Message Digest for DNS Zones
draft-wessels-dns-zone-digest-03
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Duane Wessels , Piet Barber , Matt Weinberg , Warren "Ace" Kumari , Wes Hardaker | ||
| Last updated | 2018-10-09 (Latest revision 2018-07-02) | ||
| Replaced by | draft-ietf-dnsop-dns-zone-digest, RFC 8976 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Candidate for WG Adoption | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-wessels-dns-zone-digest-03
Internet Engineering Task Force D. Wessels
Internet-Draft P. Barber
Intended status: Experimental M. Weinberg
Expires: April 12, 2019 Verisign
W. Kumari
Google
W. Hardaker
USC/ISI
October 9, 2018
Message Digest for DNS Zones
draft-wessels-dns-zone-digest-03
Abstract
This document describes an experimental protocol and new DNS Resource
Record that can be used to provide an 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 is designed
to protect recursive name servers and their caches, ZONEMD protects
applications that consume zone files, whether they be authoritative
name servers, recursive name servers, or uses of zone file data.
As specified at this time, ZONEMD is not designed for use in large,
dynamic zones due to the time and resources required for digest
calculation. The ZONEMD record described in this document includes
fields reserved for future work to support large, dynamic zones.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 12, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Design Overview . . . . . . . . . . . . . . . . . . . . . 5
1.3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.1. Root Zone . . . . . . . . . . . . . . . . . . . . . . 6
1.3.2. Providers, Secondaries, and Anycast . . . . . . . . . 6
1.3.3. Response Policy Zones . . . . . . . . . . . . . . . . 6
1.3.4. Centralized Zone Data Service . . . . . . . . . . . . 7
1.3.5. General Purpose Comparison Check . . . . . . . . . . 7
1.4. Requirements Language . . . . . . . . . . . . . . . . . . 7
2. The ZONEMD Resource Record . . . . . . . . . . . . . . . . . 7
2.1. ZONEMD RDATA Wire Format . . . . . . . . . . . . . . . . 7
2.1.1. The Serial Field . . . . . . . . . . . . . . . . . . 8
2.1.2. The Digest Type Field . . . . . . . . . . . . . . . . 8
2.1.3. The Reserved Field . . . . . . . . . . . . . . . . . 8
2.1.4. The Digest Field . . . . . . . . . . . . . . . . . . 9
2.2. ZONEMD Presentation Format . . . . . . . . . . . . . . . 9
2.3. ZONEMD Example . . . . . . . . . . . . . . . . . . . . . 9
3. Calculating the Digest . . . . . . . . . . . . . . . . . . . 9
3.1. Canonical Format and Ordering . . . . . . . . . . . . . . 9
3.1.1. Order of RRsets Having the Same Owner Name . . . . . 10
3.1.2. Special Considerations for SOA RRs . . . . . . . . . 10
3.2. Add ZONEMD Placeholder . . . . . . . . . . . . . . . . . 10
3.3. Optionally Sign the Zone . . . . . . . . . . . . . . . . 10
3.4. Calculate the Digest . . . . . . . . . . . . . . . . . . 11
3.4.1. Inclusion/Exclusion Rules . . . . . . . . . . . . . . 11
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3.5. Update ZONEMD RR . . . . . . . . . . . . . . . . . . . . 11
4. Verifying Zone Message Digest . . . . . . . . . . . . . . . . 12
5. Scope of Experimentation . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
6.1. ZONEMD RRtype . . . . . . . . . . . . . . . . . . . . . . 13
6.2. ZONEMD Digest Type . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7.1. Attacks Against the Zone Digest . . . . . . . . . . . . . 13
7.2. Attacks Utilizing the Zone Digest . . . . . . . . . . . . 14
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
10. Implementation Status . . . . . . . . . . . . . . . . . . . . 14
10.1. Authors' Implementation . . . . . . . . . . . . . . . . 14
10.2. Shane Kerr's Implementation . . . . . . . . . . . . . . 15
11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 15
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . 17
12.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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
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.
This document introduces a new RR type that serves as a cryptographic
message digest of the data in a zone file. It allows a receiver of
the zone file to verify the zone file's authenticity, especially when
used in combination with DNSSEC. This technique makes the message
digest a part of the zone file itself, allowing 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
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
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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].
Unfortunately, the protections provided by these channel security
techniques are ephemeral and are not retained after the data transfer
is complete. They can ensure that the client receives the data from
the expected server, and that the data sent by the server is not
modified during transmission. However, they do not guarantee that
the server transmits the data as originally published, and do not
provide any methods to verify data that is read after transmission is
complete. For example, a name server loading saved zone data upon
restart cannot guarantee that the on-disk data has not been modified.
For these reasons, it is preferable to secure the data itself.
Why not simply rely on DNSSEC, which provides certain data security
guarantees? Certainly for zones that are signed, a recipient could
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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
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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. 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
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can certainly be signed with DNSSEC, the data is not queried
directly, and would not be subject to DNSSEC validation.
1.3.4. Centralized Zone Data Service
ICANN operates the Centralized Zone Data Service [CZDS], which is a
repository of top-level domain zone files. Users request access to
the system, and to individual zones, and are then able to download
zone data for certain uses. Adding a zone digest to these would
provide CZDS users with assurances that the data has not been
modified. Note that ZONEMD could be added to CZDS zone data
independently of the zone served by production name servers.
1.3.5. General Purpose Comparison Check
Since the zone digest does not depend on presentation format, it
could be used to compare multiple copies of a zone received from
different sources, or copies generated by different processes.
1.4. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. The ZONEMD Resource Record
This section describes the ZONEMD Resource Record, including its
fields, wire format, and presentation format. The Type value for the
ZONEMD RR is TBD. The ZONEMD RR is class independent. The RDATA of
the resource record consists of 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:
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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.
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] |
+-------+-----------------+------------+-----------+
Table 1: ZONEMD Digest Types
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.
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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 FEBE3D4CE2EC2FFA4BA9
9D46CD69D6D29711E552
17057BEE7EB1A7B641A4
7BA7FED2DD5B97AE499F
AFA4F22C6BD647DE )
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
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define a canonical ordering for RRsets having the same owner name,
that ordering is defined here.
3.1.1. Order of RRsets Having the Same Owner Name
For the purposes of calculating the zone digest, RRsets having the
same owner name MUST be numerically ordered by their numeric RR TYPE.
3.1.2. Special Considerations for SOA RRs
When AXFR is used to transfer zone data, the first and last records
are always the SOA RR ([RFC5936] Section 2.2). Because of this, zone
files on disk often contain two SOA RRs. When calculating the zone
digest, the first SOA RR MUST be included and any subsequent SOA RRs
MUST NOT be included.
Additionally, per established practices, the SOA record is generally
the first record in a zone file. However, according to the
requirement to sort RRsets with the same owner name by type, the SOA
RR (type value 6) will not be first in the digest calculation. The
zone's NS RRset (type value 2) at the apex MUST be processed before
the SOA RR.
3.2. Add ZONEMD Placeholder
In preparation for calculating the zone digest, any existing ZONEMD
record MUST first be deleted from the zone.
Prior to calculation of the digest, and prior to signing with DNSSEC,
a placeholder ZONEMD record MUST be added to the zone. This serves
two purposes: (1) it allows the digest to cover the Serial, 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.
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
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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.
o More than one SOA MUST NOT be included.
o The placeholder ZONEMD RR MUST be included.
o If the zone is signed, DNSSEC RRs MUST be included, except:
o The RRSIG covering ZONEMD MUST NOT be included.
FOR DISCUSSION: Ambiguities about records that are in/out of zone.
For example, see Jinmei message to dnsop 2018-06-01 and followups.
BIND will load and AXFR data "occluded" by DNAME/NS.
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.
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Some implementations of incremental DNSSEC signing might update the
zone's serial number for each resigning. However, to preserve the
calculated digest, generation of the ZONEMD signature at this time
MUST NOT also result in a change of the SOA serial number.
4. Verifying Zone Message Digest
The recipient of a zone that has a message digest record can verify
the zone by calculating the digest as follows:
1. The verifier SHOULD first determine whether or not to expect
DNSSEC records in the zone. This can be done by examining
locally configured trust anchors, or querying for (and
validating) DS RRs in the parent zone. For zones that are
provably unsigned, digest validation continues at step 4 below.
2. For zones that are provably signed, the existence of the ZONEMD
record MUST be verified. If the ZONEMD record provably does not
exist, digest verification cannot be done. If the ZONEMD record
does provably exist, but is not found in the zone, digest
verification MUST NOT be considered successful.
3. For zones that are provably signed, the SOA RR and ZONEMD RR(set)
MUST have valid signatures, chaining up to a trust anchor. If
DNSSEC validation of the SOA or ZONEMD records fails, digest
verification MUST NOT be considered successful.
4. If the zone contains more than one 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 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.
8. The calculated digest is compared to the received digest. If the
two digest values match, verification is considered successful.
Otherwise, verification MUST NOT be considered successful.
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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.
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.
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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.
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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.
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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.
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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>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References
[CZDS] Internet Corporation for Assigned Names and Numbers,
"Centralized Zone Data Service", October 2018,
<https://czds.icann.org/>.
[dns-over-https]
Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", draft-ietf-doh-dns-over-https-12 (work in
progress), June 2018, <https://tools.ietf.org/html/
draft-ietf-doh-dns-over-https-12>.
[InterNIC]
ICANN, "InterNIC FTP site", May 2018,
<ftp://ftp.internic.net/domain/>.
[ldns-zone-digest]
Verisign, "Implementation of Message Digests for DNS Zones
using the ldns library", July 2018,
<https://github.com/verisign/ldns-zone-digest>.
[RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
DOI 10.17487/RFC1995, August 1996,
<https://www.rfc-editor.org/info/rfc1995>.
[RFC2065] Eastlake 3rd, D. and C. Kaufman, "Domain Name System
Security Extensions", RFC 2065, DOI 10.17487/RFC2065,
January 1997, <https://www.rfc-editor.org/info/rfc2065>.
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, DOI 10.17487/RFC2136, April 1997,
<https://www.rfc-editor.org/info/rfc2136>.
[RFC2535] Eastlake 3rd, D., "Domain Name System Security
Extensions", RFC 2535, DOI 10.17487/RFC2535, March 1999,
<https://www.rfc-editor.org/info/rfc2535>.
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
<https://www.rfc-editor.org/info/rfc2845>.
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[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
2000, <https://www.rfc-editor.org/info/rfc2931>.
[RFC3851] Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Message Specification",
RFC 3851, DOI 10.17487/RFC3851, July 2004,
<https://www.rfc-editor.org/info/rfc3851>.
[RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R.
Thayer, "OpenPGP Message Format", RFC 4880,
DOI 10.17487/RFC4880, November 2007,
<https://www.rfc-editor.org/info/rfc4880>.
[RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
(AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
<https://www.rfc-editor.org/info/rfc5936>.
[RFC7706] Kumari, W. and P. Hoffman, "Decreasing Access Time to Root
Servers by Running One on Loopback", RFC 7706,
DOI 10.17487/RFC7706, November 2015,
<https://www.rfc-editor.org/info/rfc7706>.
[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, <https://www.rfc-editor.org/info/rfc7719>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RootServers]
Root Server Operators, "Root Server Technical Operations",
July 2018, <https://www.root-servers.org/>.
[RPZ] Vixie, P. and V. Schryver, "DNS Response Policy Zones
(RPZ)", draft-vixie-dnsop-dns-rpz-00 (work in progress),
June 2018, <https://tools.ietf.org/html/
draft-vixie-dnsop-dns-rpz-00>.
[ZoneDigestHackathon]
Kerr, S., "Prototype implementation of ZONEMD for the IETF
102 hackathon in Python", July 2018,
<https://github.com/shane-kerr/ZoneDigestHackathon>.
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Authors' Addresses
Duane Wessels
Verisign
12061 Bluemont Way
Reston, VA 20190
Phone: +1 703 948-3200
Email: dwessels@verisign.com
URI: http://verisign.com
Piet Barber
Verisign
12061 Bluemont Way
Reston, VA 20190
Phone: +1 703 948-3200
Email: pbarber@verisign.com
URI: http://verisign.com
Matt Weinberg
Verisign
12061 Bluemont Way
Reston, VA 20190
Phone: +1 703 948-3200
Email: mweinberg@verisign.com
URI: http://verisign.com
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
Email: warren@kumari.net
Wes Hardaker
USC/ISI
P.O. Box 382
Davis, CA 95617
Email: ietf@hardakers.net
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