Requirements Related to DNS Security (DNSSEC) Trust Anchor Rollover
RFC 4986

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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