Subject: [DNSOP] Review of draft-wessels-dns-zone-digest-04.txt

From: Mukund Sivaraman <[email-masked]>
Date: Mon, 29 Oct 2018 21:25:24 +0530

After a reading, despite what is said in Section 5, I'd like to see such
a scheme to be generally useful for larger zones and zones with high
rates of updates. There are some kinds of zones in common use which can
benefit from better performance. So I recommend working on an
incremental scheme now than having multiple types of schemes later.

The simplest incremental scheme would be a XOR type checksum, but that
is hardly suitable for cryptographic security. With strong cryptographic
one-way hashes, designing an incremental scheme becomes more difficult.

Merkle trees can be naively adopted to the domain name space graph with
a specification of how to generate a hash of the data "in" a domain,
whose inputs contain hashes of all child domains and the RRs of the node
at the domain's name. Although incremental in a navive sense, this could
still not perform very well if there are many child nodes at a given
node (such as in a TLD zone, or in the case of some large RPZs).

A more finely granular hash tree, computed with the domain name space
represented as a binary tree (much like it is typically represented in
memory in some DNS implementations) could reduce the amount of data that
has to be hashed, however specifying and then implementing the canonical
form of such a tree to be hashed may become a lot of work. It may be
easy too (haven't given it more thought now).

Other ideas have been suggested, e.g., by Mark Andrews about using a
scheme similar to NSEC.

It is commendable that this draft has been written, and such a scheme
has been considered, as a zone message digest can be useful. I ask that
this draft not stop here with this basic under-performing approach.

----

Comments on the text of this draft (including nits) are below.

>    This document describes an experimental protocol and new DNS Resource
>    Record that can be used to provide an message digest over DNS zone

s/an/a/

>    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 is designed
>    to protect recursive name servers and their caches, ZONEMD protects

I wouldn't say this. DNNSEC authenticates RRsets (zone data at a fine
granularity). Protecting recursive name servers and caches may mean
several other things.

>    applications that consume zone files, whether they be authoritative
>    name servers, recursive name servers, or uses of zone file data.

I'd replace this sentence with "ZONEMD protects a zone's data as a whole
unit, whether they are consumed by authoritative name severs, 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.

> 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 between name servers

Fine nit.. I'd use "distributed among" or "transferred between".

>    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 file.

Perhaps this meant to say, "Currently there is no standard way to verify
the authenticity of a stand-alone zone." ?

This draft does not propose a standard way for zone *files*, many
non-canonical forms of which could represent the same data.

>    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

Again, it appears use of zone *file* is incorrect. It seems to appear
several times in this memo, and I'll not repeat this observation.

>    used in combination with DNSSEC.  This technique makes the message
>    digest a part of the zone file itself, allowing verification the zone
>    file as a whole, no matter how it is transmitted.  Furthermore, the
>    digest is based on the wire format of zone data.  Thus, it

s/it/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 file 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 file,
>    regardless of how it is transmitted.  A consumer of zone file 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.  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].

I think this is premature at this point. DNS over TLS is not specified
for zone transfers right now, is not in such prominent use.

>    Unfortunately, the protections provided by these channel security
>    techniques are ephemeral and are not retained after the data transfer
>    is complete.

Rather than ephemeral (they can be implemented to be non-ephemeral -
nothing in the protocol prevents saving of keys), their main
disadvantage compared to DNSSEC is that they don't facilitate end-to-end
producer-to-consumer trust validation/authentication of zone data, only
peer-to-peer trust.

>    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.

Nod, this is better.

>    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 zone files.

>    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
>    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 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 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 perhaps the most widely distributed DNS
>    zone on the Internet, served by 930 separate instances [RootServers]
>    at the time of this writing.

It can be argued, but I think popular RPZ zones have a lot more
distribution. More below.

>    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 zone files, 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.

RPZ seems like a good candidate for end-to-end authentication of data
without having to trust the peer a resolver got the data from, esp. for
open(unrestricted) policy zones. Some popular RPZ zones are very large,
and change very frequently (sooner than a minute). The current memo's
performance is inadequate to be used with such zones.

> 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 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  |   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.

Why is this field necessary? Can't the serial number be determined from
the SOA's field?

> 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] and values found in the IANA protocol
>    registry for DS digest types [iana-ds-digest-types].

>    The status of ZONEMD digest types (e.g., mandatory, optional,
>    deprecated), however, are independent of those for DS digest types.

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

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

I had mentioned this in my first reply to an early version of this draft.

May I implore that that you avoid other hash types and make SHA-384 as
mandatory? So many types are not needed. SHA-512(/384) is a faster hash
to calculate on many 64-bit platforms (what will be typically used by
this draft's target market) than SHA-256, and its hash construction and
size (compared to the rest of the zone) are not very different from
SHA-256 to require SHA-256 as well. Speed is good, especially in this
simplistic version of this scheme. If you want to include more hash
algorithms, pick a different hash construction such as SHA-3.

> 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.

Some explanation of how an 8-bit field is going to help will be useful
to those interested in implementing it. Why not a separate ZONEMD2 RR
type instead when that time comes?

> 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.

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

:)

>    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 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 by their numeric RR TYPE.

in ascending or descending order? (I don't blame you.. RFC 4034 also
makes no mention of that except "sorting the names").

> 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.

Is this fair to say.. the "often" part? In my experience, zone files in
RFC 1035 master format often don't contain two SOA RRs except if
transferred with a tool like dig without specifying +onesoa. E.g.,
named(BIND), when it is a slave and transfers a zone via AXFR to a
"masterfile-format text" zonefile obviously does not store the trailing
SOA in its in-memory representation or in the on-disk
respresentation. I'd assume this is the case with other nameserver
implementations too, that update an internal zone data structure and
serialize that to disk.

> 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
>    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,
>    Reserved, 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.

>    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 Digest field MUST be set to all
>    zeroes and of length appropriate for the chosen digest algorithm.

Should the reserved field not be set to zero here? Can it be set to 0
later?

> 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:

>    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.

Some more words about "glue" may be useful for this document. Often
there are zones, which have had updates, with occluded data due to
non-origin NS. These are loaded, served, and also saved as regular zones
by popular implementations. A generous definition of "glue"
traditionally includes all such records, and because such zones are
common, it would be good to clarify what "glue" is in this context.

>    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: How should the protocol handle occluded data?  A
>    DNAME/NS record can occlude existing data, technically making it out-
>    of-zone.  However, BIND (and others) will load and AXFR such occluded
>    data.

Sorry I missed seeing this earlier.

> 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
>        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(set)

Isn't >1 RR for ZONEMD prohibited by this draft? The distinction
"RR(set)" isn't clear vs. "SOA 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.

I didn't follow the purpose of this field in the ZONEMD RDATA. The only
context of its use seems to be for the comparison in this step, but the
reason is unclear.

>    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 zone digest is calculated using the algorithm described in
>        Section 3.4.  Note in particular that the digested ZONEMD RR MUST
>        be a placeholder and its RRSIGs MUST NOT be included in the
>        digest.

It would be better to rewrite this text as it appears to be a weak
description of what has to be done. State clearly (inspired by RFC 2845):

(1) The zone digest type and digest are copied to a temporary location.

(2) The ZONEMD RR's RDATA is reset to the placeholder values described
in section 3.2.

(3) The zone digest is computed over the zone as described in section
3.4.

>    8.  The calculated digest is compared to the received digest.

(4) 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.

(5) The ZONEMD RR's RDATA is reset to the received digest type and digest.

>    9.  If the zone is to be served and transferred, the original (not
>        placeholder) ZONEMD RR MUST be sent to recipients so that
>        downstream clients can 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 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.  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.

Sorry I'm seeing this after writing some comments earlier. This
experimental Merkle tree scheme needs to be described more thoroughly to
make sense of "depth" to be encoded in the reserved field.

>    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 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.

> 6.2.  ZONEMD Digest Type

>    The ZONEMD Digest Type field has the same values as the DS RR Digest
>    Type field, but with independent implementation status.  Therefore,
>    this document expects IANA will create a new "ZONEMD Digest Types"
>    registry.

> 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, 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 file and output a zone file with the ZONEMD
>       placeholder.

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

>    o  Re-compute DNSSEC signature over the ZONEMD record.

>    o  Verify the zone digest from an input zone file.

>    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 file and a output zone file with ZONEMD record.

>    o  Verify the zone digest from an input zone file.

>    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.

>    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.

> 12.  References

> 12.1.  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>.

>    [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>.

>    [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>.

> 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>.

>    [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>.

> Appendix A.  Example Zones With Digests

>    This appendex contains example zone files 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 for digest type 2 (SHA256).

>    example.        86400   IN      SOA     ns1 admin 2018031900 (
>                                            1800 900 604800 86400 )
>                    86400   IN      NS      ns1
>                    86400   IN      NS      ns2
>                    86400   IN      ZONEMD  2018031900 2 0 (
>                                            2d1dc6806312e79b
>                                            a86e64bad290e1c1
>                                            61f4ee8cb9d490e9
>                                            5a00d1e686b12826 )
>    ns1     3600    IN      A       127.0.0.1
>    ns2     3600    IN      AAAA    ::1

> A.2.  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
>        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= )
>    ftp.uri.arpa.     3600    IN      RRSIG   NSEC 8 3 3600 (
>        20181028080856 20181007175821 47155 uri.arpa.
>        HClGAqPxzkYkAT7Q/QNtQeB6YrkP6EPOef+9Qo5/2zngwAewXEAQiyF9
>        jD1USJiroM11QqBS3v3aIdW/LXORs4Ez3hLcKNO1cKHsOuWAqzmE+BPP
>        Arfh8N95jqh/q6vpaB9UtMkQ53tM2fYU1GszOLN0knxbHgDHAh2axMGH lqM= )
>    ftp.uri.arpa.     604800  IN      RRSIG   NAPTR 8 3 604800 (
>        20181028103644 20181007205525 47155 uri.arpa.
>        WoLi+vZzkxaoLr2IGZnwkRvcDf6KxiWQd1WZP/U+AWnV+7MiqsWPZaf0

>        9toRErerGoFOiOASNxZjBGJrRgjmavOM9U+LZSconP9zrNFd4dIu6kp5
>        YxlQJ0uHOvx1ZHFCj6lAt1ACUIw04ZhMydTmi27c8MzEOMepvn7iH7r7 k7k= )
>    ftp.uri.arpa.     3600    IN      NSEC    http.uri.arpa. NAPTR (
>        RRSIG NSEC )
>    ftp.uri.arpa.     604800  IN      NAPTR   0 0 "" "" (
>        "!^ftp://([^:/?#]*).*$!\\1!i" . )
>    http.uri.arpa.    3600    IN      RRSIG   NSEC 8 3 3600 (
>        20181029010647 20181007175821 47155 uri.arpa.
>        U03NntQ73LHWpfLmUK8nMsqkwVsOGW2KdsyuHYAjqQSZvKbtmbv7HBmE
>        H1+Ii3Z+wtfdMZBy5aC/6sHdx69BfZJs16xumycMlAy6325DKTQbIMN+
>        ift9GrKBC7cgCd2msF/uzSrYxxg4MJQzBPvlkwXnY3b7eJSlIXisBIn7 3b8= )
>    http.uri.arpa.    604800  IN      RRSIG   NAPTR 8 3 604800 (
>        20181029011815 20181007205525 47155 uri.arpa.
>        T7mRrdag+WSmG+n22mtBSQ/0Y3v+rdDnfQV90LN5Fq32N5K2iYFajF7F
>        Tp56oOznytfcL4fHrqOE0wRc9NWOCCUec9C7Wa1gJQcllEvgoAM+L6f0
>        RsEjWq6+9jvlLKMXQv0xQuMX17338uoD/xiAFQSnDbiQKxwWMqVAimv5 7Zs= )
>    http.uri.arpa.    3600    IN      NSEC    mailto.uri.arpa. NAPTR (
>        RRSIG NSEC )
>    http.uri.arpa.    604800  IN      NAPTR   0 0 "" "" (
>        "!^http://([^:/?#]*).*$!\\1!i" . )
>    mailto.uri.arpa.  3600    IN      RRSIG   NSEC 8 3 3600 (
>        20181028110727 20181007175821 47155 uri.arpa.
>        GvxzVL85rEukwGqtuLxek9ipwjBMfTOFIEyJ7afC8HxVMs6mfFa/nEM/
>        IdFvvFg+lcYoJSQYuSAVYFl3xPbgrxVSLK125QutCFMdC/YjuZEnq5cl
>        fQciMRD7R3+znZfm8d8u/snLV9w4D+lTBZrJJUBe1Efc8vum5vvV7819 ZoY= )
>    mailto.uri.arpa.  604800  IN      RRSIG   NAPTR 8 3 604800 (
>        20181028141825 20181007205525 47155 uri.arpa.
>        MaADUgc3fc5v++M0YmqjGk3jBdfIA5RuP62hUSlPsFZO4k37erjIGCfF
>        j+g84yc+QgbSde0PQHszl9fE/+SU5ZXiS9YdcbzSZxp2erFpZOTchrpg
>        916T4vx6i59scodjb0l6bDyZ+mtIPrc1w6b4hUyOUTsDQoAJYxdfEuMg Vy4= )
>    mailto.uri.arpa.  3600    IN      NSEC    urn.uri.arpa. NAPTR (
>        RRSIG NSEC )
>    mailto.uri.arpa.  604800  IN      NAPTR   0 0 "" "" (
>        "!^mailto:(.*)@(.*)$!\\2!i" . )
>    urn.uri.arpa.     3600    IN      RRSIG   NSEC 8 3 3600 (
>        20181028123243 20181007175821 47155 uri.arpa.
>        Hgsw4Deops1O8uWyELGe6hpR/OEqCnTHvahlwiQkHhO5CSEQrbhmFAWe
>        UOkmGAdTEYrSz+skLRQuITRMwzyFf4oUkZihGyhZyzHbcxWfuDc/Pd/9
>        DSl56gdeBwy1evn5wBTms8yWQVkNtphbJH395gRqZuaJs3LD/qTyJ5Dp LvA= )
>    urn.uri.arpa.     604800  IN      RRSIG   NAPTR 8 3 604800 (
>        20181029071816 20181007205525 47155 uri.arpa.
>        ALIZD0vBqAQQt40GQ0Efaj8OCyE9xSRJRdyvyn/H/wZVXFRFKrQYrLAS
>        D/K7q6CMTOxTRCu2J8yes63WJiaJEdnh+dscXzZkmOg4n5PsgZbkvUSW
>        BiGtxvz5jNncM0xVbkjbtByrvJQAO1cU1mnlDKe1FmVB1uLpVdA9Ib4J hMU= )
>    urn.uri.arpa.     3600    IN      NSEC    uri.arpa. NAPTR RRSIG (
>        NSEC )
>    urn.uri.arpa.     604800  IN      NAPTR   0 0 "" "" (
>        "/urn:([^:]+)/\\1/i" . )

>    uri.arpa.         3600    IN      SOA     sns.dns.icann.org. (
>        noc.dns.icann.org. 2018100702 10800 3600 1209600 3600 )
>    ;; Query time: 66 msec
>    ;; SERVER: 192.0.32.132#53(192.0.32.132)
>    ;; WHEN: Sun Oct 21 20:39:28 UTC 2018
>    ;; XFR size: 34 records (messages 1, bytes 3941)
>    uri.arpa.       3600    IN      ZONEMD  2018100702 2 0 (
>        a921ef5658f31bc6ac3e72a000f8d60a1a933153cf1df8be8153925
>        60c665b14 )

> A.3.  The ROOT-SERVERS.NET Zone with SHA384

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

> Wessels, et al.          Expires April 25, 2019                [Page 24]
> 
> Internet-Draft               DNS Zone Digest                October 2018

>    root-servers.net.     3600000 IN  SOA     a.root-servers.net. (
>        nstld.verisign-grs.com. 2018091100 14400 7200 1209600 3600000 )
>    root-servers.net.     3600000 IN  NS      a.root-servers.net.
>    root-servers.net.     3600000 IN  NS      b.root-servers.net.
>    root-servers.net.     3600000 IN  NS      c.root-servers.net.
>    root-servers.net.     3600000 IN  NS      d.root-servers.net.
>    root-servers.net.     3600000 IN  NS      e.root-servers.net.
>    root-servers.net.     3600000 IN  NS      f.root-servers.net.
>    root-servers.net.     3600000 IN  NS      g.root-servers.net.
>    root-servers.net.     3600000 IN  NS      h.root-servers.net.
>    root-servers.net.     3600000 IN  NS      i.root-servers.net.
>    root-servers.net.     3600000 IN  NS      j.root-servers.net.
>    root-servers.net.     3600000 IN  NS      k.root-servers.net.
>    root-servers.net.     3600000 IN  NS      l.root-servers.net.
>    root-servers.net.     3600000 IN  NS      m.root-servers.net.
>    a.root-servers.net.   3600000 IN  AAAA    2001:503:ba3e::2:30
>    a.root-servers.net.   3600000 IN  A       198.41.0.4
>    b.root-servers.net.   3600000 IN  MX      20 mail.isi.edu.
>    b.root-servers.net.   3600000 IN  AAAA    2001:500:200::b
>    b.root-servers.net.   3600000 IN  A       199.9.14.201
>    c.root-servers.net.   3600000 IN  AAAA    2001:500:2::c
>    c.root-servers.net.   3600000 IN  A       192.33.4.12
>    d.root-servers.net.   3600000 IN  AAAA    2001:500:2d::d
>    d.root-servers.net.   3600000 IN  A       199.7.91.13
>    e.root-servers.net.   3600000 IN  AAAA    2001:500:a8::e
>    e.root-servers.net.   3600000 IN  A       192.203.230.10
>    f.root-servers.net.   3600000 IN  AAAA    2001:500:2f::f
>    f.root-servers.net.   3600000 IN  A       192.5.5.241
>    g.root-servers.net.   3600000 IN  AAAA    2001:500:12::d0d
>    g.root-servers.net.   3600000 IN  A       192.112.36.4
>    h.root-servers.net.   3600000 IN  AAAA    2001:500:1::53
>    h.root-servers.net.   3600000 IN  A       198.97.190.53
>    i.root-servers.net.   3600000 IN  MX      10 mx.i.root-servers.org.
>    i.root-servers.net.   3600000 IN  AAAA    2001:7fe::53
>    i.root-servers.net.   3600000 IN  A       192.36.148.17
>    j.root-servers.net.   3600000 IN  AAAA    2001:503:c27::2:30
>    j.root-servers.net.   3600000 IN  A       192.58.128.30
>    k.root-servers.net.   3600000 IN  AAAA    2001:7fd::1
>    k.root-servers.net.   3600000 IN  A       193.0.14.129
>    l.root-servers.net.   3600000 IN  AAAA    2001:500:9f::42
>    l.root-servers.net.   3600000 IN  A       199.7.83.42
>    m.root-servers.net.   3600000 IN  AAAA    2001:dc3::35
>    m.root-servers.net.   3600000 IN  A       202.12.27.33
>    root-servers.net.     3600000 IN  SOA     a.root-servers.net. (
>        nstld.verisign-grs.com. 2018091100 14400 7200 1209600 3600000 )
>    root-servers.net.     3600000 IN  ZONEMD  2018091100 4 0 (
>        327b45e1f70a95eb83e1b9aaaa0642b9e1d0f007db5ce45858cd336a79
>        78a0239f4517edfd11445f2b9f70900816fdfd )

> Wessels, et al.          Expires April 25, 2019                [Page 25]
> 
> Internet-Draft               DNS Zone Digest                October 2018

> Authors' Addresses

>    Duane Wessels
>    Verisign
>    12061 Bluemont Way
>    Reston, VA  20190

>    Phone: +1 703 948-3200
>    Email: [email-masked]
>    URI:   http://verisign.com

>    Piet Barber
>    Verisign
>    12061 Bluemont Way
>    Reston, VA  20190

>    Phone: +1 703 948-3200
>    Email: [email-masked]
>    URI:   http://verisign.com

>    Matt Weinberg
>    Verisign
>    12061 Bluemont Way
>    Reston, VA  20190

>    Phone: +1 703 948-3200
>    Email: [email-masked]
>    URI:   http://verisign.com

>    Warren Kumari
>    Google
>    1600 Amphitheatre Parkway
>    Mountain View, CA  94043

>    Email: [email-masked]

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

>    Email: [email-masked]

		Mukund

---

From: "Wessels, Duane" <[email-masked]>
Date: Mon, 29 Oct 2018 22:26:42 +0000

Mukund,

Thanks for the comments. I have incorporated most of them.  I will follow up below on items I did not incorporate.

> On Oct 29, 2018, at 8:55 AM, Mukund Sivaraman <[email-masked]> wrote:
> 

The feedback I have received regarding this point has been mixed.  I have
some folks saying "make it work with stable zones now, figure out dynamic
zones later" and others saying "have to support incremental updates now."

The proposal to have a reserved-for-future use field is an attempt to find
compromise.  I personally think incremental updates can be efficiently
supported with a variable-depth Merkle tree.  But I have concerns about
the complexity / benefit tradeoff.  I presented on this at the last DNS-OARC
meeting (not sure if you had a chance to see it).

This is why the authors propose proceeding with the Reserved field at this time.
If it later turns out we can agree on a way to support incremental updates by
using this 8-bit field, then that would be great.  If not, we can, as you say,
consume another RR type and the wasted 8-bits stays Reserved indefinitely.

> several times in this memo, and I'll not repeat this observation.

My apologies.  I've fixed it for the next revision.

> distribution. More below.

[citation needed]? 

> performance is inadequate to be used with such zones.

Out of curiosity, are these large RPZ zones signed?  

I ask because some people say ZONEMD is worthless without DNSSEC and, as far as I know,
policy zones don't necessarily need to align with the name space.

> Why is this field necessary? Can't the serial number be determined from

This was a point of discussion in earlier revisions:

   FOR DISCUSSION: the serial number is included 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 zone file.  If there is agreement that ZONEMD responses
   are not useful, this field could be removed.  See also the end of
   Security Considerations.

Based on feedback from that revision, seems like there was consensus to
keep the Serial field and allow ZONEMD queries/responses.

> algorithms, pick a different hash construction such as SHA-3.

I was thinking it would be useful to have ZONEMD digest types track DS digest
types, so that it wouldn't require a new RFC to define a new ZONEMD digest type.
But I'm not sensing much support for this approach.

As an implementor, you would be okay with, say SHA384 having value 4 when used
in as a DS digest type, but value 1 when used as a ZONEMD digest type?

> makes no mention of that except "sorting the names").

Does "... RRsets having the same owner name MUST be processed in numerically
ascending order by their numeric RR TYPE" work for you?

> Is this fair to say.. the "often" part? 

How about "sometimes" instead of often?

> "RR(set)" isn't clear vs. "SOA RR".

Yes.  There was a time when the draft was less clear about single/multiple
ZONEMD records and I missed this one when cleaning it up.

> make sense of "depth" to be encoded in the reserved field.

Assuming the document were to move forward with this reserved-for-future-use field,
I'm not sure what would be the appropriate level of detail to put here.  I'd rather not
get too caught up in those details yet.

DW

---

From: Paul Wouters <[email-masked]>
Date: Mon, 29 Oct 2018 22:42:48 -0400 (EDT)

> consume another RR type and the wasted 8-bits stays Reserved indefinitely.

This seems fine, although rather than yet another document, I think it
would be better to handle it right the first time in this document.

> keep the Serial field and allow ZONEMD queries/responses.

Makes sense to me.

> But I'm not sensing much support for this approach.

I think I lean towards not doing this, just so that when a new DS digest
type is introduced, people don't have to update the zonemd code (or
forget to do this, and thus limiting the real zonemd digest that can be
used in practise)

> in as a DS digest type, but value 1 when used as a ZONEMD digest type?

As a non-DNS implementor, I see no problem with this.

Paul

---

From: Mukund Sivaraman <[email-masked]>
Date: Tue, 30 Oct 2018 09:20:14 +0530

Hi Duane

> consume another RR type and the wasted 8-bits stays Reserved indefinitely.

I'll look for the OARC presentation. While this initial scheme is
simple, its usefulness (for zone instances where such a scheme is
desired) to me appears limited outside the root. This is why it seems
better to have a more complicated scheme that scales well.

> > distribution. More below.

I replied in response to the 930 separate instances mentioned and the
(small) set of servers that run root on loopback, or hijack root
traffic, etc.

Some RPZ zones from proprietary DNS implementation vendors appear to me
in wider use, but I have nothing to cite for it here.

I'd just remove the "most" word, and say "The root zone is a widely
distributed DNS zone..."

> I ask because some people say ZONEMD is worthless without DNSSEC and,
> as far as I know, policy zones don't necessarily need to align with
> the name space.

They are not signed, and you're right that they do not belong in the
DNS, and aren't meant to be QUERY'd. However, they _can_ be signed, and
verified with a local trust anchor. The point I intended to make was
that RPZ can benefit from a message digest where the "master" side
nameserver serving the feed may not be necessarily trusted, but it can
be established that the RPZ feed is authentic. It has importantance for
this application as the contents of the RPZ zones obtained from outside
are used to filter replies.

> keep the Serial field and allow ZONEMD queries/responses.

That is a good reason. Please do retain the description in the
draft. Often when reading RFCs, I see a specification of *what* needs to
be done, but not *why* and the purpose that a field/behavior solves is
mysterious.  Sometimes, not knowing the purpose can cause mistakes in
implementation (though not in this case).

> But I'm not sensing much support for this approach.
The two are not related, and it's best not to somehow co-relate
them. The choice of function have different requirements which determine
picking a hash function. For example, apart from the fact that crypto
hash functions are needed:

* It would be desired to have short hashes for DS as several of them may
  be returned in a delegation response, and delegation responses are a
  common answer in the public DNS. Though having a well-performing hash
  function would be nice, it is not an important requirement as only the
  DNSKEY's key is hashed by it.

* It would be desired to primarily have fast performing hash functions
  for ZONEMD as it hashes all the data in the zone. Though having a
  short hash is desirable, it is not a big deal even if the hash bloated
  up the DNS reply message to the entire 64kB.

> in as a DS digest type, but value 1 when used as a ZONEMD digest type?

Implementations already deal with hash function identifiers for
different use cases, and it is not a big burden to implement one more,
considering the rest of the ZONEMD implementation.

I feel relating the DS and ZONEMD tables is wrong. You can pick the same
hash function identifier values for now if you choose, but it would be
hard to keep the values in sync, with the separate new registry in 6.2.

> ascending order by their numeric RR TYPE" work for you?

That works, or very simply add:

"MUST be numerically ordered" + " in ascending order" + " by their numeric RR TYPE."

> How about "sometimes" instead of often?

Sounds good. I typed a lot of text.. much ado over nothing. :)

> get too caught up in those details yet.

Sorry, I messed up conveying what - the clarification asked was just to
follow why this is an 8-bit Reserved field and not a 16-bit or 32-bit
Reserved field - some justification for what ranges of values are going
to be stored in it.

		Mukund