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Internet Engineering Task Force                               D. Wessels
Internet-Draft                                                 P. Barber
Intended status: Experimental                                M. Weinberg
Expires: May 11, 2019                                           Verisign
                                                               W. Kumari
                                                                  Google
                                                             W. Hardaker
                                                                 USC/ISI
                                                        November 7, 2018


                      Message Digest for DNS Zones
                    draft-wessels-dns-zone-digest-05

Abstract

   This document describes an experimental protocol and new DNS Resource
   Record that can be used to provide a message digest over DNS zone
   data.  The ZONEMD Resource Record conveys the message 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
   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 includes
   fields reserved for future work 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 May 11, 2019.

Copyright Notice

   Copyright (c) 2018 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 . . . . . . . . . . . . . . . . . . . . .   5
     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.  ZONEMD RDATA Wire Format  . . . . . . . . . . . . . . . .   8
       2.1.1.  The Serial Field  . . . . . . . . . . . . . . . . . .   8
       2.1.2.  The Digest Type Field . . . . . . . . . . . . . . . .   8
       2.1.3.  The Reserved Field  . . . . . . . . . . . . . . . . .   8
       2.1.4.  The Digest Field  . . . . . . . . . . . . . . . . . .   8
     2.2.  ZONEMD Presentation Format  . . . . . . . . . . . . . . .   9
     2.3.  ZONEMD Example  . . . . . . . . . . . . . . . . . . . . .   9
   3.  Calculating the Digest  . . . . . . . . . . . . . . . . . . .   9
     3.1.  Canonical Format and Ordering . . . . . . . . . . . . . .   9
       3.1.1.  Order of RRSets Having the Same Owner Name  . . . . .   9
       3.1.2.  Duplicate RRs . . . . . . . . . . . . . . . . . . . .  10
     3.2.  Add ZONEMD Placeholder  . . . . . . . . . . . . . . . . .  10
     3.3.  Optionally Sign the Zone  . . . . . . . . . . . . . . . .  10
     3.4.  Calculate the Digest  . . . . . . . . . . . . . . . . . .  10
       3.4.1.  Inclusion/Exclusion Rules . . . . . . . . . . . . . .  11



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     3.5.  Update ZONEMD RR  . . . . . . . . . . . . . . . . . . . .  11
   4.  Verifying Zone Message Digest . . . . . . . . . . . . . . . .  11
   5.  Scope of Experimentation  . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  ZONEMD RRtype . . . . . . . . . . . . . . . . . . . . . .  13
     6.2.  ZONEMD Digest Type  . . . . . . . . . . . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
     7.1.  Attacks Against the Zone Digest . . . . . . . . . . . . .  14
     7.2.  Attacks Utilizing the Zone Digest . . . . . . . . . . . .  14
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  15
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   10. Implementation Status . . . . . . . . . . . . . . . . . . . .  15
     10.1.  Authors' Implementation  . . . . . . . . . . . . . . . .  15
     10.2.  Shane Kerr's Implementation  . . . . . . . . . . . . . .  15
   11. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  16
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     12.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Example Zones With Digests . . . . . . . . . . . . .  21
     A.1.  Simple EXAMPLE Zone . . . . . . . . . . . . . . . . . . .  21
     A.2.  Complex EXAMPLE Zone  . . . . . . . . . . . . . . . . . .  21
     A.3.  The URI.ARPA Zone . . . . . . . . . . . . . . . . . . . .  22
     A.4.  The ROOT-SERVERS.NET Zone . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   In the DNS, a zone is the collection of authoritative resource
   records (RRs) sharing a common origin ([RFC7719]).  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 message 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 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:



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   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
   [dns-over-https], 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
   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




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   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.  Thus, changes to delegation and glue
   records cannot be detected by DNSSEC alone.  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 [RFC3851].  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.

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




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   signing are similar (i.e., both require the same ordering of RRs) and
   can be done 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 does, however, reserve a field in the
   ZONEMD record for future work to support incremental zone digest
   algorithms (e.g. using Merkle trees).

   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 930 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-
   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.






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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 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 TBD.  The ZONEMD RR is class independent.  The RDATA of
   the resource record consists of four fields: Serial, Digest Type,
   Reserved, and Digest.

   FOR DISCUSSION: This document is currently written as though a zone
   MUST NOT contain more than one ZONEMD RR.  Having exactly one ZONEMD
   record per zone simplifies this protocol and eliminates confusion
   around downgrade attacks, at the expense of algorithm agility.





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2.1.  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                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Digest Type  |   Reserved    |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                             Digest                            |
   /                                                               /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.1.1.  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 message 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.

2.1.2.  The Digest Type Field

   The Digest Type field is an 8-bit unsigned integer that identifies
   the algorithm used to construct the digest.

   At the time of this writing, SHA384, with value 1, is the only Digest
   Type defined for ZONEMD records.  The Digest Type registry is further
   described in Section 6.

2.1.3.  The Reserved Field

   The Reserved field is an 8-bit unsigned integer, which is always set
   to zero.  This field is reserved for future work to support efficient
   incremental updates.

2.1.4.  The Digest Field

   The Digest field is a variable-length sequence of octets containing
   the message digest.  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.



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2.2.  ZONEMD Presentation Format

   The presentation format of the RDATA portion is as follows:

   The Serial field MUST be represented as an unsigned decimal integer.

   The Digest Type field MUST be represented as an unsigned decimal
   integer.

   The Reserved field MUST be represented as an unsigned decimal integer
   set to zero.

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

2.3.  ZONEMD Example

   The following example shows a ZONEMD RR.

   example.com. 86400 IN ZONEMD 2018031500 4 0 (
       FEBE3D4CE2EC2FFA4BA99D46CD69D6D29711E55217057BEE
       7EB1A7B641A47BA7FED2DD5B97AE499FAFA4F22C6BD647DE )

3.  Calculating the Digest

3.1.  Canonical Format and Ordering

   Calculation of the zone digest REQUIRES the RRs in a zone to be
   processed in a consistent format and ordering.  Correct ordering of
   the zone depends on (1) ordering of owner names in the zone, (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.

3.1.1.  Order of RRSets Having the Same Owner Name

   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.





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3.1.2.  Duplicate RRs

   As stated in Section 5 of [RFC2181], it is meaningless for a zone to
   have multiple RRs with equal owner name, class, type, and RDATA.  In
   the interest of consistency and interoperability, such duplicate RRs
   MUST NOT be included in the calculation of a zone digest.

3.2.  Add ZONEMD Placeholder

   In preparation for calculating the zone digest, any existing ZONEMD
   record at the zone apex MUST first be deleted.

   FOR DISCUSSION: Should non-apex ZONEMD records be allowed in a zone?
   Or forbidden?

   Prior to calculation of the digest, and prior to signing with DNSSEC,
   a placeholder ZONEMD record MUST be added to the zone apex.  This
   serves two purposes: (1) it allows the digest to cover the Serial,
   Digest Type, and Reserved field values, and (2) ensures that
   appropriate denial-of-existence (NSEC, NSEC3) records are created if
   the zone is signed with DNSSEC.

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

   In the placeholder record, the Serial field MUST be set to the
   current SOA Serial.  The Digest Type field MUST be set to the value
   for the chosen digest algorithm.  The Reserved field MUST be set to
   zero.  The Digest field MUST be set to all zeroes and of length
   appropriate for the chosen digest algorithm.

3.3.  Optionally Sign the Zone

   Following addition of the placeholder record, 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 that record 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.

3.4.  Calculate the Digest

   The zone digest is calculated by concatenating the canonical on-the-
   wire form (without name compression) of all RRs in the zone, in the
   order described above, subject to the inclusion/exclusion rules
   described below, and then applying the digest algorithm:





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

   where "|" denotes concatenation, and

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

3.4.1.  Inclusion/Exclusion Rules

   When calculating the digest, 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  Duplicate RRs with equal owner, class, type, and RDATA MUST NOT be
      included.

   o  The placeholder ZONEMD RR MUST be included.

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

   o  The RRSIG covering ZONEMD MUST NOT be included.

3.5.  Update ZONEMD RR

   Once the zone digest has been calculated, its value is then copied to
   the Digest field of the ZONEMD record.

   If the zone is signed with DNSSEC, the appropriate RRSIG records
   covering the ZONEMD record 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 implementations of incremental DNSSEC signing might update the
   zone's serial number for each resigning.  However, to preserve the
   calculated digest, generation of the ZONEMD signature at this time
   MUST NOT also result in a change of the SOA serial number.

4.  Verifying Zone Message Digest

   The recipient of a zone that has a message digest record can verify
   the zone by calculating the digest as follows:

   1.   The verifier SHOULD 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



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        validating) DS RRs in the parent zone.  For zones that are
        provably unsigned, digest validation continues at step 4 below.

   2.   For zones that are provably signed, 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 signed, the SOA RR and ZONEMD RR
        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 zone contains more than one apex ZONEMD RR, digest
        verification MUST NOT be considered successful.

   5.   The SOA Serial field MUST exactly match the ZONEMD Serial field.
        If the fields to not match, digest verification MUST NOT be
        considered successful.

   6.   The ZONEMD Digest Type field MUST be checked.  If the verifier
        does not support the given digest type, it SHOULD report that
        the zone digest could not be verified due to an unsupported
        algorithm.

   7.   The Reserved field MUST be checked.  If the Reserved field value
        is not zero, verification MUST NOT be considered successful.

   8.   The received Digest Type and Digest values are copied to a
        temporary location.

   9.   The ZONEMD RR's RDATA is reset to the placeholder values
        described in Section 3.2.

   10.  The zone digest is computed over the zone data as described in
        Section 3.4.

   11.  The calculated digest is compared to the received digest stored
        in the temporary location.  If the two digest values match,
        verification is considered successful.  Otherwise, verification
        MUST NOT be considered successful.

   12.  The ZONEMD RR's RDATA is reset to the received Digest Type and
        Digest stored in the temporary location.  Thus, any downstream
        clients can similarly verify the zone.





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5.  Scope of Experimentation

   This memo is published as an Experimental RFC.  The purpose of the
   experimental period is to provide the community time to analyze and
   evaluate to the methods defined in this document, particularly with
   regard to the wide variety of DNS zones in use on the Internet.

   Additionally, the ZONEMD record defined in this document includes a
   Reserved field in the form of an 8-bit integer.  The authors have a
   particular future use in mind for this field, namely to support
   efficient digests in large, dynamic zones.  We intend to conduct
   future experiments using Merkle trees of varying depth.  The choice
   of tree depth can be encoded in this reserved field.  We expect
   values for tree depth to range from 0 to 10, requiring at most four
   bits of this field.  This leaves another four bits available for
   other future uses, if absolutely necessary.

   FOR DISCUSSION: The authors are willing to remove the Reserved field
   from this specification if the working group would prefer it.  It
   would mean, however, that a future version of this protocol designed
   to efficiently support large, dynamic zones would most likely require
   a new RR type.

   The duration of the experiment is expected to be no less than two
   years from the publication of this document.  If the experiment is
   successful, it is expected that the findings of the experiment will
   result in an updated document for Standards Track approval.

6.  IANA Considerations

6.1.  ZONEMD RRtype

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

   Type: ZONEMD

   Value: TBD

   Meaning: Message Digest Over Zone Data

   Reference: This document








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6.2.  ZONEMD Digest Type

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

              +-------+-------------+-----------+-----------+
              | Value | Description | Status    | Reference |
              +-------+-------------+-----------+-----------+
              | 1     | SHA384      | Mandatory | [RFC6605] |
              +-------+-------------+-----------+-----------+

                       Table 1: ZONEMD Digest Types

7.  Security Considerations

7.1.  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 RECOMMENDS that the verifier determine whether
   or not to expect DNSSEC signatures for the zone in step 1.

   The attacker might perform a downgrade attack by removing the ZONEMD
   record.  This is why Section 4 REQUIRES that the verifier checks
   DNSSEC denial-of-existence proofs in step 2.

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

7.2.  Attacks Utilizing the Zone Digest

   Nothing in this specification prevents clients from making, and
   servers from responding to, ZONEMD queries.  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 currently defined digest types.  Certainly other query
   types result in larger amplification effects (i.e., DNSKEY).





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8.  Privacy Considerations

   This specification has no impacts 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, Olafur Gudmundsson,
   Paul Hoffman, Evan Hunt, Shumon Huque, Tatuya Jinmei, Burt Kaliski,
   Shane Kerr, Matt Larson, John Levine, Ed Lewis, Mukund Sivaraman,
   Petr Spacek, Ondrej Sury, Florian Weimer, Tim Wicinksi, 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.

   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.

   o  Support the Gost digest algorithm.

   o  Output the ZONEMD record in its defined presentation format.

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 a output zone with ZONEMD record.

   o  Verify the zone digest from an input zone.




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   o  Output the ZONEMD record in its defined presentation format.

   o  Generate Gost digests.

   This implementation does not:

   o  Re-compute DNSSEC signature over the ZONEMD record.

   o  Perform DNSSEC validation of the ZONEMD record.

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.



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   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.

   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.





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   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.

   o  IANA Considerations section now more specific.

   o  Added complex zone to examples.

   o

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>.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
              <https://www.rfc-editor.org/info/rfc2181>.

   [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>.

   [RFC6605]  Hoffman, P. and W. Wijngaards, "Elliptic Curve Digital
              Signature Algorithm (DSA) for DNSSEC", RFC 6605,
              DOI 10.17487/RFC6605, April 2012,
              <https://www.rfc-editor.org/info/rfc6605>.





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   [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/>.

   [dns-over-https]
              Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", draft-ietf-doh-dns-over-https-12 (work in
              progress), June 2018, <https://tools.ietf.org/html/
              draft-ietf-doh-dns-over-https-12>.

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

   [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>.





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   [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>.

   [RFC3851]  Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail
              Extensions (S/MIME) Version 3.1 Message Specification",
              RFC 3851, DOI 10.17487/RFC3851, July 2004,
              <https://www.rfc-editor.org/info/rfc3851>.

   [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>.

   [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>.

   [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>.

   [RFC7719]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", RFC 7719, DOI 10.17487/RFC7719, December
              2015, <https://www.rfc-editor.org/info/rfc7719>.

   [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>.

   [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>.






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Appendix A.  Example Zones With Digests

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

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 0 (
                                     f32765ce15c50477
                                     42a08be15d9a0efb
                                     749417eaadcfa28b
                                     1bf751b6bc49f9be
                                     a615c4a386cfd6a5
                                     d85e2d2182691249 )
   ns1           3600    IN  A       127.0.0.1
   ns2           3600    IN  AAAA    ::1

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 0 (
                                     686a6d74d5638612
                                     64ea4e6cc12c22d1
                                     7ebc529791d393bd
                                     e164a45390f714e9
                                     9ede0d05a5644573
                                     da4bbcc83744acf2 )
   ns1           3600    IN  A       127.0.0.1
   ns2           3600    IN  AAAA    ::1
   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"


A.3.  The URI.ARPA Zone

   The URI.ARPA zone retreived 2018-10-21.

   ; <<>> 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 (
       20181028152832 20181007175821 15796 uri.arpa.
       nzpbnh0OqsgBBP8St28pLvPEQ3wZAUdEBuUwil+rtjjWlYYiqjPxZ286
       XF4Rq1usfV5x71jZz5IqswOaQgia91ylodFpLuXD6FTGs2nXGhNKkg1V



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       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
       7wIsLxinXirprtQrbor+EtvlHp9qXE6ARTZDzf4jvsNpKvLFZtmxzFf3
       e/UJz5eHjpwDSiZL7xE8aE1o1nGfPtJx9ZnB3bapltaJ5wY+5XOCKgY0
       xmJVvNQlwdE= )



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       20181029071816 20181007205525 47155 uri.arpa.
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   ;; Query time: 66 msec
   ;; SERVER: 192.0.32.132#53(192.0.32.132)
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A.4.  The ROOT-SERVERS.NET Zone

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






























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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
   Verisign
   12061 Bluemont Way
   Reston, VA  20190

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





Wessels, et al.           Expires May 11, 2019                 [Page 27]


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