
DNSEXT Working Group                                    Brian Wellington
INTERNET-DRAFT                                        Olafur Gudmundsson
<draft-ietf-dnsext-ad-is-secure-03.txt>                        July 2001

Updates: RFC 2535

                       Redefinition of DNS AD bit


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Comments should be sent to the authors or the DNSEXT WG mailing list
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   This draft expires on January  17, 2002.

   Copyright Notice

   Copyright (C) The Internet Society (2001).  All rights reserved.



Abstract

   Based on implementation experience, the current definition of the AD
   bit in the DNS header is not useful.  This draft changes the
   specification so that the AD bit is only set on answers where
   signatures have been cryptographically verified.




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1 - Introduction

   Familiarity with the DNS system [RFC1035] and DNS security extensions
   [RFC2535] is helpful but not necessary.

   As specified in RFC 2535 (section 6.1), the AD bit indicates in a
   response that all the data included in the answer and authority
   portion of the response has been authenticated by the server
   according to the policies of that server. This is not especially
   useful in practice, since a conformant server should never reply with
   data that failed its security policy.

   This draft proposes to redefine the AD bit such that it is only set
   if all data in the response has been cryptographically verified.
   Thus, a response containing properly delegated insecure data will not
   have AD set, neither will a response from a server configured without
   DNSSEC keys.  As before, data which failed to verify will not be
   returned.  An application can then use the value of the AD bit to
   determine if the data is secure or not.

1.1 - Requirements

   The key words "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in this
   document are to be interpreted as described in RFC2119.


1.2 - Updated documents and sections

   The definition of the AD bit in RFC2535, Section 6.1, is changed.

2 - Setting of AD bit

   Section 6.1 of RFC2535 says:

   "The AD bit MUST NOT be set on a response unless all of the RRs in
   the answer and authority sections of the response are either
   Authenticated or Insecure."

   The changes are to delete the words "either" and "or Insecure" from
   the sentence.

   The replacement text reads:

   "The AD bit MUST NOT be set on a response unless all of the RRsets in
   the answer and authority sections of the response are Authenticated."

   "The AD bit SHOULD be set if and only if all RRs in the answer
   section and any relevant negative response RRs in that authority



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   section are Authenticated."

   AD should be set if and only if all RRs in the answer section, and
   any relevant negative response RRs in the authority section are
   Authenticated.

   The AD bit MUST NOT be set on a response unless all of the RRsets in
   the answer and authority sections are Authenticated.
   A resolver MUST NOT blindly trust the AD bit unless it communicates
   with the server over secure transport mechanism or using message
   authentication such as TSIG[RFC2845] or SIG(0)[RFC2931], and the
   resolver policy is that it can trust the server.

   Any DNS server supporting the OK bit MUST support this definition of
   the AD bit. A DNS server following this modified specification will
   only set the AD bit when it has cryptographically verified the data
   in the answer.  In the case of a primary server for a secure zone,
   the data MAY be considered Authenticated, depending on local policy.
   Secondary servers SHOULD NOT consider data Authenticated unless the
   zone was transfered securely or the data was verified.

3 - Interpretation of the AD bit

   A response containing data marked Insecure in the answer or authority
   section will never have the AD bit set.  In this case, the resolver
   SHOULD treat the data as Insecure whether or not SIG records are
   present.

4 - Security Considerations:

   This document redefines a bit in the DNS header.  If a resolver
   trusts the value of the AD bit, it must be sure that the server is
   using the updated definition, which is any server supporting the OK
   bit.

















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5 - IANA Considerations:

   None

6 - Acknowledgments:

   The following people have provided input on this document: Andreas
   Gustafsson, Bob Halley, Steven Jacob.

References:

[RFC1035]  P. Mockapetris, ``Domain Names - Implementation and
           Specification'', STD 13, RFC 1035, November 1987.

[RFC2535]  D. Eastlake, ``Domain Name System Security Extensions'', RFC
           2535, March 1999.

[RFC2845]  P. Vixie, O. Gudmundsson, D. Eastlake, B. Wellington,
           ``Secret Key Transaction Authentication for DNS (TSIG)'', RFC
           2845, May 2000.

[RFC2931]  D. Eastlake, ``DNS Request and Transaction Signatures
           (SIG(0))'', RFC 2931, September 2000.


Authors Addresses

      Brian Wellington                        Olafur Gudmundsson
      Nominum Inc.
      950 Charter Street                      3826 Legation Street, NW
      Redwood City, CA, 94063                 Washington, DC, 20015
      USA                                     USA
      <Brian.Wellington@nominum.com>          <ogud@ogud.com>


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   developing Internet standards in which case the procedures for
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