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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'Mnemonic' is mentioned on line 1173, but not defined == Missing Reference: 'RSAMD5' is mentioned on line 1176, but not defined == Missing Reference: 'DH' is mentioned on line 1177, but not defined == Missing Reference: 'DSA' is mentioned on line 1178, but not defined == Missing Reference: 'ECC' is mentioned on line 1179, but not defined == Missing Reference: 'RSASHA1' is mentioned on line 1180, but not defined == Missing Reference: 'INDIRECT' is mentioned on line 1181, but not defined == Missing Reference: 'PRIVATEDNS' is mentioned on line 1182, but not defined == Missing Reference: 'PRIVATEOID' is mentioned on line 1183, but not defined == Unused Reference: 'RFC2671' is defined on line 1055, but no explicit reference was found in the text ** Obsolete normative reference: RFC 1521 (Obsoleted by RFC 2045, RFC 2046, RFC 2047, RFC 2048, RFC 2049) ** Obsolete normative reference: RFC 2671 (Obsoleted by RFC 6891) ** Obsolete normative reference: RFC 3445 (Obsoleted by RFC 4033, RFC 4034, RFC 4035) ** Obsolete normative reference: RFC 3658 (Obsoleted by RFC 4033, RFC 4034, RFC 4035) == Outdated reference: draft-ietf-dnsext-dnssec-intro has been published as RFC 4033 == Outdated reference: draft-ietf-dnsext-dnssec-protocol has been published as RFC 4035 == Outdated reference: draft-ietf-dnsext-keyrr-key-signing-flag has been published as RFC 3757 == Outdated reference: draft-ietf-dnsext-dnssec-2535typecode-change has been published as RFC 3755 -- Obsolete informational reference (is this intentional?): RFC 2535 (Obsoleted by RFC 4033, RFC 4034, RFC 4035) Summary: 5 errors (**), 0 flaws (~~), 18 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNS Extensions R. Arends 3 Internet-Draft Telematica Instituut 4 Expires: August 16, 2004 R. Austein 5 ISC 6 M. Larson 7 VeriSign 8 D. Massey 9 USC/ISI 10 S. Rose 11 NIST 12 February 16, 2004 14 Resource Records for the DNS Security Extensions 15 draft-ietf-dnsext-dnssec-records-07 17 Status of this Memo 19 This document is an Internet-Draft and is in full conformance with 20 all provisions of Section 10 of RFC2026. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that other 24 groups may also distribute working documents as Internet-Drafts. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 The list of current Internet-Drafts can be accessed at http:// 32 www.ietf.org/ietf/1id-abstracts.txt. 34 The list of Internet-Draft Shadow Directories can be accessed at 35 http://www.ietf.org/shadow.html. 37 This Internet-Draft will expire on August 16, 2004. 39 Copyright Notice 41 Copyright (C) The Internet Society (2004). All Rights Reserved. 43 Abstract 45 This document is part of a family of documents that describes the DNS 46 Security Extensions (DNSSEC). The DNS Security Extensions are a 47 collection of resource records and protocol modifications that 48 provide source authentication for the DNS. This document defines the 49 public key (DNSKEY), delegation signer (DS), resource record digital 50 signature (RRSIG), and authenticated denial of existence (NSEC) 51 resource records. The purpose and format of each resource record is 52 described in detail, and an example of each resource record is given. 54 This document obsoletes RFC 2535 and incorporates changes from all 55 updates to RFC 2535. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 60 1.1 Background and Related Documents . . . . . . . . . . . . . . 4 61 1.2 Reserved Words . . . . . . . . . . . . . . . . . . . . . . . 4 62 1.3 Editors' Notes . . . . . . . . . . . . . . . . . . . . . . . 4 63 1.3.1 Open Technical Issues . . . . . . . . . . . . . . . . . . . 4 64 1.3.2 Technical Changes or Corrections . . . . . . . . . . . . . . 4 65 1.3.3 Typos and Minor Corrections . . . . . . . . . . . . . . . . 5 66 2. The DNSKEY Resource Record . . . . . . . . . . . . . . . . . 6 67 2.1 DNSKEY RDATA Wire Format . . . . . . . . . . . . . . . . . . 6 68 2.1.1 The Flags Field . . . . . . . . . . . . . . . . . . . . . . 6 69 2.1.2 The Protocol Field . . . . . . . . . . . . . . . . . . . . . 7 70 2.1.3 The Algorithm Field . . . . . . . . . . . . . . . . . . . . 7 71 2.1.4 The Public Key Field . . . . . . . . . . . . . . . . . . . . 7 72 2.1.5 Notes on DNSKEY RDATA Design . . . . . . . . . . . . . . . . 7 73 2.2 The DNSKEY RR Presentation Format . . . . . . . . . . . . . 7 74 2.3 DNSKEY RR Example . . . . . . . . . . . . . . . . . . . . . 8 75 3. The RRSIG Resource Record . . . . . . . . . . . . . . . . . 9 76 3.1 RRSIG RDATA Wire Format . . . . . . . . . . . . . . . . . . 9 77 3.1.1 The Type Covered Field . . . . . . . . . . . . . . . . . . . 10 78 3.1.2 The Algorithm Number Field . . . . . . . . . . . . . . . . . 10 79 3.1.3 The Labels Field . . . . . . . . . . . . . . . . . . . . . . 10 80 3.1.4 Original TTL Field . . . . . . . . . . . . . . . . . . . . . 11 81 3.1.5 Signature Expiration and Inception Fields . . . . . . . . . 11 82 3.1.6 The Key Tag Field . . . . . . . . . . . . . . . . . . . . . 11 83 3.1.7 The Signer's Name Field . . . . . . . . . . . . . . . . . . 12 84 3.1.8 The Signature Field . . . . . . . . . . . . . . . . . . . . 12 85 3.2 The RRSIG RR Presentation Format . . . . . . . . . . . . . . 13 86 3.3 RRSIG RR Example . . . . . . . . . . . . . . . . . . . . . . 13 87 4. The NSEC Resource Record . . . . . . . . . . . . . . . . . . 15 88 4.1 NSEC RDATA Wire Format . . . . . . . . . . . . . . . . . . . 15 89 4.1.1 The Next Domain Name Field . . . . . . . . . . . . . . . . . 15 90 4.1.2 The Type Bit Maps Field . . . . . . . . . . . . . . . . . . 16 91 4.1.3 Inclusion of Wildcard Names in NSEC RDATA . . . . . . . . . 17 92 4.2 The NSEC RR Presentation Format . . . . . . . . . . . . . . 17 93 4.3 NSEC RR Example . . . . . . . . . . . . . . . . . . . . . . 17 94 5. The DS Resource Record . . . . . . . . . . . . . . . . . . . 19 95 5.1 DS RDATA Wire Format . . . . . . . . . . . . . . . . . . . . 19 96 5.1.1 The Key Tag Field . . . . . . . . . . . . . . . . . . . . . 20 97 5.1.2 The Algorithm Field . . . . . . . . . . . . . . . . . . . . 20 98 5.1.3 The Digest Type Field . . . . . . . . . . . . . . . . . . . 20 99 5.1.4 The Digest Field . . . . . . . . . . . . . . . . . . . . . . 20 100 5.2 Processing of DS RRs When Validating Responses . . . . . . . 20 101 5.3 The DS RR Presentation Format . . . . . . . . . . . . . . . 21 102 5.4 DS RR Example . . . . . . . . . . . . . . . . . . . . . . . 21 103 6. Canonical Form and Order of Resource Records . . . . . . . . 22 104 6.1 Canonical DNS Name Order . . . . . . . . . . . . . . . . . . 22 105 6.2 Canonical RR Form . . . . . . . . . . . . . . . . . . . . . 22 106 6.3 Canonical RR Ordering Within An RRset . . . . . . . . . . . 23 107 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 24 108 8. Security Considerations . . . . . . . . . . . . . . . . . . 26 109 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 27 110 Normative References . . . . . . . . . . . . . . . . . . . . 28 111 Informative References . . . . . . . . . . . . . . . . . . . 30 112 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 30 113 A. DNSSEC Algorithm and Digest Types . . . . . . . . . . . . . 32 114 A.1 DNSSEC Algorithm Types . . . . . . . . . . . . . . . . . . . 32 115 A.1.1 Private Algorithm Types . . . . . . . . . . . . . . . . . . 32 116 A.2 DNSSEC Digest Types . . . . . . . . . . . . . . . . . . . . 33 117 B. Key Tag Calculation . . . . . . . . . . . . . . . . . . . . 34 118 B.1 Key Tag for Algorithm 1 (RSA/MD5) . . . . . . . . . . . . . 35 119 Intellectual Property and Copyright Statements . . . . . . . 36 121 1. Introduction 123 The DNS Security Extensions (DNSSEC) introduce four new DNS resource 124 record types: DNSKEY, RRSIG, NSEC, and DS. This document defines the 125 purpose of each resource record (RR), the RR's RDATA format, and its 126 presentation format (ASCII representation). 128 1.1 Background and Related Documents 130 The reader is assumed to be familiar with the basic DNS concepts 131 described in RFC1034 [RFC1034], RFC1035 [RFC1035] and subsequent RFCs 132 that update them: RFC2136 [RFC2136], RFC2181 [RFC2181] and RFC2308 133 [RFC2308]. 135 This document is part of a family of documents that define the DNS 136 security extensions. The DNS security extensions (DNSSEC) are a 137 collection of resource records and DNS protocol modifications that 138 add source authentication and data integrity to the Domain Name 139 System (DNS). An introduction to DNSSEC and definitions of common 140 terms can be found in [I-D.ietf-dnsext-dnssec-intro]. A description 141 of DNS protocol modifications can be found in 142 [I-D.ietf-dnsext-dnssec-protocol]. This document defines the DNSSEC 143 resource records. 145 1.2 Reserved Words 147 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 148 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 149 document are to be interpreted as described in RFC 2119 [RFC2119]. 151 1.3 Editors' Notes 153 1.3.1 Open Technical Issues 155 The cryptographic algorithm types (Appendix A) requires input from 156 the working group. The DSA algorithm was moved to OPTIONAL. This 157 had strong consensus in workshops and various discussions and a 158 separate Internet-Draft solely to move DSA from MANDATORY to OPTIONAL 159 seemed excessive. This draft solicits input on that proposed change. 161 1.3.2 Technical Changes or Corrections 163 Please report technical corrections to dnssec-editors@east.isi.edu. 164 To assist the editors, please indicate the text in error and point 165 out the RFC that defines the correct behavior. For a technical 166 change where no RFC that defines the correct behavior, or if there's 167 more than one applicable RFC and the definitions conflict, please 168 post the issue to namedroppers. 170 An example correction to dnssec-editors might be: Page X says 171 "DNSSEC RRs SHOULD be automatically returned in responses." This was 172 true in RFC 2535, but RFC 3225 (Section 3, 3rd paragraph) says the 173 DNSSEC RR types MUST NOT be included in responses unless the resolver 174 indicated support for DNSSEC. 176 1.3.3 Typos and Minor Corrections 178 Please report any typos corrections to dnssec-editors@east.isi.edu. 179 To assist the editors, please provide enough context for us to find 180 the incorrect text quickly. 182 An example message to dnssec-editors might be: page X says "the 183 DNSSEC standard has been in development for over 1 years". It 184 should read "over 10 years". 186 2. The DNSKEY Resource Record 188 DNSSEC uses public key cryptography to sign and authenticate DNS 189 resource record sets (RRsets). The public keys are stored in DNSKEY 190 resource records and are used in the DNSSEC authentication process 191 described in [I-D.ietf-dnsext-dnssec-protocol]: A zone signs its 192 authoritative RRsets using a private key and stores the corresponding 193 public key in a DNSKEY RR. A resolver can then use the public key to 194 authenticate signatures covering the RRsets in the zone. 196 The DNSKEY RR is not intended as a record for storing arbitrary 197 public keys, and MUST NOT be used to store certificates or public 198 keys that do not directly relate to the DNS infrastructure. 200 The Type value for the DNSKEY RR type is 48. 202 The DNSKEY RR is class independent. 204 The DNSKEY RR has no special TTL requirements. 206 2.1 DNSKEY RDATA Wire Format 208 The RDATA for a DNSKEY RR consists of a 2 octet Flags Field, a 1 209 octet Protocol Field, a 1 octet Algorithm Field, and the Public Key 210 Field. 212 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 213 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 1 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 215 | Flags | Protocol | Algorithm | 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 / / 218 / Public Key / 219 / / 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 2.1.1 The Flags Field 224 Bit 7 of the Flags field is the Zone Key flag. If bit 7 has value 1, 225 then the DNSKEY record holds a DNS zone key and the DNSKEY RR's owner 226 name MUST be the name of a zone. If bit 7 has value 0, then the 227 DNSKEY record holds some other type of DNS public key, such as a 228 public key used by TKEY and MUST NOT be used to verify RRSIGs that 229 cover RRsets. 231 Bit 15 of the Flags field is the Secure Entry Point flag, described 232 in [I-D.ietf-dnsext-keyrr-key-signing-flag]. If bit 15 has value 1, 233 then the DNSKEY record holds a key intended for use as a secure entry 234 point. This flag is only intended to be to a hint to zone signing or 235 debugging software as to the intended use of this DNSKEY record; 236 security-aware resolvers MUST NOT alter their behavior during the 237 signature validation process in any way based on the setting of this 238 bit. 240 Bits 0-6 and 8-14 are reserved: these bits MUST have value 0 upon 241 creation of the DNSKEY RR, and MUST be ignored upon reception. 243 2.1.2 The Protocol Field 245 The Protocol Field MUST have value 3 and MUST be treated as invalid 246 during signature verification if found to be some value other than 3. 248 2.1.3 The Algorithm Field 250 The Algorithm field identifies the public key's cryptographic 251 algorithm and determines the format of the Public Key field. A list 252 of DNSSEC algorithm types can be found in Appendix A.1 254 2.1.4 The Public Key Field 256 The Public Key Field holds the public key material. The format 257 depends on the algorithm of the key being stored and are described in 258 separate documents. 260 2.1.5 Notes on DNSKEY RDATA Design 262 Although the Protocol Field always has value 3, it is retained for 263 backward compatibility with early versions of the KEY record. 265 2.2 The DNSKEY RR Presentation Format 267 The presentation format of the RDATA portion is as follows: 269 The Flag field MUST be represented as an unsigned decimal integer 270 with a value of 0, 256, or 257. 272 The Protocol Field MUST be represented as an unsigned decimal integer 273 with a value of 3. 275 The Algorithm field MUST be represented either as an unsigned 276 decimal integer or as an algorithm mnemonic as specified in Appendix 277 A.1. 279 The Public Key field MUST be represented as a Base64 encoding of the 280 Public Key. Whitespace is allowed within the Base64 text. For a 281 definition of Base64 encoding, see [RFC1521] Section 5.2. 283 2.3 DNSKEY RR Example 285 The following DNSKEY RR stores a DNS zone key for example.com. 287 example.com. 86400 IN DNSKEY 256 3 5 ( AQPSKmynfzW4kyBv015MUG2DeIQ3 288 Cbl+BBZH4b/0PY1kxkmvHjcZc8no 289 kfzj31GajIQKY+5CptLr3buXA10h 290 WqTkF7H6RfoRqXQeogmMHfpftf6z 291 Mv1LyBUgia7za6ZEzOJBOztyvhjL 292 742iU/TpPSEDhm2SNKLijfUppn1U 293 aNvv4w== ) 295 The first four text fields specify the owner name, TTL, Class, and RR 296 type (DNSKEY). Value 256 indicates that the Zone Key bit (bit 7) in 297 the Flags field has value 1. Value 3 is the fixed Protocol value. 298 Value 5 indicates the public key algorithm. Appendix A.1 identifies 299 algorithm type 5 as RSA/SHA1 and indicates that the format of the 300 RSA/SHA1 public key field is defined in [RFC3110]. The remaining 301 text is a Base64 encoding of the public key. 303 3. The RRSIG Resource Record 305 DNSSEC uses public key cryptography to sign and authenticate DNS 306 resource record sets (RRsets). Digital signatures are stored in 307 RRSIG resource records and are used in the DNSSEC authentication 308 process described in [I-D.ietf-dnsext-dnssec-protocol]. A 309 security-aware resolver can use these RRSIG RRs to authenticate 310 RRsets from the zone. The RRSIG RR MUST only be used to carry 311 verification material (digital signatures) used to secure DNS 312 operations. 314 An RRSIG record contains the signature for an RRset with a particular 315 name, class, and type. The RRSIG RR specifies a validity interval 316 for the signature and uses the Algorithm, the Signer's Name, and the 317 Key Tag to identify the DNSKEY RR containing the public key that a 318 resolver can use to verify the signature. 320 Because every authoritative RRset in a zone must be protected by a 321 digital signature, RRSIG RRs must be present for names containing a 322 CNAME RR. This is a change to the traditional DNS specification 323 [RFC1034] that stated that if a CNAME is present for a name, it is 324 the only type allowed at that name. A RRSIG and NSEC (see Section 4) 325 MUST exist for the same name as a CNAME resource record in a secure 326 zone. 328 The Type value for the RRSIG RR type is 46. 330 The RRSIG RR is class independent. 332 An RRSIG RR MUST have the same class as the RRset it covers. 334 The TTL value of an RRSIG RR SHOULD match the TTL value of the RRset 335 it covers. This is an exception to the [RFC2181] rules for TTL 336 values of individual RRs within a RRset: individual RRSIG with the 337 same owner name will have different TTL values if the RRsets that 338 they cover have different TTL values. 340 3.1 RRSIG RDATA Wire Format 342 The RDATA for an RRSIG RR consists of a 2 octet Type Covered field, a 343 1 octet Algorithm field, a 1 octet Labels field, a 4 octet Original 344 TTL field, a 4 octet Signature Expiration field, a 4 octet Signature 345 Inception field, a 2 octet Key tag, the Signer's Name field, and the 346 Signature field. 348 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 349 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 1 350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 351 | Type Covered | Algorithm | Labels | 352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 353 | Original TTL | 354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 355 | Signature Expiration | 356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 357 | Signature Inception | 358 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 359 | Key Tag | / 360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Signer's Name / 361 / / 362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 363 / / 364 / Signature / 365 / / 366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 368 3.1.1 The Type Covered Field 370 The Type Covered field identifies the type of the RRset which is 371 covered by this RRSIG record. 373 3.1.2 The Algorithm Number Field 375 The Algorithm Number field identifies the cryptographic algorithm 376 used to create the signature. A list of DNSSEC algorithm types can 377 be found in Appendix A.1 379 3.1.3 The Labels Field 381 The Labels field specifies the number of labels in the original RRSIG 382 RR owner name. The significance of this field is that from it a 383 verifier can determine if the answer was synthesized from a wildcard. 384 If so, it can be used to determine what owner name was used in 385 generating the signature. 387 To validate a signature, the validator needs the original owner name 388 that was used to create the signature. If the original owner name 389 contains a wildcard label ("*"), the owner name may have been 390 expanded by the server during the response process, in which case the 391 validator will need to reconstruct the original owner name in order 392 to validate the signature. [I-D.ietf-dnsext-dnssec-protocol] 393 describes how to use the Labels field to reconstruct the original 394 owner name. 396 The value of the Labels field MUST NOT count either the null (root) 397 label that terminates the owner name or the wildcard label (if 398 present). The value of the Labels field MUST be less than or equal 399 to the number of labels in the RRSIG owner name. For example, 400 "www.example.com." has a Labels field value of 3, and 401 "*.example.com." has a Labels field value of 2. Root (".") has a 402 Labels field value of 0. 404 Although the wildcard label is not included in the count stored in 405 the Labels field of the RRSIG RR, the wildcard label is part of the 406 RRset's owner name when generating or verifying the signature. 408 3.1.4 Original TTL Field 410 The Original TTL field specifies the TTL of the covered RRset as it 411 appears in the authoritative zone. 413 The Original TTL field is necessary because a caching resolver 414 decrements the TTL value of a cached RRset. In order to validate a 415 signature, a resolver requires the original TTL. 416 [I-D.ietf-dnsext-dnssec-protocol] describes how to use the Original 417 TTL field value to reconstruct the original TTL. 419 3.1.5 Signature Expiration and Inception Fields 421 The Signature Expiration and Inception fields specify a validity 422 period for the signature. The RRSIG record MUST NOT be used for 423 authentication prior to the inception date and MUST NOT be used for 424 authentication after the expiration date. 426 Signature Expiration and Inception field values are in POSIX.1 time 427 format: a 32-bit unsigned number of seconds elapsed since 1 January 428 1970 00:00:00 UTC, ignoring leap seconds, in network byte order. The 429 longest interval which can be expressed by this format without 430 wrapping is approximately 136 years. An RRSIG RR can have an 431 Expiration field value which is numerically smaller than the 432 Inception field value if the expiration field value is near the 433 32-bit wrap-around point or if the signature is long lived. Because 434 of this, all comparisons involving these fields MUST use "Serial 435 number arithmetic" as defined in [RFC1982]. As a direct consequence, 436 the values contained in these fields cannot refer to dates more than 437 68 years in either the past or the future. 439 3.1.6 The Key Tag Field 441 The Key Tag field contains the key tag value of the DNSKEY RR that 442 validates this signature. Appendix B explains how to calculate Key 443 Tag values. 445 3.1.7 The Signer's Name Field 447 The Signer's Name field value identifies the owner name of the DNSKEY 448 RR which a security-aware resolver should use to validate this 449 signature. The Signer's Name field MUST contain the name of the zone 450 of the covered RRset. A sender MUST NOT use DNS name compression on 451 the Signer's Name field when transmitting a RRSIG RR. A receiver 452 which receives an RRSIG RR containing a compressed Signer's Name 453 field SHOULD decompress the field value. 455 3.1.8 The Signature Field 457 The Signature field contains the cryptographic signature which covers 458 the RRSIG RDATA (excluding the Signature field) and the RRset 459 specified by the RRSIG owner name, RRSIG class, and RRSIG Type 460 Covered field. The format of this field depends on the algorithm in 461 use and these formats are described in separate companion documents. 463 3.1.8.1 Signature Calculation 465 A signature covers the RRSIG RDATA (excluding the Signature Field) 466 and covers the data RRset specified by the RRSIG owner name, RRSIG 467 class, and RRSIG Type Covered fields. The RRset is in canonical form 468 (see Section 6) and the set RR(1),...RR(n) is signed as follows: 470 signature = sign(RRSIG_RDATA | RR(1) | RR(2)... ) where 472 "|" denotes concatenation; 474 RRSIG_RDATA is the wire format of the RRSIG RDATA fields 475 with the Signer's Name field in canonical form and 476 the Signature field excluded; 478 RR(i) = owner | class | type | TTL | RDATA length | RDATA; 480 "owner" is the fully qualified owner name of the RRset in 481 canonical form (for RRs with wildcard owner names, the 482 wildcard label is included in the owner name); 484 Each RR MUST have the same owner name as the RRSIG RR; 486 Each RR MUST have the same class as the RRSIG RR; 488 Each RR in the RRset MUST have the RR type listed in the 489 RRSIG RR's Type Covered field; 491 Each RR in the RRset MUST have the TTL listed in the 492 RRSIG Original TTL Field; 493 Any DNS names in the RDATA field of each RR MUST be in 494 canonical form; and 496 The RRset MUST be sorted in canonical order. 498 3.2 The RRSIG RR Presentation Format 500 The presentation format of the RDATA portion is as follows: 502 The Type Covered field value MUST be represented either as an 503 unsigned decimal integer or as the mnemonic for the covered RR type. 505 The Algorithm field value MUST be represented either as an unsigned 506 decimal integer or as an algorithm mnemonic as specified in Appendix 507 A.1. 509 The Labels field value MUST be represented as an unsigned decimal 510 integer. 512 The Original TTL field value MUST be represented as an unsigned 513 decimal integer. 515 The Signature Expiration Time and Inception Time field values MUST be 516 represented in the form YYYYMMDDHHmmSS in UTC, where: 518 YYYY is the year (0000-9999, but see Section 3.1.5); 520 MM is the month number (01-12); 522 DD is the day of the month (01-31); 524 HH is the hour in 24 hours notation (00-23); 526 mm is the minute (00-59); 528 SS is the second (00-59). 530 The Key Tag field MUST be represented as an unsigned decimal integer. 532 The Signer's Name field value MUST be represented as a domain name. 534 The Signature field is represented as a Base64 encoding of the 535 signature. Whitespace is allowed within the Base64 text. For a 536 definition of Base64 encoding see [RFC1521] Section 5.2. 538 3.3 RRSIG RR Example 539 The following an RRSIG RR stores the signature for the A RRset of 540 host.example.com: 542 host.example.com. 86400 IN RRSIG A 5 3 86400 20030322173103 ( 543 20030220173103 2642 example.com. 544 oJB1W6WNGv+ldvQ3WDG0MQkg5IEhjRip8WTr 545 PYGv07h108dUKGMeDPKijVCHX3DDKdfb+v6o 546 B9wfuh3DTJXUAfI/M0zmO/zz8bW0Rznl8O3t 547 GNazPwQKkRN20XPXV6nwwfoXmJQbsLNrLfkG 548 J5D6fwFm8nN+6pBzeDQfsS3Ap3o= ) 550 The first four fields specify the owner name, TTL, Class, and RR type 551 (RRSIG). The "A" represents the Type Covered field. The value 5 552 identifies the algorithm used (RSA/SHA1) to create the signature. 553 The value 3 is the number of Labels in the original owner name. The 554 value 86400 in the RRSIG RDATA is the Original TTL for the covered A 555 RRset. 20030322173103 and 20030220173103 are the expiration and 556 inception dates, respectively. 2642 is the Key Tag, and example.com. 557 is the Signer's Name. The remaining text is a Base64 encoding of the 558 signature. 560 Note that combination of RRSIG RR owner name, class, and Type Covered 561 indicate that this RRSIG covers the "host.example.com" A RRset. The 562 Label value of 3 indicates that no wildcard expansion was used. The 563 Algorithm, Signer's Name, and Key Tag indicate this signature can be 564 authenticated using an example.com zone DNSKEY RR whose algorithm is 565 5 and key tag is 2642. 567 4. The NSEC Resource Record 569 The NSEC resource record lists two separate things: the owner name of 570 the next authoritative RRset in the canonical ordering of the zone, 571 and the set of RR types present at the NSEC RR's owner name. The 572 complete set of NSEC RRs in a zone both indicate which authoritative 573 RRsets exist in a zone and also form a chain of authoritative owner 574 names in the zone. This information is used to provide authenticated 575 denial of existence for DNS data, as described in 576 [I-D.ietf-dnsext-dnssec-protocol]. 578 Because every authoritative name in a zone must be part of the NSEC 579 chain, NSEC RRs must be present for names containing a CNAME RR. 580 This is a change to the traditional DNS specification [RFC1034] that 581 stated that if a CNAME is present for a name, it is the only type 582 allowed at that name. An RRSIG (see Section 3) and NSEC MUST exist 583 for the same name as a CNAME resource record in a secure zone. 585 The type value for the NSEC RR is 47. 587 The NSEC RR is class independent. 589 The NSEC RR SHOULD have the same TTL value as the SOA minimum TTL 590 field. This is in the spirt of negative caching [RFC2308]. 592 4.1 NSEC RDATA Wire Format 594 The RDATA of the NSEC RR is as shown below: 596 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 597 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 1 598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 599 / Next Domain Name / 600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 601 / Type Bit Maps / 602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 4.1.1 The Next Domain Name Field 606 The Next Domain Name field contains the owner name of the next 607 authoritative owner name in the canonical ordering of the zone; see 608 Section 6.1 for an explanation of canonical ordering. The value of 609 the Next Domain Name field in the last NSEC record in the zone is the 610 name of the zone apex (the owner name of the zone's SOA RR). 612 A sender MUST NOT use DNS name compression on the Next Domain Name 613 field when transmitting an NSEC RR. A receiver which receives an 614 NSEC RR containing a compressed Next Domain Name field SHOULD 615 decompress the field value. 617 Owner names of RRsets not authoritative for the given zone (such as 618 glue records) MUST NOT be listed in the Next Domain Name unless at 619 least one authoritative RRset exists at the same owner name. 621 4.1.2 The Type Bit Maps Field 623 The Type Bit Maps field identifies the RRset types which exist at the 624 NSEC RR's owner name. 626 The RR type space is split into 256 window blocks, each representing 627 the low-order 8 bits of the 16-bit RR type space. Each block that has 628 at least one active RR type is encoded using a single octet window 629 number (from 0 to 255), a single octet bitmap length (from 1 to 32) 630 indicating the number of octets used for the window block's bitmap, 631 and up to 32 octets (256 bits) of bitmap. 633 Blocks are present in the NSEC RR RDATA in increasing numerical 634 order. 636 Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )+ 638 where "|" denotes concatenation. 640 Each bitmap encodes the low-order 8 bits of RR types within the 641 window block, in network bit order. The first bit is bit 0. For 642 window block 0, bit 1 corresponds to RR type 1 (A), bit 2 corresponds 643 to RR type 2 (NS), and so forth. For window block 1, bit 1 644 corresponds to RR type 257, bit 2 to RR type 258. If a bit is set to 645 1, it indicates that an RRset of that type is present for the NSEC 646 RR's owner name. If a bit is set to 0, it indicates that no RRset of 647 that type is present for the NSEC RR's owner name. 649 Since bit 0 in window block 0 refers to the non-existent RR type 0, 650 it MUST be set to 0. After verification, the validator MUST ignore 651 the value of bit 0 in window block 0. 653 Bits representing pseudo-types MUST be set to 0, since they do not 654 appear in zone data. If encountered, they MUST be ignored upon 655 reading. 657 Blocks with no types present MUST NOT be included. Trailing zero 658 octets in the bitmap MUST be omitted. The length of each block's 659 bitmap is determined by the type code with the largest numerical 660 value, within that block, among the set of RR types present at the 661 NSEC RR's owner name. Trailing zero octets not specified MUST be 662 interpreted as zero octets. 664 A zone MUST NOT generate an NSEC RR for any domain name that only 665 holds glue records. 667 4.1.3 Inclusion of Wildcard Names in NSEC RDATA 669 If a wildcard owner name appears in a zone, the wildcard label ("*") 670 is treated as a literal symbol and is treated the same as any other 671 owner name for purposes of generating NSEC RRs. Wildcard owner names 672 appear in the Next Domain Name field without any wildcard expansion. 673 [I-D.ietf-dnsext-dnssec-protocol] describes the impact of wildcards 674 on authenticated denial of existence. 676 4.2 The NSEC RR Presentation Format 678 The presentation format of the RDATA portion is as follows: 680 The Next Domain Name field is represented as a domain name. 682 The Type Bit Maps field is represented as a sequence of RR type 683 mnemonics. When the mnemonic is not known, the TYPE representation 684 as described in [RFC3597] (section 5) MUST be used. 686 4.3 NSEC RR Example 688 The following NSEC RR identifies the RRsets associated with 689 alfa.example.com. and identifies the next authoritative name after 690 alfa.example.com. 692 alfa.example.com. 86400 IN NSEC host.example.com. ( 693 A MX RRSIG NSEC TYPE1234 ) 695 The first four text fields specify the name, TTL, Class, and RR type 696 (NSEC). The entry host.example.com. is the next authoritative name 697 after alfa.example.com. in canonical order. The A, MX, RRSIG, NSEC, 698 and TYPE1234 mnemonics indicate there are A, MX, RRSIG, NSEC, and 699 TYPE1234 RRsets associated with the name alfa.example.com. 701 The RDATA section of the NSEC RR above would be encoded as: 703 0x04 'h' 'o' 's' 't' 704 0x07 'e' 'x' 'a' 'm' 'p' 'l' 'e' 705 0x03 'c' 'o' 'm' 0x00 706 0x00 0x06 0x40 0x01 0x00 0x00 0x00 0x03 707 0x04 0x1b 0x00 0x00 0x00 0x00 0x00 0x00 708 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 709 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 710 0x00 0x00 0x00 0x00 0x20 712 Assuming that the resolver can authenticate this NSEC record, it 713 could be used to prove that beta.example.com does not exist, or could 714 be used to prove there is no AAAA record associated with 715 alfa.example.com. Authenticated denial of existence is discussed in 716 [I-D.ietf-dnsext-dnssec-protocol]. 718 5. The DS Resource Record 720 The DS Resource Record refers to a DNSKEY RR and is used in the DNS 721 DNSKEY authentication process. A DS RR refers to a DNSKEY RR by 722 storing the key tag, algorithm number, and a digest of the DNSKEY RR. 723 Note that while the digest should be sufficient to identify the 724 public key, storing the key tag and key algorithm helps make the 725 identification process more efficient. By authenticating the DS 726 record, a resolver can authenticate the DNSKEY RR to which the DS 727 record points. The key authentication process is described in 728 [I-D.ietf-dnsext-dnssec-protocol]. 730 The DS RR and its corresponding DNSKEY RR have the same owner name, 731 but they are stored in different locations. The DS RR appears only 732 on the upper (parental) side of a delegation, and is authoritative 733 data in the parent zone. For example, the DS RR for "example.com" is 734 stored in the "com" zone (the parent zone) rather than in the 735 "example.com" zone (the child zone). The corresponding DNSKEY RR is 736 stored in the "example.com" zone (the child zone). This simplifies 737 DNS zone management and zone signing, but introduces special response 738 processing requirements for the DS RR; these are described in 739 [I-D.ietf-dnsext-dnssec-protocol]. 741 The type number for the DS record is 43. 743 The DS resource record is class independent. 745 The DS RR has no special TTL requirements. 747 5.1 DS RDATA Wire Format 749 The RDATA for a DS RR consists of a 2 octet Key Tag field, a one 750 octet Algorithm field, a one octet Digest Type field, and a Digest 751 field. 753 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 754 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 1 755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 756 | Key Tag | Algorithm | Digest Type | 757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 758 / / 759 / Digest / 760 / / 761 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 763 5.1.1 The Key Tag Field 765 The Key Tag field lists the key tag of the DNSKEY RR referred to by 766 the DS record. 768 The Key Tag used by the DS RR is identical to the Key Tag used by 769 RRSIG RRs. Appendix B describes how to compute a Key Tag. 771 5.1.2 The Algorithm Field 773 The Algorithm field lists the algorithm number of the DNSKEY RR 774 referred to by the DS record. 776 The algorithm number used by the DS RR is identical to the algorithm 777 number used by RRSIG and DNSKEY RRs. Appendix A.1 lists the algorithm 778 number types. 780 5.1.3 The Digest Type Field 782 The DS RR refers to a DNSKEY RR by including a digest of that DNSKEY 783 RR. The Digest Type field identifies the algorithm used to construct 784 the digest. Appendix A.2 lists the possible digest algorithm types. 786 5.1.4 The Digest Field 788 The DS record refers to a DNSKEY RR by including a digest of that 789 DNSKEY RR. 791 The digest is calculated by concatenating the canonical form of the 792 fully qualified owner name of the DNSKEY RR with the DNSKEY RDATA, 793 and then applying the digest algorithm. 795 digest = digest_algorithm( DNSKEY owner name | DNSKEY RDATA); 797 "|" denotes concatenation 799 DNSKEY RDATA = Flags | Protocol | Algorithm | Public Key. 801 The size of the digest may vary depending on the digest algorithm and 802 DNSKEY RR size. As of the time of writing, the only defined digest 803 algorithm is SHA-1, which produces a 20 octet digest. 805 5.2 Processing of DS RRs When Validating Responses 807 The DS RR links the authentication chain across zone boundaries, so 808 the DS RR requires extra care in processing. The DNSKEY RR referred 809 to in the DS RR MUST be a DNSSEC zone key. The DNSKEY RR Flags MUST 810 have Flags bit 7 set to value 1. If the key tag does not indicate a 811 DNSSEC zone key, the DS RR (and DNSKEY RR it references) MUST NOT be 812 used in the validation process. 814 5.3 The DS RR Presentation Format 816 The presentation format of the RDATA portion is as follows: 818 The Key Tag field MUST be represented as an unsigned decimal integer. 820 The Algorithm field MUST be represented either as an unsigned decimal 821 integer or as an algorithm mnemonic specified in Appendix A.1. 823 The Digest Type field MUST be represented as an unsigned decimal 824 integer. 826 The Digest MUST be represented as a sequence of case-insensitive 827 hexadecimal digits. Whitespace is allowed within the hexadecimal 828 text. 830 5.4 DS RR Example 832 The following example shows a DNSKEY RR and its corresponding DS RR. 834 dskey.example.com. 86400 IN DNSKEY 256 3 5 ( AQOeiiR0GOMYkDshWoSKz9Xz 835 fwJr1AYtsmx3TGkJaNXVbfi/ 836 2pHm822aJ5iI9BMzNXxeYCmZ 837 DRD99WYwYqUSdjMmmAphXdvx 838 egXd/M5+X7OrzKBaMbCVdFLU 839 Uh6DhweJBjEVv5f2wwjM9Xzc 840 nOf+EPbtG9DMBmADjFDc2w/r 841 ljwvFw== 842 ) ; key id = 60485 844 dskey.example.com. 86400 IN DS 60485 5 1 ( 2BB183AF5F22588179A53B0A 845 98631FAD1A292118 ) 847 The first four text fields specify the name, TTL, Class, and RR type 848 (DS). Value 60485 is the key tag for the corresponding 849 "dskey.example.com." DNSKEY RR, and value 5 denotes the algorithm 850 used by this "dskey.example.com." DNSKEY RR. The value 1 is the 851 algorithm used to construct the digest, and the rest of the RDATA 852 text is the digest in hexadecimal. 854 6. Canonical Form and Order of Resource Records 856 This section defines a canonical form for resource records, a 857 canonical ordering of DNS names, and a canonical ordering of resource 858 records within an RRset. A canonical name order is required to 859 construct the NSEC name chain. A canonical RR form and ordering 860 within an RRset are required to construct and verify RRSIG RRs. 862 6.1 Canonical DNS Name Order 864 For purposes of DNS security, owner names are ordered by treating 865 individual labels as unsigned left-justified octet strings. The 866 absence of a octet sorts before a zero value octet, and upper case 867 US-ASCII letters are treated as if they were lower case US-ASCII 868 letters. 870 To compute the canonical ordering of a set of DNS names, start by 871 sorting the names according to their most significant (rightmost) 872 labels. For names in which the most significant label is identical, 873 continue sorting according to their next most significant label, and 874 so forth. 876 For example, the following names are sorted in canonical DNS name 877 order. The most significant label is "example". At this level, 878 "example" sorts first, followed by names ending in "a.example", then 879 names ending "z.example". The names within each level are sorted in 880 the same way. 882 example 883 a.example 884 yljkjljk.a.example 885 Z.a.example 886 zABC.a.EXAMPLE 887 z.example 888 \001.z.example 889 *.z.example 890 \200.z.example 892 6.2 Canonical RR Form 894 For purposes of DNS security, the canonical form of an RR is the wire 895 format of the RR where: 897 1. Every domain name in the RR is fully expanded (no DNS name 898 compression) and fully qualified; 900 2. All uppercase US-ASCII letters in the owner name of the RR are 901 replaced by the corresponding lowercase US-ASCII letters; 903 3. If the type of the RR is NS, MD, MF, CNAME, SOA, MB, MG, MR, PTR, 904 HINFO, MINFO, MX, HINFO, RP, AFSDB, RT, SIG, PX, NXT, NAPTR, KX, 905 SRV, DNAME, A6, RRSIG or NSEC, all uppercase US-ASCII letters in 906 the DNS names contained within the RDATA are replaced by the 907 corresponding lowercase US-ASCII letters; 909 4. If the owner name of the RR is a wildcard name, the owner name is 910 in its original unexpanded form, including the "*" label (no 911 wildcard substitution); and 913 5. The RR's TTL is set to its original value as it appears in the 914 originating authoritative zone or the Original TTL field of the 915 covering RRSIG RR. 917 6.3 Canonical RR Ordering Within An RRset 919 For purposes of DNS security, RRs with the same owner name, class, 920 and type are sorted by treating the RDATA portion of the canonical 921 form of each RR as a left-justified unsigned octet sequence where the 922 absence of an octet sorts before a zero octet. 924 [RFC2181] specifies that an RRset is not allowed to contain duplicate 925 records (multiple RRs with the same owner name, class, type, and 926 RDATA). Therefore, if an implementation detects duplicate RRs during 927 RRset canonicalization, the implementation MUST treat this as a 928 protocol error. If the implementation chooses to handle this 929 protocol error in the spirit of the robustness principle (being 930 liberal in what it accepts), the implementation MUST remove all but 931 one of the duplicate RR(s) for purposes of calculating the canonical 932 form of the RRset. 934 7. IANA Considerations 936 This document introduces no new IANA considerations, because all of 937 the protocol parameters used in this document have already been 938 assigned by previous specifications. However, since the evolution of 939 DNSSEC has been long and somewhat convoluted, this section attempts 940 to describe the current state of the IANA registries and other 941 protocol parameters which are (or once were) related to DNSSEC. 943 Please refer to [I-D.ietf-dnsext-dnssec-protocol] for additional IANA 944 considerations. 946 DNS Resource Record Types: [RFC2535] assigned types 24, 25, and 30 to 947 the SIG, KEY, and NXT RRs, respectively. [RFC3658] assigned DNS 948 Resource Record Type 43 to DS. 949 [I-D.ietf-dnsext-dnssec-2535typecode-change] assigned types 46, 950 47, and 48 to the RRSIG, NSEC, and DNSKEY RRs, respectively. 951 [I-D.ietf-dnsext-dnssec-2535typecode-change] also marked type 30 952 (NXT) as Obsolete, and restricted use of types 24 (SIG) and 25 953 (KEY) to the "SIG(0)" transaction security protocol described in 954 [RFC2931] and the transaction KEY Resource Record described in 955 [RFC2930]. 957 DNS Security Algorithm Numbers: [RFC2535] created an IANA registry 958 for DNSSEC Resource Record Algorithm field numbers, and assigned 959 values 1-4 and 252-255. [RFC3110] assigned value 5. 960 [I-D.ietf-dnsext-dnssec-2535typecode-change] altered this registry 961 to include flags for each entry regarding its use with the DNS 962 security extensions. Each algorithm entry could refer to an 963 algorithm that can be used for zone signing, transaction security 964 (see [RFC2931]) or both. Values 6-251 are available for assignment 965 by IETF standards action. See Appendix A for a full listing of the 966 DNS Security Algorithm Numbers entries at the time of writing and 967 their status of use in DNSSEC. 969 [RFC3658] created an IANA registry for DNSSEC DS Digest Types, and 970 assigned value 0 to reserved and value 1 to SHA-1. 972 KEY Protocol Values: [RFC2535] created an IANA Registry for KEY 973 Protocol Values, but [RFC3445] re-assigned all assigned values 974 other than 3 to reserved and closed this IANA registry. The 975 registry remains closed, and all KEY and DNSKEY records are 976 required to have Protocol Octet value of 3. 978 Flag bits in the KEY and DNSKEY RRs: 979 [I-D.ietf-dnsext-dnssec-2535typecode-change] created an IANA 980 registry for the DNSSEC KEY and DNSKEY RR flag bits. Initially, 981 this registry only contains an assignment for bit 7 (the ZONE bit) 982 and a reservation for bit 15 for the Secure Entry Point flag (SEP 983 bit) [I-D.ietf-dnsext-keyrr-key-signing-flag]. Bits 0-6 and 8-14 984 are available for assignment by IETF Standards Action. 986 8. Security Considerations 988 This document describes the format of four DNS resource records used 989 by the DNS security extensions, and presents an algorithm for 990 calculating a key tag for a public key. Other than the items 991 described below, the resource records themselves introduce no 992 security considerations. Please see [I-D.ietf-dnsext-dnssec-intro] 993 and [I-D.ietf-dnsext-dnssec-protocol] for additional security 994 considerations related to the use of these records. 996 The DS record points to a DNSKEY RR using a cryptographic digest, the 997 key algorithm type and a key tag. The DS record is intended to 998 identify an existing DNSKEY RR, but it is theoretically possible for 999 an attacker to generate a DNSKEY that matches all the DS fields. The 1000 probability of constructing such a matching DNSKEY depends on the 1001 type of digest algorithm in use. The only currently defined digest 1002 algorithm is SHA-1, and the working group believes that constructing 1003 a public key which would match the algorithm, key tag, and SHA-1 1004 digest given in a DS record would be a sufficiently difficult problem 1005 that such an attack is not a serious threat at this time. 1007 The key tag is used to help select DNSKEY resource records 1008 efficiently, but it does not uniquely identify a single DNSKEY 1009 resource record. It is possible for two distinct DNSKEY RRs to have 1010 the same owner name, the same algorithm type, and the same key tag. 1011 An implementation which used only the key tag to select a DNSKEY RR 1012 might select the wrong public key in some circumstances. 1014 9. Acknowledgments 1016 This document was created from the input and ideas of the members of 1017 the DNS Extensions Working Group and working group mailing list. The 1018 editors would like to express their thanks for the comments and 1019 suggestions received during the revision of these security extension 1020 specifications. While explicitly listing everyone who has 1021 contributed during the decade during which DNSSEC has been under 1022 development would be an impossible task, 1023 [I-D.ietf-dnsext-dnssec-intro] includes a list of some of the 1024 participants who were kind enough to comment on these documents. 1026 Normative References 1028 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 1029 STD 13, RFC 1034, November 1987. 1031 [RFC1035] Mockapetris, P., "Domain names - implementation and 1032 specification", STD 13, RFC 1035, November 1987. 1034 [RFC1521] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet 1035 Mail Extensions) Part One: Mechanisms for Specifying and 1036 Describing the Format of Internet Message Bodies", RFC 1037 1521, September 1993. 1039 [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, 1040 August 1996. 1042 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1043 Requirement Levels", BCP 14, RFC 2119, March 1997. 1045 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic 1046 Updates in the Domain Name System (DNS UPDATE)", RFC 2136, 1047 April 1997. 1049 [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 1050 Specification", RFC 2181, July 1997. 1052 [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS 1053 NCACHE)", RFC 2308, March 1998. 1055 [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 1056 2671, August 1999. 1058 [RFC2931] Eastlake, D., "DNS Request and Transaction Signatures ( 1059 SIG(0)s)", RFC 2931, September 2000. 1061 [RFC3110] Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain 1062 Name System (DNS)", RFC 3110, May 2001. 1064 [RFC3445] Massey, D. and S. Rose, "Limiting the Scope of the KEY 1065 Resource Record (RR)", RFC 3445, December 2002. 1067 [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record 1068 (RR) Types", RFC 3597, September 2003. 1070 [RFC3658] Gudmundsson, O., "Delegation Signer (DS) Resource Record 1071 (RR)", RFC 3658, December 2003. 1073 [I-D.ietf-dnsext-dnssec-intro] 1074 Arends, R., Austein, R., Larson, M., Massey, D. and S. 1075 Rose, "DNS Security Introduction and Requirements", 1076 draft-ietf-dnsext-dnssec-intro-09 (work in progress), 1077 February 2004. 1079 [I-D.ietf-dnsext-dnssec-protocol] 1080 Arends, R., Austein, R., Larson, M., Massey, D. and S. 1081 Rose, "Protocol Modifications for the DNS Security 1082 Extensions", draft-ietf-dnsext-dnssec-protocol-05 (work in 1083 progress), February 2004. 1085 [I-D.ietf-dnsext-keyrr-key-signing-flag] 1086 Kolkman, O., Schlyter, J. and E. Lewis, "KEY RR Secure 1087 Entry Point Flag", 1088 draft-ietf-dnsext-keyrr-key-signing-flag-12 (work in 1089 progress), December 2003. 1091 [I-D.ietf-dnsext-dnssec-2535typecode-change] 1092 Weiler, S., "Legacy Resolver Compatibility for Delegation 1093 Signer", draft-ietf-dnsext-dnssec-2535typecode-change-06 1094 (work in progress), December 2003. 1096 Informative References 1098 [RFC2535] Eastlake, D., "Domain Name System Security Extensions", 1099 RFC 2535, March 1999. 1101 [RFC2930] Eastlake, D., "Secret Key Establishment for DNS (TKEY 1102 RR)", RFC 2930, September 2000. 1104 Authors' Addresses 1106 Roy Arends 1107 Telematica Instituut 1108 Drienerlolaan 5 1109 7522 NB Enschede 1110 NL 1112 EMail: roy.arends@telin.nl 1114 Rob Austein 1115 Internet Systems Consortium 1116 950 Charter Street 1117 Redwood City, CA 94063 1118 USA 1120 EMail: sra@isc.org 1122 Matt Larson 1123 VeriSign, Inc. 1124 21345 Ridgetop Circle 1125 Dulles, VA 20166-6503 1126 USA 1128 EMail: mlarson@verisign.com 1130 Dan Massey 1131 USC Information Sciences Institute 1132 3811 N. Fairfax Drive 1133 Arlington, VA 22203 1134 USA 1136 EMail: masseyd@isi.edu 1137 Scott Rose 1138 National Institute for Standards and Technology 1139 100 Bureau Drive 1140 Gaithersburg, MD 20899-8920 1141 USA 1143 EMail: scott.rose@nist.gov 1145 Appendix A. DNSSEC Algorithm and Digest Types 1147 The DNS security extensions are designed to be independent of the 1148 underlying cryptographic algorithms. The DNSKEY, RRSIG, and DS 1149 resource records all use a DNSSEC Algorithm Number to identify the 1150 cryptographic algorithm in use by the resource record. The DS 1151 resource record also specifies a Digest Algorithm Number to identify 1152 the digest algorithm used to construct the DS record. The currently 1153 defined Algorithm and Digest Types are listed below. Additional 1154 Algorithm or Digest Types could be added as advances in cryptography 1155 warrant. 1157 A DNSSEC aware resolver or name server MUST implement all MANDATORY 1158 algorithms. 1160 A.1 DNSSEC Algorithm Types 1162 The DNSKEY, RRSIG, and DS RRs use an 8-bit number used to identify 1163 the security algorithm being used. These values are stored in the 1164 "Algorithm number" field in the resource record RDATA. 1166 Some algorithms are usable only for zone signing (DNSSEC), some only 1167 for transaction security mechanisms (SIG(0) and TSIG), and some for 1168 both. Those usable for zone signing may appear in DNSKEY, RRSIG, and 1169 DS RRs. Those usable for transaction security would be present in 1170 SIG(0) and KEY RRs as described in [RFC2931] 1172 Zone 1173 Value Algorithm [Mnemonic] Signing References Status 1174 ----- -------------------- --------- ---------- --------- 1175 0 reserved 1176 1 RSA/MD5 [RSAMD5] n RFC 2537 NOT RECOMMENDED 1177 2 Diffie-Hellman [DH] n RFC 2539 - 1178 3 DSA/SHA-1 [DSA] y RFC 2536 OPTIONAL 1179 4 Elliptic Curve [ECC] TBA - 1180 5 RSA/SHA-1 [RSASHA1] y RFC 3110 MANDATORY 1181 252 Indirect [INDIRECT] n - 1182 253 Private [PRIVATEDNS] y see below OPTIONAL 1183 254 Private [PRIVATEOID] y see below OPTIONAL 1184 255 reserved 1186 6 - 251 Available for assignment by IETF Standards Action. 1188 A.1.1 Private Algorithm Types 1190 Algorithm number 253 is reserved for private use and will never be 1191 assigned to a specific algorithm. The public key area in the DNSKEY 1192 RR and the signature area in the RRSIG RR begin with a wire encoded 1193 domain name, which MUST NOT be compressed. The domain name indicates 1194 the private algorithm to use and the remainder of the public key area 1195 is determined by that algorithm. Entities should only use domain 1196 names they control to designate their private algorithms. 1198 Algorithm number 254 is reserved for private use and will never be 1199 assigned to a specific algorithm. The public key area in the DNSKEY 1200 RR and the signature area in the RRSIG RR begin with an unsigned 1201 length byte followed by a BER encoded Object Identifier (ISO OID) of 1202 that length. The OID indicates the private algorithm in use and the 1203 remainder of the area is whatever is required by that algorithm. 1204 Entities should only use OIDs they control to designate their private 1205 algorithms. 1207 A.2 DNSSEC Digest Types 1209 A "Digest Type" field in the DS resource record types identifies the 1210 cryptographic digest algorithm used by the resource record. The 1211 following table lists the currently defined digest algorithm types. 1213 VALUE Algorithm STATUS 1214 0 Reserved - 1215 1 SHA-1 MANDATORY 1216 2-255 Unassigned - 1218 Appendix B. Key Tag Calculation 1220 The Key Tag field in the RRSIG and DS resource record types provides 1221 a mechanism for selecting a public key efficiently. In most cases, a 1222 combination of owner name, algorithm, and key tag can efficiently 1223 identify a DNSKEY record. Both the RRSIG and DS resource records 1224 have corresponding DNSKEY records. The Key Tag field in the RRSIG 1225 and DS records can be used to help select the corresponding DNSKEY RR 1226 efficiently when more than one candidate DNSKEY RR is available. 1228 However, it is essential to note that the key tag is not a unique 1229 identifier. It is theoretically possible for two distinct DNSKEY RRs 1230 to have the same owner name, the same algorithm, and the same key 1231 tag. The key tag is used to limit the possible candidate keys, but it 1232 does not uniquely identify a DNSKEY record. Implementations MUST NOT 1233 assume that the key tag uniquely identifies a DNSKEY RR. 1235 The key tag is the same for all DNSKEY algorithm types except 1236 algorithm 1 (please see Appendix B.1 for the definition of the key 1237 tag for algorithm 1). The key tag algorithm is the sum of the wire 1238 format of the DNSKEY RDATA broken into 2 octet groups. First the 1239 RDATA (in wire format) is treated as a series of 2 octet groups, 1240 these groups are then added together ignoring any carry bits. A 1241 reference implementation of the key tag algorithm is as an ANSI C 1242 function is given below with the RDATA portion of the DNSKEY RR is 1243 used as input. It is not necessary to use the following reference 1244 code verbatim, but the numerical value of the Key Tag MUST be 1245 identical to what the reference implementation would generate for the 1246 same input. 1248 Please note that the algorithm for calculating the Key Tag is almost 1249 but not completely identical to the familiar ones complement checksum 1250 used in many other Internet protocols. Key Tags MUST be calculated 1251 using the algorithm described here rather than the ones complement 1252 checksum. 1254 The following ANSI C reference implementation calculates the value of 1255 a Key Tag. This reference implementation applies to all algorithm 1256 types except algorithm 1 (see Appendix B.1). The input is the wire 1257 format of the RDATA portion of the DNSKEY RR. The code is written 1258 for clarity, not efficiency. 1260 /* 1261 * Assumes that int is at least 16 bits. 1262 * First octet of the key tag is the most significant 8 bits of the 1263 * return value; 1264 * Second octet of the key tag is the least significant 8 bits of the 1265 * return value. 1267 */ 1269 unsigned int 1270 keytag ( 1271 unsigned char key[], /* the RDATA part of the DNSKEY RR */ 1272 unsigned int keysize /* the RDLENGTH */ 1273 ) 1274 { 1275 unsigned long ac; /* assumed to be 32 bits or larger */ 1276 int i; /* loop index */ 1278 for ( ac = 0, i = 0; i < keysize; ++i ) 1279 ac += (i & 1) ? key[i] : key[i] << 8; 1280 ac += (ac >> 16) & 0xFFFF; 1281 return ac & 0xFFFF; 1282 } 1284 B.1 Key Tag for Algorithm 1 (RSA/MD5) 1286 The key tag for algorithm 1 (RSA/MD5) is defined differently than the 1287 key tag for all other algorithms, for historical reasons. For a 1288 DNSKEY RR with algorithm 1, the key tag is defined to be the most 1289 significant 16 bits of the least significant 24 bits in the public 1290 key modulus (in other words, the 4th to last and 3rd to last octets 1291 of the public key modulus). 1293 Please note that Algorithm 1 is NOT RECOMMENDED. 1295 Intellectual Property Statement 1297 The IETF takes no position regarding the validity or scope of any 1298 intellectual property or other rights that might be claimed to 1299 pertain to the implementation or use of the technology described in 1300 this document or the extent to which any license under such rights 1301 might or might not be available; neither does it represent that it 1302 has made any effort to identify any such rights. Information on the 1303 IETF's procedures with respect to rights in standards-track and 1304 standards-related documentation can be found in BCP-11. 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