[Docs] [txt|pdf] [draft-ietf-dnsext...] [Diff1] [Diff2] [IPR] [Errata]

Updated by: 4470, 6014, 6840, 6944 PROPOSED STANDARD
Errata Exist
Network Working Group                                          R. Arends
Request for Comments: 4034                          Telematica Instituut
Obsoletes: 2535, 3008, 3090, 3445, 3655, 3658,                R. Austein
           3755, 3757, 3845                                          ISC
Updates: 1034, 1035, 2136, 2181, 2308, 3225,                   M. Larson
         3007, 3597, 3226                                       VeriSign
Category: Standards Track                                      D. Massey
                                               Colorado State University
                                                                 S. Rose
                                                                    NIST
                                                              March 2005


            Resource Records for the DNS Security Extensions

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 (2005).

Abstract

   This document is part of a family of documents that describe 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
   signature (RRSIG), and authenticated denial of existence (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.











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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.  Background and Related Documents . . . . . . . . . . .  3
       1.2.  Reserved Words . . . . . . . . . . . . . . . . . . . .  3
   2.  The DNSKEY Resource Record . . . . . . . . . . . . . . . . .  4
       2.1.  DNSKEY RDATA Wire Format . . . . . . . . . . . . . . .  4
             2.1.1.  The Flags Field. . . . . . . . . . . . . . . .  4
             2.1.2.  The Protocol Field . . . . . . . . . . . . . .  5
             2.1.3.  The Algorithm Field. . . . . . . . . . . . . .  5
             2.1.4.  The Public Key Field . . . . . . . . . . . . .  5
             2.1.5.  Notes on DNSKEY RDATA Design . . . . . . . . .  5
       2.2.  The DNSKEY RR Presentation Format. . . . . . . . . . .  5
       2.3.  DNSKEY RR Example  . . . . . . . . . . . . . . . . . .  6
   3.  The RRSIG Resource Record  . . . . . . . . . . . . . . . . .  6
       3.1.  RRSIG RDATA Wire Format. . . . . . . . . . . . . . . .  7
             3.1.1.  The Type Covered Field . . . . . . . . . . . .  7
             3.1.2.  The Algorithm Number Field . . . . . . . . . .  8
             3.1.3.  The Labels Field . . . . . . . . . . . . . . .  8
             3.1.4.  Original TTL Field . . . . . . . . . . . . . .  8
             3.1.5.  Signature Expiration and Inception Fields. . .  9
             3.1.6.  The Key Tag Field. . . . . . . . . . . . . . .  9
             3.1.7.  The Signer's Name Field. . . . . . . . . . . .  9
             3.1.8.  The Signature Field. . . . . . . . . . . . . .  9
       3.2.  The RRSIG RR Presentation Format . . . . . . . . . . . 10
       3.3.  RRSIG RR Example . . . . . . . . . . . . . . . . . . . 11
   4.  The NSEC Resource Record . . . . . . . . . . . . . . . . . . 12
       4.1.  NSEC RDATA Wire Format . . . . . . . . . . . . . . . . 13
             4.1.1.  The Next Domain Name Field . . . . . . . . . . 13
             4.1.2.  The Type Bit Maps Field. . . . . . . . . . . . 13
             4.1.3.  Inclusion of Wildcard Names in NSEC RDATA. . . 14
       4.2.  The NSEC RR Presentation Format. . . . . . . . . . . . 14
       4.3.  NSEC RR Example. . . . . . . . . . . . . . . . . . . . 15
   5.  The DS Resource Record . . . . . . . . . . . . . . . . . . . 15
       5.1.  DS RDATA Wire Format . . . . . . . . . . . . . . . . . 16
             5.1.1.  The Key Tag Field. . . . . . . . . . . . . . . 16
             5.1.2.  The Algorithm Field. . . . . . . . . . . . . . 16
             5.1.3.  The Digest Type Field. . . . . . . . . . . . . 17
             5.1.4.  The Digest Field . . . . . . . . . . . . . . . 17
       5.2.  Processing of DS RRs When Validating Responses . . . . 17
       5.3.  The DS RR Presentation Format. . . . . . . . . . . . . 17
       5.4.  DS RR Example. . . . . . . . . . . . . . . . . . . . . 18
   6.  Canonical Form and Order of Resource Records . . . . . . . . 18
       6.1.  Canonical DNS Name Order . . . . . . . . . . . . . . . 18
       6.2.  Canonical RR Form. . . . . . . . . . . . . . . . . . . 19
       6.3.  Canonical RR Ordering within an RRset. . . . . . . . . 20
   7.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . 20
   8.  Security Considerations. . . . . . . . . . . . . . . . . . . 21



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   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
       10.1. Normative References . . . . . . . . . . . . . . . . . 22
       10.2. Informative References . . . . . . . . . . . . . . . . 23
   A.  DNSSEC Algorithm and Digest Types. . . . . . . . . . . . . . 24
       A.1.  DNSSEC Algorithm Types . . . . . . . . . . . . . . . . 24
             A.1.1.  Private Algorithm Types. . . . . . . . . . . . 25
       A.2.  DNSSEC Digest Types. . . . . . . . . . . . . . . . . . 25
   B.  Key Tag Calculation. . . . . . . . . . . . . . . . . . . . . 25
       B.1.  Key Tag for Algorithm 1 (RSA/MD5). . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 29

1.  Introduction

   The DNS Security Extensions (DNSSEC) introduce four new DNS resource
   record types: DNS Public Key (DNSKEY), Resource Record Signature
   (RRSIG), Next Secure (NSEC), and Delegation Signer (DS).  This
   document defines the purpose of each resource record (RR), the RR's
   RDATA format, and its presentation format (ASCII representation).

1.1.  Background and Related Documents

   This document is part of a family of documents defining DNSSEC, which
   should be read together as a set.

   [RFC4033] contains an introduction to DNSSEC and definition of common
   terms; the reader is assumed to be familiar with this document.
   [RFC4033] also contains a list of other documents updated by and
   obsoleted by this document set.

   [RFC4035] defines the DNSSEC protocol operations.

   The reader is also assumed to be familiar with the basic DNS concepts
   described in [RFC1034], [RFC1035], and the subsequent documents that
   update them, particularly [RFC2181] and [RFC2308].

   This document defines the DNSSEC resource records.  All numeric DNS
   type codes given in this document are decimal integers.

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 [RFC2119].






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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 [RFC4035]: A zone signs its authoritative RRsets by
   using a private key and stores the corresponding public key in a
   DNSKEY RR.  A resolver can then use the public key to validate
   signatures covering the RRsets in the zone, and thus to authenticate
   them.

   The DNSKEY RR is not intended as a record for storing arbitrary
   public keys and 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 RR'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 and MUST
   NOT be used to verify RRSIGs that cover RRsets.

   Bit 15 of the Flags field is the Secure Entry Point flag, described
   in [RFC3757].  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



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   intended to be a hint to zone signing or debugging software as to the
   intended use of this DNSKEY record; validators MUST NOT alter their
   behavior during the signature validation process in any way based on
   the setting of this bit.  This also means that a DNSKEY RR with the
   SEP bit set would also need the Zone Key flag set in order to be able
   to generate signatures legally.  A DNSKEY RR with the SEP set and the
   Zone Key flag not set MUST NOT be used to verify RRSIGs that cover
   RRsets.

   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 receipt.

2.1.2.  The Protocol Field

   The Protocol Field MUST have value 3, and the DNSKEY RR MUST be
   treated as invalid during signature verification if it is 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.  The format
   depends on the algorithm of the key being stored and is described in
   separate documents.

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.
   Given the currently defined flags, the possible values are: 0, 256,
   and 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.



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   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 [RFC3548].

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.

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 [RFC4035].  A validator 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.

   An 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
   validator can use to verify the signature.

   Because every authoritative RRset in a zone must be protected by a
   digital signature, RRSIG RRs must be present for names containing a
   CNAME RR.  This is a change to the traditional DNS specification
   [RFC1034], which stated that if a CNAME is present for a name, it is
   the only type allowed at that name.  A RRSIG and NSEC (see Section 4)
   MUST exist for the same name as a CNAME resource record in a signed
   zone.




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   The Type value for the RRSIG RR type is 46.

   The RRSIG RR is class independent.

   An RRSIG RR MUST have the same class as the RRset it covers.

   The TTL value of an RRSIG RR MUST match the TTL value of the RRset it
   covers.  This is an exception to the [RFC2181] rules for TTL values
   of individual RRs within a RRset: individual RRSIG RRs with the same
   owner name will have different TTL values if the RRsets they cover
   have different TTL values.

3.1.  RRSIG RDATA Wire Format

   The RDATA for an 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         /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               /
   /                            Signature                          /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.1.1.  The Type Covered Field

   The Type Covered field identifies the type of the RRset that is
   covered by this RRSIG record.







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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 a validator
   uses it to determine whether 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 have to reconstruct the original owner name in order
   to validate the signature.  [RFC4035] describes how to use the Labels
   field to reconstruct the original owner name.

   The value of the Labels field MUST NOT count either the null (root)
   label that terminates the owner name or the wildcard label (if
   present).  The value of the Labels field MUST be less than or equal
   to the number of labels in the RRSIG owner name.  For example,
   "www.example.com." has a Labels field value of 3, and
   "*.example.com." has a Labels field value of 2.  Root (".") has a
   Labels field value of 0.

   Although the wildcard label is not included in the count stored in
   the Labels field of the RRSIG RR, the wildcard label is part of the
   RRset's owner name when the signature is generated or verified.

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 validator requires the original TTL.  [RFC4035]
   describes how to use the Original TTL field value to reconstruct the
   original TTL.







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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.

   The Signature Expiration and Inception field values specify a date
   and time in the form of 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 that can be expressed by this
   format without wrapping is approximately 136 years.  An RRSIG RR can
   have an Expiration field value that 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, in network byte order.  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 that a validator is supposed to 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.

3.1.8.  The Signature Field

   The Signature field contains the cryptographic signature that covers
   the RRSIG RDATA (excluding the Signature field) and the RRset
   specified by the RRSIG owner name, RRSIG class, and RRSIG Type
   Covered field.  The format of this field depends on the algorithm in
   use, and these formats are described in separate companion documents.

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 fields.  The RRset is in canonical form
   (see Section 6), and the set RR(1),...RR(n) is signed as follows:



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         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 | type | class | 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.

   See Sections 6.2 and 6.3 for details on canonical form and ordering
   of RRsets.

3.2.  The RRSIG RR Presentation Format

   The presentation format of the RDATA portion is as follows:

   The Type Covered field is represented as an RR type mnemonic.  When
   the mnemonic is not known, the TYPE representation as described in
   [RFC3597], Section 5, MUST be used.

   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.





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   The Original TTL field value MUST be represented as an unsigned
   decimal integer.

   The Signature Expiration Time and Inception Time field values MUST be
   represented either as an unsigned decimal integer indicating seconds
   since 1 January 1970 00:00:00 UTC, or in the form YYYYMMDDHHmmSS in
   UTC, where:

      YYYY is the year (0001-9999, 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 hour notation (00-23);
      mm is the minute (00-59); and
      SS is the second (00-59).

   Note that it is always possible to distinguish between these two
   formats because the YYYYMMDDHHmmSS format will always be exactly 14
   digits, while the decimal representation of a 32-bit unsigned integer
   can never be longer than 10 digits.

   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.  See
   Section 2.2.

3.3.  RRSIG RR Example

   The following 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
                                  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




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   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
   indicates 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 that this signature
   can be authenticated using an example.com zone DNSKEY RR whose
   algorithm is 5 and whose key tag is 2642.

4.  The NSEC Resource Record

   The NSEC resource record lists two separate things: the next owner
   name (in the canonical ordering of the zone) that contains
   authoritative data or a delegation point NS RRset, and the set of RR
   types present at the NSEC RR's owner name [RFC3845].  The complete
   set of NSEC RRs in a zone indicates 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 [RFC4035].

   Because every authoritative name in a zone must be part of the NSEC
   chain, NSEC RRs must be present for names containing a CNAME RR.
   This is a change to the traditional DNS specification [RFC1034],
   which stated that if a CNAME is present for a name, it is the only
   type allowed at that name.  An RRSIG (see Section 3) and NSEC MUST
   exist for the same name as does a CNAME resource record in a signed
   zone.

   See [RFC4035] for discussion of how a zone signer determines
   precisely which NSEC RRs it has to include in a zone.

   The type value for the NSEC RR is 47.

   The NSEC RR is class independent.

   The NSEC RR SHOULD have the same TTL value as the SOA minimum TTL
   field.  This is in the spirit of negative caching ([RFC2308]).












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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 Maps                           /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.1.1.  The Next Domain Name Field

   The Next Domain field contains the next owner name (in the canonical
   ordering of the zone) that has authoritative data or contains a
   delegation point NS RRset; 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 of the zone's SOA RR).  This indicates that the owner name of
   the NSEC RR is the last name in the canonical ordering of the zone.

   A sender MUST NOT use DNS name compression on the Next Domain Name
   field when transmitting an NSEC RR.

   Owner names of RRsets for which the given zone is not authoritative
   (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.

4.1.2.  The Type Bit Maps Field

   The Type Bit Maps field identifies the RRset types that exist at the
   NSEC RR's owner name.

   The RR type space is split into 256 window blocks, each representing
   the low-order 8 bits of the 16-bit RR type space.  Each block that
   has at least one active RR type is encoded using a single octet
   window number (from 0 to 255), a single octet bitmap length (from 1
   to 32) indicating the number of octets used for the window block's
   bitmap, and up to 32 octets (256 bits) of bitmap.

   Blocks are present in the NSEC RR RDATA in increasing numerical
   order.

      Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )+

      where "|" denotes concatenation.



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   Each bitmap encodes the low-order 8 bits of RR types within the
   window block, in network bit order.  The first bit is bit 0.  For
   window block 0, bit 1 corresponds to RR type 1 (A), bit 2 corresponds
   to RR type 2 (NS), and so forth.  For window block 1, bit 1
   corresponds to RR type 257, and bit 2 to RR type 258.  If a bit is
   set, it indicates that an RRset of that type is present for the NSEC
   RR's owner name.  If a bit is clear, it indicates that no RRset of
   that type is present for the NSEC RR's owner name.

   Bits representing pseudo-types MUST be clear, as they do not appear
   in zone data.  If encountered, they MUST be ignored upon being read.

   Blocks with no types present MUST NOT be included.  Trailing zero
   octets in the bitmap MUST be omitted.  The length of each block's
   bitmap is determined by the type code with the largest numerical
   value, within that block, 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 bitmap for the NSEC RR at a delegation point requires special
   attention.  Bits corresponding to the delegation NS RRset and the RR
   types for which the parent zone has authoritative data MUST be set;
   bits corresponding to any non-NS RRset for which the parent is not
   authoritative MUST be clear.

   A zone MUST NOT include an NSEC RR for any domain name that only
   holds glue records.

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 the purposes of generating NSEC RRs.  Wildcard owner
   names appear in the Next Domain Name field without any wildcard
   expansion.  [RFC4035] 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.

   The Type Bit Maps field is represented as a sequence of RR type
   mnemonics.  When the mnemonic is not known, the TYPE representation
   described in [RFC3597], Section 5, MUST be used.





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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 TYPE1234 )

   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, NSEC,
   and TYPE1234 mnemonics indicate that there are A, MX, RRSIG, NSEC,
   and TYPE1234 RRsets associated with the name alfa.example.com.

   The RDATA section of the NSEC RR above would be encoded as:

            0x04 'h'  'o'  's'  't'
            0x07 'e'  'x'  'a'  'm'  'p'  'l'  'e'
            0x03 'c'  'o'  'm'  0x00
            0x00 0x06 0x40 0x01 0x00 0x00 0x00 0x03
            0x04 0x1b 0x00 0x00 0x00 0x00 0x00 0x00
            0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
            0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
            0x00 0x00 0x00 0x00 0x20

   Assuming that the validator can authenticate this NSEC record, it
   could be used to prove that beta.example.com does not exist, or to
   prove that there is no AAAA record associated with alfa.example.com.
   Authenticated denial of existence is discussed in [RFC4035].

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
   public 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
   [RFC4035].

   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



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   "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
   [RFC4035].

   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 1 octet
   Algorithm field, a 1 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                             /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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, in network byte order.

   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.








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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 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.  As of the time of this writing, 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
   have Flags bit 7 set.  If the DNSKEY flags do not indicate a DNSSEC
   zone key, the DS RR (and the 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.






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   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.

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 in order to construct and verify RRSIG
   RRs.

6.1.  Canonical DNS Name Order

   For the 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 uppercase
   US-ASCII letters are treated as if they were lowercase US-ASCII
   letters.







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   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
   by 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 the 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
       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, A6, RRSIG, or NSEC, 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.





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6.3.  Canonical RR Ordering within an RRset

   For the purposes of DNS security, RRs with the same owner name,
   class, and type are sorted by treating the RDATA portion of the
   canonical form of each RR as a left-justified unsigned octet sequence
   in which the absence of an octet sorts before a zero octet.

   [RFC2181] specifies that an RRset is not allowed to contain duplicate
   records (multiple RRs with the same owner name, class, type, and
   RDATA).  Therefore, if an implementation detects duplicate RRs when
   putting the RRset in canonical form, it MUST treat this as a protocol
   error.  If the implementation chooses to handle this protocol error
   in the spirit of the robustness principle (being liberal in what it
   accepts), it MUST remove all but one of the duplicate RR(s) for the
   purposes of calculating the canonical form of the RRset.

7.  IANA Considerations

   This document introduces no new IANA considerations, as 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 that are (or once were) related to DNSSEC.

   Please refer to [RFC4035] for additional IANA considerations.

   DNS Resource Record Types: [RFC2535] assigned types 24, 25, and 30 to
      the SIG, KEY, and NXT RRs, respectively.  [RFC3658] assigned DNS
      Resource Record Type 43 to DS.  [RFC3755] assigned types 46, 47,
      and 48 to the RRSIG, NSEC, and DNSKEY RRs, respectively.
      [RFC3755] 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] and to the transaction
      KEY Resource Record described in [RFC2930].

   DNS Security 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.  [RFC3755]
      altered this registry to include flags for each entry regarding
      its use with the DNS security extensions.  Each algorithm entry
      could refer to an algorithm that can be used for zone signing,
      transaction security (see [RFC2931]), or both.  Values 6-251 are
      available for assignment by IETF standards action ([RFC3755]).
      See Appendix A for a full listing of the DNS Security Algorithm
      Numbers entries at the time of this writing and their status for
      use in DNSSEC.




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      [RFC3658] 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] reassigned all 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 a
      Protocol Octet value of 3.

   Flag bits in the KEY and DNSKEY RRs: [RFC3755] created an IANA
      registry for the DNSSEC KEY and DNSKEY RR flag bits.  Initially,
      this registry only contains assignments for bit 7 (the ZONE bit)
      and bit 15 (the Secure Entry Point flag (SEP) bit; see [RFC3757]).
      As stated in [RFC3755], bits 0-6 and 8-14 are available for
      assignment by IETF Standards Action.

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.  Please see [RFC4033] and [RFC4035] for
   additional security considerations related to the use of these
   records.

   The DS record points to a DNSKEY RR by 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 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 that 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 that uses only the key tag to select a DNSKEY RR
   might select the wrong public key in some circumstances.  Please see
   Appendix B for further details.







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   The table of algorithms in Appendix A and the key tag calculation
   algorithms in Appendix B include the RSA/MD5 algorithm for
   completeness, but the RSA/MD5 algorithm is NOT RECOMMENDED, as
   explained in [RFC3110].

9.  Acknowledgements

   This document was created from the input and ideas of the members of
   the DNS Extensions Working Group and working group mailing list.  The
   editors would like to express their thanks for the comments and
   suggestions received during the revision of these security extension
   specifications.  Although explicitly listing everyone who has
   contributed during the decade in which DNSSEC has been under
   development would be impossible, [RFC4033] includes a list of some of
   the participants who were kind enough to comment on these documents.

10.  References

10.1.  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.

   [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.

   [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.

   [RFC2536]  Eastlake 3rd, D., "DSA KEYs and SIGs in the Domain Name
              System (DNS)", RFC 2536, March 1999.

   [RFC2931]  Eastlake 3rd, D., "DNS Request and Transaction Signatures
              ( SIG(0)s )", RFC 2931, September 2000.

   [RFC3110]  Eastlake 3rd, D., "RSA/SHA-1 SIGs and RSA KEYs in the
              Domain Name System (DNS)", RFC 3110, May 2001.





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   [RFC3445]  Massey, D. and S. Rose, "Limiting the Scope of the KEY
              Resource Record (RR)", RFC 3445, December 2002.

   [RFC3548]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 3548, July 2003.

   [RFC3597]  Gustafsson, A., "Handling of Unknown DNS Resource Record
              (RR) Types", RFC 3597, September 2003.

   [RFC3658]  Gudmundsson, O., "Delegation Signer (DS) Resource Record
              (RR)", RFC 3658, December 2003.

   [RFC3755]  Weiler, S., "Legacy Resolver Compatibility for Delegation
              Signer (DS)", RFC 3755, May 2004.

   [RFC3757]  Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name
              System KEY (DNSKEY) Resource Record (RR) Secure Entry
              Point (SEP) Flag", RFC 3757, April 2004.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

10.2.  Informative References

   [RFC2535]  Eastlake 3rd, D., "Domain Name System Security
              Extensions", RFC 2535, March 1999.

   [RFC2537]  Eastlake 3rd, D., "RSA/MD5 KEYs and SIGs in the Domain
              Name System (DNS)", RFC 2537, March 1999.

   [RFC2539]  Eastlake 3rd, D., "Storage of Diffie-Hellman Keys in the
              Domain Name System (DNS)", RFC 2539, March 1999.

   [RFC2930]  Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY
              RR)", RFC 2930, September 2000.

   [RFC3845]  Schlyter, J., "DNS Security (DNSSEC) NextSECure (NSEC)
              RDATA Format", RFC 3845, August 2004.








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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 them.

   A DNSSEC aware resolver or name server MUST implement all MANDATORY
   algorithms.

A.1.  DNSSEC Algorithm Types

   The DNSKEY, RRSIG, and DS RRs use an 8-bit number to identify the
   security algorithm being used.  These values are stored in the
   "Algorithm number" field in the resource record RDATA.

   Some algorithms are usable only for zone signing (DNSSEC), some only
   for transaction security mechanisms (SIG(0) and TSIG), and some for
   both.  Those usable for zone signing may appear in DNSKEY, RRSIG, and
   DS RRs.  Those usable for transaction security would be present in
   SIG(0) and KEY RRs, as described in [RFC2931].

                                Zone
   Value Algorithm [Mnemonic]  Signing  References   Status
   ----- -------------------- --------- ----------  ---------
     0   reserved
     1   RSA/MD5 [RSAMD5]         n      [RFC2537]  NOT RECOMMENDED
     2   Diffie-Hellman [DH]      n      [RFC2539]   -
     3   DSA/SHA-1 [DSA]          y      [RFC2536]  OPTIONAL
     4   Elliptic Curve [ECC]              TBA       -
     5   RSA/SHA-1 [RSASHA1]      y      [RFC3110]  MANDATORY
   252   Indirect [INDIRECT]      n                  -
   253   Private [PRIVATEDNS]     y      see below  OPTIONAL
   254   Private [PRIVATEOID]     y      see below  OPTIONAL
   255   reserved

   6 - 251  Available for assignment by IETF Standards Action.









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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.

   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                 -

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.





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RFC 4034                DNSSEC Resource Records               March 2005


   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 an 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.
    */

   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;
   }



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RFC 4034                DNSSEC Resource Records               March 2005


B.1.  Key Tag for Algorithm 1 (RSA/MD5)

   The key tag for algorithm 1 (RSA/MD5) is defined differently from 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.









































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RFC 4034                DNSSEC Resource Records               March 2005


Authors' Addresses

   Roy Arends
   Telematica Instituut
   Brouwerijstraat 1
   7523 XC  Enschede
   NL

   EMail: roy.arends@telin.nl


   Rob Austein
   Internet Systems Consortium
   950 Charter Street
   Redwood City, CA  94063
   USA

   EMail: sra@isc.org


   Matt Larson
   VeriSign, Inc.
   21345 Ridgetop Circle
   Dulles, VA  20166-6503
   USA

   EMail: mlarson@verisign.com


   Dan Massey
   Colorado State University
   Department of Computer Science
   Fort Collins, CO 80523-1873

   EMail: massey@cs.colostate.edu


   Scott Rose
   National Institute for Standards and Technology
   100 Bureau Drive
   Gaithersburg, MD  20899-8920
   USA

   EMail: scott.rose@nist.gov







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RFC 4034                DNSSEC Resource Records               March 2005


Full Copyright Statement

   Copyright (C) The Internet Society (2005).

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   Internet Society.







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