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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 6975

DNS Extensions Working Group                                  S. Crocker
Internet-Draft                                             Shinkuro Inc.
Intended status: Standards Track                                 S. Rose
Expires: January 7, 2012                                            NIST
                                                            July 6, 2011


       Signaling Cryptographic Algorithm Understanding in DNSSEC
                draft-ietf-dnsext-dnssec-algo-signal-02

Abstract

   The DNS Security Extensions (DNSSEC) were 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.

Requirements Language

   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 [RFC2119].

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 http://datatracker.ietf.org/drafts/current/.

   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 January 7, 2012.

Copyright Notice

   Copyright (c) 2011 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



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   Provisions Relating to IETF Documents
   (http://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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3

   2.  Signaling DNSSEC Algorithm Understood (DAU) Using EDNS  . . . . 3

   3.  Client Considerations . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Stub Resolvers  . . . . . . . . . . . . . . . . . . . . . . 5
     3.2.  Validating Stub Resolvers . . . . . . . . . . . . . . . . . 5
     3.3.  Non-Validating Stub Resolvers . . . . . . . . . . . . . . . 5
     3.4.  Recursive Resolvers . . . . . . . . . . . . . . . . . . . . 5
       3.4.1.  Validating Recursive Resolvers  . . . . . . . . . . . . 5
       3.4.2.  Non-validating Recursive Resolvers  . . . . . . . . . . 6

   4.  Intermediate System Considerations  . . . . . . . . . . . . . . 6

   5.  Server Considerations . . . . . . . . . . . . . . . . . . . . . 6

   6.  Traffic Analysis Considerations . . . . . . . . . . . . . . . . 6

   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7

   8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7

   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7

















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1.  Introduction

   The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and
   [RFC4035] were developed to provide origin authentication and
   integrity protection for DNS data by using digital signatures.  Each
   digital signature RR (RRSIG) contains an algorithm code number.
   These algorithm codes tells validators which cryptographic algorithm
   was used to generate the digital signature.  Authentication across
   delegation boundaries is maintained by storing a hash of a subzone's
   key in the parent zone stored in a Delegation Signer (DS) RR.  These
   DS RR's contain a second code number to identify the hash algorithm
   used to construct the DS RR.

   This draft sets out to specify a way for validating end-system
   resolvers to tell a server which cryptographic and/or hash algorithms
   they support in a DNS query.  This is done using the EDNS attribute
   values in the OPT meta-RR [RFC2671].

   This proposed EDNS option serves to measure the acceptance and use of
   new digital signing and hash 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 or hash algorithm used with DNSSEC.  A zone
   administrator may be able to determine when to stop serving the old
   algorithm when the server sees that a significant number of its
   clients signal that they are able to accept the new algorithm.  Note
   that this survey may be conducted over the period of years before a
   tipping point is seen.

   This draft does not seek to include another process for including new
   algorithms for use with DNSSEC (see .  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.

2.  Signaling DNSSEC Algorithm Understood (DAU) Using EDNS

   The ENDS0 specification outlined in [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 defines
   a new EDNS0 option for a client to signal which algorithms the client
   supports.








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   The figure below shows how the signaling attribute is defined in the
   RDATA of the OPT RR specified in [RFC2671]:

       0                       8                      16
       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       |                 OPTION-CODE (TBD)             |
       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       |             DIGITAL-SIG-LIST-LENGTH           |
       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       |       ALG-CODE        |        ...            \
       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       |              DS-HASH-LIST-LENGTH              |
       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       |       HASH-CODE       |        ...            \
       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+



   OPTION-CODE is the code for the DNSSEC Algorithm Understood (DAU)
   option.  Its value is fixed at TBD.

   DIGITAL-SIG-LIST-LENGTH is the length of the list of digital
   signature algorithms in octets.  DNSSEC algorithm codes are 1 octet
   long so this value is the number of octets.

   ALG-CODE is the list of assigned values of DNSSEC zone signing
   algorithms that the client indicates as understood.  The values
   SHOULD be in descending order of preference, with the most preferred
   algorithm first.  For example, if a validating client implements RSA/
   SHA-1, RSA/SHA-256 and prefers the latter, the value of ALG-CODE
   would be: 8 (RSA/SHA-256), 5 (RSA/SHA-1).

   DS-HASH-LIST-LENGTH is the length of the list of hash algorithms in
   octets.  DNSSEC DS hash codes are 1 octet long so this value is the
   number of octets.

   HASH-CODE is the list of assigned values of DNSSEC DS hash algorithms
   that the client indicates as understood.  Like the ALG-CODE above,
   the values SHOULD be in descending order of preference, with the most
   preferred algorithm first.

3.  Client Considerations

   A validating end-system resolver sets the DAU 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 the most preferred
   algorithm(s) first as described in section 2.  The end-system
   resolver SHOULD also set the DNSSEC-OK bit [RFC4035] to indicate that



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   it wishes to receive DNSSEC RRs in the response.

   Note that the PRIVATEDNS (253) and/or the PRIVATEOID (254) codes
   cover a potentially wide range of algorithms and are likely not
   useful to a server.  There is no compelling reason for a client to
   include these codes in its list of understood algorithms.

3.1.  Stub Resolvers

   Typically, stub resolvers rely on an upstream recursive server (or
   cache) to provide a response.  So optimal setting of the DAU option
   depends on whether the stub resolver performs its own DNSSEC
   validation or doesn't perform its own validation.

3.2.  Validating Stub Resolvers

   A validating stub resolver already (usually) sets the DO bit
   [RFC4035] to indicate that it wishes to receive additional DNSSEC RRs
   (i.e.  RRSIG RR's) in the response.  Such validating resolvers SHOULD
   include the DAU option in the OPT RR when sending a query.  This way
   thee validating stub resolver indicates which cryptographic
   algorithm(s) it supports by setting the values(s) in the order of
   preference, with the most preferred algorithm(s) first as described
   in Section 2.

3.3.  Non-Validating Stub Resolvers

   The DAU EDNS option is NOT RECOMMENDED for non-validating stub
   resolvers.

3.4.  Recursive Resolvers

3.4.1.  Validating Recursive Resolvers

   A validating recursive resolver sets the DAU option when performing
   recursion based on the DO and CD flags in the client request
   [RFC4035].  If the client of the recursive resolver did not include
   the DO bit in the query the recursive resolver SHOULD include the DAU
   option according to its own local policy.

   If the client did include the DO and CD bits, but did not include the
   DAU option in the query, the validating recursive resolver SHOULD NOT
   include the DAU option to avoid conflicts.

   If the client did set the DO bit and the DAU option in the query, the
   validating recursive resolver SHOULD include the DAU option based on
   the setting of the CD bit.  If the CD bit is set, the validating
   recursive resolver SHOULD include the DAU option based on the client



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   query or a superset of the client DAU option list and the validator's
   own list (if different).  If the CD bit is not set, the validating
   recursive resolver MAY copy the client DAU option or substitute its
   own DAU option list.

3.4.2.  Non-validating Recursive Resolvers

   Recursive resolvers that do not do validation or caching SHOULD copy
   the DAU option seen in received queries as they represent the wishes
   of the validating downstream resolver that issued the original query.

4.  Intermediate System Considerations

   Intermediate proxies [RFC5625] that understand DNS SHOULD behave like
   a comparable recursive resolver when dealing with the DAU option.

5.  Server Considerations

   When an authoritative server sees the DAU option in the OPT meta-RR
   in a request the normal algorithm for servicing requests is followed.
   The DAU option does not trigger any special processing on the server
   side.

   If the DAU option is present but the DNSSEC-OK (OK) bit is not set,
   the server does not do any DNSSEC processing, including any recording
   of the DAU option.

6.  Traffic Analysis Considerations

   Zone administrators that are planning or are in the process of a
   cryptographic algorithm rollover operation should monitor DNS query
   traffic and record the values of the DAU 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.

   Zone administrators can use this data to set plans for starting an
   algorithm rollover and determine when older algorithms can be phased
   out without disrupting a significant number of clients.  In order to
   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.  This may be in the
   order of years rather than months.  Note that clients that do not
   implement the DAU option are likely to be older implementations which
   would also not implement any newly deployed algorithm.





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7.  IANA Considerations

   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.

   This draft seeks to update the "DNS EDNS0 Options" registry by adding
   the DAU option and referencing this document.  The code for the
   option should be TBD.

8.  Security Considerations

   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.

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2671]  Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
              RFC 2671, August 1999.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC5625]  Bellis, R., "DNS Proxy Implementation Guidelines",
              BCP 152, RFC 5625, August 2009.









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Authors' Addresses

   Steve Crocker
   Shinkuro Inc.
   5110 Edgemoor Lane
   Bethesda, MD  20814
   USA

   EMail: steve@shinkuro.com


   Scott Rose
   NIST
   100 Bureau Dr.
   Gaithersburg, MD  20899
   USA

   Phone: +1-301-975-8439
   EMail: scottr.nist@gmail.com
































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