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Collision Free Keytags for DNSSEC
draft-huque-dnsop-keytags-00

Document Type Active Internet-Draft (individual)
Authors Mark P. Andrews , Shumon Huque , Elias Heftrig
Last updated 2024-07-25
RFC stream (None)
Intended RFC status (None)
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draft-huque-dnsop-keytags-00
Internet Engineering Task Force                               M. Andrews
Internet-Draft                               Internet Systems Consortium
Updates: 4034, 4035 (if approved)                               S. Huque
Intended status: Standards Track                              Salesforce
Expires: 25 January 2025                                      E. Heftrig
                                                    Fraunhofer Institute
                                                            24 July 2024

                   Collision Free Keytags for DNSSEC
                      draft-huque-dnsop-keytags-00

Abstract

   DNSSEC employs a Key Tag field in the RRSIG and DS resource records
   in order to efficiently identify the key that produced a DNSSEC
   signature and the key that should be used as secure entry point into
   a delegated zone.  The Key Tag was not intended to be a unique
   identifier.  Key tag collisions can occur in practice for keys in the
   same zone, though they are relatively rare in normal operation.
   Colliding key tags impose additional work on a validating resolver,
   which then has to check signatures for each of the candidate set of
   keys identified by the Key Tag.  Furthermore, they open up resolvers
   to computational denial of service attacks by adversaries deploying
   specially crafted zones with many intentionally colliding key tags.
   This document specifies updates to the DNSSEC protocol and the
   process of key generation to avoid colliding keys and enforce the
   uniqueness of key tags.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Source for this draft and an issue tracker can be found at
   https://github.com/shuque/ietf-dns-keytags.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 25 January 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Protocol Behavior . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Updates to RFCs . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   DNSSEC [RFC4033] [RFC4034] [RFC4035] employs a Key Tag field in the
   RRSIG and DS resource records in order to efficiently identify the
   key that produced a DNSSEC signature the key that should be used as
   secure entry point into a delegated zone.  The Key Tag was not
   intended to be a unique identifier.  Key tag collisions can occur in
   practice for keys in the same zone, though they are relatively rare
   in normal operation.  Colliding key tags impose additional work on a
   validating resolver, which then has to check signatures for each of
   the candidate set of keys identified by the Key Tag.  Furthermore,
   they open up resolvers to computational denial of service attacks by
   adversaries deploying specially crafted zones with many intentionally
   colliding key tags [KEYTRAP].  This document specifies updates to the
   DNSSEC protocol and the process of key generation to avoid colliding

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   keys and enforce the uniqueness of key tags.

2.  Protocol Behavior

   *  New DNSKEY algorithms MUST have DNSKEY RRsets that do not have
      colliding key tags

   *  What about existing algorithms?  Should we have new aliases for
      existing algorithms that allow us to incorporate the non collision
      requirement?

   *  Can we propose a future flag date after which existing algorithms
      will be required to enforce this requirement?

   *  Outline the general process by which key generation software
      should ensure uniqueness of keytags.

   *  Special considerations for multi-signer configurations, where
      multiple distinct parties generate their own keys for the same
      zone (i) partition the keytag space between each signer/provider,
      and have each provider re-generate keys if necessary until they
      obtain one whose keytag is contained in their partition (ii) Use a
      central key broker to enforce keytag uniqueness, (iii) each signer
      when generating new keys, queries all DNSKEYs in the multi-signer
      group to avoid colliding keys.  To avoid race conditions, ideally
      the providers should not generate keys at the same time, and
      plausibly the zone owner could enforce non-conflicting key
      generation schedules across the multi-signer group.

   *  Describe what to do when a validator encounters a zone with both
      old and new DNSKEY algorithm numbers.

   *  For possible discussion: recommend the use DNS cookies to avoid
      offpath computational DoS attacks.

3.  Updates to RFCs

   TBD

4.  Security Considerations

   Lorem ipsum.

5.  IANA Considerations

   Lorem ipsum.

6.  References

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6.1.  Normative References

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <https://www.rfc-editor.org/info/rfc4033>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <https://www.rfc-editor.org/info/rfc4034>.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
              <https://www.rfc-editor.org/info/rfc4035>.

6.2.  Informative References

   [KEYTRAP]  Heftrig, E., Schulmann, H., Vogel, N., and M. Waidner,
              "The KeyTrap Denial-of-Service Algorithmic Complexity
              Attacks on DNS", <https://www.athene-
              center.de/fileadmin/content/PDF/Keytrap_2401.pdf>.

Authors' Addresses

   Mark Andrews
   Internet Systems Consortium
   Email: marka@isc.org

   Shumon Huque
   Salesforce
   Email: shuque@gmail.com

   Elias Heftrig
   Fraunhofer Institute
   Email: elias.heftrig@sit.fraunhofer.de

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