DNSEXT Working Group                                    Brian WellingtonINTERNET-DRAFT                                        Olafur Gudmundsson<draft-ietf-dnsext-ad-is-secure-06.txt>                        June 2002Updates: RFC 2535                       Redefinition of DNS AD bitStatus 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   other groups may also distribute working documents as Internet-   Drafts.   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.''   The list of current Internet-Drafts can be accessed at   http://www.ietf.org/ietf/1id-abstracts.txt   The list of Internet-Draft Shadow Directories can be accessed at   http://www.ietf.org/shadow.html   Comments should be sent to the authors or the DNSEXT WG mailing list   namedroppers@ops.ietf.org   This draft expires on December 25, 2002.   Copyright Notice   Copyright (C) The Internet Society (2002).  All rights reserved.Abstract   Based on implementation experience, the RFC2535 definition of the   Authenticated Data (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 or the   server is authoritative for the data and is allowed to set the bit by   policy.Expires December 2002                                           [Page 1]INTERNET-DRAFT        AD bit set on secure answers             June 20021 - 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 (Authenticated Data)   bit indicates in a response that all data included in the answer and   authority sections of the response have 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 redefines the AD bit such that it is only set if all data   in the response has been cryptographically verified or otherwise   meets the server's local security policy.  Thus, a response   containing properly delegated insecure data will not have AD set, nor   will a response from a server configured without DNSSEC keys.  As   before, data which failed to verify will not be returned.  An   application running on a host that has a trust relationship with the   server performing the recursive query can now use the value of the AD   bit to determine if the data is secure or not.1.1 - Motivation   A full DNSSEC capable resolver called directly from an application   can return to the application the security status of the RRsets in   the answer.  However, most applications use a limited stub resolver   that relies on an external full resolver.  The remote resolver can   use the AD bit in a response to indicate the security status of the   data in the answer, and the local resolver can pass this information   to the application.  The application in this context can be either a   human using a DNS tool or a software application.   The AD bit SHOULD be used by the local resolver if and only if it has   been explicitly configured to trust the remote resolver.  The AD bit   SHOULD be ignored when the remote resolver is not trusted.   An alternate solution would be to embed a full DNSSEC resolver into   every application.  This has several disadvantages.   - DNSSEC validation is both CPU and network intensive, and caching   SHOULD be used whenever possible.   - DNSSEC requires non-trivial configuration - the root key must be   configured, as well as keys for any "islands of security" that will   exist until DNSSEC is fully deployed.  The number of configuration   points should be minimized.Expires December 2002                                           [Page 2]INTERNET-DRAFT        AD bit set on secure answers             June 20021.2 - Requirements   The key words "MAY", "MAY NOT" "MUST", "MUST NOT", "SHOULD", "SHOULD   NOT", "RECOMMENDED", in this document are to be interpreted as   described in RFC2119.1.3 - Updated documents and sections   The definition of the AD bit in RFC2535, Section 6.1, is changed.2 - Setting of AD bit   The presence of the CD (Checking Disabled) bit in a query does not   affect the setting of the AD bit in the response.  If the CD bit is   set, the server will not perform checking, but SHOULD still set the   AD bit if the data has already been cryptographically verified or   complies with local policy.  The AD bit MUST only be set if DNSSEC   records have been requested via the OK bit [RFC3225] and relevant SIG   records are returned.2.1 - Setting of AD bit by recursive servers   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 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 the authority   section are Authenticated."   A recursive DNS server following this modified specification will   only set the AD bit when it has cryptographically verified the data   in the answer.2.2 - Setting of AD bit by authoritative servers   A primary server for a secure zone MAY have the policy of treating   authoritative secure zones as Authenticated.  Secondary servers MAY   have the same policy, but SHOULD NOT consider zone data Authenticated   unless the zone was transferred securely and/or the data was   verified.  An authoritative server MUST only set the AD bit for   authoritative answers from a secure zone if it has been explicitly   configured to do so.  The default for this behavior SHOULD be off.Expires December 2002                                           [Page 3]INTERNET-DRAFT        AD bit set on secure answers             June 20022.2.1 - Justification for setting AD bit w/o verifying data   The setting of the AD bit by authoritative servers affects only a   small set of resolvers that are configured to directly query and   trust authoritative servers.  This only affects servers that function   as both recursive and authoritative.  All recursive resolvers SHOULD   ignore the AD bit.   The cost of verifying all signatures on load by an authoritative   server can be high and increases the delay before it can begin   answering queries.  Verifying signatures at query time is also   expensive and could lead to resolvers timing out on many queries   after the server reloads zones.   Organizations that require that all DNS responses contain   cryptographically verified data MUST separate the functions of   authoritative and recursive servers, as authoritative servers are not   required to validate local secure data.3 - Interpretation of the AD bit   A response containing data marked Insecure in the answer or authority   section MUST never have the AD bit set.  In this case, the resolver   SHOULD treat the data as Insecure whether or not SIG records are   present.   A resolver MUST NOT blindly trust the AD bit unless it communicates   with the full function resolver over a secure transport mechanism or   using message authentication such as TSIG [RFC2845] or SIG(0)   [RFC2931] and is explicitly configured to trust this resolver.4 - Applicability statement   The AD bit is intended to allow the transmission of the indication   that a resolver has verified the DNSSEC signatures accompanying the   records in the Answer and Authority section.  The AD bit MUST only be   trusted when the end consumer of the DNS data has confidence that the   intermediary resolver setting the AD bit is trustworthy. This can   only be accomplished via out of band mechanism such as:    - Fiat: An organization can dictate that it is OK to trust certain DNS      servers.    - Personal: Because of a personal relationship or the reputation of a      resolver operator, a DNS consumer can decide to trust that      resolver.    - Knowledge: If a resolver operator posts the configured policy of a      resolver a consumer can decide that resolver is trustworthy.   In the absence of one or more of these factors AD bit from a resolver   SHOULD NOT be trusted.  For example, home users frequently depend onExpires December 2002                                           [Page 4]INTERNET-DRAFT        AD bit set on secure answers             June 2002   their ISP to provide recursive DNS service; it is not advisable to   trust these resolvers.  A roaming/traveling host SHOULD not use DNS   resolvers offered by DHCP when looking up information where security   status matters.   When faced with a situation where there are no satisfactory recursive   resolvers available, running one locally is RECOMMENDED.  This has   the advantage that it can be trusted, and the AD bit can still be   used to allow applications to use stub resolvers.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 responder is   using the updated definition, which is any DNS server/resolver   supporting the OK bit[RFC3225].   Authoritative servers can be explicitly configured to set the AD bit   on answers without doing cryptographic checks. This behavior MUST be   off by default.  The only affected resolvers are those that directly   query and trust the authoritative server, and this functionality   SHOULD only be used on servers that act both as authoritative servers   and recursive resolver.   Resolvers (full or stub) that trust the AD bit on answers from a   configured set of resolvers are DNSSEC security compliant.5 - IANA Considerations:   None.6 - Internationalization Considerations:   None.  This document does not change any textual data in any   protocol.7 - Acknowledgments:   The following people have provided input on this document: Robert   Elz, Andreas Gustafsson, Bob Halley, Steven Jacob, Erik Nordmark,   Edward Lewis, Jakob Schlyter, Roy Arends, Ted Lindgreen.Normative References:[RFC1035]  P. Mockapetris, ``Domain Names - Implementation and           Specification'', STD 13, RFC 1035, November 1987.Expires December 2002                                           [Page 5]INTERNET-DRAFT        AD bit set on secure answers             June 2002[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.[RFC3225]  D. Conrad, ``Indicating Resolver Support of DNSSEC'', RFC           3225, December 2001.Authors Addresses      Brian Wellington                        Olafur Gudmundsson      Nominum Inc.      2385 Bay Road                           3826 Legation Street, NW      Redwood City, CA, 94063                 Washington, DC, 20015      USA                                     USA      <Brian.Wellington@nominum.com>          <ogud@ogud.com>Full Copyright Statement   Copyright (C) The Internet Society (2002>.  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATIONExpires December 2002                                           [Page 6]INTERNET-DRAFT        AD bit set on secure answers             June 2002   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."Expires December 2002                                           [Page 7]