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DNSOP O. Kolkman
Internet-Draft RIPE NCC
Expires: September 2, 2005 R. Gieben
NLnet Labs
March 2005
DNSSEC Operational Practices
draft-ietf-dnsop-dnssec-operational-practices-04.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 2, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document describes a set of practices for operating the DNS with
security extensions (DNSSEC). The target audience is zone
administrators deploying DNSSEC.
The document discusses operational aspects of using keys and
signatures in the DNS. It discusses issues as key generation, key
storage, signature generation, key rollover and related policies.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 The Use of the Term 'key' . . . . . . . . . . . . . . . . 4
1.2 Time Definitions . . . . . . . . . . . . . . . . . . . . . 5
2. Keeping the Chain of Trust Intact . . . . . . . . . . . . . . 5
3. Keys Generation and Storage . . . . . . . . . . . . . . . . . 6
3.1 Zone and Key Signing Keys . . . . . . . . . . . . . . . . 6
3.1.1 Motivations for the KSK and ZSK Separation . . . . . . 6
3.1.2 KSKs for high level zones . . . . . . . . . . . . . . 7
3.2 Randomness . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 Key Effectivity Period . . . . . . . . . . . . . . . . . . 8
3.4 Key Algorithm . . . . . . . . . . . . . . . . . . . . . . 9
3.5 Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . 9
3.6 Private Key Storage . . . . . . . . . . . . . . . . . . . 10
4. Signature generation, Key Rollover and Related Policies . . . 11
4.1 Time in DNSSEC . . . . . . . . . . . . . . . . . . . . . . 11
4.1.1 Time Considerations . . . . . . . . . . . . . . . . . 11
4.2 Key Rollovers . . . . . . . . . . . . . . . . . . . . . . 13
4.2.1 Zone-signing Key Rollovers . . . . . . . . . . . . . . 13
4.2.2 Key-signing Key Rollovers . . . . . . . . . . . . . . 17
4.2.3 Difference Between ZSK and KSK Rollovers . . . . . . . 18
4.2.4 Automated Key Rollovers . . . . . . . . . . . . . . . 19
4.3 Planning for Emergency Key Rollover . . . . . . . . . . . 19
4.3.1 KSK Compromise . . . . . . . . . . . . . . . . . . . . 20
4.3.2 ZSK Compromise . . . . . . . . . . . . . . . . . . . . 20
4.3.3 Compromises of Keys Anchored in Resolvers . . . . . . 20
4.4 Parental Policies . . . . . . . . . . . . . . . . . . . . 21
4.4.1 Initial Key Exchanges and Parental Policies
Considerations . . . . . . . . . . . . . . . . . . . . 21
4.4.2 Storing Keys or Hashes? . . . . . . . . . . . . . . . 21
4.4.3 Security Lameness . . . . . . . . . . . . . . . . . . 22
4.4.4 DS Signature Validity Period . . . . . . . . . . . . . 22
5. Security Considerations . . . . . . . . . . . . . . . . . . . 23
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.1 Normative References . . . . . . . . . . . . . . . . . . . 24
7.2 Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 25
A. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 25
B. Zone-signing Key Rollover Howto . . . . . . . . . . . . . . . 26
C. Typographic Conventions . . . . . . . . . . . . . . . . . . . 26
D. Document Details and Changes . . . . . . . . . . . . . . . . . 29
D.1 draft-ietf-dnsop-dnssec-operational-practices-00 . . . . . 29
D.2 draft-ietf-dnsop-dnssec-operational-practices-01 . . . . . 29
D.3 draft-ietf-dnsop-dnssec-operational-practices-02 . . . . . 29
D.4 draft-ietf-dnsop-dnssec-operational-practices-03 . . . . . 29
D.5 draft-ietf-dnsop-dnssec-operational-practices-04 . . . . . 30
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Intellectual Property and Copyright Statements . . . . . . . . 31
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1. Introduction
During workshops and early operational deployment tests, operators
and system administrators gained experience about operating the DNS
with security extensions (DNSSEC). This document translates these
experiences into a set of practices for zone administrators. At the
time of writing, there exists very little experience with DNSSEC in
production environments; this document should therefore explicitly
not be seen as representing 'Best Current Practices'.
The procedures herein are focused on the maintenance of signed zones
(i.e. signing and publishing zones on authoritative servers). It is
intended that maintenance of zones such as resigning or key rollovers
be transparent to any verifying clients on the Internet.
The structure of this document is as follows. In Section 2 we
discuss the importance of keeping the "chain of trust" intact.
Aspects of key generation and storage of private keys are discussed
in Section 3; the focus in this section is mainly on the private part
of the key(s). Section 4 describes considerations concerning the
public part of the keys. Since these public keys appear in the DNS
one has to take into account all kinds of timing issues, which are
discussed in Section 4.1. Section 4.2 and Section 4.3 deal with the
rollover, or which, of keys. Finally Section 4.4 discusses
considerations on how parents deal with their children's public keys
in order to maintain chains of trust.
The typographic conventions used in this document are explained in
Appendix C.
Since this is a document with operational suggestions and there are
no protocol specifications, the RFC2119 [4] language does not apply.
This document obsoletes RFC2541 [7]
1.1 The Use of the Term 'key'
It is assumed that the reader is familiar with the concept of
asymmetric keys on which DNSSEC is based (Public Key Cryptography
[11]). Therefore, this document will use the term 'key' rather
loosely. Where it is written that 'a key is used to sign data' it is
assumed that the reader understands that it is the private part of
the key-pair that is used for signing. It is also assumed that the
reader understands that the public part of the key-pair is published
in the DNSKEY resource record and that it is the public part that is
used in key-exchanges.
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1.2 Time Definitions
In this document we will be using a number of time related terms.
The following definitions apply:
o "Signature validity period"
The period that a signature is valid. It starts at the time
specified in the signature inception field of the RRSIG RR and
ends at the time specified in the expiration field of the RRSIG
RR.
o "Signature publication period"
Time after which a signature (made with a specific key) is
replaced with a new signature (made with the same key). This
replacement takes place by publishing the relevant RRSIG in the
master zone file.
After one stopped publishing an RRSIG in a zone it may take a
while before the RRSIG has expired from caches and has actually
been removed from the DNS.
o "Key effectivity period"
The period which a key pair is expected to be effective. This
period is defined as the time between the first inception time
stamp and the last expiration date of any signature made with
this key.
The key effectivity period can span multiple signature validity
periods.
o "Maximum/Minimum Zone TTL"
The maximum or minimum value of the TTLs from the complete set
of RRs in a zone.
2. Keeping the Chain of Trust Intact
Maintaining a valid chain of trust is important because broken chains
of trust will result in data being marked as Bogus (as defined in [2]
section 5), which may cause entire (sub)domains to become invisible
to verifying clients. The administrators of secured zones have to
realize that their zone is, to their clients, part of a chain of
trust.
As mentioned in the introduction, the procedures herein are intended
to ensure maintenance of zones, such as resigning or key rollovers,
will be transparent to the verifying clients on the Internet.
Administrators of secured zones will have to keep in mind that data
published on an authoritative primary server will not be immediately
seen by verifying clients; it may take some time for the data to be
transfered to other secondary authoritative nameservers and clients
may be fetching data from caching non-authoritative servers.
For the verifying clients it is important that data from secured
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zones can be used to build chains of trust regardless of whether the
data came directly from an authoritative server, a caching nameserver
or some middle box. Only by carefully using the available timing
parameters can a zone administrator assure that the data necessary
for verification can be obtained.
The responsibility for maintaining the chain of trust is shared by
administrators of secured zones in the chain of trust. This is most
obvious in the case of a 'key compromise' when a trade off between
maintaining a valid chain of trust and replacing the compromised keys
as soon as possible must be made. Then zone administrators will have
to make a trade off, between keeping the chain of trust intact -
thereby allowing for attacks with the compromised key - or to
deliberately break the chain of trust and making secured sub domains
invisible to security aware resolvers. Also see Section 4.3.
3. Keys Generation and Storage
This section describes a number of considerations with respect to the
security of keys. It deals with the generation, effectivity period,
size and storage of private keys.
3.1 Zone and Key Signing Keys
The DNSSEC validation protocol does not distinguish between DNSKEYs.
All DNSKEYs can be used during the validation. In practice operators
use Key Signing and Zone Signing Keys and use the so-called (Secure
Entry Point) SEP flag to distinguish between them during operations.
The dynamics and considerations are discussed below.
To make zone resigning and key rollover procedures easier to
implement, it is possible to use one or more keys as Key Signing Keys
(KSK). These keys will only sign the apex DNSKEY RR set in a zone.
Other keys can be used to sign all the RRsets in a zone and are
referred to as Zone Signing Keys (ZSK). In this document we assume
that KSKs are the subset of keys that are used for key exchanges with
the parent and potentially for configuration as trusted anchors - the
SEP keys. In this document we assume a one-to-one mapping between
KSK and SEP keys and we assume the SEP flag [1] to be set on all
KSKs.
3.1.1 Motivations for the KSK and ZSK Separation
Differentiating between the KSK and ZSK functions has several
advantages:
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o No parent/child interaction is required when ZSKs are updated.
o The KSK can be made stronger (i.e. using more bits in the key
material). This has little operational impact since it is only
used to sign a small fraction of the zone data. Also when
verifying the KSK is only used to verify the zone's keyset.
o As the KSK is only used to sign a key set, which is most probably
updated less frequently than other data in the zone, it can be
stored separately from and in a safer location than the ZSK.
o A KSK can have a longer key effectivity period.
For almost any method of key management and zone signing the KSK is
used less frequently than the ZSK. Once a key set is signed with the
KSK all the keys in the key set can be used as ZSK. If a ZSK is
compromised, it can be simply dropped from the key set. The new key
set is then resigned with the KSK.
Given the assumption that for KSKs the SEP flag is set, the KSK can
be distinguished from a ZSK by examining the flag field in the DNSKEY
RR. If the flag field is an odd number it is a KSK. If it is an
even number it is a ZSK.
The zone-signing key can be used to sign all the data in a zone on a
regular basis. When a zone-signing key is to be rolled, no
interaction with the parent is needed. This allows for "Signature
Validity Periods" on the order of days.
The key-signing key is only to be used to sign the DNSKEY RRs in a
zone. If a key-signing key is to be rolled over, there will be
interactions with parties other than the zone administrator. These
can include the registry of the parent zone or administrators of
verifying resolvers that have the particular key configured as
trusted entry points. Hence, the key effectivity period of these
keys can and should be made much longer. Although, given a long
enough key, the Key Usage Time can be on the order of years we
suggest planning for a key effectivity of the order of a few months
so that a key rollover remains an operational routine.
3.1.2 KSKs for high level zones
Higher level zones are generally more sensitive than lower level
zones. Anyone controlling or breaking the security of a zone thereby
obtains authority over all of its sub domains (except in the case of
resolvers that have locally configured the public key of a sub
domain). Therefore, extra care should be taken with high level zones
and strong keys used.
The root zone is the most critical of all zones. Someone controlling
or compromising the security of the root zone would control the
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entire DNS name space of all resolvers using that root zone (except
in the case of resolvers that have locally configured the public key
of a sub domain). Therefore, the utmost care must be taken in the
securing of the root zone. The strongest and most carefully handled
keys should be used. The root zone private key should always be kept
off line.
Many resolvers will start at a root server for their access to and
authentication of DNS data. Securely updating the trust anchors in
an enormous population of resolvers around the world will be
extremely difficult.
3.2 Randomness
Careful generation of all keys is a sometimes overlooked but
absolutely essential element in any cryptographically secure system.
The strongest algorithms used with the longest keys are still of no
use if an adversary can guess enough to lower the size of the likely
key space so that it can be exhaustively searched. Technical
suggestions for the generation of random keys will be found in
RFC1750 [3]. One should carefully assess if the random number
generator used during key generation adheres to these suggestions.
Keys with a long effectivity period are particularly sensitive as
they will represent a more valuable target and be subject to attack
for a longer time than short period keys. It is strongly recommended
that long term key generation occur off-line in a manner isolated
from the network via an air gap or, at a minimum, high level secure
hardware.
3.3 Key Effectivity Period
For various reasons keys in DNSSEC need to be changed once in a
while. The longer a key is in use, the greater the probability that
it will have been compromised through carelessness, accident,
espionage, or cryptanalysis. Furthermore when key rollovers are too
rare an event, they will not become part of the operational habit and
there is risk that nobody on-site will remember the procedure for
rollover when the need is there.
For Key Signing Keys a reasonable key effectivity period is 13
months, with the intent to replace them after 12 months. An intended
key effectivity period of a month is reasonable for Zone Signing
Keys.
Using these recommendations will lead to rollovers occurring
frequently enough to become part of 'operational habits'; the
procedure does not have to be reinvented every time a key is
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replaced.
Key effectivity periods can be made very short, as in the order of a
few minutes. But when replacing keys one has to take the
considerations from Section 4.1 and Section 4.2 into account.
3.4 Key Algorithm
There are currently three different types of algorithms that can be
used in DNSSEC: RSA, DSA and elliptic curve cryptography. The latter
is fairly new and still needs to be standardized for usage in DNSSEC.
RSA has been developed in an open and transparent manner. As the
patent on RSA expired in 2000, its use is now also free.
DSA has been developed by NIST. The creation of signatures is
roughly done at the same speed as with RSA, but is 10 to 40 times as
slow for verification [11].
We suggest the use of RSA/SHA-1 as the preferred algorithm for the
key. The current known attacks on RSA can be defeated by making your
key longer. As the MD5 hashing algorithm is showing (theoretical)
cracks, we recommend the usage of SHA1.
In 2005 some discoveries were made that SHA-1 also has some
weaknesses. Currently SHA-1 is strong enough for DNSSEC. It is
expected that a new hashing algorithm is rolled out, before any
attack becomes practical.
3.5 Key Sizes
When choosing key sizes, zone administrators will need to take into
account how long a key will be used and how much data will be signed
during the key publication period. It is hard to give precise
recommendations but Lenstra and Verheul [10] supplied the following
table with lower bound estimates for cryptographic key sizes. Their
recommendations are based on a set of explicitly formulated parameter
settings, combined with existing data points about cryptographic
systems. For details we refer to the original paper.
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Year RSA Key Sizes Year RSA Key Sizes
2000 952 2015 1613
2001 990 2016 1664
2002 1028 2017 1717
2003 1068 2018 1771
2004 1108 2019 1825
2005 1149 2020 1881
2006 1191 2021 1937
2007 1235 2022 1995
2008 1279 2023 2054
2009 1323 2024 2113
2026 2236 2025 2174
2010 1369 2027 2299
2011 1416 2028 2362
2012 1464 2029 2427
2013 1513
2014 1562
For example, should you wish your key to last three years from 2003,
check the RSA key size values for 2006 in this table. In this case
it should be at least 1191 bits.
Please keep in mind that nobody can see into the future, and that
these key lengths are only provided here as a guide.
When determining a key size one should take into account that a large
key will be slower during generation and verification. For RSA,
verification, the most common operation, will vary roughly with the
square of the key size; signing will vary with the cube of the key
size length; and key generation will vary with the fourth power of
the modulus length. Besides larger keys will increase the sizes of
the RRSIG and DNSKEY records and will therefore increase the chance
of DNS UDP packet overflow. Also see Section 3.1.1 for a discussion
of how keys serving different roles (ZSK v. KSK) may need different
key strengths.
3.6 Private Key Storage
It is recommended that, where possible, zone private keys and the
zone file master copy be kept and used in off-line, non-network
connected, physically secure machines only. Periodically an
application can be run to add authentication to a zone by adding
RRSIG and NSEC RRs. Then the augmented file can be transferred,
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perhaps by sneaker-net, to the networked zone primary server machine.
The ideal situation is to have a one way information flow to the
network to avoid the possibility of tampering from the network.
Keeping the zone master file on-line on the network and simply
cycling it through an off-line signer does not do this. The on-line
version could still be tampered with if the host it resides on is
compromised. For maximum security, the master copy of the zone file
should be off net and should not be updated based on an unsecured
network mediated communication.
In general keeping a zone-file off-line will not be practical and the
machines on which zone files are maintained will be connected to a
network. Operators are advised to take security measures to shield
unauthorized access to the master copy.
For dynamically updated secured zones [5] both the master copy and
the private key that is used to update signatures on updated RRs will
need to be on line.
4. Signature generation, Key Rollover and Related Policies
4.1 Time in DNSSEC
Without DNSSEC all times in DNS are relative. The SOA RR's refresh,
retry and expiration timers are counters that are used to determine
the time elapsed after a slave server synchronized (or tried to
synchronize) with a master server. The Time to Live (TTL) value and
the SOA RR minimum TTL parameter [6] are used to determine how long a
forwarder should cache data after it has been fetched from an
authoritative server. By using a signature validity period, DNSSEC
introduces the notion of an absolute time in the DNS. Signatures in
DNSSEC have an expiration date after which the signature is marked as
invalid and the signed data is to be considered Bogus.
4.1.1 Time Considerations
Because of the expiration of signatures, one should consider the
following:
o We suggest the Maximum Zone TTL of your zone data to be a fraction
of your signature validity period.
If the TTL would be of similar order as the signature validity
period, then all RRsets fetched during the validity period
would be cached until the signature expiration time. Section
7.1 of [2] suggests that "the resolver may use the time
remaining before expiration of the signature validity period of
a signed RRset as an upper bound for the TTL". As a result
query load on authoritative servers would peak at signature
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expiration time, as this is also the time at which records
simultaneously expire from caches.
To avoid query load peaks we suggest the TTL on all the RRs in
your zone to be at least a few times smaller than your
signature validity period.
o We suggest the signature publication period to be at least one
maximum TTL smaller than the signature validity period.
Resigning a zone shortly before the end of the signature
validity period may cause simultaneous expiration of data from
caches. This in turn may lead to peaks in the load on
authoritative servers.
o We suggest the minimum zone TTL to be long enough to both fetch
and verify all the RRs in the authentication chain. A low TTL
could cause two problems:
1. During validation, some data may expire before the
validation is complete. The validator should be able to keep
all data, until is completed. This applies to all RRs needed
to complete the chain of trust: DSs, DNSKEYs, RRSIGs, and the
final answers i.e. the RR set that is returned for the initial
query.
2. Frequent verification causes load on recursive nameservers.
Data at delegation points, DSs, DNSKEYs and RRSIGs benefit from
caching. The TTL on those should be relatively long.
o Slave servers will need to be able to fetch newly signed zones
well before the RRSIGs in the zone served by the slave server pass
their signature expiration time.
When a slave server is out of sync with its master and data in
a zone is signed by expired signatures it may be better for the
slave server not to give out any answer.
Normally a slave server that is not able to contact a master
server for an extended period will expire a zone. When that
happens the zone will not respond on queries. The time of
expiration is set in the SOA record and is relative to the last
successful refresh between the master and the slave server.
There exists no coupling between the signature expiration of
RRSIGs in the zone and the expire parameter in the SOA.
If the server serves a DNSSEC zone than it may well happen that
the signatures expire well before the SOA expiration timer
counts down to zero. It is not possible to completely prevent
this from happening by tweaking the SOA parameters.
However, the effects can be minimized where the SOA expiration
time is equal or smaller than the signature validity period.
The consequence of an authoritative server not being able to
update a zone, whilst that zone includes expired signatures, is
that non-secure resolvers will continue to be able to resolve
data served by the particular slave servers while security
aware resolvers will experience problems because of answers
being marked as Bogus.
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We suggest the SOA expiration timer being approximately one
third or one fourth of the signature validity period. It will
allow problems with transfers from the master server to be
noticed before the actual signature time out.
We also suggest that operators of nameservers that supply
secondary services develop 'watch dogs' to spot upcoming
signature expirations in zones they slave, and take appropriate
action.
When determining the value for the expiration parameter one has
to take the following into account: What are the chances that
all my secondary zones expire; How quickly can I reach an
administrator of secondary servers to load a valid zone? All
these arguments are not DNSSEC specific but may influence the
choice of your signature validity intervals.
4.2 Key Rollovers
A DNSSEC key cannot be used forever (see Section 3.3). So key
rollovers -- or supercessions, as they are sometimes called -- are a
fact of life when using DNSSEC. Zone administrators who are in the
process of rolling their keys have to take into account that data
published in previous versions of their zone still lives in caches.
When deploying DNSSEC, this becomes an important consideration;
ignoring data that may be in caches may lead to loss of service for
clients.
The most pressing example of this is when zone material signed with
an old key is being validated by a resolver which does not have the
old zone key cached. If the old key is no longer present in the
current zone, this validation fails, marking the data Bogus.
Alternatively, an attempt could be made to validate data which is
signed with a new key against an old key that lives in a local cache,
also resulting in data being marked Bogus.
4.2.1 Zone-signing Key Rollovers
For zone-signing key rollovers there are two ways to make sure that
during the rollover data still cached can be verified with the new
key sets or newly generated signatures can be verified with the keys
still in caches. One schema, described in Section 4.2.1.2, uses
double signatures; the other uses key pre-publication
(Section 4.2.1.1). The pros, cons and recommendations are described
in Section 4.2.1.3.
4.2.1.1 Pre-publish key set Rollover
This section shows how to perform a ZSK rollover without the need to
sign all the data in a zone twice - the so-called "pre-publish
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rollover".This method has advantages in the case of a key compromise.
If the old key is compromised, the new key has already been
distributed in the DNS. The zone administrator is then able to
quickly switch to the new key and remove the compromised key from the
zone. Another major advantage is that the zone size does not double,
as is the case with the double signature ZSK rollover. A small
"HOWTO" for this kind of rollover can be found in Appendix B.
normal pre-roll roll after
SOA0 SOA1 SOA2 SOA3
RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2) RRSIG11(SOA3)
DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1
DNSKEY10 DNSKEY10 DNSKEY10 DNSKEY11
DNSKEY11 DNSKEY11
RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG1(DNSKEY) RRSIG1 (DNSKEY)
RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY)
normal: Version 0 of the zone: DNSKEY 1 is the key-signing key.
DNSKEY 10 is used to sign all the data of the zone, the zone-
signing key.
pre-roll: DNSKEY 11 is introduced into the key set. Note that no
signatures are generated with this key yet, but this does not
secure against brute force attacks on the public key. The minimum
duration of this pre-roll phase is the time it takes for the data
to propagate to the authoritative servers plus TTL value of the
key set. This equates to two times the Maximum Zone TTL.
roll: At the rollover stage (SOA serial 2) DNSKEY 11 is used to sign
the data in the zone exclusively (i.e. all the signatures from
DNSKEY 10 are removed from the zone). DNSKEY 10 remains published
in the key set. This way data that was loaded into caches from
version 1 of the zone can still be verified with key sets fetched
from version 2 of the zone.
The minimum time that the key set including DNSKEY 10 is to be
published is the time that it takes for zone data from the
previous version of the zone to expire from old caches i.e. the
time it takes for this zone to propagate to all authoritative
servers plus the Maximum Zone TTL value of any of the data in the
previous version of the zone.
after: DNSKEY 10 is removed from the zone. The key set, now only
containing DNSKEY 1 and DNSKEY 11 is resigned with the DNSKEY 1.
The above scheme can be simplified by always publishing the "future"
key immediately after the rollover. The scheme would look as follows
(we show two rollovers); the future key is introduced in "after" as
DNSKEY 12 and again a newer one, numbered 13, in "2nd after":
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normal roll after
SOA0 SOA2 SOA3
RRSIG10(SOA0) RRSIG11(SOA2) RRSIG11(SOA3)
DNSKEY1 DNSKEY1 DNSKEY1
DNSKEY10 DNSKEY10 DNSKEY11
DNSKEY11 DNSKEY11 DNSKEY12
RRSIG1(DNSKEY) RRSIG1 (DNSKEY) RRSIG1(DNSKEY)
RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY)
2nd roll 2nd after
SOA4 SOA5
RRSIG12(SOA4) RRSIG12(SOA5)
DNSKEY1 DNSKEY1
DNSKEY11 DNSKEY12
DNSKEY12 DNSKEY13
RRSIG1(DNSKEY) RRSIG1(DNSKEY)
RRSIG12(DNSKEY) RRSIG12(DNSKEY)
Note that the key introduced after the rollover is not used for
production yet; the private key can thus be stored in a physically
secure manner and does not need to be 'fetched' every time a zone
needs to be signed.
4.2.1.2 Double Signature Zone-signing Key Rollover
This section shows how to perform a ZSK key rollover using the double
zone data signature scheme, aptly named "double sig rollover".
During the rollover stage the new version of the zone file will need
to propagate to all authoritative servers and the data that exists in
(distant) caches will need to expire, requiring at least the maximum
Zone TTL.
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normal roll after
SOA0 SOA1 SOA2
RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2)
RRSIG11(SOA1)
DNSKEY1 DNSKEY1 DNSKEY1
DNSKEY10 DNSKEY10 DNSKEY11
DNSKEY11
RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY)
RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY)
RRSIG11(DNSKEY)
normal: Version 0 of the zone: DNSKEY 1 is the key-signing key.
DNSKEY 10 is used to sign all the data of the zone, the zone-
signing key.
roll: At the rollover stage (SOA serial 1) DNSKEY 11 is introduced
into the key set and all the data in the zone is signed with
DNSKEY 10 and DNSKEY 11. The rollover period will need to exist
until all data from version 0 of the zone has expired from remote
caches. This will take at least the maximum Zone TTL of version 0
of the zone.
after: DNSKEY 10 is removed from the zone. All the signatures from
DNSKEY 10 are removed from the zone. The key set, now only
containing DNSKEY 11, is resigned with DNSKEY 1.
At every instance, RRSIGs from the previous version of the zone can
be verified with the DNSKEY RRset from the current version and the
other way around. The data from the current version can be verified
with the data from the previous version of the zone. The duration of
the rollover phase and the period between rollovers should be at
least the "Maximum Zone TTL".
Making sure that the rollover phase lasts until the signature
expiration time of the data in version 0 of the zone is recommended.
This way all caches are cleared of the old signatures. However, this
date could be considerably longer than the Maximum Zone TTL, making
the rollover a lengthy procedure.
Note that in this example we assumed that the zone was not modified
during the rollover. New data can be introduced in the zone as long
as it is signed with both keys.
4.2.1.3 Pros and Cons of the Schemes
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Pre-publish-key set rollover: This rollover does not involve signing
the zone data twice. Instead, before the actual rollover, the new
key is published in the key set and thus available for
cryptanalysis attacks. A small disadvantage is that this process
requires four steps. Also the pre-publish scheme involves more
parental work when used for KSK rollovers as explained in
Section 4.2.
Double signature rollover: The drawback of this signing scheme is
that during the rollover the number of signatures in your zone
doubles, this may be prohibitive if you have very big zones. An
advantage is that it only requires three steps.
4.2.2 Key-signing Key Rollovers
For the rollover of a key-signing key the same considerations as for
the rollover of a zone-signing key apply. However we can use a
double signature scheme to guarantee that old data (only the apex key
set) in caches can be verified with a new key set and vice versa.
Since only the key set is signed with a KSK, zone size considerations
do not apply.
normal roll after
SOA0 SOA1 SOA2
RRSIG10(SOA0) RRSIG10(SOA1) RRSIG10(SOA2)
DNSKEY1 DNSKEY1 DNSKEY2
DNSKEY2
DNSKEY10 DNSKEY10 DNSKEY10
RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG2(DNSKEY)
RRSIG2 (DNSKEY)
RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY)
normal: Version 0 of the zone. The parental DS points to DNSKEY1.
Before the rollover starts the child will have to verify what the
TTL is of the DS RR that points to DNSKEY1 - it is needed during
the rollover and we refer to the value as TTL_DS.
roll: During the rollover phase the zone administrator generates a
second KSK, DNSKEY2. The key is provided to the parent and the
child will have to wait until a new DS RR has been generated that
points to DNSKEY2. After that DS RR has been published on all
servers authoritative for the parent's zone, the zone
administrator has to wait at least TTL_DS to make sure that the
old DS RR has expired from caches.
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after: DNSKEY1 has been removed.
The scenario above puts the responsibility for maintaining a valid
chain of trust with the child. It also is based on the premises that
the parent only has one DS RR (per algorithm) per zone. An
alternative mechanism has been considered. Using an established
trust relation, the interaction can be performed in-band, and the
removal of the keys by the child can possibly be signaled by the
parent. In this mechanism there are periods where there are two DS
RRs at the parent. Since at the moment of writing the protocol for
this interaction has not been developed further discussion is out of
scope for this document.
4.2.3 Difference Between ZSK and KSK Rollovers
Note that KSK rollovers and ZSK rollovers are different. A zone-key
rollover can be handled in two different ways: pre-publish (Section
Section 4.2.1.1) and double signature (Section Section 4.2.1.2).
As the KSK is used to validate the key set and because the KSK is not
changed during a ZSK rollover, a cache is able to validate the new
key set of the zone. The pre-publish method would work for a KSK
rollover. The record that are to be pre-published are the parental
DS RRs.
The pre-publish method has some drawbacks. We first describe the
rollover scheme and then indicate these drawbacks.
normal pre-roll roll after
Parent:
SOA0 SOA1 SOA2 SOA3
RRSIGpar(SOA0) RRSIGpar(SOA1) RRSIGpar(SOA2) RRSIGpar(SOA3)
DS1 DS1 DS1 DS2
DS2 DS2
RRSIGpar(DS) RRSIGpar(DS) RRSIGpar(DS) RRSIGpar(DS)
Child:
SOA0 SOA0 SOA1 SOA1
RRSIG10(SOA0) RRSIG10(SOA0) RRSIG10(SOA1) RRSIG10(SOA1)
DNSKEY1 DNSKEY1 DNSKEY2 DNSKEY2
DNSKEY10 DNSKEY10 DNSKEY10 DNSKEY10
RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG2(DNSKEY) RRSIG2 (DNSKEY)
RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY)
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When the child zone wants to roll it notifies the parent during the
pre-roll phase and submits the new key to the parent. The parent
publishes DS1 and DS2, pointing to DNSKEY1 and DNSKEY2 respectively.
During the rollover, which can take place as soon as the new DS set
propagated through the DNS, the child replaces DNSKEY1 with DNSKEY2.
Immediately after that it can notify the parent that the old DS
record can be deleted.
The drawbacks of these scheme are that during the pre-roll phase the
parent cannot verify the match between the DS RR and DNSKEY2 using
the DNS. Besides, we introduce a "security lame" DS record
Section 4.4.3. Finally the child-parent interaction consists of two
steps. The "double signature" method only needs one interaction.
4.2.4 Automated Key Rollovers
As keys must be renewed periodically, there is some motivation to
automate the rollover process. Consider that:
o ZSK rollovers are easy to automate as only the local zone is
involved.
o A KSK rollover needs interaction between the parent and child.
Data exchange is needed to provide the new keys to the parent,
consequently, this data must be authenticated and integrity must
be guaranteed in order to avoid attacks on the rollover.
o All time and TTL considerations presented in Section 4.2 apply to
an automated rollover.
4.3 Planning for Emergency Key Rollover
This section deals with preparation for a possible key compromise.
Our advice is to have a documented procedure ready for when a key
compromise is suspected or confirmed.
When the private material of one of your keys is compromised it can
be used for as long as a valid authentication chain exists. An
authentication chain remains intact for:
o as long as a signature over the compromised key in the
authentication chain is valid,
o as long as a parental DS RR (and signature) points to the
compromised key,
o as long as the key is anchored in a resolver and is used as a
starting point for validation. (This is generally the hardest to
update.)
While an authentication chain to your compromised key exists, your
name-space is vulnerable to abuse by anyone who has obtained
illegitimate possession of the key.Zone operators have to make a
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trade off if the abuse of the compromised key is worse than having
data in caches that cannot be validated. If the zone operator
chooses to break the authentication chain to the compromised key,
data in caches signed with this key cannot be validated. However, if
the zone administrator chooses to take the path of a regular roll-
over, the malicious key holder can spoof data so that it appears to
be valid. Note that this kind of attack is more likely to occur in a
localized part of the network topology i.e. downstream from where the
spoof takes place.
4.3.1 KSK Compromise
When the KSK has been compromised the parent must be notified as soon
as possible using secure means. The key set of the zone should be
resigned as soon as possible. Care must be taken to not break the
authentication chain. The local zone can only be resigned with the
new KSK after the parent's zone has created and reloaded its zone
with the DS created from the new KSK. Before this update takes place
it would be best to drop the security status of a zone all together:
the parent removes the DS of the child at the next zone update.
After that the child can be made secure again.
An additional danger of a key compromise is that the compromised key
can be used to facilitate a legitimate DNSKEY/DS and/or nameserver
rollover at the parent. When that happens the domain can be in
dispute. An authenticated out of band and secure notify mechanism to
contact a parent is needed in this case.
4.3.2 ZSK Compromise
Primarily because there is no parental interaction required when a
ZSK is compromised, the situation is less severe than with with a KSK
compromise. The zone must still be resigned with a new ZSK as soon
as possible. As this is a local operation and requires no
communication between the parent and child this can be achieved
fairly quickly. However, one has to take into account that just as
with a normal rollover the immediate disappearance from the old
compromised key may lead to verification problems. The pre-
publication scheme as discussed above minimizes such problems.
4.3.3 Compromises of Keys Anchored in Resolvers
A key can also be pre-configured in resolvers. For instance, if
DNSSEC is successfully deployed the root key may be pre-configured in
most security aware resolvers.
If trust-anchor keys are compromised, the resolvers using these keys
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should be notified of this fact. Zone administrators may consider
setting up a mailing list to communicate the fact that a SEP key is
about to be rolled over. This communication will of course need to
be authenticated e.g. by using digital signatures.
End-users faced with the task of updating an anchored key should
always validate the new key. New keys should be authenticated out of
the DNS, for example, looking them up on an SSL secured announcement
website.
4.4 Parental Policies
4.4.1 Initial Key Exchanges and Parental Policies Considerations
The initial key exchange is always subject to the policies set by the
parent (or its registry). When designing a key exchange policy one
should take into account that the authentication and authorization
mechanisms used during a key exchange should be as strong as the
authentication and authorization mechanisms used for the exchange of
delegation information between parent and child. I.e. there is no
implicit need in DNSSEC to make the authentication process stronger
than it was in DNS.
Using the DNS itself as the source for the actual DNSKEY material,
with an off-band check on the validity of the DNSKEY, has the benefit
that it reduces the chances of user error. A parental DNSKEY
download tool can make use of the SEP bit [1] to select the proper
key from a DNSSEC key set; thereby reducing the chance that the wrong
DNSKEY is sent. It can validate the self-signature over a key;
thereby verifying the ownership of the private key material.
Fetching the DNSKEY from the DNS ensures that the chain of trust
remains intact once the parent publishes the DS RR indicating the
child is secure.
Note: the off-band verification is still needed when the key-material
is fetched via the DNS. The parent can never be sure whether the
DNSKEY RRs have been spoofed or not.
4.4.2 Storing Keys or Hashes?
When designing a registry system one should consider which of the
DNSKEYs and/or the corresponding DSs to store. Since a child zone
might wish to have a DS published using a message digest algorithm
not yet understood by the registry, the registry can't count on being
able to generate the DS record from a raw DNSKEY. Thus, we recommend
that registry system at least support storing DS records.
It may also be useful to store DNSKEYs, since having them may help
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during troubleshooting and, so long as the child's chosen message
digest is supported, the overhead of generating DS records from them
is minimal. Having an out-of-band mechanism, such as a Whois
database, to find out which keys are used to generate DS Resource
Records for specific owners and/or zones may also help with
troubleshooting.
The storage considerations also relate the design of the customer
interface and the method by which data is transfered between
registrant and registry; Will the child zone owner be able to upload
DS RRs with unknown hash algorithms or does the interface only allows
DNSKEYs? In the registry-registrar model one can use the DNSSEC EPP
protocol extensions [9] which allows transfer of DS RRs and
optionally DNSKEY RRs.
4.4.3 Security Lameness
Security Lameness is defined as what happens when a parent has a DS
RR pointing to a non-existing DNSKEY RR. During key exchange a
parent should make sure that the child's key is actually configured
in the DNS before publishing a DS RR in its zone. Failure to do so
could cause the child's zone being marked as Bogus.
Child zones should be very careful removing DNSKEY material,
specifically SEP keys, for which a DS RR exists.
Once a zone is "security lame", a fix (e.g. removing a DS RR) will
take time to propagate through the DNS.
4.4.4 DS Signature Validity Period
Since the DS can be replayed as long as it has a valid signature, a
short signature validity period over the DS minimizes the time a
child is vulnerable in the case of a compromise of the child's
KSK(s). A signature validity period that is too short introduces the
possibility that a zone is marked Bogus in case of a configuration
error in the signer. There may not be enough time to fix the
problems before signatures expire. Something as mundane as operator
unavailability during weekends shows the need for DS signature
validity periods longer than 2 days. We recommend the minimum for a
DS signature validity period of a few days.
The maximum signature validity period of the DS record depends on how
long child zones are willing to be vulnerable after a key compromise.
Other considerations, such as how often the zone is (re)signed can
also be taken into account.
We consider a signature validity period of around one week to be a
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good compromise between the operational constraints of the parent and
minimizing damage for the child.
In addition to the signature validity period, which sets a lower
bound on the amount of times the zone owner will need to sign the
zone data and which sets an upper bound to the time a child is
vulnerable after key compromise, there is the TTL value on the DS
RRs. By lowering the TTL, the authoritative servers will see more
queries, on the other hand a low TTL increases the speed with which
new DS RRs propagate through the DNS. As argued in Section 4.1.1,
the TTL should be a fraction of the signature validity period.
5. Security Considerations
DNSSEC adds data integrity to the DNS. This document tries to assess
the operational considerations to maintain a stable and secure DNSSEC
service. Not taking into account the 'data propagation' properties
in the DNS will cause validation failures and may make secured zones
unavailable to security aware resolvers.
6. Acknowledgments
Most of the ideas in this draft were the result of collective efforts
during workshops, discussions and try outs.
At the risk of forgetting individuals who were the original
contributors of the ideas we would like to acknowledge people who
were actively involved in the compilation of this document. In
random order: Rip Loomis, Olafur Gudmundsson, Wesley Griffin, Michael
Richardson, Scott Rose, Rick van Rein, Tim McGinnis, Gilles Guette
Olivier Courtay, Sam Weiler, Jelte Jansen and Niall O'Reilly.
Some material in this document has been shamelessly copied from
RFC2541 [7] by Donald Eastlake.
Mike StJohns designed the key exchange between parent and child
mentioned in the last paragraph of Section 4.2.2
Section 4.2.4 was supplied by G. Guette and O. Courtay.
Emma Bretherick, Adrian Bedford and Lindy Foster corrected many of
the spelling and style issues.
Kolkman and Gieben take the blame for introducing all miscakes(SIC).
7. References
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7.1 Normative References
[1] Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name System KEY
(DNSKEY) Resource Record (RR) Secure Entry Point (SEP) Flag",
RFC 3757, May 2004.
[2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"DNS Security Introduction and Requirements", RFC 4033,
March 2005.
7.2 Informative References
[3] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[5] Eastlake, D., "Secure Domain Name System Dynamic Update",
RFC 2137, April 1997.
[6] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)",
RFC 2308, March 1998.
[7] Eastlake, D., "DNS Security Operational Considerations",
RFC 2541, March 1999.
[8] Gudmundsson, O., "Delegation Signer (DS) Resource Record (RR)",
RFC 3658, December 2003.
[9] Hollenbeck, S., "Domain Name System (DNS) Security Extensions
Mapping for the Extensible Provisioning Protocol (EPP)",
draft-hollenbeck-epp-secdns-07 (work in progress), March 2005.
[10] Lenstra, A. and E. Verheul, "Selecting Cryptographic Key
Sizes", The Journal of Cryptology 14 (255-293), 2001.
[11] Schneier, B., "Applied Cryptography: Protocols, Algorithms, and
Source Code in C", 1996.
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Authors' Addresses
Olaf M. Kolkman
RIPE NCC
Singel 256
Amsterdam 1016 AB
The Netherlands
Phone: +31 20 535 4444
Email: olaf@ripe.net
URI: http://www.ripe.net/
Miek Gieben
NLnet Labs
Kruislaan 419
Amsterdam 1098 VA
The Netherlands
Email: miek@nlnetlabs.nl
URI: http://www.nlnetlabs.nl
Appendix A. Terminology
In this document there is some jargon used that is defined in other
documents. In most cases we have not copied the text from the
documents defining the terms but given a more elaborate explanation
of the meaning. Note that these explanations should not be seen as
authoritative.
Anchored Key: A DNSKEY configured in resolvers around the globe.
This key is hard to update, hence the term anchored.
Bogus: Also see Section 5 of [2]. An RRset in DNSSEC is marked
"Bogus" when a signature of a RRset does not validate against a
DNSKEY.
Key-Signing Key or KSK: A Key-Signing Key (KSK) is a key that is used
exclusively for signing the apex key set. The fact that a key is
a KSK is only relevant to the signing tool.
Private and Public Keys: DNSSEC secures the DNS through the use of
public key cryptography. Public key cryptography is based on the
existence of two keys, a public key and a private key. The public
keys are published in the DNS by use of the DNSKEY Resource Record
(DNSKEY RR). Private keys should remain private.
Key Rollover: A key rollover (also called key supercession in some
environments) is the act of replacing one key pair by another at
the end of a key effectivity period.
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Secure Entry Point key or SEP Key: A KSK that has a parental DS
record pointing to it. Note: this is not enforced in the
protocol. A SEP Key with no parental DS is security lame.
Singing the Zone File: The term used for the event where an
administrator joyfully signs its zone file while producing melodic
sound patterns.
Signer: The system that has access to the private key material and
signs the Resource Record sets in a zone. A signer may be
configured to sign only parts of the zone e.g. only those RRsets
for which existing signatures are about to expire.
Zone-Signing Key or ZSK: A Zone Signing Key (ZSK) is a key that is
used for signing all data in a zone. The fact that a key is a ZSK
is only relevant to the signing tool.
Zone Administrator: The 'role' that is responsible for signing a zone
and publishing it on the primary authoritative server.
Appendix B. Zone-signing Key Rollover Howto
Using the pre-published signature scheme and the most conservative
method to assure oneself that data does not live in caches here
follows the "HOWTO".
Step 0: The preparation: Create two keys and publish both in your key
set. Mark one of the keys as "active" and the other as
"published". Use the "active" key for signing your zone data.
Store the private part of the "published" key, preferably off-
line.
The protocol does not provide for attributes to mark a key as
active or published. This is something you have to do on your
own, through the use of a notebook or key management tool.
Step 1: Determine expiration: At the beginning of the rollover make a
note of the highest expiration time of signatures in your zone
file created with the current key marked as "active".
Wait until the expiration time marked in Step 1 has passed
Step 2: Then start using the key that was marked as "published" to
sign your data i.e. mark it as "active". Stop using the key that
was marked as "active", mark it as "rolled".
Step 3: It is safe to engage in a new rollover (Step 1) after at
least one "signature validity period".
Appendix C. Typographic Conventions
The following typographic conventions are used in this document:
Key notation: A key is denoted by KEYx, where x is a number, x could
be thought of as the key id.
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RRset notations: RRs are only denoted by the type. All other
information - owner, class, rdata and TTL - is left out. Thus:
"example.com 3600 IN A 192.168.1.1" is reduced to "A". RRsets are
a list of RRs. A example of this would be: "A1,A2", specifying
the RRset containing two "A" records. This could again be
abbreviated to just "A".
Signature notation: Signatures are denoted as RRSIGx(RRset), which
means that RRset is signed with DNSKEYx.
Zone representation: Using the above notation we have simplified the
representation of a signed zone by leaving out all unnecessary
details such as the names and by representing all data by "SOAx"
SOA representation: SOA's are represented as SOAx, where x is the
serial number.
Using this notation the following zone:
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example.net. 600 IN SOA ns.example.net. bert.example.net. (
10 ; serial
450 ; refresh (7 minutes 30 seconds)
600 ; retry (10 minutes)
345600 ; expire (4 days)
300 ; minimum (5 minutes)
)
600 RRSIG SOA 5 2 600 20130522213204 (
20130422213204 14 example.net.
cmL62SI6iAX46xGNQAdQ... )
600 NS a.iana-servers.net.
600 NS b.iana-servers.net.
600 RRSIG NS 5 2 600 20130507213204 (
20130407213204 14 example.net.
SO5epiJei19AjXoUpFnQ ... )
3600 DNSKEY 256 3 5 (
EtRB9MP5/AvOuVO0I8XDxy0...
) ; key id = 14
3600 DNSKEY 256 3 5 (
gsPW/Yy19GzYIY+Gnr8HABU...
) ; key id = 15
3600 RRSIG DNSKEY 5 2 3600 20130522213204 (
20130422213204 14 example.net.
J4zCe8QX4tXVGjV4e1r9... )
3600 RRSIG DNSKEY 5 2 3600 20130522213204 (
20130422213204 15 example.net.
keVDCOpsSeDReyV6O... )
600 RRSIG NSEC 5 2 600 20130507213204 (
20130407213204 14 example.net.
obj3HEp1GjnmhRjX... )
a.example.net. 600 IN TXT "A label"
600 RRSIG TXT 5 3 600 20130507213204 (
20130407213204 14 example.net.
IkDMlRdYLmXH7QJnuF3v... )
600 NSEC b.example.com. TXT RRSIG NSEC
600 RRSIG NSEC 5 3 600 20130507213204 (
20130407213204 14 example.net.
bZMjoZ3bHjnEz0nIsPMM... )
...
is reduced to the following representation:
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SOA10
RRSIG14(SOA10)
DNSKEY14
DNSKEY15
RRSIG14(KEY)
RRSIG15(KEY)
The rest of the zone data has the same signature as the SOA record,
i.e a RRSIG created with DNSKEY 14.
Appendix D. Document Details and Changes
This section is to be removed by the RFC editor if and when the
document is published.
$Id: draft-ietf-dnsop-dnssec-operational-practices.xml,v 1.31.2.14
2005/03/21 15:51:41 dnssec Exp $
D.1 draft-ietf-dnsop-dnssec-operational-practices-00
Submission as working group document. This document is a modified
and updated version of draft-kolkman-dnssec-operational-practices-00.
D.2 draft-ietf-dnsop-dnssec-operational-practices-01
changed the definition of "Bogus" to reflect the one in the protocol
draft.
Bad to Bogus
Style and spelling corrections
KSK - SEP mapping made explicit.
Updates from Sam Weiler added
D.3 draft-ietf-dnsop-dnssec-operational-practices-02
Style and errors corrected.
Added Automatic rollover requirements from I-D.ietf-dnsop-key-
rollover-requirements.
D.4 draft-ietf-dnsop-dnssec-operational-practices-03
Added the definition of Key effectivity period and used that term
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instead of Key validity period.
Modified the order of the sections, based on a suggestion by Rip
Loomis.
Included parts from RFC2541 [7]. Most of its ground was already
covered. This document obsoletes RFC2541 [7]. Section 3.1.2
deserves some review as it in contrast to RFC2541 does _not_ give
recomendations about root-zone keys.
added a paragraph to Section 4.4.4
D.5 draft-ietf-dnsop-dnssec-operational-practices-04
Somewhat more details added about the pre-publish KSK rollover. Also
moved that subsection down a bit.
Editorial and content nits that came in during wg last call were
fixed.
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