Internet DRAFT - draft-ogud-dnsop-maintain-ds
draft-ogud-dnsop-maintain-ds
Network Working Group O. Gudmundsson
Internet-Draft CloudFlare
Intended status: Informational P. Wouters
Expires: April 17, 2016 Red Hat
October 15, 2015
Managing DS records from parent via CDS/CDNSKEY
draft-ogud-dnsop-maintain-ds-00
Abstract
RFC7344 specifies how DNS trust can be maintained in-band between
parent and child. There are two features missing in that
specification: initial trust setup and removal of trust anchor. This
document addresses both these omissions.
Changing a domain's DNSSEC status can be a complicated matter
involving many parties. Some of these parties, such as the DNS
operator, might not even be known by all organisations involved. The
inability to enable or disable DNSSEC via in-band signalling is seen
as a problem or liability that prevents DNSSEC adoption at large
scale. This document adds a method for in-band signalling of DNSSEC
status changes.
Initial trust is considered a much harder problem, this document will
seek to clarify and simplify the initial acceptance policy.
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 http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 17, 2016.
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Copyright Notice
Copyright (c) 2015 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Removing DS . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Introducing DS . . . . . . . . . . . . . . . . . . . . . 3
1.3. Notation . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. The Three Uses of CDS . . . . . . . . . . . . . . . . . . . . 4
2.1. The meaning of CDS ? . . . . . . . . . . . . . . . . . . 4
3. Enabling DNSSEC via CDS/CDNSKEY . . . . . . . . . . . . . . . 5
3.1. Accept policy via authenticated channel . . . . . . . . . 5
3.2. Accept with extra checks . . . . . . . . . . . . . . . . 5
3.3. Accept after delay . . . . . . . . . . . . . . . . . . . 5
3.4. Accept with challenge . . . . . . . . . . . . . . . . . . 6
4. DNSSEC Delete Algorithm . . . . . . . . . . . . . . . . . . . 6
5. Security considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
CDS/CDNSKEY [RFC7344] records are used to signal changes in trust
anchors, this is a great way to maintain delegations when the DNS
operator has no other way to inform the parent that changes are
needed. RFC7344 contains no "delete" signal for the child to tell
the parent that it wants to change the DNSSEC security of its domain.
[RFC7344] punted the Initial Trust establishment question and left it
to each parent to come up with an acceptance policy.
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1.1. Removing DS
This document introduces the delete option for both CDS and CDNSKEY.
to allow a child to signal the parent to turn off DNSSEC. When a
domain is moved from one DNS operator to another one, sometimes it is
necessary to turn off DNSSEC to facilitate the change of DNS
operator. Common scenarios include:
1 moving from a DNSSEC operator to a non-DNSSEC capable one or one
that does not support the same algorithms as the old one.
2 moving to one that cannot/does-not-want to do a proper DNSSEC
rollover.
3 the domain holder does not want DNSSEC.
4 when moving between two DNS operators that use disjoint sets of
algorithms to sign the zone, thus algorithm roll can not be
performed.
Whatever the reason, the lack of a "remove my DNSSEC" option is
turning into the latest excuse as why DNSSEC cannot be deployed.
Turing off DNSSEC reduces the security of the domain and thus should
only be done carefully, and that decision should be fully under the
child domain's control.
1.2. Introducing DS
The converse issue is how does a child domain instruct the parent it
wants to have a DS record added. This problem is not as hard as many
have assumed, given a few simplifying assumptions. This document
makes the assumption that there are reasonable policies that can be
applied and will allow automation of trust introduction.
Not being able to enable trust via an easily automated mechanism is
hindering DNSSEC at scale by anyone that does not have automated
access to its parent's "registry".
1.3. Notation
When this document uses the word CDS it implies that the same applies
to CDNSKEY and vice versa, the only difference between the two
records is how information is represented.
When the document uses the word "parent" it implies an entity that is
authorized to insert into parent zone information about this child
domain. Which entity this is exactly does not matter. It could be
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the Registrar or Reseller that the child domain was purchased from.
It could be the Registry that the domain is registered in when
allowed. It could be some other entity when the RRR framework is not
used.
We use RRR to mean Registry Registrar Reseller in the context of DNS
domain markets.
1.4. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. The Three Uses of CDS
In general there are three operations that a domain wants to
influence on its parent:
1 Roll over KSK, this means updating the DS records in the parent to
reflect the new set of KSK's at the child. This could be an ADD
operation, a Delete operation on one or more records while keeping
at least one DS RR, or a full Replace operation
2 Turn off DNSSEC validation, i.e. delete all the DS records
3 Enable DNSSEC validation, i.e. place initial DS RRset in the
parent.
Operation 1 is covered in [RFC7344], operations 2 and 3 are defined
in this document. In many people's minds, those two later operations
carry more risk than the first one. This document argues that 2 is
identical to 1 and the final one is different (but not that
different).
2.1. The meaning of CDS ?
The fundamental question is what is the semantic meaning of
publishing a CDS RRset in a zone? We offer the following
interpretation:
"Publishing a CDS or CDNSKEY record signifies to the parent that the
child is ready for the corresponding DS records to be synchronized.
Every parent or parental agent should have an acceptance policy of
these records for the three different use cases involved: Initial DS
publication, Key rollover, and Returning to Insecure."
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In short, the CDS RRset is an instruction to the parent to modify DS
RRset if the CDS and DS RRsets differ. The acceptance policy for CDS
in the rollover case is "seeing" according to [RFC7344]. The
acceptance policy in the Delete case is just seeing a CDS RRset with
the delete operation specified in this document.
3. Enabling DNSSEC via CDS/CDNSKEY
There are number of different models for managing initial trust, but
in the general case, the child wants to enable global validation for
the future. Thus during the period from the time the child publishes
the CDS until the corresponding DS is published is the period that
DNS answers for the child could be forged. The goal is to keep this
period as short as possible.
One important case is how a 3rd party DNS operator can upload its
DNSSEC information to the parent, so the parent can publish a DS
record for the child. In this case there is a possibility of setting
up some kind of authentication mechanism and submission mechanism
that is outside the scope of this document.
Below are some policies that parents can use. These policies assume
that the notifications are can be authenticated and/or identified.
3.1. Accept policy via authenticated channel
In this case the parent is notified via UI/API that CDS exists, the
parent retrieves the CDS and inserts the DS record as requested, if
the request comes over an authenticated channel.
3.2. Accept with extra checks
In this case the parent checks that the source of the notification is
allowed to request the DS insertion. The checks could include
whether this is a trusted entity, whether the nameservers correspond
to the requestor, whether there have been any changes in registration
in the last few days, etc, or the parent can send a notification
requesting an confirmation.
The end result is that the CDS is accepted at the end of the checks
or when the out-of-band confirmation is received.
3.3. Accept after delay
In this case, if the parent deems the request valid, it starts
monitoring the CDS records at the child nameservers over period of
time to make sure nothing changes. After number of checks,
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preferably from different vantage points, the parent accepts the CDS
records as a valid signal to update.
3.4. Accept with challenge
In this case the parent instructs the requestor to insert some record
into the child domain to prove it has the ability to do so (i.e., it
is the operator of the zone).
4. DNSSEC Delete Algorithm
The DNSKEY algorithm registry contains two reserved values: 0 and
255[RFC4034]. The CERT record [RFC4398] defines the value 0 to mean
the algorithm in the CERT record is not defined in DNSSEC.
[rfc-editor remove before publication] For this reason, using the
value 0 in CDS/CDNSKEY delete operations is potentially problematic,
but we propose that here anyway as the risk is minimal. The
alternative is to reserve one DNSSEC algorithm number for this
purpose. [rfc-editor end remove]
Right now, no DNSSEC validator understands algorithm 0 as a valid
signature algorithm, thus if the validator sees a DNSKEY or DS record
with this value, it will treat it as unknown. Accordingly, the zone
is treated as unsigned unless there are other algorithms present.
In the context of CDS and CDNSKEY records, DNSSEC algorithm 0 is
defined and means the entire DS set MUST be removed. The contents of
the records MUST contain only the fixed fields as show below.
1 CDS 0 0 0
2 CDNSKEY 0 3 0
There is no keying material payload in the records, just the command
to delete all DS records. This record is signed in the same way as
CDS/CDNSKEY is signed.
Strictly speaking the CDS record could be "CDS X 0 X" as only the
DNSKEY algorithm is what signals the delete operation, but for
clarity the "0 0 0" notation is mandated, this is not a definition of
DS Digest algorithm 0. Same argument applies to "CDNSKEY 0 3 0".
Once the parent has verified the CDS/CDNSKEY record and it has passed
other acceptance tests, the DS record MUST be removed. At this point
the child can start the process of turning DNSSEC off.
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5. Security considerations
This document is about avoiding validation failures when a domain
moves from one DNS operator to another one. Turing off DNSSEC
reduces the security of the domain and thus should only be done as a
last resort.
In most cases it is preferable that operators collaborate on the
rollover by doing a KSK+ZSK rollover as part of the handoff, but that
is not always possible. This document addresses the case where
unsigned state is needed.
Users SHOULD keep in mind that re-establishing trust in delegation
can be hard and take a long time thus before going to unsigned all
options SHOULD be considered.
A parent should ensure that when it is allowing a child to become
securely delegated, that it has a reasonable assurance that the CDS/
CDNSKEY that is used to bootstrap the security on is visible from a
geographically and network topology diverse view. It should also
ensure the the zone would validate if the parent published the DS
record. A parent zone might also consider sending an email to its
contact addresses to give the child a warning that security will be
enabled after a certain about of wait time - thus allowing a child
administrator to cancel the request.
This document does not introduce any new problems, but like Negative
Trust Anchor[I-D.ietf-dnsop-negative-trust-anchors], it addresses
operational reality.
6. IANA considerations
This document updates the following IANA registries: "DNS Security
Algorithm Numbers"
Algorithm 0 adds a reference to this document.
7. References
7.1. Normative References
[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,
<http://www.rfc-editor.org/info/rfc4034>.
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[RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
DNSSEC Delegation Trust Maintenance", RFC 7344, DOI
10.17487/RFC7344, September 2014,
<http://www.rfc-editor.org/info/rfc7344>.
7.2. Informative References
[I-D.ietf-dnsop-negative-trust-anchors]
Ebersman, P., Kumari, W., Griffiths, C., Livingood, J.,
and R. Weber, "Definition and Use of DNSSEC Negative Trust
Anchors", draft-ietf-dnsop-negative-trust-anchors-13 (work
in progress), August 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4398] Josefsson, S., "Storing Certificates in the Domain Name
System (DNS)", RFC 4398, DOI 10.17487/RFC4398, March 2006,
<http://www.rfc-editor.org/info/rfc4398>.
Appendix A. Acknowledgements
This document is generated using the mmark tool that Miek Gieben has
developed.
Authors' Addresses
Olafur Gudmundsson
CloudFlare
Email: olafur+ietf@cloudflare.com
Paul Wouters
Red Hat
Email: pwouters@redhat.com
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