DNSEXT Working Group Brian Wellington INTERNET-DRAFT Olafur Gudmundsson
<draft-ietf-dnsext-ad-is-secure-02.txt> June<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 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 email@example.com This draft expires on December 18, 2001.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. 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, asneither 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 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.definition, which is any server supporting the OK bit. 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> <firstname.lastname@example.org> Full Copyright Statement Copyright (C) The Internet Society (2001). 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. 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