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<!ENTITY MAINTAINDS PUBLIC "" "http://xml2rfc.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-dnsop-maintain-ds.xml">
]>

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<rfc ipr="trust200902" docName="draft-wouters-sury-dnsop-algorithm-update-02" category="std" obsoletes="6944">
  <front>
    <title abbrev="DNSSEC Cryptographic Algorithms">Algorithm Implementation Requirements and Usage Guidance for DNSSEC</title>
    <author fullname="Paul Wouters" initials="P." surname="Wouters">
      <organization>Red Hat</organization>
      <address>
        <email>pwouters@redhat.com</email>
      </address>
    </author>
    <author fullname="Ondrej Sury" initials="O." surname="Sury">
      <organization>CZ.NIC</organization>
      <address>
        <email>ondrej.sury@nic.cz</email>
      </address>
    </author>
    <date year="2016"/>
    <area>Security</area>
    <workgroup>dnsop</workgroup>
    <keyword>Internet-Draft</keyword>
    <abstract>
      <t>
	The DNSSEC protocol makes use of various cryptographic
	algorithms in order to provide authentication of DNS data and
	proof of non-existence.  To ensure interoperability between
	DNS resolvers and DNS authoritative servers, it is necessary
	to specify a set of algorithm implementation requirements and
	usage guidance to ensure that there is at least one algorithm
	that all implementations support.  This document defines the
	current algorithm implementation requirements and usage
	guidance for DNSSEC. This document obsoletes RFC-6944.
      </t>
    </abstract>
  </front>
  <!-- ====================================================================== -->
  <middle>

    <section anchor="introduction" title="Introduction">
      <t>
	The DNSSEC signing algorithms are defined by various RFCs,
	including <xref target="RFC4034"/>, <xref target="RFC5155"/>,
	<xref target="RFC5702"/>, <xref target="RFC5933"/>, <xref
	target="RFC6605"/>, <xref target="I-D.ietf-curdle-dnskey-eddsa"/>.
	 DNSSEC is used to provide authentication of data. To ensure interoperability,
	a set of "mandatory-to-implement" DNSKEY algorithms are defined.
	This document obsoletes <xref target="RFC6944"/>.
      </t>

      <section title="Updating Algorithm Implementation Requirements and Usage Guidance">
	<t>
	  The field of cryptography evolves continuously.  New stronger
	  algorithms appear and existing algorithms are found to be
	  less secure then originally thought.  Therefore, algorithm
	  implementation requirements and usage guidance need to be
	  updated from time to time to reflect the new reality.  The
	  choices for algorithms must be conservative to minimize the
	  risk of algorithm compromise.
	</t>
      </section>

      <section title="Updating Algorithm Requirement Levels">
	<t>
	  The mandatory-to-implement algorithm of tomorrow should
	  already be available in most implementations of DNSSEC by the
	  time it is made mandatory.  This document attempts to
	  identify and introduce those algorithms for future
	  mandatory-to-implement status.  There is no guarantee that
	  the algorithms in use today may become mandatory in the
	  future.  Published algorithms are continuously subjected to
	  cryptographic attack and may become too weak or could become
	  completely broken before this document is updated.
	</t>

	<t>
	  This document only provides recommendations for the
	  mandatory-to-implement algorithms or algorithms too weak that
	  are recommended not to be implemented.  As a result, any
	  algorithm listed at the <xref target="DNSKEY-IANA"/> and
	  <xref target="DS-IANA"/> registries not mentioned in this
	  document MAY be implemented.  For clarification and consistency,
	  an algorithm will be set to MAY only when it has been downgraded.
	</t>

	<t>
	  Although this document updates the algorithms to keep the
	  DNSSEC authentication secure over time, it also aims at
	  providing recommendations so that DNSSEC implementations
	  remain interoperable.  DNSSEC interoperability is addressed
	  by an incremental introduction or deprecation of algorithms.
	</t>

	<t>
	  It is expected that deprecation of an algorithm is performed
	  gradually.  This provides time for various implementations to
	  update their implemented algorithms while remaining
	  interoperable.  Unless there are strong security reasons, an
	  algorithm is expected to be downgraded from MUST to MUST- or
	  SHOULD, instead of MUST NOT.  Similarly, an algorithm that
	  has not been mentioned as mandatory-to-implement is expected
	  to be introduced with a SHOULD instead of a MUST.
	</t>

	<t>
	  Since the effects of using an unknown DNSKEY algorithm is for
	  the zone to be treated as insecure, it is recommended that
	  algorithms downgraded to SHOULD- or below are no longer used
	  by authoritative nameservers and DNSSEC signers to create new
	  DNSKEY's.  This will allow for algorithms to slowly become
	  more unused over time.  Once deployment has reached a
	  sufficiently low point these algorithms can finally be marked
	  as MUST NOT so that recursive nameservers can remove support
	  for these algorithms.
	</t>

	<t>
	  Recursive nameservers are encouraged to keep support for all
	  algorithms not marked as MUST NOT.
	</t>
      </section>

      <section title="Document Audience">
	<t>
	  The recommendations of this document mostly target DNSSEC
	  implementers as implementations need to meet both high
	  security expectations as well as high interoperability
	  between various vendors and with different versions.
	  Interoperability requires a smooth move to more secure
	  algorithms.  This may differ from a user point of view that
	  may deploy and configure DNSSEC with only the safest
	  algorithm.  On the other hand, comments and recommendations
	  from this document are also expected to be useful for such
	  users.
	</t>
      </section>

    </section>
    <section anchor="mustshouldmay" title="Conventions Used in This Document">

      <t>
	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 <xref target="RFC2119"/>.
      </t>

      <t>
	We define some additional terms here:
      </t>

      <texttable anchor="tbl" style="none" suppress-title="true">
	<ttcol align="left" width="12%"/>
	<ttcol align="left" />
	<c>SHOULD+</c>
	<c>
	  This term means the same as SHOULD.  However, it is likely
	  that an algorithm marked as SHOULD+ will be promoted at some
	  future time to be a MUST.
	</c>

	<c>SHOULD-</c>
	<c>
	  This term means the same as SHOULD.  However, an algorithm
	  marked as SHOULD- may be deprecated to a MAY in a future
	  version of this document.
	</c>

	<c>MUST-</c>
	<c>
	  This term means the same as MUST.  However, it is expected at some
	  point in the near future that this algorithm will no longer be a MUST in a
	  future document.  Although its status will be determined at a
	  later time, it is reasonable to expect that if a future
	  revision of a document alters the status of a MUST-
	  algorithm, it will remain at least a SHOULD or a SHOULD-.
	</c>
      </texttable>

    </section>

    <section anchor="algs" title="Algorithm Selection">

      <section anchor="algs_dnskey" title="DNSKEY Algorithms">

	<t>
	  Recommendations for DNSKEY algorithms <xref target="DNSKEY-IANA"/>
	</t>

	<texttable anchor="tbl_dnskey" suppress-title="true">
          <ttcol align="left">Number</ttcol>
          <ttcol align="left">Mnemonics</ttcol>
          <ttcol align="left">DNSSEC Signing</ttcol>
          <ttcol align="left">DNSSEC Validation</ttcol>

          <c>1</c><c>RSAMD5</c><c>MUST NOT</c><c>MUST NOT</c>
          <c>3</c><c>DSA</c><c>MUST NOT</c><c>MUST NOT</c>
          <c>5</c><c>RSASHA1</c><c>MUST-</c><c>MUST-</c>
          <c>6</c><c>DSA-NSEC3-SHA1</c><c>MUST NOT</c><c>MUST NOT</c>
          <c>7</c><c>RSASHA1-NSEC3-SHA1</c><c>MUST-</c><c>MUST-</c>
          <c>8</c><c>RSASHA256</c><c>MUST</c><c>MUST</c>
          <c>10</c><c>RSASHA512</c><c>SHOULD-</c><c>MUST</c>
          <c>12</c><c>ECC-GOST</c><c>SHOULD NOT</c><c>SHOULD-</c>
          <c>13</c><c>ECDSAP256SHA256</c><c>SHOULD-</c><c>MUST-</c>
          <c>14</c><c>ECDSAP384SHA384</c><c>SHOULD NOT</c><c>SHOULD-</c>
	  <c>TBD</c><c>ED25519</c><c>SHOULD+</c><c>SHOULD+</c>
	  <c>TBD</c><c>ED448</c><c>SHOULD+</c><c>SHOULD+</c>
	</texttable>

	<t>
	  RSAMD5 is not widely deployed and there is an industry-wide
	  trend to deprecate MD5 usage.
	</t>

	<t>
	  RSASHA1 and RSASHA1-NSEC3-SHA1 are widely deployed, although
	  zones deploying it are recommended to switch to RSASHA256 as
	  there is an industry-wide trend to deprecate SHA1 usage.
	  RSASHA1 does not support NSEC3.  RSASHA1-NSEC3-SHA1 can be
	  used with or without NSEC3.
	</t>

        <t>
	  DSA and DSA-NSEC3-SHA1 are not widely deployed and
	  vulnerable to private key compromise when generating
	  signatures using a weak or compromised random number
	  generator.
	</t>

        <t>
	  RSASHA512 is at the SHOULD level for DNSSEC Signing because
	  it has not seen wide deployment, but there are some
	  deployments hence DNSSEC Validation MUST implement RSASHA512
	  to ensure interoperability.
	</t>

        <t>
	  ECC-GOST is at the SHOULD NOT level because it has not seen wide
	  deployment and the algorithm has not seen wide scrutiny in the
          crypto community.
	</t>

        <t>
	  ECDSAP256SHA256 and ECDSAP384SHA384 provide more strength
	  for signature size than RSASHA256 and RSASHA512 variants.
	  ECDSAP256SHA256 has seen increased deployment and has been
	  raised to MUST- level for resolving and SHOULD- for signing. It
	  is seen as a temporary improvement over RSA until the <xref
	  target="I-D.ietf-curdle-dnskey-eddsa"/> algorithms are published,
	  implemented and deployed.
	  ECDSAP384SHA384 offers little over ECDSAP256SHA256
	  and has not seen wide deployment, so the use is discouraged,
	  especially for signing.
	</t>

	<t>
	  ED25519 and ED448 uses Edwards-curve Digital Security Algorithm
	  (EdDSA).  There are three main advantages of the EdDSA
	  algorithm: It does not require the use of a unique random number
	  for each signature, there are no padding or truncation issues as
	  with ECDSA, and it is more resilient to side-channel attacks.
	  Hence it is expected that these algorithms will be raised to
	  SHOULD for signing and MUST for resolving once it has seen
	  more implementations and deployement.
	</t>

      </section>

      <section anchor="algs_ds" title="DS and CDS Algorithms">

	<t>
	  Recommendations for Delegation Signer Digest Algorithms <xref target="DNSKEY-IANA"/>
	  These also apply to the CDS RRTYPE as specified in <xref target="RFC7344"/>
	</t>

	<texttable anchor="tbl_ds" suppress-title="true">
          <ttcol align="left">Number</ttcol>
          <ttcol align="left">Mnemonics</ttcol>
          <ttcol align="left">DNSSEC Delegation</ttcol>
          <ttcol align="left">DNSSEC Validation</ttcol>

          <c>0</c><c>NULL (CDS only)</c><c>MUST NOT [*]</c><c>MUST NOT [*]</c>
          <c>1</c><c>SHA-1</c><c>SHOULD NOT</c><c>MUST-</c>
          <c>2</c><c>SHA-256</c><c>MUST</c><c>MUST</c>
          <c>3</c><c>GOST R 34.11-94</c><c>MAY</c><c>SHOULD</c>
          <c>4</c><c>SHA-384</c><c>MAY</c><c>SHOULD+</c>
         <postamble>
          [*] - This is a special type of CDS record signaling removal of
	  DS at the parent in <xref target="I-D.ietf-dnsop-maintain-ds"/>
         </postamble>
	</texttable>

	<t>
	  NULL is a special case, see <xref target="I-D.ietf-dnsop-maintain-ds"/>
	</t>

	<t>
	  SHA-1 is in wide use for DS records, but its use is discouraged
	  as it is an aging algorithm. Users of SHA-1 SHOULD upgrade to SHA-256.
	</t>

        <t>
	  SHA-256 is in wide use and considered strong.
	</t>

        <t>
	  GOST R 34.11-94 is not in wide use. It is still recommended
	  to be supported in validators so that adoption can increase.
	</t>

	<t>
	  SHA-384 is not in wide use. It is still recommended to be
	  supported in validators so that adoption can increase.
	</t>

      </section>
    </section>

    <section anchor="security" title="Security Considerations">

      <t>
	The security of cryptographic-based systems depends on both
	the strength of the cryptographic algorithms chosen and the
	strength of the keys used with those algorithms.  The security
	also depends on the engineering of the protocol used by the
	system to ensure that there are no non-cryptographic ways to
	bypass the security of the overall system.
      </t>

      <t>
	This document concerns itself with the selection of
	cryptographic algorithms for the use of DNSSEC, specifically
	with the selection of "mandatory-to-implement" algorithms.  The
	algorithms identified in this document as "MUST implement" or
	"SHOULD implement" are not known to be broken at the current
	time, and cryptographic research so far leads us to believe
	that they will likely remain secure into the foreseeable
	future.  However, this isn't necessarily forever and it is
	expected that new revisions of this document will be issued
	from time to time to reflect the current best practice in this
	area.
      </t>

      <t>
	Retiring an algorithm too soon would result in a signed zone
	with such an algorithm to be downgraded to the equivalent of
	an unsigned zone.  Therefore, algorithm deprecation must be
	done very slowly and only after careful consideration and
	measurements of its use.
      </t>
    </section>

    <section anchor="operation" title="Operational Considerations">
      <t>
	DNSKEY algorithm rollover in a live zone is a complex
	process.  See <xref target="RFC6781"/> and <xref target="RFC7583"/>
	for guidelines on how to perform algorithm rollovers.
      </t>
    </section>

    <section anchor="iana" title="IANA Considerations">
      <t>This document makes no requests of IANA.</t>
    </section>

    <section anchor="ack" title="Acknowledgements">
      <t>
	This document borrows text from RFC 4307 by Jeffrey
	I.  Schiller of the Massachusetts Institute of Technology (MIT)
	and the 4307bis document by Yoav Nir, Tero Kivinen, Paul
	Wouters and Daniel Migault.  Much of the original text has been
	copied verbatim.
      </t>
      <t>
	We wish to thank Olafur Gudmundsson and Paul Hoffman for their imminent feedback.
      </t>
    </section>

  </middle>
  <!-- ====================================================================== -->
  <back>
    <references title="Normative References">
      &RFC2119;
    </references>
    <references title="Informative References">
      &RFC4034;
      &RFC5155;
      &RFC5702;
      &RFC5933;
      &RFC6605;
      &RFC6781;
      &RFC6944;
      &RFC7344;
      &RFC7583;
      &EDDSA;
      &MAINTAINDS;
      <reference anchor="DNSKEY-IANA" target="http://www.iana.org/assignments/dns-sec-alg-numbers/dns-sec-alg-numbers.xhtml">
        <front>
          <title>DNSKEY Algorithms</title>
          <author initials="" surname="" fullname="">
            <organization />
          </author>
          <date />
        </front>
      </reference>
      <reference anchor="DS-IANA" target="http://www.iana.org/assignments/ds-rr-types/ds-rr-types.xhtml">
        <front>
          <title>Delegation Signer Digest Algorithms</title>
          <author initials="" surname="" fullname="">
            <organization />
          </author>
          <date />
        </front>
      </reference>
    </references>
    <!-- ====================================================================== -->
  </back>
</rfc>
