draft-ietf-dnsext-dnssec-opt-in-05.txt

bind-3.2.

DNSEXT                                                         R. Arends
Internet-Draft                                      Telematica Instituut
Expires: August 28, 2003                                      M. Kosters
                                                               D. Blacka
                                                          Verisign, Inc.
                                                       February 27, 2003


                             DNSSEC Opt-In
                   draft-ietf-dnsext-dnssec-opt-in-05

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
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at http://
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 28, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   In RFC 2535, delegations to unsigned subzones are cryptographically
   secured.  Maintaining this cryptography is not practical or
   necessary.  This document describes an "Opt-In" model that allows
   administrators to omit this cryptography and manage the cost of
   adopting DNSSEC with large zones.








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Table of Contents

   1.    Definitions and Terminology  . . . . . . . . . . . . . . . .  3
   2.    Overview . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.    Protocol Additions . . . . . . . . . . . . . . . . . . . . .  5
   3.1   Server Considerations  . . . . . . . . . . . . . . . . . . .  6
   3.1.1 Delegations Only . . . . . . . . . . . . . . . . . . . . . .  6
   3.1.2 Insecure Delegation Responses  . . . . . . . . . . . . . . .  6
   3.1.3 Wildcards and Opt-In . . . . . . . . . . . . . . . . . . . .  6
   3.1.4 Dynamic Update . . . . . . . . . . . . . . . . . . . . . . .  7
   3.2   Client Considerations  . . . . . . . . . . . . . . . . . . .  7
   3.2.1 Delegations Only . . . . . . . . . . . . . . . . . . . . . .  7
   3.2.2 Validation Process Changes . . . . . . . . . . . . . . . . .  7
   3.2.3 NXT Record Caching . . . . . . . . . . . . . . . . . . . . .  8
   3.2.4 Use of the AD bit  . . . . . . . . . . . . . . . . . . . . .  8
   4.    Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.    Example  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   6.    Transition Issues  . . . . . . . . . . . . . . . . . . . . . 13
   7.    Security Considerations  . . . . . . . . . . . . . . . . . . 14
   8.    IANA Considerations  . . . . . . . . . . . . . . . . . . . . 16
   9.    Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . 17
         Normative References . . . . . . . . . . . . . . . . . . . . 18
         Informative References . . . . . . . . . . . . . . . . . . . 19
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 19
   A.    Implementing Opt-In using "Views"  . . . . . . . . . . . . . 21
   B.    Changes from Prior Versions  . . . . . . . . . . . . . . . . 23
         Intellectual Property and Copyright Statements . . . . . . . 25
























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1. Definitions and Terminology

   Throughout this document, familiarity with the DNS system, RFC 1035
   [1], DNS security extensions, RFC 2535 [2], and DNSSEC terminology
   RFC 3090 [8] is assumed.

   The following abbreviations and terms are used in this document:

   RR: is used to refer to a DNS resource record.

   RRset: refers to a Resource Record Set, as defined by [6].  In this
      document, the RRset is also defined to include the covering SIG
      records, if any exist.

   signed name: refers to a DNS name that has, at minimum, a (signed)
      NXT record.

   unsigned name: refers to a DNS name that does not (at least) have a
      NXT record.

   covering NXT record/RRset: is the NXT record used to prove
      (non)existence of a particular name or RRset. This means that for
      a RRset or name 'N', the covering NXT record has the name 'N', or
      has an owner name less than 'N' and "next" name greater than 'N'.

   delegation: refers to a NS RRset with a name different from the
      current zone apex (non-zone-apex), signifying a delegation to a
      subzone.

   secure delegation: refers to a signed name containing a delegation
      (NS RRset), and a signed DS RRset, signifying a delegation to a
      signed subzone.

   2535/DS insecure delegation: refers to a signed name containing a
      delegation (NS RRset), but lacking a DS RRset, signifying a
      delegation to an unsigned subzone.

   Opt-In insecure delegation: refers to an unsigned name containing
      only a delegation NS RRset.  The covering NXT record uses the
      Opt-In methodology described in this document.

   The key words "MUST, "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY, and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [5].







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2. Overview

   The cost to cryptographically secure delegations to unsigned zones is
   high for large delegation-centric zones and zones where insecure
   delegations will be updated rapidly.  For these zones, the costs of
   maintaining the NXT record chain may be extremely high relative to
   the gain of cryptographically authenticating existence of unsecured
   zones.

   This document describes a method of eliminating the superfluous
   cryptography present in secure delegations to insecure zones.  Using
   "Opt-In", a zone administrator can choose to remove insecure
   delegations from the NXT chain.  This is accomplished by extending
   the semantics of the NXT record by using a redundant bit in the type
   map.




































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3. Protocol Additions

   In RFC 2535, delegation NS RRsets are not signed, but are instead
   accompanied by a NXT RRset of the same name, and possibly a
   ("no-key") KEY RR [2] or DS record [3].  The security status of the
   subzone is determined by the presence of the KEY or DS records,
   cryptographically proven by the NXT record.  Opt-In expands this
   definition by allowing insecure delegations to exist within an
   otherwise signed zone without the corresponding NXT record at the
   delegation's owner name.  These insecure delegations are proven
   insecure by using a covering NXT record.

   Since this represents a change of the interpretation of NXT records,
   resolvers must be able to distinguish between RFC 2535 NXT records
   and Opt-In NXT records.  This is accomplished by "tagging" the NXT
   records that cover (or potentially cover) insecure delegation nodes.
   This tag is indicated by the absence of the NXT bit in the type map.
   Since the NXT bit in the type map merely indicates the existence of
   the record itself, this bit is redundant and safe for use as a tag.

   An Opt-In tagged NXT record does not assert the (non)existence of the
   delegations that it covers (except for a delegation with the same
   name).  This allows for the addition or removal of these delegations
   without recalculating or resigning the NXT chain.  However, Opt-In
   tagged NXT records do assert the (non)existence of other RRsets.

   An Opt-In NXT record MAY have the same name as an insecure
   delegation.  In this case, the delegation is proven insecure by the
   lack of a DS bit in type map, or the presence of a "no-key" KEY
   RRset, and the NXT record does assert the existence of the
   delegation.

   Zones using Opt-In MAY contain a mixture of Opt-In tagged NXT records
   and RFC 2535 NXT records.  If a NXT record is not Opt-In, there MUST
   NOT be any insecure delegations (or any other records) between it and
   the RRsets indicated by the 'next domain name' in the NXT RDATA.  If
   it is Opt-In, there MUST only be insecure delegations between it and
   the next node indicated by the 'next domain name' in the NXT RDATA.

   In summary,

   o  An Opt-In NXT type is identified by a zero-valued (or
      not-specified) NXT bit in the type bit map of the NXT record.

   o  A RFC2535 NXT type is identified by a one-valued NXT bit in the
      type bit map of the NXT record.

   and,



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   o  An Opt-In NXT record does not assert the non-existence of a name
      between its owner name and "next" name, although it does assert
      that any name in this span MUST be an insecure delegation.

   o  An Opt-In NXT record does assert the (non)existence of RRsets with
      the same owner name.


3.1 Server Considerations

   Opt-In imposes some new requirements on authoritative DNS servers.

3.1.1 Delegations Only

   This specification dictates that only insecure delegations may exist
   between the owner and "next" names of an Opt-In tagged NXT record.
   Signing tools SHOULD NOT generate signed zones that violate this
   restriction. Servers SHOULD refuse to load and/or serve zones that
   violate this restriction.

3.1.2 Insecure Delegation Responses

   When returning an Opt-In insecure delegation, the server MUST return
   the covering NXT RRset in the Authority section.

   This presents a change from RFC 2535, where the "no-key" KEY RRset
   would be returned instead.  However, in the delegation signer
   proposal, NXT records already must be returned along with the
   insecure delegation.  The primary difference that this proposal
   introduces is that the Opt-In tagged NXT record will have a different
   owner name from the delegation RRset.  This may require
   implementations to do a NXT search on cached responses.

3.1.3 Wildcards and Opt-In

   RFC 2535, in section 5.3, describes the practice of returning NXT
   records to prove the non-existence of an applicable wildcard in
   non-existent name responses.  This NXT record can be described as a
   "negative wildcard proof". The use of Opt-In NXT records changes the
   necessity for this practice. For non-existent name responses when the
   query name (qname) is covered by an Opt-In tagged NXT record, servers
   MAY choose to omit the wildcard proof record, and clients MUST NOT
   treat the absence of this NXT record as a validation error.

   The intent of the RFC 2535 negative wildcard proof requirement is to
   prevent malicious users from undetectably removing valid wildcard
   responses.  In order for this cryptographic proof to work, the
   resolver must be able to prove:



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   1.  The exact qname does not exist.  This is done by the "normal" NXT
       record.

   2.  No applicable wildcard exists.  This is done by returning a NXT
       record proving that the wildcard does not exist (negative
       wildcard proof).

   However, if the NXT record covering the exact qname is an Opt-In NXT
   record, the resolver will not be able to prove the first part of this
   equation, as the qname might exist as an insecure delegation.  Thus,
   since the total proof cannot be completed, the negative wildcard
   proof record is not useful.

   The negative wildcard proof is also not useful when returned as part
   of an Opt-In insecure delegation response for a similar reason: the
   resolver cannot prove that the qname does or does not exist, and
   therefore cannot prove that a wildcard expansion is valid.

   The presence of an Opt-In tagged NXT record does not change the
   practice of returning a NXT along with a wildcard expansion.  Even
   though the Opt-In NXT will not be able to prove that the wildcard
   expansion is valid, it will prove that the wildcard expansion is not
   masking any signed records.

3.1.4 Dynamic Update

   Opt-In changes the semantics of Secure DNS Dynamic Update [7].  In
   particular, it introduces the need for rules that describe when to
   add or remove a delegation name from the NXT chain.  This document
   does not attempt to define these rules.  Until these rules are
   defined, servers MUST NOT process DNS Dynamic Update requests against
   zones that use Opt-In NXT records.

3.2 Client Considerations

   Opt-In imposes some new requirements on DNS resolvers (caching or
   otherwise).

3.2.1 Delegations Only

   As stated in the "Server Considerations" section above, this
   specification restricts the namespace covered by Opt-In tagged NXT
   records to insecure delegations only.  Thus, resolvers MUST reject as
   invalid any records that fall within an Opt-In NXT record's span that
   are not NS records or corresponding glue records.

3.2.2 Validation Process Changes




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   This specification does not change the resolver's resolution
   algorithm.  However, it does change the DNSSEC validation process.
   Resolvers MUST be able to use Opt-In tagged NXT records to
   cryptographically prove the validity and security status (as
   insecure) of a referral.  Resolvers determine the security status of
   the referred-to zone as follows:

   o  In RFC 2535, the security status is proven by existence of a
      verified "no-key" KEY RRset.  The absence of the "no-key" KEY
      RRset indicates that the referred-to zone is secure.

   o  Using Delegation Signer, the security status is proven by the
      existence or absence of a DS RRset at the same name as the
      delegation.  The existence of the DS RRset indicates that the
      referred-to zone is secure. The absence of the DS RRset is proven
      using a verified NXT record of the same name that does not have
      the DS bit set in the type map.  This NXT record MAY also be
      tagged as Opt-In.

   o  Using Opt-In, the security status is proven by the existence of a
      DS record (for secure) or the presence of a verified Opt-In tagged
      NXT record that covers the delegation name.  That is, the NXT
      record does not have the NXT bit set in the type map, and the
      delegation name falls between the NXT's owner and "next" name.

   Using Opt-In does not substantially change the nature of following
   referrals within DNSSEC.  At every delegation point, the resolver
   will have cryptographic proof that the subzone is secure or insecure.

   When receiving either an Opt-In insecure delegation response or a
   non-existent name response where that name is covered by an Opt-In
   tagged NXT record, the resolver MUST NOT require proof (in the form
   of a NXT record) that a wildcard did not exist.

3.2.3 NXT Record Caching

   Caching resolvers MUST be able to retrieve the appropriate covering
   Opt-In NXT record when returning referrals that need them.  This
   requirement differs from Delegation Signer in that the covering NXT
   will not have the same owner name as the delegation.  Some
   implementations may have to use new methods for finding these NXT
   records.

3.2.4 Use of the AD bit

   The AD bit, as defined by [4], MUST NOT be set when:

   o  sending a non-existent name (NXDOMAIN) response where the covering



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      NXT is tagged as Opt-In.

   o  sending an Opt-In insecure delegation response, unless the
      covering (Opt-In) NXT record's owner name equals the delegation
      name.

   This rule is based on what the Opt-In NXT record actually proves.
   For names that exist between the Opt-In NXT record's owner and "next"
   names, the Opt-In NXT record cannot prove the non-existence or
   existence of the name.  As such, not all data in the response has
   been cryptographically verified, so the AD bit cannot be set.