idnits 2.17.1 draft-wessels-dns-zone-digest-02.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (July 2, 2018) is 2124 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 3658 (Obsoleted by RFC 4033, RFC 4034, RFC 4035) -- Obsolete informational reference (is this intentional?): RFC 2065 (Obsoleted by RFC 2535) -- Obsolete informational reference (is this intentional?): RFC 2535 (Obsoleted by RFC 4033, RFC 4034, RFC 4035) -- Obsolete informational reference (is this intentional?): RFC 2845 (Obsoleted by RFC 8945) -- Obsolete informational reference (is this intentional?): RFC 3851 (Obsoleted by RFC 5751) -- Obsolete informational reference (is this intentional?): RFC 7706 (Obsoleted by RFC 8806) -- Obsolete informational reference (is this intentional?): RFC 7719 (Obsoleted by RFC 8499) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force D. Wessels 3 Internet-Draft P. Barber 4 Intended status: Standards Track M. Weinberg 5 Expires: January 3, 2019 Verisign 6 W. Kumari 7 Google 8 W. Hardaker 9 USC/ISI 10 July 2, 2018 12 Message Digest for DNS Zones 13 draft-wessels-dns-zone-digest-02 15 Abstract 17 This document describes a protocol and DNS Resource Record used to 18 provide a message digest over DNS zone data. In particular, it 19 describes how to compute, sign, represent, and use the message digest 20 to verify the contents of a zone for accuracy and completeness. The 21 ZONEMD Resource Record type is introduced for conveying the message 22 digest data. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on January 3, 2019. 41 Copyright Notice 43 Copyright (c) 2018 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3 60 1.2. Design Overview . . . . . . . . . . . . . . . . . . . . . 5 61 1.3. Requirements Language . . . . . . . . . . . . . . . . . . 6 62 2. The ZONEMD Resource Record . . . . . . . . . . . . . . . . . 6 63 2.1. ZONEMD RDATA Wire Format . . . . . . . . . . . . . . . . 6 64 2.1.1. The Serial Field . . . . . . . . . . . . . . . . . . 6 65 2.1.2. The Digest Type Field . . . . . . . . . . . . . . . . 6 66 2.1.3. The Digest Field . . . . . . . . . . . . . . . . . . 7 67 2.2. ZONEMD Presentation Format . . . . . . . . . . . . . . . 7 68 2.3. ZONEMD Example . . . . . . . . . . . . . . . . . . . . . 7 69 3. Calculating the Digest . . . . . . . . . . . . . . . . . . . 8 70 3.1. Canonical Format and Ordering . . . . . . . . . . . . . . 8 71 3.1.1. Order of RRsets Having the Same Owner Name . . . . . 8 72 3.1.2. Special Considerations for SOA RRs . . . . . . . . . 8 73 3.2. Add ZONEMD Placeholder . . . . . . . . . . . . . . . . . 8 74 3.3. Optionally Sign the Zone . . . . . . . . . . . . . . . . 9 75 3.4. Calculate the Digest . . . . . . . . . . . . . . . . . . 9 76 3.4.1. Inclusion/Exclusion Rules . . . . . . . . . . . . . . 9 77 3.5. Update ZONEMD RR . . . . . . . . . . . . . . . . . . . . 10 78 4. Verifying Zone Message Digest . . . . . . . . . . . . . . . . 10 79 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 80 5.1. ZONEMD RRtype . . . . . . . . . . . . . . . . . . . . . . 11 81 5.2. ZONEMD Digest Type . . . . . . . . . . . . . . . . . . . 11 82 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 83 6.1. Attacks Against the Zone Digest . . . . . . . . . . . . . 11 84 6.2. Attacks Utilizing the Zone Digest . . . . . . . . . . . . 12 85 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12 86 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 87 9. Implementation Status . . . . . . . . . . . . . . . . . . . . 12 88 9.1. Authors' Implementation . . . . . . . . . . . . . . . . . 12 89 10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 13 90 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 91 11.1. Normative References . . . . . . . . . . . . . . . . . . 13 92 11.2. Informative References . . . . . . . . . . . . . . . . . 14 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 95 1. Introduction 97 In the DNS, a zone is the collection of authoritative resource 98 records (RRs) sharing a common origin ([RFC7719]), which can be 99 distributed from primary to secondary name servers. Zones are often 100 stored as files on disk in the so-called master file format 101 [RFC1034]. Sometimes zones are distributed outside of the DNS, with 102 such protocols as FTP, HTTP, rsync, and so on. Currently there is no 103 standard way to verify the authenticity of a stand-alone zone file. 105 This document introduces a new RR type that serves as a cryptographic 106 message digest of the data in a zone file. It allows a receiver of 107 the zone file to verify the zone file's authenticity, especially when 108 used in combination with DNSSEC. This technique makes the message 109 digest a part of the zone file itself, allowing anything to verify 110 the zone file as a whole, no matter how it is transmitted. 112 DNSSEC provides three strong security guarantees relevant to this 113 protocol: 115 1. whether or not to expect DNSSEC records in the zone, 117 2. whether or not to expect a ZONEMD record in a signed zone, and 119 3. whether or not the ZONEMD record has been altered since it was 120 signed. 122 This specification is OPTIONAL to implement by both publishers and 123 consumers of zone file data. 125 1.1. Motivation 127 The motivation and design of this protocol enhancement is tied to the 128 DNS root zone [InterNIC]. The root zone is perhaps the most widely 129 distributed DNS zone on the Internet, served by 930 separate 130 instances [RootServers] at the time of this writing. Additionally, 131 many organizations configure their own name servers to serve the root 132 zone locally. Reasons for doing so include privacy and reduced 133 access time. [RFC7706] describes one, but not the only, way to do 134 this. As the root zone spreads beyond its traditional deployment 135 boundaries, the need for verification of the completeness of the zone 136 contents becomes increasingly important. 138 One approach to preventing data tampering and corruption is to secure 139 the distribution channel. The DNS has a number of features that can 140 already be used for channel security. Perhaps the most widely used 141 is DNS transaction signatures (TSIG [RFC2845]). TSIG uses shared 142 secret keys and a message digest to protect individual query and 143 response messages. It is generally used to authenticate and validate 144 UPDATE [RFC2136], AXFR [RFC5936], and IXFR [RFC1995] messages. 146 DNS Request and Transaction Signatures (SIG(0) [RFC2931]) is another 147 protocol extension designed to authenticate individual DNS 148 transactions. Whereas SIG records were originally designed to cover 149 specific RR types, SIG(0) is used to sign an entire DNS message. 150 Unlike TSIG, SIG(0) uses public key cryptography rather than shared 151 secrets. 153 The Transport Layer Security protocol suite is also designed to 154 provide channel security. It is entirely possible, for example, to 155 perform zone transfers using DNS-over-TLS ([RFC7858]). Furthermore, 156 one can easily imagine the distribution of zone files over HTTPS- 157 enabled web servers, as well as DNS-over-HTTPS [dns-over-https]. 159 Unfortunately, the protections provided by these channel security 160 techniques are ephemeral and are not retained after the data transfer 161 is complete. They can ensure that the client receives the data from 162 the expected server, and that the data sent by the server is not 163 modified during transmission. However, they do not guarantee that 164 the server transmits the data as originally published, and do not 165 provide any methods to verify data that is read after transmission is 166 complete. For example, a name server loading saved zone data upon 167 restart cannot guarantee that the on-disk data has not been modified. 168 For these reasons, it is preferable to secure the data itself. 170 DNSSEC provides certain data security guarantees. For zones that are 171 signed, a recipient can validate all of the signed RRsets. 172 Additionally, the denial-of-existence records can prove that RRsets 173 have not been added or removed. However, not all RRsets in a zone 174 are signed. The design of DNSSEC stipulates that delegations (non- 175 apex NS records) are not signed, and neither are any glue records. 176 Thus, changes to delegation and glue records cannot be detected by 177 DNSSEC alone. Furthermore, zones that employ NSEC3 with opt-out are 178 susceptible to the removal or addition of names between the signed 179 nodes. 181 There are existing tools and protocols that provide data security, 182 such as OpenPGP [RFC4880] and S/MIME [RFC3851]. In fact, the 183 internic.net site publishes PGP signatures along side the root zone 184 and other files available there. However, this is a detached 185 signature with no strong association to the corresponding zone file 186 other than its timestamp. Non-detached signatures are, of course, 187 possible, but these necessarily change the format of the file being 188 distributed. That is, a zone file signed with OpenPGP or S/MIME no 189 longer looks like a zone file and could not directly be loaded into a 190 name server. Once loaded the signature data is lost, so it does not 191 survive further propagation. 193 It seems the desire for data security in DNS zones was envisioned as 194 far back as 1997. [RFC2065] is an obsoleted specification of the 195 first generation DNSSEC Security Extensions. It describes a zone 196 transfer signature, aka AXFR SIG, which is similar to the technique 197 proposed by this document. That is, it proposes ordering all RRsets 198 in a zone, hashing their signatures, and then signing the zone hash. 199 The AXFR SIG is described only for use during zone transfers. It did 200 not postulate the need to validate zone data distributed outside of 201 the DNS. Furthermore, its successor, [RFC2535], omits the AXFR SIG, 202 while at the same time introducing an IXFR SIG. 204 1.2. Design Overview 206 This document introduces a new Resource Record type designed to 207 convey a message digest of the content of a zone file. The digest is 208 calculated at the time of zone publication. Ideally the zone is 209 signed with DNSSEC to guarantee that any modifications of the digest 210 can be detected. 212 The zone digest is designed to be used on zones that are relatively 213 stable and have infrequent updates. As currently specified, the 214 digest is re-calculated over the entire zone content each time. This 215 specification does not provide an efficient mechanism for incremental 216 updates of zone data. The authors believe that the incremental 217 updates represent significant complexity which could be a barrier to 218 implementation at this time (see DNS Camel). Nothing in this 219 specification prevents future work to support incremental zone digest 220 algorithms (e.g. using Merkle trees and a different RR type). 222 The cryptographic algorithms available for zone digest are exactly 223 the same as for DS records. This avoids the need for a separate 224 digest algorithm registry. Any updates to the DS algorithms 225 automatically updates the algorithm status for zone digests. 227 It is expected that verification of a zone digest will be implemented 228 in name server software. That is, a name server can verify the zone 229 data it was given and refuse to serve a zone which fails 230 verification. For signed zones, the name server would need a trust 231 anchor for DNSSEC validation. For signed non-root zones, the name 232 server may need to send queries to validate a chain-of-trust. Digest 233 verification may also be performed externally. 235 1.3. Requirements Language 237 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 238 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 239 "OPTIONAL" in this document are to be interpreted as described in BCP 240 14 [RFC2119] [RFC8174] when, and only when, they appear in all 241 capitals, as shown here. 243 2. The ZONEMD Resource Record 245 This section describes the ZONEMD Resource Record, including its 246 fields, wire format, and presentation format. The Type value for the 247 ZONEMD RR is TBD. The ZONEMD RR is class independent. The RDATA of 248 the resource record consists of three fields: Serial, Digest Type, 249 and Digest. 251 FOR DISCUSSION: This document is currently written as though a zone 252 MUST NOT contain more than one ZONEMD RR. Having exactly one ZONEMD 253 record per zone simplifies this protocol and eliminates confusion 254 around downgrade attacks, at the expense of algorithm agility. 256 2.1. ZONEMD RDATA Wire Format 258 The ZONEMD RDATA wire format is encoded as follows: 260 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 261 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 1 262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 263 | Serial | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 265 | Digest Type | | 266 +-+-+-+-+-+-+-+-+ Digest + 267 / / 268 / / 269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 271 2.1.1. The Serial Field 273 The Serial field is a 32-bit unsigned integer in network order. It 274 is equal to the serial number from the zone's SOA record ([RFC1035] 275 section 3.3.13) for which the message digest was generated. 277 2.1.2. The Digest Type Field 279 The Digest Type field is an 8-bit unsigned integer, with meaning 280 equivalent to the Digest Type of the DS resource record, as defined 281 in section 5.1.3 of [RFC4034]. 283 The status of ZONEMD digest types (e.g., mandatory, optional, 284 deprecated) SHALL always match the status for DS records. This 285 information can be found in the IANA protocol registry for DS digest 286 types [iana-ds-digest-types]. 288 At the time of this writing the following digest types are defined: 290 +-------+-----------------+-----------+-----------+ 291 | Value | Description | Status | Reference | 292 +-------+-----------------+-----------+-----------+ 293 | 1 | SHA1 | Mandatory | [RFC3658] | 294 | 2 | SHA256 | Mandatory | [RFC4509] | 295 | 3 | GOST R 34.11-94 | Optional | [RFC5933] | 296 | 4 | SHA384 | Optional | [RFC6605] | 297 +-------+-----------------+-----------+-----------+ 299 Table 1: Digest Types 301 2.1.3. The Digest Field 303 The Digest field is a variable-length sequence of octets containing 304 the message digest. Section 3 describes how to calculate the digest 305 for a zone. Section 4 describes how to use the digest to verify the 306 contents of a zone. 308 2.2. ZONEMD Presentation Format 310 The presentation format of the RDATA portion is as follows: 312 The Serial field MUST be represented as an unsigned decimal integer. 314 The Digest Type field MUST be represented as an unsigned decimal 315 integer. 317 The Digest MUST be represented as a sequence of case-insensitive 318 hexadecimal digits. Whitespace is allowed within the hexadecimal 319 text. 321 2.3. ZONEMD Example 323 The following example shows a ZONEMD RR. 325 example.com. 86400 IN ZONEMD ( 2018031500 4 FEBE3D4CE2EC2FFA4BA9 326 9D46CD69D6D29711E552 327 17057BEE7EB1A7B641A4 328 7BA7FED2DD5B97AE499F 329 AFA4F22C6BD647DE ) 331 3. Calculating the Digest 333 3.1. Canonical Format and Ordering 335 Calculation of the zone digest REQUIRES the RRs in a zone to be in a 336 consistent format and ordering. Correct ordering of the zone depends 337 on (1) ordering of owner names in the zone, (2) ordering of RRsets 338 with the same owner name, and (3) ordering of RRs within an RRset. 340 This specification adopts DNSSEC's canonical ordering for names 341 (Section 6.1 of [RFC4034]), and canonical ordering for RRs within an 342 RRset (Section 6.3 of [RFC4034]). It also adopts DNSSEC's canonical 343 RR form (Section 6.2 of [RFC4034]). However, since DNSSEC does not 344 define a canonical ordering for RRsets having the same owner name, 345 that ordering is defined here. 347 3.1.1. Order of RRsets Having the Same Owner Name 349 For the purposes of calculating the zone digest, RRsets having the 350 same owner name MUST be numerically ordered by their numeric RR TYPE. 352 3.1.2. Special Considerations for SOA RRs 354 When AXFR is used to transfer zone data, the first and last records 355 are always the SOA RR ([RFC5936] Section 2.2). Because of this, zone 356 files on disk often contain two SOA RRs. When calculating the zone 357 digest, the first SOA RR MUST be included and any subsequent SOA RRs 358 MUST NOT be included. 360 Additionally, per established practices, the SOA record is generally 361 the first record in a zone file. However, according to the 362 requirement to sort RRsets with the same owner name by type, the SOA 363 RR (type value 6) will not be first in the digest calculation. The 364 zone's NS RRset (type value 2) at the apex MUST be processed before 365 the SOA RR. 367 3.2. Add ZONEMD Placeholder 369 In preparation for calculating the zone digest, any existing ZONEMD 370 records MUST first be deleted from the zone. 372 Prior to calculation of the digest, and prior to signing with DNSSEC, 373 a placeholder ZONEMD record MUST be added to the zone. This serves 374 two purposes: (1) it allows the digest to cover the Serial and Digest 375 Type field values, and (2) ensures that appropriate denial-of- 376 existence (NSEC, NSEC3) records are created if the zone is signed 377 with DNSSEC. 379 In the placeholder record, the Serial field MUST be set to the 380 current SOA Serial. The Digest Type field MUST be set to the value 381 for the chosen digest algorithm. The Digest field MUST be set to all 382 zeroes and of length appropriate for the chosen digest algorithm. 384 3.3. Optionally Sign the Zone 386 Following addition of the placeholder record, the zone MAY be signed 387 with DNSSEC. Note that when the digest calculation is complete, and 388 the ZONEMD record is updated, the signature(s) for that record MUST 389 be recalculated and updated as well. Therefore, the signer is not 390 required to calculate a signature over the placeholder record at this 391 step in the process, but it is harmless to do so. 393 3.4. Calculate the Digest 395 The zone digest is calculated by concatenating the canonical on-the- 396 wire form of all RRs in the zone, in the order described above, 397 subject to the inclusion/exclusion rules described below, and then 398 applying the digest algorithm: 400 digest = digest_algorithm( RR(1) | RR(2) | RR(3) | ... ) 402 where "|" denotes concatenation, and 404 RR(i) = owner | type | class | TTL | RDATA length | RDATA 406 3.4.1. Inclusion/Exclusion Rules 408 When calculating the digest, the following inclusion/exclusion rules 409 apply: 411 o All records in the zone including glue records MUST be included. 413 o More than one SOA MUST NOT be included. 415 o The placeholder ZONEMD RR MUST be included. 417 o If the zone is signed, DNSSEC RRs MUST be included, except: 419 o The RRSIG covering ZONEMD MUST NOT be included. 421 FOR DISCUSSION: Ambiguities about records that are in/out of zone. 422 For example, see Jinmei message to dnsop 2018-06-01 and followups. 423 BIND will load and axfr data "occluded" by DNAME/NS. 425 3.5. Update ZONEMD RR 427 Once the zone digest has been calculated, its value is then copied to 428 the Digest field of the ZONEMD record. 430 If the zone is signed with DNSSEC, the appropriate RRSIG records 431 covering the ZONEMD record MUST then be added. Because the ZONEMD 432 placeholder was added prior to signing, the zone will already have 433 the appropriate denial-of-existence (NSEC, NSEC3) records. 435 Some implementations of incremental DNSSEC signing might update the 436 zone's serial number for each resigning. However, to preserve the 437 calculated digest, generation of the ZONEMD signature at this time 438 MUST NOT also result in a change of the SOA serial number. 440 4. Verifying Zone Message Digest 442 The recipient of a zone that has a message digest record can verify 443 the zone by calculating the digest as follows: 445 1. The verifier SHOULD first determine whether or not to expect 446 DNSSEC records in the zone. This can be done by examining 447 locally configured trust anchors, or querying for (and 448 validating) DS RRs in the parent zone. For zones that are 449 provably unsigned, digest validation continues at step 4 below. 451 2. For zones that are provably signed, the existence of the ZONEMD 452 record MUST be verified. If the ZONEMD record provably does not 453 exist, digest verification cannot be done. If the ZONEMD record 454 does provably exist, but is not found in the zone, digest 455 verification MUST NOT be considered successful. 457 3. For zones that are provably signed, the SOA RR and ZONEMD RR(set) 458 MUST have valid signatures, chaining up to a trust anchor. If 459 DNSSEC validation of the SOA or ZONEMD records fails, digest 460 verification MUST NOT be considered successful. 462 4. The SOA Serial field MUST exactly match the ZONEMD Serial field. 463 If the fields to not match, digest verification MUST NOT be 464 considered successful. 466 5. The ZONEMD Digest Type field MUST be checked. If the verifier 467 does not support the given digest type, it SHOULD report that the 468 zone digest could not be verified due to an unsupported 469 algorithm. 471 6. The zone digest is calculated using the algorithm described in 472 Section 3.4. Note in particular that digested ZONEMD RRs MUST be 473 placeholders and their RRSIGs are not included in the digest. 475 7. The calculated digest is compared to the received digest. If the 476 two digest values match, verification is considered successful. 477 Otherwise, verification MUST NOT be considered successful. 479 8. If the zone is to be served and transferred, the original (not 480 placeholder) ZONEMD RRs MUST be sent to recipients so that 481 downstream clients can verify the zone. 483 5. IANA Considerations 485 5.1. ZONEMD RRtype 487 This document uses a new DNS RR type, ZONEMD, whose value TBD has 488 been allocated by IANA from the "Resource Record (RR) TYPEs" 489 subregistry of the "Domain Name System (DNS) Parameters" registry. 491 5.2. ZONEMD Digest Type 493 The ZONEMD Digest Type field has the same semantics as the DS RR 494 Digest Type field. Thus, it does not add new IANA protocol registry 495 requirements. 497 6. Security Considerations 499 6.1. Attacks Against the Zone Digest 501 The zone digest allows the receiver to verify that the zone contents 502 haven't been modified since the zone was generated/published. 503 Verification is strongest when the zone is also signed with DNSSEC. 504 An attacker, whose goal is to modify zone content before it is used 505 by the victim, may consider a number of different approaches. 507 The attacker might perform a downgrade attack to an unsigned zone. 508 This is why Section 4 RECOMMENDS that the verifier determine whether 509 or not to expect DNSSEC signatures for the zone in step 1. 511 The attacker might perform a downgrade attack by removing the ZONEMD 512 record. This is why Section 4 REQUIRES that the verifier checks 513 DNSSEC denial-of-existence proofs in step 2. 515 The attacker might alter the Digest Type or Digest fields of the 516 ZONEMD record. Such modifications are detectable only with DNSSEC 517 validation. 519 6.2. Attacks Utilizing the Zone Digest 521 Nothing in this specification prevents clients from making, and 522 servers from responding to, ZONEMD queries. One might consider how 523 well ZONEMD responses could be used in a distributed denial-of- 524 service amplification attack. 526 The ZONEMD RR is moderately sized, much like the DS RR. A single 527 ZONEMD RR contributes approximately 40 to 65 octets to a DNS 528 response, for currently defined digest types. Certainly other query 529 types result in larger amplification effects (i.e., DNSKEY). 531 FOR DISCUSSION: The primary purpose of the ZONEMD record is to verify 532 a zone file prior to being loaded or served by a name server. We 533 could allow a name server implementation to respond to ZONEMD queries 534 with the REFUSED RCODE without loss of functionality. Note that 535 refusal would prevent ensuring that a zone-walk is complete. 537 7. Privacy Considerations 539 This specification has no impacts on user privacy. 541 8. Acknowledgments 543 The authors wish to thank David Blacka, Scott Hollenbeck, and Rick 544 Wilhelm for providing feedback on early drafts of this document. 545 Additionally, they thank Mark Andrews, Olafur Gudmundsson, Shumon 546 Huque, Tatuya Jinmei, Shane Kerr, Mukund Sivaraman, Petr Spacek, and 547 other members of the dnsop working group for their input. 549 9. Implementation Status 551 9.1. Authors' Implementation 553 The authors are currently working on an implementation in C, using 554 the ldns library [ldns]. This implementation is able to perform the 555 following functions: 557 o Read input zone file, output zone file with ZONEMD placeholder. 559 o Compute zone digest over signed zone file and update ZONEMD 560 record. 562 o Re-compute DNSSEC signature over ZONEMD record. 564 o Verify zone digest from input zone file. 566 The authors expect to be able to release this implementation as open 567 source following submission of this Internet-Draft. 569 10. Change Log 571 RFC Editor: Please remove this section. 573 This section lists substantial changes to the document as it is being 574 worked on. 576 From -00 to -01: 578 o Removed requirement to sort by RR CLASS. 580 o Added Kumari and Hardaker as coauthors. 582 o Added Change Log section. 584 o Minor clarifications and grammatical edits. 586 11. References 588 11.1. Normative References 590 [iana-ds-digest-types] 591 IANA, "Delegation Signer (DS) Resource Record (RR) Type 592 Digest Algorithms", April 2012, 593 . 596 [ldns] NLNet Labs, "The ldns Library", March 2018, 597 . 599 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 600 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 601 . 603 [RFC1035] Mockapetris, P., "Domain names - implementation and 604 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 605 November 1987, . 607 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 608 Requirement Levels", BCP 14, RFC 2119, 609 DOI 10.17487/RFC2119, March 1997, 610 . 612 [RFC3658] Gudmundsson, O., "Delegation Signer (DS) Resource Record 613 (RR)", RFC 3658, DOI 10.17487/RFC3658, December 2003, 614 . 616 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 617 Rose, "Resource Records for the DNS Security Extensions", 618 RFC 4034, DOI 10.17487/RFC4034, March 2005, 619 . 621 [RFC4509] Hardaker, W., "Use of SHA-256 in DNSSEC Delegation Signer 622 (DS) Resource Records (RRs)", RFC 4509, 623 DOI 10.17487/RFC4509, May 2006, 624 . 626 [RFC5933] Dolmatov, V., Ed., Chuprina, A., and I. Ustinov, "Use of 627 GOST Signature Algorithms in DNSKEY and RRSIG Resource 628 Records for DNSSEC", RFC 5933, DOI 10.17487/RFC5933, July 629 2010, . 631 [RFC6605] Hoffman, P. and W. Wijngaards, "Elliptic Curve Digital 632 Signature Algorithm (DSA) for DNSSEC", RFC 6605, 633 DOI 10.17487/RFC6605, April 2012, 634 . 636 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 637 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 638 May 2017, . 640 11.2. Informative References 642 [dns-over-https] 643 Hoffman, P. and P. McManus, "DNS Queries over HTTPS 644 (DoH)", draft-ietf-doh-dns-over-https-12 (work in 645 progress), June 2018, . 648 [InterNIC] 649 ICANN, "InterNIC FTP site", May 2018, 650 . 652 [RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, 653 DOI 10.17487/RFC1995, August 1996, 654 . 656 [RFC2065] Eastlake 3rd, D. and C. Kaufman, "Domain Name System 657 Security Extensions", RFC 2065, DOI 10.17487/RFC2065, 658 January 1997, . 660 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 661 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 662 RFC 2136, DOI 10.17487/RFC2136, April 1997, 663 . 665 [RFC2535] Eastlake 3rd, D., "Domain Name System Security 666 Extensions", RFC 2535, DOI 10.17487/RFC2535, March 1999, 667 . 669 [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. 670 Wellington, "Secret Key Transaction Authentication for DNS 671 (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000, 672 . 674 [RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures 675 ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September 676 2000, . 678 [RFC3851] Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail 679 Extensions (S/MIME) Version 3.1 Message Specification", 680 RFC 3851, DOI 10.17487/RFC3851, July 2004, 681 . 683 [RFC4880] Callas, J., Donnerhacke, L., Finney, H., Shaw, D., and R. 684 Thayer, "OpenPGP Message Format", RFC 4880, 685 DOI 10.17487/RFC4880, November 2007, 686 . 688 [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol 689 (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010, 690 . 692 [RFC7706] Kumari, W. and P. Hoffman, "Decreasing Access Time to Root 693 Servers by Running One on Loopback", RFC 7706, 694 DOI 10.17487/RFC7706, November 2015, 695 . 697 [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 698 Terminology", RFC 7719, DOI 10.17487/RFC7719, December 699 2015, . 701 [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., 702 and P. Hoffman, "Specification for DNS over Transport 703 Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May 704 2016, . 706 [RootServers] 707 Root Server Operators, "Root Server Technical Operations", 708 July 2018, . 710 Authors' Addresses 712 Duane Wessels 713 Verisign 714 12061 Bluemont Way 715 Reston, VA 20190 717 Phone: +1 703 948-3200 718 Email: dwessels@verisign.com 719 URI: http://verisign.com 721 Piet Barber 722 Verisign 723 12061 Bluemont Way 724 Reston, VA 20190 726 Phone: +1 703 948-3200 727 Email: pbarber@verisign.com 728 URI: http://verisign.com 730 Matt Weinberg 731 Verisign 732 12061 Bluemont Way 733 Reston, VA 20190 735 Phone: +1 703 948-3200 736 Email: mweinberg@verisign.com 737 URI: http://verisign.com 739 Warren Kumari 740 Google 741 1600 Amphitheatre Parkway 742 Mountain View, CA 94043 744 Email: warren@kumari.net 745 Wes Hardaker 746 USC/ISI 747 P.O. Box 382 748 Davis, CA 95617 750 Email: ietf@hardakers.net