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RFC4034 - Resource Records for the DNS Security Extensions

王朝other·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

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.

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

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].

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

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.

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.

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.

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.

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:

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.

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

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]).

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.

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.

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

"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.

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.

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.

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.

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.

[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.

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.

[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.

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.

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.

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;

}

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.

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

Full Copyright Statement

Copyright (C) The Internet Society (2005).

This document is subject to the rights, licenses and restrictions

contained in BCP 78, and except as set forth therein, the authors

retain all their rights.

This document and the information contained herein are provided on an

"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS

OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET

ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,

INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE

INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED

WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

The IETF takes no position regarding the validity or scope of any

Intellectual Property Rights or other rights that might be claimed to

pertain to the implementation or use of the technology described in

this document or the extent to which any license under such rights

might or might not be available; nor does it represent that it has

made any independent effort to identify any such rights. Information

on the procedures with respect to rights in RFC documents can be

found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat and any

assurances of licenses to be made available, or the result of an

attempt made to obtain a general license or permission for the use of

such proprietary rights by implementers or users of this

specification can be obtained from the IETF on-line IPR repository at

http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any

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rights that may cover technology that may be required to implement

this standard. Please address the information to the IETF at ietf-

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Acknowledgement

Funding for the RFC Editor function is currently provided by the

Internet Society.

 
 
 
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