Internet Engineering Task Force D. Wessels
Internet-Draft P. Barber
Intended status: Experimental M. Weinberg
Expires: March 8, 2020 Verisign
W. Kumari
W. Hardaker
September 5, 2019

Message Digest for DNS Zones


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

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 March 8, 2020.

Copyright Notice

Copyright (c) 2019 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 ( 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

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:

  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 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 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 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.

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

This specification utilizes ZONEMD RRs located at the zone apex. Non-apex ZONEMD RRs are not forbidden, but have no meaning in this specification.

A zone MAY contain multiple ZONEMD RRs to support algorithm agility [RFC7696] and rollovers. Each ZONEMD RR MUST specify a unique Digest Type. It is RECOMMENDED that a zone include only one ZONEMD RR, unless the zone publisher is in the process of transitioning to a new Digest Type.

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 standardized Digest Type defined for ZONEMD records. The Digest Type registry is further described in Section 6.

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

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. 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.

2.2. 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. 86400 IN ZONEMD 2018031500 1 0 (
    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.

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 records at the zone apex MUST first be deleted.

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.

If multiple digests are to be published in the zone, e.g., during an algorithm rollover, there MUST be one placeholder record for each Digest Type.

3.3. 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.

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:

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:

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 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 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 insecure, 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 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.

4.1. Verifying Multiple Digests

If multiple digests are present in the zone, e.g., during an algorithm rollover, a match using any one of the recipient's supported Digest Type algorithms is sufficient to verify the zone.

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 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.

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 63 has been allocated by IANA from the "Resource Record (RR) TYPEs" subregistry of the "Domain Name System (DNS) Parameters" registry:


Value: 63

Meaning: Message Digest Over Zone Data

Reference: This document

6.2. ZONEMD Digest Type

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

ZONEMD Digest Types
Value Description Status Reference
1 SHA384 Mandatory [RFC6605]
240-254 Private Use [RFC8126]

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).

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, Matt Pounsett, 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:

This implementation does not:

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:

This implementation does not:

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:

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From -04 to -05:

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

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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.
[RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997.
[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.
[RFC6605] Hoffman, P. and W. Wijngaards, "Elliptic Curve Digital Signature Algorithm (DSA) for DNSSEC", RFC 6605, DOI 10.17487/RFC6605, April 2012.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.

12.2. Informative References

[CZDS] Internet Corporation for Assigned Names and Numbers, "Centralized Zone Data Service", October 2018.
[dns-over-https] Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", Internet-Draft draft-ietf-doh-dns-over-https-12, June 2018.
[InterNIC] ICANN, "InterNIC FTP site", May 2018.
[ldns-zone-digest] Verisign, "Implementation of Message Digests for DNS Zones using the ldns library", July 2018.
[RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, DOI 10.17487/RFC1995, August 1996.
[RFC2065] Eastlake 3rd, D. and C. Kaufman, "Domain Name System Security Extensions", RFC 2065, DOI 10.17487/RFC2065, January 1997.
[RFC2136] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, DOI 10.17487/RFC2136, April 1997.
[RFC2535] Eastlake 3rd, D., "Domain Name System Security Extensions", RFC 2535, DOI 10.17487/RFC2535, March 1999.
[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.
[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September 2000.
[RFC3851] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions (S​/​MIME) Version 3.1 Message Specification", RFC 3851, DOI 10.17487/RFC3851, July 2004.
[RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D. and R. Thayer, "OpenPGP Message Format", RFC 4880, DOI 10.17487/RFC4880, November 2007.
[RFC5936] Lewis, E. and A. Hoenes, "DNS Zone Transfer Protocol (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm Agility and Selecting Mandatory-to-Implement Algorithms", BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015.
[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.
[RFC7719] Hoffman, P., Sullivan, A. and K. Fujiwara, "DNS Terminology", RFC 7719, DOI 10.17487/RFC7719, December 2015.
[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.
[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.
[RootServers] Root Server Operators, "Root Server Technical Operations", July 2018.
[RPZ] Vixie, P. and V. Schryver, "DNS Response Policy Zones (RPZ)", Internet-Draft draft-vixie-dnsop-dns-rpz-00, June 2018.
[ZoneDigestHackathon] Kerr, S., "Prototype implementation of ZONEMD for the IETF 102 hackathon in Python", July 2018.

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.

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 (
                                  5bef4f27e6a87b13 )
ns1           3600    IN  A
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.

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 (
                                  ad5c834f5a4bce16 )
ns1           3600    IN  A
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"
non-apex      900     IN  ZONEMD  2018031900 1 0 (
                                  2e20616c6c6f7765 )

A.3. EXAMPLE Zone with multiple digests

Here, the EXAMPLE zone contains multiple ZONEMD records. Since only one Digest Type is defined at this time (SHA384), this example utilizes additional ZONEMD records with Digest Type values in the private range (240-254). These additional private-range digests are not verifiable, but note that their other fields (Serial, Reserved, Digest Type) are included in the calculation of all ZONEMD digests.

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 0 (
                                  0457c87870bc8cdd )
example.      86400   IN  ZONEMD  2018031900 240 0 (
                                  96c5a8f44607bbee )
example.      86400   IN  ZONEMD  2018031900 241 0 (
                                  314adb6b4769bdd2 )
example.      86400   IN  ZONEMD  2018031900 242 0 (
                                  496b6395 )
example.      86400   IN  ZONEMD  2018031900 243 0 (
                                  3dfe0837 )
example.      86400   IN  ZONEMD  2018031900 244 0 (
                                  05fc283e )
ns1.example.  3600    IN  A
ns2.example.  86400   IN  TXT     "This example has multiple digests"
ns2.example.  3600    IN  AAAA    ::1

A.4. The URI.ARPA Zone

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

; <<>> DiG 9.9.4 <<>> axfr
; (2 servers found)
;; global options: +cmd         3600    IN      SOA ( 2018100702 10800 3600 1209600 3600 )         3600    IN      RRSIG   NSEC 8 2 3600 (
    20181028142623 20181007205525 47155 
    HAE9EDDzoNVfL1PyV/2fde9tDeUuAGVVwmD399NGq9jWYMRpyri2kysr q/g= )         86400   IN      RRSIG   NS 8 2 86400 (
    20181028172020 20181007175821 47155 
    Bsvs2b1qDZemBfkz/IfAhUTJKnto0vSUicJKfItu0GjyYNJCz2CqEuGD Wxc= )         600     IN      RRSIG   MX 8 2 600 (
    20181028170556 20181007175821 47155 
    A3mR95IpevuVIZvvJ+GcCAQpBo6KRODYvJ/c/ZG6sfYWkZ7qg/Em5/+3 4UI= )         3600    IN      RRSIG   DNSKEY 8 2 3600 (
    20181028152832 20181007175821 15796 
    5R0A1w== )         3600    IN      RRSIG   DNSKEY 8 2 3600 (
    20181028152832 20181007175821 55480 
    1HeBfw== )         3600    IN      RRSIG   SOA 8 2 3600 (
    20181029114753 20181008222815 47155 
    9BUQHy9SoV16wYm3kBTEPyxW5FFm8vcdnKAF7sxSY8BbaYNpRIEjDx4A JUc= )         3600    IN      NSEC NS SOA (
    MX RRSIG NSEC DNSKEY )         86400   IN      NS         86400   IN      NS         86400   IN      NS         86400   IN      NS         86400   IN      NS         600     IN      MX      10         3600    IN      DNSKEY  256 3 8 (
    SdJjlH0B )         3600    IN      DNSKEY  257 3 8 (
    l3wpbp+Wpm8= )         3600    IN      DNSKEY  257 3 8 (
    xmJVvNQlwdE= )     3600    IN      RRSIG   NSEC 8 3 3600 (
    20181028080856 20181007175821 47155 
    Arfh8N95jqh/q6vpaB9UtMkQ53tM2fYU1GszOLN0knxbHgDHAh2axMGH lqM= )     604800  IN      RRSIG   NAPTR 8 3 604800 (
    20181028103644 20181007205525 47155 
    YxlQJ0uHOvx1ZHFCj6lAt1ACUIw04ZhMydTmi27c8MzEOMepvn7iH7r7 k7k= )     3600    IN      NSEC NAPTR (
    RRSIG NSEC )     604800  IN      NAPTR   0 0 "" "" (
    "!^ftp://([^:/?#]*).*$!\\1!i" . )    3600    IN      RRSIG   NSEC 8 3 3600 (
    20181029010647 20181007175821 47155 
    ift9GrKBC7cgCd2msF/uzSrYxxg4MJQzBPvlkwXnY3b7eJSlIXisBIn7 3b8= )    604800  IN      RRSIG   NAPTR 8 3 604800 (
    20181029011815 20181007205525 47155 
    RsEjWq6+9jvlLKMXQv0xQuMX17338uoD/xiAFQSnDbiQKxwWMqVAimv5 7Zs= )    3600    IN      NSEC NAPTR (
    RRSIG NSEC )    604800  IN      NAPTR   0 0 "" "" (
    "!^http://([^:/?#]*).*$!\\1!i" . )  3600    IN      RRSIG   NSEC 8 3 3600 (
    20181028110727 20181007175821 47155 
    fQciMRD7R3+znZfm8d8u/snLV9w4D+lTBZrJJUBe1Efc8vum5vvV7819 ZoY= )  604800  IN      RRSIG   NAPTR 8 3 604800 (
    20181028141825 20181007205525 47155 
    916T4vx6i59scodjb0l6bDyZ+mtIPrc1w6b4hUyOUTsDQoAJYxdfEuMg Vy4= )  3600    IN      NSEC NAPTR (
    RRSIG NSEC )  604800  IN      NAPTR   0 0 "" "" (
    "!^mailto:(.*)@(.*)$!\\2!i" . )     3600    IN      RRSIG   NSEC 8 3 3600 (
    20181028123243 20181007175821 47155 
    DSl56gdeBwy1evn5wBTms8yWQVkNtphbJH395gRqZuaJs3LD/qTyJ5Dp LvA= )     604800  IN      RRSIG   NAPTR 8 3 604800 (
    20181029071816 20181007205525 47155 
    BiGtxvz5jNncM0xVbkjbtByrvJQAO1cU1mnlDKe1FmVB1uLpVdA9Ib4J hMU= )     3600    IN      NSEC NAPTR RRSIG (
    NSEC )     604800  IN      NAPTR   0 0 "" "" (
    "/urn:([^:]+)/\\1/i" . )         3600    IN      SOA ( 2018100702 10800 3600 1209600 3600 )
;; Query time: 66 msec
;; WHEN: Sun Oct 21 20:39:28 UTC 2018
;; XFR size: 34 records (messages 1, bytes 3941)       3600    IN      ZONEMD  2018100702 1 0 (
    c9974d03323e7cd39ccc5e70e797179633f4007bad )


The ROOT-SERVERS.NET zone retreived 2018-10-21.     3600000 IN  SOA ( 2018091100 14400 7200 1209600 3600000 )     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS     3600000 IN  NS   3600000 IN  AAAA    2001:503:ba3e::2:30   3600000 IN  A   3600000 IN  MX      20   3600000 IN  AAAA    2001:500:200::b   3600000 IN  A   3600000 IN  AAAA    2001:500:2::c   3600000 IN  A   3600000 IN  AAAA    2001:500:2d::d   3600000 IN  A   3600000 IN  AAAA    2001:500:a8::e   3600000 IN  A   3600000 IN  AAAA    2001:500:2f::f   3600000 IN  A   3600000 IN  AAAA    2001:500:12::d0d   3600000 IN  A   3600000 IN  AAAA    2001:500:1::53   3600000 IN  A   3600000 IN  MX      10   3600000 IN  AAAA    2001:7fe::53   3600000 IN  A   3600000 IN  AAAA    2001:503:c27::2:30   3600000 IN  A   3600000 IN  AAAA    2001:7fd::1   3600000 IN  A   3600000 IN  AAAA    2001:500:9f::42   3600000 IN  A   3600000 IN  AAAA    2001:dc3::35   3600000 IN  A     3600000 IN  SOA ( 2018091100 14400 7200 1209600 3600000 )     3600000 IN  ZONEMD  2018091100 1 0 (
    291f4132b8840da47ddab4401cc9088d04a14a )

Authors' Addresses

Duane Wessels Verisign 12061 Bluemont Way Reston, VA 20190 Phone: +1 703 948-3200 EMail: URI:
Piet Barber Verisign 12061 Bluemont Way Reston, VA 20190 Phone: +1 703 948-3200 EMail: URI:
Matt Weinberg Verisign 12061 Bluemont Way Reston, VA 20190 Phone: +1 703 948-3200 EMail: URI:
Warren Kumari Google 1600 Amphitheatre Parkway Mountain View, CA 94043 EMail:
Wes Hardaker USC/ISI P.O. Box 382 Davis, CA 95617 EMail: