





DNSEXT Working Group                       Brian Wellington    (Nominum)
INTERNET-DRAFT                             Olafur Gudmundsson (NAI Labs)
<draft-ietf-dnsext-ad-is-secure-01.txt>                     January 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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   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
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   Comments should be sent to the authors or the DNSEXT WG mailing list
   namedroppers@ops.ietf.org

   This draft expires on July 19, 2001.

   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, as 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."






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   If the answer section contains any data, the server MUST NOT include
   data in the authority section that would cause the AD bit to be
   unset.

   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.

   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.

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.



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[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.                            NAI Labs
      950 Charter Street                      3060 Washington Road (Rt. 97)
      Redwood City, CA, 94063                 Glenwood, MD, 21738
      USA                                     USA
      +1 650 381 6022                         +1 443 259 2389
      <Brian.Wellington@nominum.com>          <ogud@tislabs.com>


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