draft-ietf-dnsext-ad-is-secure-06.txt   rfc3655.txt 
DNSEXT Working Group Brian Wellington Network Working Group B. Wellington
INTERNET-DRAFT Olafur Gudmundsson Request for Comments: 3655 O. Gudmundsson
<draft-ietf-dnsext-ad-is-secure-06.txt> June 2002 Updates: 2535 November 2003
Category: Standards Track
Updates: RFC 2535
Redefinition of DNS AD bit Redefinition of DNS Authenticated Data (AD) bit
Status of this Memo Status of this Memo
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This draft expires on December 25, 2002.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2002). All rights reserved. Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract Abstract
Based on implementation experience, the RFC2535 definition of the This document alters the specification defined in RFC 2535. Based on
Authenticated Data (AD) bit in the DNS header is not useful. This implementation experience, the Authenticated Data (AD) bit in the DNS
draft changes the specification so that the AD bit is only set on header is not useful. This document redefines the AD bit such that
answers where signatures have been cryptographically verified or the it is only set if all answers or records proving that no answers
server is authoritative for the data and is allowed to set the bit by exist in the response has been cryptographically verified or
policy. otherwise meets the server's local security 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 (Authenticated Data) 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 bit indicates in a response that all data included in the answer and
authority sections of the response have been authenticated by the authority sections of the response have been authenticated by the
server according to the policies of that server. This is not server according to the policies of that server. This is not
especially useful in practice, since a conformant server SHOULD never especially useful in practice, since a conformant server SHOULD never
reply with data that failed its security policy. reply with data that failed its security policy.
This draft redefines the AD bit such that it is only set if all data This document redefines the AD bit such that it is only set if all
in the response has been cryptographically verified or otherwise data in the response has been cryptographically verified or otherwise
meets the server's local security policy. Thus, a response meets the server's local security policy. Thus, neither a response
containing properly delegated insecure data will not have AD set, nor containing properly delegated insecure data, nor a server configured
will a response from a server configured without DNSSEC keys. As without DNSSEC keys, will have the AD set. As before, data that
before, data which failed to verify will not be returned. An failed to verify will not be returned. An application running on a
application running on a host that has a trust relationship with the host that has a trust relationship with the server performing the
server performing the recursive query can now use the value of the AD recursive query can now use the value of the AD bit to determine
bit to determine if the data is secure or not. whether the data is secure.
1.1 - Motivation 1.1. Motivation
A full DNSSEC capable resolver called directly from an application A full DNSSEC capable resolver called directly from an application
can return to the application the security status of the RRsets in can return to the application the security status of the RRsets in
the answer. However, most applications use a limited stub resolver the answer. However, most applications use a limited stub resolver
that relies on an external full resolver. The remote resolver can that relies on an external recursive name server which incorporates a
use the AD bit in a response to indicate the security status of the full resolver. The recursive nameserver can use the AD bit in a
data in the answer, and the local resolver can pass this information response to indicate the security status of the data in the answer,
to the application. The application in this context can be either a and the local resolver can pass this information to the application.
human using a DNS tool or a software 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 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 been explicitly configured to trust the remote resolver. The AD bit
SHOULD be ignored when the remote resolver is not trusted. SHOULD be ignored when the recursive name server is not trusted.
An alternate solution would be to embed a full DNSSEC resolver into An alternate solution would be to embed a full DNSSEC resolver into
every application. This has several disadvantages. every application, but this has several disadvantages.
- DNSSEC validation is both CPU and network intensive, and caching - DNSSEC validation is both CPU and network intensive, and caching
SHOULD be used whenever possible. SHOULD be used whenever possible.
- DNSSEC requires non-trivial configuration - the root key must be - DNSSEC requires non-trivial configuration - the root key must be
configured, as well as keys for any "islands of security" that will configured, as well as keys for any "islands of security" that
exist until DNSSEC is fully deployed. The number of configuration will exist until DNSSEC is fully deployed. The number of
points should be minimized. configuration points should be minimized.
1.2 - Requirements 1.2. Requirements
The key words "MAY", "MAY NOT" "MUST", "MUST NOT", "SHOULD", "SHOULD The key words "MAY", "MAY NOT" "MUST", "MUST NOT", "SHOULD", "SHOULD
NOT", "RECOMMENDED", in this document are to be interpreted as NOT", "RECOMMENDED", in this document are to be interpreted as
described in RFC2119. described in BCP 14, RFC 2119 [RFC2119].
1.3 - Updated documents and sections 1.3. Updated documents and sections
The definition of the AD bit in RFC2535, Section 6.1, is changed. The definition of the AD bit in RFC 2535, 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 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 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 set, the server will not perform checking, but SHOULD still set the
AD bit if the data has already been cryptographically verified or AD bit if the data has already been cryptographically verified or
complies with local policy. The AD bit MUST only be set if DNSSEC 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 have been requested via the DO bit [RFC3225] and relevant SIG
records are returned. records are returned.
2.1 - Setting of AD bit by recursive servers 2.1. Setting of AD bit by recursive servers
Section 6.1 of RFC2535 says: Section 6.1 of RFC 2535 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 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 the authority section and any relevant negative response RRs in the authority
section are Authenticated." section are Authenticated."
A recursive DNS server following this modified specification will A recursive DNS server following this modified specification will
only set the AD bit when it has cryptographically verified the data only set the AD bit when it has cryptographically verified the data
in the answer. in the answer.
2.2 - Setting of AD bit by authoritative servers 2.2. Setting of AD bit by authoritative servers
A primary server for a secure zone MAY have the policy of treating A primary server for a secure zone MAY have the policy of treating
authoritative secure zones as Authenticated. Secondary servers MAY authoritative secure zones as Authenticated. Secondary servers MAY
have the same policy, but SHOULD NOT consider zone data Authenticated have the same policy, but SHOULD NOT consider zone data Authenticated
unless the zone was transferred securely and/or the data was unless the zone was transferred securely and/or the data was
verified. An authoritative server MUST only set the AD bit for verified. An authoritative server MUST only set the AD bit for
authoritative answers from a secure zone if it has been explicitly authoritative answers from a secure zone if it has been explicitly
configured to do so. The default for this behavior SHOULD be off. configured to do so. The default for this behavior SHOULD be off.
2.2.1 - Justification for setting AD bit w/o verifying data Note that having the AD bit clear on an authoritative answer is
normal and expected behavior.
The setting of the AD bit by authoritative servers affects only a 2.2.1. Justification for setting AD bit w/o verifying data
The setting of the AD bit by authoritative servers affects only the
small set of resolvers that are configured to directly query and small set of resolvers that are configured to directly query and
trust authoritative servers. This only affects servers that function trust authoritative servers. This only affects servers that function
as both recursive and authoritative. All recursive resolvers SHOULD as both recursive and authoritative. Iterative resolvers SHOULD
ignore the AD bit. ignore the AD bit.
The cost of verifying all signatures on load by an authoritative The cost of verifying all signatures on load by an authoritative
server can be high and increases the delay before it can begin server can be high and increases the delay before it can begin
answering queries. Verifying signatures at query time is also answering queries. Verifying signatures at query time is also
expensive and could lead to resolvers timing out on many queries expensive and could lead to resolvers timing out on many queries
after the server reloads zones. after the server reloads zones.
Organizations that require that all DNS responses contain Organizations requiring that all DNS responses contain
cryptographically verified data MUST separate the functions of cryptographically verified data will need to separate the
authoritative and recursive servers, as authoritative servers are not authoritative name server and signature verification functions, since
required to validate local secure data. name servers are not required to validate signatures of data for
which they are authoritative.
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 MUST never have the AD bit set. In this case, the resolver 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 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 A resolver MUST NOT blindly trust the AD bit unless it communicates
with the full function resolver over a secure transport mechanism or with a recursive nameserver over a secure transport mechanism or
using message authentication such as TSIG [RFC2845] or SIG(0) using a message authentication such as TSIG [RFC2845] or SIG(0)
[RFC2931] and is explicitly configured to trust this resolver. [RFC2931] and is explicitly configured to trust this recursive name
server.
4 - Applicability statement 4. Applicability statement
The AD bit is intended to allow the transmission of the indication The AD bit is intended to allow the transmission of the indication
that a resolver has verified the DNSSEC signatures accompanying the that a resolver has verified the DNSSEC signatures accompanying the
records in the Answer and Authority section. The AD bit MUST only be 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 trusted when the end consumer of the DNS data has confidence that the
intermediary resolver setting the AD bit is trustworthy. This can intermediary resolver setting the AD bit is trustworthy. This can
only be accomplished via out of band mechanism such as: only be accomplished via an out of band mechanism such as:
- Fiat: An organization can dictate that it is OK to trust certain DNS - Fiat: An organization that can dictate whether it is OK to trust
servers. 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 - Personal: Because of a personal relationship or the reputation of
SHOULD NOT be trusted. For example, home users frequently depend on a recursive nameserver operator, a DNS consumer can decide to
their ISP to provide recursive DNS service; it is not advisable to trust that recursive nameserver.
trust these resolvers. A roaming/traveling host SHOULD not use DNS
resolvers offered by DHCP when looking up information where security - Knowledge: If a recursive nameserver operator posts the configured
status matters. policy of a recursive nameserver, a consumer can decide that
recursive nameserver is trustworthy.
In the absence of one or more of these factors AD bit from a
recursive name server SHOULD NOT be trusted. For example, home users
frequently depend on their ISP to provide recursive DNS service; it
is not advisable to trust these recursive nameservers. A
roaming/traveling host SHOULD not use recursive DNS servers offered
by DHCP when looking up information where security status matters.
In the latter two cases, the end consumer must also completely trust
the path to the trusted recursive name servers, or a secure transport
must be employed to protect the traffic.
When faced with a situation where there are no satisfactory recursive When faced with a situation where there are no satisfactory recursive
resolvers available, running one locally is RECOMMENDED. This has nameservers available, running one locally is RECOMMENDED. This has
the advantage that it can be trusted, and the AD bit can still be the advantage that it can be trusted, and the AD bit can still be
used to allow applications to use stub resolvers. used to allow applications to use stub resolvers.
4 - Security Considerations: 5. 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 responder is 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 using the updated definition, which is any DNS server/resolver
supporting the OK bit[RFC3225]. supporting the DO bit [RFC3225].
Authoritative servers can be explicitly configured to set the AD bit Authoritative servers can be explicitly configured to set the AD bit
on answers without doing cryptographic checks. This behavior MUST be on answers without doing cryptographic checks. This behavior MUST be
off by default. The only affected resolvers are those that directly off by default. The only affected resolvers are those that directly
query and trust the authoritative server, and this functionality query and trust the authoritative server, and this functionality
SHOULD only be used on servers that act both as authoritative servers SHOULD only be used on servers that act both as authoritative and
and recursive resolver. recursive name servers.
Resolvers (full or stub) that trust the AD bit on answers from a Resolvers (full or stub) that blindly trust the AD bit without
configured set of resolvers are DNSSEC security compliant. knowing the security policy of the server generating the answer can
not be considered security aware.
5 - IANA Considerations: A resolver MUST NOT blindly trust the AD bit unless it communicates
such as IPsec, or using message authentication such as TSIG [RFC2845]
or SIG(0) [RFC2931]. In addition, the resolver must have been
explicitly configured to trust this recursive name server.
6. IANA Considerations
None. None.
6 - Internationalization Considerations: 7. Internationalization Considerations
None. This document does not change any textual data in any None. This document does not change any textual data in any
protocol. protocol.
7 - Acknowledgments: 8. Intellectual Property Rights Notice
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
9. Acknowledgments
The following people have provided input on this document: Robert The following people have provided input on this document: Robert
Elz, Andreas Gustafsson, Bob Halley, Steven Jacob, Erik Nordmark, Elz, Andreas Gustafsson, Bob Halley, Steven Jacob, Erik Nordmark,
Edward Lewis, Jakob Schlyter, Roy Arends, Ted Lindgreen. Edward Lewis, Jakob Schlyter, Roy Arends, Ted Lindgreen.
Normative References: 10. Normative References
[RFC1035] P. Mockapetris, ``Domain Names - Implementation and [RFC1035] Mockapetris, P., "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 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
2535, March 1999. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2845] P. Vixie, O. Gudmundsson, D. Eastlake, B. Wellington, [RFC2535] Eastlake, D., "Domain Name System Security Extensions", RFC
``Secret Key Transaction Authentication for DNS (TSIG)'', RFC 2535, March 1999.
2845, May 2000.
[RFC2931] D. Eastlake, ``DNS Request and Transaction Signatures [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D. and B.
(SIG(0))'', RFC 2931, September 2000. Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, May 2000.
[RFC3225] D. Conrad, ``Indicating Resolver Support of DNSSEC'', RFC [RFC2931] Eastlake, D., "DNS Request and Transaction Signatures
3225, December 2001. (SIG(0))", RFC 2931, September 2000.
Authors Addresses [RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC", RFC
3225, December 2001.
Brian Wellington Olafur Gudmundsson 11. Authors' Addresses
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 Brian Wellington
Nominum Inc.
2385 Bay Road
Redwood City, CA, 94063
USA
Copyright (C) The Internet Society (2002>. All Rights Reserved. EMail: Brian.Wellington@nominum.com
Olafur Gudmundsson
3821 Village Park Drive
Chevy Chase, MD, 20815
USA
EMail: ogud@ogud.com
12. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
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and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
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document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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