DNSEXT Working Group Brian Wellington (Nominum)
INTERNET-DRAFT Olafur Gudmundsson (NAI Labs)
<draft-ietf-dnsext-ad-is-secure-00.txt> November 2000
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 May 17, 2001.
Copyright Notice
Copyright (C) The Internet Society (2000). 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 [RFC1034, 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 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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