Network Working Group M. Kosters
Internet-Draft Network Solutions, Inc.
Expires: December 25, 2001 June 26, 2001
DNSSEC Opt-in for Large Zones
draft-ietf-dnsext-dnssec-opt-in-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on December 25, 2001.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
In order for DNSSEC to be deployed operationally with large zones
and little operational impact, there needs to be included a
mechanism that allows for the separation of secure versus unsecure
views of zones. This needs to be done in a transparent fashion that
allows DNSSEC to be deployed in an incremental manner. This
document proposes a method using views to allow for incremental
growth of delegations that are registered as secure. This is
accomplished by extending the use of the NXT record to deal with
non-secure delegations as well as for non-existence.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Additions . . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
DNS is an unsecure system. The key features that give DNS its power
can also be its chief weaknesses. One feature is the facility to
delegate branches of information from one set of servers to another.
Currently, this is done in a non-cryptographically verified way that
allows spoofing attacks. For example, in July 1997, an alternative
domain registry called AlterNIC exploited this vulnerability to
redirect the www.netsol.com and www.internic.net websites to the
AtlerNIC website. If this delegated information had been
cryptographically verified, this attack would not have been able to
occur.
In recent years, there has been much work within the IETF regarding
DNS security. There are a number of RFCs that integrate public key
technology within DNS to enable cryptographically-verified answers.
To this end, three new resource record types (RR's) have been
defined:
o KEY - one of the public keys of the zone
o SIG - a signature of an accompanying RR set
o NXT - a record that indicates the range of labels to show
negative proof
A zone's authoritative RR's are combined into groups for signing. A
set of RR's will be in the same group if and only if they have the
same name and the same RR type. Each group is then signed with each
of the zone's keys, and each of these signings produces one SIG
record. Each zone KEY RR can be verified hierarchically with a SIG
RR from the direct parent zone. For unsecure delegations, a NULL KEY
RR is inserted in the parent zone to verifiably attest the subdomain
is insecure. Finally, NXT RR's and their accompanying SIG RR's are
issued in the case of a negative reply.
As a zone maintainer, transitioning to a secure zone has a high
overhead in the following areas:
KEY RR
At a delegation point, the zone maintainer needs to place a NULL
KEY and accompanying SIG RR's when the child zone is not known to
be secure.
NXT RR
Each delegation needs to be lexigraphically ordered so that a NXT
RR can be generated and signed with SIG RR's. For large zone
operators, ordering the zone file is a very time-consuming
process. In the resolution process, NXT lookups require that the
server replace efficient hash structures with a lexigraphically
ordered search structure that degrades lookup performance. This
lookup performance is a critical element for a high-query rate
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DNS server.
Thus, the net effect is when one initially secures a zone as defined
in RFC2535[4], the amount of processing is massive because of the
following factors:
1. Zone ordering and maintenance for large zones is difficult and
expensive.
2. Adding NULL KEY RR's, NXT RR's and their accompanying SIG RR's
for unsecure delegations will consume large amounts of memory
(six times the current memory requirements).
3. Having a less efficient lookup algorithm to provide answers to
queries will degrade overall performance.
4. There is very little initial payoff (anticipate only a small
fraction of delegations to be signed. This equates to less than
1% over the first six months).
5. Unsecured delegations are more expensive at the parent than
secure delegations (NULL KEY).
2. Rationale
As DNSSEC is initially deployed, it is anticipated that DNSSEC
adoption will be slow to materialize. It is also anticipated that
DNSSEC security resolution will be top-down. Thus for DNSSEC to be
widely adopted, the root zone and GTLD zones will need to be signed.
Based on the implications previously listed, a large zone maintainer
such as the administrator of COM, needs to create an infrastructure
that is an order of magnitude larger than its current state with
very little initial benefit.
This document proposes an alternative opt-in approach that minimizes
the expense and complexity of DNSSEC adoption by large zones. This
is done by allowing for an alternate view with only secured
delegations.
3. Protocol Additions
The opt-in proposal allows for a zone operator to maintain two views
of its delegations - one being signed and the other not. The
non-DNSSEC view will have all delegations - both secured and
non-secured. The DNSSEC aware view will only have secured
delegations. It is assumed that neither view will have any innate
knowledge of the other's delegations. Thus, the cost of securing a
zone is proportional to the demand of its delegations with the added
benefit of no longer having to maintain NULL KEY RRs for unsecure
delegations.
Since the opt-in model changes the semantics of the NXT RR, the
resolver needs to know if the zone itself follows a RFC2535[4] style
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model or the opt-in model. An opt-in zone is identified by setting
bit 4 of the flags section within the KEY RR for that particular
zone.
To determine which view each DNS query packet is to be queried
against, there is a simple algorithm to be followed:
1. The DNSSEC view MUST be queried when the DO bit is set within
the EDNS0 OPT meta RR as indicated in [6] Additionally,
2. The DNSSEC view MUST be queried when the query type is SIG, KEY,
or NXT.
If the query does not follow either case (1) or (2), the non-DNSSEC
view MUST be consulted by default.
Since the DNSSEC view will have a subset of the actual delegations
of that zone, it will not be able to respond to an unsecured
delegation query. To that end, one of the two following events will
occur:
1) If the RR set exists within the unsecure view, the answer will
show up normally with in the Answer and Additional sections.
Additionally, the NXT RR from the secure view is folded into the
Authority section along with the related KEY RR's and its SIG in the
Additional section. The NXT RR is added to prove the answer does not
exist in the secure view.
2) If the RR set does not exist within the unsecure view, the RCODE
will be set to NXDOMAIN. Additionally, the NXT RR from the secure
view is sent in the Authority section along with the related KEY
RR's and its SIG in the Additional section. Again, the NXT RR is
added to prove the answer does not exist in the secure view.
Example:
Consider a zone with the secure names 3, 6, and 9, and unsecure
names 2, 4, 5, 7, and 8.
Unsecured zone Contents:
@ SOA
2 NS
3 NS
4 NS
5 NS
6 NS
7 NS
8 NS
9 NS
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Secured zone Contents:
@ SOA, SIG SOA, NXT(3), SIG NXT
3 NS, SIG NS, NXT(6), SIG NXT
6 NS, SIG NS, NXT(9), SIG NXT
9 NS, SIG NS, NXT(@), SIG NXT
1. A query for 5 RR type A with EDNS0 DO bit set would return with
the following response:
RCODE=NOERROR
Authority Section:
5 NS
3 NXT(6), SIG NXT
Additional Section:
KEY, SIG KEY
The secure server would see that 5 is lexographically between 3
and 6 and therefore know that 5 is insecure.
2. A query for 55 RR type A with EDNS0 DO bit set would return with
the following response:
RCODE=NXDOMAIN
Authority Section:
SOA, SIG SOA, 3 NXT(6), SIG NXT
Additional Section:
KEY, SIG KEY
The secure server would see that 55 is lexographically between
3 and 6 and therefore know that 55 is definitely does not exist
in the secure realm.
3. A query for 3 RR type KEY without EDNS DO bit set would return
with an response as defined in RFC2535[4].
4. A Query for 3 RR type A, with EDNS0 DO bit set would return with
a response as defined in RFC2535[4].
5. A Query for 6 RR type A, without EDNS0 DO bit set would return
with a response as defined in RFC1035[2].
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4. Security Considerations
This draft is different and separate from RFC2535[4] in that it
allows for secured delegation paths to exist but does not allow for
secure answers to unsecured delegations at the parent level.
Increased exposure will be marginal given that the children are
unsecure.
5. IANA Considerations
The IANA is requested to reserve the use of the fourth bit of the
KEY RR to indicate that the zone is an opt-in zone.
6. Acknowledgements
This document is based on a rough draft by Brian Wellington along
with input from Olafur Gudmundsson, David Blacka, and Mike
Schiraldi.
References
[1] Mockapetris, P.V., "Domain names - concepts and facilities",
RFC 1034, STD 13, Nov 1987.
[2] Mockapetris, P.V., "Domain names - implementation and
specification", RFC 1035, STD 13, Nov 1987.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
[4] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[5] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
August 1999.
[6] Conrad, D. R., "Indicating Resolver Support of DNSSEC (work in
progress)", August 2000.
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Author's Address
Mark Kosters
Network Solutions, Inc.
505 Huntmar Park Drive
Herndon, VA 22070
US
Phone: +1 703 948-3362
EMail: markk@netsol.com
URI: http://www.netsol.com
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Acknowledgement
Funding for the RFC editor function is currently provided by the
Internet Society.
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