draft-ietf-dnsop-dnssec-operational-practices-08.txt   rfc4641.txt 
DNSOP O. Kolkman Network Working Group O. Kolkman
Internet-Draft R. Gieben Request for Comments: 4641 R. Gieben
Obsoletes: 2541 (if approved) NLnet Labs Obsoletes: 2541 NLnet Labs
Expires: September 7, 2006 March 6, 2006 Category: Informational September 2006
DNSSEC Operational Practices DNSSEC Operational Practices
draft-ietf-dnsop-dnssec-operational-practices-08.txt
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Abstract Abstract
This document describes a set of practices for operating the DNS with This document describes a set of practices for operating the DNS with
security extensions (DNSSEC). The target audience is zone security extensions (DNSSEC). The target audience is zone
administrators deploying DNSSEC. administrators deploying DNSSEC.
The document discusses operational aspects of using keys and The document discusses operational aspects of using keys and
signatures in the DNS. It discusses issues as key generation, key signatures in the DNS. It discusses issues of key generation, key
storage, signature generation, key rollover and related policies. storage, signature generation, key rollover, and related policies.
This document obsoletes RFC 2541, as it covers more operational This document obsoletes RFC 2541, as it covers more operational
ground and gives more up to date requirements with respect to key ground and gives more up-to-date requirements with respect to key
sizes and the new DNSSEC specification. sizes and the new DNSSEC specification.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction ....................................................3
1.1. The Use of the Term 'key' . . . . . . . . . . . . . . . . 4 1.1. The Use of the Term 'key' ..................................4
1.2. Time Definitions . . . . . . . . . . . . . . . . . . . . . 5 1.2. Time Definitions ...........................................4
2. Keeping the Chain of Trust Intact . . . . . . . . . . . . . . 5 2. Keeping the Chain of Trust Intact ...............................5
3. Keys Generation and Storage . . . . . . . . . . . . . . . . . 6 3. Keys Generation and Storage .....................................6
3.1. Zone and Key Signing Keys . . . . . . . . . . . . . . . . 6 3.1. Zone and Key Signing Keys ..................................6
3.1.1. Motivations for the KSK and ZSK Separation . . . . . . 7 3.1.1. Motivations for the KSK and ZSK Separation ..........6
3.1.2. KSKs for High Level Zones . . . . . . . . . . . . . . 8 3.1.2. KSKs for High-Level Zones ...........................7
3.2. Key Generation . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Key Generation .............................................8
3.3. Key Effectivity Period . . . . . . . . . . . . . . . . . . 9 3.3. Key Effectivity Period .....................................8
3.4. Key Algorithm . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Key Algorithm ..............................................9
3.5. Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . 10 3.5. Key Sizes ..................................................9
3.6. Private Key Storage . . . . . . . . . . . . . . . . . . . 12 3.6. Private Key Storage .......................................11
4. Signature generation, Key Rollover and Related Policies . . . 12 4. Signature Generation, Key Rollover, and Related Policies .......12
4.1. Time in DNSSEC . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Time in DNSSEC ............................................12
4.1.1. Time Considerations . . . . . . . . . . . . . . . . . 13 4.1.1. Time Considerations ................................12
4.2. Key Rollovers . . . . . . . . . . . . . . . . . . . . . . 14 4.2. Key Rollovers .............................................14
4.2.1. Zone Signing Key Rollovers . . . . . . . . . . . . . . 15 4.2.1. Zone Signing Key Rollovers .........................14
4.2.2. Key Signing Key Rollovers . . . . . . . . . . . . . . 19 4.2.1.1. Pre-Publish Key Rollover ..................15
4.2.3. Difference Between ZSK and KSK Rollovers . . . . . . . 20 4.2.1.2. Double Signature Zone Signing Key
4.2.4. Automated Key Rollovers . . . . . . . . . . . . . . . 21 Rollover ..................................17
4.3. Planning for Emergency Key Rollover . . . . . . . . . . . 22 4.2.1.3. Pros and Cons of the Schemes ..............18
4.3.1. KSK Compromise . . . . . . . . . . . . . . . . . . . . 22 4.2.2. Key Signing Key Rollovers ..........................18
4.3.2. ZSK Compromise . . . . . . . . . . . . . . . . . . . . 24 4.2.3. Difference Between ZSK and KSK Rollovers ...........20
4.3.3. Compromises of Keys Anchored in Resolvers . . . . . . 24 4.2.4. Automated Key Rollovers ............................21
4.4. Parental Policies . . . . . . . . . . . . . . . . . . . . 24 4.3. Planning for Emergency Key Rollover .......................21
4.3.1. KSK Compromise .....................................22
4.3.1.1. Keeping the Chain of Trust Intact .........22
4.3.1.2. Breaking the Chain of Trust ...............23
4.3.2. ZSK Compromise .....................................23
4.3.3. Compromises of Keys Anchored in Resolvers ..........24
4.4. Parental Policies .........................................24
4.4.1. Initial Key Exchanges and Parental Policies 4.4.1. Initial Key Exchanges and Parental Policies
Considerations . . . . . . . . . . . . . . . . . . . . 24 Considerations .....................................24
4.4.2. Storing Keys or Hashes? . . . . . . . . . . . . . . . 25 4.4.2. Storing Keys or Hashes? ............................25
4.4.3. Security Lameness . . . . . . . . . . . . . . . . . . 25 4.4.3. Security Lameness ..................................25
4.4.4. DS Signature Validity Period . . . . . . . . . . . . . 26 4.4.4. DS Signature Validity Period .......................26
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 5. Security Considerations ........................................26
6. Security Considerations . . . . . . . . . . . . . . . . . . . 27 6. Acknowledgments ................................................26
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27 7. References .....................................................27
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.1. Normative References ......................................27
8.1. Normative References . . . . . . . . . . . . . . . . . . . 27 7.2. Informative References ....................................28
8.2. Informative References . . . . . . . . . . . . . . . . . . 28 Appendix A. Terminology ...........................................30
Appendix A. Terminology . . . . . . . . . . . . . . . . . . . . . 29 Appendix B. Zone Signing Key Rollover How-To ......................31
Appendix B. Zone Signing Key Rollover Howto . . . . . . . . . . . 30 Appendix C. Typographic Conventions ...............................32
Appendix C. Typographic Conventions . . . . . . . . . . . . . . . 31
Appendix D. Document Details and Changes . . . . . . . . . . . . 33
D.1. draft-ietf-dnsop-dnssec-operational-practices-00 . . . . . 33
D.2. draft-ietf-dnsop-dnssec-operational-practices-01 . . . . . 33
D.3. draft-ietf-dnsop-dnssec-operational-practices-02 . . . . . 33
D.4. draft-ietf-dnsop-dnssec-operational-practices-03 . . . . . 33
D.5. draft-ietf-dnsop-dnssec-operational-practices-04 . . . . . 34
D.6. draft-ietf-dnsop-dnssec-operational-practices-05 . . . . . 34
D.7. draft-ietf-dnsop-dnssec-operational-practices-06 . . . . . 34
D.8. draft-ietf-dnsop-dnssec-operational-practices-07 . . . . . 34
D.9. draft-ietf-dnsop-dnssec-operational-practices-08 . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . . 36
1. Introduction 1. Introduction
This document describes how to run a DNSSEC (DNS SECure) enabled This document describes how to run a DNS Security (DNSSEC)-enabled
environment. It is intended for operators who have knowledge of the environment. It is intended for operators who have knowledge of the
DNS (see RFC 1034 [1] and RFC 1035 [2]) and want deploy DNSSEC. See DNS (see RFC 1034 [1] and RFC 1035 [2]) and want to deploy DNSSEC.
RFC 4033 [4] for an introduction into DNSSEC and RFC 4034 [5] for the See RFC 4033 [4] for an introduction to DNSSEC, RFC 4034 [5] for the
newly introduced Resource Records and finally RFC 4035 [6] for the newly introduced Resource Records (RRs), and RFC 4035 [6] for the
protocol changes. protocol changes.
During workshops and early operational deployment tests, operators During workshops and early operational deployment tests, operators
and system administrators have gained experience about operating the and system administrators have gained experience about operating the
DNS with security extensions (DNSSEC). This document translates DNS with security extensions (DNSSEC). This document translates
these experiences into a set of practices for zone administrators. these experiences into a set of practices for zone administrators.
At the time of writing, there exists very little experience with At the time of writing, there exists very little experience with
DNSSEC in production environments; this document should therefore DNSSEC in production environments; this document should therefore
explicitly not be seen as representing 'Best Current Practices'. explicitly not be seen as representing 'Best Current Practices'.
The procedures herein are focused on the maintenance of signed zones The procedures herein are focused on the maintenance of signed zones
(i.e. signing and publishing zones on authoritative servers). It is (i.e., signing and publishing zones on authoritative servers). It is
intended that maintenance of zones such as re-signing or key intended that maintenance of zones such as re-signing or key
rollovers be transparent to any verifying clients on the Internet. rollovers be transparent to any verifying clients on the Internet.
The structure of this document is as follows. In Section 2 we The structure of this document is as follows. In Section 2, we
discuss the importance of keeping the "chain of trust" intact. discuss the importance of keeping the "chain of trust" intact.
Aspects of key generation and storage of private keys are discussed 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 in Section 3; the focus in this section is mainly on the private part
of the key(s). Section 4 describes considerations concerning the of the key(s). Section 4 describes considerations concerning the
public part of the keys. Since these public keys appear in the DNS 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 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 discussed in Section 4.1. Section 4.2 and Section 4.3 deal with the
rollover, or supercession, of keys. Finally Section 4.4 discusses rollover, or supercession, of keys. Finally, Section 4.4 discusses
considerations on how parents deal with their children's public keys considerations on how parents deal with their children's public keys
in order to maintain chains of trust. in order to maintain chains of trust.
The typographic conventions used in this document are explained in The typographic conventions used in this document are explained in
Appendix C. Appendix C.
Since this is a document with operational suggestions and there are Since this is a document with operational suggestions and there are
no protocol specifications, the RFC 2119 [9] language does not apply. no protocol specifications, the RFC 2119 [7] language does not apply.
This document obsoletes RFC 2541 [12]. This document obsoletes RFC 2541 [12] to reflect the evolution of the
underlying DNSSEC protocol since then. Changes in the choice of
cryptographic algorithms, DNS record types and type names, and the
parent-child key and signature exchange demanded a major rewrite and
additional information and explanation.
1.1. The Use of the Term 'key' 1.1. The Use of the Term 'key'
It is assumed that the reader is familiar with the concept of It is assumed that the reader is familiar with the concept of
asymmetric keys on which DNSSEC is based (Public Key Cryptography asymmetric keys on which DNSSEC is based (public key cryptography
[18]). Therefore, this document will use the term 'key' rather [17]). Therefore, this document will use the term 'key' rather
loosely. Where it is written that 'a key is used to sign data' it is 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 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 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 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 in the DNSKEY Resource Record and that it is the public part that is
used in key exchanges. used in key exchanges.
1.2. Time Definitions 1.2. Time Definitions
In this document we will be using a number of time related terms. In this document, we will be using a number of time-related terms.
The following definitions apply: The following definitions apply:
o "Signature validity period"
The period that a signature is valid. It starts at the time o "Signature validity period" The period that a signature is valid.
specified in the signature inception field of the RRSIG RR and It starts at the time specified in the signature inception field
ends at the time specified in the expiration field of the RRSIG of the RRSIG RR and ends at the time specified in the expiration
RR. field of the RRSIG RR.
o "Signature publication period"
Time after which a signature (made with a specific key) is o "Signature publication period" Time after which a signature (made
replaced with a new signature (made with the same key). This with a specific key) is replaced with a new signature (made with
replacement takes place by publishing the relevant RRSIG in the the same key). This replacement takes place by publishing the
master zone file. relevant RRSIG in the master zone file. After one stops
After one stops publishing an RRSIG in a zone it may take a publishing an RRSIG in a zone, it may take a while before the
while before the RRSIG has expired from caches and has actually RRSIG has expired from caches and has actually been removed from
been removed from the DNS. the DNS.
o "Key effectivity period"
The period during which a key pair is expected to be effective. o "Key effectivity period" The period during which a key pair is
This period is defined as the time between the first inception expected to be effective. This period is defined as the time
time stamp and the last expiration date of any signature made between the first inception time stamp and the last expiration
with this key, regardless of any discontinuity in the use of date of any signature made with this key, regardless of any
the key. discontinuity in the use of the key. The key effectivity period
The key effectivity period can span multiple signature validity can span multiple signature validity periods.
periods.
o "Maximum/Minimum Zone Time to Live (TTL)" o "Maximum/Minimum Zone Time to Live (TTL)" The maximum or minimum
The maximum or minimum value of the TTLs from the complete set value of the TTLs from the complete set of RRs in a zone. Note
of RRs in a zone. Note that the minimum TTL is not the same as that the minimum TTL is not the same as the MINIMUM field in the
the MINIMUM field in the SOA RR. See [11] for more SOA RR. See [11] for more information.
information.
2. Keeping the Chain of Trust Intact 2. Keeping the Chain of Trust Intact
Maintaining a valid chain of trust is important because broken chains Maintaining a valid chain of trust is important because broken chains
of trust will result in data being marked as Bogus (as defined in [4] of trust will result in data being marked as Bogus (as defined in [4]
section 5), which may cause entire (sub)domains to become invisible Section 5), which may cause entire (sub)domains to become invisible
to verifying clients. The administrators of secured zones have to to verifying clients. The administrators of secured zones have to
realize that their zone is, to verifying clients, part of a chain of realize that their zone is, to verifying clients, part of a chain of
trust. trust.
As mentioned in the introduction, the procedures herein are intended As mentioned in the introduction, the procedures herein are intended
to ensure that maintenance of zones, such as re-signing or key to ensure that maintenance of zones, such as re-signing or key
rollovers, will be transparent to the verifying clients on the rollovers, will be transparent to the verifying clients on the
Internet. Internet.
Administrators of secured zones will have to keep in mind that data Administrators of secured zones will have to keep in mind that data
published on an authoritative primary server will not be immediately published on an authoritative primary server will not be immediately
seen by verifying clients; it may take some time for the data to be seen by verifying clients; it may take some time for the data to be
transferred to other secondary authoritative nameservers and clients transferred to other secondary authoritative nameservers and clients
may be fetching data from caching non-authoritative servers. In this may be fetching data from caching non-authoritative servers. In this
light it is good to note that the time for a zone transfer from light, note that the time for a zone transfer from master to slave is
master to slave is negligible when using NOTIFY [8] and IXFR [7], negligible when using NOTIFY [9] and incremental transfer (IXFR) [8].
increasing by reliance on AXFR, and more if you rely on the SOA It increases when full zone transfers (AXFR) are used in combination
timing parameters for zone refresh. with NOTIFY. It increases even more if you rely on full zone
transfers based on only the SOA timing parameters for refresh.
For the verifying clients it is important that data from secured For the verifying clients, it is important that data from secured
zones can be used to build chains of trust regardless of whether the zones can be used to build chains of trust regardless of whether the
data came directly from an authoritative server, a caching nameserver data came directly from an authoritative server, a caching
or some middle box. Only by carefully using the available timing nameserver, or some middle box. Only by carefully using the
parameters can a zone administrator assure that the data necessary available timing parameters can a zone administrator ensure that the
for verification can be obtained. data necessary for verification can be obtained.
The responsibility for maintaining the chain of trust is shared by The responsibility for maintaining the chain of trust is shared by
administrators of secured zones in the chain of trust. This is most 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 obvious in the case of a 'key compromise' when a trade-off between
maintaining a valid chain of trust and replacing the compromised keys maintaining a valid chain of trust and replacing the compromised keys
as soon as possible must be made. Then zone administrators will have as soon as possible must be made. Then zone administrators will have
to make a trade off, between keeping the chain of trust intact - to make a trade-off, between keeping the chain of trust intact --
thereby allowing for attacks with the compromised key - or to thereby allowing for attacks with the compromised key -- or
deliberately break the chain of trust and making secured sub domains deliberately breaking the chain of trust and making secured
invisible to security aware resolvers. Also see Section 4.3. subdomains invisible to security-aware resolvers. Also see Section
4.3.
3. Keys Generation and Storage 3. Keys Generation and Storage
This section describes a number of considerations with respect to the This section describes a number of considerations with respect to the
security of keys. It deals with the generation, effectivity period, security of keys. It deals with the generation, effectivity period,
size and storage of private keys. size, and storage of private keys.
3.1. Zone and Key Signing Keys 3.1. Zone and Key Signing Keys
The DNSSEC validation protocol does not distinguish between different The DNSSEC validation protocol does not distinguish between different
types of DNSKEYs. All DNSKEYs can be used during the validation. In types of DNSKEYs. All DNSKEYs can be used during the validation. In
practice operators use Key Signing and Zone Signing Keys and use the practice, operators use Key Signing and Zone Signing Keys and use the
so-called (Secure Entry Point) SEP [3] flag to distinguish between so-called Secure Entry Point (SEP) [3] flag to distinguish between
them during operations. The dynamics and considerations are them during operations. The dynamics and considerations are
discussed below. discussed below.
To make zone re-signing and key rollover procedures easier to To make zone re-signing and key rollover procedures easier to
implement, it is possible to use one or more keys as Key Signing Keys implement, it is possible to use one or more keys as Key Signing Keys
(KSK). These keys will only sign the apex DNSKEY RRSet in a zone. (KSKs). These keys will only sign the apex DNSKEY RRSet in a zone.
Other keys can be used to sign all the RRSets in a zone and are 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 referred to as Zone Signing Keys (ZSKs). In this document, we assume
that KSKs are the subset of keys that are used for key exchanges with that KSKs are the subset of keys that are used for key exchanges with
the parent and potentially for configuration as trusted anchors - the the parent and potentially for configuration as trusted anchors --
SEP keys. In this document we assume a one-to-one mapping between the SEP keys. In this document, we assume a one-to-one mapping
KSK and SEP keys and we assume the SEP flag to be set on all KSKs. between KSK and SEP keys and we assume the SEP flag to be set on all
KSKs.
3.1.1. Motivations for the KSK and ZSK Separation 3.1.1. Motivations for the KSK and ZSK Separation
Differentiating between the KSK and ZSK functions has several Differentiating between the KSK and ZSK functions has several
advantages: advantages:
o No parent/child interaction is required when ZSKs are updated. 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
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 material). This has little operational impact since it is only
used to sign a small fraction of the zone data. Also the KSK is used to sign a small fraction of the zone data. Also, the KSK is
only used to verify the zone's key set, not for other RRSets in only used to verify the zone's key set, not for other RRSets in
the zone. the zone.
o As the KSK is only used to sign a key set, which is most probably 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 updated less frequently than other data in the zone, it can be
stored separately from and in a safer location than the ZSK. stored separately from and in a safer location than the ZSK.
o A KSK can have a longer key effectivity period. o A KSK can have a longer key effectivity period.
For almost any method of key management and zone signing the KSK is 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 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 KSK, all the keys in the key set can be used as ZSKs. If a ZSK is
compromised, it can be simply dropped from the key set. The new key compromised, it can be simply dropped from the key set. The new key
set is then re-signed with the KSK. set is then re-signed with the KSK.
Given the assumption that for KSKs the SEP flag is set, the KSK can 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 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 RR. If the flag field is an odd number it is a KSK. If it is an
even number it is a ZSK. even number it is a ZSK.
The zone signing key can be used to sign all the data in a zone on a 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 regular basis. When a Zone Signing Key is to be rolled, no
interaction with the parent is needed. This allows for "Signature interaction with the parent is needed. This allows for signature
Validity Periods" on the order of days. validity periods on the order of days.
The key signing key is only to be used to sign the DNSKEY RRs in a 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 zone. If a Key Signing Key is to be rolled over, there will be
interactions with parties other than the zone administrator. These interactions with parties other than the zone administrator. These
can include the registry of the parent zone or administrators of can include the registry of the parent zone or administrators of
verifying resolvers that have the particular key configured as secure verifying resolvers that have the particular key configured as secure
entry points. Hence, the key effectivity period of these keys can entry points. Hence, the key effectivity period of these keys can
and should be made much longer. Although, given a long enough key, and should be made much longer. Although, given a long enough key,
the Key Effectivity Period can be on the order of years we suggest the key effectivity period can be on the order of years, we suggest
planning for a key effectivity of the order of a few months so that a planning for a key effectivity on the order of a few months so that a
key rollover remains an operational routine. key rollover remains an operational routine.
3.1.2. KSKs for High Level Zones 3.1.2. KSKs for High-Level Zones
Higher level zones are generally more sensitive than lower level Higher-level zones are generally more sensitive than lower-level
zones. Anyone controlling or breaking the security of a zone thereby zones. Anyone controlling or breaking the security of a zone thereby
obtains authority over all of its sub domains (except in the case of obtains authority over all of its sub domains (except in the case of
resolvers that have locally configured the public key of a sub resolvers that have locally configured the public key of a subdomain,
domain, in which case this, and only this, sub domain wouldn't be in which case this, and only this, subdomain wouldn't be affected by
affected by the compromise of the parent zone). Therefore, extra the compromise of the parent zone). Therefore, extra care should be
care should be taken with high level zones and strong keys should taken with high-level zones, and strong keys should be used.
used.
The root zone is the most critical of all zones. Someone controlling The root zone is the most critical of all zones. Someone controlling
or compromising the security of the root zone would control the or compromising the security of the root zone would control the
entire DNS name space of all resolvers using that root zone (except entire DNS namespace of all resolvers using that root zone (except in
in the case of resolvers that have locally configured the public key the case of resolvers that have locally configured the public key of
of a sub domain). Therefore, the utmost care must be taken in the a subdomain). Therefore, the utmost care must be taken in the
securing of the root zone. The strongest and most carefully handled securing of the root zone. The strongest and most carefully handled
keys should be used. The root zone private key should always be kept keys should be used. The root zone private key should always be kept
off line. off-line.
Many resolvers will start at a root server for their access to and Many resolvers will start at a root server for their access to and
authentication of DNS data. Securely updating the trust anchors in authentication of DNS data. Securely updating the trust anchors in
an enormous population of resolvers around the world will be an enormous population of resolvers around the world will be
extremely difficult. extremely difficult.
3.2. Key Generation 3.2. Key Generation
Careful generation of all keys is a sometimes overlooked but Careful generation of all keys is a sometimes overlooked but
absolutely essential element in any cryptographically secure system. absolutely essential element in any cryptographically secure system.
The strongest algorithms used with the longest keys are still of no 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 use if an adversary can guess enough to lower the size of the likely
key space so that it can be exhaustively searched. Technical key space so that it can be exhaustively searched. Technical
suggestions for the generation of random keys will be found in RFC suggestions for the generation of random keys will be found in RFC
4086 [15]. One should carefully assess if the random number 4086 [14]. One should carefully assess if the random number
generator used during key generation adheres to these suggestions. generator used during key generation adheres to these suggestions.
Keys with a long effectivity period are particularly sensitive as Keys with a long effectivity period are particularly sensitive as
they will represent a more valuable target and be subject to attack they will represent a more valuable target and be subject to attack
for a longer time than short period keys. It is strongly recommended for a longer time than short-period keys. It is strongly recommended
that long term key generation occur off-line in a manner isolated 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 from the network via an air gap or, at a minimum, high-level secure
hardware. hardware.
3.3. Key Effectivity Period 3.3. Key Effectivity Period
For various reasons keys in DNSSEC need to be changed once in a 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 while. The longer a key is in use, the greater the probability that
it will have been compromised through carelessness, accident, it will have been compromised through carelessness, accident,
espionage, or cryptanalysis. Furthermore when key rollovers are too espionage, or cryptanalysis. Furthermore, when key rollovers are too
rare an event, they will not become part of the operational habit and 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 there is risk that nobody on-site will remember the procedure for
rollover when the need is there. rollover when the need is there.
From a purely operational perspective a reasonable key effectivity From a purely operational perspective, a reasonable key effectivity
period for Key Signing Keys is 13 months, with the intent to replace period for Key Signing Keys is 13 months, with the intent to replace
them after 12 months. An intended key effectivity period of a month them after 12 months. An intended key effectivity period of a month
is reasonable for Zone Signing Keys. is reasonable for Zone Signing Keys.
For key sizes that matches these effectivity periods see Section 3.5. For key sizes that match these effectivity periods, see Section 3.5.
As argued in Section 3.1.2 securely updating trust anchors will be As argued in Section 3.1.2, securely updating trust anchors will be
extremely difficult. On the other hand the "operational habit" extremely difficult. On the other hand, the "operational habit"
argument does also apply to trust anchor reconfiguration. If a short argument does also apply to trust anchor reconfiguration. If a short
key-effectivity period is used and the trust anchor configuration has key effectivity period is used and the trust anchor configuration has
to be revisited on a regular basis the odds that the configuration to be revisited on a regular basis, the odds that the configuration
tends to be forgotten is smaller. The trade-off is against a system tends to be forgotten is smaller. The trade-off is against a system
that is so dynamic that administrators of the validating clients will that is so dynamic that administrators of the validating clients will
not be able to follow the modifications. not be able to follow the modifications.
Key effectivity periods can be made very short, as in the order of a Key effectivity periods can be made very short, as in a few minutes.
few minutes. But when replacing keys one has to take the But when replacing keys one has to take the considerations from
considerations from Section 4.1 and Section 4.2 into account. Section 4.1 and Section 4.2 into account.
3.4. Key Algorithm 3.4. Key Algorithm
There are currently three different types of algorithms that can be There are currently three different types of algorithms that can be
used in DNSSEC: RSA, DSA and elliptic curve cryptography. The latter used in DNSSEC: RSA, DSA, and elliptic curve cryptography. The
is fairly new and has yet to be standardized for usage in DNSSEC. latter is fairly new and has yet to be standardized for usage in
DNSSEC.
RSA has been developed in an open and transparent manner. As the RSA has been developed in an open and transparent manner. As the
patent on RSA expired in 2000, its use is now also free. patent on RSA expired in 2000, its use is now also free.
DSA has been developed by NIST. The creation of signatures takes DSA has been developed by the National Institute of Standards and
roughly the same time as with RSA, but is 10 to 40 times as slow for Technology (NIST). The creation of signatures takes roughly the same
verification [18]. time as with RSA, but is 10 to 40 times as slow for verification
[17].
We suggest the use of RSA/SHA-1 as the preferred algorithm for the 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. The current known attacks on RSA can be defeated by making your
key longer. As the MD5 hashing algorithm is showing (theoretical) key longer. As the MD5 hashing algorithm is showing cracks, we
cracks, we recommend the usage of SHA-1. recommend the usage of SHA-1.
At the time of publication it is known that the SHA-1 hash has At the time of publication, it is known that the SHA-1 hash has
cryptanalysis issues. There is work in progress on addressing these cryptanalysis issues. There is work in progress on addressing these
issues. We recommend the use of public key algorithms based on issues. We recommend the use of public key algorithms based on
hashes stronger than SHA-1, e.g. SHA-256, as soon as these hashes stronger than SHA-1 (e.g., SHA-256), as soon as these
algorithms are available in protocol specifications (See [20] and algorithms are available in protocol specifications (see [19] and
[21] ) and implementations. [20]) and implementations.
3.5. Key Sizes 3.5. Key Sizes
When choosing key sizes, zone administrators will need to take into When choosing key sizes, zone administrators will need to take into
account how long a key will be used, how much data will be signed account how long a key will be used, how much data will be signed
during the key publication period (See Section 8.10 of [18]) and, during the key publication period (see Section 8.10 of [17]), and,
optionally, how large the key size of the parent is. As the chain of optionally, how large the key size of the parent is. As the chain of
trust really is "a chain", there is not much sense in making one of trust really is "a chain", there is not much sense in making one of
the keys in the chain several times larger then the others. As the keys in the chain several times larger then the others. As
always, it's the weakest link that defines the strength of the entire always, it's the weakest link that defines the strength of the entire
chain. Also see Section 3.1.1 for a discussion of how keys serving chain. Also see Section 3.1.1 for a discussion of how keys serving
different roles (ZSK v. KSK) may need different key sizes. different roles (ZSK vs. KSK) may need different key sizes.
Generating a key of the correct size is a difficult problem, RFC 3766 Generating a key of the correct size is a difficult problem; RFC 3766
[14] tries to deal with that problem. The first part of the [13] tries to deal with that problem. The first part of the
selection procedure in Section 1 of the RFC states: selection procedure in Section 1 of the RFC states:
1. Determine the attack resistance necessary to satisfy the 1. Determine the attack resistance necessary to satisfy the
security requirements of the application. Do this by security requirements of the application. Do this by
estimating the minimum number of computer operations that estimating the minimum number of computer operations that the
the attacker will be forced to do in order to compromise attacker will be forced to do in order to compromise the
the security of the system and then take the logarithm base security of the system and then take the logarithm base two of
two of that number. Call that logarithm value "n". that number. Call that logarithm value "n".
A 1996 report recommended 90 bits as a good all-around choice A 1996 report recommended 90 bits as a good all-around choice
for system security. The 90 bit number should be increased for system security. The 90 bit number should be increased by
by about 2/3 bit/year, or about 96 bits in 2005. about 2/3 bit/year, or about 96 bits in 2005.
[14] goes on to explain how this number "n" can be used to calculate [13] goes on to explain how this number "n" can be used to calculate
the key sizes in public key cryptography. This culminated in the the key sizes in public key cryptography. This culminated in the
table given below (slightly modified for our purpose): table given below (slightly modified for our purpose):
+-------------+-----------+--------------+ +-------------+-----------+--------------+
| System | | | | System | | |
| requirement | Symmetric | RSA or DSA | | requirement | Symmetric | RSA or DSA |
| for attack | key size | modulus size | | for attack | key size | modulus size |
| resistance | (bits) | (bits) | | resistance | (bits) | (bits) |
| (bits) | | | | (bits) | | |
+-------------+-----------+--------------+ +-------------+-----------+--------------+
skipping to change at page 11, line 25 skipping to change at page 10, line 35
| 100 | 100 | 1926 | | 100 | 100 | 1926 |
| 150 | 150 | 4575 | | 150 | 150 | 4575 |
| 200 | 200 | 8719 | | 200 | 200 | 8719 |
| 250 | 250 | 14596 | | 250 | 250 | 14596 |
+-------------+-----------+--------------+ +-------------+-----------+--------------+
The key sizes given are rather large. This is because these keys are The key sizes given are rather large. This is because these keys are
resilient against a trillionaire attacker. Assuming this rich resilient against a trillionaire attacker. Assuming this rich
attacker will not attack your key and that the key is rolled over attacker will not attack your key and that the key is rolled over
once a year, we come to the following recommendations about KSK once a year, we come to the following recommendations about KSK
sizes; 1024 bits low value domains, 1300 for medium value and 2048 sizes: 1024 bits for low-value domains, 1300 bits for medium-value
for the high value domains. domains, and 2048 bits for high-value domains.
Whether a domain is of low, medium, high value depends solely on the Whether a domain is of low, medium, or high value depends solely on
views of the zone owner. One could for instance view leaf nodes in the views of the zone owner. One could, for instance, view leaf
the DNS as of low value and TLDs or the root zone of high value. The nodes in the DNS as of low value, and top-level domains (TLDs) or the
suggested key sizes should be safe for the next 5 years. root zone of high value. The suggested key sizes should be safe for
the next 5 years.
As ZSKs can be rolled over more easily (and thus more often) the key As ZSKs can be rolled over more easily (and thus more often), the key
sizes can be made smaller. But as said in the introduction of this sizes can be made smaller. But as said in the introduction of this
paragraph, making the ZSKs' key sizes too small (in relation to the paragraph, making the ZSKs' key sizes too small (in relation to the
KSKs' sizes) doesn't make much sense. Try to limit the difference in KSKs' sizes) doesn't make much sense. Try to limit the difference in
size to about 100 bits. size to about 100 bits.
Note that nobody can see into the future, and that these key sizes Note that nobody can see into the future and that these key sizes are
are only provided here as a guide. Further information can be found only provided here as a guide. Further information can be found in
in [17] and Section 7.5 of [18]. It should be noted though that [17] [16] and Section 7.5 of [17]. It should be noted though that [16] is
is already considered overly optimistic about what key sizes are already considered overly optimistic about what key sizes are
considered safe. considered safe.
One final note concerning key sizes. Larger keys will increase the One final note concerning key sizes. Larger keys will increase the
sizes of the RRSIG and DNSKEY records and will therefore increase the sizes of the RRSIG and DNSKEY records and will therefore increase the
chance of DNS UDP packet overflow. Also the time it takes to chance of DNS UDP packet overflow. Also, the time it takes to
validate and create RRSIGs increases with larger keys, so don't validate and create RRSIGs increases with larger keys, so don't
needlessly double your key sizes. needlessly double your key sizes.
3.6. Private Key Storage 3.6. Private Key Storage
It is recommended that, where possible, zone private keys and the It is recommended that, where possible, zone private keys and the
zone file master copy that is to be signed, be kept and used in off- zone file master copy that is to be signed be kept and used in off-
line, non-network connected, physically secure machines only. line, non-network-connected, physically secure machines only.
Periodically an application can be run to add authentication to a Periodically, an application can be run to add authentication to a
zone by adding RRSIG and NSEC RRs. Then the augmented file can be zone by adding RRSIG and NSEC RRs. Then the augmented file can be
transferred. transferred.
When relying on dynamic update to manage a signed zone [10], be aware When relying on dynamic update to manage a signed zone [10], be aware
that at least one private key of the zone will have to reside on the that at least one private key of the zone will have to reside on the
master server. This key is only as secure as the amount of exposure master server. This key is only as secure as the amount of exposure
the server receives to unknown clients and the security of the host. the server receives to unknown clients and the security of the host.
Although not mandatory one could administer the DNS in the following Although not mandatory, one could administer the DNS in the following
way. The master that processes the dynamic updates is unavailable way. The master that processes the dynamic updates is unavailable
from generic hosts on the Internet, it is not listed in the NS RR from generic hosts on the Internet, it is not listed in the NS RR
set, although its name appears in the SOA RRs MNAME field. The set, although its name appears in the SOA RRs MNAME field. The
nameservers in the NS RR set are able to receive zone updates through nameservers in the NS RRSet are able to receive zone updates through
NOTIFY, IXFR, AXFR or an out-of-band distribution mechanism. This NOTIFY, IXFR, AXFR, or an out-of-band distribution mechanism. This
approach is known as the "hidden master" setup. approach is known as the "hidden master" setup.
The ideal situation is to have a one way information flow to the The ideal situation is to have a one-way information flow to the
network to avoid the possibility of tampering from the network. network to avoid the possibility of tampering from the network.
Keeping the zone master file on-line on the network and simply 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 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 version could still be tampered with if the host it resides on is
compromised. For maximum security, the master copy of the zone file compromised. For maximum security, the master copy of the zone file
should be off net and should not be updated based on an unsecured should be off-net and should not be updated based on an unsecured
network mediated communication. network mediated communication.
In general keeping a zone-file off-line will not be practical and the In general, keeping a zone file off-line will not be practical and
machines on which zone files are maintained will be connected to a the machines on which zone files are maintained will be connected to
network. Operators are advised to take security measures to shield a network. Operators are advised to take security measures to shield
unauthorized access to the master copy. unauthorized access to the master copy.
For dynamically updated secured zones [10] both the master copy and For dynamically updated secured zones [10], both the master copy and
the private key that is used to update signatures on updated RRs will the private key that is used to update signatures on updated RRs will
need to be on-line. need to be on-line.
4. Signature generation, Key Rollover and Related Policies 4. Signature Generation, Key Rollover, and Related Policies
4.1. Time in DNSSEC 4.1. Time in DNSSEC
Without DNSSEC all times in DNS are relative. The SOA fields Without DNSSEC, all times in the DNS are relative. The SOA fields
REFRESH, RETRY and EXPIRATION are timers used to determine the time REFRESH, RETRY, and EXPIRATION are timers used to determine the time
elapsed after a slave server synchronized with a master server. The elapsed after a slave server synchronized with a master server. The
Time to Live (TTL) value and the SOA RR minimum TTL parameter [11] Time to Live (TTL) value and the SOA RR minimum TTL parameter [11]
are used to determine how long a forwarder should cache data after it are used to determine how long a forwarder should cache data after it
has been fetched from an authoritative server. By using a signature has been fetched from an authoritative server. By using a signature
validity period, DNSSEC introduces the notion of an absolute time in validity period, DNSSEC introduces the notion of an absolute time in
the DNS. Signatures in DNSSEC have an expiration date after which the DNS. Signatures in DNSSEC have an expiration date after which
the signature is marked as invalid and the signed data is to be the signature is marked as invalid and the signed data is to be
considered Bogus. considered Bogus.
4.1.1. Time Considerations 4.1.1. Time Considerations
skipping to change at page 13, line 15 skipping to change at page 12, line 28
has been fetched from an authoritative server. By using a signature has been fetched from an authoritative server. By using a signature
validity period, DNSSEC introduces the notion of an absolute time in validity period, DNSSEC introduces the notion of an absolute time in
the DNS. Signatures in DNSSEC have an expiration date after which the DNS. Signatures in DNSSEC have an expiration date after which
the signature is marked as invalid and the signed data is to be the signature is marked as invalid and the signed data is to be
considered Bogus. considered Bogus.
4.1.1. Time Considerations 4.1.1. Time Considerations
Because of the expiration of signatures, one should consider the Because of the expiration of signatures, one should consider the
following: following:
o We suggest the Maximum Zone TTL of your zone data to be a fraction o We suggest the Maximum Zone TTL of your zone data to be a fraction
of your signature validity period. of your signature validity period.
If the TTL would be of similar order as the signature validity If the TTL would be of similar order as the signature validity
period, then all RRSets fetched during the validity period period, then all RRSets fetched during the validity period
would be cached until the signature expiration time. Section would be cached until the signature expiration time. Section
7.1 of [4] suggests that "the resolver may use the time 7.1 of [4] suggests that "the resolver may use the time
remaining before expiration of the signature validity period of remaining before expiration of the signature validity period of
a signed RRSet as an upper bound for the TTL". As a result a signed RRSet as an upper bound for the TTL". As a result,
query load on authoritative servers would peak at signature query load on authoritative servers would peak at signature
expiration time, as this is also the time at which records expiration time, as this is also the time at which records
simultaneously expire from caches. simultaneously expire from caches.
To avoid query load peaks we suggest the TTL on all the RRs in
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 your zone to be at least a few times smaller than your
signature validity period. signature validity period.
o We suggest the Signature Publication Period to end at least one
Maximum Zone TTL duration before the end of the Signature Validity o We suggest the signature publication period to end at least one
Period. Maximum Zone TTL duration before the end of the signature validity
period.
Re-signing a zone shortly before the end of the signature Re-signing a zone shortly before the end of the signature
validity period may cause simultaneous expiration of data from validity period may cause simultaneous expiration of data from
caches. This in turn may lead to peaks in the load on caches. This in turn may lead to peaks in the load on
authoritative servers. authoritative servers.
o We suggest the minimum zone TTL to be long enough to both fetch
o We suggest the Minimum Zone TTL to be long enough to both fetch
and verify all the RRs in the trust chain. In workshop and verify all the RRs in the trust chain. In workshop
environments it has been demonstrated [19] that a low TTL (under 5 environments, it has been demonstrated [18] that a low TTL (under
to 10 minutes) caused disruptions because of the following two 5 to 10 minutes) caused disruptions because of the following two
problems: problems:
1. During validation, some data may expire before the 1. During validation, some data may expire before the
validation is complete. The validator should be able to keep validation is complete. The validator should be able to
all data, until is completed. This applies to all RRs needed keep all data until it is completed. This applies to all
to complete the chain of trust: DSs, DNSKEYs, RRSIGs, and the RRs needed to complete the chain of trust: DSes, DNSKEYs,
final answers i.e. the RRSet that is returned for the initial RRSIGs, and the final answers, i.e., the RRSet that is
query. returned for the initial query.
2. Frequent verification causes load on recursive nameservers. 2. Frequent verification causes load on recursive nameservers.
Data at delegation points, DSs, DNSKEYs and RRSIGs benefit from Data at delegation points, DSes, DNSKEYs, and RRSIGs
caching. The TTL on those should be relatively long. benefit from caching. The TTL on those should be
relatively long.
o Slave servers will need to be able to fetch newly signed zones 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 well before the RRSIGs in the zone served by the slave server pass
their signature expiration time. their signature expiration time.
When a slave server is out of sync with its master and data in 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 a zone is signed by expired signatures, it may be better for
slave server not to give out any answer. the slave server not to give out any answer.
Normally a slave server that is not able to contact a master
Normally, a slave server that is not able to contact a master
server for an extended period will expire a zone. When that server for an extended period will expire a zone. When that
happens the server will respond differently to queries for that happens, the server will respond differently to queries for
zone. Some servers issue SERVFAIL while others turn off the that zone. Some servers issue SERVFAIL, whereas others turn
'AA' bit in the answers. The time of expiration is set in the off the 'AA' bit in the answers. The time of expiration is set
SOA record and is relative to the last successful refresh in the SOA record and is relative to the last successful
between the master and the slave server. There exists no refresh between the master and the slave servers. There exists
coupling between the signature expiration of RRSIGs in the zone no coupling between the signature expiration of RRSIGs in the
and the expire parameter in the SOA. zone and the expire parameter in the SOA.
If the server serves a DNSSEC zone then it may well happen that
the signatures expire well before the SOA expiration timer If the server serves a DNSSEC zone, then 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 counts down to zero. It is not possible to completely prevent
this from happening by tweaking the SOA parameters. this from happening by tweaking the SOA parameters. However,
However, the effects can be minimized where the SOA expiration the effects can be minimized where the SOA expiration time is
time is equal or shorter than the signature validity period. equal to or shorter than the signature validity period. The
The consequence of an authoritative server not being able to consequence of an authoritative server not being able to update
update a zone, whilst that zone includes expired signatures, is a zone, whilst that zone includes expired signatures, is that
that non-secure resolvers will continue to be able to resolve non-secure resolvers will continue to be able to resolve data
data served by the particular slave servers while security served by the particular slave servers while security-aware
aware resolvers will experience problems because of answers resolvers will experience problems because of answers being
being marked as Bogus. marked as Bogus.
We suggest the SOA expiration timer being approximately one We suggest the SOA expiration timer being approximately one
third or one fourth of the signature validity period. It will third or one fourth of the signature validity period. It will
allow problems with transfers from the master server to be allow problems with transfers from the master server to be
noticed before the actual signature times out. noticed before the actual signature times out. We also suggest
We also suggest that operators of nameservers that supply that operators of nameservers that supply secondary services
secondary services develop 'watch dogs' to spot upcoming develop 'watch dogs' to spot upcoming signature expirations in
signature expirations in zones they slave, and take appropriate zones they slave, and take appropriate action.
action.
When determining the value for the expiration parameter one has When determining the value for the expiration parameter one has
to take the following into account: What are the chances that to take the following into account: What are the chances that
all my secondaries expire the zone; How quickly can I reach an all my secondaries expire the zone? How quickly can I reach an
administrator of secondary servers to load a valid zone? All administrator of secondary servers to load a valid zone? These
these arguments are not DNSSEC specific but may influence the questions are not DNSSEC specific but may influence the choice
choice of your signature validity intervals. of your signature validity intervals.
4.2. Key Rollovers 4.2. Key Rollovers
A DNSSEC key cannot be used forever (see Section 3.3). So key A DNSSEC key cannot be used forever (see Section 3.3). So key
rollovers -- or supercessions, as they are sometimes called -- are a rollovers -- or supercessions, as they are sometimes called -- are a
fact of life when using DNSSEC. Zone administrators who are in the fact of life when using DNSSEC. Zone administrators who are in the
process of rolling their keys have to take into account that data process of rolling their keys have to take into account that data
published in previous versions of their zone still lives in caches. published in previous versions of their zone still lives in caches.
When deploying DNSSEC, this becomes an important consideration; When deploying DNSSEC, this becomes an important consideration;
ignoring data that may be in caches may lead to loss of service for ignoring data that may be in caches may lead to loss of service for
clients. clients.
The most pressing example of this occurs when zone material signed The most pressing example of this occurs when zone material signed
with an old key is being validated by a resolver which does not have with an old key is being validated by a resolver that does not have
the old zone key cached. If the old key is no longer present in the the old zone key cached. If the old key is no longer present in the
current zone, this validation fails, marking the data Bogus. current zone, this validation fails, marking the data "Bogus".
Alternatively, an attempt could be made to validate data which is Alternatively, an attempt could be made to validate data that is
signed with a new key against an old key that lives in a local cache, signed with a new key against an old key that lives in a local cache,
also resulting in data being marked Bogus. also resulting in data being marked "Bogus".
4.2.1. Zone Signing Key Rollovers 4.2.1. Zone Signing Key Rollovers
For zone signing key rollovers there are two ways to make sure that For "Zone Signing Key rollovers", there are two ways to make sure
during the rollover data still cached can be verified with the new that during the rollover data still cached can be verified with the
key sets or newly generated signatures can be verified with the keys new key sets or newly generated signatures can be verified with the
still in caches. One schema, described in Section 4.2.1.2, uses keys still in caches. One schema, described in Section 4.2.1.2, uses
double signatures; the other uses key pre-publication double signatures; the other uses key pre-publication (Section
(Section 4.2.1.1). The pros, cons and recommendations are described 4.2.1.1). The pros, cons, and recommendations are described in
in Section 4.2.1.3. Section 4.2.1.3.
4.2.1.1. Pre-publish Key Rollover 4.2.1.1. Pre-Publish Key Rollover
This section shows how to perform a ZSK rollover without the need to 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 sign all the data in a zone twice -- the "pre-publish key rollover".
rollover".This method has advantages in the case of a key compromise. This method has advantages in the case of a key compromise. If the
If the old key is compromised, the new key has already been old key is compromised, the new key has already been distributed in
distributed in the DNS. The zone administrator is then able to the DNS. The zone administrator is then able to quickly switch to
quickly switch to the new key and remove the compromised key from the the new key and remove the compromised key from the zone. Another
zone. Another major advantage is that the zone size does not double, major advantage is that the zone size does not double, as is the case
as is the case with the double signature ZSK rollover. A small with the double signature ZSK rollover. A small "how-to" for this
"HOWTO" for this kind of rollover can be found in Appendix B. kind of rollover can be found in Appendix B.
Pre-publish Key Rollover involves four stages as follows: Pre-publish key rollover involves four stages as follows:
----------------------------------------------------------------
initial new DNSKEY new RRSIGs DNSKEY removal initial new DNSKEY new RRSIGs DNSKEY removal
----------------------------------------------------------------
SOA0 SOA1 SOA2 SOA3 SOA0 SOA1 SOA2 SOA3
RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2) RRSIG11(SOA3) RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2) RRSIG11(SOA3)
DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1
DNSKEY10 DNSKEY10 DNSKEY10 DNSKEY11 DNSKEY10 DNSKEY10 DNSKEY10 DNSKEY11
DNSKEY11 DNSKEY11 DNSKEY11 DNSKEY11
RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG1(DNSKEY) RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG1(DNSKEY) RRSIG1 (DNSKEY)
RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY)
initial: Initial version 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-Publish Key Rollover
initial: Initial version 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.
new DNSKEY: DNSKEY 11 is introduced into the key set. Note that no new DNSKEY: DNSKEY 11 is introduced into the key set. Note that no
signatures are generated with this key yet, but this does not signatures are generated with this key yet, but this does not
secure against brute force attacks on the public key. The minimum 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 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 to propagate to the authoritative servers plus TTL value of the
key set. key set.
new RRSIGs: At the "new RRSIGs" stage (SOA serial 2) DNSKEY 11 is
used to sign the data in the zone exclusively (i.e. all the new RRSIGs: At the "new RRSIGs" 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 signatures from DNSKEY 10 are removed from the zone). DNSKEY 10
remains published in the key set. This way data that was loaded 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 into caches from version 1 of the zone can still be verified with
key sets fetched from version 2 of the zone. key sets fetched from version 2 of the zone. The minimum time
The minimum time that the key set including DNSKEY 10 is to be that the key set including DNSKEY 10 is to be published is the
published is the time that it takes for zone data from the time that it takes for zone data from the previous version of the
previous version of the zone to expire from old caches i.e. the zone to expire from old caches, i.e., the time it takes for this
time it takes for this zone to propagate to all authoritative zone to propagate to all authoritative servers plus the Maximum
servers plus the Maximum Zone TTL value of any of the data in the Zone TTL value of any of the data in the previous version of the
previous version of the zone. zone.
DNSKEY removal: DNSKEY 10 is removed from the zone. The key set, now DNSKEY removal: DNSKEY 10 is removed from the zone. The key set, now
only containing DNSKEY 1 and DNSKEY 11 is re-signed with the only containing DNSKEY 1 and DNSKEY 11, is re-signed with the
DNSKEY 1. DNSKEY 1.
The above scheme can be simplified by always publishing the "future" The above scheme can be simplified by always publishing the "future"
key immediately after the rollover. The scheme would look as follows key immediately after the rollover. The scheme would look as follows
(we show two rollovers); the future key is introduced in "new DNSKEY" (we show two rollovers); the future key is introduced in "new DNSKEY"
as DNSKEY 12 and again a newer one, numbered 13, in "new DNSKEY as DNSKEY 12 and again a newer one, numbered 13, in "new DNSKEY
(II)": (II)":
----------------------------------------------------------------
initial new RRSIGs new DNSKEY initial new RRSIGs new DNSKEY
----------------------------------------------------------------
SOA0 SOA1 SOA2 SOA0 SOA1 SOA2
RRSIG10(SOA0) RRSIG11(SOA1) RRSIG11(SOA2) RRSIG10(SOA0) RRSIG11(SOA1) RRSIG11(SOA2)
DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1
DNSKEY10 DNSKEY10 DNSKEY11 DNSKEY10 DNSKEY10 DNSKEY11
DNSKEY11 DNSKEY11 DNSKEY12 DNSKEY11 DNSKEY11 DNSKEY12
RRSIG1(DNSKEY) RRSIG1 (DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1 (DNSKEY) RRSIG1(DNSKEY)
RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY)
----------------------------------------------------------------
----------------------------------------------------------------
new RRSIGs (II) new DNSKEY (II) new RRSIGs (II) new DNSKEY (II)
----------------------------------------------------------------
SOA3 SOA4 SOA3 SOA4
RRSIG12(SOA3) RRSIG12(SOA4) RRSIG12(SOA3) RRSIG12(SOA4)
DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1
DNSKEY11 DNSKEY12 DNSKEY11 DNSKEY12
DNSKEY12 DNSKEY13 DNSKEY12 DNSKEY13
RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY)
RRSIG12(DNSKEY) RRSIG12(DNSKEY) RRSIG12(DNSKEY) RRSIG12(DNSKEY)
----------------------------------------------------------------
Pre-Publish Key Rollover, showing two rollovers. Pre-Publish Key Rollover, Showing Two Rollovers
Note that the key introduced in the "new DNSKEY" phase is not used Note that the key introduced in the "new DNSKEY" phase is not used
for production yet; the private key can thus be stored in a for production yet; the private key can thus be stored in a
physically secure manner and does not need to be 'fetched' every time physically secure manner and does not need to be 'fetched' every time
a zone needs to be signed. a zone needs to be signed.
4.2.1.2. Double Signature Zone Signing Key Rollover 4.2.1.2. Double Signature Zone Signing Key Rollover
This section shows how to perform a ZSK key rollover using the double This section shows how to perform a ZSK key rollover using the double
zone data signature scheme, aptly named "double sig rollover". zone data signature scheme, aptly named "double signature rollover".
During the "new DNSKEY" stage the new version of the zone file will During the "new DNSKEY" stage the new version of the zone file will
need to propagate to all authoritative servers and the data that need to propagate to all authoritative servers and the data that
exists in (distant) caches will need to expire, requiring at least exists in (distant) caches will need to expire, requiring at least
the maximum Zone TTL. the Maximum Zone TTL.
Double Signature Zone Signing Key Rollover involves three stages as Double signature ZSK rollover involves three stages as follows:
follows:
----------------------------------------------------------------
initial new DNSKEY DNSKEY removal initial new DNSKEY DNSKEY removal
----------------------------------------------------------------
SOA0 SOA1 SOA2 SOA0 SOA1 SOA2
RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2) RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2)
RRSIG11(SOA1) RRSIG11(SOA1)
DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY1
DNSKEY10 DNSKEY10 DNSKEY11 DNSKEY10 DNSKEY10 DNSKEY11
DNSKEY11 DNSKEY11
RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY)
RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY)
RRSIG11(DNSKEY) RRSIG11(DNSKEY)
----------------------------------------------------------------
Double Signature Zone Signing Key Rollover
initial: Initial Version 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.
initial: Initial Version 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.
new DNSKEY: At the "New DNSKEY" stage (SOA serial 1) DNSKEY 11 is new DNSKEY: At the "New DNSKEY" stage (SOA serial 1) DNSKEY 11 is
introduced into the key set and all the data in the zone is signed 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 with DNSKEY 10 and DNSKEY 11. The rollover period will need to
continue until all data from version 0 of the zone has expired continue until all data from version 0 of the zone has expired
from remote caches. This will take at least the maximum Zone TTL from remote caches. This will take at least the Maximum Zone TTL
of version 0 of the zone. of version 0 of the zone.
DNSKEY removal: DNSKEY 10 is removed from the zone. All the DNSKEY removal: DNSKEY 10 is removed from the zone. All the
signatures from DNSKEY 10 are removed from the zone. The key set, signatures from DNSKEY 10 are removed from the zone. The key set,
now only containing DNSKEY 11, is re-signed with DNSKEY 1. now only containing DNSKEY 11, is re-signed with DNSKEY 1.
At every instance, RRSIGs from the previous version of the zone can At every instance, RRSIGs from the previous version of the zone can
be verified with the DNSKEY RRSet from the current version and the be verified with the DNSKEY RRSet from the current version and the
other way around. The data from the current version can be verified 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 with the data from the previous version of the zone. The duration of
the "new DNSKEY" phase and the period between rollovers should be at the "new DNSKEY" phase and the period between rollovers should be at
least the Maximum Zone TTL. least the Maximum Zone TTL.
skipping to change at page 19, line 7 skipping to change at page 18, line 24
recommended. This way all caches are cleared of the old signatures. recommended. This way all caches are cleared of the old signatures.
However, this duration could be considerably longer than the Maximum However, this duration could be considerably longer than the Maximum
Zone TTL, making the rollover a lengthy procedure. Zone TTL, making the rollover a lengthy procedure.
Note that in this example we assumed that the zone was not modified 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 during the rollover. New data can be introduced in the zone as long
as it is signed with both keys. as it is signed with both keys.
4.2.1.3. Pros and Cons of the Schemes 4.2.1.3. Pros and Cons of the Schemes
Pre-publish Key Rollover: This rollover does not involve signing the Pre-publish key rollover: This rollover does not involve signing the
zone data twice. Instead, before the actual rollover, the new key zone data twice. Instead, before the actual rollover, the new key
is published in the key set and thus available for cryptanalysis is published in the key set and thus is available for
attacks. A small disadvantage is that this process requires four cryptanalysis attacks. A small disadvantage is that this process
steps. Also the pre-publish scheme involves more parental work requires four steps. Also the pre-publish scheme involves more
when used for KSK rollovers as explained in Section 4.2.3. parental work when used for KSK rollovers as explained in Section
Double Signature Zone-signing Key Rollover: The drawback of this 4.2.3.
signing scheme is that during the rollover the number of
signatures in your zone doubles, this may be prohibitive if you Double signature ZSK rollover: The drawback of this signing scheme is
have very big zones. An advantage is that it only requires three that during the rollover the number of signatures in your zone
steps. 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 4.2.2. Key Signing Key Rollovers
For the rollover of a key signing key the same considerations as for 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 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 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. 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 Since only the key set is signed with a KSK, zone size considerations
do not apply. do not apply.
--------------------------------------------------------------------
initial new DNSKEY DS change DNSKEY removal initial new DNSKEY DS change DNSKEY removal
--------------------------------------------------------------------
Parent: Parent:
SOA0 --------> SOA1 --------> SOA0 --------> SOA1 -------->
RRSIGpar(SOA0) --------> RRSIGpar(SOA1) --------> RRSIGpar(SOA0) --------> RRSIGpar(SOA1) -------->
DS1 --------> DS2 --------> DS1 --------> DS2 -------->
RRSIGpar(DS) --------> RRSIGpar(DS) --------> RRSIGpar(DS) --------> RRSIGpar(DS) -------->
Child: Child:
SOA0 SOA1 --------> SOA2 SOA0 SOA1 --------> SOA2
RRSIG10(SOA0) RRSIG10(SOA1) --------> RRSIG10(SOA2) RRSIG10(SOA0) RRSIG10(SOA1) --------> RRSIG10(SOA2)
--------> -------->
DNSKEY1 DNSKEY1 --------> DNSKEY2 DNSKEY1 DNSKEY1 --------> DNSKEY2
DNSKEY2 --------> DNSKEY2 -------->
DNSKEY10 DNSKEY10 --------> DNSKEY10 DNSKEY10 DNSKEY10 --------> DNSKEY10
RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) --------> RRSIG2 (DNSKEY) RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) --------> RRSIG2 (DNSKEY)
RRSIG2 (DNSKEY) --------> RRSIG2 (DNSKEY) -------->
RRSIG10(DNSKEY) RRSIG10(DNSKEY) --------> RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) --------> RRSIG10(DNSKEY)
--------------------------------------------------------------------
Stages of Deployment for Key Signing Key Rollover. Stages of Deployment for a Double Signature Key Signing Key Rollover
initial: Initial version of the zone. The parental DS points to initial: Initial version of the zone. The parental DS points to
DNSKEY1. Before the rollover starts the child will have to verify DNSKEY1. Before the rollover starts, the child will have to
what the TTL is of the DS RR that points to DNSKEY1 - it is needed verify what the TTL is of the DS RR that points to DNSKEY1 -- it
during the rollover and we refer to the value as TTL_DS. is needed during the rollover and we refer to the value as TTL_DS.
new DNSKEY: During the "new DNSKEY" phase the zone administrator
new DNSKEY: During the "new DNSKEY" phase, the zone administrator
generates a second KSK, DNSKEY2. The key is provided to the 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 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 generated that points to DNSKEY2. After that DS RR has been
published on all servers authoritative for the parent's zone, the published on all servers authoritative for the parent's zone, the
zone administrator has to wait at least TTL_DS to make sure that zone administrator has to wait at least TTL_DS to make sure that
the old DS RR has expired from caches. the old DS RR has expired from caches.
DS change: The parent replaces DS1 with DS2. DS change: The parent replaces DS1 with DS2.
DNSKEY removal: DNSKEY1 has been removed. DNSKEY removal: DNSKEY1 has been removed.
The scenario above puts the responsibility for maintaining a valid The scenario above puts the responsibility for maintaining a valid
chain of trust with the child. It also is based on the premises that chain of trust with the child. It also is based on the premise that
the parent only has one DS RR (per algorithm) per zone. An the parent only has one DS RR (per algorithm) per zone. An
alternative mechanism has been considered. Using an established alternative mechanism has been considered. Using an established
trust relation, the interaction can be performed in-band, and the trust relation, the interaction can be performed in-band, and the
removal of the keys by the child can possibly be signaled by 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 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 RRs at the parent. Since at the moment of writing the protocol for
this interaction has not been developed, further discussion is out of this interaction has not been developed, further discussion is out of
scope for this document. scope for this document.
4.2.3. Difference Between ZSK and KSK Rollovers 4.2.3. Difference Between ZSK and KSK Rollovers
Note that KSK rollovers and ZSK rollovers are different in the sense Note that KSK rollovers and ZSK rollovers are different in the sense
that a KSK rollover requires interaction with the parent (and that a KSK rollover requires interaction with the parent (and
possibly replacing of trust anchors) and the ensuing delay while possibly replacing of trust anchors) and the ensuing delay while
waiting for it. waiting for it.
A zone key rollover can be handled in two different ways: pre-publish A zone key rollover can be handled in two different ways: pre-publish
(Section Section 4.2.1.1) and double signature (Section (Section 4.2.1.1) and double signature (Section 4.2.1.2).
Section 4.2.1.2).
As the KSK is used to validate the key set and because the KSK is not 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 changed during a ZSK rollover, a cache is able to validate the new
key set of the zone. The pre-publish method would also work for a key set of the zone. The pre-publish method would also work for a
KSK rollover. The records that are to be pre-published are the KSK rollover. The records that are to be pre-published are the
parental DS RRs. The pre-publish method has some drawbacks for KSKs. parental DS RRs. The pre-publish method has some drawbacks for KSKs.
We first describe the rollover scheme and then indicate these We first describe the rollover scheme and then indicate these
drawbacks. drawbacks.
--------------------------------------------------------------------
initial new DS new DNSKEY DS/DNSKEY removal initial new DS new DNSKEY DS/DNSKEY removal
--------------------------------------------------------------------
Parent: Parent:
SOA0 SOA1 --------> SOA2 SOA0 SOA1 --------> SOA2
RRSIGpar(SOA0) RRSIGpar(SOA1) --------> RRSIGpar(SOA2) RRSIGpar(SOA0) RRSIGpar(SOA1) --------> RRSIGpar(SOA2)
DS1 DS1 --------> DS2 DS1 DS1 --------> DS2
DS2 --------> DS2 -------->
RRSIGpar(DS) RRSIGpar(DS) --------> RRSIGpar(DS) RRSIGpar(DS) RRSIGpar(DS) --------> RRSIGpar(DS)
Child: Child:
SOA0 --------> SOA1 SOA1 SOA0 --------> SOA1 SOA1
RRSIG10(SOA0) --------> RRSIG10(SOA1) RRSIG10(SOA1) RRSIG10(SOA0) --------> RRSIG10(SOA1) RRSIG10(SOA1)
--------> -------->
DNSKEY1 --------> DNSKEY2 DNSKEY2 DNSKEY1 --------> DNSKEY2 DNSKEY2
--------> -------->
DNSKEY10 --------> DNSKEY10 DNSKEY10 DNSKEY10 --------> DNSKEY10 DNSKEY10
RRSIG1 (DNSKEY) --------> RRSIG2(DNSKEY) RRSIG2 (DNSKEY) RRSIG1 (DNSKEY) --------> RRSIG2(DNSKEY) RRSIG2 (DNSKEY)
RRSIG10(DNSKEY) --------> RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) --------> RRSIG10(DNSKEY) RRSIG10(DNSKEY)
--------------------------------------------------------------------
Stages of Deployment for a Pre-publish Key Signing Key rollover. Stages of Deployment for a Pre-Publish Key Signing Key Rollover
When the child zone wants to roll, it notifies the parent during the
When the child zone wants to roll it notifies the parent during the
"new DS" phase and submits the new key (or the corresponding DS) to "new DS" phase and submits the new key (or the corresponding DS) to
the parent. The parent publishes DS1 and DS2, pointing to DNSKEY1 the parent. The parent publishes DS1 and DS2, pointing to DNSKEY1
and DNSKEY2 respectively. During the rollover ("new DNSKEY" phase), and DNSKEY2, respectively. During the rollover ("new DNSKEY" phase),
which can take place as soon as the new DS set propagated through the which can take place as soon as the new DS set propagated through the
DNS, the child replaces DNSKEY1 with DNSKEY2. Immediately after that DNS, the child replaces DNSKEY1 with DNSKEY2. Immediately after that
("DS/DNSKEY removal" phase) it can notify the parent that the old DS ("DS/DNSKEY removal" phase), it can notify the parent that the old DS
record can be deleted. record can be deleted.
The drawbacks of this scheme are that during the "new DS" phase the The drawbacks of this scheme are that during the "new DS" phase the
parent cannot verify the match between the DS2 RR and DNSKEY2 using parent cannot verify the match between the DS2 RR and DNSKEY2 using
the DNS -- as DNSKEY2 is not yet published. Besides, we introduce a the DNS -- as DNSKEY2 is not yet published. Besides, we introduce a
"security lame" key (See Section 4.4.3). Finally the child-parent "security lame" key (see Section 4.4.3). Finally, the child-parent
interaction consists of two steps. The "double signature" method interaction consists of two steps. The "double signature" method
only needs one interaction. only needs one interaction.
4.2.4. Automated Key Rollovers 4.2.4. Automated Key Rollovers
As keys must be renewed periodically, there is some motivation to As keys must be renewed periodically, there is some motivation to
automate the rollover process. Consider that: automate the rollover process. Consider the following:
o ZSK rollovers are easy to automate as only the child zone is o ZSK rollovers are easy to automate as only the child zone is
involved. involved.
o A KSK rollover needs interaction between parent and child. Data o A KSK rollover needs interaction between parent and child. Data
exchange is needed to provide the new keys to the parent, exchange is needed to provide the new keys to the parent;
consequently, this data must be authenticated and integrity must consequently, this data must be authenticated and integrity must
be guaranteed in order to avoid attacks on the rollover. be guaranteed in order to avoid attacks on the rollover.
4.3. Planning for Emergency Key Rollover 4.3. Planning for Emergency Key Rollover
This section deals with preparation for a possible key compromise. This section deals with preparation for a possible key compromise.
Our advice is to have a documented procedure ready for when a key Our advice is to have a documented procedure ready for when a key
compromise is suspected or confirmed. compromise is suspected or confirmed.
When the private material of one of your keys is compromised it can When the private material of one of your keys is compromised it can
be used for as long as a valid trust chain exists. A trust chain be used for as long as a valid trust chain exists. A trust chain
remains intact for: remains intact for
o as long as a signature over the compromised key in the trust chain o as long as a signature over the compromised key in the trust chain
is valid, is valid,
o as long as a parental DS RR (and signature) points to the o as long as a parental DS RR (and signature) points to the
compromised key, compromised key,
o as long as the key is anchored in a resolver and is used as a 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 starting point for validation (this is generally the hardest to
update). update).
While a trust chain to your compromised key exists, your name-space While a trust chain to your compromised key exists, your namespace is
is vulnerable to abuse by anyone who has obtained illegitimate vulnerable to abuse by anyone who has obtained illegitimate
possession of the key. Zone operators have to make a trade off if possession of the key. Zone operators have to make a trade-off if
the abuse of the compromised key is worse than having data in caches 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 that cannot be validated. If the zone operator chooses to break the
trust chain to the compromised key, data in caches signed with this trust chain to the compromised key, data in caches signed with this
key cannot be validated. However, if the zone administrator chooses key cannot be validated. However, if the zone administrator chooses
to take the path of a regular roll-over, the malicious key holder can to take the path of a regular rollover, the malicious key holder can
spoof data so that it appears to be valid. spoof data so that it appears to be valid.
4.3.1. KSK Compromise 4.3.1. KSK Compromise
A zone containing a DNSKEY RRSet with a compromised KSK is vulnerable A zone containing a DNSKEY RRSet with a compromised KSK is vulnerable
as long as the compromised KSK is configured as trust anchor or a as long as the compromised KSK is configured as trust anchor or a
parental DS points to it. parental DS points to it.
A compromised KSK can be used to sign the key set of an attacker's A compromised KSK can be used to sign the key set of an attacker's
zone. That zone could be used to poison the DNS. zone. That zone could be used to poison the DNS.
Therefore when the KSK has been compromised, the trust anchor or the Therefore, when the KSK has been compromised, the trust anchor or the
parental DS, should be replaced as soon as possible. It is local parental DS should be replaced as soon as possible. It is local
policy whether to break the trust chain during the emergency policy whether to break the trust chain during the emergency
rollover. The trust chain would be broken when the compromised KSK rollover. The trust chain would be broken when the compromised KSK
is removed from the child's zone while the parent still has a DS is removed from the child's zone while the parent still has a DS
pointing to the compromised KSK (the assumption is that there is only pointing to the compromised KSK (the assumption is that there is only
one DS at the parent. If there are multiple DSs this does not apply one DS at the parent. If there are multiple DSes this does not apply
-- however the chain of trust of this particular key is broken). -- however the chain of trust of this particular key is broken).
Note that an attacker's zone still uses the compromised KSK and the Note that an attacker's zone still uses the compromised KSK and the
presence of a parental DS would cause the data in this zone to appear presence of a parental DS would cause the data in this zone to appear
as valid. Removing the compromised key would cause the attacker's as valid. Removing the compromised key would cause the attacker's
zone to appear as valid and the child's zone as Bogus. Therefore we zone to appear as valid and the child's zone as Bogus. Therefore, we
advise not to remove the KSK before the parent has a DS to a new KSK advise not to remove the KSK before the parent has a DS to a new KSK
in place. in place.
4.3.1.1. Keeping the Chain of Trust Intact 4.3.1.1. Keeping the Chain of Trust Intact
If we follow this advice the timing of the replacement of the KSK is If we follow this advice, the timing of the replacement of the KSK is
somewhat critical. The goal is to remove the compromised KSK as soon somewhat critical. The goal is to remove the compromised KSK as soon
as the new DS RR is available at the parent. And also make sure that as the new DS RR is available at the parent. And also make sure that
the signature made with a new KSK over the key set with the the signature made with a new KSK over the key set with the
compromised KSK in it expires just after the new DS appears at the compromised KSK in it expires just after the new DS appears at the
parent. Thus removing the old cruft in one swoop. parent, thus removing the old cruft in one swoop.
The procedure is as follows: The procedure is as follows:
1. Introduce a new KSK into the key set, keep the compromised KSK in 1. Introduce a new KSK into the key set, keep the compromised KSK in
the key set. the key set.
2. Sign the key set, with a short validity period. The validity 2. Sign the key set, with a short validity period. The validity
period should expire shortly after the DS is expected to appear period should expire shortly after the DS is expected to appear
in the parent and the old DSs have expired from caches. in the parent and the old DSes have expired from caches.
3. Upload the DS for this new key to the parent. 3. Upload the DS for this new key to the parent.
4. Follow the procedure of the regular KSK rollover: Wait for the DS 4. Follow the procedure of the regular KSK rollover: Wait for the DS
to appear in the authoritative servers and then wait as long as to appear in the authoritative servers and then wait as long as
the TTL of the old DS RRs. If necessary re-sign the DNSKEY RRSet the TTL of the old DS RRs. If necessary re-sign the DNSKEY RRSet
and modify/extend the expiration time. and modify/extend the expiration time.
5. Remove the compromised DNSKEY RR from the zone and re-sign the 5. Remove the compromised DNSKEY RR from the zone and re-sign the
key set using your "normal" validity interval. key set using your "normal" validity interval.
An additional danger of a key compromise is that the compromised key An additional danger of a key compromise is that the compromised key
could be used to facilitate a legitimate DNSKEY/DS rollover and/or could be used to facilitate a legitimate DNSKEY/DS rollover and/or
nameserver changes at the parent. When that happens the domain may nameserver changes at the parent. When that happens, the domain may
be in dispute. An authenticated out-of-band and secure notify be in dispute. An authenticated out-of-band and secure notify
mechanism to contact a parent is needed in this case. mechanism to contact a parent is needed in this case.
Note that this is only a problem when the DNSKEY and or DS records Note that this is only a problem when the DNSKEY and or DS records
are used for authentication at the parent. are used for authentication at the parent.
4.3.1.2. Breaking the Chain of Trust 4.3.1.2. Breaking the Chain of Trust
There are two methods to break the chain of trust. The first method There are two methods to break the chain of trust. The first method
causes the child zone to appear as 'Bogus' to validating resolvers. causes the child zone to appear 'Bogus' to validating resolvers. The
The other causes the the child zone to appear as 'insecure'. These other causes the child zone to appear 'insecure'. These are
are described below. described below.
In the method that causes the child zone to appear as 'Bogus' to In the method that causes the child zone to appear 'Bogus' to
validating resolvers, the child zone replaces the current KSK with a validating resolvers, the child zone replaces the current KSK with a
new one and resigns the key set. Next it sends the DS of the new key new one and re-signs the key set. Next it sends the DS of the new
to the parent. Only after the parent has placed the new DS in the key to the parent. Only after the parent has placed the new DS in
zone, the child's chain of trust is repaired. the zone is the child's chain of trust repaired.
An alternative method of breaking the chain of trust is by removing An alternative method of breaking the chain of trust is by removing
the DS RRs from the parent zone altogether. As a result the child the DS RRs from the parent zone altogether. As a result, the child
zone would become insecure. zone would become insecure.
4.3.2. ZSK Compromise 4.3.2. ZSK Compromise
Primarily because there is no parental interaction required when a Primarily because there is no parental interaction required when a
ZSK is compromised, the situation is less severe than with a KSK ZSK is compromised, the situation is less severe than with a KSK
compromise. The zone must still be re-signed with a new ZSK as soon compromise. The zone must still be re-signed with a new ZSK as soon
as possible. As this is a local operation and requires no as possible. As this is a local operation and requires no
communication between the parent and child this can be achieved communication between the parent and child, this can be achieved
fairly quickly. However, one has to take into account that just as fairly quickly. However, one has to take into account that just as
with a normal rollover the immediate disappearance of the old with a normal rollover the immediate disappearance of the old
compromised key may lead to verification problems. Also note that as compromised key may lead to verification problems. Also note that as
long as the RRSIG over the compromised ZSK is not expired the zone long as the RRSIG over the compromised ZSK is not expired the zone
may be still at risk. may be still at risk.
4.3.3. Compromises of Keys Anchored in Resolvers 4.3.3. Compromises of Keys Anchored in Resolvers
A key can also be pre-configured in resolvers. For instance, if A key can also be pre-configured in resolvers. For instance, if
DNSSEC is successfully deployed the root key may be pre-configured in DNSSEC is successfully deployed the root key may be pre-configured in
most security aware resolvers. most security aware resolvers.
If trust-anchor keys are compromised, the resolvers using these keys If trust-anchor keys are compromised, the resolvers using these keys
should be notified of this fact. Zone administrators may consider should be notified of this fact. Zone administrators may consider
setting up a mailing list to communicate the fact that a SEP key is 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 about to be rolled over. This communication will of course need to
be authenticated e.g. by using digital signatures. be authenticated, e.g., by using digital signatures.
End-users faced with the task of updating an anchored key should End-users faced with the task of updating an anchored key should
always validate the new key. New keys should be authenticated out- always validate the new key. New keys should be authenticated out-
of-band, for example, looking them up on an SSL secured announcement of-band, for example, through the use of an announcement website that
website. is secured using secure sockets (TLS) [21].
4.4. Parental Policies 4.4. Parental Policies
4.4.1. Initial Key Exchanges and Parental Policies Considerations 4.4.1. Initial Key Exchanges and Parental Policies Considerations
The initial key exchange is always subject to the policies set by the The initial key exchange is always subject to the policies set by the
parent. When designing a key exchange policy one should take into parent. When designing a key exchange policy one should take into
account that the authentication and authorization mechanisms used account that the authentication and authorization mechanisms used
during a key exchange should be as strong as the authentication and during a key exchange should be as strong as the authentication and
authorization mechanisms used for the exchange of delegation authorization mechanisms used for the exchange of delegation
information between parent and child. I.e. there is no implicit need information between parent and child. That is, there is no implicit
in DNSSEC to make the authentication process stronger than it was in need in DNSSEC to make the authentication process stronger than it
DNS. was in DNS.
Using the DNS itself as the source for the actual DNSKEY material, Using the DNS itself as the source for the actual DNSKEY material,
with an out-of-band check on the validity of the DNSKEY, has the with an out-of-band check on the validity of the DNSKEY, has the
benefit that it reduces the chances of user error. A DNSKEY query benefit that it reduces the chances of user error. A DNSKEY query
tool can make use of the SEP bit [3] to select the proper key from a tool can make use of the SEP bit [3] to select the proper key from a
DNSSEC key set; thereby reducing the chance that the wrong DNSKEY is DNSSEC key set, thereby reducing the chance that the wrong DNSKEY is
sent. It can validate the self-signature over a key; thereby sent. It can validate the self-signature over a key; thereby
verifying the ownership of the private key material. Fetching the verifying the ownership of the private key material. Fetching the
DNSKEY from the DNS ensures that the chain of trust remains intact DNSKEY from the DNS ensures that the chain of trust remains intact
once the parent publishes the DS RR indicating the child is secure. once the parent publishes the DS RR indicating the child is secure.
Note: the out-of-band verification is still needed when the key- Note: the out-of-band verification is still needed when the key
material is fetched via the DNS. The parent can never be sure material is fetched via the DNS. The parent can never be sure
whether the DNSKEY RRs have been spoofed or not. whether or not the DNSKEY RRs have been spoofed.
4.4.2. Storing Keys or Hashes? 4.4.2. Storing Keys or Hashes?
When designing a registry system one should consider which of the When designing a registry system one should consider which of the
DNSKEYs and/or the corresponding DSs to store. Since a child zone DNSKEYs and/or the corresponding DSes to store. Since a child zone
might wish to have a DS published using a message digest algorithm 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 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 able to generate the DS record from a raw DNSKEY. Thus, we recommend
that registry systems at least support storing DS records. that registry systems at least support storing DS records.
It may also be useful to store DNSKEYs, since having them may help It may also be useful to store DNSKEYs, since having them may help
during troubleshooting and, as long as the child's chosen message during troubleshooting and, as long as the child's chosen message
digest is supported, the overhead of generating DS records from them digest is supported, the overhead of generating DS records from them
is minimal. Having an out-of-band mechanism, such as a registry is minimal. Having an out-of-band mechanism, such as a registry
directory (e.g. Whois), to find out which keys are used to generate directory (e.g., Whois), to find out which keys are used to generate
DS Resource Records for specific owners and/or zones may also help DS Resource Records for specific owners and/or zones may also help
with troubleshooting. with troubleshooting.
The storage considerations also relate to the design of the customer The storage considerations also relate to the design of the customer
interface and the method by which data is transferred between interface and the method by which data is transferred between
registrant and registry; Will the child zone administrator be able to registrant and registry; Will the child zone administrator be able to
upload DS RRs with unknown hash algorithms or does the interface only upload DS RRs with unknown hash algorithms or does the interface only
allow DNSKEYs? In the registry-registrar model one can use the allow DNSKEYs? In the registry-registrar model, one can use the
DNSSEC EPP protocol extension [16] which allows transfer of DS RRs DNSSEC extensions to the Extensible Provisioning Protocol (EPP) [15],
and optionally DNSKEY RRs. which allows transfer of DS RRs and optionally DNSKEY RRs.
4.4.3. Security Lameness 4.4.3. Security Lameness
Security Lameness is defined as what happens when a parent has a DS Security lameness is defined as what happens when a parent has a DS
RR pointing to a non-existing DNSKEY RR. When this happens the RR pointing to a non-existing DNSKEY RR. When this happens, the
child's zone may be marked as "Bogus" by verifying DNS clients. child's zone may be marked "Bogus" by verifying DNS clients.
As part of a comprehensive delegation check the parent could, at key As part of a comprehensive delegation check, the parent could, at key
exchange time, verify that the child's key is actually configured in exchange time, verify that the child's key is actually configured in
the DNS. However if a parent does not understand the hashing the DNS. However, if a parent does not understand the hashing
algorithm used by child the parental checks are limited to only algorithm used by child, the parental checks are limited to only
comparing the key id. comparing the key id.
Child zones should be very careful removing DNSKEY material, Child zones should be very careful in removing DNSKEY material,
specifically SEP keys, for which a DS RR exists. specifically SEP keys, for which a DS RR exists.
Once a zone is "security lame", a fix (e.g. removing a DS RR) will Once a zone is "security lame", a fix (e.g., removing a DS RR) will
take time to propagate through the DNS. take time to propagate through the DNS.
4.4.4. DS Signature Validity Period 4.4.4. DS Signature Validity Period
Since the DS can be replayed as long as it has a valid signature, a 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 short signature validity period over the DS minimizes the time a
child is vulnerable in the case of a compromise of the child's 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 KSK(s). A signature validity period that is too short introduces the
possibility that a zone is marked Bogus in case of a configuration 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 error in the signer. There may not be enough time to fix the
problems before signatures expire. Something as mundane as operator problems before signatures expire. Something as mundane as operator
unavailability during weekends shows the need for DS signature unavailability during weekends shows the need for DS signature
validity periods longer than 2 days. We recommend an absolute validity periods longer than 2 days. We recommend an absolute
minimum for a DS signature validity period of a few days. minimum for a DS signature validity period of a few days.
The maximum signature validity period of the DS record depends on how The maximum signature validity period of the DS record depends on how
long child zones are willing to be vulnerable after a key compromise. long child zones are willing to be vulnerable after a key compromise.
On the other hand shortening the DS signature validity interval On the other hand, shortening the DS signature validity interval
increases the operational risk for the parent. Therefore the parent increases the operational risk for the parent. Therefore, the parent
may have policy to use a signature validity interval that is may have policy to use a signature validity interval that is
considerably longer than the child would hope for. considerably longer than the child would hope for.
A compromise between the operational constraints of the parent and A compromise between the operational constraints of the parent and
minimizing damage for the child may result in a DS signature validity minimizing damage for the child may result in a DS signature validity
period somewhere between the order of a week to order of months. period somewhere between a week and months.
In addition to the signature validity period, which sets a lower In addition to the signature validity period, which sets a lower
bound on the number of times the zone owner will need to sign the bound on the number of times the zone owner will need to sign the
zone data and which sets an upper bound to the time a child is 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 vulnerable after key compromise, there is the TTL value on the DS
RRs. Shortening the TTL means that the authoritative servers will RRs. Shortening the TTL means that the authoritative servers will
see more queries. But on the other hand, a short TTL lowers the see more queries. But on the other hand, a short TTL lowers the
persistence of DS RRSets in caches thereby increases the speed with persistence of DS RRSets in caches thereby increasing the speed with
which updated DS RRSets propagate through the DNS. which updated DS RRSets propagate through the DNS.
5. IANA Considerations 5. Security Considerations
This overview document introduces no new IANA considerations.
6. Security Considerations
DNSSEC adds data integrity to the DNS. This document tries to assess DNSSEC adds data integrity to the DNS. This document tries to assess
the operational considerations to maintain a stable and secure DNSSEC the operational considerations to maintain a stable and secure DNSSEC
service. Not taking into account the 'data propagation' properties service. Not taking into account the 'data propagation' properties
in the DNS will cause validation failures and may make secured zones in the DNS will cause validation failures and may make secured zones
unavailable to security aware resolvers. unavailable to security-aware resolvers.
7. Acknowledgments 6. Acknowledgments
Most of the ideas in this draft were the result of collective efforts Most of the ideas in this document were the result of collective
during workshops, discussions and try outs. efforts during workshops, discussions, and tryouts.
At the risk of forgetting individuals who were the original At the risk of forgetting individuals who were the original
contributors of the ideas we would like to acknowledge people who contributors of the ideas, we would like to acknowledge people who
were actively involved in the compilation of this document. In were actively involved in the compilation of this document. In
random order: Rip Loomis, Olafur Gudmundsson, Wesley Griffin, Michael random order: Rip Loomis, Olafur Gudmundsson, Wesley Griffin, Michael
Richardson, Scott Rose, Rick van Rein, Tim McGinnis, Gilles Guette Richardson, Scott Rose, Rick van Rein, Tim McGinnis, Gilles Guette
Olivier Courtay, Sam Weiler, Jelte Jansen, Niall O'Reilly, Holger Olivier Courtay, Sam Weiler, Jelte Jansen, Niall O'Reilly, Holger
Zuleger, Ed Lewis, Hilarie Orman, Marcos Sanz and Peter Koch. Zuleger, Ed Lewis, Hilarie Orman, Marcos Sanz, and Peter Koch.
Some material in this document has been copied from RFC 2541 [12]. Some material in this document has been copied from RFC 2541 [12].
Mike StJohns designed the key exchange between parent and child Mike StJohns designed the key exchange between parent and child
mentioned in the last paragraph of Section 4.2.2 mentioned in the last paragraph of Section 4.2.2
Section 4.2.4 was supplied by G. Guette and O. Courtay. Section 4.2.4 was supplied by G. Guette and O. Courtay.
Emma Bretherick, Adrian Bedford and Lindy Foster corrected many of Emma Bretherick, Adrian Bedford, and Lindy Foster corrected many of
the spelling and style issues. the spelling and style issues.
Kolkman and Gieben take the blame for introducing all miscakes(SIC). Kolkman and Gieben take the blame for introducing all miscakes (sic).
Kolkman was employed by the RIPE NCC while working on this document. While working on this document, Kolkman was employed by the RIPE NCC
and Gieben was employed by NLnet Labs.
8. References 7. References
8.1. Normative References 7.1. Normative References
[1] Mockapetris, P., "Domain names - concepts and facilities", [1] Mockapetris, P., "Domain names - concepts and facilities", STD
STD 13, RFC 1034, November 1987. 13, RFC 1034, November 1987.
[2] Mockapetris, P., "Domain names - implementation and [2] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
[3] Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name System KEY [3] Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name System
(DNSKEY) Resource Record (RR) Secure Entry Point (SEP) Flag", KEY (DNSKEY) Resource Record (RR) Secure Entry Point (SEP)
RFC 3757, May 2004. Flag", RFC 3757, May 2004.
[4] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [4] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"DNS Security Introduction and Requirements", RFC 4033, "DNS Security Introduction and Requirements", RFC 4033, March
March 2005. 2005.
[5] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [5] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Resource Records for the DNS Security Extensions", RFC 4034, "Resource Records for the DNS Security Extensions", RFC 4034,
March 2005. March 2005.
[6] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [6] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Protocol Modifications for the DNS Security Extensions", "Protocol Modifications for the DNS Security Extensions", RFC
RFC 4035, March 2005. 4035, March 2005.
8.2. Informative References 7.2. Informative References
[7] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, [7] Bradner, S., "Key words for use in RFCs to Indicate Requirement
August 1996. Levels", BCP 14, RFC 2119, March 1997.
[8] Vixie, P., "A Mechanism for Prompt Notification of Zone Changes [8] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, August
(DNS NOTIFY)", RFC 1996, August 1996. 1996.
[9] Bradner, S., "Key words for use in RFCs to Indicate Requirement [9] Vixie, P., "A Mechanism for Prompt Notification of Zone Changes
Levels", BCP 14, RFC 2119, March 1997. (DNS NOTIFY)", RFC 1996, August 1996.
[10] Eastlake, D., "Secure Domain Name System Dynamic Update", [10] Wellington, B., "Secure Domain Name System (DNS) Dynamic
RFC 2137, April 1997. Update", RFC 3007, November 2000.
[11] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", [11] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)",
RFC 2308, March 1998. RFC 2308, March 1998.
[12] Eastlake, D., "DNS Security Operational Considerations", [12] Eastlake, D., "DNS Security Operational Considerations", RFC
RFC 2541, March 1999. 2541, March 1999.
[13] Gudmundsson, O., "Delegation Signer (DS) Resource Record (RR)",
RFC 3658, December 2003.
[14] Orman, H. and P. Hoffman, "Determining Strengths For Public [13] Orman, H. and P. Hoffman, "Determining Strengths For Public
Keys Used For Exchanging Symmetric Keys", BCP 86, RFC 3766, Keys Used For Exchanging Symmetric Keys", BCP 86, RFC 3766,
April 2004. April 2004.
[15] Eastlake, D., Schiller, J., and S. Crocker, "Randomness [14] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005. Requirements for Security", BCP 106, RFC 4086, June 2005.
[16] Hollenbeck, S., "Domain Name System (DNS) Security Extensions [15] Hollenbeck, S., "Domain Name System (DNS) Security Extensions
Mapping for the Extensible Provisioning Protocol (EPP)", Mapping for the Extensible Provisioning Protocol (EPP)", RFC
RFC 4310, December 2005. 4310, December 2005.
[17] Lenstra, A. and E. Verheul, "Selecting Cryptographic Key [16] Lenstra, A. and E. Verheul, "Selecting Cryptographic Key
Sizes", The Journal of Cryptology 14 (255-293), 2001. Sizes", The Journal of Cryptology 14 (255-293), 2001.
[18] Schneier, B., "Applied Cryptography: Protocols, Algorithms, and [17] Schneier, B., "Applied Cryptography: Protocols, Algorithms, and
Source Code in C", ISBN (hardcover) 0-471-12845-7, ISBN Source Code in C", ISBN (hardcover) 0-471-12845-7, ISBN
(paperback) 0-471-59756-2, Published by John Wiley & Sons Inc., (paperback) 0-471-59756-2, Published by John Wiley & Sons Inc.,
1996. 1996.
[19] Rose, S., "NIST DNSSEC workshop notes", June 2001. [18] Rose, S., "NIST DNSSEC workshop notes", June 2001.
[20] Jansen, J., "Use of RSA/SHA-256 DNSKEY and RRSIG Resource [19] Jansen, J., "Use of RSA/SHA-256 DNSKEY and RRSIG Resource
Records in DNSSEC", draft-ietf-dnsext-dnssec-rsasha256-00.txt Records in DNSSEC", Work in Progress, January 2006.
(work in progress), January 2006.
[21] Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer (DS) [20] Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer (DS)
Resource Records (RRs)", draft-ietf-dnsext-ds-sha256-04.txt Resource Records (RRs)", RFC 4509, May 2006.
(work in progress), January 2006.
[21] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and
T. Wright, "Transport Layer Security (TLS) Extensions", RFC
4366, April 2006.
Appendix A. Terminology Appendix A. Terminology
In this document there is some jargon used that is defined in other 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. In most cases, we have not copied the text from the
documents defining the terms but given a more elaborate explanation documents defining the terms but have given a more elaborate
of the meaning. Note that these explanations should not be seen as explanation of the meaning. Note that these explanations should not
authoritative. be seen as authoritative.
Anchored Key: A DNSKEY configured in resolvers around the globe. Anchored key: A DNSKEY configured in resolvers around the globe.
This key is hard to update, hence the term anchored. This key is hard to update, hence the term anchored.
Bogus: Also see Section 5 of [4]. An RRSet in DNSSEC is marked Bogus: Also see Section 5 of [4]. An RRSet in DNSSEC is marked
"Bogus" when a signature of a RRSet does not validate against a "Bogus" when a signature of an RRSet does not validate against a
DNSKEY. DNSKEY.
Key Signing Key or KSK: A Key Signing Key (KSK) is a key that is used 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 exclusively for signing the apex key set. The fact that a key is
a KSK is only relevant to the signing tool. a KSK is only relevant to the signing tool.
Key size: The term 'key size' can be substituted by 'modulus size' Key size: The term 'key size' can be substituted by 'modulus size'
throughout the document. It is mathematically more correct to use throughout the document. It is mathematically more correct to use
modulus size, but as this is a document directed at operators we modulus size, but as this is a document directed at operators we
feel more at ease with the term key size. feel more at ease with the term key size.
Private and Public Keys: DNSSEC secures the DNS through the use of
Private and public keys: DNSSEC secures the DNS through the use of
public key cryptography. Public key cryptography is based on the public key cryptography. Public key cryptography is based on the
existence of two (mathematically related) keys, a public key and a existence of two (mathematically related) keys, a public key and a
private key. The public keys are published in the DNS by use of private key. The public keys are published in the DNS by use of
the DNSKEY Resource Record (DNSKEY RR). Private keys should the DNSKEY Resource Record (DNSKEY RR). Private keys should
remain private. remain private.
Key Rollover: A key rollover (also called key supercession in some Key rollover: A key rollover (also called key supercession in some
environments) is the act of replacing one key pair by another at environments) is the act of replacing one key pair with another at
the end of a key effectivity period. the end of a key effectivity period.
Secure Entry Point key or SEP Key: A KSK that has a parental DS
record pointing to it or is configured as a trust anchor. Secure Entry Point (SEP) key: A KSK that has a parental DS record
Although not required by the protocol we recommend that the SEP pointing to it or is configured as a trust anchor. Although not
flag [3] is set on these keys. required by the protocol, we recommend that the SEP flag [3] is
Self-signature: This is only applies to signatures over DNSKEYs; a set on these keys.
Self-signature: This only applies to signatures over DNSKEYs; a
signature made with DNSKEY x, over DNSKEY x is called a self- signature made with DNSKEY x, over DNSKEY x is called a self-
signature. Note: without further information self-signatures signature. Note: without further information, self-signatures
convey no trust, they are useful to check the authenticity of the convey no trust. They are useful to check the authenticity of the
DNSKEY, i.e. they can be used as a hash. DNSKEY, i.e., they can be used as a hash.
Singing the Zone File: The term used for the event where an
Singing the zone file: The term used for the event where an
administrator joyfully signs its zone file while producing melodic administrator joyfully signs its zone file while producing melodic
sound patterns. sound patterns.
Signer: The system that has access to the private key material and Signer: The system that has access to the private key material and
signs the Resource Record sets in a zone. A signer may be 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 configured to sign only parts of the zone, e.g., only those RRSets
for which existing signatures are about to expire. 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 Zone Signing Key (ZSK): A key that is used for signing all data in a
is only relevant to the signing tool. zone. The fact that a key is a ZSK is only relevant to the
Zone Administrator: The 'role' that is responsible for signing a zone signing tool.
Zone administrator: The 'role' that is responsible for signing a zone
and publishing it on the primary authoritative server. and publishing it on the primary authoritative server.
Appendix B. Zone Signing Key Rollover Howto Appendix B. Zone Signing Key Rollover How-To
Using the pre-published signature scheme and the most conservative Using the pre-published signature scheme and the most conservative
method to assure oneself that data does not live in caches, here method to assure oneself that data does not live in caches, here
follows the "HOWTO". follows the "how-to".
Step 0: The preparation: Create two keys and publish both in your key 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 set. Mark one of the keys "active" and the other "published".
"published". Use the "active" key for signing your zone data. Use the "active" key for signing your zone data. Store the
Store the private part of the "published" key, preferably off- private part of the "published" key, preferably off-line. The
line. protocol does not provide for attributes to mark a key as active
The protocol does not provide for attributes to mark a key as or published. This is something you have to do on your own,
active or published. This is something you have to do on your through the use of a notebook or key management tool.
own, through the use of a notebook or key management tool.
Step 1: Determine expiration: At the beginning of the rollover make a Step 1: Determine expiration: At the beginning of the rollover make a
note of the highest expiration time of signatures in your zone note of the highest expiration time of signatures in your zone
file created with the current key marked as "active". file created with the current key marked as active. Wait until
Wait until the expiration time marked in Step 1 has passed 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 Step 2: Then start using the key that was marked "published" to sign
was marked as "active", mark it as "rolled". your data (i.e., mark it "active"). Stop using the key that was
marked "active"; mark it "rolled".
Step 3: It is safe to engage in a new rollover (Step 1) after at Step 3: It is safe to engage in a new rollover (Step 1) after at
least one "signature validity period". least one signature validity period.
Appendix C. Typographic Conventions Appendix C. Typographic Conventions
The following typographic conventions are used in this document: The following typographic conventions are used in this document:
Key notation: A key is denoted by DNSKEYx, where x is a number or an Key notation: A key is denoted by DNSKEYx, where x is a number or an
identifier, x could be thought of as the key id. identifier, x could be thought of as the key id.
RRSet notations: RRs are only denoted by the type. All other RRSet notations: RRs are only denoted by the type. All other
information - owner, class, rdata and TTL - is left out. Thus: information -- owner, class, rdata, and TTL--is left out. Thus:
"example.com 3600 IN A 192.0.2.1" is reduced to "A". RRSets are a "example.com 3600 IN A 192.0.2.1" is reduced to "A". RRSets are a
list of RRs. A example of this would be: "A1, A2", specifying the list of RRs. A example of this would be "A1, A2", specifying the
RRSet containing two "A" records. This could again be abbreviated RRSet containing two "A" records. This could again be abbreviated to
to just "A". just "A".
Signature notation: Signatures are denoted as RRSIGx(RRSet), which Signature notation: Signatures are denoted as RRSIGx(RRSet), which
means that RRSet is signed with DNSKEYx. means that RRSet is signed with DNSKEYx.
Zone representation: Using the above notation we have simplified the Zone representation: Using the above notation we have simplified the
representation of a signed zone by leaving out all unnecessary representation of a signed zone by leaving out all unnecessary
details such as the names and by representing all data by "SOAx" details such as the names and by representing all data by "SOAx"
SOA representation: SOAs are represented as SOAx, where x is the SOA representation: SOAs are represented as SOAx, where x is the
serial number. serial number.
Using this notation the following signed zone: Using this notation the following signed zone:
example.net. 86400 IN SOA ns.example.net. bert.example.net. ( example.net. 86400 IN SOA ns.example.net. bert.example.net. (
2006022100 ; serial 2006022100 ; serial
86400 ; refresh ( 24 hours) 86400 ; refresh ( 24 hours)
7200 ; retry ( 2 hours) 7200 ; retry ( 2 hours)
3600000 ; expire (1000 hours) 3600000 ; expire (1000 hours)
28800 ) ; minimum ( 8 hours) 28800 ) ; minimum ( 8 hours)
86400 RRSIG SOA 5 2 86400 20130522213204 ( 86400 RRSIG SOA 5 2 86400 20130522213204 (
20130422213204 14 example.net. 20130422213204 14 example.net.
skipping to change at page 33, line 4 skipping to change at page 33, line 31
SOA2006022100 SOA2006022100
RRSIG14(SOA2006022100) RRSIG14(SOA2006022100)
DNSKEY14 DNSKEY14
DNSKEY15 DNSKEY15
RRSIG14(KEY) RRSIG14(KEY)
RRSIG15(KEY) RRSIG15(KEY)
The rest of the zone data has the same signature as the SOA record, The rest of the zone data has the same signature as the SOA record,
i.e a RRSIG created with DNSKEY 14. i.e., an 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
instead of Key validity period.
Modified the order of the sections, based on a suggestion by Rip
Loomis.
Included parts from RFC 2541 [12]. Most of its ground was already
covered. This document obsoletes RFC 2541 [12]. Section 3.1.2
deserves some review as it in contrast to RFC 2541 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.
D.6. draft-ietf-dnsop-dnssec-operational-practices-05
Applied some another set of comments that came in _after_ the the
WGLC.
Applied comments from Hilarie Orman and made a referece to RFC 3766.
Deleted of a lot of key length discussion and took over the
recommendations from RFC 3766.
Reworked all the heading of the rollover figures
D.7. draft-ietf-dnsop-dnssec-operational-practices-06
One comment from Scott Rose applied.
Marcos Sanz gave a lots of editorial nits. Almost all are
incorporated.
D.8. draft-ietf-dnsop-dnssec-operational-practices-07
Peter Koch's comments applied.
SHA-1/SHA-256 remarks added
D.9. draft-ietf-dnsop-dnssec-operational-practices-08
IESG comments applied. Added headers and some captions to the tables
and applied all the nits.
IESG DISCUSS comments applied
Authors' Addresses Authors' Addresses
Olaf M. Kolkman Olaf M. Kolkman
NLnet Labs NLnet Labs
Kruislaan 419 Kruislaan 419
Amsterdam 1098 VA Amsterdam 1098 VA
The Netherlands The Netherlands
Email: olaf@nlnetlabs.nl EMail: olaf@nlnetlabs.nl
URI: http://www.nlnetlabs.nl URI: http://www.nlnetlabs.nl
Miek Gieben R. (Miek) Gieben
NLnet Labs
Kruislaan 419
Amsterdam 1098 VA
The Netherlands
Email: miek@nlnetlabs.nl EMail: miek@miek.nl
URI: http://www.nlnetlabs.nl
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This document is subject to the rights, licenses and restrictions
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This document and the information contained herein are provided on an
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skipping to change at page 36, line 29 skipping to change at page 35, line 45
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This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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