[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Nits]

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: May 13, 2011                                               NIST
                                                        November 9, 2010


       Signaling Cryptographic Algorithm Understanding in DNSSEC
                draft-ietf-dnsext-dnssec-algo-signal-00

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 May 13, 2011.

Copyright Notice

   Copyright (c) 2010 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



Crocker & Rose            Expires May 13, 2011                  [Page 1]

Internet-Draft              Algorithm-Signal               November 2010


   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
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

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

   2.  Signaling Algorithm Understood (AU) 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 Middlebox Considerations . . . . . . . . . . . . . 6

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

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

   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6

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

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

















Crocker & Rose            Expires May 13, 2011                  [Page 2]

Internet-Draft              Algorithm-Signal               November 2010


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 boundries 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 contruct 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 all or almost all of its clients
   signal that they are able to accept the new algorithm.

   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 Algorithm Understood (AU) 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.










Crocker & Rose            Expires May 13, 2011                  [Page 3]

Internet-Draft              Algorithm-Signal               November 2010


   The figure below shows how the signally 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 Algorithm Understood (AU) 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 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 the most preferred
   algorithm(s) first as described in section 2.  The end-system
   resolver MUST also set the DNSSEC-OK bit [RFC4035] to indicate that



Crocker & Rose            Expires May 13, 2011                  [Page 4]

Internet-Draft              Algorithm-Signal               November 2010


   it wishes to receive DNSSEC RRs in the response.

   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.

3.1.  Stub Resolvers

   Typically, stub resolvers rely on an upstream recursive server (or
   cache) to provide a response; any algorithm support on the stub
   resolver's side could be overruled by the upstream recursive server.

3.2.  Validating Stub Resolvers

   A validating stub resolver MUST set the DO bit [RFC4035] to indicate
   that it wishes to receive DNSSEC RRs in the response.  Such
   validating resolvers MAY include the AU option in the OPT RR when
   sending a query.  The validating resolver that way indicates which
   cryptographic algorithm(s) in 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 AU EDNS option is NOT RECOMMENDED for non-validating stub
   resolvers.

3.4.  Recursive Resolvers

3.4.1.  Validating Recursive Resolvers

   A validating recursive resolver MUST set the DO bit [RFC4035] to
   indicate that is wishes to receive DNSSEC RRs in the response.  If
   the client the recursive resolver did not include the DO bit in the
   query the recursive resolver MAY include the AU option according to
   its own local policy.

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

   If the client did set the DO bit and the AU option in the query, the
   validating recursive resolver MAY include the AU option based on its
   own local policy if it does validation.  If not, the recursive
   resolver SHOULD copy the value of the AU option in the client query.






Crocker & Rose            Expires May 13, 2011                  [Page 5]

Internet-Draft              Algorithm-Signal               November 2010


3.4.2.  Non-validating Recursive Resolvers

   Recursive resolvers 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.

4.  Intermediate Middlebox Considerations

   Intermediate middleboxes SHOULD behave like a comperable recursive
   resolver when dealing with the AU option.

5.  Server Considerations

   When an authoritative server sees the AU option in the OPT meta-RR in
   a request the normal algorithm for servicing requests is followed.

   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.

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 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.

   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 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.  Note that clients that do not
   implement the AU option may be older implementations which would also
   not implement any newly deployed algorithm.

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 AU option and referencing this document.  The code for the option
   should be TBD.



Crocker & Rose            Expires May 13, 2011                  [Page 6]

Internet-Draft              Algorithm-Signal               November 2010


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.

Authors' Addresses

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

   EMail: steve@shinkuro.com












Crocker & Rose            Expires May 13, 2011                  [Page 7]

Internet-Draft              Algorithm-Signal               November 2010


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

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











































Crocker & Rose            Expires May 13, 2011                  [Page 8]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/