draft-ietf-dnsext-dnssec-bis-updates-10.txt   draft-ietf-dnsext-dnssec-bis-updates-11.txt 
Network Working Group S. Weiler Network Working Group S. Weiler
Internet-Draft SPARTA, Inc. Internet-Draft SPARTA, Inc.
Updates: 4033, 4034, 4035, 5155 D. Blacka Updates: 4033, 4034, 4035, 5155 D. Blacka
(if approved) VeriSign, Inc. (if approved) VeriSign, Inc.
Intended status: Standards Track March 8, 2010 Intended status: Standards Track March 27, 2010
Expires: September 9, 2010 Expires: September 28, 2010
Clarifications and Implementation Notes for DNSSECbis Clarifications and Implementation Notes for DNSSECbis
draft-ietf-dnsext-dnssec-bis-updates-10 draft-ietf-dnsext-dnssec-bis-updates-11
Abstract Abstract
This document is a collection of technical clarifications to the This document is a collection of technical clarifications to the
DNSSECbis document set. It is meant to serve as a resource to DNSSECbis document set. It is meant to serve as a resource to
implementors as well as a repository of DNSSECbis errata. implementors as well as a repository of DNSSECbis errata.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 9, 2010. This Internet-Draft will expire on September 28, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the BSD License. described in the BSD License.
Table of Contents Table of Contents
1. Introduction and Terminology . . . . . . . . . . . . . . . . . 3 1. Introduction and Terminology . . . . . . . . . . . . . . . . . 3
1.1. Structure of this Document . . . . . . . . . . . . . . . . 3 1.1. Structure of this Document . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Important Additions to DNSSSECbis . . . . . . . . . . . . . . 3 2. Important Additions to DNSSSECbis . . . . . . . . . . . . . . 3
2.1. NSEC3 Support . . . . . . . . . . . . . . . . . . . . . . 3 2.1. NSEC3 Support . . . . . . . . . . . . . . . . . . . . . . 3
2.2. SHA-256 Support . . . . . . . . . . . . . . . . . . . . . 4 2.2. SHA-2 Support . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Concerns . . . . . . . . . . . . . . . . . . . . . . 4 3. Scaling Concerns . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Clarifications on Non-Existence Proofs . . . . . . . . . . 4 3.1. Implement a BAD cache . . . . . . . . . . . . . . . . . . 4
3.2. Validating Responses to an ANY Query . . . . . . . . . . . 5 4. Security Concerns . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Check for CNAME . . . . . . . . . . . . . . . . . . . . . 5 4.1. Clarifications on Non-Existence Proofs . . . . . . . . . . 4
3.4. Insecure Delegation Proofs . . . . . . . . . . . . . . . . 5 4.2. Validating Responses to an ANY Query . . . . . . . . . . . 5
4. Interoperability Concerns . . . . . . . . . . . . . . . . . . 5 4.3. Check for CNAME . . . . . . . . . . . . . . . . . . . . . 5
4.1. Errors in Canonical Form Type Code List . . . . . . . . . 5 4.4. Insecure Delegation Proofs . . . . . . . . . . . . . . . . 5
4.2. Unknown DS Message Digest Algorithms . . . . . . . . . . . 6 5. Interoperability Concerns . . . . . . . . . . . . . . . . . . 6
4.3. Private Algorithms . . . . . . . . . . . . . . . . . . . . 6 5.1. Errors in Canonical Form Type Code List . . . . . . . . . 6
4.4. Caution About Local Policy and Multiple RRSIGs . . . . . . 7 5.2. Unknown DS Message Digest Algorithms . . . . . . . . . . . 6
4.5. Key Tag Calculation . . . . . . . . . . . . . . . . . . . 7 5.3. Private Algorithms . . . . . . . . . . . . . . . . . . . . 7
4.6. Setting the DO Bit on Replies . . . . . . . . . . . . . . 7 5.4. Caution About Local Policy and Multiple RRSIGs . . . . . . 7
4.7. Setting the AD Bit on Queries . . . . . . . . . . . . . . 8 5.5. Key Tag Calculation . . . . . . . . . . . . . . . . . . . 8
4.8. Setting the AD Bit on Replies . . . . . . . . . . . . . . 8 5.6. Setting the DO Bit on Replies . . . . . . . . . . . . . . 8
4.9. Setting the CD bit on Requests . . . . . . . . . . . . . . 8 5.7. Setting the AD Bit on Queries . . . . . . . . . . . . . . 8
4.10. Nested Trust Anchors . . . . . . . . . . . . . . . . . . . 8 5.8. Setting the AD Bit on Replies . . . . . . . . . . . . . . 8
4.10.1. Closest Encloser . . . . . . . . . . . . . . . . . . 9 5.9. Handling Queries With the CD Bit Set . . . . . . . . . . . 8
4.10.2. Accept Any Success . . . . . . . . . . . . . . . . . 9 5.10. Nested Trust Anchors . . . . . . . . . . . . . . . . . . . 9
4.10.3. Preference Based on Source . . . . . . . . . . . . . 10 5.10.1. Closest Encloser . . . . . . . . . . . . . . . . . . 9
5. Minor Corrections and Clarifications . . . . . . . . . . . . . 10 5.10.2. Accept Any Success . . . . . . . . . . . . . . . . . 10
5.1. Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . 10 5.10.3. Preference Based on Source . . . . . . . . . . . . . 10
5.2. Clarifications on DNSKEY Usage . . . . . . . . . . . . . . 10 6. Minor Corrections and Clarifications . . . . . . . . . . . . . 10
5.3. Errors in Examples . . . . . . . . . . . . . . . . . . . . 11 6.1. Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . 11
5.4. Errors in RFC 5155 . . . . . . . . . . . . . . . . . . . . 11 6.2. Clarifications on DNSKEY Usage . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6.3. Errors in Examples . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6.4. Errors in RFC 5155 . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 13 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction and Terminology 1. Introduction and Terminology
This document lists some additions, clarifications and corrections to This document lists some additions, clarifications and corrections to
the core DNSSECbis specification, as originally described in the core DNSSECbis specification, as originally described in
[RFC4033], [RFC4034], and [RFC4035], and later amended by [RFC5155]. [RFC4033], [RFC4034], and [RFC4035], and later amended by [RFC5155].
(See section Section 2 for more recent additions to that core (See section Section 2 for more recent additions to that core
document set.) document set.)
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records for hashed denial of existence. Validator implementations records for hashed denial of existence. Validator implementations
are strongly encouraged to include support for NSEC3 because a number are strongly encouraged to include support for NSEC3 because a number
of highly visible zones are expected to use it. Validators that do of highly visible zones are expected to use it. Validators that do
not support validation of responses using NSEC3 will likely be not support validation of responses using NSEC3 will likely be
hampered in validating large portions of the DNS space. hampered in validating large portions of the DNS space.
[RFC5155] should be considered part of the DNS Security Document [RFC5155] should be considered part of the DNS Security Document
Family as described by [RFC4033], Section 10. Family as described by [RFC4033], Section 10.
Note that the algorithm identifiers defined in RFC5155 (DSA-NSEC3- Note that the algorithm identifiers defined in RFC5155 (DSA-NSEC3-
SHA1 and RSASHA1-NSEC3-SHA1) signal that a zone MAY be using NSEC3, SHA1 and RSASHA1-NSEC3-SHA1) and RFC5702 (RSASHA256 and RSASHA512)
rather than NSEC. The zone MAY indeed be using either and validators signal that a zone MAY be using NSEC3, rather than NSEC. The zone
supporting these algorithms MUST support both NSEC3 and NSEC MAY indeed be using either and validators supporting these algorithms
responses. MUST support both NSEC3 and NSEC responses.
2.2. SHA-256 Support 2.2. SHA-2 Support
[RFC4509] describes the use of SHA-256 as a digest algorithm in [RFC4509] describes the use of SHA-256 as a digest algorithm in
Delegation Signer (DS) RRs. [RFC5702] describes the use of the Delegation Signer (DS) RRs. [RFC5702] describes the use of the
RSASHA256 algorithm in DNSKEY and RRSIG RRs. Validator RSASHA256 and RSASHA512 algorithms in DNSKEY and RRSIG RRs.
implementations are strongly encouraged to include support for this Validator implementations are strongly encouraged to include support
algorithm for DS, DNSKEY, and RRSIG records. for these algorithms for DS, DNSKEY, and RRSIG records.
Both [RFC4509] and [RFC5702] should also be considered part of the Both [RFC4509] and [RFC5702] should also be considered part of the
DNS Security Document Family as described by [RFC4033], Section 10. DNS Security Document Family as described by [RFC4033], Section 10.
3. Security Concerns 3. Scaling Concerns
This is a placeholder section. New text is forthcoming with general
themes of "please play well with others", "don't flood authoritative
servers with queries" and "don't try TOO hard to recover from
validation failures".
3.1. Implement a BAD cache
Section 4.7 of RFC4035 permits security-aware resolvers to implement
a BAD cache. Because of the concerns outlined above, that guidance
has changed: security-aware resolvers SHOULD implement a BAD cache,
as described in RFC4035.
4. Security Concerns
This section provides clarifications that, if overlooked, could lead This section provides clarifications that, if overlooked, could lead
to security issues. to security issues.
3.1. Clarifications on Non-Existence Proofs 4.1. Clarifications on Non-Existence Proofs
[RFC4035] Section 5.4 under-specifies the algorithm for checking non- [RFC4035] Section 5.4 under-specifies the algorithm for checking non-
existence proofs. In particular, the algorithm as presented would existence proofs. In particular, the algorithm as presented would
incorrectly allow an NSEC or NSEC3 RR from an ancestor zone to prove incorrectly allow an NSEC or NSEC3 RR from an ancestor zone to prove
the non-existence of RRs in the child zone. the non-existence of RRs in the child zone.
An "ancestor delegation" NSEC RR (or NSEC3 RR) is one with: An "ancestor delegation" NSEC RR (or NSEC3 RR) is one with:
o the NS bit set, o the NS bit set,
o the SOA bit clear, and o the SOA bit clear, and
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that (original) owner name other than DS RRs, and all RRs below that that (original) owner name other than DS RRs, and all RRs below that
owner name regardless of type. owner name regardless of type.
Similarly, the algorithm would also allow an NSEC RR at the same Similarly, the algorithm would also allow an NSEC RR at the same
owner name as a DNAME RR, or an NSEC3 RR at the same original owner owner name as a DNAME RR, or an NSEC3 RR at the same original owner
name as a DNAME, to prove the non-existence of names beneath that name as a DNAME, to prove the non-existence of names beneath that
DNAME. An NSEC or NSEC3 RR with the DNAME bit set MUST NOT be used DNAME. An NSEC or NSEC3 RR with the DNAME bit set MUST NOT be used
to assume the non-existence of any subdomain of that NSEC/NSEC3 RR's to assume the non-existence of any subdomain of that NSEC/NSEC3 RR's
(original) owner name. (original) owner name.
3.2. Validating Responses to an ANY Query 4.2. Validating Responses to an ANY Query
[RFC4035] does not address how to validate responses when QTYPE=*. [RFC4035] does not address how to validate responses when QTYPE=*.
As described in Section 6.2.2 of [RFC1034], a proper response to As described in Section 6.2.2 of [RFC1034], a proper response to
QTYPE=* may include a subset of the RRsets at a given name. That is, QTYPE=* may include a subset of the RRsets at a given name. That is,
it is not necessary to include all RRsets at the QNAME in the it is not necessary to include all RRsets at the QNAME in the
response. response.
When validating a response to QTYPE=*, all received RRsets that match When validating a response to QTYPE=*, all received RRsets that match
QNAME and QCLASS MUST be validated. If any of those RRsets fail QNAME and QCLASS MUST be validated. If any of those RRsets fail
validation, the answer is considered Bogus. If there are no RRsets validation, the answer is considered Bogus. If there are no RRsets
matching QNAME and QCLASS, that fact MUST be validated according to matching QNAME and QCLASS, that fact MUST be validated according to
the rules in [RFC4035] Section 5.4 (as clarified in this document). the rules in [RFC4035] Section 5.4 (as clarified in this document).
To be clear, a validator must not expect to receive all records at To be clear, a validator must not expect to receive all records at
the QNAME in response to QTYPE=*. the QNAME in response to QTYPE=*.
3.3. Check for CNAME 4.3. Check for CNAME
Section 5 of [RFC4035] says little about validating responses based Section 5 of [RFC4035] says little about validating responses based
on (or that should be based on) CNAMEs. When validating a NOERROR/ on (or that should be based on) CNAMEs. When validating a NOERROR/
NODATA response, validators MUST check the CNAME bit in the matching NODATA response, validators MUST check the CNAME bit in the matching
NSEC or NSEC3 RR's type bitmap in addition to the bit for the query NSEC or NSEC3 RR's type bitmap in addition to the bit for the query
type. Without this check, an attacker could successfully transform a type. Without this check, an attacker could successfully transform a
positive CNAME response into a NOERROR/NODATA response. positive CNAME response into a NOERROR/NODATA response.
3.4. Insecure Delegation Proofs 4.4. Insecure Delegation Proofs
[RFC4035] Section 5.2 specifies that a validator, when proving a [RFC4035] Section 5.2 specifies that a validator, when proving a
delegation is not secure, needs to check for the absence of the DS delegation is not secure, needs to check for the absence of the DS
and SOA bits in the NSEC (or NSEC3) type bitmap. The validator also and SOA bits in the NSEC (or NSEC3) type bitmap. The validator also
needs to check for the presence of the NS bit in the matching NSEC needs to check for the presence of the NS bit in the matching NSEC
(or NSEC3) RR (proving that there is, indeed, a delegation), or (or NSEC3) RR (proving that there is, indeed, a delegation), or
alternately make sure that the delegation is covered by an NSEC3 RR alternately make sure that the delegation is covered by an NSEC3 RR
with the Opt-Out flag set. If this is not checked, spoofed unsigned with the Opt-Out flag set. If this is not checked, spoofed unsigned
delegations might be used to claim that an existing signed record is delegations might be used to claim that an existing signed record is
not signed. not signed.
4. Interoperability Concerns 5. Interoperability Concerns
4.1. Errors in Canonical Form Type Code List 5.1. Errors in Canonical Form Type Code List
When canonicalizing DNS names, DNS names in the RDATA section of NSEC When canonicalizing DNS names, DNS names in the RDATA section of NSEC
and RRSIG resource records are not downcased. and RRSIG resource records are not downcased.
[RFC4034] Section 6.2 item 3 has a list of resource record types for [RFC4034] Section 6.2 item 3 has a list of resource record types for
which DNS names in the RDATA are downcased for purposes of DNSSEC which DNS names in the RDATA are downcased for purposes of DNSSEC
canonical form (for both ordering and signing). That list canonical form (for both ordering and signing). That list
erroneously contains NSEC and RRSIG. According to [RFC3755], DNS erroneously contains NSEC and RRSIG. According to [RFC3755], DNS
names in the RDATA of NSEC and RRSIG should not be downcased. names in the RDATA of NSEC and RRSIG should not be downcased.
The same section also erroneously lists HINFO, and twice at that. The same section also erroneously lists HINFO, and twice at that.
Since HINFO records contain no domain names, they are not subject to Since HINFO records contain no domain names, they are not subject to
downcasing. downcasing.
4.2. Unknown DS Message Digest Algorithms 5.2. Unknown DS Message Digest Algorithms
Section 5.2 of [RFC4035] includes rules for how to handle delegations Section 5.2 of [RFC4035] includes rules for how to handle delegations
to zones that are signed with entirely unsupported public key to zones that are signed with entirely unsupported public key
algorithms, as indicated by the key algorithms shown in those zone's algorithms, as indicated by the key algorithms shown in those zone's
DS RRsets. It does not explicitly address how to handle DS records DS RRsets. It does not explicitly address how to handle DS records
that use unsupported message digest algorithms. In brief, DS records that use unsupported message digest algorithms. In brief, DS records
using unknown or unsupported message digest algorithms MUST be using unknown or unsupported message digest algorithms MUST be
treated the same way as DS records referring to DNSKEY RRs of unknown treated the same way as DS records referring to DNSKEY RRs of unknown
or unsupported public key algorithms. or unsupported public key algorithms.
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To paraphrase the above, when determining the security status of a To paraphrase the above, when determining the security status of a
zone, a validator disregards any DS records listing unknown or zone, a validator disregards any DS records listing unknown or
unsupported algorithms. If none are left, the zone is treated as if unsupported algorithms. If none are left, the zone is treated as if
it were unsigned. it were unsigned.
Modified to consider DS message digest algorithms, a validator also Modified to consider DS message digest algorithms, a validator also
disregards any DS records using unknown or unsupported message digest disregards any DS records using unknown or unsupported message digest
algorithms. algorithms.
4.3. Private Algorithms 5.3. Private Algorithms
As discussed above, section 5.2 of [RFC4035] requires that validators As discussed above, section 5.2 of [RFC4035] requires that validators
make decisions about the security status of zones based on the public make decisions about the security status of zones based on the public
key algorithms shown in the DS records for those zones. In the case key algorithms shown in the DS records for those zones. In the case
of private algorithms, as described in [RFC4034] Appendix A.1.1, the of private algorithms, as described in [RFC4034] Appendix A.1.1, the
eight-bit algorithm field in the DS RR is not conclusive about what eight-bit algorithm field in the DS RR is not conclusive about what
algorithm(s) is actually in use. algorithm(s) is actually in use.
If no private algorithms appear in the DS set or if any supported If no private algorithms appear in the DS set or if any supported
algorithm appears in the DS set, no special processing will be algorithm appears in the DS set, no special processing will be
needed. In the remaining cases, the security status of the zone needed. In the remaining cases, the security status of the zone
depends on whether or not the resolver supports any of the private depends on whether or not the resolver supports any of the private
algorithms in use (provided that these DS records use supported hash algorithms in use (provided that these DS records use supported hash
functions, as discussed in Section 4.2). In these cases, the functions, as discussed in Section 5.2). In these cases, the
resolver MUST retrieve the corresponding DNSKEY for each private resolver MUST retrieve the corresponding DNSKEY for each private
algorithm DS record and examine the public key field to determine the algorithm DS record and examine the public key field to determine the
algorithm in use. The security-aware resolver MUST ensure that the algorithm in use. The security-aware resolver MUST ensure that the
hash of the DNSKEY RR's owner name and RDATA matches the digest in hash of the DNSKEY RR's owner name and RDATA matches the digest in
the DS RR. If they do not match, and no other DS establishes that the DS RR. If they do not match, and no other DS establishes that
the zone is secure, the referral should be considered Bogus data, as the zone is secure, the referral should be considered Bogus data, as
discussed in [RFC4035]. discussed in [RFC4035].
This clarification facilitates the broader use of private algorithms, This clarification facilitates the broader use of private algorithms,
as suggested by [RFC4955]. as suggested by [RFC4955].
4.4. Caution About Local Policy and Multiple RRSIGs 5.4. Caution About Local Policy and Multiple RRSIGs
When multiple RRSIGs cover a given RRset, [RFC4035] Section 5.3.3 When multiple RRSIGs cover a given RRset, [RFC4035] Section 5.3.3
suggests that "the local resolver security policy determines whether suggests that "the local resolver security policy determines whether
the resolver also has to test these RRSIG RRs and how to resolve the resolver also has to test these RRSIG RRs and how to resolve
conflicts if these RRSIG RRs lead to differing results." In most conflicts if these RRSIG RRs lead to differing results." In most
cases, a resolver would be well advised to accept any valid RRSIG as cases, a resolver would be well advised to accept any valid RRSIG as
sufficient. If the first RRSIG tested fails validation, a resolver sufficient. If the first RRSIG tested fails validation, a resolver
would be well advised to try others, giving a successful validation would be well advised to try others, giving a successful validation
result if any can be validated and giving a failure only if all result if any can be validated and giving a failure only if all
RRSIGs fail validation. RRSIGs fail validation.
If a resolver adopts a more restrictive policy, there's a danger that If a resolver adopts a more restrictive policy, there's a danger that
properly-signed data might unnecessarily fail validation, perhaps properly-signed data might unnecessarily fail validation, perhaps
because of cache timing issues. Furthermore, certain zone management because of cache timing issues. Furthermore, certain zone management
techniques, like the Double Signature Zone-signing Key Rollover techniques, like the Double Signature Zone-signing Key Rollover
method described in section 4.2.1.2 of [RFC4641] might not work method described in section 4.2.1.2 of [RFC4641] might not work
reliably. reliably.
4.5. Key Tag Calculation 5.5. Key Tag Calculation
[RFC4034] Appendix B.1 incorrectly defines the Key Tag field [RFC4034] Appendix B.1 incorrectly defines the Key Tag field
calculation for algorithm 1. It correctly says that the Key Tag is calculation for algorithm 1. It correctly says that the Key Tag is
the most significant 16 of the least significant 24 bits of the the most significant 16 of the least significant 24 bits of the
public key modulus. However, [RFC4034] then goes on to incorrectly public key modulus. However, [RFC4034] then goes on to incorrectly
say that this is 4th to last and 3rd to last octets of the public key say that this is 4th to last and 3rd to last octets of the public key
modulus. It is, in fact, the 3rd to last and 2nd to last octets. modulus. It is, in fact, the 3rd to last and 2nd to last octets.
4.6. Setting the DO Bit on Replies 5.6. Setting the DO Bit on Replies
As stated in [RFC3225], the DO bit of the query MUST be copied in the As stated in [RFC3225], the DO bit of the query MUST be copied in the
response. At least one implementation has done something different, response. At least one implementation has done something different,
so it may be wise for resolvers to be liberal in what they accept. so it may be wise for resolvers to be liberal in what they accept.
4.7. Setting the AD Bit on Queries 5.7. Setting the AD Bit on Queries
The use of the AD bit in the query was previously undefined. This The use of the AD bit in the query was previously undefined. This
document defines it as a signal indicating that the requester document defines it as a signal indicating that the requester
understands and is interested in the value of the AD bit in the understands and is interested in the value of the AD bit in the
response. This allows a requestor to indicate that it understands response. This allows a requestor to indicate that it understands
the AD bit without also requesting DNSSEC data via the DO bit. the AD bit without also requesting DNSSEC data via the DO bit.
4.8. Setting the AD Bit on Replies 5.8. Setting the AD Bit on Replies
Section 3.2.3 of [RFC4035] describes under which conditions a Section 3.2.3 of [RFC4035] describes under which conditions a
validating resolver should set or clear the AD bit in a response. In validating resolver should set or clear the AD bit in a response. In
order to protect legacy stub resolvers and middleboxes, validating order to protect legacy stub resolvers and middleboxes, validating
resolvers SHOULD only set the AD bit when a response both meets the resolvers SHOULD only set the AD bit when a response both meets the
conditions listed in RFC 4035, section 3.2.3, and the request conditions listed in RFC 4035, section 3.2.3, and the request
contained either a set DO bit or a set AD bit. contained either a set DO bit or a set AD bit.
4.9. Setting the CD bit on Requests 5.9. Handling Queries With the CD Bit Set
When processing a request with the CD bit set, a resolver SHOULD When processing a request with the CD bit set, a resolver SHOULD
attempt to return all responsive data, even data that has failed attempt to return all responsive data, even data that has failed
DNSSEC validation. RFC4035 section 3.2.2 requires a resolver DNSSEC validation. RFC4035 section 3.2.2 requires a resolver
processing a request with the CD bit set to set the CD bit on its processing a request with the CD bit set to set the CD bit on its
upstream queries. upstream queries.
The guidance in RFC4035 is ambiguous about what to do when a cached The guidance in RFC4035 is ambiguous about what to do when a cached
response was obtained with the CD bit not set. In the typical case, response was obtained with the CD bit not set. In the typical case,
no new query is required, nor does the cache need to track the state no new query is required, nor does the cache need to track the state
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the cached response is a server failure (RCODE 2), which may indicate the cached response is a server failure (RCODE 2), which may indicate
that the requested data failed DNSSEC validation at an upstream that the requested data failed DNSSEC validation at an upstream
validating resolver. (RFC2308 permits caching of server failures for validating resolver. (RFC2308 permits caching of server failures for
up to five minutes.) In these cases, a new query with the CD bit set up to five minutes.) In these cases, a new query with the CD bit set
is required. is required.
For efficiency, a validator may wish to set the CD bit on all For efficiency, a validator may wish to set the CD bit on all
upstream queries when it has a trust anchor at or above the QNAME upstream queries when it has a trust anchor at or above the QNAME
(and thus can reasonably expect to be able to validate the response). (and thus can reasonably expect to be able to validate the response).
4.10. Nested Trust Anchors 5.10. Nested Trust Anchors
A DNSSEC validator may be configured such that, for a given response, A DNSSEC validator may be configured such that, for a given response,
more than one trust anchor could be used to validate the chain of more than one trust anchor could be used to validate the chain of
trust to the response zone. For example, imagine a validator trust to the response zone. For example, imagine a validator
configured with trust anchors for "example." and "zone.example." configured with trust anchors for "example." and "zone.example."
When the validator is asked to validate a response to When the validator is asked to validate a response to
"www.sub.zone.example.", either trust anchor could apply. "www.sub.zone.example.", either trust anchor could apply.
When presented with this situation, DNSSEC validators have a choice When presented with this situation, DNSSEC validators have a choice
of which trust anchor(s) to use. Which to use is a matter of of which trust anchor(s) to use. Which to use is a matter of
implementation choice. It is possible and perhaps advisable to implementation choice. It is possible and perhaps advisable to
expose the choice of policy as a configuration option. The rest of expose the choice of policy as a configuration option. The rest of
this section discusses some possible policies. As a default, we this section discusses some possible policies. As a default, we
suggest that validators implement the "Accept Any Success" policy suggest that validators implement the "Accept Any Success" policy
described below in Section 4.10.2 while exposing other policies as described below in Section 5.10.2 while exposing other policies as
configuration options. configuration options.
4.10.1. Closest Encloser 5.10.1. Closest Encloser
One policy is to choose the trust anchor closest to the QNAME of the One policy is to choose the trust anchor closest to the QNAME of the
response. In our example, that would be the "zone.example." trust response. In our example, that would be the "zone.example." trust
anchor. anchor.
This policy has the advantage of allowing the operator to trivially This policy has the advantage of allowing the operator to trivially
override a parent zone's trust anchor with one that the operator can override a parent zone's trust anchor with one that the operator can
validate in a stronger way, perhaps because the resolver operator is validate in a stronger way, perhaps because the resolver operator is
affiliated with the zone in question. This policy also minimizes the affiliated with the zone in question. This policy also minimizes the
number of public key operations needed, which may be of benefit in number of public key operations needed, which may be of benefit in
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This policy has the disadvantage of possibly giving the user some This policy has the disadvantage of possibly giving the user some
unexpected and unnecessary validation failures when sub-zone trust unexpected and unnecessary validation failures when sub-zone trust
anchors are neglected. As a concrete example, consider a validator anchors are neglected. As a concrete example, consider a validator
that configured a trust anchor for "zone.example." in 2009 and one that configured a trust anchor for "zone.example." in 2009 and one
for "example." in 2011. In 2012, "zone.example." rolls its KSK and for "example." in 2011. In 2012, "zone.example." rolls its KSK and
updates its DS records, but the validator operator doesn't update its updates its DS records, but the validator operator doesn't update its
trust anchor. With the "closest encloser" policy, the validator gets trust anchor. With the "closest encloser" policy, the validator gets
validation failures. validation failures.
4.10.2. Accept Any Success 5.10.2. Accept Any Success
Another policy is to try all applicable trust anchors until one gives Another policy is to try all applicable trust anchors until one gives
a validation result of Secure, in which case the final validation a validation result of Secure, in which case the final validation
result is Secure. If and only if all applicable trust anchors give a result is Secure. If and only if all applicable trust anchors give a
result of Insecure, the final validation result is Insecure. If one result of Insecure, the final validation result is Insecure. If one
or more trust anchors lead to a Bogus result and there is no Secure or more trust anchors lead to a Bogus result and there is no Secure
result, then the final validation result is Bogus. result, then the final validation result is Bogus.
This has the advantage of causing the fewer validation failures, This has the advantage of causing the fewer validation failures,
which may deliver a better user experience. If one trust anchor is which may deliver a better user experience. If one trust anchor is
out of date (as in our above example), the user may still be able to out of date (as in our above example), the user may still be able to
get a Secure validation result (and see DNS responses). get a Secure validation result (and see DNS responses).
This policy has the disadvantage of making the validator subject to This policy has the disadvantage of making the validator subject to
compromise of the weakest of these trust anchors while making its compromise of the weakest of these trust anchors while making its
relatively painless to keep old trust anchors configured in relatively painless to keep old trust anchors configured in
perpetuity. perpetuity.
4.10.3. Preference Based on Source 5.10.3. Preference Based on Source
When the trust anchors have come from different sources (e.g. When the trust anchors have come from different sources (e.g.
automated updates ([RFC5011]), one or more DLV registries automated updates ([RFC5011]), one or more DLV registries
([RFC5074]), and manually configured), a validator may wish to choose ([RFC5074]), and manually configured), a validator may wish to choose
between them based on the perceived reliability of those sources. between them based on the perceived reliability of those sources.
The order of precedence might be exposed as a configuration option. The order of precedence might be exposed as a configuration option.
For example, a validator might choose to prefer trust anchors found For example, a validator might choose to prefer trust anchors found
in a DLV registry over those manually configured on the theory that in a DLV registry over those manually configured on the theory that
the manually configured ones will not be as aggressively maintained. the manually configured ones will not be as aggressively maintained.
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that the manually configured ones have been more carefully that the manually configured ones have been more carefully
authenticated. authenticated.
Or the validator might do something more complicated: prefer a sub- Or the validator might do something more complicated: prefer a sub-
set of manually configured trust anchors (based on a configuration set of manually configured trust anchors (based on a configuration
option), then trust anchors that have been updated using the RFC5011 option), then trust anchors that have been updated using the RFC5011
mechanism, then trust anchors from one DLV registry, then trust mechanism, then trust anchors from one DLV registry, then trust
anchors from a different DLV registry, then the rest of the manually anchors from a different DLV registry, then the rest of the manually
configured trust anchors. configured trust anchors.
5. Minor Corrections and Clarifications 6. Minor Corrections and Clarifications
6.1. Finding Zone Cuts
5.1. Finding Zone Cuts
Appendix C.8 of [RFC4035] discusses sending DS queries to the servers Appendix C.8 of [RFC4035] discusses sending DS queries to the servers
for a parent zone. To do that, a resolver may first need to apply for a parent zone. To do that, a resolver may first need to apply
special rules to discover what those servers are. special rules to discover what those servers are.
As explained in Section 3.1.4.1 of [RFC4035], security-aware name As explained in Section 3.1.4.1 of [RFC4035], security-aware name
servers need to apply special processing rules to handle the DS RR, servers need to apply special processing rules to handle the DS RR,
and in some situations the resolver may also need to apply special and in some situations the resolver may also need to apply special
rules to locate the name servers for the parent zone if the resolver rules to locate the name servers for the parent zone if the resolver
does not already have the parent's NS RRset. Section 4.2 of does not already have the parent's NS RRset. Section 4.2 of
[RFC4035] specifies a mechanism for doing that. [RFC4035] specifies a mechanism for doing that.
5.2. Clarifications on DNSKEY Usage 6.2. Clarifications on DNSKEY Usage
Questions of the form "can I use a different DNSKEY for signing this Questions of the form "can I use a different DNSKEY for signing this
RRset" have occasionally arisen. RRset" have occasionally arisen.
The short answer is "yes, absolutely". You can even use a different The short answer is "yes, absolutely". You can even use a different
DNSKEY for each RRset in a zone, subject only to practical limits on DNSKEY for each RRset in a zone, subject only to practical limits on
the size of the DNSKEY RRset. However, be aware that there is no way the size of the DNSKEY RRset. However, be aware that there is no way
to tell resolvers what a particularly DNSKEY is supposed to be used to tell resolvers what a particularly DNSKEY is supposed to be used
for -- any DNSKEY in the zone's signed DNSKEY RRset may be used to for -- any DNSKEY in the zone's signed DNSKEY RRset may be used to
authenticate any RRset in the zone. For example, if a weaker or less authenticate any RRset in the zone. For example, if a weaker or less
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Furthermore, note that the SEP bit setting has no effect on how a Furthermore, note that the SEP bit setting has no effect on how a
DNSKEY may be used -- the validation process is specifically DNSKEY may be used -- the validation process is specifically
prohibited from using that bit by [RFC4034] section 2.1.2. It is prohibited from using that bit by [RFC4034] section 2.1.2. It is
possible to use a DNSKEY without the SEP bit set as the sole secure possible to use a DNSKEY without the SEP bit set as the sole secure
entry point to the zone, yet use a DNSKEY with the SEP bit set to entry point to the zone, yet use a DNSKEY with the SEP bit set to
sign all RRsets in the zone (other than the DNSKEY RRset). It's also sign all RRsets in the zone (other than the DNSKEY RRset). It's also
possible to use a single DNSKEY, with or without the SEP bit set, to possible to use a single DNSKEY, with or without the SEP bit set, to
sign the entire zone, including the DNSKEY RRset itself. sign the entire zone, including the DNSKEY RRset itself.
5.3. Errors in Examples 6.3. Errors in Examples
The text in [RFC4035] Section C.1 refers to the examples in B.1 as The text in [RFC4035] Section C.1 refers to the examples in B.1 as
"x.w.example.com" while B.1 uses "x.w.example". This is painfully "x.w.example.com" while B.1 uses "x.w.example". This is painfully
obvious in the second paragraph where it states that the RRSIG labels obvious in the second paragraph where it states that the RRSIG labels
field value of 3 indicates that the answer was not the result of field value of 3 indicates that the answer was not the result of
wildcard expansion. This is true for "x.w.example" but not for wildcard expansion. This is true for "x.w.example" but not for
"x.w.example.com", which of course has a label count of 4 "x.w.example.com", which of course has a label count of 4
(antithetically, a label count of 3 would imply the answer was the (antithetically, a label count of 3 would imply the answer was the
result of a wildcard expansion). result of a wildcard expansion).
The first paragraph of [RFC4035] Section C.6 also has a minor error: The first paragraph of [RFC4035] Section C.6 also has a minor error:
the reference to "a.z.w.w.example" should instead be "a.z.w.example", the reference to "a.z.w.w.example" should instead be "a.z.w.example",
as in the previous line. as in the previous line.
5.4. Errors in RFC 5155 6.4. Errors in RFC 5155
A NSEC3 record that matches an Empty Non-Terminal effectively has no A NSEC3 record that matches an Empty Non-Terminal effectively has no
type associated with it. This NSEC3 record has an empty type bit type associated with it. This NSEC3 record has an empty type bit
map. Section 3.2.1 of [RFC5155] contains the statement: map. Section 3.2.1 of [RFC5155] contains the statement:
Blocks with no types present MUST NOT be included. Blocks with no types present MUST NOT be included.
However, the same section contains a regular expression: However, the same section contains a regular expression:
Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )+ Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )+
The plus sign in the regular expression indicates that there is one The plus sign in the regular expression indicates that there is one
or more of the preceding element. This means that there must be at or more of the preceding element. This means that there must be at
least one window block. If this window block has no types, it least one window block. If this window block has no types, it
contradicts with the first statement. Therefore, the correct text in contradicts with the first statement. Therefore, the correct text in
RFC 5155 3.2.1 should be: RFC 5155 3.2.1 should be:
Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )* Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )*
6. IANA Considerations 7. IANA Considerations
This document specifies no IANA Actions. This document specifies no IANA Actions.
7. Security Considerations 8. Security Considerations
This document adds two cryptographic features to the core DNSSEC This document adds two cryptographic features to the core DNSSEC
protocol. Additionally, it addresses some ambiguities and omissions protocol. Additionally, it addresses some ambiguities and omissions
in the core DNSSEC documents that, if not recognized and addressed in in the core DNSSEC documents that, if not recognized and addressed in
implementations, could lead to security failures. In particular, the implementations, could lead to security failures. In particular, the
validation algorithm clarifications in Section 3 are critical for validation algorithm clarifications in Section 4 are critical for
preserving the security properties DNSSEC offers. Furthermore, preserving the security properties DNSSEC offers. Furthermore,
failure to address some of the interoperability concerns in Section 4 failure to address some of the interoperability concerns in Section 5
could limit the ability to later change or expand DNSSEC, including could limit the ability to later change or expand DNSSEC, including
adding new algorithms. adding new algorithms.
8. References 9. References
9.1. Normative References
8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC", [RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC",
RFC 3225, December 2001. RFC 3225, December 2001.
skipping to change at page 13, line 16 skipping to change at page 14, line 38
(DS) Resource Records (RRs)", RFC 4509, May 2006. (DS) Resource Records (RRs)", RFC 4509, May 2006.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, March 2008. Existence", RFC 5155, March 2008.
[RFC5702] Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY [RFC5702] Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY
and RRSIG Resource Records for DNSSEC", RFC 5702, and RRSIG Resource Records for DNSSEC", RFC 5702,
October 2009. October 2009.
8.2. Informative References 9.2. Informative References
[RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation [RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation
Signer (DS)", RFC 3755, May 2004. Signer (DS)", RFC 3755, May 2004.
[RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices", [RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
RFC 4641, September 2006. RFC 4641, September 2006.
[RFC4955] Blacka, D., "DNS Security (DNSSEC) Experiments", RFC 4955, [RFC4955] Blacka, D., "DNS Security (DNSSEC) Experiments", RFC 4955,
July 2007. July 2007.
skipping to change at page 13, line 43 skipping to change at page 15, line 18
Appendix A. Acknowledgments Appendix A. Acknowledgments
The editors would like the thank Rob Austein for his previous work as The editors would like the thank Rob Austein for his previous work as
an editor of this document. an editor of this document.
The editors are extremely grateful to those who, in addition to The editors are extremely grateful to those who, in addition to
finding errors and omissions in the DNSSECbis document set, have finding errors and omissions in the DNSSECbis document set, have
provided text suitable for inclusion in this document. provided text suitable for inclusion in this document.
The lack of specificity about handling private algorithms, as The lack of specificity about handling private algorithms, as
described in Section 4.3, and the lack of specificity in handling ANY described in Section 5.3, and the lack of specificity in handling ANY
queries, as described in Section 3.2, were discovered by David queries, as described in Section 4.2, were discovered by David
Blacka. Blacka.
The error in algorithm 1 key tag calculation, as described in The error in algorithm 1 key tag calculation, as described in
Section 4.5, was found by Abhijit Hayatnagarkar. Donald Eastlake Section 5.5, was found by Abhijit Hayatnagarkar. Donald Eastlake
contributed text for Section 4.5. contributed text for Section 5.5.
The bug relating to delegation NSEC RR's in Section 3.1 was found by The bug relating to delegation NSEC RR's in Section 4.1 was found by
Roy Badami. Roy Arends found the related problem with DNAME. Roy Badami. Roy Arends found the related problem with DNAME.
The errors in the [RFC4035] examples were found by Roy Arends, who The errors in the [RFC4035] examples were found by Roy Arends, who
also contributed text for Section 5.3 of this document. also contributed text for Section 6.3 of this document.
The editors would like to thank Alfred Hoenes, Ed Lewis, Danny Mayer, The editors would like to thank Alfred Hoenes, Ed Lewis, Danny Mayer,
Olafur Gudmundsson, Suzanne Woolf, and Scott Rose for their Olafur Gudmundsson, Suzanne Woolf, Rickard Bellgrim, Mike St. Johns,
substantive comments on the text of this document. and Scott Rose for their substantive comments on the text of this
document.
Authors' Addresses Authors' Addresses
Samuel Weiler Samuel Weiler
SPARTA, Inc. SPARTA, Inc.
7110 Samuel Morse Drive 7110 Samuel Morse Drive
Columbia, Maryland 21046 Columbia, Maryland 21046
US US
Email: weiler@tislabs.com Email: weiler@tislabs.com
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