6vpaB9UtMkQ53tM2fYU1GszOLN0knxbHgDHAh2axMGH lqM= )
   ftp.uri.arpa.     604800  IN      RRSIG   NAPTR 8 3 604800 (
       20181028103644 20181007205525 47155 uri.arpa.
       WoLi+vZzkxaoLr2IGZnwkRvcDf6KxiWQd1WZP/U+AWnV+7MiqsWPZaf0
       9toRErerGoFOiOASNxZjBGJrRgjmavOM9U+LZSconP9zrNFd4dIu6kp5
       YxlQJ0uHOvx1ZHFCj6lAt1ACUIw04ZhMydTmi27c8MzEOMepvn7iH7r7 k7k= )
   ftp.uri.arpa.     3600    IN      NSEC    http.uri.arpa. NAPTR (
       RRSIG NSEC )
   ftp.uri.arpa.     604800  IN      NAPTR   0 0 "" "" (
       "!^ftp://([^:/?#]*).*$!\\1!i" . )
   http.uri.arpa.    3600    IN      RRSIG   NSEC 8 3 3600 (
       20181029010647 20181007175821 47155 uri.arpa.
       U03NntQ73LHWpfLmUK8nMsqkwVsOGW2KdsyuHYAjqQSZvKbtmbv7HBmE
       H1+Ii3Z+wtfdMZBy5aC/6sHdx69BfZJs16xumycMlAy6325DKTQbIMN+
       ift9GrKBC7cgCd2msF/uzSrYxxg4MJQzBPvlkwXnY3b7eJSlIXisBIn7 3b8= )
   http.uri.arpa.    604800  IN      RRSIG   NAPTR 8 3 604800 (
       20181029011815 20181007205525 47155 uri.arpa.
       T7mRrdag+WSmG+n22mtBSQ/0Y3v+rdDnfQV90LN5Fq32N5K2iYFajF7F
       Tp56oOznytfcL4fHrqOE0wRc9NWOCCUec9C7Wa1gJQcllEvgoAM+L6f0
       RsEjWq6+9jvlLKMXQv0xQuMX17338uoD/xiAFQSnDbiQKxwWMqVAimv5 7Zs= )
   http.uri.arpa.    3600    IN      NSEC    mailto.uri.arpa. NAPTR (
       RRSIG NSEC )
   http.uri.arpa.    604800  IN      NAPTR   0 0 "" "" (
       "!^http://([^:/?#]*).*$!\\1!i" . )
   mailto.uri.arpa.  3600    IN      RRSIG   NSEC 8 3 3600 (
       20181028110727 20181007175821 47155 uri.arpa.
       GvxzVL85rEukwGqtuLxek9ipwjBMfTOFIEyJ7afC8HxVMs6mfFa/nEM/
       IdFvvFg+lcYoJSQYuSAVYFl3xPbgrxVSLK125QutCFMdC/YjuZEnq5cl
       fQciMRD7R3+znZfm8d8u/snLV9w4D+lTBZrJJUBe1Efc8vum5vvV7819 ZoY= )
   mailto.uri.arpa.  604800  IN      RRSIG   NAPTR 8 3 604800 (
       20181028141825 20181007205525 47155 uri.arpa.
       MaADUgc3fc5v++M0YmqjGk3jBdfIA5RuP62hUSlPsFZO4k37erjIGCfF
       j+g84yc+QgbSde0PQHszl9fE/+SU5ZXiS9YdcbzSZxp2erFpZOTchrpg
       916T4vx6i59scodjb0l6bDyZ+mtIPrc1w6b4hUyOUTsDQoAJYxdfEuMg Vy4= )
   mailto.uri.arpa.  3600    IN      NSEC    urn.uri.arpa. NAPTR (
       RRSIG NSEC )
   mailto.uri.arpa.  604800  IN      NAPTR   0 0 "" "" (
       "!^mailto:(.*)@(.*)$!\\2!i" . )
   urn.uri.arpa.     3600    IN      RRSIG   NSEC 8 3 3600 (
       20181028123243 20181007175821 47155 uri.arpa.
       Hgsw4Deops1O8uWyELGe6hpR/OEqCnTHvahlwiQkHhO5CSEQrbhmFAWe



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       UOkmGAdTEYrSz+skLRQuITRMwzyFf4oUkZihGyhZyzHbcxWfuDc/Pd/9
       DSl56gdeBwy1evn5wBTms8yWQVkNtphbJH395gRqZuaJs3LD/qTyJ5Dp LvA= )
   urn.uri.arpa.     604800  IN      RRSIG   NAPTR 8 3 604800 (
       20181029071816 20181007205525 47155 uri.arpa.
       ALIZD0vBqAQQt40GQ0Efaj8OCyE9xSRJRdyvyn/H/wZVXFRFKrQYrLAS
       D/K7q6CMTOxTRCu2J8yes63WJiaJEdnh+dscXzZkmOg4n5PsgZbkvUSW
       BiGtxvz5jNncM0xVbkjbtByrvJQAO1cU1mnlDKe1FmVB1uLpVdA9Ib4J hMU= )
   urn.uri.arpa.     3600    IN      NSEC    uri.arpa. NAPTR RRSIG (
       NSEC )
   urn.uri.arpa.     604800  IN      NAPTR   0 0 "" "" (
       "/urn:([^:]+)/\\1/i" . )
   uri.arpa.         3600    IN      SOA     sns.dns.icann.org. (
       noc.dns.icann.org. 2018100702 10800 3600 1209600 3600 )
   ;; Query time: 66 msec
   ;; SERVER: 192.0.32.132#53(192.0.32.132)
   ;; WHEN: Sun Oct 21 20:39:28 UTC 2018
   ;; XFR size: 34 records (messages 1, bytes 3941)
   uri.arpa.       3600    IN      ZONEMD  2018100702 1 1 (
       1291b78ddf7669b1a39d014d87626b709b55774c5d7d58fa
       dc556439889a10eaf6f11d615900a4f996bd46279514e473 )

A.5.  The ROOT-SERVERS.NET Zone

   The ROOT-SERVERS.NET zone retreived 2018-10-21.



























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   root-servers.net.     3600000 IN  SOA     a.root-servers.net. (
       nstld.verisign-grs.com. 2018091100 14400 7200 1209600 3600000 )
   root-servers.net.     3600000 IN  NS      a.root-servers.net.
   root-servers.net.     3600000 IN  NS      b.root-servers.net.
   root-servers.net.     3600000 IN  NS      c.root-servers.net.
   root-servers.net.     3600000 IN  NS      d.root-servers.net.
   root-servers.net.     3600000 IN  NS      e.root-servers.net.
   root-servers.net.     3600000 IN  NS      f.root-servers.net.
   root-servers.net.     3600000 IN  NS      g.root-servers.net.
   root-servers.net.     3600000 IN  NS      h.root-servers.net.
   root-servers.net.     3600000 IN  NS      i.root-servers.net.
   root-servers.net.     3600000 IN  NS      j.root-servers.net.
   root-servers.net.     3600000 IN  NS      k.root-servers.net.
   root-servers.net.     3600000 IN  NS      l.root-servers.net.
   root-servers.net.     3600000 IN  NS      m.root-servers.net.
   a.root-servers.net.   3600000 IN  AAAA    2001:503:ba3e::2:30
   a.root-servers.net.   3600000 IN  A       198.41.0.4
   b.root-servers.net.   3600000 IN  MX      20 mail.isi.edu.
   b.root-servers.net.   3600000 IN  AAAA    2001:500:200::b
   b.root-servers.net.   3600000 IN  A       199.9.14.201
   c.root-servers.net.   3600000 IN  AAAA    2001:500:2::c
   c.root-servers.net.   3600000 IN  A       192.33.4.12
   d.root-servers.net.   3600000 IN  AAAA    2001:500:2d::d
   d.root-servers.net.   3600000 IN  A       199.7.91.13
   e.root-servers.net.   3600000 IN  AAAA    2001:500:a8::e
   e.root-servers.net.   3600000 IN  A       192.203.230.10
   f.root-servers.net.   3600000 IN  AAAA    2001:500:2f::f
   f.root-servers.net.   3600000 IN  A       192.5.5.241
   g.root-servers.net.   3600000 IN  AAAA    2001:500:12::d0d
   g.root-servers.net.   3600000 IN  A       192.112.36.4
   h.root-servers.net.   3600000 IN  AAAA    2001:500:1::53
   h.root-servers.net.   3600000 IN  A       198.97.190.53
   i.root-servers.net.   3600000 IN  MX      10 mx.i.root-servers.org.
   i.root-servers.net.   3600000 IN  AAAA    2001:7fe::53
   i.root-servers.net.   3600000 IN  A       192.36.148.17
   j.root-servers.net.   3600000 IN  AAAA    2001:503:c27::2:30
   j.root-servers.net.   3600000 IN  A       192.58.128.30
   k.root-servers.net.   3600000 IN  AAAA    2001:7fd::1
   k.root-servers.net.   3600000 IN  A       193.0.14.129
   l.root-servers.net.   3600000 IN  AAAA    2001:500:9f::42
   l.root-servers.net.   3600000 IN  A       199.7.83.42
   m.root-servers.net.   3600000 IN  AAAA    2001:dc3::35
   m.root-servers.net.   3600000 IN  A       202.12.27.33
   root-servers.net.     3600000 IN  SOA     a.root-servers.net. (
       nstld.verisign-grs.com. 2018091100 14400 7200 1209600 3600000 )
   root-servers.net.     3600000 IN  ZONEMD  2018091100 1 1 (
       f1ca0ccd91bd5573d9f431c00ee0101b2545c97602be0a97
       8a3b11dbfc1c776d5b3e86ae3d973d6b5349ba7f04340f79 )



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Authors' Addresses

   Duane Wessels
   Verisign
   12061 Bluemont Way
   Reston, VA  20190

   Phone: +1 703 948-3200
   Email: dwessels@verisign.com
   URI:   http://verisign.com


   Piet Barber
   Verisign
   12061 Bluemont Way
   Reston, VA  20190

   Phone: +1 703 948-3200
   Email: pbarber@verisign.com
   URI:   http://verisign.com


   Matt Weinberg
   Amazon

   Email: matweinb@amazon.com
   URI:   http://amazon.com


   Warren Kumari
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043

   Email: warren@kumari.net


   Wes Hardaker
   USC/ISI
   P.O. Box 382
   Davis, CA  95617

   Email: ietf@hardakers.net








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