From c6b8cd34ad699adeffdb85f58cd5f33bc2da0801 Mon Sep 17 00:00:00 2001 From: Mark Andrews Date: Tue, 1 May 2012 10:45:26 +1000 Subject: [PATCH] new draft --- ...aft-ietf-dnsext-dnssec-bis-updates-18.txt} | 736 +++++++++--------- 1 file changed, 368 insertions(+), 368 deletions(-) rename doc/draft/{draft-ietf-dnsext-dnssec-bis-updates-16.txt => draft-ietf-dnsext-dnssec-bis-updates-18.txt} (69%) diff --git a/doc/draft/draft-ietf-dnsext-dnssec-bis-updates-16.txt b/doc/draft/draft-ietf-dnsext-dnssec-bis-updates-18.txt similarity index 69% rename from doc/draft/draft-ietf-dnsext-dnssec-bis-updates-16.txt rename to doc/draft/draft-ietf-dnsext-dnssec-bis-updates-18.txt index 205413ab4e..e52f9a3b2c 100644 --- a/doc/draft/draft-ietf-dnsext-dnssec-bis-updates-16.txt +++ b/doc/draft/draft-ietf-dnsext-dnssec-bis-updates-18.txt @@ -4,13 +4,13 @@ Network Working Group S. Weiler Internet-Draft SPARTA, Inc. Updates: 4033, 4034, 4035, 5155 D. Blacka -(if approved) VeriSign, Inc. -Intended status: Standards Track January 14, 2012 -Expires: July 17, 2012 +(if approved) Verisign, Inc. +Intended status: Standards Track April 30, 2012 +Expires: November 1, 2012 Clarifications and Implementation Notes for DNSSECbis - draft-ietf-dnsext-dnssec-bis-updates-16 + draft-ietf-dnsext-dnssec-bis-updates-18 Abstract @@ -37,7 +37,7 @@ Status of this Memo time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on July 17, 2012. + This Internet-Draft will expire on November 1, 2012. Copyright Notice @@ -52,9 +52,9 @@ Copyright Notice -Weiler & Blacka Expires July 17, 2012 [Page 1] +Weiler & Blacka Expires November 1, 2012 [Page 1] -Internet-Draft DNSSECbis Implementation Notes January 2012 +Internet-Draft DNSSECbis Implementation Notes April 2012 to this document. Code Components extracted from this document must @@ -108,9 +108,9 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 -Weiler & Blacka Expires July 17, 2012 [Page 2] +Weiler & Blacka Expires November 1, 2012 [Page 2] -Internet-Draft DNSSECbis Implementation Notes January 2012 +Internet-Draft DNSSECbis Implementation Notes April 2012 Table of Contents @@ -128,7 +128,7 @@ Table of Contents 4.2. Validating Responses to an ANY Query . . . . . . . . . . . 6 4.3. Check for CNAME . . . . . . . . . . . . . . . . . . . . . 6 4.4. Insecure Delegation Proofs . . . . . . . . . . . . . . . . 6 - 5. Interoperability Concerns . . . . . . . . . . . . . . . . . . 6 + 5. Interoperability Concerns . . . . . . . . . . . . . . . . . . 7 5.1. Errors in Canonical Form Type Code List . . . . . . . . . 7 5.2. Unknown DS Message Digest Algorithms . . . . . . . . . . . 7 5.3. Private Algorithms . . . . . . . . . . . . . . . . . . . . 8 @@ -137,25 +137,26 @@ Table of Contents 5.6. Setting the DO Bit on Replies . . . . . . . . . . . . . . 9 5.7. Setting the AD Bit on Queries . . . . . . . . . . . . . . 9 5.8. Setting the AD Bit on Replies . . . . . . . . . . . . . . 9 - 5.9. Always set the CD bit on Queries . . . . . . . . . . . . . 9 + 5.9. Always set the CD bit on Queries . . . . . . . . . . . . . 10 5.10. Nested Trust Anchors . . . . . . . . . . . . . . . . . . . 10 - 5.10.1. Closest Encloser . . . . . . . . . . . . . . . . . . 10 - 5.10.2. Accept Any Success . . . . . . . . . . . . . . . . . 11 - 5.10.3. Preference Based on Source . . . . . . . . . . . . . 11 - 5.11. Mandatory Algorithm Rules . . . . . . . . . . . . . . . . 12 - 5.12. Expect Extra Signatures From Strange Keys . . . . . . . . 12 - 6. Minor Corrections and Clarifications . . . . . . . . . . . . . 13 - 6.1. Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . 13 - 6.2. Clarifications on DNSKEY Usage . . . . . . . . . . . . . . 13 - 6.3. Errors in Examples . . . . . . . . . . . . . . . . . . . . 13 - 6.4. Errors in RFC 5155 . . . . . . . . . . . . . . . . . . . . 14 - 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 14 - 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 - 9.1. Normative References . . . . . . . . . . . . . . . . . . . 15 - 9.2. Informative References . . . . . . . . . . . . . . . . . . 15 - Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 16 - Appendix B. Discussion of Setting the CD Bit . . . . . . . . . . 17 + 5.11. Mandatory Algorithm Rules . . . . . . . . . . . . . . . . 11 + 5.12. Ignore Extra Signatures From Unknown Keys . . . . . . . . 11 + 6. Minor Corrections and Clarifications . . . . . . . . . . . . . 12 + 6.1. Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . 12 + 6.2. Clarifications on DNSKEY Usage . . . . . . . . . . . . . . 12 + 6.3. Errors in Examples . . . . . . . . . . . . . . . . . . . . 12 + 6.4. Errors in RFC 5155 . . . . . . . . . . . . . . . . . . . . 13 + 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 + 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 + 9.1. Normative References . . . . . . . . . . . . . . . . . . . 14 + 9.2. Informative References . . . . . . . . . . . . . . . . . . 14 + Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 15 + Appendix B. Discussion of Setting the CD Bit . . . . . . . . . . 15 + Appendix C. Discussion of Trust Anchor Preference Options . . . . 18 + C.1. Closest Encloser . . . . . . . . . . . . . . . . . . . . . 18 + C.2. Accept Any Success . . . . . . . . . . . . . . . . . . . . 19 + C.3. Preference Based on Source . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 @@ -163,10 +164,9 @@ Table of Contents - -Weiler & Blacka Expires July 17, 2012 [Page 3] +Weiler & Blacka Expires November 1, 2012 [Page 3] -Internet-Draft DNSSECbis Implementation Notes January 2012 +Internet-Draft DNSSECbis Implementation Notes April 2012 1. Introduction and Terminology @@ -183,8 +183,8 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 1.1. Structure of this Document - The clarifications to DNSSECbis are sorted according to their - importance, starting with ones which could, if ignored, lead to + The clarifications and changes to DNSSECbis are sorted according to + their importance, starting with ones which could, if ignored, lead to security problems and progressing down to clarifications that are expected to have little operational impact. @@ -207,9 +207,9 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 [RFC5155] describes the use and behavior of the NSEC3 and NSEC3PARAM records for hashed denial of existence. Validator implementations are strongly encouraged to include support for NSEC3 because a number - of highly visible zones are expected to use it. Validators that do - not support validation of responses using NSEC3 will likely be - hampered in validating large portions of the DNS space. + of highly visible zones use it. Validators that do not support + validation of responses using NSEC3 will be hampered in validating + large portions of the DNS space. [RFC5155] should be considered part of the DNS Security Document Family as described by [RFC4033], Section 10. @@ -220,13 +220,13 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 -Weiler & Blacka Expires July 17, 2012 [Page 4] +Weiler & Blacka Expires November 1, 2012 [Page 4] -Internet-Draft DNSSECbis Implementation Notes January 2012 +Internet-Draft DNSSECbis Implementation Notes April 2012 - MAY indeed be using either and validators supporting these algorithms - MUST support both NSEC3 and NSEC responses. + MAY be using either and validators supporting these algorithms MUST + support both NSEC3 and NSEC responses. 2.2. SHA-2 Support @@ -247,7 +247,7 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 Section 4.7 of RFC4035 permits security-aware resolvers to implement a BAD cache. Because of scaling concerns not discussed in this document, that guidance has changed: security-aware resolvers SHOULD - implement a BAD cache, as described in RFC4035. + implement a BAD cache as described in RFC4035. 4. Security Concerns @@ -276,9 +276,9 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 -Weiler & Blacka Expires July 17, 2012 [Page 5] +Weiler & Blacka Expires November 1, 2012 [Page 5] -Internet-Draft DNSSECbis Implementation Notes January 2012 +Internet-Draft DNSSECbis Implementation Notes April 2012 Similarly, the algorithm would also allow an NSEC RR at the same @@ -310,33 +310,42 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 on (or that should be based on) CNAMEs. When validating a NOERROR/ 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 - type. Without this check, an attacker could successfully transform a - positive CNAME response into a NOERROR/NODATA response. + type. + + Without this check, an attacker could successfully transform a + positive CNAME response into a NOERROR/NODATA response by (e.g.) + simply stripping the CNAME RRset from the response. A naive + validator would then note that the QTYPE was not present in the + matching NSEC/NSEC3 RR, but fail to notice that the CNAME bit was + set, and thus the response should have been a positive CNAME + response. 4.4. Insecure Delegation Proofs [RFC4035] Section 5.2 specifies that a validator, when proving a 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 - 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 + MUST check for the presence of the NS bit in the matching NSEC (or + NSEC3) RR (proving that there is, indeed, a delegation), or 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 - delegations might be used to claim that an existing signed record is - not signed. + with the Opt-Out flag set. + + + +Weiler & Blacka Expires November 1, 2012 [Page 6] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + + Without this check, an attacker could reuse an NSEC or NSEC3 RR + matching a non-delegation name to spoof an unsigned delegation at + that name. This would claim that an existing signed RRset (or set of + signed RRsets) is below an unsigned delegation, thus not signed and + vulnerable to further attack. 5. Interoperability Concerns - - - - -Weiler & Blacka Expires July 17, 2012 [Page 6] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - - 5.1. Errors in Canonical Form Type Code List When canonicalizing DNS names (for both ordering and signing), DNS @@ -374,47 +383,56 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 authenticated NSEC RRset proving that no DS RRset exists, as described above. - To paraphrase the above, when determining the security status of a - zone, a validator disregards any DS records listing unknown or - unsupported algorithms. If none are left, the zone is treated as if - it were unsigned. - - Modified to consider DS message digest algorithms, a validator also - disregards any DS records using unknown or unsupported message digest - algorithms. + In other words, when determining the security status of a zone, a + validator disregards any authenticated DS records that specify - - - -Weiler & Blacka Expires July 17, 2012 [Page 7] +Weiler & Blacka Expires November 1, 2012 [Page 7] -Internet-Draft DNSSECbis Implementation Notes January 2012 +Internet-Draft DNSSECbis Implementation Notes April 2012 + unknown or unsupported DNSKEY algorithms. If none are left, the zone + is treated as if it were unsigned. + + This document modifies the above text to additionally disregard + authenticated DS records using unknown or unsupported message digest + 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 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 eight-bit algorithm field in the DS RR is not conclusive about what algorithm(s) is actually in use. - If no private algorithms appear in the DS set or if any supported - algorithm appears in the DS set, no special processing will be - needed. In the remaining cases, the security status of the zone - depends on whether or not the resolver supports any of the private - algorithms in use (provided that these DS records use supported hash - functions, as discussed in Section 5.2). In these cases, the - resolver MUST retrieve the corresponding DNSKEY for each private - algorithm DS record and examine the public key field to determine 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 - 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 - discussed in [RFC4035]. + If no private algorithms appear in the DS RRset, or if any supported + algorithm appears in the DS RRset, no special processing is needed. + Furthermore, if the validator implementation does not support any + private algorithms, or only supports private algorithms using an + algorithm number not present in the DS RRset, no special processing + is needed. + + In the remaining cases, the security status of the zone depends on + whether or not the resolver supports any of the private algorithms in + use (provided that these DS records use supported hash functions, as + discussed in Section 5.2). In these cases, the resolver MUST + retrieve the corresponding DNSKEY for each private algorithm DS + record and examine the public key field to determine 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 the DS RR as + described in Section 5.2 of [RFC4035], authenticating the DNSKEY. If + all of the retrieved and authenticated DNSKEY RRs use unknown or + unsupported private algorithms, then the zone is treated as if it + were unsigned. + + Note that if none of the private algorithm DS RRs can be securely + matched to DNSKEY RRs and no other DS establishes that the zone is + secure, the referral should be considered Bogus data as discussed in + [RFC4035]. This clarification facilitates the broader use of private algorithms, as suggested by [RFC4955]. @@ -423,31 +441,28 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 When multiple RRSIGs cover a given RRset, [RFC4035] Section 5.3.3 suggests that "the local resolver security policy determines whether + + + +Weiler & Blacka Expires November 1, 2012 [Page 8] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + the resolver also has to test these RRSIG RRs and how to resolve - conflicts if these RRSIG RRs lead to differing results." In most - cases, a resolver would be well advised to accept any valid RRSIG as - sufficient. If the first RRSIG tested fails validation, a resolver - would be well advised to try others, giving a successful validation - result if any can be validated and giving a failure only if all + conflicts if these RRSIG RRs lead to differing results." + + This document specifies that a resolver SHOULD accept any valid RRSIG + as sufficient, and only determine that an RRset is Bogus if all RRSIGs fail validation. If a resolver adopts a more restrictive policy, there's a danger that - properly-signed data might unnecessarily fail validation, perhaps - because of cache timing issues. Furthermore, certain zone management - techniques, like the Double Signature Zone-signing Key Rollover - method described in section 4.2.1.2 of [RFC4641] might not work - reliably. - - - - - - - -Weiler & Blacka Expires July 17, 2012 [Page 8] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - + properly-signed data might unnecessarily fail validation due to cache + timing issues. Furthermore, certain zone management techniques, like + the Double Signature Zone-signing Key Rollover method described in + section 4.2.1.2 of [RFC4641], will not work reliably. Such a + resolver is also vulnerable to malicious insertion of gibberish + signatures. 5.5. Key Tag Calculation @@ -461,8 +476,9 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 5.6. Setting the DO Bit on Replies As stated in [RFC3225], the DO bit of the query MUST be copied in the - response. At least one implementation has done something different, - so it may be wise for resolvers to be liberal in what they accept. + response. However, in order to interoperate with implementations + that ignore this rule on sending, resolvers MUST ignore the DO bit in + responses. 5.7. Setting the AD Bit on Queries @@ -476,39 +492,36 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 Section 3.2.3 of [RFC4035] describes under which conditions a validating resolver should set or clear the AD bit in a response. In - order to protect legacy stub resolvers and middleboxes, validating - 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 - contained either a set DO bit or a set AD bit. + order to interoperate with legacy stub resolvers and middleboxes that + neither understand nor ignore the AD bit, validating 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 contained either a set DO + bit or a set AD bit. + + + +Weiler & Blacka Expires November 1, 2012 [Page 9] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + 5.9. Always set the CD bit on Queries When processing a request with the CD bit set, a resolver SHOULD - attempt to return all responsive data, even data that has failed - 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 - upstream queries. + attempt to return all response data, even data that has failed 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 upstream + queries. - Prevailing wisdom suggests that a validating resolver SHOULD set the - CD bit on every upstream query regardless of whether the CD bit was - set on the incoming query or whether it has a trust anchor at or - above the QNAME. In other words, a validating resolver should - attempt to retrieve all possible data -- even that which it can not - validate itself -- on the grounds that a later query might come with - the CD bit set. + This document further specifies that validating resolvers SHOULD set + the CD bit on every upstream query. This is regardless of whether + the CD bit was set on the incoming query or whether it has a trust + anchor at or above the QNAME. - - - -Weiler & Blacka Expires July 17, 2012 [Page 9] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - - - RFC4035 is ambiguous about what to do when a cached response was - obtained with the CD bit not set, a case that only arises when the + [RFC4035] is ambiguous about what to do when a cached response was + obtained with the CD bit unset, a case that only arises when the resolver chooses not to set the CD bit on all upstream queries, as - suggested above. In the typical case, no new query is required, nor + specified above. In the typical case, no new query is required, nor does the cache need to track the state of the CD bit used to make a given query. The problem arises when the cached response is a server failure (RCODE 2), which may indicate that the requested data failed @@ -530,103 +543,39 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 When presented with this situation, DNSSEC validators have a choice of which trust anchor(s) to use. Which to use is a matter of - implementation choice. It is possible and perhaps advisable to - expose the choice of policy as a configuration option. The rest of - this section discusses some possible policies. As a default, we - suggest that validators implement the "Accept Any Success" policy - described below in Section 5.10.2 while exposing other policies as - configuration options. + implementation choice. Appendix C discusses several possible + algorithms. -5.10.1. Closest Encloser + It is possible and advisable to expose the choice of policy as a + configuration option. As a default, it is suggested that validators + implement the "Accept Any Success" policy described in Appendix C.2 + while exposing other policies as configuration options. - 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 - anchor. - - This policy has the advantage of allowing the operator to trivially - override a parent zone's trust anchor with one that the operator can - validate in a stronger way, perhaps because the resolver operator is - affiliated with the zone in question. This policy also minimizes the - number of public key operations needed, which may be of benefit in - resource-constrained environments. - - This policy has the disadvantage of possibly giving the user some - unexpected and unnecessary validation failures when sub-zone trust - anchors are neglected. As a concrete example, consider a validator + The "Accept Any Success" policy is to try all applicable trust + anchors until one gives a validation result of Secure, in which case -Weiler & Blacka Expires July 17, 2012 [Page 10] +Weiler & Blacka Expires November 1, 2012 [Page 10] -Internet-Draft DNSSECbis Implementation Notes January 2012 +Internet-Draft DNSSECbis Implementation Notes April 2012 - that configured a trust anchor for "zone.example." in 2009 and one - for "example." in 2011. In 2012, "zone.example." rolls its KSK and - updates its DS records, but the validator operator doesn't update its - trust anchor. With the "closest encloser" policy, the validator gets - validation failures. - -5.10.2. Accept Any Success - - Another policy is to try all applicable trust anchors until one gives - 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 of Insecure, the final validation result is Insecure. If one - or more trust anchors lead to a Bogus result and there is no Secure - result, then the final validation result is Bogus. - - This has the advantage of causing the fewer validation failures, - 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 - get a Secure validation result (and see DNS responses). - - This policy has the disadvantage of making the validator subject to - compromise of the weakest of these trust anchors while making its - relatively painless to keep old trust anchors configured in - perpetuity. - -5.10.3. Preference Based on Source - - When the trust anchors have come from different sources (e.g. - automated updates ([RFC5011]), one or more DLV registries - ([RFC5074]), and manually configured), a validator may wish to choose - between them based on the perceived reliability of those sources. - The order of precedence might be exposed as a configuration option. - - For example, a validator might choose to prefer trust anchors found - in a DLV registry over those manually configured on the theory that - the manually configured ones will not be as aggressively maintained. - - Conversely, a validator might choose to prefer manually configured - trust anchors over those obtained from a DLV registry on the theory - that the manually configured ones have been more carefully - authenticated. - - Or the validator might do something more complicated: prefer a sub- - set of manually configured trust anchors (based on a configuration - option), then trust anchors that have been updated using the RFC5011 - mechanism, then trust anchors from one DLV registry, then trust - anchors from a different DLV registry, then the rest of the manually - configured trust anchors. - - - -Weiler & Blacka Expires July 17, 2012 [Page 11] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - + the final validation result is Secure. If and only if all applicable + trust anchors give a 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 result, then the final validation result is Bogus. 5.11. Mandatory Algorithm Rules - The last paragraph of RFC4035 Section 2.2 includes rules for which - algorithms must be used to sign a zone. Since these rules have been - confusing, we restate them in different language here: + The last paragraph of RFC4035 Section 2.2 includes rules describing + which algorithms must be used to sign a zone. Since these rules have + been confusing, they are restated using different language here: The DS RRset and DNSKEY RRset are used to signal which algorithms - are used to sign a zone. The pressence of an algorithm in a - zone's DS or DNSKEY RRset set signals that that algorithm is used - to sign the entire zone. + are used to sign a zone. The presence of an algorithm in either a + zone's DS or DNSKEY RRset signals that that algorithm is used to + sign the entire zone. A signed zone MUST include a DNSKEY for each algorithm present in the zone's DS RRset and expected trust anchors for the zone. The @@ -643,19 +592,17 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 Lastly, note that this a requirement at the server side, not the client side. Validators SHOULD accept any single valid path. They - SHOULD NOT insist that all algorithms signalled in the DS RRset work, - and they MUST NOT insist that all algorithms signalled in the DNSKEY + SHOULD NOT insist that all algorithms signaled in the DS RRset work, + and they MUST NOT insist that all algorithms signaled in the DNSKEY RRset work. A validator MAY have a configuration option to perform a signature completeness test to support troubleshooting. -5.12. Expect Extra Signatures From Strange Keys +5.12. Ignore Extra Signatures From Unknown Keys - Validating resolvers should not be surprised to find RRSIGs in a zone - that do not (currently) have a corresponding DNSKEY in the zone. - Likewise, a validating resolver should not be surprised to find - RRSIGs with algorithm types that don't exist in the DNSKEY RRset or - DNSKEYs with algorithm types that don't appear in the zone's DS - RRset. + Validating resolvers MUST disregard RRSIGs in a zone that do not + (currently) have a corresponding DNSKEY in the zone. Similarly, a + validating resolver MUST disregard RRSIGs with algorithm types that + don't exist in the DNSKEY RRset. Good key rollover and algorithm rollover practices, as discussed in RFC4641 and its successor documents and as suggested by the rules in @@ -665,12 +612,9 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 - - - -Weiler & Blacka Expires July 17, 2012 [Page 12] +Weiler & Blacka Expires November 1, 2012 [Page 11] -Internet-Draft DNSSECbis Implementation Notes January 2012 +Internet-Draft DNSSECbis Implementation Notes April 2012 6. Minor Corrections and Clarifications @@ -690,18 +634,17 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 6.2. Clarifications on DNSKEY Usage - Questions of the form "can I use a different DNSKEY for signing this - RRset" have occasionally arisen. - - 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 - 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 - 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 - trusted DNSKEY is being used to authenticate NSEC RRsets or all - dynamically updated records, that same DNSKEY can also be used to - sign any other RRsets from the zone. + It is possible to use different DNSKEYs to sign different subsets of + a zone, constrained only by the rules in Section 5.11. It is even + possible to use a different DNSKEY for each RRset in a zone, subject + only to practical limits on the size of the DNSKEY RRset and the + above rules. However, be aware that there is no way to tell + resolvers what a particular DNSKEY is supposed to be used 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 trusted + DNSKEY is being used to authenticate NSEC RRsets or all dynamically + updated records, that same DNSKEY can also be used to sign any other + RRsets from the zone. Furthermore, note that the SEP bit setting has no effect on how a DNSKEY may be used -- the validation process is specifically @@ -721,16 +664,15 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 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 (antithetically, a label count of 3 would imply the answer was the - - - -Weiler & Blacka Expires July 17, 2012 [Page 13] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - - result of a wildcard expansion). + + +Weiler & Blacka Expires November 1, 2012 [Page 12] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + 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", as in the previous line. @@ -763,7 +705,7 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 8. Security Considerations - This document adds two cryptographic features to the core DNSSEC + This document adds SHA-2 and NSEC3 support to the core DNSSEC protocol. Security considerations for those features are discussed in the documents defining them. Additionally, this document addresses some ambiguities and omissions in the core DNSSEC documents @@ -777,17 +719,16 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 The recommendation in Section 5.9 to always set the CD bit has security implications. By setting the CD bit, a resolver will not benefit from more stringent validation rules or a more complete set - - - -Weiler & Blacka Expires July 17, 2012 [Page 14] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - - of trust anchors at an upstream validator. + + +Weiler & Blacka Expires November 1, 2012 [Page 13] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + 9. References 9.1. Normative References @@ -833,17 +774,17 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 RFC 4641, September 2006. [RFC4955] Blacka, D., "DNS Security (DNSSEC) Experiments", RFC 4955, - - - -Weiler & Blacka Expires July 17, 2012 [Page 15] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - - July 2007. [RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) + + + +Weiler & Blacka Expires November 1, 2012 [Page 14] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + Trust Anchors", RFC 5011, September 2007. [RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074, @@ -887,42 +828,38 @@ Appendix A. Acknowledgments document. - - - - - -Weiler & Blacka Expires July 17, 2012 [Page 16] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - - Appendix B. Discussion of Setting the CD Bit RFC 4035 may be read as relying on the implicit assumption that there - is (at least usually) at most one validating system between the stub - resolver and the authoritative server for a given zone. It is - entirely possible, however, for more than one validator to stand - between a stub resolver and an authoritative server. If these - different validators have disjoint trust anchors configured, then it - will be possible that each would be able to validate some portion of - the DNS tree but neither will be able to validate all of it. - Accordingly, it might be argued that it is desirable not to set the - CD bit on upstream queries, because that will allow for maximal - validation. + is at most one validating system between the stub resolver and the + authoritative server for a given zone. It is entirely possible, - In Section 5.9 of the present memo, it is recommended to set the CD - bit on an upstream query even when the incoming query arrives with + + +Weiler & Blacka Expires November 1, 2012 [Page 15] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + + however, for more than one validator to exist between a stub resolver + and an authoritative server. If these different validators have + disjoint trust anchors configured, then it is possible that each + would be able to validate some portion of the DNS tree but neither is + able to validate all of it. Accordingly, it might be argued that it + is desirable not to set the CD bit on upstream queries, because that + allows for maximal validation. + + In section Section 5.9 of this document, it is recommended to set the + CD bit on an upstream query even when the incoming query arrives with CD=0. This is for two reasons: it encourages a more predictable - validation experience (because it means that one validator is always - doing the validation), and it ensures that all DNSSEC data that - exists may be available from the local cache should a query with CD=1 - arrive. + validation experience as only one validator is always doing the + validation, and it ensures that all DNSSEC data that exists may be + available from the local cache should a query with CD=1 arrive. As a matter of policy, it is possible to set the CD bit differently than suggested in Section 5.9. A different choice will, of course, not always yield the benefits listed above. It is beyond the scope - of this memo to outline all of the considerations and counter + of this document to outline all of the considerations and counter considerations for all possible policies. Nevertheless, it is possible to describe three approaches and their underlying philosophy of operation. These are laid out in the tables below. @@ -930,14 +867,14 @@ Appendix B. Discussion of Setting the CD Bit The table that describes each model has five columns. The first column indicates the value of the CD bit that the resolver receives (for instance, on the name server side in an iterative resolver, or - as local policy or from the API in the case of a stub). The next + as local policy or from the API in the case of a stub). The second column indicates whether the query needs to be forwarded for - resolution (F) or can be satisfied from a local cache (C). The next + resolution (F) or can be satisfied from a local cache (C). The third column is a line number, so that it can be referred to later in the - table. The next column indicates any relevant conditions at the - resolver: whether the resolver has a covering trust anchor and so on - (if there are no parameters here, the column is empty). The final - column indicates what the resolver does. + table. The fourth column indicates any relevant conditions at the + resolver: whether the resolver has a covering trust anchor and so on. + If there are no parameters here, the column is empty. The fifth and + final column indicates what action the resolver takes. The tables differentiate between "cached data" and "cached RCODE=2". This is a shorthand; the point is that one has to treat RCODE=2 as @@ -945,30 +882,32 @@ Appendix B. Discussion of Setting the CD Bit upstream. The distinction is really between "cached RCODE=2" and "cached everything else". - - - -Weiler & Blacka Expires July 17, 2012 [Page 17] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - - The tables are probably easiest to think of in terms of describing what happens when a stub resolver sends a query to an intermediate resolver, but they are perfectly general and can be applied to any validating resolver. + + + + + +Weiler & Blacka Expires November 1, 2012 [Page 16] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + Model 1: "always set" This model is so named because the validating resolver sets the CD - bit on queries it makes reegardless of whether it has a covering - trust anchor for the query. It is the model recommended in - Section 5.9 of this memo. The general philosophy represented by this + bit on queries it makes regardless of whether it has a covering trust + anchor for the query. The general philosophy represented by this table is that only one resolver should be responsible for validation irrespective of the possibility that an upstream resolver may be - present and with TAs that cover different or additional QNAMEs. + present with trust anchors that cover different or additional QNAMEs. + It is the model recommended in Section 5.9 of this document. - CD F/C line conditions action + CD F/C line conditions action ==================================================================== 1 F A1 Set CD=1 on upstream query 0 F A2 Set CD=1 on upstream query @@ -986,30 +925,11 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 The general philosophy represented by this table is that more than one resolver may take responsibility for validating a QNAME and that a validation failure for a QNAME by any resolver in the chain is a - validation failure for the query. Using this model instead of model - 1 is NOT RECOMMENDED. + validation failure for the query. Using this model is NOT + RECOMMENDED. - - - - - - - - - - - - - - -Weiler & Blacka Expires July 17, 2012 [Page 18] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - - - CD F/C line conditions action + CD F/C line conditions action ==================================================================== 1 F N1 Set CD=1 on upstream query 0 F N2 Set CD=0 on upstream query @@ -1025,20 +945,28 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 generated with CD=0 + + + +Weiler & Blacka Expires November 1, 2012 [Page 17] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + Model 3: "sometimes set" This model is so named because it sets the CD bit on upstream queries triggered by received CD=0 queries based on whether the validator has - a TA configured that covers the query. If there is no covering TA, - the resolver clears the CD bit in the upstream query. If there is a - covering TA, it sets CD=1 and performs validation itself. The - general philosophy represented by this table is that a resolver - should try and validate QNAMEs for which is has trust anchors and - should not preclude validation by other resolvers for QNAMEs for - which it does not have covering trust anchors. Using this model - instead of model 1 is NOT RECOMMENDED. + a trust anchor configured that covers the query. If there is no + covering trust anchor, the resolver clears the CD bit in the upstream + query. If there is a covering trust anchor, the resolver sets CD=1 + and performs validation itself. The general philosophy represented + by this table is that a resolver should try and validate QNAMEs for + which is has trust anchors and should not preclude validation by + other resolvers for QNAMEs for which it does not have covering trust + anchors. Using this model is NOT RECOMMENDED. - CD F/C line conditions action + CD F/C line conditions action ==================================================================== 1 F S1 Set CD=1 on upstream query 0 F S2 covering TA Set CD=1 on upstream query @@ -1057,18 +985,99 @@ Internet-Draft DNSSECbis Implementation Notes January 2012 was generated with CD=1 & no covering - - - -Weiler & Blacka Expires July 17, 2012 [Page 19] - -Internet-Draft DNSSECbis Implementation Notes January 2012 - - TA +Appendix C. Discussion of Trust Anchor Preference Options + + This section presents several different policies for validating + resolvers to use when they have a choice of trust anchors available + for validating a given answer. + +C.1. Closest Encloser + + One policy is to choose the trust anchor closest to the QNAME of the + response. For example, consider a validator configured with trust + anchors for "example." and "zone.example." When asked to validate a + response for "www.sub.zone.example.", a validator using the "Closest + + + +Weiler & Blacka Expires November 1, 2012 [Page 18] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + + Encloser" policy would choose the "zone.example." trust anchor. + + This policy has the advantage of allowing the operator to trivially + override a parent zone's trust anchor with one that the operator can + validate in a stronger way, perhaps because the resolver operator is + affiliated with the zone in question. This policy also minimizes the + number of public key operations needed, which is of benefit in + resource-constrained environments. + + This policy has the disadvantage of giving the user some unexpected + and unnecessary validation failures when sub-zone trust anchors are + neglected. As a concrete example, consider a validator that + configured a trust anchor for "zone.example." in 2009 and one for + "example." in 2011. In 2012, "zone.example." rolls its KSK and + updates its DS records, but the validator operator doesn't update its + trust anchor. With the "closest encloser" policy, the validator gets + validation failures. + +C.2. Accept Any Success + + Another policy is to try all applicable trust anchors until one gives + 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 of Insecure, the final validation result is Insecure. If one + or more trust anchors lead to a Bogus result and there is no Secure + result, then the final validation result is Bogus. + + This has the advantage of causing the fewest validation failures, + 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 + get a Secure validation result (and see DNS responses). + + This policy has the disadvantage of making the validator subject to + the compromise of the weakest of these trust anchors while making it + relatively painless to keep old trust anchors configured in + perpetuity. + +C.3. Preference Based on Source + + When the trust anchors have come from different sources (e.g. + automated updates ([RFC5011]), one or more DLV registries + ([RFC5074]), and manually configured), a validator may wish to choose + between them based on the perceived reliability of those sources. + The order of precedence might be exposed as a configuration option. + + For example, a validator might choose to prefer trust anchors found + in a DLV registry over those manually configured on the theory that + the manually configured ones will not be as aggressively maintained. + + + +Weiler & Blacka Expires November 1, 2012 [Page 19] + +Internet-Draft DNSSECbis Implementation Notes April 2012 + + + Conversely, a validator might choose to prefer manually configured + trust anchors over those obtained from a DLV registry on the theory + that the manually configured ones have been more carefully + authenticated. + + Or the validator might do something more complex: prefer a sub-set of + manually configured trust anchors (based on a configuration option), + then trust anchors that have been updated using the RFC5011 + mechanism, then trust anchors from one DLV registry, then trust + anchors from a different DLV registry, then the rest of the manually + configured trust anchors. + + Authors' Addresses Samuel Weiler @@ -1081,9 +1090,9 @@ Authors' Addresses David Blacka - VeriSign, Inc. - 21345 Ridgetop Circle - Dulles, VA 20166 + Verisign, Inc. + 12061 Bluemont Way + Reston, VA 20190 US Email: davidb@verisign.com @@ -1107,14 +1116,5 @@ Authors' Addresses - - - - - - - - - -Weiler & Blacka Expires July 17, 2012 [Page 20] +Weiler & Blacka Expires November 1, 2012 [Page 20]