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draft-thomassen-dnsop-dnssec-bootstrapping-03.txt
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DNSOP Working Group P. Thomassen
Internet-Draft deSEC, Secure Systems Engineering
Intended status: Standards Track N. Wisiol
Expires: 2 June 2022 deSEC, Technische Universität Berlin
29 November 2021
Automatic DNSSEC Bootstrapping using Authenticated Signals from the
Zone's Operator
draft-thomassen-dnsop-dnssec-bootstrapping-03
Abstract
This document introduces an in-band method for DNS operators to
publish arbitrary information about the zones they are authoritative
for, in an authenticated fashion and on a per-zone basis. The
mechanism allows managed DNS operators to securely announce DNSSEC
key parameters for zones under their management, including for zones
that are not currently securely delegated.
Whenever DS records are absent for a zone's delegation, this signal
enables the parent's registry or registrar to cryptographically
validate the CDS/CDNSKEY records found at the child's apex. The
parent can then provision DS records for the delegation without
resorting to out-of-band validation or weaker types of cross-checks
such as "Accept after Delay" ([RFC8078]).
This document updates [RFC8078] and replaces its Section 3 with
Section 3.2 of this document.
[ Ed note: Text inside square brackets ([]) is additional background
information, answers to frequently asked questions, general musings,
etc. They will be removed before publication. This document is
being collaborated on at https://github.com/desec-io/draft-thomassen-
dnsop-dnssec-bootstrapping/ (https://github.com/desec-io/draft-
thomassen-dnsop-dnssec-bootstrapping/). The most recent version of
the document, open issues, etc. should all be available there. The
authors gratefully accept pull requests. ]
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/.
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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 2 June 2022.
Copyright Notice
Copyright (c) 2021 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Requirements Notation . . . . . . . . . . . . . . . . . . 5
2. Signaling . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Chain of Trust . . . . . . . . . . . . . . . . . . . . . 5
2.2. Signaling Names . . . . . . . . . . . . . . . . . . . . . 5
3. Bootstrapping a DNSSEC Delegation . . . . . . . . . . . . . . 5
3.1. Signaling Consent to Act as the Child's Signer . . . . . 6
3.1.1. Example . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Validating CDS/CDNSKEY Records for DNSSEC
Bootstrapping . . . . . . . . . . . . . . . . . . . . . . 6
3.2.1. Example . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Triggers . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4. Limitations . . . . . . . . . . . . . . . . . . . . . . . 9
4. Operational Recommendations . . . . . . . . . . . . . . . . . 9
4.1. Child DNS Operator . . . . . . . . . . . . . . . . . . . 9
4.2. Parental Agent . . . . . . . . . . . . . . . . . . . . . 10
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 10
5.1. Child DNS Operator-side . . . . . . . . . . . . . . . . . 10
5.2. Parental Agent-side . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. Normative References . . . . . . . . . . . . . . . . . . . . 12
Appendix A. Change History (to be removed before publication) . 13
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Securing a DNS delegation for the first time requires that the
Child's DNSSEC parameters be conveyed to the Parent through some
trusted channel. How exactly this is done depends on the
relationship the Child has with the Parent.
In general, the communication has to occur between the DNSSEC key
holder and the Parent registry. It is often the case that the key is
held by the Child DNS Operator. Furthermore, depending on the
circumstances, the communication may also involve the Registrar,
possibly via the Registrant (for details, see [RFC7344], Appendix A).
As observed in [RFC7344], this is often a manual process -- and not
an easy one. Any manual process is susceptible to mistakes and/or
errors. In addition, due to the annoyance factor of the process,
involved parties may avoid the process of getting a DS record set
published in the first place.
To alleviate these problems, automated provisioning of DS records has
been specified in ([RFC8078]). It is based on the Parental Agent
(registry or registrar) fetching DNSSEC key parameters in the form of
CDS and CDNSKEY records ([RFC7344]) from the Child zone's apex, and
validating them somehow. This validation can be done using DNSSEC
itself if the objective is to update an existing DS record (such as
during key rollover). However, when bootstrapping a DNSSEC
delegation, the Child zone has no existing DNSSEC validation path,
and other means to ensure the CDS/CDNSKEY records' legitimacy must be
found.
For lack of a comprehensive DNS-innate solution, either out-of-band
methods have been used so far to complete the chain of trust, or
cryptographic validation has been entirely dispensed with, in
exchange for weaker types of cross-checks such as "Accept after
Delay" ([RFC8078] Section 3.3). An in-band validation method for
enabling DNSSEC has been missing.
This document aims to close this gap by introducing an in-band method
for DNS Operators to publish arbitrary information about the zones
they are authoritative for, in an authenticated manner and on a per-
zone basis. The mechanism allows managed DNS Operators to securely
announce DNSSEC key parameters for zones under their management. The
Parent can then use this signal to cryptographically validate the
CDS/CDNSKEY records found at an insecure Child zone's apex, and upon
success secure the delegation.
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While applicable to the vast majority of domains, the protocol does
not support certain edge cases, such as excessively long Child zone
names, or DNSSEC bootstrapping for in-bailiwick domains (see
Section 3.4).
Readers are expected to be familiar with DNSSEC, including [RFC4033],
[RFC4034], [RFC4035], [RFC6781], [RFC7344], and [RFC8078].
1.1. Terminology
This section defines the terminology used in this document.
Child The entity on record that has the delegation of the domain
from the Parent.
Parent The domain in which the Child in registered.
Child DNS Operator The entity that maintains and publishes the zone
information for the Child DNS.
Parental Agent The entity that has the authority to insert DS
records into the Parent zone on behalf of the Child. (It could
the the registry, registrar, a reseller, or some other authorized
entity.)
Signaling Domain A hostname from the Child's NS record set, prefixed
with the label "_dsauth". There are as many Signaling Domains as
there are distinct NS targets.
Signaling Zone The zone which is authoritative for a given Signaling
Domain.
Signaling Name The labels that are prefixed to a Signaling Domain in
order to identify a Child zone's name (see Section 2.2).
Signaling Record A DNS record located at a Signaling Name under a
Signaling Domain. Signaling Records are used by the Child DNS
Operator to publish information about the Child.
CDS/CDNSKEY This notation refers to CDS and/or CDNSKEY, i.e., one or
both.
Base32hex Encoding "Base 32 Encoding with Extended Hex Alphabet" as
per [RFC4648].
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1.2. Requirements Notation
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. Signaling
When setting up initial trust, the Child zone's CDS/CDNSKEY RRsets
need to be authenticated. This is achieved using an authentication
signal from the Child DNS Operator that the Parent can discover and
validate, thus transferring trust from the Child DNS Operator to the
Child zone.
2.1. Chain of Trust
If a Child DNS Operator implements the protocol, each Signaling Zone
MUST be securely delegated, i.e. have a valid DNSSEC chain of trust.
For example, when performing DNSSEC bootstrapping for a Child zone
with NS records "ns1.example.net" and "ns2.example.net", the Child
DNS Operator needs to ensure that a valid DNSSEC chain of trust
exists for the zone(s) that are authoritative for the Signaling
Domains "_dsauth.ns1.example.net" and "_dsauth.ns2.example.net".
2.2. Signaling Names
To publish a piece of information about the Child zone in an
authenticated fashion, the Child DNS Operator MUST publish one or
more Signaling Records at the Child's Signaling Name under each
Signaling Domain.
Signaling Records MUST be accompanied by RRSIG records created with
the corresponding Signaling Zone's key(s). The type and contents of
these Signaling Records are detailed in Section 3.1.
The Signaling Name is identical to the Child name, with the final
root label removed.
3. Bootstrapping a DNSSEC Delegation
Child DNS Operators and Parental Agents who wish to use CDS/CDNSKEY
records for DNSSEC bootstrapping SHOULD support the protocol
described in this section.
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3.1. Signaling Consent to Act as the Child's Signer
To confirm its willingness to act as the Child's delegated signer and
authenticate the Child's CDS/CDNSKEY RRsets, the Child DNS Operator
MUST co-publish them at the corresponding Signaling Name under each
Signaling Domain as defined in Section 2.2.
Existing use of CDS/CDNSKEY records is specified at the Child apex
only ([RFC7344], Section 4.1). This protocol extends the use of
these record types to non-apex owner names for the purpose of DNSSEC
bootstrapping. To exclude the possibility of semantic collision,
there MUST NOT be a zone cut at a Signaling Name.
Unlike the CDS/CDNSKEY records at the Child's apex, Signaling Records
MUST be signed with the corresponding Signaling Zone's key(s). Their
contents MUST be identical to the corresponding records published at
the Child's apex.
3.1.1. Example
For the purposes of bootstrapping the Child zone "example.co.uk" with
NS records "ns1.example.net" and "ns2.example.net", the required
Signaling Domains are "_dsauth.ns1.example.net" and
"_dsauth.ns2.example.net".
In the zones containing these domains, the Child DNS Operator
authenticates the CDS/CDNSKEY records found at the Child's apex by
co-publishing them at the names:
example.co.uk._dsauth.ns1.example.net
example.co.uk._dsauth.ns2.example.net
The records are accompanied by RRSIG records created using the key(s)
of the respective Signaling Zone.
3.2. Validating CDS/CDNSKEY Records for DNSSEC Bootstrapping
This section replaces Section 3 of [RFC8078].
To validate a Child's CDS/CDNSKEY RRset for DNSSEC bootstrapping, the
Parental Agent, knowing both the Child zone name and its NS
hostnames, MUST execute the following steps:
1. verify that the Child is not currently securely delegated;
2. query the CDS/CDNSKEY records at the Child zone apex directly
from each of the authoritative servers listed in the delegation's
NS record set;
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3. query the CDS/CDNSKEY records located at the Signaling Name under
each Signaling Domain using a trusted DNS resolver and enforce
DNSSEC validation;
4. check (separately by record type) that all record sets retrieved
in Steps 2 and 3 have equal contents;
If the above steps succeed without error, the CDS/CDNSKEY records are
successfully validated, and the Parental Agent can proceed with the
publication of the DS record set under the precautions described in
[RFC8078], Section 5.
If, however, an error condition occurs, in particular:
* in Step 1: the Child is already securely delegated;
* in Step 2: any failure during the retrieval of the CDS/CDNSKEY
records located at the Child apex from any of the authoritative
nameservers, with an empty record set qualifying as a failure;
* in Step 3: any failure to retrieve the CDS/CDNSKEY RRsets located
at the Signaling Name under any Signaling Domain, including
failure of DNSSEC validation, unauthenticated data (AD bit not
set), or an empty record set;
* in Step 4: inconsistent responses;
the Parental Agent MUST abort the procedure.
3.2.1. Example
To verify the CDS/CDNSKEY records for the Child "example.co.uk", the
Parental Agent (assuming that the Child delegation's NS records are
"ns1.example.net" and "ns2.example.net")
1. checks that the Child zone is not yet securely delegated;
2. queries CDS/CDNSKEY records for "example.co.uk" directly from
"ns1.example.net" and "ns2.example.net";
3. queries the CDS/CDNSKEY records located at (see Section 2.2)
example.co.uk._dsauth.ns1.example.net
example.co.uk._dsauth.ns2.example.net
4. checks that the CDS/CDNSKEY record sets retrieved in Steps 2 and
3 agree across responses.
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If all these steps succeed, the Parental Agent can proceed to publish
a DS record set as indicated by the validated CDS/CDNSKEY records.
3.3. Triggers
[ Clarity of this section needs to be improved. ]
Parental Agents SHOULD trigger the procedure described in Section 3.2
once one of the following conditions is fulfilled:
* The Parental Agent receives a new or updated NS record set for a
Child;
* The Parental Agent encounters Signaling Records for its Children
during a scan (e.g. daily) of known Signaling Domains (derived
from the NS records found in the Parent zone).
To perform such a scan, the Parental Agent iterates over some or
all of its delegations and strips the first label off each one to
construct the set of immediate ancestors of its children. (For
delegations one level below the Parent's apex, such as second-
level domain registrations, this will simply be the name of the
Parent zone.) The Parental Agent then uses these names to compute
the second label of the Signaling Names as described in
Section 2.2. The scan is completed by either
- performing a targeted NSEC walk starting one level below the
Signaling Domain, at the label that encodes the Child's
ancestor; or by
- performing a zone transfer of the zone containing the (relevant
part of the) Signaling Domain, if the Signaling Zone operator
allows it, and iterating over its contents.
The Child's name is constructed by prepending the first label of
the encountered Signaling Names to the ancestor name from which
the Signaling Name's second label was computed;
* The Parental Agent encounters Signaling Records during a
proactive, opportunistic scan (e.g. daily queries for the
Signaling Records of some or all of its delegations);
* Any other condition as deemed appropriate by local policy.
One of the inputs of the bootstrapping algorithm in Section 3.2 is
the NS record set of the Child's delegation. It is therefore
necessary to establish knowledge of the delegation's NS record set
before firing the trigger.
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In some cases, the trigger context contains reliable information
about the Child's delegation, such as when bootstrapping is triggered
by the registrant changing their NS record set, or during a daily
scan of existing delegations. In such cases, the delegation's NS
RRset can be used as is.
In cases where the trigger context does not provide sufficient
knowledge of the NS record set, the Parental Agent MUST fetch the
delegation's NS record set and ensure that the proper NS record set
is fed to the bootstrapping algorithm (Section 3.2).
In particular, when discovering Signaling Names by means of an NSEC
walk or zone transfer, the Parental Agent MUST NOT assume that the
nameserver(s) under whose Signaling Domain(s) a Signaling Name is
discovered is in fact authoritative for the corresponding Child.
Before firing the trigger for a particular candidate Child, the
Parental Agent MUST ascertain that the Child's delegation actually
contains the nameserver hostname under whose Signaling Domain the
scan occurred.
3.4. Limitations
As a consequence of Step 3 in Section 3.2, DS bootstrapping does not
work for in-bailiwick delegations, as no pre-existing chain of trust
to the Child domain is available during bootstrapping.
The protocol is further restricted by the fact that the fully
qualified Signaling Names fit within the general limits that apply to
DNS names (such as their length and their label count).
4. Operational Recommendations
4.1. Child DNS Operator
To keep the size of the Signaling Zones minimal and bulk processing
efficient (such as via NSEC walks or zone transfers), Child DNS
Operators SHOULD remove Signaling Records which are found to have
been acted upon.
Signaling Domains SHOULD be delegated as zones of their own, so that
the Signaling Zone's apex coincides with the Signaling Domain (such
as "_dsauth.ns1.example.net"). While it is permissible for the
Signaling Domain to be contained in a Signaling Zone of fewer labels
(such as "example.net"), a zone cut ensures that bootstrapping
activities do not require modifications of the zone containing the
nameserver hostname.
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In addition, Signaling Zones SHOULD use NSEC to allow efficient
discovery of pending bootstrapping operations by means of zone
walking (see Section 3.3). This is especially useful for bulk
processing after a Child DNS Operator has enabled the protocol.
4.2. Parental Agent
It is RECOMMENDED to perform queries within Signaling Domains
(Section 3.2) with an (initially) cold resolver cache as to retrieve
the most current information regardless of TTL. (When a batch job is
used to attempt bootstrapping for a large number of delegations, the
cache does not need to get cleared in between.)
[It is expected that Signaling Records have few consumers only, so
that caching would not normally have a performance benefit. On the
other hand, perhaps it is better to RECOMMEND low TTLs instead?]
5. Implementation Status
*Note to the RFC Editor*: please remove this entire section before
publication.
5.1. Child DNS Operator-side
* Knot DNS supports manual creation of non-apex CDS/CDNSKEY records.
* PowerDNS supports manual creation of non-apex CDS/CDNSKEY records.
* Proof-of-concept Signaling Domains with several thousand Signaling
Names exist at "_dsauth.ns1.desec.io" and "_dsauth.ns2.desec.org".
Signaling Names can be discovered via NSEC walking. Some other
operators are planning an experimental implementation.
* A tool to automatically generate signaling records for
bootstrapping purposes is under development by the authors.
5.2. Parental Agent-side
* A tool to retrieve and process Signaling Records for bootstrapping
purposes, either directly or via zone walking, is available at
https://github.com/desec-io/dsbootstrap (https://github.com/desec-
io/dsbootstrap). The tool outputs the validated DS records which
then can be added to the Parent zone.
* Some registries/registrars are planning experimental
implementations of the protocol.
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6. Security Considerations
The protocol adds authentication to the CDS/CDNSKEY-based
bootstrapping concept of [RFC8078], while removing nothing. Its
security level is therefore strictly higher than that of existing
approaches described in that document (e.g. "Accept after Delay").
Apart from this general improvement, the same Security Considerations
apply as in [RFC8078].
The level of rigor in Section 3.2 is needed to prevent publication of
a half-backed DS RRset (authorized only under a subset of NS
hostnames). This ensures that an operator in a multi-homed setup
cannot enable DNSSEC unless all other operators agree. [ TODO In
principle, this applies to any CDS update. Should we phrase it as a
general update to [RFC8078]? ]
[ Thoughts on the Chain of Trust:
Actors in the chain(s) of trust of the Signaling Zone(s) (the DNS
Operator themselves, plus entities further up in the chain) can
undermine the protocol. However,
* that's possible with CDS/CDNSKEY, too (new method is not weaker);
* if the Child DNS Operator doesn't trust the zones in which its NS
hostnames live (including their nameservers' A records) because
their path from the root is untrusted, you probably don't want to
trust that operator as a whole;
* when bootstrapping is done upon receipt of a new NS record set,
the window of opportunity is very small;
* mitigation exists by diversifying e.g. the nameserver hostname's
TLDs, which is advisable anyways;
* correct bootstrapping is easily monitored by the Child DNS
Operator.
]
7. IANA Considerations
*TODO:* reserve "_dsauth"?
This document has no IANA actions.
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8. Acknowledgements
Thanks to Brian Dickson, Ondřej Caletka, John R. Levine,
Christian Elmerot, and Oli Schacher for reviewing draft proposals and
offering comments and suggestions.
Thanks also to Steve Crocker, Hugo Salgado, and Ulrich Wisser for
early-stage brainstorming.
9. Normative References
[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>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.
[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>.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<https://www.rfc-editor.org/info/rfc4035>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
Operational Practices, Version 2", RFC 6781,
DOI 10.17487/RFC6781, December 2012,
<https://www.rfc-editor.org/info/rfc6781>.
[RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
DNSSEC Delegation Trust Maintenance", RFC 7344,
DOI 10.17487/RFC7344, September 2014,
<https://www.rfc-editor.org/info/rfc7344>.
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[RFC8078] Gudmundsson, O. and P. Wouters, "Managing DS Records from
the Parent via CDS/CDNSKEY", RFC 8078,
DOI 10.17487/RFC8078, March 2017,
<https://www.rfc-editor.org/info/rfc8078>.
[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>.
Appendix A. Change History (to be removed before publication)
* draft-thomassen-dnsop-dnssec-bootstrapping-03
| Clarified importance of record cleanup by moving paragraph up.
|
| Pointed out limitations.
|
| Replace [RFC8078] Section 3 with our Section 3.2.
|
| Changed "_boot" label to "_dsauth".
|
| Removed hashing of Child name components in Signaling Names.
|
| Editorial changes.
* draft-thomassen-dnsop-dnssec-bootstrapping-02
| Reframed as an authentication mechanism for RFC 8078.
|
| Removed multi-signer use case (focus on RFC 8078 authentication).
|
| Triggers need to fetch NS records (if not implicit from context).
|
| Improved title.
|
| Recognized that hash collisions are dealt with by Child apex
| check.
* draft-thomassen-dnsop-dnssec-bootstrapping-01
| Add section on Triggers.
|
| Clarified title.
|
| Improved abstract.
|
| Require CDS/CDNSKEY records at the Child.
|
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| Reworked Signaling Name scheme.
|
| Recommend using cold cache for consumption.
|
| Updated terminology (replace "Bootstrapping" by "Signaling").
|
| Added NSEC recommendation for Bootstrapping Zones.
|
| Added multi-signer use case.
|
| Editorial changes.
* draft-thomassen-dnsop-dnssec-bootstrapping-00
| Initial public draft.
Authors' Addresses
Peter Thomassen
deSEC, Secure Systems Engineering
Berlin
Germany
Email: [email protected]
Nils Wisiol
deSEC, Technische Universität Berlin
Berlin
Germany
Email: [email protected]
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