draft-ietf-dnsext-ad-is-secure-03.txt   draft-ietf-dnsext-ad-is-secure-04.txt 
DNSEXT Working Group Brian Wellington DNSEXT Working Group Brian Wellington
INTERNET-DRAFT Olafur Gudmundsson INTERNET-DRAFT Olafur Gudmundsson
<draft-ietf-dnsext-ad-is-secure-03.txt> July 2001 <draft-ietf-dnsext-ad-is-secure-04.txt> February 2002
Updates: RFC 2535 Updates: RFC 2535
Redefinition of DNS AD bit Redefinition of DNS AD bit
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
skipping to change at page 1, line 35 skipping to change at page 1, line 35
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Comments should be sent to the authors or the DNSEXT WG mailing list Comments should be sent to the authors or the DNSEXT WG mailing list
namedroppers@ops.ietf.org namedroppers@ops.ietf.org
This draft expires on January 17, 2002. This draft expires on July 10, 2002.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2001). All rights reserved. Copyright (C) The Internet Society (2002). All rights reserved.
Abstract Abstract
Based on implementation experience, the current definition of the AD Based on implementation experience, the current definition of the AD
bit in the DNS header is not useful. This draft changes the bit in the DNS header is not useful. This draft changes the
specification so that the AD bit is only set on answers where specification so that the AD bit is only set on answers where
signatures have been cryptographically verified. signatures have been cryptographically verified or the server is
authoritative for the data and is allowed to set the bit by policy.
1 - Introduction 1 - Introduction
Familiarity with the DNS system [RFC1035] and DNS security extensions Familiarity with the DNS system [RFC1035] and DNS security extensions
[RFC2535] is helpful but not necessary. [RFC2535] is helpful but not necessary.
As specified in RFC 2535 (section 6.1), the AD bit indicates in a 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 response that all data included in the answer and authority sections
portion of the response has been authenticated by the server of the response have been authenticated by the server according to
according to the policies of that server. This is not especially the policies of that server. This is not especially to the policies
useful in practice, since a conformant server should never reply with of that server. This is not especially useful in practice, since a
data that failed its security policy. 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 This draft proposes to redefine the AD bit such that it is only set
if all data in the response has been cryptographically verified. if all data in the response has been cryptographically verified or
Thus, a response containing properly delegated insecure data will not otherwise meets the server's local security policy. Thus, a response
have AD set, neither will a response from a server configured without containing properly delegated insecure data will not have AD set, nor
DNSSEC keys. As before, data which failed to verify will not be will a response from a server configured without DNSSEC keys. As
returned. An application can then use the value of the AD bit to before, data which failed to verify will not be returned. An
determine if the data is secure or not. application running on a host that has 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 - Requirements 1.1 - Requirements
The key words "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in this The key words "MAY", "MAY NOT" "MUST", "MUST NOT", "SHOULD", "SHOULD
document are to be interpreted as described in RFC2119. NOT", in this document are to be interpreted as described in RFC2119.
1.2 - Updated documents and sections 1.2 - Updated documents and sections
The definition of the AD bit in RFC2535, Section 6.1, is changed. The definition of the AD bit in RFC2535, Section 6.1, is changed.
2 - Setting of AD bit 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 checked or complies with local
policy. The AD bit MUST only be set if DNSSEC records have been
requested [RFC3225] and relevant SIG records are returned.
2.1 - Setting of AD bit by recursive servers
Section 6.1 of RFC2535 says: Section 6.1 of RFC2535 says:
"The AD bit MUST NOT be set on a response unless all of the RRs in "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 the answer and authority sections of the response are either
Authenticated or Insecure." Authenticated or Insecure."
The changes are to delete the words "either" and "or Insecure" from
the sentence.
The replacement text reads: The replacement text reads:
"The AD bit MUST NOT be set on a response unless all of the RRsets in "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 answer and authority sections of the response are Authenticated."
"The AD bit SHOULD be set if and only if all RRs in the answer "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 and any relevant negative response RRs in the authority
section are Authenticated." section are Authenticated."
AD should be set if and only if all RRs in the answer section, and A recursive DNS server following this modified specification will
any relevant negative response RRs in the authority section are only set the AD bit when it has cryptographically verified the data
Authenticated. in the answer.
The AD bit MUST NOT be set on a response unless all of the RRsets in 2.2 - Setting of AD bit by authorative servers
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 A primary server for a secure zone the data MAY have a policy of
the AD bit. A DNS server following this modified specification will treating authoritative secure zones as Authenticated. Secondary
only set the AD bit when it has cryptographically verified the data servers MAY have the same policy, but SHOULD NOT consider zone data
in the answer. In the case of a primary server for a secure zone, Authenticated unless the zone was transfered securely and/or the data
the data MAY be considered Authenticated, depending on local policy. was verified. An authoritative server MUST only set the AD bit for
Secondary servers SHOULD NOT consider data Authenticated unless the authoritative answers from a secure zone if it has been explicitly
zone was transfered securely or the data was verified. configured to do so. The default for this behavior SHOULD be off.
2.2.1 - 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 authorative. 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 answer 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 3 - Interpretation of the AD bit
A response containing data marked Insecure in the answer or authority A response containing data marked Insecure in the answer or authority
section will never have the AD bit set. In this case, the resolver 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 SHOULD treat the data as Insecure whether or not SIG records are
present. present.
A resolver MUST NOT blindly trust the AD bit unless it communicates
with the server over a secure transport mechanism or using message
authentication such as TSIG [RFC2845] or SIG(0) [RFC2931] and is
configured to trust the server.
4 - Security Considerations: 4 - Security Considerations:
This document redefines a bit in the DNS header. If a resolver 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 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 using the updated definition, which is any server supporting the OK
bit. bit.
Authoritative servers that set the AD bit on answers without doing
cryptographic checks must only do so if explicitly configured to.
This only affects resolvers 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.
Authorative servers that set the AD bit on answers without doing
cryptographic checks must only do so on explicit zone by zone
enablement. This only affects resolvers that trust the server and
this functionality should only be used on servers that act both as
authorative servers and recursive resolver.
Resolvers (full or stub) that blindly trust the AD bit without
knowing the security policy of the server generating the answer can
not be considered security aware.
5 - IANA Considerations: 5 - IANA Considerations:
None None
6 - Acknowledgments: 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: Andreas The following people have provided input on this document: Andreas
Gustafsson, Bob Halley, Steven Jacob. Gustafsson, Bob Halley, Steven Jacob, Edward Lewis, Jakob Schlyter,
Roy Arends, Ted Lindgreen.
References: References:
[RFC1035] P. Mockapetris, ``Domain Names - Implementation and [RFC1035] P. Mockapetris, ``Domain Names - Implementation and
Specification'', STD 13, RFC 1035, November 1987. Specification'', STD 13, RFC 1035, November 1987.
[RFC2535] D. Eastlake, ``Domain Name System Security Extensions'', RFC [RFC2535] D. Eastlake, ``Domain Name System Security Extensions'', RFC
2535, March 1999. 2535, March 1999.
[RFC2845] P. Vixie, O. Gudmundsson, D. Eastlake, B. Wellington, [RFC2845] P. Vixie, O. Gudmundsson, D. Eastlake, B. Wellington,
``Secret Key Transaction Authentication for DNS (TSIG)'', RFC ``Secret Key Transaction Authentication for DNS (TSIG)'', RFC
2845, May 2000. 2845, May 2000.
[RFC2931] D. Eastlake, ``DNS Request and Transaction Signatures [RFC2931] D. Eastlake, ``DNS Request and Transaction Signatures
(SIG(0))'', RFC 2931, September 2000. (SIG(0))'', RFC 2931, September 2000.
[RFC3225] D. Conrad, ``Indicating Resolver Support of DNSSEC'', RFC
3225, December 2001.
Authors Addresses Authors Addresses
Brian Wellington Olafur Gudmundsson Brian Wellington Olafur Gudmundsson
Nominum Inc. Nominum Inc.
950 Charter Street 3826 Legation Street, NW 2385 Bay Street 3826 Legation Street, NW
Redwood City, CA, 94063 Washington, DC, 20015 Redwood City, CA, 94063 Washington, DC, 20015
USA USA USA USA
<Brian.Wellington@nominum.com> <ogud@ogud.com> <Brian.Wellington@nominum.com> <ogud@ogud.com>
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
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