Intentionally Temporarily Insecure
draft-hardaker-dnsop-intentionally-temporary-insec-00

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Author Wes Hardaker 
Last updated 2021-02-21
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Network Working Group                                        W. Hardaker
Internet-Draft                                                   USC/ISI
Intended status: Best Current Practice                 February 21, 2021
Expires: August 25, 2021

                   Intentionally Temporarily Insecure
         draft-hardaker-dnsop-intentionally-temporary-insec-00

Abstract

   Performing DNSKEY algorithm transitions with DNSSEC signing is
   unfortunately challenging to get right in practice without decent
   tooling support.  This document weighs the correct, completely secure
   way of rolling keys against an alternate, significantly simplified,
   method that takes a zone through an insecure state.

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
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   This Internet-Draft will expire on August 25, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements notation . . . . . . . . . . . . . . . . . .   3
   2.  Transitioning temporarily through insecurity  . . . . . . . .   3
   3.  Operational considerations  . . . . . . . . . . . . . . . . .   4
   4.  Security considerations . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   6
   Appendix B.  Github Version of this document  . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Performing DNSKEY [RFC4035] algorithm transitions with DNSSEC
   [RFC4033] signing is unfortunately challenging to get right in
   practice without decent tooling support.  This document weighs the
   correct, completely secure way of rolling keys against an alternate,
   significantly simplified, method that takes a zone through an
   insecure state.

   Section 4.1.4 of [RFC6781] describes the necessary steps required
   when a new signing key is published for a zone that uses a different
   signing algorithm than the currently published keys.  These are the
   steps that MUST be followed when zone owners wish to have
   uninterrupted DNSSEC protection for their zones.  The steps in this
   document are designed to ensure that all DNSKEY records and all DS
   [RFC4509] records (and the rest of a zone records) are properly
   validatable by validating resolvers throughout the entire process.

   Unfortunately, there are a number of these steps that are challenging
   to accomplish either because the timing is tricky to get right or
   because current software doesn't support automating the process
   easily.  For example, the second step in Section 4.1.4 of [RFC6781]
   requires that a new key with the new algorithm (which we refer to as
   K_new) be created, but not yet published.  This step also requires
   that both the old key (K_old) and K_new sign and generate signatures
   for the zone, but with only the K_old key is published even though
   signatures from K_new are included.  After this odd mix has been
   published for a sufficient time length, based on the TTL, can K_new
   be safely introduced and published into the zone as well.

   Although many DNSSEC signing solutions may automate the algorithm
   rollover steps (making operator involvement unnecessary), many other
   tools do not support automated algorithm updates.  In these
   environments, the most challenging step is requiring that certain

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   RRSIGs be published without the corresponding DNSKEYs that created
   them.  This will likely require operators to use a text editor on the
   contents of a signed zone to carefully select zone records to extract
   before publication.  This introduces potentially significant operator
   error(s).

   This document proposes an alternate, potentially more operationally
   robust but less secure, approach to performing algorithm DNSKEY
   rollovers for use in these situations.

1.1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Transitioning temporarily through insecurity

   An alternate approach to rolling DNSKEYs, especially when the
   toolsets being used do not provide easy algorithm rollover
   approaches, is to intentionally make the zone become insecure while
   the DNSKEYs and algorithms are swapped.  At a high level, this means
   removing all DS records from the parent zone during the removal of
   the old key and the introduction of a new key using a new algorithm.
   Zone TTLs may be significantly shortened during this period to
   minimize the period of insecurity.

   Below are the enumerated steps required by this alternate transition
   mechanism.  Note that there are still two critical waiting time
   requirements (steps 2 and 6) that must be followed carefully.

   1.  Optional: lower the TTLs of the zone's DS record (if possible)
       and the SOA's negative TTL (MINIMUM) [RFC1035].

   2.  Remove all DS records from the parent zone.

   3.  Ensure the zone is considered unsigned by all validating
       resolvers by waiting 2 times the maximum TTL length for the DS
       record to expire from caches.  This is the most critical timing.
       The author of this document failed to wait the required time
       once.  It was not pretty.

   4.  Replace the old DNSKEY(s) with the old algorithm with new
       DNSKEY(s) with the new algorithm(s) in the zone and publish the
       zone.

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   5.  Wait 2 times the zone SOA's published negative cache time to
       ensure the new DNSKEYs will be found by validating resolvers.

   6.  Add the DS record(s) for the new DNSKEYs to the parent zone.

   7.  If the TTLs were modified in the optional step 1, change them
       back to their preferred values.

3.  Operational considerations

   The process of replacing a DNSKEY with an older algorithm, such as
   RSAMD5 or RSASHA1 with a more modern one such as RSASHA512 or
   ECDSAP256SHA256 can be a daunting task if the zone's current tooling
   doesn't provide an easy-to-use solution.  This is the case for zone
   owners that potentially use command line tools that are integrated
   into their zone production environment.

   This document describes an alternative approach to rolling DNSKEY
   algorithms that may be significantly less prone to operational
   mistakes.  However, understanding of the security considerations of
   using this approach is paramount.

   The document recommends waiting 2 times TTL values in certain cases
   for added assurance that the waiting period is long enough for caches
   to expire.  In reality, waiting only 1 TTL may be sufficient assuming
   all clocks around the world are operating with perfection.

4.  Security considerations

   DNSSEC provides an data integrity protection for DNS data.  This
   document specifically calls out a reason why a zone owner may desire
   to deliberately turn off DNSSEC while changing the zone's DNSKEY's
   cryptographic algorithms.  Thus, this is deliberately turning off
   security which is potentially harmful if an attacker knows when this
   will occur and can use that time window to launch DNS modification
   attacks (for example, cache poisoning attacks) against validating
   resolvers or other validating DNS infrastructure.

   Most importantly, this will deliberately break certain types of DNS
   records that must be validatable for them to be effective.  This
   includes for example, but not limited to, all DS records for child
   zones, DANE [RFC6698][RFC7671][RFC7672], PGP keys [RFC7929], and
   SSHFP[RFC4255].  Zone owners must carefully consider which records
   within their zone depend on DNSSEC being available before using the
   procedure outlined in this document.

   Given all of this, it leaves the question of: "why would a zone owner
   want to deliberately turn off security temporarily then?", to which

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   there is one principal answer.  Simply put, if the the complexity of
   doing it the correct way is difficult with existing tooling then the
   chances of performing the more complex procedure and introducing an
   error, likely making the entire zone unavailable during that time
   period, may be significantly higher than the chances of the zone
   being attacked during the transition period of the simpler approach
   where zone availability is less likely to be impacted.  Simply put,
   an invalid zone created by a botched algorithm roll is potentially
   worse than an unsigned but still available zone.

5.  References

5.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

   [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>.

   [RFC4509]  Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer
              (DS) Resource Records (RRs)", RFC 4509,
              DOI 10.17487/RFC4509, May 2006,
              <https://www.rfc-editor.org/info/rfc4509>.

   [RFC6781]  Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
              Operational Practices, Version 2", RFC 6781,
              DOI 10.17487/RFC6781, December 2012,
              <https://www.rfc-editor.org/info/rfc6781>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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5.2.  Informative References

   [RFC4255]  Schlyter, J. and W. Griffin, "Using DNS to Securely
              Publish Secure Shell (SSH) Key Fingerprints", RFC 4255,
              DOI 10.17487/RFC4255, January 2006,
              <https://www.rfc-editor.org/info/rfc4255>.

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
              2012, <https://www.rfc-editor.org/info/rfc6698>.

   [RFC7671]  Dukhovni, V. and W. Hardaker, "The DNS-Based
              Authentication of Named Entities (DANE) Protocol: Updates
              and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
              October 2015, <https://www.rfc-editor.org/info/rfc7671>.

   [RFC7672]  Dukhovni, V. and W. Hardaker, "SMTP Security via
              Opportunistic DNS-Based Authentication of Named Entities
              (DANE) Transport Layer Security (TLS)", RFC 7672,
              DOI 10.17487/RFC7672, October 2015,
              <https://www.rfc-editor.org/info/rfc7672>.

   [RFC7929]  Wouters, P., "DNS-Based Authentication of Named Entities
              (DANE) Bindings for OpenPGP", RFC 7929,
              DOI 10.17487/RFC7929, August 2016,
              <https://www.rfc-editor.org/info/rfc7929>.

Appendix A.  Acknowledgments

   The author has discussed the pros and cons of this approach with
   multiple people, including Viktor Dukhovni and Warren Kumari.

Appendix B.  Github Version of this document

   While this document is under development, it can be viewed, tracked,
   issued, pushed with PRs, ... here:

   https://github.com/hardaker/draft-hardaker-dnsop-intentionally-
   temporarily-insecure

Author's Address

   Wes Hardaker
   USC/ISI

   Email: ietf@hardakers.net

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