DNS Extensions R. Arends Internet-Draft Telematica Instituut Expires: March 16, 2004 R. Austein ISC M. Larson VeriSign D. Massey USC/ISI S. Rose NIST September 16, 2003 Resource Records for the DNS Security Extensions draft-ietf-dnsext-dnssec-records-04 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 16, 2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document is part of a family of documents that describes the DNS Security Extensions (DNSSEC). The DNS Security Extensions are a collection of resource records and protocol modifications that provide source authentication for the DNS. This document defines the public key (DNSKEY), delegation signer (DS), resource record digital Arends, et al. Expires March 16, 2004 [Page 1] Internet-Draft DNSSEC Resource Records September 2003 signature (RRSIG), and authenticated denial of existance (NSEC) resource records. The purpose and format of each resource record is described in detail, and an example of each resource record is given. This document obsoletes RFC 2535 and incorporates changes from all updates to RFC 2535. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Background and Related Documents . . . . . . . . . . . . . . 4 1.2 Reserved Words . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Editors' Notes . . . . . . . . . . . . . . . . . . . . . . . 4 1.3.1 Open Technical Issues . . . . . . . . . . . . . . . . . . . 4 1.3.2 Technical Changes or Corrections . . . . . . . . . . . . . . 4 1.3.3 Typos and Minor Corrections . . . . . . . . . . . . . . . . 5 2. The DNSKEY Resource Record . . . . . . . . . . . . . . . . . 6 2.1 DNSKEY RDATA Wire Format . . . . . . . . . . . . . . . . . . 6 2.1.1 The Flags Field . . . . . . . . . . . . . . . . . . . . . . 6 2.1.2 The Protocol Field . . . . . . . . . . . . . . . . . . . . . 7 2.1.3 The Algorithm Field . . . . . . . . . . . . . . . . . . . . 7 2.1.4 The Public Key Field . . . . . . . . . . . . . . . . . . . . 7 2.1.5 Notes on DNSKEY RDATA Design . . . . . . . . . . . . . . . . 7 2.2 The DNSKEY RR Presentation Format . . . . . . . . . . . . . 7 2.3 DNSKEY RR Example . . . . . . . . . . . . . . . . . . . . . 8 3. The RRSIG Resource Record . . . . . . . . . . . . . . . . . 9 3.1 RRSIG RDATA Wire Format . . . . . . . . . . . . . . . . . . 9 3.1.1 The Type Covered Field . . . . . . . . . . . . . . . . . . . 10 3.1.2 The Algorithm Number Field . . . . . . . . . . . . . . . . . 10 3.1.3 The Labels Field . . . . . . . . . . . . . . . . . . . . . . 10 3.1.4 Original TTL Field . . . . . . . . . . . . . . . . . . . . . 11 3.1.5 Signature Expiration and Inception Fields . . . . . . . . . 11 3.1.6 The Key Tag Field . . . . . . . . . . . . . . . . . . . . . 11 3.1.7 The Signer's Name Field . . . . . . . . . . . . . . . . . . 11 3.1.8 The Signature Field . . . . . . . . . . . . . . . . . . . . 12 3.2 The RRSIG RR Presentation Format . . . . . . . . . . . . . . 13 3.3 RRSIG RR Example . . . . . . . . . . . . . . . . . . . . . . 13 4. The NSEC Resource Record . . . . . . . . . . . . . . . . . . 15 4.1 NSEC RDATA Wire Format . . . . . . . . . . . . . . . . . . . 15 4.1.1 The Next Domain Name Field . . . . . . . . . . . . . . . . . 15 4.1.2 The Type Bit Map Field . . . . . . . . . . . . . . . . . . . 16 4.1.3 Inclusion of Wildcard Names in NSEC RDATA . . . . . . . . . 16 4.2 The NSEC RR Presentation Format . . . . . . . . . . . . . . 16 4.3 NSEC RR Example . . . . . . . . . . . . . . . . . . . . . . 17 5. The DS Resource Record . . . . . . . . . . . . . . . . . . . 18 5.1 DS RDATA Wire Format . . . . . . . . . . . . . . . . . . . . 18 5.1.1 The Key Tag Field . . . . . . . . . . . . . . . . . . . . . 19 5.1.2 The Algorithm Field . . . . . . . . . . . . . . . . . . . . 19 Arends, et al. Expires March 16, 2004 [Page 2] Internet-Draft DNSSEC Resource Records September 2003 5.1.3 The Digest Type Field . . . . . . . . . . . . . . . . . . . 19 5.1.4 The Digest Field . . . . . . . . . . . . . . . . . . . . . . 19 5.2 Processing of DS RRs When Validating Responses . . . . . . . 19 5.3 The DS RR Presentation Format . . . . . . . . . . . . . . . 20 5.4 DS RR Example . . . . . . . . . . . . . . . . . . . . . . . 20 6. Canonical Form and Order of Resource Records . . . . . . . . 21 6.1 Canonical DNS Name Order . . . . . . . . . . . . . . . . . . 21 6.2 Canonical RR Form . . . . . . . . . . . . . . . . . . . . . 21 6.3 Canonical RR Ordering Within An RRset . . . . . . . . . . . 22 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 23 8. Security Considerations . . . . . . . . . . . . . . . . . . 25 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 26 Normative References . . . . . . . . . . . . . . . . . . . . 27 Informative References . . . . . . . . . . . . . . . . . . . 29 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 29 A. DNSSEC Algorithm and Digest Types . . . . . . . . . . . . . 31 A.1 DNSSEC Algorithm Types . . . . . . . . . . . . . . . . . . . 31 A.1.1 Private Algorithm Types . . . . . . . . . . . . . . . . . . 31 A.2 DNSSEC Digest Types . . . . . . . . . . . . . . . . . . . . 32 B. Key Tag Calculation . . . . . . . . . . . . . . . . . . . . 33 B.1 Key Tag for Algorithm 1 (RSA/MD5) . . . . . . . . . . . . . 34 Intellectual Property and Copyright Statements . . . . . . . 35 Arends, et al. Expires March 16, 2004 [Page 3] Internet-Draft DNSSEC Resource Records September 2003 1. Introduction The DNS Security Extensions (DNSSEC) introduce four new DNS resource record types: DNSKEY, RRSIG, NSEC, and DS. This document defines the purpose of each resource record (RR), the RR's RDATA format, and its ASCII representation. 1.1 Background and Related Documents The reader is assumed to be familiar with the basic DNS concepts described in RFC1034 [RFC1034], RFC1035 [RFC1035] and subsequent RFC's that update them: RFC2136 [RFC2136], RFC2181 [RFC2181] and RFC2308 [RFC2308]. This document is part of a family of documents that define the DNS security extensions. The DNS security extensions (DNSSEC) are a collection of resource records and DNS protocol modifications that add source authentication and data integrity the Domain Name System (DNS). An introduction to DNSSEC and definition of common terms can be found in [I-D.ietf-dnsext-dnssec-intro]. A description of DNS protocol modifications can be found in [I-D.ietf-dnsext-dnssec-protocol]. This document defines the DNSSEC resource records. 1.2 Reserved Words 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]. 1.3 Editors' Notes 1.3.1 Open Technical Issues The cryptographic algorithm types (Appendix A) requires input from the working group. The DSA algorithm was moved to OPTIONAL. This had strong consensus in workshops and various discussions and a separate internet draft solely to move DSA from MANDATORY to OPTIONAL seemed excessive. This draft solicits input on that proposed change. 1.3.2 Technical Changes or Corrections Please report technical corrections to dnssec-editors@east.isi.edu. To assist the editors, please indicate the text in error and point out the RFC that defines the correct behavior. For a technical change where no RFC that defines the correct behavior, or if there's more than one applicable RFC and the definitions conflict, please post the issue to namedroppers. Arends, et al. Expires March 16, 2004 [Page 4] Internet-Draft DNSSEC Resource Records September 2003 An example correction to dnssec-editors might be: Page X says "DNSSEC RRs SHOULD be automatically returned in responses." This was true in RFC 2535, but RFC 3225 (Section 3, 3rd paragraph) says the DNSSEC RR types MUST NOT be included in responses unless the resolver indicated support for DNSSEC. 1.3.3 Typos and Minor Corrections Please report any typos corrections to dnssec-editors@east.isi.edu. To assist the editors, please provide enough context for us to find the incorrect text quickly. An example message to dnssec-editors might be: page X says "the DNSSEC standard has been in development for over 1 years". It should read "over 10 years". Arends, et al. Expires March 16, 2004 [Page 5] Internet-Draft DNSSEC Resource Records September 2003 2. The DNSKEY Resource Record DNSSEC uses public key cryptography to sign and authenticate DNS resource record sets (RRsets). The public keys are stored in DNSKEY resource records and are used in the DNSSEC authentication process described in [I-D.ietf-dnsext-dnssec-protocol]. For example, a zone signs its authoritative RRsets using a private key and stores the corresponding public key in a DNSKEY RR. A resolver can then use these signatures to authenticate RRsets from the zone. The DNSKEY RR may also be used to store public keys associated with other DNS operations such as TKEY [RFC2930]. The DNSKEY RR is not, however, intended as a record for storing arbitrary public keys. The DNSKEY RR MUST NOT be used to store certificates or public keys that do not directly relate to the DNS infrastructure. The Type value for the DNSKEY RR type is 48. The DNSKEY RR is class independent. The DNSKEY RR has no special TTL requirements. 2.1 DNSKEY RDATA Wire Format The RDATA for a DNSKEY RR consists of a 2 octet Flags Field, a 1 octet Protocol Field, a 1 octet Algorithm Field , and the Public Key Field. 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Protocol | Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Public Key / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.1.1 The Flags Field Bit 7 of the Flags field is the Zone Key flag. If bit 7 has value 1, then the DNSKEY record holds a DNS zone key and the DNSKEY's owner name MUST be the name of a zone. If bit 7 has value 0, then the DNSKEY record holds some other type of DNS public key, such as a public key used by TKEY. Bit 15 of the Flags field is the Secure Entry Point flag, described Arends, et al. Expires March 16, 2004 [Page 6] Internet-Draft DNSSEC Resource Records September 2003 in [I-D.ietf-dnsext-keyrr-key-signing-flag]. If bit 15 has value 1, then the DNSKEY record holds a key intended for use as a secure entry point. This flag is only intended to be to a hint to zone signing or debugging software as to the intended use of this DNSKEY record; security-aware resolvers MUST NOT alter their behavior during the signature validation process in any way based on the setting of this bit. Bits 0-6 and 8-14 are reserved: these bits MUST have value 0 upon creation of the DNSKEY RR, and MUST be ignored upon reception. 2.1.2 The Protocol Field The Protocol Field MUST have value 3 and MUST be treated as invalid during signature verification if found to be some value other than 3. 2.1.3 The Algorithm Field The Algorithm field identifies the public key's cryptographic algorithm and determines the format of the Public Key field. A list of DNSSEC algorithm types can be found in Appendix A.1 2.1.4 The Public Key Field The Public Key Field holds the public key material itself. 2.1.5 Notes on DNSKEY RDATA Design Although the Protocol Field always has value 3, it is retained for backward compatibility with early versions of the KEY record. 2.2 The DNSKEY RR Presentation Format The presentation format of the RDATA portion is as follows: The Flag field MUST be represented as an unsigned decimal integer with a value of 0, 256, or 257. The Protocol Field MUST be represented as an unsigned decimal integer with a value of 3. The Algorithm field MUST be represented either as an unsigned decimal integer or as an algorithm mnemonic as specified in Appendix A.1. The Public Key field MUST be represented as a Base64 encoding of the Public Key. Whitespace is allowed within the Base64 text. For a definition of Base64 encoding, see [RFC1521] Section 5.2. Arends, et al. Expires March 16, 2004 [Page 7] Internet-Draft DNSSEC Resource Records September 2003 2.3 DNSKEY RR Example The following DNSKEY RR stores a DNS zone key for example.com. example.com. 86400 IN DNSKEY 256 3 5 ( AQPSKmynfzW4kyBv015MUG2DeIQ3 Cbl+BBZH4b/0PY1kxkmvHjcZc8no kfzj31GajIQKY+5CptLr3buXA10h WqTkF7H6RfoRqXQeogmMHfpftf6z Mv1LyBUgia7za6ZEzOJBOztyvhjL 742iU/TpPSEDhm2SNKLijfUppn1U aNvv4w== ) The first four text fields specify the owner name, TTL, Class, and RR type (DNSKEY). Value 256 indicates that the Zone Key bit (bit 7) in the Flags field has value 1. Value 3 is the fixed Protocol value. Value 5 indicates the public key algorithm. Appendix A.1 identifies algorithm type 5 as RSA/SHA1 and indicates that the format of the RSA/SHA1 public key field is defined in [RFC3110]. The remaining text is a Base64 encoding of the public key. Arends, et al. Expires March 16, 2004 [Page 8] Internet-Draft DNSSEC Resource Records September 2003 3. The RRSIG Resource Record DNSSEC uses public key cryptography to sign and authenticate DNS resource record sets (RRsets). Digital signatures are stored in RRSIG resource records and are used in the DNSSEC authentication process described in [I-D.ietf-dnsext-dnssec-protocol]. A security-aware resolver can use these RRSIG RRs to authenticate RRsets from the zone. The RRSIG RR MUST only be used to carry verification material (digital signatures) used to secure DNS operations. A RRSIG record contains the signature for an RRset with a particular name, class, and type. The RRSIG RR specifies a validity interval for the signature and uses the Algorithm, the Signer's Name, and the Key Tag to identify the DNSKEY RR containing the public key that a resolver can use to verify the signature. The Type value for the RRSIG RR type is 46. The RRSIG RR is class independent. A RRSIG RR MUST have the same class as the RRset it covers. The TTL value of an RRSIG RR SHOULD match the TTL value of the RRset it covers. 3.1 RRSIG RDATA Wire Format The RDATA for a RRSIG RR consists of a 2 octet Type Covered field, a 1 octet Algorithm field, a 1 octet Labels field, a 4 octet Original TTL field, a 4 octet Signature Expiration field, a 4 octet Signature Inception field, a 2 octet Key tag, the Signer's Name field, and the Signature field. 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type Covered | Algorithm | Labels | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Original TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Signature Expiration | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Signature Inception | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key Tag | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Signer's Name / / / Arends, et al. Expires March 16, 2004 [Page 9] Internet-Draft DNSSEC Resource Records September 2003 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Signature / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3.1.1 The Type Covered Field The Type Covered field identifies the type of the RRset which is covered by this RRSIG record. 3.1.2 The Algorithm Number Field The Algorithm Number field identifies the cryptographic algorithm used to create the signature. A list of DNSSEC algorithm types can be found in Appendix A.1 3.1.3 The Labels Field The Labels field specifies the number of labels in the original RRSIG RR owner name. The significance of this field is that from it a verifier can determine if the answer was synthesized from a wildcard. If so, it can be used to determine what owner name was used in generating the signature. To validate a signature, the validator needs the original owner name that was used to create the signature. If the original owner name contains a wildcard label ("*"), the owner name may have been expanded by the server during the response process, in which case the validator will need to reconstruct the original owner name in order to validate the signature. [I-D.ietf-dnsext-dnssec-protocol] describes how to use the Labels field to reconstruct the original owner name. The value of the Label field MUST NOT count either the null (root) label that terminates the owner name or the wildcard label (if present). The value of the Label field MUST be less than or equal to the number of labels in the RRSIG owner name. For example, "www.example.com." has a Label field value of 3, and "*.example.com." has a Label field value of 2. Root (".") has a Label field value of 0. Note that, although the wildcard label is not included in the count stored in the Label field of the RRSIG RR, the wildcard label is part of the RRset's owner name when generating or verifying the signature. Arends, et al. Expires March 16, 2004 [Page 10] Internet-Draft DNSSEC Resource Records September 2003 3.1.4 Original TTL Field The Original TTL field specifies the TTL of the covered RRset as it appears in the authoritative zone. The Original TTL field is necessary because a caching resolver decrements the TTL value of a cached RRset. In order to validate a signature, a resolver requires the original TTL. [I-D.ietf-dnsext-dnssec-protocol] describes how to use the Original TTL field value to reconstruct the original TTL. The Original TTL value MUST be greater than or equal to the TTL value of the RRSIG record itself. 3.1.5 Signature Expiration and Inception Fields The Signature Expiration and Inception fields specify a validity period for the signature. The RRSIG record MUST NOT be used for authentication prior to the inception date and MUST NOT be used for authentication after the expiration date. Signature Expiration and Inception field values are in POSIX.1 time format: a 32-bit unsigned number of seconds elapsed since 1 January 1970 00:00:00 UTC, ignoring leap seconds, in network byte order. The longest interval which can be expressed by this format without wrapping is approximately 136 years. A RRSIG RR can have an Expiration field value which is numerically smaller than the Inception field value if the expiration field value is near the 32-bit wrap-around point or if the signature is long lived. Because of this, all comparisons involving these fields MUST use "Serial number arithmetic" as defined in [RFC1982]. As a direct consequence, the values contained in these fields cannot refer to dates more than 68 years in either the past or the future. 3.1.6 The Key Tag Field The Key Tag field contains the key tag value of the DNSKEY RR that validates this signature. Appendix B explains how to calculate Key Tag values. 3.1.7 The Signer's Name Field The Signer's Name field value identifies the owner name of the DNSKEY RR which a security-aware resolver should use to validate this signature. The Signer's Name field MUST contain the name of the zone of the covered RRset. A sender MUST NOT use DNS name compression on the Signer's Name field when transmitting a RRSIG RR. A receiver which receives a RRSIG RR containing a compressed Signer's Name field Arends, et al. Expires March 16, 2004 [Page 11] Internet-Draft DNSSEC Resource Records September 2003 SHOULD decompress the field value. 3.1.8 The Signature Field The Signature field contains the cryptographic signature which covers the RRSIG RDATA (excluding the Signature field) and the RRset specified by the RRSIG owner name, RRSIG class, and RRSIG Type Covered field. 3.1.8.1 Signature Calculation A signature covers the RRSIG RDATA (excluding the Signature Field) and covers the data RRset specified by the RRSIG owner name, RRSIG class, and RRSIG Type Covered field. The RRset is in canonical form (see Section 6) and the set RR(1),...RR(n) is signed as follows: signature = sign(RRSIG_RDATA | RR(1) | RR(2)... ) where "|" denotes concatenation; RRSIG_RDATA is the wire format of the RRSIG RDATA fields with the Signer's Name field in canonical form and the Signature field excluded; RR(i) = owner | class | type | TTL | RDATA length | RDATA; "owner" is the fully qualified owner name of the RRset in canonical form (for RRs with wildcard owner names, the wildcard label is included in the owner name); Each RR MUST have the same owner name as the RRSIG RR; Each RR MUST have the same class as the RRSIG RR; Each RR in the RRset MUST have the RR type listed in the RRSIG RR's Type Covered field; Each RR in the RRset MUST have the TTL listed in the RRSIG Original TTL Field; Any DNS names in the RDATA field of each RR MUST be in canonical form; and The RRset MUST be sorted in canonical order. Arends, et al. Expires March 16, 2004 [Page 12] Internet-Draft DNSSEC Resource Records September 2003 3.2 The RRSIG RR Presentation Format The presentation format of the RDATA portion is as follows: The Type Covered field value MUST be represented either as an unsigned decimal integer or as the mnemonic for the covered RR type. The Algorithm field value MUST be represented either as an unsigned decimal integer or as an algorithm mnemonic as specified in Appendix A.1. The Labels field value MUST be represented as an unsigned decimal integer. The Original TTL field value MUST be represented as an unsigned decimal integer. The Signature Inception Time and Expiration Time field values MUST be represented in the form YYYYMMDDHHmmSS in UTC, where: YYYY is the year (0000-9999, but see Section 3.1.5); MM is the month number (01-12); DD is the day of the month (01-31); HH is the hour in 24 hours notation (00-23); mm is the minute (00-59); SS is the second (00-59). The Key Tag field MUST be represented as an unsigned decimal integer. The Signer's Name field value MUST be represented as a domain name. The Signature field is represented as a Base64 encoding of the signature. Whitespace is allowed within the Base64 text. For a definition of Base64 encoding see [RFC1521] Section 5.2. 3.3 RRSIG RR Example The following a RRSIG RR stores the signature for the A RRset of host.example.com: host.example.com. 86400 IN RRSIG A 5 3 86400 20030322173103 ( 20030220173103 2642 example.com. oJB1W6WNGv+ldvQ3WDG0MQkg5IEhjRip8WTr Arends, et al. Expires March 16, 2004 [Page 13] Internet-Draft DNSSEC Resource Records September 2003 PYGv07h108dUKGMeDPKijVCHX3DDKdfb+v6o B9wfuh3DTJXUAfI/M0zmO/zz8bW0Rznl8O3t GNazPwQKkRN20XPXV6nwwfoXmJQbsLNrLfkG J5D6fwFm8nN+6pBzeDQfsS3Ap3o= ) The first four fields specify the owner name, TTL, Class, and RR type (RRSIG). The "A" represents the Type Covered field. The value 5 identifies the Algorithm used (RSA-SHA1) to create the signature. The value 3 is the number of Labels in the original owner name. The value 86400 in the RRSIG RDATA is the Original TTL for the covered A RRset. 20030322173103 and 20030220173103 are the expiration and inception dates, respectively. 2642 is the Key Tag, and example.com. is the Signer's Name. The remaining text is a Base64 encoding of the signature. Note that combination of RRSIG RR owner name, class, and Type Covered indicate that this RRSIG covers the "host.example.com" A RRset. The Label value of 3 indicates that no wildcard expansion was used. The Algorithm, Signer's Name, and Key Tag indicate this signature can be authenticated using an example.com zone DNSKEY RR whose algorithm is 5 and key tag is 2642. Arends, et al. Expires March 16, 2004 [Page 14] Internet-Draft DNSSEC Resource Records September 2003 4. The NSEC Resource Record The NSEC resource record lists two separate things: the owner name of the next authoritative RRset in the canonical ordering of the zone, and the set of RR types present at the NSEC RR's owner name. The complete set of NSEC RRs in a zone both indicate which authoritative RRsets exist in a zone and also form a chain of authoritative owner names in the zone. This information is used to provide authenticated denial of existence for DNS data, as described in [I-D.ietf-dnsext-dnssec-protocol]. The type value for the NSEC RR is 47. The NSEC RR is class independent. The NSEC RR has no special TTL requirements. 4.1 NSEC RDATA Wire Format The RDATA of the NSEC RR is as shown below: 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Next Domain Name / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Type Bit Map / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4.1.1 The Next Domain Name Field The Next Domain Name field contains the owner name of the next authoritative RRset in the canonical ordering of the zone; see Section 6.1 for an explanation of canonical ordering. The value of the Next Domain Name field in the last NSEC record in the zone is the name of the zone apex (the owner name name of the zone's SOA RR). A sender MUST NOT use DNS name compression on the Next Domain Name field when transmitting an NSEC RR. A receiver which receives an NSEC RR containing a compressed Next Domain Name field SHOULD decompress the field value. Owner names of RRsets not authoritative for the given zone (such as glue records) MUST NOT be listed in the Next Domain Name unless at least one authoritative RRset exists at the same owner name. Arends, et al. Expires March 16, 2004 [Page 15] Internet-Draft DNSSEC Resource Records September 2003 4.1.2 The Type Bit Map Field The Type Bit Map field identifies the RRset types which exist at the NSEC RR's owner name. Each bit in the Type Bit Map field corresponds to an RR type. Bit 1 corresponds to RR type 1 (A), bit 2 corresponds to RR type 2 (NS), and so forth. If a bit is set to 1, it indicates that an RRset of that type is present for the NSEC's owner name. If a bit is set to 0, it indicates that no RRset of that type present for the NSEC's owner name. A zone MUST NOT generate an NSEC RR for any domain name that only holds glue records. Bits representing pseudo-RR types MUST be set to 0, since they do not appear in zone data. If encountered, they must be ignored upon reading. Trailing zero octets MUST be omitted. The length of the Type Bit Map field varies, and is determined by the type code with the largest numerical value among the set of RR types present at the NSEC RR's owner name. Trailing zero octets not specified MUST be interpreted as zero octets. The above Type Bit Map format MUST NOT be used when an RR type code with numerical value greater than 127 is present. Bit 0 in the Type Bit Map field indicates the Type Bit Map format. A value of 0 in bit 0 denotes the format described above, therefore bit 0 MUST have a value of 0. The format and meaning of a Type Bit Map with a value of 1 in bit 0 is undefined. 4.1.3 Inclusion of Wildcard Names in NSEC RDATA If a wildcard owner name appears in a zone, the wildcard label ("*") is treated as a literal symbol and is treated the same as any other owner name for purposes of generating NSEC RRs. Wildcard owner names appear in the Next Domain Name field without any wildcard expansion. [I-D.ietf-dnsext-dnssec-protocol] describes the impact of wildcards on authenticated denial of existence. 4.2 The NSEC RR Presentation Format The presentation format of the RDATA portion is as follows: The Next Domain Name field is represented as a domain name. Arends, et al. Expires March 16, 2004 [Page 16] Internet-Draft DNSSEC Resource Records September 2003 The Type Bit Map field is represented either as a sequence of RR type mnemonics or as a sequence of unsigned decimal integers denoting the RR type codes. 4.3 NSEC RR Example The following NSEC RR identifies the RRsets associated with alfa.example.com. and identifies the next authoritative name after alfa.example.com. alfa.example.com. 86400 IN NSEC host.example.com. A MX RRSIG NSEC The first four text fields specify the name, TTL, Class, and RR type (NSEC). The entry host.example.com. is the next authoritative name after alfa.example.com. in canonical order. The A, MX, RRSIG and NSEC mnemonics indicate there are A, MX, RRSIG and NSEC RRsets associated with the name alfa.example.com. Note that the NSEC record can be used in authenticated denial of existence proofs. If the example NSEC record were authenticated, it could be used to prove that beta.example.com does not exist or could be used to prove there is no AAAA record associated with alfa.example.com. Authenticated denial of existence is discussed in [I-D.ietf-dnsext-dnssec-protocol]. Arends, et al. Expires March 16, 2004 [Page 17] Internet-Draft DNSSEC Resource Records September 2003 5. The DS Resource Record The DS Resource Record refers to a DNSKEY RR and is used in the DNS DNSKEY authentication process. A DS RR refers to a DNSKEY RR by storing the key tag, algorithm number, and a digest of the DNSKEY RR. Note that while the digest should be sufficient to identify the key, storing the key tag and key algorithm helps make the identification process more efficient. By authenticating the DS record, a resolver can authenticate the DNSKEY RR to which the DS record points. The key authentication process is described in [I-D.ietf-dnsext-dnssec-protocol]. The DS RR and its corresponding DNSKEY RR have the same owner name, but they are stored in different locations. The DS RR appears only on the upper (parental) side of a delegation, and is authoritative data in the parent zone. For example, the DS RR for "example.com" is stored in the "com" zone (the parent zone) rather than in the "example.com" zone (the child zone). The corresponding DNSKEY RR is stored in the "example.com" zone (the child zone). This simplifies DNS zone management and zone signing, but introduces special response processing requirements for the DS RR; these are described in [I-D.ietf-dnsext-dnssec-protocol]. The type number for the DS record is 43. The DS resource record is class independent. The DS RR has no special TTL requirements. 5.1 DS RDATA Wire Format The RDATA for a DS RR consists of a 2 octet Key Tag field, a one octet Algorithm field, a one octet Digest Type field, and a Digest field. 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key Tag | Algorithm | Digest Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Digest / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Arends, et al. Expires March 16, 2004 [Page 18] Internet-Draft DNSSEC Resource Records September 2003 5.1.1 The Key Tag Field The Key Tag field lists the key tag of the DNSKEY RR referred to by the DS record. The Key Tag used by the DS RR is identical to the Key Tag used by RRSIG RRs. Appendix B describes how to compute a Key Tag. 5.1.2 The Algorithm Field The Algorithm field lists the algorithm number of the DNSKEY RR referred to by the DS record. The algorithm number used by the DS RR is identical to the algorithm number used by RRSIG and DNSKEY RRs. Appendix A.1 lists the algorithm number types. 5.1.3 The Digest Type Field The DS RR refers to a DNSKEY RR by including a digest of that DNSKEY RR. The Digest Type field identifies the algorithm used to construct the digest. Appendix A.2 lists the possible digest algorithm types. 5.1.4 The Digest Field The DS record refers to a DNSKEY RR by including a digest of that DNSKEY RR. The Digest field holds the digest. The digest is calculated by concatenating the canonical form of the fully qualified owner name of the DNSKEY RR with the DNSKEY RDATA, and then applying the digest algorithm. digest = digest_algorithm( DNSKEY owner name | DNSKEY RDATA); "|" denotes concatenation DNSKEY RDATA = Flags | Protocol | Algorithm | Public Key. The size of the digest may vary depending on the digest algorithm and DNSKEY RR size. Currently, the only defined digest algorithm is SHA-1, which produces a 20 octet digest. 5.2 Processing of DS RRs When Validating Responses The DS RR links the authentication chain across zone boundaries, so the DS RR requires extra care in processing. The DNSKEY RR referred to in the DS RR MUST be a DNSSEC zone key. The DNSKEY RR Flags MUST Arends, et al. Expires March 16, 2004 [Page 19] Internet-Draft DNSSEC Resource Records September 2003 have Flags bit 7 set to value 1. If the key tag does not indicate a DNSSEC zone key, the DS RR (and DNSKEY RR it references) MUST NOT be used in the validation process. 5.3 The DS RR Presentation Format The presentation format of the RDATA portion is as follows: The Key Tag field MUST be represented as an unsigned decimal integer. The Algorithm field MUST be represented either as an unsigned decimal integer or as an algorithm mnemonic specified in Appendix A.1. The Digest Type field MUST be represented as an unsigned decimal integer. The Digest MUST be represented as a sequence of case-insensitive hexadecimal digits. Whitespace is allowed within the hexadecimal text. 5.4 DS RR Example The following example shows a DNSKEY RR and its corresponding DS RR. dskey.example.com. 86400 IN DNSKEY 256 3 5 ( AQOeiiR0GOMYkDshWoSKz9Xz fwJr1AYtsmx3TGkJaNXVbfi/ 2pHm822aJ5iI9BMzNXxeYCmZ DRD99WYwYqUSdjMmmAphXdvx egXd/M5+X7OrzKBaMbCVdFLU Uh6DhweJBjEVv5f2wwjM9Xzc nOf+EPbtG9DMBmADjFDc2w/r ljwvFw== ) ; key id = 60485 dskey.example.com. 86400 IN DS 60485 5 1 ( 2BB183AF5F22588179A53B0A 98631FAD1A292118 ) The first four text fields specify the name, TTL, Class, and RR type (DS). Value 60485 is the key tag for the corresponding "dskey.example.com." DNSKEY RR, and value 5 denotes the algorithm used by this "dskey.example.com." DNSKEY RR. The value 1 is the algorithm used to construct the digest, and the rest of the RDATA text is the digest in hexadecimal. Arends, et al. Expires March 16, 2004 [Page 20] Internet-Draft DNSSEC Resource Records September 2003 6. Canonical Form and Order of Resource Records This section defines a canonical form for resource records, a canonical ordering of DNS names, and a canonical ordering of resource records within an RRset. A canonical name order is required to construct the NSEC name chain. A canonical RR form and ordering within an RRset are required to construct and verify RRSIG RRs. 6.1 Canonical DNS Name Order For purposes of DNS security, owner names are ordered by treating individual labels as unsigned left-justified octet strings. The absence of a octet sorts before a zero value octet, and upper case US-ASCII letters are treated as if they were lower case US-ASCII letters. To compute the canonical ordering of a set of DNS names, start by sorting the names according to their most significant (rightmost) labels. For names in which the most significant label is identical, continue sorting according to their next most significant label, and so forth. For example, the following names are sorted in canonical DNS name order. The most significant label is "example". At this level, "example" sorts first, followed by names ending in "a.example", then names ending "z.example". The names within each level are sorted in the same way. example a.example yljkjljk.a.example Z.a.example zABC.a.EXAMPLE z.example \001.z.example *.z.example \200.z.example 6.2 Canonical RR Form For purposes of DNS security, the canonical form of an RR is the wire format of the RR where: 1. Every domain name in the RR is fully expanded (no DNS name compression) and fully qualified; 2. All uppercase US-ASCII letters in the owner name of the RR are Arends, et al. Expires March 16, 2004 [Page 21] Internet-Draft DNSSEC Resource Records September 2003 replaced by the corresponding lowercase US-ASCII letters; 3. If the type of the RR is NS, MD, MF, CNAME, SOA, MB, MG, MR, PTR, HINFO, MINFO, MX, HINFO, RP, AFSDB, RT, SIG, PX, NXT, NAPTR, KX, SRV, DNAME, or A6, all uppercase US-ASCII letters in the DNS names contained within the RDATA are replaced by the corresponding lowercase US-ASCII letters; 4. If the owner name of the RR is a wildcard name, the owner name is in its original unexpanded form, including the "*" label (no wildcard substitution); and 5. The RR's TTL is set to its original value as it appears in the originating authoritative zone or the Original TTL field of the covering RRSIG RR. 6.3 Canonical RR Ordering Within An RRset For purposes of DNS security, RRs with same owner name, same class, and same type are sorted by RDATA: first by RDATA length, shortest to longest, then by the canonical form of the RDATA itself in the case of length equality, treating the RDATA portion of the canonical form of each RR as a left justified unsigned octet sequence. The absence of an octet sorts before a zero octet. Arends, et al. Expires March 16, 2004 [Page 22] Internet-Draft DNSSEC Resource Records September 2003 7. IANA Considerations This document introduces no new IANA considerations, because all of the protocol parameters used in this document have already been assigned by previous specifications. However, since the evolution of DNSSEC has been long and somewhat convoluted, this section attempts to describe the current state of the IANA registries and other protocol parameters which are (or once were) related to DNSSEC. DNS Resource Record Types: [RFC2535] assigned types 24, 25, and 30 to the SIG, KEY, and NXT RRs, respectively. [I-D.ietf-dnsext-delegation-signer] assigned DNS Resource Record Type 43 to DS. [I-D.ietf-dnsext-dnssec-2535typecode-change] assigned types 46, 47, and 48 to the RRSIG, NSEC, and DNSKEY RRs, respectively. [I-D.ietf-dnsext-dnssec-2535typecode-change] also marked type 30 (NXT) as Obsolete, and restricted use of types 24 (SIG) and 25 (KEY) to the "SIG(0)" transaction security protocol described in [RFC2931]. SIG(0) Algorithm Numbers: [RFC2535] created an IANA registry for DNSSEC Resource Record Algorithm field numbers, and assigned values 1-4 and 252-255. [RFC3110] assigned value 5. [I-D.ietf-dnsext-dnssec-2535typecode-change] renamed this registry to "SIG(0) Algorithm Numbers" to indicate that this registry is now used only by the "SIG(0)" transaction security protocol described in [RFC2931]. DNS Security Algorithm Numbers: [I-D.ietf-dnsext-dnssec-2535typecode-change] created a new "DNS Security Algorithm Numbers" registry, assigned initial values to algorithms 2 (Diffie-Hellman), 3 (DSA/SHA-1), 5 (RSA/SHA-1), 253 (private algorithms - domain name) and 254 (private algorithms - OID), and reserved values 0, 1, and 255. As stated in [I-D.ietf-dnsext-dnssec-2535typecode-change], value 4 and values 6-252 are available for assignment by IETF Standards Action. [I-D.ietf-dnsext-delegation-signer] created an IANA registry for DNSSEC DS Digest Types, and assigned value 0 to reserved and value 1 to SHA-1. KEY Protocol Values: [RFC2535] created an IANA Registry for KEY Protocol Values, but [RFC3445] re-assigned all assigned values other than 3 to reserved and closed this IANA registry. The registry remains closed, and all KEY and DNSKEY records are required to have Protocol Octet value of 3. Arends, et al. Expires March 16, 2004 [Page 23] Internet-Draft DNSSEC Resource Records September 2003 Flag bits in the KEY and DNSKEY RRs: The Flag bits in the KEY and DNSKEY RRs are not assigned by IANA, and there is no IANA registry for these flags. All changes to the meaning of the Flag bits in the KEY and DNSKEY RRs require a standards action. Bit zero of Type Bit Map in NSEC RRs: The meaning of a value of 1 in bit zero of the Type Bit Map of an NSEC RR can only be assigned by a standards action. Arends, et al. Expires March 16, 2004 [Page 24] Internet-Draft DNSSEC Resource Records September 2003 8. Security Considerations This document describes the format of four DNS resource records used by the DNS security extensions, and presents an algorithm for calculating a key tag for a public key. Other than the items described below, the resource records themselves introduce no security considerations. The use of these records is specified in a separate document, and security considerations related to the use these resource records are discussed in that document. The DS record points to a DNSKEY RR using a cryptographic digest, the key algorithm type and a key tag. The DS record is intended to identify an existing DNSKEY RR, but it is theoretically possible for an attacker to generate a DNSKEY that matches all the DS fields. The probability of constructing such a matching DNSKEY depends on the type of digest algorithm in use. The only currently defined digest algorithm is SHA-1, and the working group believes that constructing a public key which would match the algorithm, key tag, and SHA-1 digest given in a DS record would be a sufficiently difficult problem that such an attack is not a serious threat at this time. The key tag is used to help select DNSKEY resource records efficiently, but it does not uniquely identify a single DNSKEY resource record. It is possible for two distinct DNSKEY RRs to have the same owner name, the same algorithm type, and the same key tag. An implementation which used only the key tag to select a DNSKEY RR might select the wrong public key in some circumstances. Arends, et al. Expires March 16, 2004 [Page 25] Internet-Draft DNSSEC Resource Records September 2003 9. Acknowledgments This document was created from the input and ideas of several members of the DNS Extensions Working Group and working group mailing list. The co-authors of this draft would like to express their thanks for the comments and suggestions received during the revision of these security extension specifications. Arends, et al. Expires March 16, 2004 [Page 26] Internet-Draft DNSSEC Resource Records September 2003 Normative 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. [RFC1521] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, September 1993. [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, August 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2136] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997. [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, July 1997. [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", RFC 2308, March 1998. [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671, August 1999. [RFC2931] Eastlake, D., "DNS Request and Transaction Signatures ( SIG(0)s)", RFC 2931, September 2000. [RFC3110] Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS)", RFC 3110, May 2001. [RFC3445] Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource Record (RR)", RFC 3445, December 2002. [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record (RR) Types", RFC 3597, September 2003. [I-D.ietf-dnsext-delegation-signer] Gudmundsson, O., "Delegation Signer Resource Record", draft-ietf-dnsext-delegation-signer-15 (work in progress), June 2003. Arends, et al. Expires March 16, 2004 [Page 27] Internet-Draft DNSSEC Resource Records September 2003 [I-D.ietf-dnsext-dnssec-intro] Arends, R., Austein, R., Larson, M., Massey, D. and S. Rose, "DNS Security Introduction and Requirements", draft-ietf-dnsext-dnssec-intro-06 (work in progress), September 2003. [I-D.ietf-dnsext-dnssec-protocol] Arends, R., Austein, R., Larson, M., Massey, D. and S. Rose, "Protocol Modifications for the DNS Security Extensions", draft-ietf-dnsext-dnssec-protocol-02 (work in progress), September 2003. [I-D.ietf-dnsext-keyrr-key-signing-flag] Kolkman, O., Schlyter, J. and E. Lewis, "KEY RR Secure Entry Point (SEP) Flag", draft-ietf-dnsext-keyrr-key-signing-flag-08 (work in progress), July 2003. [I-D.ietf-dnsext-dnssec-2535typecode-change] Weiler, S., "Legacy Resolver Compatibility for Delegation Signer", draft-ietf-dnsext-dnssec-2535typecode-change-04 (work in progress), August 2003. Arends, et al. Expires March 16, 2004 [Page 28] Internet-Draft DNSSEC Resource Records September 2003 Informative References [RFC2535] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. [RFC2930] Eastlake, D., "Secret Key Establishment for DNS (TKEY RR)", RFC 2930, September 2000. Authors' Addresses Roy Arends Telematica Instituut Drienerlolaan 5 7522 NB Enschede NL EMail: roy.arends@telin.nl Rob Austein Internet Software Consortium 40 Gavin Circle Reading, MA 01867 USA EMail: sra@isc.org Matt Larson VeriSign, Inc. 21345 Ridgetop Circle Dulles, VA 20166-6503 USA EMail: mlarson@verisign.com Dan Massey USC Information Sciences Institute 3811 N. Fairfax Drive Arlington, VA 22203 USA EMail: masseyd@isi.edu Arends, et al. Expires March 16, 2004 [Page 29] Internet-Draft DNSSEC Resource Records September 2003 Scott Rose National Institute for Standards and Technology 100 Bureau Drive Gaithersburg, MD 20899-8920 USA EMail: scott.rose@nist.gov Arends, et al. Expires March 16, 2004 [Page 30] Internet-Draft DNSSEC Resource Records September 2003 Appendix A. DNSSEC Algorithm and Digest Types The DNS security extensions are designed to be independent of the underlying cryptographic algorithms. The DNSKEY, RRSIG, and DS resource records all use a DNSSEC Algorithm Number to identify the cryptographic algorithm in use by the resource record. The DS resource record also specifies a Digest Algorithm Number to identify the digest algorithm used to construct the DS record. The currently defined Algorithm and Digest Types are listed below. Additional Algorithm or Digest Types could be added as advances in cryptography warrant. A DNSSEC aware resolver or name server MUST implement all MANDATORY algorithms. A.1 DNSSEC Algorithm Types An "Algorithm Number" field in the DNSKEY, RRSIG, and DS resource record types identifies the cryptographic algorithm used by the resource record. Algorithm specific formats are described in separate documents. The following table lists the currently defined algorithm types and provides references to their supporting documents: VALUE Algorithm [mnemonic] RFC STATUS 0 Reserved - - 1 RSA/MD5 [RSA/MD5] RFC 2537 NOT RECOMMENDED 2 Diffie-Hellman [DH] RFC 2539 OPTIONAL 3 DSA [DSA] RFC 2536 OPTIONAL 4 elliptic curve [ECC] TBA OPTIONAL 5 RSA/SHA1 [RSA/SHA1] RFC 3110 MANDATORY 6-251 available for assignment - 252 reserved - 253 private [PRIVATE_DNS] see below OPTIONAL 254 private [PRIVATE_OID] see below OPTIONAL 255 reserved - - A.1.1 Private Algorithm Types Algorithm number 253 is reserved for private use and will never be assigned to a specific algorithm. The public key area in the DNSKEY RR and the signature area in the RRSIG RR begin with a wire encoded domain name, which MUST NOT be compressed. The domain name indicates the private algorithm to use and the remainder of the public key area is determined by that algorithm. Entities should only use domain names they control to designate their private algorithms. Arends, et al. Expires March 16, 2004 [Page 31] Internet-Draft DNSSEC Resource Records September 2003 Algorithm number 254 is reserved for private use and will never be assigned to a specific algorithm. The public key area in the DNSKEY RR and the signature area in the RRSIG RR begin with an unsigned length byte followed by a BER encoded Object Identifier (ISO OID) of that length. The OID indicates the private algorithm in use and the remainder of the area is whatever is required by that algorithm. Entities should only use OIDs they control to designate their private algorithms. A.2 DNSSEC Digest Types A "Digest Type" field in the DS resource record types identifies the cryptographic digest algorithm used by the resource record. The following table lists the currently defined digest algorithm types. VALUE Algorithm STATUS 0 Reserved - 1 SHA-1 MANDATORY 2-255 Unassigned - Arends, et al. Expires March 16, 2004 [Page 32] Internet-Draft DNSSEC Resource Records September 2003 Appendix B. Key Tag Calculation The Key Tag field in the RRSIG and DS resource record types provides a mechanism for selecting a public key efficiently. In most cases, a combination of owner name, algorithm, and key tag can efficiently identify a DNSKEY record. Both the RRSIG and DS resource records have corresponding DNSKEY records. The Key Tag field in the RRSIG and DS records can be used to help select the corresponding DNSKEY RR efficiently when more than one candidate DNSKEY RR is available. However, it is essential to note that the key tag is not a unique identifier. It is theoretically possible for two distinct DNSKEY RRs to have the same owner name, the same algorithm, and the same key tag. The key tag is used to limit the possible candidate keys, but it does not uniquely identify a DNSKEY record. Implementations MUST NOT assume that the key tag uniquely identifies a DNSKEY RR. The key tag is the same for all DNSKEY algorithm types except algorithm 1 (please see Appendix B.1 for the definition of the key tag for algorithm 1). The key tag algorithm is the sum of the wire format of the DNSKEY RDATA broken into 2 octet groups. First the RDATA (in wire format) is treated as a series of 2 octet groups, these groups are then added together ignoring any carry bits. A reference implementation of the key tag algorithm is as am ANSI C function is given below with the RDATA portion of the DNSKEY RR is used as input. It is not necessary to use the following reference code verbatim, but the numerical value of the Key Tag MUST be identical to what the reference implementation would generate for the same input. Please note that the algorithm for calculating the Key Tag is almost but not completely identical to the familiar ones complement checksum used in many other Internet protocols. Key Tags MUST be calculated using the algorithm described here rather than the ones complement checksum. The following ANSI C reference implementation calculates the value of a Key Tag. This reference implementation applies to all algorithm types except algorithm 1 (see Appendix B.1). The input is the wire format of the RDATA portion of the DNSKEY RR. The code is written for clarity, not efficiency. /* * Assumes that int is at least 16 bits. * First octet of the key tag is the most significant 8 bits of the * return value; * Second octet of the key tag is the least significant 8 bits of the * return value. Arends, et al. Expires March 16, 2004 [Page 33] Internet-Draft DNSSEC Resource Records September 2003 */ unsigned int keytag ( unsigned char key[], /* the RDATA part of the DNSKEY RR */ unsigned int keysize /* the RDLENGTH */ ) { unsigned long ac; /* assumed to be 32 bits or larger */ int i; /* loop index */ for ( ac = 0, i = 0; i < keysize; ++i ) ac += (i & 1) ? key[i] : key[i] << 8; ac += (ac >> 16) & 0xFFFF; return ac & 0xFFFF; } B.1 Key Tag for Algorithm 1 (RSA/MD5) The key tag for algorithm 1 (RSA/MD5) is defined differently than the key tag for all other algorithms, for historical reasons. For a DNSKEY RR with algorithm 1, the key tag is defined to be the most significant 16 bits of the least significant 24 bits in the public key modulus (in other words, the 4th to last and 3rd to last octets of the public key modulus). Please note that Algorithm 1 is NOT RECOMMENDED. Arends, et al. Expires March 16, 2004 [Page 34] Internet-Draft DNSSEC Resource Records September 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication 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 implementors or users of this specification can be obtained from the IETF Secretariat. 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Expires March 16, 2004 [Page 35] Internet-Draft DNSSEC Resource Records September 2003 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. Arends, et al. Expires March 16, 2004 [Page 36]