DNSEXT O. Kolkman Internet-Draft RIPE NCC Expires: March 21, 2003 J. Ihren Autonomica R. Arends A.R.E.N.D.S. September 20, 2002 DNSSEC Wildcard optimization draft-olaf-dnsext-dnssec-wildcard-optimization-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 21, 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. te root zone) only one NXT RR and Kolkman, et al. Expires March 21, 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 Signaling the existence of a wildcard . . . . . . . . . . . 3 2. DNSSEC Protocol changes . . . . . . . . . . . . . . . . . . 4 2.1 Server responses . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Resolver actions . . . . . . . . . . . . . . . . . . . . . . 4 3. Security considerations . . . . . . . . . . . . . . . . . . 5 4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 5 References . . . . . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 6 A. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6 A.1 Zone without wildcards . . . . . . . . . . . . . . . . . . . 6 A.2 Zone with wildcards . . . . . . . . . . . . . . . . . . . . 7 A.2.1 Optimized proof . . . . . . . . . . . . . . . . . . . . . . 8 A.2.2 NXDOMAIN with additional proof for no wildcard . . . . . . . 8 A.2.3 Another optimized proof . . . . . . . . . . . . . . . . . . 9 A.2.4 Denial of existence of close match . . . . . . . . . . . . . 9 A.2.5 The NXT dname proving existence of a wildcard . . . . . . . 10 Full Copyright Statement . . . . . . . . . . . . . . . . . . 11 Kolkman, et al. Expires March 21, 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 a 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] dictates that the non-existence of a match against a wildcard is proven by a set of number 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 Signaling 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. Since a SIG and a NXT RR are always returned in a DNSSEC response both of these bits are available for other signaling purposes. We propose to use the 24th (SIG) bit in the type bitmap to signal if a wildcard is available in a zone. We refer to this bit as the NTAS bit (NXT type array sig bit). If the NTAS bit is set to 0 then the NXT RR signals that there is no wildcard match possible against the query name, only if the bit is set to 1 then further processing needs to be done. For zones without wildcards the NTAS bit will always be set to 0. 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 1 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 21, 2003 [Page 3] Internet-Draft DNSSEC Wildcard optimization September 2002 2. DNSSEC Protocol changes This is an update to the RFC2535 protocol. It is not backwards compatible. At zone signing time, when the NXT RRs are generated, the NTAS bit MUST be set to zero when the owner name has the following property: there exists a wildcard for the owner name(s) in this zone with the leftmost label(s) chopped off. In other words, if the owner name of the NXT RR is label(j).label(j-1).label(j-2) ... label(0) then the NTAS bit is set to 1 if *.label(i).label(i-1)...label(0) exists for any i < j. For all other NXT RRs the NTAS bit is set to 1. A NXT RR that proves the non-existence of a full match of the QNAME will also prove that there is no match of the QNAME to any wildcard that may exist in the zone if the NTAS bit is set to 0. 2.1 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 then the NTAS bit is per definition set to 0 at signing time and the 1 NXT RR is sufficient (more NXT RRs MAY NOT be supplied). If the NTAS bit for the NXT RR that proves non- existence of the queryname is set to 1 then NXT RRs that prove the non-existence of possible wildcard matches MUST be returned as well. The proof algorithm conforms to RFC2535. 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 additional section (conforming to RFC2535). 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. 2.2 Resolver actions Resolvers that receive a packet to a given query MUST, in case of a If the match is a wildcard match then the resolver will need to Kolkman, et al. Expires March 21, 2003 [Page 4] Internet-Draft DNSSEC Wildcard optimization September 2002 verify that the exact name does not exist. The NXT RR that supplies this proof will, per definition, have it's NTAS bit set to 1. Additional NXT RRs will need to prove that there is no closer match. (again 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 NTAS bit set to 0. A DNS packet containing an NXDOMAIN response accompanied by a NXT RR that has it's NTAS bit set to 1 will need to contain proof that there are no wildcard matches against the QNAME (conforming to RFC2535). The NXT data and the NTAS bit together supply the proof on the non- existence of a wildcard. There is one situation where the NTAS bit is set to 0 but the NXT dname proves that there is a wildcard. This is when the dname itself contains a wildcard. Resolvers that verify NXDOMAIN replies MUST verify the NXT dname first before the NTAS bit. Also see example Appendix A.2.5. Note that the NXT RR might have their NTAS bit set to 0 but may by virtue of the dname in the RDATA proof that there must be a wildcard match. 3. Security considerations The draft provides an optimization for wildcard handling. Resolvers MUST carefully check for the denial of existence of matches or the denial of existence of closer matches when an answer is returned and the NTAS bit is set to 1. 4. Acknowledgments Daniel Karrenberg for providing a number of comments on earlier versions of this document. References [1] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. Kolkman, et al. Expires March 21, 2003 [Page 5] Internet-Draft DNSSEC Wildcard optimization September 2002 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 Appendix A. Examples A.1 Zone without wildcards In the following example zone file there are no wildcards. All NTAS bits are set to zero (SIG does not occur in the type bitmap.) The actual SIG RRs and the KEY RRs at the apex are left out for clarity. Kolkman, et al. Expires March 21, 2003 [Page 6] Internet-Draft DNSSEC Wildcard optimization September 2002 $ORIGIN example. @ IN SOA @ NXT a SOA NXT ; NTAS bit set to 0 a A 10.0.0.1 a NXT a.b A NXT ; NTAS bit set to 0 a.b A 10.0.0.2 a.b NXT a.c A NXT ; NTAS bit set to 0 a.c A 10.0.0.4 a.c NXT a.b.c A NXT ; NTAS bit set to 0 a.b.c A 10.0.0.5 a.b.c NXT f A NXT ; NTAS bit set to 0 f A 10.0.0.6 f NXT @ A NXT ; NTAS bit set to 0 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 NTAS bit bing 0, 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 SIG NXT ;; Additional (... skipped ... ) A.2 Zone with wildcards In the following example zone file there are two wildcards. Some NTAS bits are set to 1, others for which there is no wildcard in the zone if the leftmost labels are chopped off, have there NTAS 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 NTAS bit set to 1, there proof for the non-existing closer match is to be supplied and checked by the resolver. Kolkman, et al. Expires March 21, 2003 [Page 7] Internet-Draft DNSSEC Wildcard optimization September 2002 $ORIGIN example. @ IN SOA @ NXT a SOA NXT ; NTAS bit set to 0 a A 10.0.0.1 a NXT a.b A NXT ; NTAS bit set to 0 a.b A 10.0.0.2 a.b NXT *.c A NXT ; NTAS bit set to 0 *.c A 10.0.0.3 *.c NXT a.c A NXT SIG ; NTAS bit set to 1 a.c A 10.0.0.4 a.c NXT a.b.c A NXT SIG ; NTAS bit set to 1 a.b.c A 10.0.0.5 a.b.c NXT f A NXT SIG ; NTAS bit set to 1 f A 10.0.0.6 f NXT @ A NXT ; NTAS bit set to 0 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 ; NTAS bit set to 0 ; 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 21, 2003 [Page 8] 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 ; NTAS bit set to 1, ; proves no full match SIG NXT a.c.example. NXT a.b.c.example A NXT SIG ; NTAS bit set to 1, ; proves no *.b.c.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 NTAS 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 ; NTAS bit set to 0 ; proves no full match ;; Additional (... skipped ... ) A.2.4 Denial of existence of close 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 21, 2003 [Page 9] Internet-Draft DNSSEC Wildcard optimization September 2002 QNAME= d.b.c.example. QTYPE=A RCODE=ANSWER ;; Answer a.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 ; NTAS bit set to 1, ; proves no full match, SIG NXT example. NXT a.example. A NXT ; NTAS bit set to 0 ; proves no *.example. SIG NXT ;; Additional (... skipped ... ) A.2.5 The NXT dname proving existence of a wildcard In the zone above the a.b NXT RR has it's NTAS bit set to 0. 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 ; NTAS bit set to 0 ; but *.c exists Kolkman, et al. Expires March 21, 2003 [Page 10] 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. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Kolkman, et al. Expires March 21, 2003 [Page 11]