draft-ietf-dnsop-dnssec-trust-anchor-01.txt   draft-ietf-dnsop-dnssec-trust-anchor-02.txt 
DNS Operations M. Larson DNS Operations M. Larson
Internet-Draft VeriSign Internet-Draft VeriSign
Expires: August 14, 2008 O. Gudmundsson Expires: January 15, 2009 O. Gudmundsson
OGUD Consulting LLC OGUD Consulting LLC
February 11, 2008 July 14, 2008
DNSSEC Trust Anchor Configuration and Maintenance DNSSEC Trust Anchor Configuration and Maintenance
draft-ietf-dnsop-dnssec-trust-anchor-01 draft-ietf-dnsop-dnssec-trust-anchor-02
Status of this Memo Status of this Memo
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract Abstract
This document recommends a preferred format for specifying trust This document recommends a preferred format for specifying trust
anchors in DNSSEC validating security-aware resolvers and describes anchors in DNSSEC validating security-aware resolvers and describes
how such a resolver should initialize trust anchors for use. This how such a resolver should initialize trust anchors for use. This
document also describes different mechanisms for keeping trust document also describes different mechanisms for keeping trust
anchors up to date over time. anchors up to date over time.
Table of Contents Table of Contents
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6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 10 6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 12 8.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 14
1. Introduction 1. Introduction
The DNSSEC standards documents ([2], [3] and [4]) describe the need The DNSSEC standards documents ([RFC4033], [RFC4034] and [RFC4035])
for trust anchors and how they are used. A validating security-aware describe the need for trust anchors and how they are used. A
resolver (subsequently referred to as a "validating resolver") needs validating security-aware resolver (subsequently referred to as a
to be configured with one or more trust anchors, which specify the "validating resolver") needs to be configured with one or more trust
public keys of signed zones. To authenticate DNS data, a validating anchors, which specify the public keys of signed zones. To
resolver builds a chain of trust from a configured trust anchor to authenticate DNS data, a validating resolver builds a chain of trust
that data. from a configured trust anchor to that data.
In a widespread public DNSSEC deployment, the DNS root zone would be In a widespread public DNSSEC deployment, the DNS root zone would be
signed and a validating resolver would need to be configured with at signed and a validating resolver would need to be configured with at
least the root zone's trust anchor. A validating resolver might need least the root zone's trust anchor. A validating resolver might need
additional trust anchors configured to accommodate islands of additional trust anchors configured to accommodate islands of
security. (An island of security is a signed, delegated zone that security. (An island of security is a signed, delegated zone that
does not have an authentication chain from its delegating parent.) does not have an authentication chain from its delegating parent.)
For example, consider the situation where the root zone is signed but For example, consider the situation where the root zone is signed but
a given top-level domain (TLD) zone is not. Various second-level a given top-level domain (TLD) zone is not. Various second-level
zones under this unsigned TLD might be signed and resolver operators zones under this unsigned TLD might be signed and resolver operators
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To simplify this trust anchor configuration process that will occur To simplify this trust anchor configuration process that will occur
on a large number of resolvers, this document offers guidance to on a large number of resolvers, this document offers guidance to
validating resolver implementers by specifying a standardized format validating resolver implementers by specifying a standardized format
for describing trust anchors. The document also describes how a for describing trust anchors. The document also describes how a
validating resolver should initialize or "prime" trust anchors before validating resolver should initialize or "prime" trust anchors before
first use. Finally, the document lists options for keeping trust first use. Finally, the document lists options for keeping trust
anchor information current over time. anchor information current over time.
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 RFC 2119 [1]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Trust Anchor Format 2. Trust Anchor Format
A trust anchor is a DNSSEC public key configured in a validating A trust anchor is a DNSSEC public key configured in a validating
resolver. A validating resolver's configuration MUST allow one or resolver. A validating resolver's configuration MUST allow one or
more trust anchors to be specified. According to the definition in more trust anchors to be specified. According to the definition in
Section 2 of RFC 4033 [2], a trust anchor can be specified as either Section 2 of RFC 4033 [RFC4033], a trust anchor can be specified as
a public key from a DNSKEY resource record (RR) or the hash of a either a public key from a DNSKEY resource record (RR) or the hash of
public key as found in a DS RR. (DS records are defined in Section 5 a public key as found in a DS RR. (DS records are defined in Section
of RFC 4034 [3].) 5 of RFC 4034 [RFC4034].)
This document RECOMMENDS that a trust anchor be specified using the This document RECOMMENDS that a trust anchor be specified using the
hash of a public key rather than the key itself, i.e., the fields hash of a public key rather than the key itself, i.e., the fields
from a DS record rather than from a DNSKEY record. A trust anchor from a DS record rather than from a DNSKEY record. A trust anchor
specified in this manner will use all the fields from the specified in this manner will use all the fields from the
corresponding key's DS record, including the owner name to indicate corresponding key's DS record, including the owner name to indicate
which zone the trust anchor corresponds to as well as the various which zone the trust anchor corresponds to as well as the various
fields from the DS RDATA. The digest algorithm SHOULD be SHA-256 fields from the DS RDATA. The digest algorithm SHOULD be SHA-256
[5], which is DS digest type 2. DS records using SHA-1 (DS digest [RFC4509], which is DS digest type 2. DS records using SHA-1 (DS
type 1) to specify trust anchors are NOT RECOMMENDED: RFC 4509 digest type 1) to specify trust anchors are NOT RECOMMENDED: RFC 4509
encourages the use of DS RRs using SHA-256 over those using SHA-1. encourages the use of DS RRs using SHA-256 over those using SHA-1.
Specifying a trust anchor using a DS format instead of a DNSKEY Specifying a trust anchor using a DS format instead of a DNSKEY
format offers a slight advantage because it forces the resolver to format offers a slight advantage because it forces the resolver to
make a DNS query to obtain the trust anchor's complete DNSKEY RRSet make a DNS query to obtain the trust anchor's complete DNSKEY RRSet
during a priming operation (described below). If only a DNSKEY during a priming operation (described below). If only a DNSKEY
record were specified, resolver implementers could conceivably avoid record were specified, resolver implementers could conceivably avoid
priming the trust anchor. But priming is desirable because it causes priming the trust anchor. But priming is desirable because it causes
the resolver to retrieve an up-to-date version of a zone's DNSKEY the resolver to retrieve an up-to-date version of a zone's DNSKEY
RRSet from one of the zone's authoritative servers. It should be RRSet from one of the zone's authoritative servers. It should be
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DNSKEY format and is easier to enter manually, either by typing or DNSKEY format and is easier to enter manually, either by typing or
cutting and pasting. cutting and pasting.
Another advantage of configuring a trust anchor using a DS record is Another advantage of configuring a trust anchor using a DS record is
that the entire hash of the public key in the DS RDATA need not that the entire hash of the public key in the DS RDATA need not
necessarily be specified. A validating resolver MAY support necessarily be specified. A validating resolver MAY support
configuration using a truncated DS hash value as a human-factors configuration using a truncated DS hash value as a human-factors
convenience: shorter strings are easier to type and less prone to convenience: shorter strings are easier to type and less prone to
error when entered manually. Even with a truncated hash configured, error when entered manually. Even with a truncated hash configured,
a validating resolver can still verify that the corresponding DNSKEY a validating resolver can still verify that the corresponding DNSKEY
is present in the trust anchor zone's apex DNSKEY RRSet. is present in the trust anchor zone's apex DNSKEY RRSet. RFC 2104
[RFC2104] offers guidance on acceptable truncation lengths.
3. Trust Anchor Priming 3. Trust Anchor Priming
A validating resolver needs to obtain and validate the DNSKEY RRSet A validating resolver needs to obtain and validate the DNSKEY RRSet
corresponding to a configured DS for that trust anchor to be usable corresponding to a configured DS for that trust anchor to be usable
in DNSSEC validation. This process is called "priming" the trust in DNSSEC validation. This process is called "priming" the trust
anchor. Priming can occur when the validating resolver starts, but a anchor. Priming can occur when the validating resolver starts, but a
validating resolver SHOULD defer priming of individual trust anchors validating resolver SHOULD defer priming of individual trust anchors
until each is first needed for verification. This priming on demand until each is first needed for verification. This priming on demand
is especially important when a validating resolver is configured with is especially important when a validating resolver is configured with
a large number of trust anchors to avoid sending a large number of a large number of trust anchors to avoid sending a large number of
DNS queries on start-up. This section adds additional details to the DNS queries on start-up. This section adds additional details to the
discussion of trust anchors in Section 5 of RFC 4035 [4]. discussion of trust anchors in Section 5 of RFC 4035 [RFC4035].
Following are the steps a validating resolver SHOULD take to prime a Following are the steps a validating resolver SHOULD take to prime a
configured trust anchor: configured trust anchor:
1. Read the trust anchor's information (corresponding to the fields 1. Read the trust anchor's information (corresponding to the fields
in a DS record) from the validating resolver's configuration in a DS record) from the validating resolver's configuration
(e.g., a text file). (e.g., a text file).
2. Look up the DNSKEY RRSet corresponding to the owner name of the 2. Look up the DNSKEY RRSet corresponding to the owner name of the
trust anchor. (The validating resolver can either perform trust anchor. (The validating resolver can either perform
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zone signing key.) zone signing key.)
4. Verify that the DNSKEY RRSet is signed by one of the DNSKEYs 4. Verify that the DNSKEY RRSet is signed by one of the DNSKEYs
found in the previous step, i.e., that there exists a valid RRSIG found in the previous step, i.e., that there exists a valid RRSIG
(cryptographically and temporally) for the DNSKEY RRSet generated (cryptographically and temporally) for the DNSKEY RRSet generated
with the private key corresponding to the DNSKEY found in the with the private key corresponding to the DNSKEY found in the
previous step. previous step.
If the validating resolver can successfully complete the steps above, If the validating resolver can successfully complete the steps above,
all DNSKEY RRs in the RRSet ought to be considered authenticated and all DNSKEY RRs in the RRSet ought to be considered authenticated and
can be used authenticate RRSets at or below the trust anchor. can be used to authenticate RRSets at or below the trust anchor.
If any of the steps above result in an error, the validating resolver If any of the steps above result in an error, the validating resolver
SHOULD log them. SHOULD log them.
If there are multiple trust anchors configured for a zone, any one of If there are multiple trust anchors configured for a zone, any one of
them is sufficient to validate data in the zone. For this reason, them is sufficient to validate data in the zone. For this reason,
old trust anchors SHOULD be removed from a validating resolver's old trust anchors SHOULD be removed from a validating resolver's
trust anchor list soon after the corresponding keys are no longer trust anchor list soon after the corresponding keys are no longer
used by the zone. A validating resolver should remove a trust anchor used by the zone. If there are multiple trust anchors configured for
that has been revoked as indicated by the REVOKE bit in the a zone, any one of them is sufficient to validate data in the zone.
corresponding DNSKEY record as described in RFC 5011 [6]. For this reason, old trust anchors SHOULD be removed from a
validating resolver's trust anchor list soon after the corresponding
keys are no longer used by the zone, as described in RFC 5011
[RFC5011].
If a validating resolver is unable to retrieve a signed DNSKEY RRSet If a validating resolver is unable to retrieve a signed DNSKEY RRSet
corresponding to a trust anchor (i.e., prime the trust anchor), it corresponding to a trust anchor (i.e., prime the trust anchor), it
SHOULD log this condition as an error. Inability to prime a zone's SHOULD log this condition as an error. Inability to prime a zone's
trust anchor results in the validating resolver's inability to trust anchor results in the validating resolver's inability to
validate data from the corresponding zone. The validating resolver validate data from the corresponding zone. The validating resolver
SHOULD treat this zone as bogus. SHOULD treat this zone as bogus.
4. Trust Anchor Maintenance 4. Trust Anchor Maintenance
Trust anchors correspond to zones' key signing keys and these keys do Trust anchors correspond to zones' key signing keys and these keys do
change in the course of normal operation. Validating resolver change in the course of normal operation. It is up to validating
operators MUST ensure that configured trust anchor information resolver operators to ensure that configured trust anchor information
remains current and does not go stale: each configured trust anchor remains current and does not go stale: each configured trust anchor
SHOULD correspond to a DNSKEY RR in the trust anchor zone's apex SHOULD correspond to a DNSKEY RR in the trust anchor zone's apex
DNSKEY RRSet. This process is called trust anchor maintenance. DNSKEY RRSet. This process is called trust anchor maintenance.
(Initial trust anchor configuration requires human intervention to (Initial trust anchor configuration requires human intervention to
verify the trust anchor's authenticity using out-of-band means and is verify the trust anchor's authenticity using out-of-band means and is
outside the scope of this document.) outside the scope of this document.)
This section provides a brief overview of some possible mechanisms to This section provides a brief overview of some possible mechanisms to
keep trust anchor information current: keep trust anchor information current:
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RRSet) and updating that information. This process MAY require RRSet) and updating that information. This process MAY require
the operator to use the same out-of-band verification mechanism as the operator to use the same out-of-band verification mechanism as
used for initial configuration to ensure that the new trust anchor used for initial configuration to ensure that the new trust anchor
DS record is trustworthy. Because manual maintenance is DS record is trustworthy. Because manual maintenance is
burdensome and prone to error, and because other automated trust burdensome and prone to error, and because other automated trust
anchor maintenance processes either exist or are in development, anchor maintenance processes either exist or are in development,
manual trust anchor maintenance is NOT RECOMMENDED. manual trust anchor maintenance is NOT RECOMMENDED.
DNSSEC In-band Update: The IETF DNS Extensions Working Group has DNSSEC In-band Update: The IETF DNS Extensions Working Group has
developed a protocol to automatically update DNSSEC trust anchors, developed a protocol to automatically update DNSSEC trust anchors,
which is described in RFC 5011 [6]. This protocol relies on a which is described in RFC 5011 [RFC5011]. This protocol relies on
small DNSSEC protocol change (an additional flag in the DNSKEY a small DNSSEC protocol change (an additional flag in the DNSKEY
record) and can be implemented either in a validating resolver record) and can be implemented either in a validating resolver
itself or in an external program with access to the validating itself or in an external program with access to the validating
resolver's trust anchor configuration data. resolver's trust anchor configuration data.
Trusted update mechanism: Updated trust anchor information MAY be Trusted update mechanism: Updated trust anchor information MAY be
obtained via a trusted non-DNS update mechanism. One possibility obtained via a trusted non-DNS update mechanism. One possibility
is the operating system update mechanism provided by most software is the operating system update mechanism provided by most software
vendors. Operators already place considerable trust in this vendors. Operators already place considerable trust in this
mechanism, so it is reasonable to extend this trust to allow mechanism, so it is reasonable to extend this trust to allow
distribution and update of DNSSEC public key material. Another distribution and update of DNSSEC public key material. Another
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If multiple mechanisms are updating the trust anchor list then there If multiple mechanisms are updating the trust anchor list then there
is the possibility of conflict, such as one mechanism reinserting an is the possibility of conflict, such as one mechanism reinserting an
expired trust anchor. expired trust anchor.
Trust anchors are configuration information. A validating resolver Trust anchors are configuration information. A validating resolver
ought to treat this information differently than DNS data obtained ought to treat this information differently than DNS data obtained
over the network and never use the configured trust anchors as part over the network and never use the configured trust anchors as part
of an answer. of an answer.
A signed zone that plans to transition to an unsigned state must A signed zone that plans to transition to an unsigned state must
first give a warning that it is going insecure. Failure to do so first give a warning that it is going insecure, such as using the
will cause all validating resolvers that keep a trust anchor for the technique described in RFC 5011 [RFC5011]. Failure to do so will
zone configured to treat responses from the zone as bogus, causing cause all validating resolvers that keep a trust anchor for the zone
configured to treat responses from the zone as bogus, causing
resolution failures. resolution failures.
6. IANA considerations 6. IANA considerations
This document does not have any IANA actions. This document does not have any IANA actions.
7. Acknowledgments 7. Acknowledgments
This work was undertaken at the suggestion of the DNSSEC Deployment This work was undertaken at the suggestion of the DNSSEC Deployment
working group (www.dnssec-deployment.org). working group (www.dnssec-deployment.org).
8. References 8. References
8.1. Normative References 8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
"DNS Security Introduction and Requirements", RFC 4033, Rose, "DNS Security Introduction and Requirements",
March 2005. RFC 4033, March 2005.
[3] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
"Resource Records for the DNS Security Extensions", RFC 4034, Rose, "Resource Records for the DNS Security Extensions",
March 2005. RFC 4034, March 2005.
[4] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
"Protocol Modifications for the DNS Security Extensions", Rose, "Protocol Modifications for the DNS Security
RFC 4035, March 2005. Extensions", RFC 4035, March 2005.
[5] Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer (DS) [RFC4509] Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer
Resource Records (RRs)", RFC 4509, May 2006. (DS) Resource Records (RRs)", RFC 4509, May 2006.
[6] StJohns, M., "Automated Updates of DNS Security (DNSSEC) Trust [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Anchors", RFC 5011, September 2007. Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", RFC 5011, September 2007.
8.2. Informative References 8.2. Informative References
Authors' Addresses Authors' Addresses
Matt Larson Matt Larson
VeriSign, Inc. VeriSign, Inc.
21345 Ridgetop Circle 21345 Ridgetop Circle
Dulles, VA 20166-6503 Dulles, VA 20166-6503
USA USA
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attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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