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diff --git a/contrib/bind9/doc/rfc/rfc4470.txt b/contrib/bind9/doc/rfc/rfc4470.txt deleted file mode 100644 index ac12d65..0000000 --- a/contrib/bind9/doc/rfc/rfc4470.txt +++ /dev/null @@ -1,451 +0,0 @@ - - - - - - -Network Working Group S. Weiler -Request for Comments: 4470 SPARTA, Inc. -Updates: 4035, 4034 J. Ihren -Category: Standards Track Autonomica AB - April 2006 - - - Minimally Covering NSEC Records and DNSSEC On-line Signing - - -Status of This Memo - - This document specifies an Internet standards track protocol for the - Internet community, and requests discussion and suggestions for - improvements. Please refer to the current edition of the "Internet - Official Protocol Standards" (STD 1) for the standardization state - and status of this protocol. Distribution of this memo is unlimited. - -Copyright Notice - - Copyright (C) The Internet Society (2006). - -Abstract - - This document describes how to construct DNSSEC NSEC resource records - that cover a smaller range of names than called for by RFC 4034. By - generating and signing these records on demand, authoritative name - servers can effectively stop the disclosure of zone contents - otherwise made possible by walking the chain of NSEC records in a - signed zone. - -Table of Contents - - 1. Introduction ....................................................1 - 2. Applicability of This Technique .................................2 - 3. Minimally Covering NSEC Records .................................2 - 4. Better Epsilon Functions ........................................4 - 5. Security Considerations .........................................5 - 6. Acknowledgements ................................................6 - 7. Normative References ............................................6 - -1. Introduction - - With DNSSEC [1], an NSEC record lists the next instantiated name in - its zone, proving that no names exist in the "span" between the - NSEC's owner name and the name in the "next name" field. In this - document, an NSEC record is said to "cover" the names between its - owner name and next name. - - - -Weiler & Ihren Standards Track [Page 1] - -RFC 4470 NSEC Epsilon April 2006 - - - Through repeated queries that return NSEC records, it is possible to - retrieve all of the names in the zone, a process commonly called - "walking" the zone. Some zone owners have policies forbidding zone - transfers by arbitrary clients; this side effect of the NSEC - architecture subverts those policies. - - This document presents a way to prevent zone walking by constructing - NSEC records that cover fewer names. These records can make zone - walking take approximately as many queries as simply asking for all - possible names in a zone, making zone walking impractical. Some of - these records must be created and signed on demand, which requires - on-line private keys. Anyone contemplating use of this technique is - strongly encouraged to review the discussion of the risks of on-line - signing in Section 5. - -1.2. Keywords - - The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", - "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this - document are to be interpreted as described in RFC 2119 [4]. - -2. Applicability of This Technique - - The technique presented here may be useful to a zone owner that wants - to use DNSSEC, is concerned about exposure of its zone contents via - zone walking, and is willing to bear the costs of on-line signing. - - As discussed in Section 5, on-line signing has several security - risks, including an increased likelihood of private keys being - disclosed and an increased risk of denial of service attack. Anyone - contemplating use of this technique is strongly encouraged to review - the discussion of the risks of on-line signing in Section 5. - - Furthermore, at the time this document was published, the DNSEXT - working group was actively working on a mechanism to prevent zone - walking that does not require on-line signing (tentatively called - NSEC3). The new mechanism is likely to expose slightly more - information about the zone than this technique (e.g., the number of - instantiated names), but it may be preferable to this technique. - -3. Minimally Covering NSEC Records - - This mechanism involves changes to NSEC records for instantiated - names, which can still be generated and signed in advance, as well as - the on-demand generation and signing of new NSEC records whenever a - name must be proven not to exist. - - - - - -Weiler & Ihren Standards Track [Page 2] - -RFC 4470 NSEC Epsilon April 2006 - - - In the "next name" field of instantiated names' NSEC records, rather - than list the next instantiated name in the zone, list any name that - falls lexically after the NSEC's owner name and before the next - instantiated name in the zone, according to the ordering function in - RFC 4034 [2] Section 6.1. This relaxes the requirement in Section - 4.1.1 of RFC 4034 that the "next name" field contains the next owner - name in the zone. This change is expected to be fully compatible - with all existing DNSSEC validators. These NSEC records are returned - whenever proving something specifically about the owner name (e.g., - that no resource records of a given type appear at that name). - - Whenever an NSEC record is needed to prove the non-existence of a - name, a new NSEC record is dynamically produced and signed. The new - NSEC record has an owner name lexically before the QNAME but - lexically following any existing name and a "next name" lexically - following the QNAME but before any existing name. - - The generated NSEC record's type bitmap MUST have the RRSIG and NSEC - bits set and SHOULD NOT have any other bits set. This relaxes the - requirement in Section 2.3 of RFC4035 that NSEC RRs not appear at - names that did not exist before the zone was signed. - - The functions to generate the lexically following and proceeding - names need not be perfect or consistent, but the generated NSEC - records must not cover any existing names. Furthermore, this - technique works best when the generated NSEC records cover as few - names as possible. In this document, the functions that generate the - nearby names are called "epsilon" functions, a reference to the - mathematical convention of using the greek letter epsilon to - represent small deviations. - - An NSEC record denying the existence of a wildcard may be generated - in the same way. Since the NSEC record covering a non-existent - wildcard is likely to be used in response to many queries, - authoritative name servers using the techniques described here may - want to pregenerate or cache that record and its corresponding RRSIG. - - For example, a query for an A record at the non-instantiated name - example.com might produce the following two NSEC records, the first - denying the existence of the name example.com and the second denying - the existence of a wildcard: - - exampld.com 3600 IN NSEC example-.com ( RRSIG NSEC ) - - \).com 3600 IN NSEC +.com ( RRSIG NSEC ) - - - - - - -Weiler & Ihren Standards Track [Page 3] - -RFC 4470 NSEC Epsilon April 2006 - - - Before answering a query with these records, an authoritative server - must test for the existence of names between these endpoints. If the - generated NSEC would cover existing names (e.g., exampldd.com or - *bizarre.example.com), a better epsilon function may be used or the - covered name closest to the QNAME could be used as the NSEC owner - name or next name, as appropriate. If an existing name is used as - the NSEC owner name, that name's real NSEC record MUST be returned. - Using the same example, assuming an exampldd.com delegation exists, - this record might be returned from the parent: - - exampldd.com 3600 IN NSEC example-.com ( NS DS RRSIG NSEC ) - - Like every authoritative record in the zone, each generated NSEC - record MUST have corresponding RRSIGs generated using each algorithm - (but not necessarily each DNSKEY) in the zone's DNSKEY RRset, as - described in RFC 4035 [3] Section 2.2. To minimize the number of - signatures that must be generated, a zone may wish to limit the - number of algorithms in its DNSKEY RRset. - -4. Better Epsilon Functions - - Section 6.1 of RFC 4034 defines a strict ordering of DNS names. - Working backward from that definition, it should be possible to - define epsilon functions that generate the immediately following and - preceding names, respectively. This document does not define such - functions. Instead, this section presents functions that come - reasonably close to the perfect ones. As described above, an - authoritative server should still ensure than no generated NSEC - covers any existing name. - - To increment a name, add a leading label with a single null (zero- - value) octet. - - To decrement a name, decrement the last character of the leftmost - label, then fill that label to a length of 63 octets with octets of - value 255. To decrement a null (zero-value) octet, remove the octet - -- if an empty label is left, remove the label. Defining this - function numerically: fill the leftmost label to its maximum length - with zeros (numeric, not ASCII zeros) and subtract one. - - In response to a query for the non-existent name foo.example.com, - these functions produce NSEC records of the following: - - - - - - - - - -Weiler & Ihren Standards Track [Page 4] - -RFC 4470 NSEC Epsilon April 2006 - - - fon\255\255\255\255\255\255\255\255\255\255\255\255\255\255 - \255\255\255\255\255\255\255\255\255\255\255\255\255\255\255 - \255\255\255\255\255\255\255\255\255\255\255\255\255\255\255 - \255\255\255\255\255\255\255\255\255\255\255\255\255\255\255 - \255.example.com 3600 IN NSEC \000.foo.example.com ( NSEC RRSIG ) - - \)\255\255\255\255\255\255\255\255\255\255\255\255\255\255\255 - \255\255\255\255\255\255\255\255\255\255\255\255\255\255\255 - \255\255\255\255\255\255\255\255\255\255\255\255\255\255\255 - \255\255\255\255\255\255\255\255\255\255\255\255\255\255\255 - \255\255.example.com 3600 IN NSEC \000.*.example.com ( NSEC RRSIG ) - - The first of these NSEC RRs proves that no exact match for - foo.example.com exists, and the second proves that there is no - wildcard in example.com. - - Both of these functions are imperfect: they do not take into account - constraints on number of labels in a name nor total length of a name. - As noted in the previous section, though, this technique does not - depend on the use of perfect epsilon functions: it is sufficient to - test whether any instantiated names fall into the span covered by the - generated NSEC and, if so, substitute those instantiated owner names - for the NSEC owner name or next name, as appropriate. - -5. Security Considerations - - This approach requires on-demand generation of RRSIG records. This - creates several new vulnerabilities. - - First, on-demand signing requires that a zone's authoritative servers - have access to its private keys. Storing private keys on well-known - Internet-accessible servers may make them more vulnerable to - unintended disclosure. - - Second, since generation of digital signatures tends to be - computationally demanding, the requirement for on-demand signing - makes authoritative servers vulnerable to a denial of service attack. - - Last, if the epsilon functions are predictable, on-demand signing may - enable a chosen-plaintext attack on a zone's private keys. Zones - using this approach should attempt to use cryptographic algorithms - that are resistant to chosen-plaintext attacks. It is worth noting - that although DNSSEC has a "mandatory to implement" algorithm, that - is a requirement on resolvers and validators -- there is no - requirement that a zone be signed with any given algorithm. - - The success of using minimally covering NSEC records to prevent zone - walking depends greatly on the quality of the epsilon functions - - - -Weiler & Ihren Standards Track [Page 5] - -RFC 4470 NSEC Epsilon April 2006 - - - chosen. An increment function that chooses a name obviously derived - from the next instantiated name may be easily reverse engineered, - destroying the value of this technique. An increment function that - always returns a name close to the next instantiated name is likewise - a poor choice. Good choices of epsilon functions are the ones that - produce the immediately following and preceding names, respectively, - though zone administrators may wish to use less perfect functions - that return more human-friendly names than the functions described in - Section 4 above. - - Another obvious but misguided concern is the danger from synthesized - NSEC records being replayed. It is possible for an attacker to - replay an old but still validly signed NSEC record after a new name - has been added in the span covered by that NSEC, incorrectly proving - that there is no record at that name. This danger exists with DNSSEC - as defined in [3]. The techniques described here actually decrease - the danger, since the span covered by any NSEC record is smaller than - before. Choosing better epsilon functions will further reduce this - danger. - -6. Acknowledgements - - Many individuals contributed to this design. They include, in - addition to the authors of this document, Olaf Kolkman, Ed Lewis, - Peter Koch, Matt Larson, David Blacka, Suzanne Woolf, Jaap Akkerhuis, - Jakob Schlyter, Bill Manning, and Joao Damas. - - In addition, the editors would like to thank Ed Lewis, Scott Rose, - and David Blacka for their careful review of the document. - -7. Normative References - - [1] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, - "DNS Security Introduction and Requirements", RFC 4033, March - 2005. - - [2] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, - "Resource Records for the DNS Security Extensions", RFC 4034, - March 2005. - - [3] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, - "Protocol Modifications for the DNS Security Extensions", RFC - 4035, March 2005. - - [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement - Levels", BCP 14, RFC 2119, March 1997. - - - - - -Weiler & Ihren Standards Track [Page 6] - -RFC 4470 NSEC Epsilon April 2006 - - -Authors' Addresses - - Samuel Weiler - SPARTA, Inc. - 7075 Samuel Morse Drive - Columbia, Maryland 21046 - US - - EMail: weiler@tislabs.com - - - Johan Ihren - Autonomica AB - Bellmansgatan 30 - Stockholm SE-118 47 - Sweden - - EMail: johani@autonomica.se - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Weiler & Ihren Standards Track [Page 7] - -RFC 4470 NSEC Epsilon April 2006 - - -Full Copyright Statement - - Copyright (C) The Internet Society (2006). - - This document is subject to the rights, licenses and restrictions - contained in BCP 78, and except as set forth therein, the authors - retain all their rights. - - This document and the information contained herein are provided on an - "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS - OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET - ENGINEERING TASK FORCE DISCLAIM 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. - -Intellectual Property - - The IETF takes no position regarding the validity or scope of any - Intellectual Property Rights or other rights that might be claimed to - pertain to the implementation or use of the technology described in - this document or the extent to which any license under such rights - might or might not be available; nor does it represent that it has - made any independent effort to identify any such rights. Information - on the procedures with respect to rights in RFC documents can be - found in BCP 78 and BCP 79. - - Copies of IPR disclosures made to the IETF Secretariat and any - assurances of licenses to be made available, or the result of an - attempt made to obtain a general license or permission for the use of - such proprietary rights by implementers or users of this - specification can be obtained from the IETF on-line IPR repository at - http://www.ietf.org/ipr. - - The IETF invites any interested party to bring to its attention any - copyrights, patents or patent applications, or other proprietary - rights that may cover technology that may be required to implement - this standard. Please address the information to the IETF at - ietf-ipr@ietf.org. - -Acknowledgement - - Funding for the RFC Editor function is provided by the IETF - Administrative Support Activity (IASA). - - - - - - - -Weiler & Ihren Standards Track [Page 8] - |
