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Internet Engineering Task Force                               D. Wessels
Internet-Draft                                                 P. Barber
Intended status: Standards Track                             M. Weinberg
Expires: January 3, 2019                                        Verisign
                                                               W. Kumari
                                                                  Google
                                                             W. Hardaker
                                                                 USC/ISI
                                                            July 2, 2018


                      Message Digest for DNS Zones
                    draft-wessels-dns-zone-digest-02

Abstract

   This document describes a protocol and DNS Resource Record used to
   provide a message digest over DNS zone data.  In particular, it
   describes how to compute, sign, represent, and use the message digest
   to verify the contents of a zone for accuracy and completeness.  The
   ZONEMD Resource Record type is introduced for conveying the message
   digest data.

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
   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 January 3, 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



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   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  . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Design Overview . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Requirements Language . . . . . . . . . . . . . . . . . .   6
   2.  The ZONEMD Resource Record  . . . . . . . . . . . . . . . . .   6
     2.1.  ZONEMD RDATA Wire Format  . . . . . . . . . . . . . . . .   6
       2.1.1.  The Serial Field  . . . . . . . . . . . . . . . . . .   6
       2.1.2.  The Digest Type Field . . . . . . . . . . . . . . . .   6
       2.1.3.  The Digest Field  . . . . . . . . . . . . . . . . . .   7
     2.2.  ZONEMD Presentation Format  . . . . . . . . . . . . . . .   7
     2.3.  ZONEMD Example  . . . . . . . . . . . . . . . . . . . . .   7
   3.  Calculating the Digest  . . . . . . . . . . . . . . . . . . .   8
     3.1.  Canonical Format and Ordering . . . . . . . . . . . . . .   8
       3.1.1.  Order of RRsets Having the Same Owner Name  . . . . .   8
       3.1.2.  Special Considerations for SOA RRs  . . . . . . . . .   8
     3.2.  Add ZONEMD Placeholder  . . . . . . . . . . . . . . . . .   8
     3.3.  Optionally Sign the Zone  . . . . . . . . . . . . . . . .   9
     3.4.  Calculate the Digest  . . . . . . . . . . . . . . . . . .   9
       3.4.1.  Inclusion/Exclusion Rules . . . . . . . . . . . . . .   9
     3.5.  Update ZONEMD RR  . . . . . . . . . . . . . . . . . . . .  10
   4.  Verifying Zone Message Digest . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  ZONEMD RRtype . . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  ZONEMD Digest Type  . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
     6.1.  Attacks Against the Zone Digest . . . . . . . . . . . . .  11
     6.2.  Attacks Utilizing the Zone Digest . . . . . . . . . . . .  12
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  12
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   9.  Implementation Status . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Authors' Implementation . . . . . . . . . . . . . . . . .  12
   10. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  13
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     11.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16






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1.  Introduction

   In the DNS, a zone is the collection of authoritative resource
   records (RRs) sharing a common origin ([RFC7719]), which can be
   distributed from primary to secondary name servers.  Zones are often
   stored as files on disk in the so-called master file format
   [RFC1034].  Sometimes zones are distributed outside of the DNS, with
   such protocols as FTP, HTTP, rsync, and so on.  Currently there is no
   standard way to verify the authenticity of a stand-alone zone file.

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

   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 file data.

1.1.  Motivation

   The motivation and design of this protocol enhancement is tied to the
   DNS root zone [InterNIC].  The root zone is perhaps 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.

   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



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   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.  It is entirely possible, for example, to
   perform zone transfers using DNS-over-TLS ([RFC7858]).  Furthermore,
   one can easily imagine the distribution of zone files over HTTPS-
   enabled web servers, as well as DNS-over-HTTPS [dns-over-https].

   Unfortunately, the protections provided by these channel security
   techniques are 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 been modified.
   For these reasons, it is preferable to secure the data itself.

   DNSSEC provides certain data security guarantees.  For zones that are
   signed, a recipient can validate all of the signed RRsets.
   Additionally, the 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.

   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 file signed with OpenPGP or S/MIME no
   longer looks like a zone file and could not directly be loaded into a




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   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 RRsets
   in a zone, hashing their signatures, 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 file.  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 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.  The authors believe that the incremental
   updates represent significant complexity which could be a barrier to
   implementation at this time (see DNS Camel).  Nothing in this
   specification prevents future work to support incremental zone digest
   algorithms (e.g. using Merkle trees and a different RR type).

   The cryptographic algorithms available for zone digest are exactly
   the same as for DS records.  This avoids the need for a separate
   digest algorithm registry.  Any updates to the DS algorithms
   automatically updates the algorithm status for zone digests.

   It is expected that verification of a zone digest will 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 would need a trust
   anchor for DNSSEC validation.  For signed non-root zones, the name
   server may need to send queries to validate a chain-of-trust.  Digest
   verification may also be performed externally.







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1.3.  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 three fields: Serial, Digest Type,
   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.

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  |                                               |
   +-+-+-+-+-+-+-+-+             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.

2.1.2.  The Digest Type Field

   The Digest Type field is an 8-bit unsigned integer, with meaning
   equivalent to the Digest Type of the DS resource record, as defined
   in section 5.1.3 of [RFC4034].




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   The status of ZONEMD digest types (e.g., mandatory, optional,
   deprecated) SHALL always match the status for DS records.  This
   information can be found in the IANA protocol registry for DS digest
   types [iana-ds-digest-types].

   At the time of this writing the following digest types are defined:

            +-------+-----------------+-----------+-----------+
            | Value | Description     | Status    | Reference |
            +-------+-----------------+-----------+-----------+
            | 1     | SHA1            | Mandatory | [RFC3658] |
            | 2     | SHA256          | Mandatory | [RFC4509] |
            | 3     | GOST R 34.11-94 | Optional  | [RFC5933] |
            | 4     | SHA384          | Optional  | [RFC6605] |
            +-------+-----------------+-----------+-----------+

                           Table 1: Digest Types

2.1.3.  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.

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 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 FEBE3D4CE2EC2FFA4BA9
                                               9D46CD69D6D29711E552
                                               17057BEE7EB1A7B641A4
                                               7BA7FED2DD5B97AE499F
                                               AFA4F22C6BD647DE )




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3.  Calculating the Digest

3.1.  Canonical Format and Ordering

   Calculation of the zone digest REQUIRES the RRs in a zone to be 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 by their numeric RR TYPE.

3.1.2.  Special Considerations for SOA RRs

   When AXFR is used to transfer zone data, the first and last records
   are always the SOA RR ([RFC5936] Section 2.2).  Because of this, zone
   files on disk often contain two SOA RRs.  When calculating the zone
   digest, the first SOA RR MUST be included and any subsequent SOA RRs
   MUST NOT be included.

   Additionally, per established practices, the SOA record is generally
   the first record in a zone file.  However, according to the
   requirement to sort RRsets with the same owner name by type, the SOA
   RR (type value 6) will not be first in the digest calculation.  The
   zone's NS RRset (type value 2) at the apex MUST be processed before
   the SOA RR.

3.2.  Add ZONEMD Placeholder

   In preparation for calculating the zone digest, any existing ZONEMD
   records MUST first be deleted from the zone.

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




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   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 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 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:

   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  More than one SOA 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.

   FOR DISCUSSION: Ambiguities about records that are in/out of zone.
   For example, see Jinmei message to dnsop 2018-06-01 and followups.
   BIND will load and axfr data "occluded" by DNAME/NS.






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

   5.  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.






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   6.  The zone digest is calculated using the algorithm described in
       Section 3.4.  Note in particular that digested ZONEMD RRs MUST be
       placeholders and their RRSIGs are not included in the digest.

   7.  The calculated digest is compared to the received digest.  If the
       two digest values match, verification is considered successful.
       Otherwise, verification MUST NOT be considered successful.

   8.  If the zone is to be served and transferred, the original (not
       placeholder) ZONEMD RRs MUST be sent to recipients so that
       downstream clients can verify the zone.

5.  IANA Considerations

5.1.  ZONEMD RRtype

   This document uses 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.

5.2.  ZONEMD Digest Type

   The ZONEMD Digest Type field has the same semantics as the DS RR
   Digest Type field.  Thus, it does not add new IANA protocol registry
   requirements.

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 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.




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6.2.  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).

   FOR DISCUSSION: The primary purpose of the ZONEMD record is to verify
   a zone file prior to being loaded or served by a name server.  We
   could allow a name server implementation to respond to ZONEMD queries
   with the REFUSED RCODE without loss of functionality.  Note that
   refusal would prevent ensuring that a zone-walk is complete.

7.  Privacy Considerations

   This specification has no impacts on user privacy.

8.  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 Mark Andrews, Olafur Gudmundsson, Shumon
   Huque, Tatuya Jinmei, Shane Kerr, Mukund Sivaraman, Petr Spacek, and
   other members of the dnsop working group for their input.

9.  Implementation Status

9.1.  Authors' Implementation

   The authors are currently working on an implementation in C, using
   the ldns library [ldns].  This implementation is able to perform the
   following functions:

   o  Read input zone file, output zone file with ZONEMD placeholder.

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

   o  Re-compute DNSSEC signature over ZONEMD record.

   o  Verify zone digest from input zone file.





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   The authors expect to be able to release this implementation as open
   source following submission of this Internet-Draft.

10.  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.

11.  References

11.1.  Normative References

   [iana-ds-digest-types]
              IANA, "Delegation Signer (DS) Resource Record (RR) Type
              Digest Algorithms", April 2012,
              <https://www.iana.org/assignments/ds-rr-types/
              ds-rr-types.xhtml>.

   [ldns]     NLNet Labs, "The ldns Library", March 2018,
              <https://www.nlnetlabs.nl/projects/ldns/>.

   [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>.






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   [RFC3658]  Gudmundsson, O., "Delegation Signer (DS) Resource Record
              (RR)", RFC 3658, DOI 10.17487/RFC3658, December 2003,
              <https://www.rfc-editor.org/info/rfc3658>.

   [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>.

   [RFC4509]  Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer
              (DS) Resource Records (RRs)", RFC 4509,
              DOI 10.17487/RFC4509, May 2006,
              <https://www.rfc-editor.org/info/rfc4509>.

   [RFC5933]  Dolmatov, V., Ed., Chuprina, A., and I. Ustinov, "Use of
              GOST Signature Algorithms in DNSKEY and RRSIG Resource
              Records for DNSSEC", RFC 5933, DOI 10.17487/RFC5933, July
              2010, <https://www.rfc-editor.org/info/rfc5933>.

   [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>.

   [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>.

11.2.  Informative References

   [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/>.

   [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>.




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   [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>.

   [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>.






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

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









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

   Email: ietf@hardakers.net













































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