draft-ietf-dnsop-dnssec-operational-practices-03.txt   draft-ietf-dnsop-dnssec-operational-practices-04.txt 
DNSOP O. Kolkman DNSOP O. Kolkman
Internet-Draft RIPE NCC Internet-Draft RIPE NCC
Expires: June 23, 2005 R. Gieben Expires: September 2, 2005 R. Gieben
NLnet Labs NLnet Labs
December 23, 2004 March 2005
DNSSEC Operational Practices DNSSEC Operational Practices
draft-ietf-dnsop-dnssec-operational-practices-03.txt draft-ietf-dnsop-dnssec-operational-practices-04.txt
Status of this Memo Status of this Memo
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RFC 3668. aware will be disclosed, in accordance with Section 6 of BCP 79.
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2005).
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 as key generation, key
storage, signature generation, key rollover and related policies. storage, signature generation, key rollover and related policies.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 The Use of the Term 'key' . . . . . . . . . . . . . . . . 3 1.1 The Use of the Term 'key' . . . . . . . . . . . . . . . . 4
1.2 Time Definitions . . . . . . . . . . . . . . . . . . . . . 4 1.2 Time Definitions . . . . . . . . . . . . . . . . . . . . . 5
2. Keeping the Chain of Trust Intact . . . . . . . . . . . . . . 4 2. Keeping the Chain of Trust Intact . . . . . . . . . . . . . . 5
3. Keys Generation and Storage . . . . . . . . . . . . . . . . . 5 3. Keys Generation and Storage . . . . . . . . . . . . . . . . . 6
3.1 Zone and Key Signing Keys . . . . . . . . . . . . . . . . 5 3.1 Zone and Key Signing Keys . . . . . . . . . . . . . . . . 6
3.1.1 Motivations for the KSK and ZSK Separation . . . . . . 5 3.1.1 Motivations for the KSK and ZSK Separation . . . . . . 6
3.1.2 KSKs for high level zones . . . . . . . . . . . . . . 6 3.1.2 KSKs for high level zones . . . . . . . . . . . . . . 7
3.2 Randomness . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Randomness . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 Key Effectivity Period . . . . . . . . . . . . . . . . . . 7 3.3 Key Effectivity Period . . . . . . . . . . . . . . . . . . 8
3.4 Key Algorithm . . . . . . . . . . . . . . . . . . . . . . 8 3.4 Key Algorithm . . . . . . . . . . . . . . . . . . . . . . 9
3.5 Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . 8 3.5 Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . 9
3.6 Private Key Storage . . . . . . . . . . . . . . . . . . . 9 3.6 Private Key Storage . . . . . . . . . . . . . . . . . . . 10
4. Signature generation, Key Rollover and Related Policies . . . 10 4. Signature generation, Key Rollover and Related Policies . . . 11
4.1 Time in DNSSEC . . . . . . . . . . . . . . . . . . . . . . 10 4.1 Time in DNSSEC . . . . . . . . . . . . . . . . . . . . . . 11
4.1.1 Time Considerations . . . . . . . . . . . . . . . . . 10 4.1.1 Time Considerations . . . . . . . . . . . . . . . . . 11
4.2 Key Rollovers . . . . . . . . . . . . . . . . . . . . . . 12 4.2 Key Rollovers . . . . . . . . . . . . . . . . . . . . . . 13
4.2.1 Difference Between ZSK and KSK Rollovers . . . . . . . 12 4.2.1 Zone-signing Key Rollovers . . . . . . . . . . . . . . 13
4.2.2 Zone-signing Key Rollovers . . . . . . . . . . . . . . 13 4.2.2 Key-signing Key Rollovers . . . . . . . . . . . . . . 17
4.2.3 Key-signing Key Rollovers . . . . . . . . . . . . . . 17 4.2.3 Difference Between ZSK and KSK Rollovers . . . . . . . 18
4.2.4 Automated Key Rollovers . . . . . . . . . . . . . . . 18 4.2.4 Automated Key Rollovers . . . . . . . . . . . . . . . 19
4.3 Planning for Emergency Key Rollover . . . . . . . . . . . 18 4.3 Planning for Emergency Key Rollover . . . . . . . . . . . 19
4.3.1 KSK Compromise . . . . . . . . . . . . . . . . . . . . 19 4.3.1 KSK Compromise . . . . . . . . . . . . . . . . . . . . 20
4.3.2 ZSK Compromise . . . . . . . . . . . . . . . . . . . . 19 4.3.2 ZSK Compromise . . . . . . . . . . . . . . . . . . . . 20
4.3.3 Compromises of Keys Anchored in Resolvers . . . . . . 19 4.3.3 Compromises of Keys Anchored in Resolvers . . . . . . 20
4.4 Parental Policies . . . . . . . . . . . . . . . . . . . . 20 4.4 Parental Policies . . . . . . . . . . . . . . . . . . . . 21
4.4.1 Initial Key Exchanges and Parental Policies 4.4.1 Initial Key Exchanges and Parental Policies
Considerations . . . . . . . . . . . . . . . . . . . . 20 Considerations . . . . . . . . . . . . . . . . . . . . 21
4.4.2 Storing Keys So Hashes Can Be Regenerated . . . . . . 20 4.4.2 Storing Keys or Hashes? . . . . . . . . . . . . . . . 21
4.4.3 Security Lameness . . . . . . . . . . . . . . . . . . 21 4.4.3 Security Lameness . . . . . . . . . . . . . . . . . . 22
4.4.4 DS Signature Validity Period . . . . . . . . . . . . . 21 4.4.4 DS Signature Validity Period . . . . . . . . . . . . . 22
5. Security Considerations . . . . . . . . . . . . . . . . . . . 21 5. Security Considerations . . . . . . . . . . . . . . . . . . . 23
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.1 Normative References . . . . . . . . . . . . . . . . . . . . 22 7.1 Normative References . . . . . . . . . . . . . . . . . . . 24
7.2 Informative References . . . . . . . . . . . . . . . . . . . 23 7.2 Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 25
A. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 24 A. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 25
B. Zone-signing Key Rollover Howto . . . . . . . . . . . . . . . 24 B. Zone-signing Key Rollover Howto . . . . . . . . . . . . . . . 26
C. Typographic Conventions . . . . . . . . . . . . . . . . . . . 25 C. Typographic Conventions . . . . . . . . . . . . . . . . . . . 26
D. Document Details and Changes . . . . . . . . . . . . . . . . . 26 D. Document Details and Changes . . . . . . . . . . . . . . . . . 29
D.1 draft-ietf-dnsop-dnssec-operational-practices-00 . . . . . 27 D.1 draft-ietf-dnsop-dnssec-operational-practices-00 . . . . . 29
D.2 draft-ietf-dnsop-dnssec-operational-practices-01 . . . . . 27 D.2 draft-ietf-dnsop-dnssec-operational-practices-01 . . . . . 29
D.3 draft-ietf-dnsop-dnssec-operational-practices-02 . . . . . 27 D.3 draft-ietf-dnsop-dnssec-operational-practices-02 . . . . . 29
D.4 draft-ietf-dnsop-dnssec-operational-practices-03 . . . . . 27 D.4 draft-ietf-dnsop-dnssec-operational-practices-03 . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . . 28 D.5 draft-ietf-dnsop-dnssec-operational-practices-04 . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . . 31
1. Introduction 1. Introduction
During workshops and early operational deployment tests, operators During workshops and early operational deployment tests, operators
and system administrators gained experience about operating the DNS and system administrators gained experience about operating the DNS
with security extensions (DNSSEC). This document translates these with security extensions (DNSSEC). This document translates these
experiences into a set of practices for zone administrators. At the experiences into a set of practices for zone administrators. At the
time of writing, there exists very little experience with DNSSEC in time of writing, there exists very little experience with DNSSEC in
production environments, this document should therefore explicitly production environments; this document should therefore explicitly
not be seen as representing 'Best Current Practices'. 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 resigning or key rollovers intended that maintenance of zones such as resigning or key rollovers
be transparent to any verifying clients on the Internet. 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, these 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 supersession, of keys. Finally Section 4.4 discusses rollover, or which, 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 RFC2119 [6] language does not apply. no protocol specifications, the RFC2119 [4] language does not apply.
This document obsoletes RFC2541 [1] This document obsoletes RFC2541 [7]
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
[11]). Therefore, this document will use the term 'key' rather [11]). Therefore, this document will use the term 'key' rather
loosely. Where it is written that 'a key is used to sign data' it is 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
skipping to change at page 4, line 19 skipping to change at page 5, line 19
o "Signature validity period" o "Signature validity period"
The period that a signature is valid. It starts at the time The period that a signature is valid. It starts at the time
specified in the signature inception field of the RRSIG RR and specified in the signature inception field of the RRSIG RR and
ends at the time specified in the expiration field of the RRSIG ends at the time specified in the expiration field of the RRSIG
RR. RR.
o "Signature publication period" o "Signature publication period"
Time after which a signature (made with a specific key) is Time after which a signature (made with a specific key) is
replaced with a new signature (made with the same key). This replaced with a new signature (made with the same key). This
replacement takes place by publishing the relevant RRSIG in the replacement takes place by publishing the relevant RRSIG in the
master zone file. master zone file.
After one stopped publishing an RRSIG in a zone file it will After one stopped publishing an RRSIG in a zone it may take a
take a while before the RRSIG has actually been removed from while before the RRSIG has expired from caches and has actually
the DNS. been removed from the DNS.
o "Key effectivity period" o "Key effectivity period"
The period during a key pair is effective. This period is The period which a key pair is expected to be effective. This
defined as the time between the first inception time stamp and period is defined as the time between the first inception time
the last expiration date of any signature made with this key. stamp and the last expiration date of any signature made with
this key.
The key effectivity period can span multiple signature validity The key effectivity period can span multiple signature validity
intervals. periods.
o "Maximum/Minimum Zone TTL" o "Maximum/Minimum Zone TTL"
The maximum or minimum value of the TTLs from the complete set The maximum or minimum value of the TTLs from the complete set
of RRs in a zone. of RRs in a zone.
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, which may cause of trust will result in data being marked as Bogus (as defined in [2]
entire (sub)domains to become invisible to verifying clients. The section 5), which may cause entire (sub)domains to become invisible
administrators of secured zones have to realize that their zone is, to verifying clients. The administrators of secured zones have to
to their clients, part of a chain of trust. realize that their zone is, to their clients, part of a chain of
trust.
As mentioned in the introduction, the procedures herein are intended As mentioned in the introduction, the procedures herein are intended
to ensure maintenance of zones, such as resigning or key rollovers, to ensure maintenance of zones, such as resigning or key rollovers,
be transparent to the verifying clients on the Internet. will be transparent to the verifying clients on the 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
transfered to other secondary authoritative nameservers, during which transfered to other secondary authoritative nameservers and clients
period clients may be fetching data from caching non-authoritative may be fetching data from caching non-authoritative servers.
servers.
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 nameserver
or some middle box. Only by carefully using the available timing or some middle box. Only by carefully using the available timing
parameters can a zone administrator assure that the data necessary parameters can a zone administrator assure that the data necessary
for verification can be obtained. 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 as soon as possible must be made. Then zone administrators will have
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 to
deliberately break the chain of trust and making secured sub domains deliberately break the chain of trust and making secured sub domains
invisible to security aware resolvers. Also see Section 4.3. 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 DNSKEYs. The DNSSEC validation protocol does not distinguish between DNSKEYs.
All DNSKEYs can be used during the validation. In practice operators All DNSKEYs can be used during the validation. In practice operators
use Key Singing and Zone Signing Keys and use the so called SEP flag use Key Signing and Zone Signing Keys and use the so-called (Secure
to distinguish between them during operations. The dynamics and Entry Point) SEP flag to distinguish between them during operations.
considerations are discussed below. The dynamics and considerations are discussed below.
To make zone re-signing and key rollovers procedures easier to To make zone resigning 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 RR set in a zone. (KSK). These keys will only sign the apex DNSKEY RR set in a zone.
Other keys can be used to sign all the RRsets in a zone and are 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 (ZSK). 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 - the
so called Secure Entry Point keys (SEP). In this document we assume SEP keys. In this document we assume a one-to-one mapping between
a one-to-one mapping between KSK and SEP keys and we assume the SEP KSK and SEP keys and we assume the SEP flag [1] to be set on all
flag [2] to be set on KSKs. 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 to 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 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. used to sign a small fraction of the zone data. Also when
verifying the KSK is only used to verify the zone's keyset.
o As the KSK is only used to sign a key set, which is most probably 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.
o No parent/child interaction is required when ZSKs are updated.
The KSK is used less than ZSK, once a key set is signed with the KSK For almost any method of key management and zone signing the KSK is
all the keys in the key set can be used as ZSK. If a ZSK is used less frequently than the ZSK. Once a key set is signed with the
KSK all the keys in the key set can be used as ZSK. If a ZSK is
compromised, it can be simply dropped from the key set. The new key compromised, it can be simply dropped from the key set. The new key
set is then resigned with the KSK. set is then resigned 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 even RR. If the flag field is an odd number it is a KSK. If it is an
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" in 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 verifying resolvers that have the particular key configured as
trusted entry points. Hence, the key effectivity period of these trusted entry points. Hence, the key effectivity period of these
keys can and should be made much longer. Although, given a long keys can and should be made much longer. Although, given a long
enough key, the Key Usage Time can be on the order of years we enough key, the Key Usage Time can be on the order of years we
suggest to plan for a key effectivity of the order of a few months so suggest planning for a key effectivity of the order of a few months
that a key rollover remains an operational routine. so that a 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 sub
domain). Therefore, extra care should be taken with high level zones domain). Therefore, extra care should be taken with high level zones
and strong keys used. and strong keys 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 name space of all resolvers using that root zone (except
in the case of resolvers that have locally configured the public key in the case of resolvers that have locally configured the public key
of a sub domain). Therefore, the utmost care must be taken in the of a sub domain). 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 an authentication of DNS data. Securely updating the trust anchors in
enormous population of resolvers around the world will be extremely an enormous population of resolvers around the world will be
difficult. extremely difficult.
3.2 Randomness 3.2 Randomness
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 suggestions for the generation of random keys will be found in
RFC1750 [5]. One should carefully assess if the random number RFC1750 [3]. 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
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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 latter
is fairly new and still needs to be standardized for usage in DNSSEC. is fairly new and still needs to be standardized for usage in DNSSEC.
RSA has been developed in an open and transparent manner. As the 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 creation DSA has been developed by NIST. The creation of signatures is
is roughly the same speed as with RSA, but is 10 to 40 times as slow roughly done at the same speed as with RSA, but is 10 to 40 times as
for verification [11]. slow for verification [11].
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 (theoretical)
cracks, we recommend the usage of SHA1. cracks, we recommend the usage of SHA1.
In 2005 some discoveries were made that SHA-1 also has some
weaknesses. Currently SHA-1 is strong enough for DNSSEC. It is
expected that a new hashing algorithm is rolled out, before any
attack becomes practical.
3.5 Key Sizes 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 and how much data will be signed account how long a key will be used and how much data will be signed
during the key publication period. It is hard to give precise during the key publication period. It is hard to give precise
recommendations but Lenstra and Verheul [10] supplied the following recommendations but Lenstra and Verheul [10] supplied the following
table with lower bound estimates for cryptographic key sizes. Their table with lower bound estimates for cryptographic key sizes. Their
recommendations are based on a set of explicitly formulated parameter recommendations are based on a set of explicitly formulated parameter
settings, combined with existing data points about cryptographic settings, combined with existing data points about cryptographic
systems. For details we refer to the original paper. systems. For details we refer to the original paper.
skipping to change at page 9, line 30 skipping to change at page 10, line 30
2010 1369 2027 2299 2010 1369 2027 2299
2011 1416 2028 2362 2011 1416 2028 2362
2012 1464 2029 2427 2012 1464 2029 2427
2013 1513 2013 1513
2014 1562 2014 1562
For example, should you wish your key to last three years from 2003, For example, should you wish your key to last three years from 2003,
check the RSA key size values for 2006 in this table. In this case check the RSA key size values for 2006 in this table. In this case
it should be at least 1191 bits. it should be at least 1191 bits.
Please keep in mind that nobody can see into the future, and that
these key lengths are only provided here as a guide.
When determining a key size one should take into account that a large When determining a key size one should take into account that a large
key will be slower during generation and verification. For RSA, key will be slower during generation and verification. For RSA,
verification, the most common operation, will vary roughly with the verification, the most common operation, will vary roughly with the
square of the key size signing will vary with the cube of the key square of the key size; signing will vary with the cube of the key
size length, and key generation will vary with the fourth power of size length; and key generation will vary with the fourth power of
the modulus length. Besides larger keys will increase the sizes of the modulus length. Besides larger keys will increase the sizes of
the RRSIG and DNSKEY records and will therefore increase the chance the RRSIG and DNSKEY records and will therefore increase the chance
of DNS UDP packet overflow. Also see Section 3.1.1. of DNS UDP packet overflow. Also see Section 3.1.1 for a discussion
of how keys serving different roles (ZSK v. KSK) may need different
key strengths.
3.6 Private Key Storage 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 be kept and used in off-line, non-network zone file master copy be kept and used in off-line, non-network
connected, physically secure machines only. Periodically an connected, physically secure machines only. Periodically an
application can be run to add authentication to a zone by adding application can be run to add authentication to a zone by adding
RRSIG and NSEC RRs. Then the augmented file can be transferred, RRSIG and NSEC RRs. Then the augmented file can be transferred,
perhaps by sneaker-net, to the networked zone primary server machine. perhaps by sneaker-net, to the networked zone primary server machine.
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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 the
machines on which zone files are maintained will be connected to a machines on which zone files are maintained will be connected to a
network. Operators are advised to take security measures to shield 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 RFC2137 [7] both the master For dynamically updated secured zones [5] both the master copy and
copy and the private key that is used to update signatures on updated the private key that is used to update signatures on updated RRs will
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 RR's refresh, Without DNSSEC all times in DNS are relative. The SOA RR's refresh,
retry and expiration timers are counters that are used to determine retry and expiration timers are counters that are used to determine
the time elapsed after a slave server synchronized (or tried to the time elapsed after a slave server synchronized (or tried to
synchronize) with a master server. The Time to Live (TTL) value and synchronize) with a master server. The Time to Live (TTL) value and
the SOA RR minimum TTL parameter [8] are used to determine how long a the SOA RR minimum TTL parameter [6] are used to determine how long a
forwarder should cache data after it has been fetched from an forwarder should cache data after it has been fetched from an
authoritative server. By using a signature validity period, DNSSEC authoritative server. By using a signature validity period, DNSSEC
introduces the notion of an absolute time in the DNS. Signatures in introduces the notion of an absolute time in the DNS. Signatures in
DNSSEC have an expiration date after which the signature is marked as DNSSEC have an expiration date after which the signature is marked as
invalid and the signed data is to be considered bogus. invalid and the signed data is to be 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 [3] suggests that "the resolver may use the time 7.1 of [2] 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 be at least one o We suggest the signature publication period to be at least one
maximum TTL smaller than the signature validity period. maximum TTL smaller than the signature validity period.
Resigning a zone shortly before the end of the signature Resigning 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
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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 keep
all data, until is completed. This applies to all RRs needed all data, until is completed. This applies to all RRs needed
to complete the chain of trust: DSs, DNSKEYs, RRSIGs, and the to complete the chain of trust: DSs, DNSKEYs, RRSIGs, and the
final answers i.e. the RR set that is returned for the initial final answers i.e. the RR set that is returned for the initial
query. 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, DSs, DNSKEYs and RRSIGs benefit from
caching. The TTL on those should be relatively long. 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 server 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 the
slave server not to give out any answer. 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 zone will not respond on queries. The time of happens the zone will not respond on queries. The time of
expiration is set in the SOA record and is relative to the last expiration is set in the SOA record and is relative to the last
successful refresh between the master and the slave server. successful refresh between the master and the slave server.
There exists no coupling between the signature expiration of There exists no coupling between the signature expiration of
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the signatures expire well before the SOA expiration timer 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, the effects can be minimized where the SOA expiration However, the effects can be minimized where the SOA expiration
time is equal or smaller than the signature validity period. time is equal or smaller than the signature validity period.
The consequence of an authoritative server not being able to The consequence of an authoritative server not being able to
update a zone, whilst that zone includes expired signatures, is update a zone, whilst that zone includes expired signatures, is
that non-secure resolvers will continue to be able to resolve that non-secure resolvers will continue to be able to resolve
data served by the particular slave servers while security data served by the particular slave servers while security
aware resolvers will experience problems because of answers aware resolvers will experience problems because of answers
being marked as bogus. being 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 time out. noticed before the actual signature time out.
We also suggest that operators of nameservers with slave zones We also suggest that operators of nameservers that supply
develop 'watch dogs' to spot upcoming signature expirations in secondary services develop 'watch dogs' to spot upcoming
slave zones, and take appropriate action. signature expirations in zones they slave, and take appropriate
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 secondary zones expire; How quickly can I reach an all my secondary zones expire; How quickly can I reach an
administrator and load a valid zone? All these arguments are administrator of secondary servers to load a valid zone? All
not DNSSEC specific but may influence the choice of your these arguments are not DNSSEC specific but may influence the
signature validity intervals. choice 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 supersessions, 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 is when zone material signed with The most pressing example of this is when zone material signed with
an old key is being validated by a resolver which does not have the an old key is being validated by a resolver which does not have the
old zone key cached. If the old key is no longer present in the 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 which 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 Difference Between ZSK and KSK Rollovers
Note that KSK rollovers and ZSK rollovers are different. A zone-key
rollover can be handled in two different ways: pre-publish (Section
Section 4.2.2.1) and double signature (Section Section 4.2.2.2).
As the KSK is used to validate the key set and because the KSK is not
changed during a ZSK rollover, a cache is able to validate the new
key set of the zone. The pre-publish method does not work for a KSK
rollover. The following example demonstrates that, here rollover the
KSK from DNSKEY1 to DNSKEY2 using the NONE working pre-publish
method.
normal pre-roll roll after
SOA0 SOA1 SOA2 SOA3
RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2) RRSIG11(SOA3)
DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY2
DNSKEY10 DNSKEY2 DNSKEY2 DNSKEY10
DNSKEY10 DNSKEY10
RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG2(DNSKEY) RRSIG2 (DNSKEY)
RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY)
A cache that queries the zone during the "normal" step gets back
DNSKEY1. The DS RR and the key set are cached. If the TTL of the DS
RR is large enough, the DS RR remains in the cache until the "after"
step. If in this case, the key set TTL expires, and the cache
queries for the zone again, it will get back the new key set signed
by DNSKEY2. It will then try to validate the key set with DNSKEY1
and will fail.
4.2.2 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 that
during the rollover data still cached can be verified with the new during the rollover data still cached can be verified with the new
key sets or newly generated signatures can be verified with the keys key sets or newly generated signatures can be verified with the keys
still in caches. One schema uses double signatures, it is described still in caches. One schema, described in Section 4.2.1.2, uses
in Section 4.2.2.2, the other uses key pre-publication (Section double signatures; the other uses key pre-publication
4.2.2.1). The pros, cons and recommendations are described in (Section 4.2.1.1). The pros, cons and recommendations are described
Section 4.2.2.3. in Section 4.2.1.3.
4.2.2.1 Pre-publish key set Rollover 4.2.1.1 Pre-publish key set 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 so-called "pre-publish
rollover".This method has advantages in the case of a key compromise. rollover".This method has advantages in the case of a key compromise.
If the old key is compromised, the new key has already been If the old key is compromised, the new key has already been
distributed in the DNS. The zone administrator is then able to distributed in the DNS. The zone administrator is then able to
quickly switch to the new key and remove the compromised key from the quickly switch to the new key and remove the compromised key from the
zone. Another major advantage is that the zone size does not double, zone. Another major advantage is that the zone size does not double,
as is the case with the double signature ZSK rollover. A small as is the case with the double signature ZSK rollover. A small
"HOWTO" for this kind of rollover can be found in Appendix B. "HOWTO" for this kind of rollover can be found in Appendix B.
normal pre-roll roll after normal pre-roll roll after
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)
normal: Version 0 of the zone: DNSKEY 1 is the key-signing key. normal: Version 0 of the zone: DNSKEY 1 is the key-signing key.
DNSKEY 10 is used to sign all the data of the zone, the DNSKEY 10 is used to sign all the data of the zone, the zone-
zone-signing key. signing key.
pre-roll: DNSKEY 11 is introduced into the key set. Note that no pre-roll: 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. This equates to two times the Maximum Zone TTL. key set. This equates to two times the Maximum Zone TTL.
roll: At the rollover stage (SOA serial 1) DNSKEY 11 is used to sign roll: At the rollover stage (SOA serial 2) DNSKEY 11 is used to sign
the data in the zone exclusively (i.e. all the signatures from the data in the zone exclusively (i.e. all the signatures from
DNSKEY 10 are removed from the zone). DNSKEY 10 remains published DNSKEY 10 are removed from the zone). DNSKEY 10 remains published
in the key set. This way data that was loaded into caches from in the key set. This way data that was loaded into caches from
version 1 of the zone can still be verified with key sets fetched version 1 of the zone can still be verified with key sets fetched
from version 2 of the zone. from version 2 of the zone.
The minimum time that the key set including DNSKEY 10 is to be The minimum time that the key set including DNSKEY 10 is to be
published is the time that it takes for zone data from the published is the time that it takes for zone data from the
previous version of the zone to expire from old caches i.e. the previous version of the zone to expire from old caches i.e. the
time it takes for this zone to propagate to all authoritative time it takes for this zone to propagate to all authoritative
servers plus the Maximum Zone TTL value of any of the data in the servers plus the Maximum Zone TTL value of any of the data in the
previous version of the zone. previous version of the zone.
after: DNSKEY 10 is removed from the zone. The key set, now only after: DNSKEY 10 is removed from the zone. The key set, now only
containing DNSKEY 11 is resigned with the DNSKEY 1. containing DNSKEY 1 and DNSKEY 11 is resigned with the 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 "after" as (we show two rollovers); the future key is introduced in "after" as
DNSKEY 12 and again a newer one, numbered 13, in "2nd after": DNSKEY 12 and again a newer one, numbered 13, in "2nd after":
normal roll after normal roll after
SOA0 SOA2 SOA3 SOA0 SOA2 SOA3
RRSIG10(SOA0) RRSIG11(SOA2) RRSIG11(SOA3) RRSIG10(SOA0) RRSIG11(SOA2) RRSIG11(SOA3)
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DNSKEY11 DNSKEY12 DNSKEY11 DNSKEY12
DNSKEY12 DNSKEY13 DNSKEY12 DNSKEY13
RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY)
RRSIG12(DNSKEY) RRSIG12(DNSKEY) RRSIG12(DNSKEY) RRSIG12(DNSKEY)
Note that the key introduced after the rollover is not used for Note that the key introduced after the rollover is not used for
production yet; the private key can thus be stored in a physically production yet; the private key can thus be stored in a physically
secure manner and does not need to be 'fetched' every time a zone secure manner and does not need to be 'fetched' every time a zone
needs to be signed. needs to be signed.
4.2.2.2 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 sig rollover".
During the rollover stage the new version of the zone file will need During the rollover stage the new version of the zone file will need
to propagate to all authoritative servers and the data that exists in to propagate to all authoritative servers and the data that exists in
(distant) caches will need to expire, this will take at least the (distant) caches will need to expire, requiring at least the maximum
maximum Zone TTL . Zone TTL.
normal roll after normal roll after
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)
normal: Version 0 of the zone: DNSKEY 1 is the key-signing key. normal: Version 0 of the zone: DNSKEY 1 is the key-signing key.
DNSKEY 10 is used to sign all the data of the zone, the DNSKEY 10 is used to sign all the data of the zone, the zone-
zone-signing key. signing key.
roll: At the rollover stage (SOA serial 1) DNSKEY 11 is introduced roll: At the rollover stage (SOA serial 1) DNSKEY 11 is introduced
into the key set and all the data in the zone is signed with into the key set and all the data in the zone is signed with
DNSKEY 10 and DNSKEY 11. The rollover period will need to exist DNSKEY 10 and DNSKEY 11. The rollover period will need to exist
until all data from version 0 of the zone has expired from remote until all data from version 0 of the zone has expired from remote
caches. This will take at least the maximum Zone TTL of version 0 caches. This will take at least the maximum Zone TTL of version 0
of the zone. of the zone.
after: DNSKEY 10 is removed from the zone. All the signatures from after: DNSKEY 10 is removed from the zone. All the signatures from
DNSKEY 10 are removed from the zone. The key set, now only DNSKEY 10 are removed from the zone. The key set, now only
containing DNSKEY 11, is resigned with DNSKEY 1. containing DNSKEY 11, is resigned with DNSKEY 1.
At every instance the data from the previous version of the zone can At every instance, RRSIGs from the previous version of the zone can
be verified with the key from the current version and the other way be verified with the DNSKEY RRset from the current version and the
around. The data from the current version can be verified with the other way around. The data from the current version can be verified
data from the previous version of the zone. The duration of the with the data from the previous version of the zone. The duration of
rollover phase and the period between rollovers should be at least the rollover phase and the period between rollovers should be at
the "Maximum Zone TTL". least the "Maximum Zone TTL".
Making sure that the rollover phase lasts until the signature Making sure that the rollover phase lasts until the signature
expiration time of the data in version 0 of the zone is recommended. expiration time of the data in version 0 of the zone is recommended.
This way all caches are cleared of the old signatures. However, this This way all caches are cleared of the old signatures. However, this
date could be considerably longer than the Maximum Zone TTL, making date could be considerably longer than the Maximum Zone TTL, making
the rollover a lengthy procedure. 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.
4.2.2.3 Pros and Cons of the Schemes 4.2.1.3 Pros and Cons of the Schemes
Pre-publish-key set rollover: This rollover does not involve signing Pre-publish-key set rollover: This rollover does not involve signing
the zone data twice. Instead, just before the actual rollover, the zone data twice. Instead, before the actual rollover, the new
the new key is published in the key set and thus available for key is published in the key set and thus available for
cryptanalysis attacks. A small disadvantage is that this process cryptanalysis attacks. A small disadvantage is that this process
requires four steps. Also the pre-publish scheme will not work requires four steps. Also the pre-publish scheme involves more
for KSKs as explained in Section 4.2. parental work when used for KSK rollovers as explained in
Section 4.2.
Double signature rollover: The drawback of this signing scheme is Double signature rollover: The drawback of this signing scheme is
that during the rollover the number of signatures in your zone that during the rollover the number of signatures in your zone
doubles, this may be prohibitive if you have very big zones. An doubles, this may be prohibitive if you have very big zones. An
advantage is that it only requires three steps. advantage is that it only requires three steps.
4.2.3 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.
normal roll after normal roll after
skipping to change at page 17, line 45 skipping to change at page 17, line 46
RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY)
normal: Version 0 of the zone. The parental DS points to DNSKEY1. normal: Version 0 of the zone. The parental DS points to DNSKEY1.
Before the rollover starts the child will have to verify what the Before the rollover starts the child will have to verify what the
TTL is of the DS RR that points to DNSKEY1 - it is needed during TTL is of the DS RR that points to DNSKEY1 - it is needed during
the rollover and we refer to the value as TTL_DS. the rollover and we refer to the value as TTL_DS.
roll: During the rollover phase the zone administrator generates a roll: During the rollover phase the zone administrator generates a
second KSK, DNSKEY2. The key is provided to the parent and the second KSK, DNSKEY2. The key is provided to the parent and the
child will have to wait until a new DS RR has been generated that child will have to wait until a new DS RR has been generated that
points to DNSKEY2. After that DS RR has been published on all points to DNSKEY2. After that DS RR has been published on all
servers authoritative for the parents zone, the zone administrator servers authoritative for the parent's zone, the zone
has to wait at least TTL_DS to make sure that the old DS RR has administrator has to wait at least TTL_DS to make sure that the
expired from caches. old DS RR has expired from caches.
after: DNSKEY1 has been removed. after: 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 hat chain of trust with the child. It also is based on the premises that
the parent only has one DS RR (per algorithm) per zone. An 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 where trust relation, the interaction can be performed in-band, and the
removal of the keys by the child can be signaled by the parent. In removal of the keys by the child can possibly be signaled by the
this mechanism there are periods where there are two DS RRs at the parent. In this mechanism there are periods where there are two DS
parent. Since at the moment of writing the protocol for this RRs at the parent. Since at the moment of writing the protocol for
interaction has not been developed further discussion is out of scope this interaction has not been developed further discussion is out of
for this document. scope for this document.
4.2.3 Difference Between ZSK and KSK Rollovers
Note that KSK rollovers and ZSK rollovers are different. A zone-key
rollover can be handled in two different ways: pre-publish (Section
Section 4.2.1.1) and double signature (Section Section 4.2.1.2).
As the KSK is used to validate the key set and because the KSK is not
changed during a ZSK rollover, a cache is able to validate the new
key set of the zone. The pre-publish method would work for a KSK
rollover. The record that are to be pre-published are the parental
DS RRs.
The pre-publish method has some drawbacks. We first describe the
rollover scheme and then indicate these drawbacks.
normal pre-roll roll after
Parent:
SOA0 SOA1 SOA2 SOA3
RRSIGpar(SOA0) RRSIGpar(SOA1) RRSIGpar(SOA2) RRSIGpar(SOA3)
DS1 DS1 DS1 DS2
DS2 DS2
RRSIGpar(DS) RRSIGpar(DS) RRSIGpar(DS) RRSIGpar(DS)
Child:
SOA0 SOA0 SOA1 SOA1
RRSIG10(SOA0) RRSIG10(SOA0) RRSIG10(SOA1) RRSIG10(SOA1)
DNSKEY1 DNSKEY1 DNSKEY2 DNSKEY2
DNSKEY10 DNSKEY10 DNSKEY10 DNSKEY10
RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG2(DNSKEY) RRSIG2 (DNSKEY)
RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY)
When the child zone wants to roll it notifies the parent during the
pre-roll phase and submits the new key to the parent. The parent
publishes DS1 and DS2, pointing to DNSKEY1 and DNSKEY2 respectively.
During the rollover, which can take place as soon as the new DS set
propagated through the DNS, the child replaces DNSKEY1 with DNSKEY2.
Immediately after that it can notify the parent that the old DS
record can be deleted.
The drawbacks of these scheme are that during the pre-roll phase the
parent cannot verify the match between the DS RR and DNSKEY2 using
the DNS. Besides, we introduce a "security lame" DS record
Section 4.4.3. Finally the child-parent interaction consists of two
steps. The "double signature" method only needs one interaction.
4.2.4 Automated Key Rollovers 4.2.4 Automated Key Rollovers
As keys must be renewed periodically, there are 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 that:
o ZSK rollovers are easy to automate as only the local zone is o ZSK rollovers are easy to automate as only the local zone is
involved. involved.
o A KSK rollover needs interaction between the parent and child. o A KSK rollover needs interaction between the parent and child.
Data exchange is needed to provide the new keys to the parent, Data 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.
o All time and TTL considerations presented in Section 4.2 apply to o All time and TTL considerations presented in Section 4.2 apply to
an automated rollover. an automated rollover.
skipping to change at page 18, line 46 skipping to change at page 19, line 46
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 authentication chain exists. An be used for as long as a valid authentication chain exists. An
authentication chain remains intact for: authentication chain remains intact for:
o as long as a signature over the compromised key in the o as long as a signature over the compromised key in the
authentication chain is valid, authentication chain 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 the hardest to update.) starting point for validation. (This is generally the hardest to
update.)
While an authentication chain to your compromised key exists, your While an authentication chain to your compromised key exists, your
name-space is vulnerable to abuse by the malicious key holder (i.e. name-space is vulnerable to abuse by anyone who has obtained
the owner of the compromised key). Zone operators have to make a illegitimate possession of the key.Zone operators have to make a
trade off if the abuse of the compromised key is worse than having trade off if the abuse of the compromised key is worse than having
data in caches that cannot be validated. If the zone operator data in caches that cannot be validated. If the zone operator
chooses to break the authentication chain to the compromised key, chooses to break the authentication chain to the compromised key,
data in caches signed with this key cannot be validated. However, if data in caches signed with this key cannot be validated. However, if
the zone administrator chooses to take the path of a regular the zone administrator chooses to take the path of a regular roll-
roll-over, the malicious key holder can spoof data so that it appears over, the malicious key holder can spoof data so that it appears to
to be valid. Note that this kind of attack is more likely to occur be valid. Note that this kind of attack is more likely to occur in a
in a localized part of the network topology i.e. downstream from localized part of the network topology i.e. downstream from where the
where the spoof takes place. spoof takes place.
4.3.1 KSK Compromise 4.3.1 KSK Compromise
When the KSK has been compromised the parent must be notified as soon When the KSK has been compromised the parent must be notified as soon
as possible using secure means. The key set of the zone should be as possible using secure means. The key set of the zone should be
resigned as soon as possible. Care must be taken to not break the resigned as soon as possible. Care must be taken to not break the
authentication chain. The local zone can only be resigned with the authentication chain. The local zone can only be resigned with the
new KSK after the parent's zone has created and reloaded its zone new KSK after the parent's zone has created and reloaded its zone
with the DS created from the new KSK. Before this update takes place with the DS created from the new KSK. Before this update takes place
it would be best to drop the security status of a zone all together: it would be best to drop the security status of a zone all together:
the parent removes the DS of the child at the next zone update. the parent removes the DS of the child at the next zone update.
After that the child can be made secure again. After that the child can be made secure again.
An additional danger of a key compromise is that the compromised key An additional danger of a key compromise is that the compromised key
can be used to facilitate a legitimate DNSKEY/DS and/or nameserver can be used to facilitate a legitimate DNSKEY/DS and/or nameserver
rollover at the parent. When that happens the domain can be in rollover at the parent. When that happens the domain can be in
dispute. An out of band and secure notify mechanism to contact a dispute. An authenticated out of band and secure notify mechanism to
parent is needed in this case. contact a parent is needed in this case.
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 with a KSK ZSK is compromised, the situation is less severe than with with a KSK
compromise. The zone must still be resigned with a new ZSK as soon compromise. The zone must still be resigned 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 from the old with a normal rollover the immediate disappearance from the old
compromised key may lead to verification problems. The compromised key may lead to verification problems. The pre-
pre-publication scheme as discussed above minimizes such problems. publication scheme as discussed above minimizes such problems.
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 will be pre-configured DNSSEC is successfully deployed the root key may be pre-configured in
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-user faced with the task of updating anchored key should always End-users faced with the task of updating an anchored key should
validate the new key. New keys should be authenticated out of the always validate the new key. New keys should be authenticated out of
DNS, for example, looking them up on an x.509 secured announcement the DNS, for example, looking them up on an SSL secured announcement
website. website.
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 (or its registry). When designing a key exchange policy one parent (or its registry). When designing a key exchange policy one
should take into account that the authentication and authorization should take into account that the authentication and authorization
mechanisms used during a key exchange should be as strong as the mechanisms used during a key exchange should be as strong as the
authentication and authorization mechanisms used for the exchange of authentication and authorization mechanisms used for the exchange of
delegation information between parent and child. I.e. there is no delegation information between parent and child. I.e. there is no
implicit need in DNSSEC to make the authentication process stronger implicit need in DNSSEC to make the authentication process stronger
than it was in DNS. than it 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 off-band check on the validity of the DNSKEY, has the benefit with an off-band check on the validity of the DNSKEY, has the benefit
that it reduces the chances of user error. A parental DNSKEY that it reduces the chances of user error. A parental DNSKEY
download tool can make use of the SEP bit [2] to select the proper download tool can make use of the SEP bit [1] to select the proper
key from a DNSSEC key set; thereby reducing the chance that the wrong key from a DNSSEC key set; thereby reducing the chance that the wrong
DNSKEY is sent. It can validate the self-signature over a key; DNSKEY is sent. It can validate the self-signature over a key;
thereby verifying the ownership of the private key material. thereby verifying the ownership of the private key material.
Fetching the DNSKEY from the DNS ensures that the child will not Fetching the DNSKEY from the DNS ensures that the chain of trust
become bogus once the parent publishes the DS RR indicating the child remains intact once the parent publishes the DS RR indicating the
is secure. child is secure.
Note: the off-band verification is still needed when the key-material Note: the off-band verification is still needed when the key-material
is fetched via the DNS. The parent can never be sure whether the is fetched via the DNS. The parent can never be sure whether the
DNSKEY RRs have been spoofed or not. DNSKEY RRs have been spoofed or not.
4.4.2 Storing Keys So Hashes Can Be Regenerated 4.4.2 Storing Keys or Hashes?
When designing a registry system one should consider if the DNSKEYs When designing a registry system one should consider which of the
and/or the corresponding DSs are stored. Storing DNSKEYs will help DNSKEYs and/or the corresponding DSs to store. Since a child zone
during troubleshooting while the overhead of calculating DS records might wish to have a DS published using a message digest algorithm
from them is minimal. not yet understood by the registry, the registry can't count on being
able to generate the DS record from a raw DNSKEY. Thus, we recommend
that registry system at least support storing DS records.
Having an out-of-band mechanism, such as a Whois database, to find It may also be useful to store DNSKEYs, since having them may help
out which keys are used to generate DS Resource Records for specific during troubleshooting and, so long as the child's chosen message
owners and/or zones may also help with troubleshooting. digest is supported, the overhead of generating DS records from them
is minimal. Having an out-of-band mechanism, such as a Whois
database, to find out which keys are used to generate DS Resource
Records for specific owners and/or zones may also help with
troubleshooting.
The storage considerations also relate the design of the customer
interface and the method by which data is transfered between
registrant and registry; Will the child zone owner be able to upload
DS RRs with unknown hash algorithms or does the interface only allows
DNSKEYs? In the registry-registrar model one can use the DNSSEC EPP
protocol extensions [9] which allows transfer of DS RRs and
optionally DNSKEY RRs.
4.4.3 Security Lameness 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. During key exchange a RR pointing to a non-existing DNSKEY RR. During key exchange a
parent should make sure that the child's key is actually configured parent should make sure that the child's key is actually configured
in the DNS before publishing a DS RR in its zone. Failure to do so in the DNS before publishing a DS RR in its zone. Failure to do so
would render the child's zone being marked as bogus. could cause the child's zone being marked as Bogus.
Child zones should be very careful removing DNSKEY material, Child zones should be very careful 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. by 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 the minimum for a validity periods longer than 2 days. We recommend the minimum for a
DS signature validity period to be a few days. 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.
Other considerations, such as how often the zone is (re)signed can Other considerations, such as how often the zone is (re)signed can
also be taken into account. also be taken into account.
We consider a signature validity period of around one week to be a We consider a signature validity period of around one week to be a
good compromise between the operational constraints of the parent and good compromise between the operational constraints of the parent and
minimizing damage for the child. minimizing damage for the child.
In addition to the signature validity period, which sets the lower In addition to the signature validity period, which sets a lower
bounds on the amount of times the zone owner will need to sign the bound on the amount of times the zone owner will need to sign the
zone data and which sets an upper bound to the time a child is zone data and which sets an upper bound to the time a child is
vulnerable after key compromise there is the TTL value on the DS RRs. vulnerable after key compromise, there is the TTL value on the DS
By lowering the TTL the authoritative servers will see more queries, RRs. By lowering the TTL, the authoritative servers will see more
on the other hand a low TTL increases the speed with which new DS RRs queries, on the other hand a low TTL increases the speed with which
propagate through the DNS. As argued in Section 4.1.1 the TTL should new DS RRs propagate through the DNS. As argued in Section 4.1.1,
be a fraction of the signature validity period. the TTL should be a fraction of the signature validity period.
5. Security Considerations 5. 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
considerations to operate a stable and secure DNSSEC service. Not the operational considerations to maintain a stable and secure DNSSEC
taking into account the 'data propagation' properties in the DNS will service. Not taking into account the 'data propagation' properties
cause validation failures and may make secured zones unavailable to in the DNS will cause validation failures and may make secured zones
security aware resolvers. unavailable to security aware resolvers.
6. Acknowledgments 6. Acknowledgments
Most of the ideas in this draft were the result of collective efforts Most of the ideas in this draft were the result of collective efforts
during workshops, discussions and try outs. during workshops, discussions and try outs.
At the risk of forgetting individuals who where 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
where 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
and Olivier Courtay, Sam Weiler, Jelte Jansen. Olivier Courtay, Sam Weiler, Jelte Jansen and Niall O'Reilly.
Some material in this document has been shamelessly copied from Some material in this document has been shamelessly copied from
RFC2541 [1] by Donald Eastlake. RFC2541 [7] by Donald Eastlake.
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 4.2.3 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 and Adrian Bedford corrected many of the spelling and Emma Bretherick, Adrian Bedford and Lindy Foster corrected many of
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).
7. References 7. References
7.1 Normative References 7.1 Normative References
[1] Eastlake, D., "DNS Security Operational Considerations", RFC [1] Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name System KEY
2541, March 1999.
[2] Kolkman, O., Schlyter, J. and E. Lewis, "Domain Name System KEY
(DNSKEY) Resource Record (RR) Secure Entry Point (SEP) Flag", (DNSKEY) Resource Record (RR) Secure Entry Point (SEP) Flag",
RFC 3757, May 2004. RFC 3757, May 2004.
[3] Arends, R., "DNS Security Introduction and Requirements", [2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
draft-ietf-dnsext-dnssec-intro-11 (work in progress), March "DNS Security Introduction and Requirements", RFC 4033,
2003. March 2005.
[4] Arends, R., "Protocol Modifications for the DNS Security
Extensions", draft-ietf-dnsext-dnssec-protocol-07 (work in
progress), March 2003.
7.2 Informative References 7.2 Informative References
[5] Eastlake, D., Crocker, S. and J. Schiller, "Randomness [3] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994. Recommendations for Security", RFC 1750, December 1994.
[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[7] Eastlake, D., "Secure Domain Name System Dynamic Update", RFC [5] Eastlake, D., "Secure Domain Name System Dynamic Update",
2137, April 1997. RFC 2137, April 1997.
[8] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", [6] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)",
RFC 2308, March 1998. RFC 2308, March 1998.
[9] Gudmundsson, O., "Delegation Signer (DS) Resource Record (RR)", [7] Eastlake, D., "DNS Security Operational Considerations",
RFC 2541, March 1999.
[8] Gudmundsson, O., "Delegation Signer (DS) Resource Record (RR)",
RFC 3658, December 2003. RFC 3658, December 2003.
[9] Hollenbeck, S., "Domain Name System (DNS) Security Extensions
Mapping for the Extensible Provisioning Protocol (EPP)",
draft-hollenbeck-epp-secdns-07 (work in progress), March 2005.
[10] Lenstra, A. and E. Verheul, "Selecting Cryptographic Key [10] 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.
[11] Schneier, B., "Applied Cryptography: Protocols, Algorithms, and [11] Schneier, B., "Applied Cryptography: Protocols, Algorithms, and
Source Code in C", 1996. Source Code in C", 1996.
Authors' Addresses Authors' Addresses
Olaf M. Kolkman Olaf M. Kolkman
RIPE NCC RIPE NCC
Singel 256 Singel 256
Amsterdam 1016 AB Amsterdam 1016 AB
The Netherlands The Netherlands
Phone: +31 20 535 4444 Phone: +31 20 535 4444
EMail: olaf@ripe.net Email: olaf@ripe.net
URI: http://www.ripe.net/ URI: http://www.ripe.net/
Miek Gieben Miek Gieben
NLnet Labs NLnet Labs
Kruislaan 419 Kruislaan 419
Amsterdam 1098 VA Amsterdam 1098 VA
The Netherlands The Netherlands
EMail: miek@nlnetlabs.nl Email: miek@nlnetlabs.nl
URI: http://www.nlnetlabs.nl URI: http://www.nlnetlabs.nl
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 given a more elaborate explanation
of the meaning. Note that these explanations should not be seen as of the meaning. Note that these explanations should not be seen as
authoritative. 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 [3]. An RRset in DNSSEC is marked Bogus: Also see Section 5 of [2]. An RRset in DNSSEC is marked
"Bogus" when a signature of a RRset does not validate against a "Bogus" when a signature of a 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.
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 keys, a public key and a private key. The public existence of two keys, a public key and a private key. The public
keys are published in the DNS by use of the DNSKEY Resource Record keys are published in the DNS by use of the DNSKEY Resource Record
(DNSKEY RR). Private keys should remain private. (DNSKEY RR). Private keys should remain private.
Key Rollover: A key rollover (also called key supersession 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 by 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 Secure Entry Point key or SEP Key: A KSK that has a parental DS
record pointing to it. Note: this is not enforced in the record pointing to it. Note: this is not enforced in the
protocol. A SEP Key with no parental DS is security lame. protocol. A SEP Key with no parental DS is security lame.
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.
skipping to change at page 25, line 4 skipping to change at page 26, line 26
used for signing all data in a zone. The fact that a key is a ZSK used for signing all data in a zone. The fact that a key is a ZSK
is only relevant to the signing tool. is only relevant to the signing tool.
Zone Administrator: The 'role' that is responsible for signing a zone 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 Howto
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 "HOWTO".
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 as "active" and the other as
"published". Use the "active" key for signing your zone data. "published". Use the "active" key for signing your zone data.
Store the private part of the "published" key, preferably Store the private part of the "published" key, preferably off-
off-line. line.
The protocol does not provide for attributes to mark a key as
active or published. This is something you have to do on your
own, through the use of a notebook or key management tool.
Step 1: Determine expiration: At the beginning of the rollover make a 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 the expiration time marked in Step 1 has passed Wait until the expiration time marked in Step 1 has passed
Step 2: Then start using the key that was marked as "published" to 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 sign your data i.e. mark it as "active". Stop using the key that
was marked as "active", mark it as "rolled". was marked as "active", mark it as "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".
skipping to change at page 27, line 5 skipping to change at page 29, line 22
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 a RRSIG created with DNSKEY 14.
Appendix D. Document Details and Changes Appendix D. Document Details and Changes
This section is to be removed by the RFC editor if and when the This section is to be removed by the RFC editor if and when the
document is published. document is published.
$Id: draft-ietf-dnsop-dnssec-operational-practices.xml,v 1.31.2.7 $Id: draft-ietf-dnsop-dnssec-operational-practices.xml,v 1.31.2.14
2004/12/23 12:20:29 dnssec Exp $ 2005/03/21 15:51:41 dnssec Exp $
D.1 draft-ietf-dnsop-dnssec-operational-practices-00 D.1 draft-ietf-dnsop-dnssec-operational-practices-00
Submission as working group document. This document is a modified Submission as working group document. This document is a modified
and updated version of draft-kolkman-dnssec-operational-practices-00. and updated version of draft-kolkman-dnssec-operational-practices-00.
D.2 draft-ietf-dnsop-dnssec-operational-practices-01 D.2 draft-ietf-dnsop-dnssec-operational-practices-01
changed the definition of "Bogus" to reflect the one in the protocol changed the definition of "Bogus" to reflect the one in the protocol
draft. draft.
skipping to change at page 27, line 30 skipping to change at page 29, line 47
Style and spelling corrections Style and spelling corrections
KSK - SEP mapping made explicit. KSK - SEP mapping made explicit.
Updates from Sam Weiler added Updates from Sam Weiler added
D.3 draft-ietf-dnsop-dnssec-operational-practices-02 D.3 draft-ietf-dnsop-dnssec-operational-practices-02
Style and errors corrected. Style and errors corrected.
Added Automatic rollover requirements from Added Automatic rollover requirements from I-D.ietf-dnsop-key-
I-D.ietf-dnsop-key-rollover-requirements. rollover-requirements.
D.4 draft-ietf-dnsop-dnssec-operational-practices-03 D.4 draft-ietf-dnsop-dnssec-operational-practices-03
Added the definition of Key effectivity period and used that term Added the definition of Key effectivity period and used that term
instead of Key validity period. instead of Key validity period.
Modified the order of the sections, based on a suggestion by Rip Modified the order of the sections, based on a suggestion by Rip
Loomis. Loomis.
Included parts from RFC2541 [1]. Most of its ground was allready Included parts from RFC2541 [7]. Most of its ground was already
covered. This document obsoletes RFC2541 [1]. Section 3.1.2 covered. This document obsoletes RFC2541 [7]. Section 3.1.2
deserves some review as it in contrast to RFC2541 does _not_ give deserves some review as it in contrast to RFC2541 does _not_ give
recomendations about root-zone keys. recomendations about root-zone keys.
added a paragraph to Section 4.4.4 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.
Intellectual Property Statement Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at page 28, line 41 skipping to change at page 31, line 41
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
 End of changes. 

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