Network Working Group H. Eland
Request for Comments: 4986 Afilias Limited
Category: Informational R. Mundy
SPARTA, Inc.
S. Crocker
Shinkuro Inc.
S. Krishnaswamy
SPARTA, Inc.
August 2007
Requirements Related to DNS Security (DNSSEC) Trust Anchor Rollover
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Abstract
Every DNS security-aware resolver must have at least one Trust Anchor
to use as the basis for validating responses from DNS signed zones.
For various reasons, most DNS security-aware resolvers are expected
to have several Trust Anchors. For some operations, manual
monitoring and updating of Trust Anchors may be feasible, but many
operations will require automated methods for updating Trust Anchors
in their security-aware resolvers. This document identifies the
requirements that must be met by an automated DNS Trust Anchor
rollover solution for security-aware DNS resolvers.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Scalability . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. No Known Intellectual Property Encumbrance . . . . . . . . 6
5.3. General Applicability . . . . . . . . . . . . . . . . . . . 7
5.4. Support Private Networks . . . . . . . . . . . . . . . . . 7
5.5. Detection of Stale Trust Anchors . . . . . . . . . . . . . 7
5.6. Manual Operations Permitted . . . . . . . . . . . . . . . . 7
5.7. Planned and Unplanned Rollovers . . . . . . . . . . . . . . 7
5.8. Timeliness . . . . . . . . . . . . . . . . . . . . . . . . 8
5.9. High Availability . . . . . . . . . . . . . . . . . . . . . 8
5.10. New RR Types . . . . . . . . . . . . . . . . . . . . . . . 8
5.11. Support for Trust Anchor Maintenance Operations . . . . . . 8
5.12. Recovery from Compromise . . . . . . . . . . . . . . . . . 8
5.13. Non-Degrading Trust . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. Normative References . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
The Domain Name System Security Extensions (DNSSEC), as described in
[2], [3], and [4], define new records and protocol modifications to
DNS that permit security-aware resolvers to validate DNS Resource
Records (RRs) from one or more Trust Anchors held by such security-
aware resolvers.
Security-aware resolvers will have to initially obtain their Trust
Anchors in a trustworthy manner to ensure the Trust Anchors are
correct and valid. There are a number of ways that this initial step
can be accomplished; however, details of this step are beyond the
scope of this document. Once an operator has obtained Trust Anchors,
initially entering the Trust Anchors into their security-aware
resolvers will in many instances be a manual operation.
For some operational environments, manual management of Trust Anchors
might be a viable approach. However, many operational environments
will require a more automated, specification-based method for
updating and managing Trust Anchors. This document provides a list
of requirements that can be used to measure the effectiveness of any
proposed automated Trust Anchor rollover mechanism in a consistent
manner.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
The use of RFC 2119 words in the requirements is intended to
unambiguously describe a requirement. If a tradeoff is to be made
between conflicting requirements when choosing a solution, the
requirement with MUST language will have higher preference than
requirements with SHOULD, MAY, or RECOMMENDED language. It is
understood that a tradeoff may need to be made between requirements
that both contain RFC 2119 language.
3. Background
DNS resolvers need to have one or more starting points to use in
obtaining DNS answers. The starting points for stub resolvers are
normally the IP addresses for one or more recursive name servers.
The starting points for recursive name servers are normally IP
addresses for DNS Root name servers. Similarly, security-aware
resolvers must have one or more starting points to use for building
the authenticated chain to validate a signed DNS response. Instead
of IP addresses, DNSSEC requires that each resolver trust one or more
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DNSKEY RRs or DS RRs as their starting point. Each of these starting
points is called a Trust Anchor.
It should be noted that DNSKEY RRs and DS RRs are not Trust Anchors
when they are created by the signed zone operator nor are they Trust
Anchors because the records are published in the signed zone. A
DNSKEY RR or DS RR becomes a Trust Anchor when an operator of a
security-aware resolver determines that the public key or hash will
be used as a Trust Anchor. Thus, the signed zone operator that
created and/or published these RRs may not know if any of the DNSKEY
RRs or DS RRs associated with their zone are being used as Trust
Anchors by security-aware resolvers. The obvious exceptions are the
DNSKEY RRs for the Root Zone, which will be used as Trust Anchors by
many security-aware resolvers. For various reasons, DNSKEY RRs or DS
RRs from zones other than Root can be used by operators of security-
aware resolvers as Trust Anchors. It follows that responsibility
lies with the operator of the security-aware resolver to ensure that
the DNSKEY and/or DS RRs they have chosen to use as Trust Anchors are
valid at the time they are used by the security-aware resolver as the
starting point for building the authentication chain to validate a
signed DNS response.
When operators of security-aware resolvers choose one or more Trust
Anchors, they must also determine the method(s) they will use to
ensure that they are using valid RRs and that they are able to
determine when RRs being used as Trust Anchors should be replaced or
removed. Early adopters of DNS signed zones have published
information about the processes and methods they will use when their
DNSKEY and/or DS RRs change so that operators of security-aware
resolvers can manually change the Trust Anchors at the appropriate
time. This manual approach will not scale and, therefore, drives the
need for an automated specification-based approach for rollover of
Trust Anchors for security-aware resolvers.
4. Definitions
This document uses the definitions contained in RFC 4033, section 2,
plus the following additional definitions:
Trust Anchor: From RFC 4033, "A configured DNSKEY RR or DS RR hash
of a DNSKEY RR. A validating security-aware resolver uses this
public key or hash as a starting point for building the
authentication chain to a signed DNS response." Additionally, a
DNSKEY RR or DS RR is associated with precisely one point in the
DNS hierarchy, i.e., one DNS zone. Multiple Trust Anchors MAY be
associated with each DNS zone and MAY be held by any number of
security-aware resolvers. Security-aware resolvers MAY have Trust
Anchors from multiple DNS zones. Those responsible for the
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operation of security-aware resolvers are responsible for
determining the set of RRs that will be used as Trust Anchors by
that resolver.
Initial Trust Relationship: Operators of security-aware resolvers
must ensure that they initially obtain any Trust Anchors in a
trustworthy manner. For example, the correctness of the Root Zone
DNSKEY RR(s) could be verified by comparing what the operator
believes to be the Root Trust Anchor(s) with several 'well-known'
sources such as the IANA web site, the DNS published Root Zone and
the publication of the public key in well-known hard-copy forms.
For other Trust Anchors, the operator must ensure the accuracy and
validity of the DNSKEY and/or DS RRs before designating them Trust
Anchors. This might be accomplished through a combination of
technical, procedural, and contractual relationships, or use other
existing trust relationships outside the current DNS protocol.
Trust Anchor Distribution: The method or methods used to convey the
DNSKEY and/or DS RR(s) between the signed zone operator and the
security-aware resolver operator. The method or methods MUST be
deemed sufficiently trustworthy by the operator of the security-
aware resolver to ensure source authenticity and integrity of the
new RRs to maintain the Initial Trust Relationship required to
designate those RRs as Trust Anchors.
Trust Anchor Maintenance: Any change in a validating security-aware
resolver to add a new Trust Anchor, delete an existing Trust
Anchor, or replace an existing Trust Anchor with another. This
change might be accomplished manually or in some automated manner.
Those responsible for the operation of the security-aware resolver
are responsible for establishing policies and procedures to ensure
that a sufficient Initial Trust Relationship is in place before
adding Trust Anchors for a particular DNS zone to their security-
aware resolver configuration.
Trust Anchor Revocation and Removal: The invalidation of a
particular Trust Anchor that results when the operator of the
signed zone revokes or removes a DNSKEY RR or DS RR that is being
used as a Trust Anchor by any security-aware resolver. It is
possible that a zone administrator may invalidate more than one RR
at one point in time; therefore, it MUST be clear to both the zone
administrator and the security-aware resolver the exact RR(s) that
have been revoked or removed so the proper Trust Anchor or Trust
Anchors are removed.
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Trust Anchor Rollover: The method or methods necessary for the
secure replacement of one or multiple Trust Anchors held by
security-aware resolvers. Trust Anchor Rollover should be
considered a subset of Trust Anchor Maintenance.
Normal or Pre-Scheduled Trust Anchor Rollover: The operator of a
DNSSEC signed zone has issued a new DNSKEY and/or DS RR(s) as a
part of an operational routine.
Emergency or Non-Scheduled Trust Anchor Rollover: The operator of a
signed zone has issued a new DNSKEY and/or DS RR(s) as part of an
exceptional event.
Emergency Trust Anchor Revocation: The operator of a signed zone
wishes to indicate that the current DNSKEY and/or DS RR(s) are no
longer valid as part of an exceptional event.
5. Requirements
Following are the requirements for DNSSEC automated specification-
based Trust Anchor Rollover:
5.1. Scalability
The automated Trust Anchor Rollover solution MUST be capable of
scaling to Internet-wide usage. The probable largest number of
instances of security-aware resolvers needing to rollover a Trust
Anchor will be those that use the public key(s) for the Root Zone as
Trust Anchor(s). This number could be extremely large if a number of
applications have embedded security-aware resolvers.
The automated Trust Anchor Rollover solution MUST be able to support
Trust Anchors for multiple zones and multiple Trust Anchors for each
DNS zone. The number of Trust Anchors that might be configured into
any one validating security-aware resolver is not known with
certainty at this time; in most cases it will be less than 20 but it
may even be as high as one thousand.
5.2. No Known Intellectual Property Encumbrance
Because trust anchor rollover is likely to be "mandatory-to-
implement", section 8 of [5] requires that the technical solution
chosen must not be known to be encumbered or must be available under
royalty-free terms.
For this purpose, "royalty-free" is defined as follows: worldwide,
irrevocable, perpetual right to use, without fee, in commerce or
otherwise, where "use" includes descriptions of algorithms,
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distribution and/or use of hardware implementations, distribution
and/or use of software systems in source and/or binary form, in all
DNS or DNSSEC applications including registry, registrar, domain name
service including authority, recursion, caching, forwarding, stub
resolver, or similar.
In summary, no implementor, distributor, or operator of the
technology chosen for trust anchor management shall be expected or
required to pay any fee to any IPR holder for the right to implement,
distribute, or operate a system which includes the chosen mandatory-
to-implement solution.
5.3. General Applicability
The solution MUST provide the capability to maintain Trust Anchors in
security-aware resolvers for any and all DNS zones.
5.4. Support Private Networks
The solution MUST support private networks with their own DNS
hierarchy.
5.5. Detection of Stale Trust Anchors
The Trust Anchor Rollover solution MUST allow a validating security-
aware resolver to be able to detect if the DNSKEY and/or DS RR(s) can
no longer be updated given the current set of actual trust-anchors.
In these cases, the resolver should inform the operator of the need
to reestablish initial trust.
5.6. Manual Operations Permitted
The operator of a security-aware resolver may choose manual or
automated rollover, but the rollover protocol must allow the
implementation to support both automated and manual Trust Anchor
Maintenance operations. Implementation of the rollover protocol is
likely to be mandatory, but that's out of scope for this requirements
document.
5.7. Planned and Unplanned Rollovers
The solution MUST permit both planned (pre-scheduled) and unplanned
(non-scheduled) rollover of Trust Anchors. Support for providing an
Initial Trust Relationship is OPTIONAL.
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5.8. Timeliness
Resource Records used as Trust Anchors SHOULD be able to be
distributed to security-aware resolvers in a timely manner.
Security-aware resolvers need to acquire new and remove revoked
DNSKEY and/or DS RRs that are being used as Trust Anchors for a zone
such that no old RR is used as a Trust Anchor for long after the zone
issues new or revokes existing RRs.
5.9. High Availability
Information about the zone administrator's view of the state of
Resource Records used as Trust Anchors SHOULD be available in a
trustworthy manner at all times to security-aware resolvers.
Information about Resource Records that a zone administrator has
invalidated and that are known to be used as Trust Anchors should be
available in a trustworthy manner for a reasonable length of time.
5.10. New RR Types
If a Trust Anchor Rollover solution requires new RR types or protocol
modifications, this should be considered in the evaluation of
solutions. The working group needs to determine whether such changes
are a good thing or a bad thing or something else.
5.11. Support for Trust Anchor Maintenance Operations
The Trust Anchor Rollover solution MUST support operations that allow
a validating security-aware resolver to add a new Trust Anchor,
delete an existing Trust Anchor, or replace an existing Trust Anchor
with another.
5.12. Recovery from Compromise
The Trust Anchor Rollover solution MUST allow a security-aware
resolver to be able to recover from the compromise of any of its
configured Trust Anchors for a zone so long as at least one other
key, which is known to have not been compromised, is configured as a
Trust Anchor for that same zone at that resolver.
5.13. Non-Degrading Trust
The Trust Anchor Rollover solution MUST provide sufficient means to
ensure authenticity and integrity so that the existing trust relation
does not degrade by performing the rollover.
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6. Security Considerations
This document defines overall requirements for an automated
specification-based Trust Anchor Rollover solution for security-aware
resolvers but specifically does not define the security mechanisms
needed to meet these requirements.
7. Acknowledgements
This document reflects the majority opinion of the DNSEXT Working
Group members on the topic of requirements related to DNSSEC trust
anchor rollover. The contributions made by various members of the
working group to improve the readability and style of this document
are graciously acknowledged.
8. Normative References
[1] Bradner, S., "Key Words for Use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"DNS Security Introduction and Requirements", RFC 4033,
March 2005.
[3] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Resource Records for the DNS Security Extensions", RFC 4034,
March 2005.
[4] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"Protocol Modifications for the DNS Security Extensions",
RFC 4035, March 2005.
[5] Bradner, S., "Intellectual Property Rights in IETF Technology",
RFC 3979, March 2005.
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Authors' Addresses
Howard Eland
Afilias Limited
300 Welsh Road
Building 3, Suite 105
Horsham, PA 19044
USA
EMail: heland@afilias.info
Russ Mundy
SPARTA, Inc.
7110 Samuel Morse Dr.
Columbia, MD 21046
USA
EMail: mundy@sparta.com
Steve Crocker
Shinkuro Inc.
1025 Vermont Ave, Suite 820
Washington, DC 20005
USA
EMail: steve@shinkuro.com
Suresh Krishnaswamy
SPARTA, Inc.
7110 Samuel Morse Dr.
Columbia, MD 21046
USA
EMail: suresh@sparta.com
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RFC 4986 DNSSEC Trust Anchor Rollover Requirements August 2007
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