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+Network Working Group B. Wellington
+Request for Comments: 3008 Nominum
+Updates: 2535 November 2000
+Category: Standards Track
+
+
+ Domain Name System Security (DNSSEC) Signing Authority
+
+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 (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 2000
+
+
+2 - 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 2000
+
+
+2.5 - 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]
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+RFC 3008 DNSSEC Signing Authority November 2000
+
+
+3.1 - 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]
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+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 Lewis
+
+
+
+
+
+
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+Wellington Standards Track [Page 5]
+
+RFC 3008 DNSSEC Signing Authority November 2000
+
+
+6 - 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.com
+
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+Wellington Standards Track [Page 6]
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+RFC 3008 DNSSEC Signing Authority November 2000
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+
+8 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.
+
+ 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.
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+Wellington Standards Track [Page 7]
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