Network Working Group                                      B. WellingtonRequest for Comments: 3008                                       NominumUpdates: 2535                                              November 2000Category: Standards Track         Domain Name System Security (DNSSEC) Signing AuthorityStatus 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 (2000).  All Rights Reserved.Abstract   This document proposes a revised model of Domain Name System Security   (DNSSEC) Signing Authority.  The revised model is designed to clarify   earlier documents and add additional restrictions to simplify the   secure resolution process.  Specifically, this affects the   authorization of keys to sign sets of records.   The key words "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 [RFC2119].1 - Introduction   This document defines additional restrictions on DNSSEC signatures   (SIG) records relating to their authority to sign associated data.   The intent is to establish a standard policy followed by a secure   resolver; this policy can be augmented by local rules.  This builds   upon [RFC2535], updating section 2.3.6 of that document.   The most significant change is that in a secure zone, zone data is   required to be signed by the zone key.   Familiarity with the DNS system [RFC1034, RFC1035] and the DNS   security extensions [RFC2535] is assumed.Wellington                  Standards Track                     [Page 1]RFC 3008                DNSSEC Signing Authority           November 20002 - The SIG Record   A SIG record is normally associated with an RRset, and "covers" (that   is, demonstrates the authenticity and integrity of) the RRset.  This   is referred to as a "data SIG".  Note that there can be multiple SIG   records covering an RRset, and the same validation process should be   repeated for each of them.  Some data SIGs are considered "material",   that is, relevant to a DNSSEC capable resolver, and some are   "immaterial" or "extra-DNSSEC", as they are not relevant to DNSSEC   validation.  Immaterial SIGs may have application defined roles.  SIG   records may exist which are not bound to any RRset; these are also   considered immaterial.  The validation process determines which SIGs   are material; once a SIG is shown to be immaterial, no other   validation is necessary.   SIGs may also be used for transaction security.  In this case, a SIG   record with a type covered field of 0 is attached to a message, and   is used to protect message integrity.  This is referred to as a   SIG(0) [RFC2535, RFC2931].   The following sections define requirements for all of the fields of a   SIG record.  These requirements MUST be met in order for a DNSSEC   capable resolver to process this signature.  If any of these   requirements are not met, the SIG cannot be further processed.   Additionally, once a KEY has been identified as having generated this   SIG, there are requirements that it MUST meet.2.1 - Type Covered   For a data SIG, the type covered MUST be the same as the type of data   in the associated RRset.  For a SIG(0), the type covered MUST be 0.2.2 - Algorithm Number   The algorithm specified in a SIG MUST be recognized by the client,   and it MUST be an algorithm that has a defined SIG rdata format.2.3 - Labels   The labels count MUST be less than or equal to the number of labels   in the SIG owner name, as specified in [RFC2535, section 4.1.3].2.4 - Original TTL   The original TTL MUST be greater than or equal to the TTL of the SIG   record itself, since the TTL cannot be increased by intermediate   servers.  This field can be ignored for SIG(0) records.Wellington                  Standards Track                     [Page 2]RFC 3008                DNSSEC Signing Authority           November 20002.5 - Signature Expiration and Inception   The current time at the time of validation MUST lie within the   validity period bounded by the inception and expiration times.2.6 - Key Tag   There are no restrictions on the Key Tag field, although it is   possible that future algorithms will impose constraints.2.7 - Signer's Name   The signer's name field of a data SIG MUST contain the name of the   zone to which the data and signature belong.  The combination of   signer's name, key tag, and algorithm MUST identify a zone key if the   SIG is to be considered material.  The only exception that the   signer's name field in a SIG KEY at a zone apex SHOULD contain the   parent zone's name, unless the KEY set is self-signed.  This document   defines a standard policy for DNSSEC validation; local policy may   override the standard policy.   There are no restrictions on the signer field of a SIG(0) record.   The combination of signer's name, key tag, and algorithm MUST   identify a key if this SIG(0) is to be processed.2.8 - Signature   There are no restrictions on the signature field.  The signature will   be verified at some point, but does not need to be examined prior to   verification unless a future algorithm imposes constraints.3 - The Signing KEY Record   Once a signature has been examined and its fields validated (but   before the signature has been verified), the resolver attempts to   locate a KEY that matches the signer name, key tag, and algorithm   fields in the SIG.  If one is not found, the SIG cannot be verified   and is considered immaterial.  If KEYs are found, several fields of   the KEY record MUST have specific values if the SIG is to be   considered material and authorized.  If there are multiple KEYs, the   following checks are performed on all of them, as there is no way to   determine which one generated the signature until the verification is   performed.Wellington                  Standards Track                     [Page 3]RFC 3008                DNSSEC Signing Authority           November 20003.1 - Type Flags   The signing KEY record MUST have a flags value of 00 or 01   (authentication allowed, confidentiality optional) [RFC2535, 3.1.2].   A DNSSEC resolver MUST only trust signatures generated by keys that   are permitted to authenticate data.3.2 - Name Flags   The interpretation of this field is considerably different for data   SIGs and SIG(0) records.3.2.1 - Data SIG   If the SIG record covers an RRset, the name type of the associated   KEY MUST be 01 (zone) [RFC2535, 3.1.2].  This updates RFC 2535,   section 2.3.6.  The DNSSEC validation process performed by a resolver   MUST ignore all keys that are not zone keys unless local policy   dictates otherwise.   The primary reason that RFC 2535 allows host and user keys to   generate material DNSSEC signatures is to allow dynamic update   without online zone keys; that is, avoid storing private keys in an   online server.  The desire to avoid online signing keys cannot be   achieved, though, because they are necessary to sign NXT and SOA sets   [RFC3007].  These online zone keys can sign any incoming data.   Removing the goal of having no online keys removes the reason to   allow host and user keys to generate material signatures.   Limiting material signatures to zone keys simplifies the validation   process.  The length of the verification chain is bounded by the   name's label depth.  The authority of a key is clearly defined; a   resolver does not need to make a potentially complicated decision to   determine whether a key has the proper authority to sign data.   Finally, there is no additional flexibility granted by allowing   host/user key generated material signatures.  As long as users and   hosts have the ability to authenticate update requests to the primary   zone server, signatures by zone keys are sufficient to protect the   integrity of the data to the world at large.3.2.2 - SIG(0)   If the SIG record is a SIG(0) protecting a message, the name type of   the associated KEY SHOULD be 00 (user) or 10 (host/entity).   Transactions are initiated by a host or user, not a zone, so zone   keys SHOULD not generate SIG(0) records.Wellington                  Standards Track                     [Page 4]RFC 3008                DNSSEC Signing Authority           November 2000   A client is either explicitly executed by a user or on behalf of a   host, therefore the name type of a SIG(0) generated by a client   SHOULD be either user or host.  A nameserver is associated with a   host, and its use of SIG(0) is not associated with a particular zone,   so the name type of a SIG(0) generated by a nameserver SHOULD be   host.3.3 - Signatory Flags   This document does not assign any values to the signatory field, nor   require any values to be present.3.4 - Protocol   The signing KEY record MUST have a protocol value of 3 (DNSSEC) or   255 (ALL).  If a key is not specified for use with DNSSEC, a DNSSEC   resolver MUST NOT trust any signature that it generates.3.5 - Algorithm Number   The algorithm field MUST be identical to that of the generated SIG   record, and MUST meet all requirements for an algorithm value in a   SIG record.4 - Security Considerations   This document defines a standard baseline for a DNSSEC capable   resolver.  This is necessary for a thorough security analysis of   DNSSEC, if one is to be done.   Specifically, this document places additional restrictions on SIG   records that a resolver must validate before the signature can be   considered worthy of DNSSEC trust.  This simplifies the protocol,   making it more robust and able to withstand scrutiny by the security   community.5 - Acknowledgements   The author would like to thank the following people for review and   informative comments (in alphabetical order):   Olafur Gudmundsson   Ed LewisWellington                  Standards Track                     [Page 5]RFC 3008                DNSSEC Signing Authority           November 20006 - References   [RFC1034]  Mockapetris, P., "Domain Names - Concepts and Facilities",              STD 13, RFC 1034, November 1987.   [RFC1035]  Mockapetris, P., "Domain Names - Implementation and              Specification", STD 13, RFC 1035, November 1987.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels", BCP 14, RFC 2119, March 1997.   [RFC2136]  Vixie (Ed.), P., Thomson, S., Rekhter, Y. and J. Bound,              "Dynamic Updates in the Domain Name System", RFC 2136,              April 1997.   [RFC2535]  Eastlake, D., "Domain Name System Security Extensions",              RFC 2535, March 1999.   [RFC2931]  Eastlake, D., "DNS Request and Transaction Signatures              (SIG(0)s )", RFC 2931, September 2000.   [RFC3007]      Wellington, B., "Simple Secure Domain Name System              (DNS) Dynamic Update", RFC 3007, November 2000.7 - Author's Address   Brian Wellington   Nominum, Inc.   950 Charter Street   Redwood City, CA 94063   Phone: +1 650 381 6022   EMail: Brian.Wellington@nominum.comWellington                  Standards Track                     [Page 6]RFC 3008                DNSSEC Signing Authority           November 20008  Full Copyright Statement   Copyright (C) The Internet Society (2000).  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.   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