One document matched: draft-crocker-dnssec-algo-signal-04.xml

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<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
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<?rfc tocdepth="6"?>
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<rfc ipr="pre5378Trust200902" category="std" docName="draft-crocker-dnssec-algo-signal-04" 
updates="4035">
<front>
<title abbrev="Algorithm-Signal">Signaling Cryptographic Algorithm Understanding in DNSSEC</title>
	<author fullname="Steve Crocker" initials="S." surname="Crocker">
			<organization>Shinkuro Inc.</organization>
			<address>
				<postal>
					<street>5110 Edgemoor Lane</street>
					<city>Bethesda</city>
					<code>20814</code>
					<region>MD</region>
					<country>USA</country>
				</postal>
				<email>steve@shinkuro.com</email>
			</address>
	</author>
	<author fullname="Scott Rose" initials="S." surname="Rose">
			<organization> NIST </organization>
			<address>
				<postal>
					<street>100 Bureau Dr.</street>
					<city>Gaithersburg</city>
					<code>20899</code>
					<region>MD</region>
					<country>USA</country>
				</postal>
				<phone>+1-301-975-8439</phone>
				<email> scott.rose@nist.gov </email>
			</address>
		</author>
	
<date month="October" year="2009"/>
<area> Internet Area </area>
<workgroup> DNS Extensions Working Group </workgroup>
<keyword>DNS</keyword>
<keyword>DNSSEC</keyword>
<abstract>
	<t>
	The DNS Security Extensions (DNSSEC) was developed to provide origin 
	authentication and integrity protection for DNS data by using digital 
	signatures.  These digital signatures can be generated 
	using different algorithms.  This draft sets out to specify a way for  
	validating end-system resolvers 
    to signal to a server which cryptographic algorithms they support.
	</t>
</abstract>
	<note title="Requirements Language">
	<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">RFC 2119</xref>.
	</t>
	</note>
</front>
<middle>
<section title="Introduction">
	<t>
	The DNS Security Extensions (DNSSEC) was developed to provide origin 
	authentication and integrity protection for DNS data by using digital 
	signatures <xref target="RFC4033" />, <xref target="RFC4034" /> and
	<xref target="RFC4035" />.  Each digital signature RR (RRSIG) contains an 
    algorithm code
	number.  These algorithm codes help validators identify which 
    cryptographic algorithm was used to generate the digital signature.  
	</t>
	<t>
	This proposed EDNS option serves to measure the 
	acceptance and use of new digital signing algorithms.
	This algorithm signaling option can be used by zone administrators as a gauge
	to measure the successful deployment of code that implements a newly deployed 
	digital signature algorithm used with DNSSEC.  A zone administrator may be able 
	to determine when to stop serving the old algorithm when
	the server sees that all or almost all of its clients signal that they 
	are able to accept the new algorithm.  
	</t>
	<t>
	This draft does not seek to include a formal process for including new algorithms for
	use with DNSSEC.  It also does not address the question of which algorithms are to
	be included in any official list of mandatory or recommended cryptographic algorithms
	for use with DNSSEC.  Rather, this document specifies a means by which a client 
	query can signal a set of algorithms it implements.
	</t>
 	<t>
	This draft sets out to specify a way for validating end-system resolvers
	to signal to a server which
	cryptographic algorithms they support in a DNSSEC response.  This is done 
	using the EDNS attribute values in the OPT meta-RR <xref target="RFC2671" />.  
	</t>	
	
</section>
<section title="Signaling Algorithm Understood (AU) Using EDNS">
	<t>
	The ENDS0 specification outlined in <xref target="RFC2671" /> defines a 
    way to include new options using a standardized mechanism.  These options are 
    contained in the RDATA of the OPT meta-RR.  This document seeks to define 
    a new EDNS0 option for a client to signal which algorithms the client 
    supports. 
	</t>
	<figure><preamble>Below shows how the signaling attribute is defined in 
the RDATA of the OPT
	RR as specified in <xref target="RFC2671" />:
	</preamble>
<artwork>
    0                       8                      16
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                 OPTION-CODE (TBD)             |					
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                 OPTION-LENGTH                 |					
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |       ALG-CODE        |        ...            \					
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  
</artwork><postamble></postamble>
	</figure>
	<t>
	OPTION-CODE is the code for the Algorithm Understood (AU) option.  Its value
	is fixed at TBD.
	</t>
	<t>
	OPTION-LENGTH is the length of the data of the attribute in octets.
DNSSEC algorithm codes are 1 octet long so this value is the number of octets.
	</t>
	<t>
	ALG-CODE is the assigned DNSSEC algorithm codes that the client indicates as 
	understood. The values MUST be in descending order, with the highest algorithm code first, followed by
	as many other codes as the validator wishes to signal that it prefers. For example, if
	a validating client implements RSA/SHA-1 and RSA/SHA-256 the value of ALG-CODE
	would be: 8 (RSA/SHA-256), 5 (RSA/SHA-1) indicating that the validator implements both 
	RSA/SHA-256 and RSA/SHA-1, but does not wish to receive (or does not understand)
	RRSIGs using DSA or RSA/MD5.
	</t>
</section>
<section title="Client Considerations">
	<t>
	A validating end-system resolver sets the AU option in the OPT meta-RR when sending a 
	query.  The validating end-system resolver sets the value(s) in the order of preference,
	with highest algorithm value first as described in section 2. The end-system resolver
	MUST also set the DNSSEC-OK bit <xref target="RFC4035" /> to 
        indicate that it wishes to receive DNSSEC RRs in the response.
	</t>
	<t>
	Note that when including the PRIVATEDNS (253) and/or the PRIVATEOID (254) codes, the
	client only indicates that it understands one or more private algorithms but does not 
	indicate which algorithms.
	</t>
  <section title="Recommendations for Stub Clients">
	<t>
	Typically, stub resolvers rely on an upstream recursive server (or cache) to provide
	a response, any algorithm supportence on the stub resolver's side could be
	overruled by the upstream recursive server.  The AU EDNS option is NOT 
	RECOMMENDED for non-validating stub clients.  
	</t>
	<t>
	The exception to the above is that validating stub resolvers which set the CD
	bit in queries MAY set the AU option.  In the most common scenario, the
	validating stub indicates that it wishes to perform its own validation
	(via the CD bit) and may therefor wish to indicate which cryptographic 
	algorithm(s) it supports.
	</t>
  </section>	
  <section title="Recursive Cache Considerations">
	<t>
	DNSSEC validating recursive caches MAY set the AU option on any outgoing
	query from the cache when performing recursion on behalf of a non-DNSSEC
	aware stub client. If the stub indicates it is DNSSEC-aware, but does not
	set the AU option in the query, the DNSSEC validating recursive cache
	SHOULD NOT set the AU option to avoid conflicts.
	</t>
	<t>
	Forwarders that do not do validation or caching SHOULD copy the AU option 
	seen in received queries as they represent the wishes of the validating 
	downstream resolver that issued the original query.
	</t>
</section>
</section>
  <section title="Intermediate Middlebox Considerations">
	<t>
	Intermediate middleboxes SHOULD copy the AU option seen in queries from
	end system resolvers.  If the system is validating, it SHOULD 
	also check for the presence of the CD bit in the query.  If present, the 
	intermediate middlebox SHOULD copy the AU option as seen in the query.  If
	not set or if the DNSSEC-OK bit is not set, then the validating intermediate
	middlebox MAY chose to ignore the AU option in the query and MAY include 
	its own preference as the AU option.
	</t>
  </section>
<section title="Server Considerations">
	<t>
	When an authoritative server sees the AU option in the OPT meta-RR in a
	request the normal algorithm for servicing requests is followed.  </t>
	<t>
	If the AU option is present but the DNSSEC-OK bit is not set, then the 
	authoritative server ignores the ALG-CODE list and does not include any additional 
	DNSSEC RRs in the response.  
	</t>
</section>
<section title="Traffic Analysis Considerations">
	<t>
	Zone administrators that are planning or are in the process of completing a 
	cryptographic algorithm rollover operation should monitor DNS query traffic
	and record the values of the AU option in queries.  This monitoring can 
	measure the deployment of client code that implements (and signals) certain
	algorithms.  Exactly how to capture DNS traffic and measure new algorithm
	adoption is beyond the scope of this document.
	</t>
	<t>
	Zone administrators can use this data to set plans for starting an algorithm 
	rollover and when older algorithms can be phased out without disrupting the 
	majority of clients.  In order ot keep this disruption to a minimum, zone
	administrators should wait to complete an algorithm rollover until a large 
	majority of clients signal that they understand the new algorithm.  Note that 
	clients that do not implement the AU option may be older implementations which 
	would also not implement any newly deployed algorithm.
	</t>
</section>
<section anchor="IANA" title="IANA Considerations">
	<t>
	The algorithm codes used to identify DNSSEC algorithms has already been 
	established by IANA.  This document does not seek to alter that registry
	in any way.
	</t>
	<t>
	This draft seeks to update the "DNS EDNS0 Options" registry by adding the 
	AU option and referencing this document.  The code for the option should
	be TBD.
	</t>
</section>

<section anchor="Security" title="Security Considerations">
	<t>
	This document specifies a way for a client to signal its digital signature 
	algorithm preference to a cache or server.  It is not meant to be a 
discussion
	on algorithm superiority.  The signal is an optional code contained in
	the OPT meta-RR used with EDNS0.  The goal of this option is to signal new
	algorithm uptake in client code to allow zone administrators to know when
	it is possible to complete an algorithm rollover in a DNSSEC signed zone.
	</t>

</section>

</middle>

<back>
	<references title="Normative References">
		<?rfc include="reference.RFC.2119" ?>
		<?rfc include="reference.RFC.2671" ?>
		<?rfc include="reference.RFC.4033" ?>
		<?rfc include="reference.RFC.4034" ?>
		<?rfc include="reference.RFC.4035" ?>
	</references>
</back>
</rfc>