DNSEXT (Independent submission) O. Kolkman Internet-Draft RIPE NCC Expires: March 2, 2003 J. Ihren Autonomica R. Arends A.R.E.N.D.S. September 2002 DNSSEC Wildcard Optimization draft-olaf-dnsext-dnssec-wildcard-optimization-01.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March 2, 2003. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract Secure denial of the existence of wildcards may lead to a large number of NXT RRs and associated SIG RRs in DNS responses, even in the common case when wildcards are not present in the zone. This optimization uses one bit from the NXT type array to signal that there is no closer wildcard in the zone for a given query name. This reduces the packet size and the need for executing slow, and complicated, code paths in common queries. In cases where there are no wildcard RRs in the zone (i.e. the root zone) only one NXT RR and Kolkman, et al. Expires March 2, 2003 [Page 1] Internet-Draft DNSSEC Wildcard Optimization September 2002 corresponding SIG is needed for denial of existence of the wildcard. The key words "MAY","MAY NOT", "MUST", "MUST NOT", "REQUIRED", "RECOMMENDED", "SHOULD", and "SHOULD NOT" in this document are to be interpreted as described in RFC2119. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 RFC2535 Wildcard Processing . . . . . . . . . . . . . . . . 3 1.2 Signalling the Existence of a Wildcard . . . . . . . . . . . 3 2. DNSSEC Protocol Changes . . . . . . . . . . . . . . . . . . 4 2.1 Server Side . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.1 Zone Signing . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.2 Server Responses . . . . . . . . . . . . . . . . . . . . . . 4 2.1.3 Dynamic DNS . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Resolver Side . . . . . . . . . . . . . . . . . . . . . . . 5 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . 6 5. Internationalization Considerations . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. Document Changes . . . . . . . . . . . . . . . . . . . . . . 6 7.1 draft 00->01 . . . . . . . . . . . . . . . . . . . . . . . . 6 Normative References . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 7 A. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8 A.1 Zone without wildcards . . . . . . . . . . . . . . . . . . . 8 A.1.1 Optimized proof . . . . . . . . . . . . . . . . . . . . . . 8 A.1.2 RFC2535 proof . . . . . . . . . . . . . . . . . . . . . . . 8 A.2 Zone with wildcards . . . . . . . . . . . . . . . . . . . . 9 A.2.1 Optimized proof . . . . . . . . . . . . . . . . . . . . . . 10 A.2.2 NXDOMAIN with additional proof for no wildcard . . . . . . . 10 A.2.3 Another Optimized Proof . . . . . . . . . . . . . . . . . . 11 A.2.4 Denial of Existence of Closer Match . . . . . . . . . . . . 11 A.2.5 The NXT 'next name' Proving Existence of a Wildcard . . . . 12 Full Copyright Statement . . . . . . . . . . . . . . . . . . 13 Kolkman, et al. Expires March 2, 2003 [Page 2] Internet-Draft DNSSEC Wildcard Optimization September 2002 1. Introduction Wildcards make authenticated denial of existence complex. Many zones do not contain wildcards but still incur a penalty. If the NXT RR contains an indication that a wildcard match can not exist then less DNSSEC related RRs and less computation are needed to authoritatively deny the existence of a name in the zone. 1.1 RFC2535 Wildcard Processing RFC2535 [1] specifies that the non-existence of a match against a wildcard is proven by a set of relevant NXT records. In practice this will result to at least 2 NXT RRs and corresponding SIGs being returned. There are cases where the denial of the existence of wildcards will need many more than 2 NXT RRs. Even in zones that do not use wildcards this will lead to complex answers for which the resolvers will need to follow NXT chains and which are hard to troubleshoot by operators. 1.2 Signalling the Existence of a Wildcard The NXT RR, used to the prove the non-existence of data, uses a type bit-map to track which types are available for a given name. We propose to use one bit (see section Section 3) in the type bitmap to signal if a wildcard is available in a zone. We refer to this bit as the "NOWILD-bit". If the NOWILD-bit is set to 1 then the NXT RR signals that there is no wildcard match possible against the query name, only if the bit is set to 0 further processing needs to be done. For zones without wildcards the NOWILD-bit MAY always be set to 1. The following optimizations are realized: o Servers and resolvers will only have to execute a slow and somewhat complicated code paths if wildcard are present in the zone. o Packet size of answers reduce in most common cases; for the root zone the authority section only contains one NXT RR with associated SIGs instead of two NXT RRs with associated SIGs. o In case of absence of wildcards-matches answers will be easier to interpret by human operators troubleshooting responses; Kolkman, et al. Expires March 2, 2003 [Page 3] Internet-Draft DNSSEC Wildcard Optimization September 2002 2. DNSSEC Protocol Changes This is an update to the RFC2535 protocol. Resolvers MUST implement these changes. Servers MAY implement these changes. 2.1 Server Side 2.1.1 Zone Signing Servers that implement the optimization MAY perform the following actions at zone signing time. At zone signing time, when the NXT RRs are generated, the NOWILD-bit MUST be set to 0 if for an ownername 'label(j).label(j-1).label(j-2) ... label(0).' there is no wildcard name '*.label(i).label(i-1) ... label(0).' in the zone for all i < j. In other words the label is set to 0 if there exists a wildcard that would match QNAME=ownername while ignoring the possible existence of a domain name between the ownername and the wildcard domain. For all other ownernames the bit MUST be set to 1. If, because of implementation or policy issues, the algorithm in the previous paragraph is not applied then the bit MUST be set to 0 for all NXT RRs in the zone. Servers that do do not implement the optimization have already set their NOWILD bit to 0 by virtue of the requirements of RFC2535 section 5.2. When the algorithm is applied a NXT RR that proves the non-existence of a full match of the QNAME will also prove, when it's NOWILD-bit is set to 1, that there is no match of the QNAME to any wildcard that may exist in the zone 2.1.2 Server Responses When queried for a name for which there is no match, i.e. no full and no wildcard match, in the zone: o Servers MUST return the NXT RR that proves the non-existence of the query name in the NXDOMAIN response. If there is no match for a wildcard and the NOWILD-bit is set to 1 at signing time and the one NXT RR is sufficient. If the NOWILD-bit for the NXT RR that proves non-existence of the query name is set to 0 then NXT RRs that prove the non-existence of possible wildcard matches MUST be returned as well. When queried for a name for which there is a match in the zone: o If the match is an exact match than no NXT RRs are returned in the Kolkman, et al. Expires March 2, 2003 [Page 4] Internet-Draft DNSSEC Wildcard Optimization September 2002 additional section. o Servers for zones that contain one or more wildcards MUST return the NXT RRs that prove the non-existence of the exact match. They must also provide proof that there is no closer match for the QNAME than the match returned in the answer section. The proof algorithm for non-existence of wildcards, an exact match or closer matches conforms to RFC2535. 2.1.3 Dynamic DNS When dynamically adding or removing a name that does not contains wildcards, the 'next name' for the name immediately above the inserted, or deleted name needs to be updated. The NOWILD bit of the inserted name is to be set according to the procedure as described in Section 2.1.1. Except for setting the NOWILD bit this is similar to the RFC2535 procedure. If a name containing a wildcard is deleted from a zone one has to verify if, for all names in the zone with the bit set to 0, the NOWILD bit can be toggled. If a name containing a wildcard is added one has to verify if, for all the names in the zone, the bit needs to be set to 0. The NOWILD bit is not to be modified during an update of a name that already exists in the zone. Dynamic updates of names that contain wildcards may lead to performance penalties for large dynamic zones and one MAY therefore choose not to perform the NOWILD optimization for dynamic zones. 2.2 Resolver Side When receiving an answer to a query a resolver MUST assess if the answer is a result of a wildcard match. If the result is an exact match then there will be no NXT RRs in the authority section. If the answer is a wildcard match then the resolver will need to verify that the exact name does not exist. The NXT RRs in the additional section, which per definition have their NOWILD-bit set to 0, will need to prove that there is no closer match. ( conforming to RFC2535). If the response is NXDOMAIN (i.e. no match at all) then the resolver MUST verify if the NXT RR proves the non-existence of the exact match in the zone. No further NXT RRs are needed if the NXT RR has it's NOWILD-bit set to 1. A DNS packet containing an NXDOMAIN response Kolkman, et al. Expires March 2, 2003 [Page 5] Internet-Draft DNSSEC Wildcard Optimization September 2002 accompanied by a NXT RR that has it's NOWILD-bit set to 0 will need to contain proof that there are no wildcard matches against the QNAME (conforming to RFC2535 ). The NXT data and the NOWILD-bit together supply the proof on the non- existence of a wildcard. There is one situation where the NOWILD-bit is set to 1 but the NXT's 'next name' proves that there is a wildcard. This is when the 'next name' itself contains a wildcard. Resolvers that verify NXDOMAIN replies MUST verify the NXT 'next name' first before the NOWILD-bit. Also see example Appendix A.2.5. The fact that resolvers that obtain an answer with a NXT RR's NOWILD set to 1 do not receive additional proof for the non-existence of wildcards is incompatible with RFC2535. 3. IANA Considerations Although there is no RR record associated the NOWILD-bit. The value of the bit must be registered as a DNS RR-type. To not cause the NXT type bitmap to grow beyond 4 octets unnecessary we propose to reuse type code 31 (the EID type code is undocumented). 4. Security Considerations The draft provides an optimization for wildcard handling. Resolvers MUST verify for the denial of existence of matches or the denial of existence of closer matches when an answer is returned and the NOWILD-bit is set to 0. 5. Internationalization Considerations There are no internationalization considerations. 6. Acknowledgements Olafur Gudmundsson, Daniel Karrenberg and Ed Lewis for providing critique and input on earlier versions of this document. 7. Document Changes 7.1 draft 00->01 Reordered and reworded the 'protocol changes' section. We tried to make the fact that resolvers must and servers may implement this optimization more explicit. Change from using the SIG bit to another bit in the NXT type- bitmap, changed the name of the bit and added IANA considerations. Kolkman, et al. Expires March 2, 2003 [Page 6] Internet-Draft DNSSEC Wildcard Optimization September 2002 Note that the meaning of the bit being set and unset are changed because of the default setting. Because of the fact that we want to maintain backward compatibility with servers that do not implement this bit and the bit in the typemap is currently set to 0 the default behaviour should be follow old-style NXT proof. Corrected mistakes in the examples. Various style and spelling corrections. Normative References [1] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. Authors' Addresses Olaf M. Kolkman RIPE NCC Singel 256 1016 AB Amsterdam NL Phone: +31 20 535 4444 EMail: olaf@ripe.net URI: http://www.ripe.net/ Johan Ihren Autonomica Bellmansgatan 30 SE-118 47 Stockholm SE EMail: johani@autonomica.se Roy Arends A.R.E.N.D.S. Bankastraat 41-e 1094 EB Amsterdam NL Phone: +31206931681 EMail: Roy@logmess.com Kolkman, et al. Expires March 2, 2003 [Page 7] Internet-Draft DNSSEC Wildcard Optimization September 2002 Appendix A. Examples A.1 Zone without wildcards In the following example zone file there are no wildcards. All NOWILD bits are set to 1. The actual SIG RRs and the KEY RRs are left out from the zone data and type bitmaps for clarity only. $ORIGIN example. @ IN SOA @ NXT a SOA NXT NOWILD ; NOWILD-bit set to 1 a A 10.0.0.1 a NXT a.b A NXT NOWILD ; NOWILD-bit set to 1 a.b A 10.0.0.2 a.b NXT a.c A NXT NOWILD ; NOWILD-bit set to 1 a.c A 10.0.0.4 a.c NXT a.b.c A NXT NOWILD ; NOWILD-bit set to 1 a.b.c A 10.0.0.5 a.b.c NXT f A NXT NOWILD ; NOWILD-bit set to 1 f A 10.0.0.6 f NXT @ A NXT NOWILD ; NOWILD-bit set to 1 A.1.1 Optimized proof A query for any existing name will return a signed answer without NXT RRs in the authority section. A query for any non existing name will only return 1 NXT RR proving the non-existence of the QNAME in the zone and, by virtue of the NOWILD-bit being 1, this is sufficient proof there is no wildcard. QNAME= d.b.c.example. QTYPE=A RCODE=NXDOMAIN ;; Authority example. SOA SIG SOA a.b.c.example. NXT f.example. A NXT NOWILD SIG NXT ;; Additional (... skipped ... ) A.1.2 RFC2535 proof For comparison we supply the same answer without the optimization applied i.e. NOWILD set to 0 for all NXT RRs in the zone. The answer needs to contain prove that *.b.c.example, *.c.example and Kolkman, et al. Expires March 2, 2003 [Page 8] Internet-Draft DNSSEC Wildcard Optimization September 2002 *.example do not exist, unless a name that exists in the zone terminates the possible match of those wildcards against the QNAME. QNAME= d.b.c.example. QTYPE=A RCODE=NXDOMAIN ;; Authority example. SOA SIG SOA a.b.c.example. NXT f.example. A NXT SIG NXT ; proofs non-existence of exact match. a.c.example. NXT a.b.c.example. A NXT SIG NXT ; proofs non-existence of *.b.c.example. ;; Additional (... skipped ... ) Note that the existence of 'a.b.c.example NXT' RR terminates a wildcard match of QNAME against *.c.example. and *.example. So the answer packet does not need to contain further proof for the non- existence of those wildcards. However, a resolver will have to execute logic to verify that the existence of 'a.b.c.example.' terminates the possible match of the QNAME against the possible wildcards and that the answer is therefore complete. A.2 Zone with wildcards In the following example zone file there is a wildcard. Some NOWILD bits are set to 1, others for which there is no wildcard in the zone if the leftmost labels are chopped off, have there NOWILD-bit set to 0. The actual SIG RRs and the KEY RRs at the apex are left out for clarity. The queries for which a wildcard match is returned will have the NOWILD-bit set to 0, there proof for the non-existing closer match is to be supplied and checked by the resolver. Kolkman, et al. Expires March 2, 2003 [Page 9] Internet-Draft DNSSEC Wildcard Optimization September 2002 $ORIGIN example. @ IN SOA @ NXT a SOA NXT NOWILD ; NOWILD-bit set to 1 a A 10.0.0.1 a NXT a.b A NXT NOWILD ; NOWILD-bit set to 1 a.b A 10.0.0.2 a.b NXT *.c A NXT NOWILD ; NOWILD-bit set to 1 *.c A 10.0.0.3 *.c NXT a.c A NXT SIG ; NOWILD-bit set to 0 a.c A 10.0.0.4 a.c NXT a.b.c A NXT SIG ; NOWILD-bit set to 0 a.b.c A 10.0.0.5 a.b.c NXT f A NXT SIG ; NOWILD-bit set to 0 f A 10.0.0.6 f NXT @ A NXT NOWILD ; NOWILD-bit set to 1 A.2.1 Optimized proof QNAME= c.a.a.example. QTYPE=A RCODE=NXDOMAIN ;; Authority example. SOA SIG SOA a.example. NXT a.b.example. A NXT SIG NOWILD ; NOWILD-bit set to 1 proves no full ; match and no wildcards that match ; QNAME SIG NXT ;; Additional (... skipped ... ) A.2.2 NXDOMAIN with additional proof for no wildcard The following example contains a NXDOMAIN answer and the proof that there is no wildcard match. Kolkman, et al. Expires March 2, 2003 [Page 10] Internet-Draft DNSSEC Wildcard Optimization September 2002 QNAME= e.example. QTYPE=A RCODE=NXDOMAIN ;; Authority example.example SOA SIG SOA a.b.c.example. NXT f.example. A NXT SIG ; NOWILD-bit set to 0, ; proves no full match SIG NXT example. NXT a.example A NXT SIG NOWILD ; NOWILD-bit set to 1, ; proves no *.example. ;; Additional (... skipped ... ) A.2.3 Another Optimized Proof The following example contains a NXDOMAIN answer and the proof that there is no wildcard match. In this particular case the proof is optimized because of the NOWILD-bit on the f NXT RR being set to zero. QNAME= g.example. QTYPE=A RCODE=NXDOMAIN ;; Authority example.example SOA SIG SOA f.example. NXT example. A NXT NOWILD ; NOWILD-bit set to 1 ; proves no full match ;; Additional (... skipped ... ) A.2.4 Denial of Existence of Closer Match The following example contains an answer with wildcard expansion and the proof that there is no closer match. This is similar to a RFC2535 proof of non-existence. Kolkman, et al. Expires March 2, 2003 [Page 11] Internet-Draft DNSSEC Wildcard Optimization September 2002 QNAME= d.b.c.example. QTYPE=A RCODE=ANSWER ;; Answer d.b.c.example. A 10.0.0.3 ; expansion of *.c SIG A (labelcount=2) ; labelcount proofs wildcard ; example ;; Authority example.example. SOA SIG SOA a.b.c.example. NXT f.example. A NXT SIG ; NOWILD-bit set to 0, ; proves no exact match, SIG NXT a.c.example. NXT a.b.c.example. A NXT SIG ; NOWILD-bit set to 0 ; proves non-existence of ; *.b.c.example. ; No further proofs needed ;; Additional (... skipped ... ) A.2.5 The NXT 'next name' Proving Existence of a Wildcard In the zone above the a.b NXT RR has it's NOWILD-bit set to 1. If one would query for '#.c' which canonically orders between a.b and *.c one would get back "a.b NXT *.c". A attacker can use the this NXT RR in a malformed NXDOMAIN response. QNAME= #.c.example. QTYPE=A RCODE=NXDOMAIN ; Black hat answer !!!! ;; Authority example.example SOA SIG SOA a.b.example. NXT *.c.example. A NXT NOWILD ; NOWILD-bit set to 1 ; but *.c exists Kolkman, et al. Expires March 2, 2003 [Page 12] Internet-Draft DNSSEC Wildcard Optimization September 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Kolkman, et al. Expires March 2, 2003 [Page 13]