draft-ietf-dnsext-trustupdate-timers-04.txt   draft-ietf-dnsext-trustupdate-timers-05.txt 
Network Working Group M. StJohns Network Working Group M. StJohns
Internet-Draft Nominum, Inc. Internet-Draft Nominum, Inc.
Intended status: Informational August 14, 2006 Intended status: Informational November 29, 2006
Expires: February 15, 2007 Expires: June 2, 2007
Automated Updates of DNSSEC Trust Anchors Automated Updates of DNSSEC Trust Anchors
draft-ietf-dnsext-trustupdate-timers-04 draft-ietf-dnsext-trustupdate-timers-05
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
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have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
skipping to change at page 1, line 34 skipping to change at page 1, line 34
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on February 15, 2007. This Internet-Draft will expire on June 2, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document describes a means for automated, authenticated and This document describes a means for automated, authenticated and
authorized updating of DNSSEC "trust anchors". The method provides authorized updating of DNSSEC "trust anchors". The method provides
protection against single key compromise of a key in the trust point protection against N-1 key compromises of N keys in the trust point
key set. Based on the trust established by the presence of a current key set. Based on the trust established by the presence of a current
anchor, other anchors may be added at the same place in the anchor, other anchors may be added at the same place in the
hierarchy, and, ultimately, supplant the existing anchor. hierarchy, and, ultimately, supplant the existing anchor(s).
This mechanism will require changes to resolver management behavior This mechanism will require changes to resolver management behavior
(but not resolver resolution behavior), and the addition of a single (but not resolver resolution behavior), and the addition of a single
flag bit to the DNSKEY record. flag bit to the DNSKEY record.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Compliance Nomenclature . . . . . . . . . . . . . . . . . 3 1.1. Compliance Nomenclature . . . . . . . . . . . . . . . . . 3
1.2. Changes since -00 . . . . . . . . . . . . . . . . . . . . 4
2. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 4 2. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 4
2.1. Revocation . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Revocation . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Add Hold-Down . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Add Hold-Down . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Remove Hold-down . . . . . . . . . . . . . . . . . . . . . 6 2.3. Active Refresh . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Active Refresh . . . . . . . . . . . . . . . . . . . . . . 6 2.4. Resolver Parameters . . . . . . . . . . . . . . . . . . . 6
2.5. Resolver Parameters . . . . . . . . . . . . . . . . . . . 6 2.4.1. Add Hold-Down Time . . . . . . . . . . . . . . . . . . 6
2.5.1. Add Hold-Down Time . . . . . . . . . . . . . . . . . . 6 2.4.2. Remove Hold-Down Time . . . . . . . . . . . . . . . . 6
2.5.2. Remove Hold-Down Time . . . . . . . . . . . . . . . . 7 2.4.3. Minimum Trust Anchors per Trust Point . . . . . . . . 6
2.5.3. Minimum Trust Anchors per Trust Point . . . . . . . . 7 3. Changes to DNSKEY RDATA Wire Format . . . . . . . . . . . . . 6
3. Changes to DNSKEY RDATA Wire Format . . . . . . . . . . . . . 7 4. State Table . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. State Table . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Events . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Events . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. States . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2. States . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Trust Point Deletion . . . . . . . . . . . . . . . . . . . . . 9 5. Trust Point Deletion . . . . . . . . . . . . . . . . . . . . . 8
6. Scenarios - Informative . . . . . . . . . . . . . . . . . . . 9 6. Scenarios - Informative . . . . . . . . . . . . . . . . . . . 9
6.1. Adding A Trust Anchor . . . . . . . . . . . . . . . . . . 10 6.1. Adding a Trust Anchor . . . . . . . . . . . . . . . . . . 9
6.2. Deleting a Trust Anchor . . . . . . . . . . . . . . . . . 10 6.2. Deleting a Trust Anchor . . . . . . . . . . . . . . . . . 9
6.3. Key Roll-Over . . . . . . . . . . . . . . . . . . . . . . 10 6.3. Key Roll-Over . . . . . . . . . . . . . . . . . . . . . . 10
6.4. Active Key Compromised . . . . . . . . . . . . . . . . . . 10 6.4. Active Key Compromised . . . . . . . . . . . . . . . . . . 10
6.5. Stand-by Key Compromised . . . . . . . . . . . . . . . . . 11 6.5. Stand-by Key Compromised . . . . . . . . . . . . . . . . . 10
6.6. Trust Point Deletion . . . . . . . . . . . . . . . . . . . 11 6.6. Trust Point Deletion . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8.1. Key Ownership vs Acceptance Policy . . . . . . . . . . . . 11 8.1. Key Ownership vs Acceptance Policy . . . . . . . . . . . . 11
8.2. Multiple Key Compromise . . . . . . . . . . . . . . . . . 12 8.2. Multiple Key Compromise . . . . . . . . . . . . . . . . . 11
8.3. Dynamic Updates . . . . . . . . . . . . . . . . . . . . . 12 8.3. Dynamic Updates . . . . . . . . . . . . . . . . . . . . . 11
9. Normative References . . . . . . . . . . . . . . . . . . . . . 12 9. Normative References . . . . . . . . . . . . . . . . . . . . . 12
Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . . Editorial Comments . . . . . . . . . . . . . . . . . . . . . . . .
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 13
1. Introduction 1. Introduction
As part of the reality of fielding DNSSEC (Domain Name System As part of the reality of fielding DNSSEC (Domain Name System
Security Extensions) [RFC2535] [RFC4033][RFC4034][RFC4035], the Security Extensions) [RFC4033] [RFC4034] [RFC4035], the community has
community has come to the realization that there will not be one come to the realization that there will not be one signed name space,
signed name space, but rather islands of signed name space each but rather islands of signed name space each originating from
originating from specific points (i.e. 'trust points') in the DNS specific points (i.e. 'trust points') in the DNS tree. Each of those
tree. Each of those islands will be identified by the trust point islands will be identified by the trust point name, and validated by
name, and validated by at least one associated public key. For the at least one associated public key. For the purpose of this document
purpose of this document we'll call the association of that name and we'll call the association of that name and a particular key a 'trust
a particular key a 'trust anchor'. A particular trust point can have anchor'. A particular trust point can have more than one key
more than one key designated as a trust anchor. designated as a trust anchor.
For a DNSSEC-aware resolver to validate information in a DNSSEC For a DNSSEC-aware resolver to validate information in a DNSSEC
protected branch of the hierarchy, it must have knowledge of a trust protected branch of the hierarchy, it must have knowledge of a trust
anchor applicable to that branch. It may also have more than one anchor applicable to that branch. It may also have more than one
trust anchor for any given trust point. Under current rules, a chain trust anchor for any given trust point. Under current rules, a chain
of trust for DNSSEC-protected data that chains its way back to ANY of trust for DNSSEC-protected data that chains its way back to ANY
known trust anchor is considered 'secure'. known trust anchor is considered 'secure'.
Because of the probable balkanization of the DNSSEC tree due to Because of the probable balkanization of the DNSSEC tree due to
signing voids at key locations, a resolver may need to know literally signing voids at key locations, a resolver may need to know literally
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manual intervention, but they should be few and far between. This manual intervention, but they should be few and far between. This
document DOES NOT discuss the general problem of the initial document DOES NOT discuss the general problem of the initial
configuration of trust anchors for the resolver. configuration of trust anchors for the resolver.
1.1. Compliance Nomenclature 1.1. Compliance Nomenclature
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, [RFC2119]. document are to be interpreted as described in BCP 14, [RFC2119].
1.2. Changes since -00
N.B. This section to be deleted prior to submission to RFC editor.
Added the concept of timer triggered resolver queries to refresh the
resolvers view of the trust anchor key RRSet.
Re-submitted expired draft as -01. Updated DNSSEC RFC References.
Draft -02. Added the IANA Considerations section. Added text to
describe what happens if all trust anchors at a trust point are
deleted.
Draft -03. Revised the trust point deletion language to note
limitations.
Draft -04. Restructured section 4.3 (Trust point deletion) and 5
(Scenarios). Section 4.3 is now section 5. Section 5 is now section
6 and "Informative"
2. Theory of Operation 2. Theory of Operation
The general concept of this mechanism is that existing trust anchors The general concept of this mechanism is that existing trust anchors
can be used to authenticate new trust anchors at the same point in can be used to authenticate new trust anchors at the same point in
the DNS hierarchy. When a new SEP key (see [RFC4034] section 2.1.1) the DNS hierarchy. When a zone operator adds a new SEP key (i.e. a
is added to a trust point DNSKEY RRSet, and when that RRSet is DNSKEY with the Secure Entry Point bit set) (see [RFC4034]section
validated by an existing trust anchor, then the new key can be added 2.1.1) to a trust point DNSKEY RRSet, and when that RRSet is
to the set of trust anchors. validated by an existing trust anchor, then the resolver can add the
new key to its valid set of trust anchors for that trust point.
There are some issues with this approach which need to be mitigated. There are some issues with this approach which need to be mitigated.
For example, a compromise of one of the existing keys could allow an For example, a compromise of one of the existing keys could allow an
attacker to add their own 'valid' data. This implies a need for a attacker to add their own 'valid' data. This implies a need for a
method to revoke an existing key regardless of whether or not that method to revoke an existing key regardless of whether or not that
key is compromised. As another example assuming a single key key is compromised. As another example, assuming a single key
compromise, an attacker could add a new key and revoke all the other compromise, we need to prevent an attacker from adding a new key and
old keys. revoking all the other old keys.
2.1. Revocation 2.1. Revocation
Assume two trust anchor keys A and B. Assume that B has been Assume two trust anchor keys A and B. Assume that B has been
compromised. Without a specific revocation bit, B could invalidate A compromised. Without a specific revocation bit, B could invalidate A
simply by sending out a signed trust point key set which didn't simply by sending out a signed trust point key set which didn't
contain A. To fix this, we add a mechanism which requires knowledge contain A. To fix this, we add a mechanism which requires knowledge
of the private key of a DNSKEY to revoke that DNSKEY. of the private key of a DNSKEY to revoke that DNSKEY.
A key is considered revoked when the resolver sees the key in a self- A key is considered revoked when the resolver sees the key in a self-
signed RRSet and the key has the REVOKE bit (see Section 7 below) set signed RRSet and the key has the REVOKE bit (see Section 7 below) set
to '1'. Once the resolver sees the REVOKE bit, it MUST NOT use this to '1'. Once the resolver sees the REVOKE bit, it MUST NOT use this
key as a trust anchor or for any other purposes except validating the key as a trust anchor or for any other purposes except validating the
RRSIG over the DNSKEY RRSet specifically for the purpose of RRSIG it signed over the DNSKEY RRSet specifically for the purpose of
validating the revocation. Unlike the 'Add' operation below, validating the revocation. Unlike the 'Add' operation below,
revocation is immediate and permanent upon receipt of a valid revocation is immediate and permanent upon receipt of a valid
revocation at the resolver. revocation at the resolver.
A self-signed RRSet is a DNSKEY RRSet which contains the specific A self-signed RRSet is a DNSKEY RRSet which contains the specific
DNSKey and for which there is a corresponding validated RRSIG record. DNSKEY and for which there is a corresponding validated RRSIG record.
It's not a special DNSKEY RRSet, just a way of describing the It's not a special DNSKEY RRSet, just a way of describing the
validation requirements for that RRSet. validation requirements for that RRSet.
N.B. A DNSKEY with the REVOKE bit set has a different fingerprint N.B. A DNSKEY with the REVOKE bit set has a different fingerprint
than one without the bit set. This affects the matching of a DNSKEY than one without the bit set. This affects the matching of a DNSKEY
to DS records in the parent, or the fingerprint stored at a resolver to DS records in the parent, or the fingerprint stored at a resolver
used to configure a trust point. used to configure a trust point.
In the given example, the attacker could revoke B because it has In the given example, the attacker could revoke B because it has
knowledge of B's private key, but could not revoke A. knowledge of B's private key, but could not revoke A.
2.2. Add Hold-Down 2.2. Add Hold-Down
Assume two trust point keys A and B. Assume that B has been Assume two trust point keys A and B. Assume that B has been
compromised. An attacker could generate and add a new trust anchor compromised. An attacker could generate and add a new trust anchor
key - C (by adding C to the DNSKEY RRSet and signing it with B), and key - C (by adding C to the DNSKEY RRSet and signing it with B), and
then invalidate the compromised key. This would result in the both then invalidate the compromised key. This would result in both the
the attacker and owner being able to sign data in the zone and have attacker and owner being able to sign data in the zone and have it
it accepted as valid by resolvers. accepted as valid by resolvers.
To mitigate, but not completely solve, this problem, we add a hold- To mitigate but not completely solve this problem, we add a hold-down
down time to the addition of the trust anchor. When the resolver time to the addition of the trust anchor. When the resolver sees a
sees a new SEP key in a validated trust point DNSKEY RRSet, the new SEP key in a validated trust point DNSKEY RRSet, the resolver
resolver starts an acceptance timer, and remembers all the keys that starts an acceptance timer, and remembers all the keys that validated
validated the RRSet. If the resolver ever sees the DNSKEY RRSet the RRSet. If the resolver ever sees the DNSKEY RRSet without the
without the new key but validly signed, it stops the acceptance new key but validly signed, it stops the acceptance process for that
process and resets the acceptance timer. If all of the keys which key and resets the acceptance timer. If all of the keys which were
were originally used to validate this key are revoked prior to the originally used to validate this key are revoked prior to the timer
timer expiring, the resolver stops the acceptance process and resets expiring, the resolver stops the acceptance process and resets the
the timer. timer.
Once the timer expires, the new key will be added as a trust anchor Once the timer expires, the new key will be added as a trust anchor
the next time the validated RRSet with the new key is seen at the the next time the validated RRSet with the new key is seen at the
resolver. The resolver MUST NOT treat the new key as a trust anchor resolver. The resolver MUST NOT treat the new key as a trust anchor
until the hold down time expires AND it has retrieved and validated a until the hold down time expires AND it has retrieved and validated a
DNSKEY RRSet after the hold down time which contains the new key. DNSKEY RRSet after the hold down time which contains the new key.
N.B.: Once the resolver has accepted a key as a trust anchor, the key N.B.: Once the resolver has accepted a key as a trust anchor, the key
MUST be considered a valid trust anchor by that resolver until MUST be considered a valid trust anchor by that resolver until
explictly revoked as described above. explictly revoked as described above.
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both A and B. both A and B.
The reason this does not completely solve the problem has to do with The reason this does not completely solve the problem has to do with
the distributed nature of DNS. The resolver only knows what it sees. the distributed nature of DNS. The resolver only knows what it sees.
A determined attacker who holds one compromised key could keep a A determined attacker who holds one compromised key could keep a
single resolver from realizing that key had been compromised by single resolver from realizing that key had been compromised by
intercepting 'real' data from the originating zone and substituting intercepting 'real' data from the originating zone and substituting
their own (e.g. using the example, signed only by B). This is no their own (e.g. using the example, signed only by B). This is no
worse than the current situation assuming a compromised key. worse than the current situation assuming a compromised key.
2.3. Remove Hold-down 2.3. Active Refresh
A new key which has been seen by the resolver, but hasn't reached
it's add hold-down time, MAY be removed from the DNSKEY RRSet by the
zone owner. If the resolver sees a validated DNSKEY RRSet without
this key, it waits for the remove hold-down time and then, if the key
hasn't reappeared, SHOULD discard any information about the key.
2.4. Active Refresh
A resolver which has been configured for automatic update of keys A resolver which has been configured for automatic update of keys
from a particular trust point MUST query that trust point (e.g. do a from a particular trust point MUST query that trust point (e.g. do a
lookup for the DNSKEY RRSet and related RRSIG records) no less often lookup for the DNSKEY RRSet and related RRSIG records) no less often
than the lesser of 15 days or half the original TTL for the DNSKEY than the lesser of 15 days or half the original TTL for the DNSKEY
RRSet or half the RRSIG expiration interval. The expiration interval RRSet or half the RRSIG expiration interval and no more often than
is the amount of time from when the RRSIG was last retrieved until once per hour. The expiration interval is the amount of time from
the expiration time in the RRSIG. when the RRSIG was last retrieved until the expiration time in the
RRSIG.
If the query fails, the resolver MUST repeat the query until If the query fails, the resolver MUST repeat the query until
satisfied no more often than once an hour and no less often than the satisfied no more often than once an hour and no less often than the
lesser of 1 day or 10% of the original TTL or 10% of the original lesser of 1 day or 10% of the original TTL or 10% of the original
expiration interval. expiration interval. I.e.: retryTime = MAX (1 hour, MIN (1 day, .1 *
origTTL, .1 * expireInterval)).
2.5. Resolver Parameters 2.4. Resolver Parameters
2.5.1. Add Hold-Down Time 2.4.1. Add Hold-Down Time
The add hold-down time is 30 days or the expiration time of the TTL The add hold-down time is 30 days or the expiration time of the
of the first trust point DNSKEY RRSet which contained the key, original TTL of the first trust point DNSKEY RRSet which contained
whichever is greater. This ensures that at least two validated the new key, whichever is greater. This ensures that at least two
DNSKEY RRSets which contain the new key MUST be seen by the resolver validated DNSKEY RRSets which contain the new key MUST be seen by the
prior to the key's acceptance. resolver prior to the key's acceptance.
2.5.2. Remove Hold-Down Time 2.4.2. Remove Hold-Down Time
The remove hold-down time is 30 days. The remove hold-down time is 30 days. This parameter is solely a key
management database bookeeping parameter. Failure to remove
information about the state of defunct keys from the database will
not adversely impact the security of this protocol, but may end up
with a database cluttered with obsolete key information.
2.5.3. Minimum Trust Anchors per Trust Point 2.4.3. Minimum Trust Anchors per Trust Point
A compliant resolver MUST be able to manage at least five SEP keys A compliant resolver MUST be able to manage at least five SEP keys
per trust point. per trust point.
3. Changes to DNSKEY RDATA Wire Format 3. Changes to DNSKEY RDATA Wire Format
Bit n [msj2] of the DNSKEY Flags field is designated as the 'REVOKE' Bit n [msj2] of the DNSKEY Flags field is designated as the 'REVOKE'
flag. If this bit is set to '1', AND the resolver sees an flag. If this bit is set to '1', AND the resolver sees an
RRSIG(DNSKEY) signed by the associated key, then the resolver MUST RRSIG(DNSKEY) signed by the associated key, then the resolver MUST
consider this key permanently invalid for all purposes except for consider this key permanently invalid for all purposes except for
validing the revocation. validating the revocation.
4. State Table 4. State Table
The most important thing to understand is the resolver's view of any The most important thing to understand is the resolver's view of any
key at a trust point. The following state table describes that view key at a trust point. The following state table describes that view
at various points in the key's lifetime. The table is a normative at various points in the key's lifetime. The table is a normative
part of this specification. The initial state of the key is 'Start'. part of this specification. The initial state of the key is 'Start'.
The resolver's view of the state of the key changes as various events The resolver's view of the state of the key changes as various events
occur. occur.
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Revoked | | | | | |RemTime| Revoked | | | | | |RemTime|
---------------------------------------------------------- ----------------------------------------------------------
Removed | | | | | | | Removed | | | | | | |
---------------------------------------------------------- ----------------------------------------------------------
State Table State Table
4.1. Events 4.1. Events
NewKey The resolver sees a valid DNSKEY RRSet with a new SEP key. NewKey The resolver sees a valid DNSKEY RRSet with a new SEP key.
That key will become a new trust anchor for the named trust point That key will become a new trust anchor for the named trust point
after its been present in the RRSet for at least 'add time'. after it's been present in the RRSet for at least 'add time'.
KeyPres The key has returned to the valid DNSKEY RRSet. KeyPres The key has returned to the valid DNSKEY RRSet.
KeyRem The resolver sees a valid DNSKEY RRSet that does not contain KeyRem The resolver sees a valid DNSKEY RRSet that does not contain
this key. this key.
AddTime The key has been in every valid DNSKEY RRSet seen for at AddTime The key has been in every valid DNSKEY RRSet seen for at
least the 'add time'. least the 'add time'.
RemTime A revoked key has been missing from the trust point DNSKEY RemTime A revoked key has been missing from the trust point DNSKEY
RRSet for sufficient time to be removed from the trust set. RRSet for sufficient time to be removed from the trust set.
RevBit The key has appeared in the trust anchor DNSKEY RRSet with RevBit The key has appeared in the trust anchor DNSKEY RRSet with
its "REVOKED" bit set, and there is an RRSig over the DNSKEY RRSet its "REVOKED" bit set, and there is an RRSig over the DNSKEY RRSet
signed by this key. signed by this key.
4.2. States 4.2. States
Start The key doesn't yet exist as a trust anchor at the resolver. Start The key doesn't yet exist as a trust anchor at the resolver.
It may or may not exist at the zone server, but hasn't yet been It may or may not exist at the zone server, but either hasn't yet
seen at the resolver. been seen at the resolver or was seen but was absent from the last
DNSKEY RRSet (e.g. KeyRem event).
AddPend The key has been seen at the resolver, has its 'SEP' bit AddPend The key has been seen at the resolver, has its 'SEP' bit
set, and has been included in a validated DNSKEY RRSet. There is set, and has been included in a validated DNSKEY RRSet. There is
a hold-down time for the key before it can be used as a trust a hold-down time for the key before it can be used as a trust
anchor. anchor.
Valid The key has been seen at the resolver and has been included in Valid The key has been seen at the resolver and has been included in
all validated DNSKEY RRSets from the time it was first seen up all validated DNSKEY RRSets from the time it was first seen up
through the hold-down time. It is now valid for verifying RRSets through the hold-down time. It is now valid for verifying RRSets
that arrive after the hold down time. Clarification: The DNSKEY that arrive after the hold down time. Clarification: The DNSKEY
RRSet does not need to be continuously present at the resolver RRSet does not need to be continuously present at the resolver
(e.g. its TTL might expire). If the RRSet is seen, and is (e.g. its TTL might expire). If the RRSet is seen, and is
validated (i.e. verifies against an existing trust anchor), this validated (i.e. verifies against an existing trust anchor), this
key MUST be in the RRSet otherwise a 'KeyRem' event is triggered. key MUST be in the RRSet otherwise a 'KeyRem' event is triggered.
Missing This is an abnormal state. The key remains as a valid trust Missing This is an abnormal state. The key remains as a valid trust
point key, but was not seen at the resolver in the last validated point key, but was not seen at the resolver in the last validated
DNSKEY RRSet. This is an abnormal state because the zone operator DNSKEY RRSet. This is an abnormal state because the zone operator
should be using the REVOKE bit prior to removal. [Discussion should be using the REVOKE bit prior to removal.
item: Should a missing key be considered revoked after some period
of time?]
Revoked This is the state a key moves to once the resolver sees an Revoked This is the state a key moves to once the resolver sees an
RRSIG(DNSKEY) signed by this key where that DNSKEY RRSet contains RRSIG(DNSKEY) signed by this key where that DNSKEY RRSet contains
this key with its REVOKE bit set to '1'. Once in this state, this this key with its REVOKE bit set to '1'. Once in this state, this
key MUST permanently be considered invalid as a trust anchor. key MUST permanently be considered invalid as a trust anchor.
Removed After a fairly long hold-down time, information about this Removed After a fairly long hold-down time, information about this
key may be purged from the resolver. A key in the removed state key may be purged from the resolver. A key in the removed state
MUST NOT be considered a valid trust anchor. MUST NOT be considered a valid trust anchor. (Note: this state is
more or less equivalent to the "Start" state, except that it's bad
practice to re-introduce previously used keys - think of this as
the holding state for all the old keys for which the resolver no
longer needs to track state.)
5. Trust Point Deletion 5. Trust Point Deletion
A trust point which has all of its trust anchors revoked is A trust point which has all of its trust anchors revoked is
considered deleted and is treated as if the trust point was never considered deleted and is treated as if the trust point was never
configured. If there are no superior configured trust points, data configured. If there are no superior configured trust points, data
at and below the deleted trust point are considered insecure by the at and below the deleted trust point are considered insecure by the
resolver. If there ARE superior configured trust points, data at and resolver. If there ARE superior configured trust points, data at and
below the deleted trust point are evaluated with respect to the below the deleted trust point are evaluated with respect to the
superior trust point. superior trust point(s).
Alternately, a trust point which is subordinate to another configured Alternately, a trust point which is subordinate to another configured
trust point MAY be deleted by a resolver after 180 days where such trust point MAY be deleted by a resolver after 180 days where such
trust point validly chains to a superior trust point. The decision subordinate trust point validly chains to a superior trust point.
to delete the subordinate trust anchor is a local configuration The decision to delete the subordinate trust anchor is a local
decision. Once the subordinate trust point is deleted, validation of configuration decision. Once the subordinate trust point is deleted,
the subordinate zone is dependent on validating the chain of trust to validation of the subordinate zone is dependent on validating the
the superior trust point. chain of trust to the superior trust point.
6. Scenarios - Informative 6. Scenarios - Informative
The suggested model for operation is to have one active key and one The suggested model for operation is to have one active key and one
stand-by key at each trust point. The active key will be used to stand-by key at each trust point. The active key will be used to
sign the DNSKEY RRSet. The stand-by key will not normally sign this sign the DNSKEY RRSet. The stand-by key will not normally sign this
RRSet, but the resolver will accept it as a trust anchor if/when it RRSet, but the resolver will accept it as a trust anchor if/when it
sees the signature on the trust point DNSKEY RRSet. sees the signature on the trust point DNSKEY RRSet.
Since the stand-by key is not in active signing use, the associated Since the stand-by key is not in active signing use, the associated
private key may (and should) be provided with additional protections private key may (and should) be provided with additional protections
not normally available to a key that must be used frequently. E.g. not normally available to a key that must be used frequently. E.g.
locked in a safe, split among many parties, etc. Notionally, the locked in a safe, split among many parties, etc. Notionally, the
stand-by key should be less subject to compromise than an active key, stand-by key should be less subject to compromise than an active key,
but that will be dependent on operational concerns not addressed but that will be dependent on operational concerns not addressed
here. here.
6.1. Adding A Trust Anchor 6.1. Adding a Trust Anchor
Assume an existing trust anchor key 'A'. Assume an existing trust anchor key 'A'.
1. Generate a new key pair. 1. Generate a new key pair.
2. Create a DNSKEY record from the key pair and set the SEP and Zone 2. Create a DNSKEY record from the key pair and set the SEP and Zone
Key bits. Key bits.
3. Add the DNSKEY to the RRSet. 3. Add the DNSKEY to the RRSet.
4. Sign the DNSKEY RRSet ONLY with the existing trust anchor key - 4. Sign the DNSKEY RRSet ONLY with the existing trust anchor key -
'A'. 'A'.
5. Wait a while. 5. Wait a while (i.e. for various resolvers timers to go off and for
them to retrieve the new DNSKEY RRSet and signatures).
6. The new trust anchor will be populated at the resolvers on the 6. The new trust anchor will be populated at the resolvers on the
schedule described by the state table and update algorithm - see schedule described by the state table and update algorithm - see
Section 2 above Section 2 above
6.2. Deleting a Trust Anchor 6.2. Deleting a Trust Anchor
Assume existing trust anchors 'A' and 'B' and that you want to revoke Assume existing trust anchors 'A' and 'B' and that you want to revoke
and delete 'A'. and delete 'A'.
1. Set the revolcation bit on key 'A'. 1. Set the revocation bit on key 'A'.
2. Sign the DNSKEY RRSet with both 'A' and 'B'. 2. Sign the DNSKEY RRSet with both 'A' and 'B'.
'A' is now revoked. The operator SHOULD include the revoked 'A' in 'A' is now revoked. The operator should include the revoked 'A' in
the RRSet for at least the remove hold-down time, but then may remove the RRSet for at least the remove hold-down time, but then may remove
it from the DNSKEY RRSet. it from the DNSKEY RRSet.
6.3. Key Roll-Over 6.3. Key Roll-Over
Assume existing keys A and B. 'A' is actively in use (i.e. has been Assume existing keys A and B. 'A' is actively in use (i.e. has been
signing the DNSKEY RRSet.) 'B' was the stand-by key. (i.e. has been signing the DNSKEY RRSet.) 'B' was the stand-by key. (i.e. has been
in the DNSKEY RRSet and is a valid trust anchor, but wasn't being in the DNSKEY RRSet and is a valid trust anchor, but wasn't being
used to sign the RRSet.) used to sign the RRSet.)
1. Generate a new key pair 'C'. 1. Generate a new key pair 'C'.
2. Add 'C' to the DNSKEY RRSet. 2. Add 'C' to the DNSKEY RRSet.
3. Set the revocation bit on key 'A'. 3. Set the revocation bit on key 'A'.
4. Sign the RRSet with 'A' and 'B'. 4. Sign the RRSet with 'A' and 'B'.
'A' is now revoked, 'B' is now the active key, and 'C' will be the 'A' is now revoked, 'B' is now the active key, and 'C' will be the
stand-by key once the hold-down expires. The operator SHOULD include stand-by key once the hold-down expires. The operator should include
the revoked 'A' in the RRSet for at least the remove hold-down time, the revoked 'A' in the RRSet for at least the remove hold-down time,
but may then remove it from the DNSKEY RRSet. but may then remove it from the DNSKEY RRSet.
6.4. Active Key Compromised 6.4. Active Key Compromised
This is the same as the mechanism for Key Roll-Over (Section 6.3) This is the same as the mechanism for Key Roll-Over (Section 6.3)
above assuming 'A' is the active key. above assuming 'A' is the active key.
6.5. Stand-by Key Compromised 6.5. Stand-by Key Compromised
Using the same assumptions and naming conventions as Key Roll-Over Using the same assumptions and naming conventions as Key Roll-Over
(Section 6.3) above: (Section 6.3) above:
1. Generate a new key pair 'C'. 1. Generate a new key pair 'C'.
2. Add 'C' to the DNSKEY RRSet. 2. Add 'C' to the DNSKEY RRSet.
3. Set the revocation bit on key 'B'. 3. Set the revocation bit on key 'B'.
4. Sign the RRSet with 'A' and 'B'. 4. Sign the RRSet with 'A' and 'B'.
'B' is now revoked, 'A' remains the active key, and 'C' will be the 'B' is now revoked, 'A' remains the active key, and 'C' will be the
stand-by key once the hold-down expires. 'B' SHOULD continue to be stand-by key once the hold-down expires. 'B' should continue to be
included in the RRSet for the remove hold-down time. included in the RRSet for the remove hold-down time.
6.6. Trust Point Deletion 6.6. Trust Point Deletion
To delete a trust point which is subordinate to another configured To delete a trust point which is subordinate to another configured
trust point (e.g. example.com to .com) requires some juggling of the trust point (e.g. example.com to .com) requires some juggling of the
data. The specific process is: data. The specific process is:
1. Generate a new DNSKEY and DS record and provide the DS record to 1. Generate a new DNSKEY and DS record and provide the DS record to
the parent along with DS records for the old keys the parent along with DS records for the old keys
2. Once the parent has published the DSs, add the new DNSKEY to the 2. Once the parent has published the DSs, add the new DNSKEY to the
skipping to change at page 11, line 44 skipping to change at page 11, line 15
didn't chain to the superior zone). didn't chain to the superior zone).
7. IANA Considerations 7. IANA Considerations
The IANA will need to assign a bit in the DNSKEY flags field (see The IANA will need to assign a bit in the DNSKEY flags field (see
section 4.3 of [RFC3755]) for the REVOKE bit. There are no other section 4.3 of [RFC3755]) for the REVOKE bit. There are no other
IANA actions required. IANA actions required.
8. Security Considerations 8. Security Considerations
In addition to the following sections, see also Theory of Operation
above and especially Section 2.2 for related discussions.
8.1. Key Ownership vs Acceptance Policy 8.1. Key Ownership vs Acceptance Policy
The reader should note that, while the zone owner is responsible The reader should note that, while the zone owner is responsible for
creating and distributing keys, it's wholly the decision of the creating and distributing keys, it's wholly the decision of the
resolver owner as to whether to accept such keys for the resolver owner as to whether to accept such keys for the
authentication of the zone information. This implies the decision authentication of the zone information. This implies the decision to
update trust anchor keys based on trust for a current trust anchor update trust anchor keys based on trust for a current trust anchor
key is also the resolver owner's decision. key is also the resolver owner's decision.
The resolver owner (and resolver implementers) MAY choose to permit The resolver owner (and resolver implementers) MAY choose to permit
or prevent key status updates based on this mechanism for specific or prevent key status updates based on this mechanism for specific
trust points. If they choose to prevent the automated updates, they trust points. If they choose to prevent the automated updates, they
will need to establish a mechanism for manual or other out-of-band will need to establish a mechanism for manual or other out-of-band
updates outside the scope of this document. updates outside the scope of this document.
8.2. Multiple Key Compromise 8.2. Multiple Key Compromise
skipping to change at page 12, line 25 skipping to change at page 11, line 46
anchor key remains uncompromised. E.g. if there are three keys, you anchor key remains uncompromised. E.g. if there are three keys, you
can recover if two of them are compromised. The zone owner should can recover if two of them are compromised. The zone owner should
determine their own level of comfort with respect to the number of determine their own level of comfort with respect to the number of
active valid trust anchors in a zone and should be prepared to active valid trust anchors in a zone and should be prepared to
implement recovery procedures once they detect a compromise. A implement recovery procedures once they detect a compromise. A
manual or other out-of-band update of all resolvers will be required manual or other out-of-band update of all resolvers will be required
if all trust anchor keys at a trust point are compromised. if all trust anchor keys at a trust point are compromised.
8.3. Dynamic Updates 8.3. Dynamic Updates
Allowing a resolver to update its trust anchor set based in-band key Allowing a resolver to update its trust anchor set based on in-band
information is potentially less secure than a manual process. key information is potentially less secure than a manual process.
However, given the nature of the DNS, the number of resolvers that However, given the nature of the DNS, the number of resolvers that
would require update if a trust anchor key were compromised, and the would require update if a trust anchor key were compromised, and the
lack of a standard management framework for DNS, this approach is no lack of a standard management framework for DNS, this approach is no
worse than the existing situation. worse than the existing situation.
9. Normative References 9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2535] Eastlake, D., "Domain Name System Security Extensions",
RFC 2535, March 1999.
[RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation [RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation
Signer (DS)", RFC 3755, May 2004. Signer (DS)", RFC 3755, May 2004.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005. RFC 4033, March 2005.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions", Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005. RFC 4034, March 2005.
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