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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (November 1, 2019) is 1635 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) -- Possible downref: Non-RFC (?) normative reference: ref. 'FIPS180-4' ** Obsolete normative reference: RFC 2845 (Obsoleted by RFC 8945) ** Obsolete normative reference: RFC 4635 (Obsoleted by RFC 8945) Summary: 2 errors (**), 0 flaws (~~), 9 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force F. Dupont 3 Internet-Draft S. Morris 4 Obsoletes: 2845, 4635 (if approved) ISC 5 Intended status: Standards Track P. Vixie 6 Expires: May 4, 2020 Farsight 7 D. Eastlake 3rd 8 Futurewei 9 O. Gudmundsson 10 CloudFlare 11 B. Wellington 12 Akamai 13 November 1, 2019 15 Secret Key Transaction Authentication for DNS (TSIG) 16 draft-ietf-dnsop-rfc2845bis-06 18 Abstract 20 This document describes a protocol for transaction level 21 authentication using shared secrets and one way hashing. It can be 22 used to authenticate dynamic updates as coming from an approved 23 client, or to authenticate responses as coming from an approved name 24 server. 26 No recommendation is made here for distributing the shared secrets: 27 it is expected that a network administrator will statically configure 28 name servers and clients using some out of band mechanism. 30 This document obsoletes RFC2845 and RFC4635. 32 Status of This Memo 34 This Internet-Draft is submitted in full conformance with the 35 provisions of BCP 78 and BCP 79. 37 Internet-Drafts are working documents of the Internet Engineering 38 Task Force (IETF). Note that other groups may also distribute 39 working documents as Internet-Drafts. The list of current Internet- 40 Drafts is at https://datatracker.ietf.org/drafts/current/. 42 Internet-Drafts are draft documents valid for a maximum of six months 43 and may be updated, replaced, or obsoleted by other documents at any 44 time. It is inappropriate to use Internet-Drafts as reference 45 material or to cite them other than as "work in progress." 47 This Internet-Draft will expire on May 4, 2020. 49 Copyright Notice 51 Copyright (c) 2019 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (https://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 This document may contain material from IETF Documents or IETF 65 Contributions published or made publicly available before November 66 10, 2008. The person(s) controlling the copyright in some of this 67 material may not have granted the IETF Trust the right to allow 68 modifications of such material outside the IETF Standards Process. 69 Without obtaining an adequate license from the person(s) controlling 70 the copyright in such materials, this document may not be modified 71 outside the IETF Standards Process, and derivative works of it may 72 not be created outside the IETF Standards Process, except to format 73 it for publication as an RFC or to translate it into languages other 74 than English. 76 Table of Contents 78 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 79 1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 3 80 1.2. Protocol Overview . . . . . . . . . . . . . . . . . . . . 4 81 1.3. Document History . . . . . . . . . . . . . . . . . . . . 4 82 2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 5 83 3. Assigned Numbers . . . . . . . . . . . . . . . . . . . . . . 5 84 4. TSIG RR Format . . . . . . . . . . . . . . . . . . . . . . . 5 85 4.1. TSIG RR Type . . . . . . . . . . . . . . . . . . . . . . 5 86 4.2. TSIG Record Format . . . . . . . . . . . . . . . . . . . 6 87 4.3. MAC Computation . . . . . . . . . . . . . . . . . . . . . 8 88 4.3.1. Request MAC . . . . . . . . . . . . . . . . . . . . . 8 89 4.3.2. DNS Message . . . . . . . . . . . . . . . . . . . . . 9 90 4.3.3. TSIG Variables . . . . . . . . . . . . . . . . . . . 9 91 5. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 10 92 5.1. Generation of TSIG on Requests . . . . . . . . . . . . . 10 93 5.2. Server Processing of Request . . . . . . . . . . . . . . 10 94 5.2.1. Key Check and Error Handling . . . . . . . . . . . . 11 95 5.2.2. MAC Check and Error Handling . . . . . . . . . . . . 11 96 5.2.3. Time Check and Error Handling . . . . . . . . . . . . 12 97 5.2.4. Truncation Check and Error Handling . . . . . . . . . 12 98 5.3. Generation of TSIG on Answers . . . . . . . . . . . . . . 13 99 5.3.1. TSIG on Zone Transfer Over a TCP Connection . . . . . 13 100 5.3.2. Generation of TSIG on Error Returns . . . . . . . . . 14 101 5.4. Client Processing of Answer . . . . . . . . . . . . . . . 14 102 5.4.1. Key Error Handling . . . . . . . . . . . . . . . . . 15 103 5.4.2. MAC Error Handling . . . . . . . . . . . . . . . . . 15 104 5.4.3. Time Error Handling . . . . . . . . . . . . . . . . . 15 105 5.4.4. Truncation Error Handling . . . . . . . . . . . . . . 15 106 5.5. Special Considerations for Forwarding Servers . . . . . . 16 107 6. Algorithms and Identifiers . . . . . . . . . . . . . . . . . 16 108 7. TSIG Truncation Policy . . . . . . . . . . . . . . . . . . . 17 109 8. Shared Secrets . . . . . . . . . . . . . . . . . . . . . . . 17 110 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 111 10. Security Considerations . . . . . . . . . . . . . . . . . . . 18 112 10.1. Issue Fixed in this Document . . . . . . . . . . . . . . 19 113 10.2. Why not DNSSEC? . . . . . . . . . . . . . . . . . . . . 20 114 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 115 11.1. Normative References . . . . . . . . . . . . . . . . . . 20 116 11.2. Informative References . . . . . . . . . . . . . . . . . 21 117 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 23 118 Appendix B. Change History (to be removed before publication) . 23 119 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 121 1. Introduction 123 1.1. Background 125 The Domain Name System (DNS, [RFC1034], [RFC1035]) is a replicated 126 hierarchical distributed database system that provides information 127 fundamental to Internet operations, such as name to address 128 translation and mail handling information. 130 This document specifies use of a message authentication code (MAC), 131 generated using certain keyed hash functions, to provide an efficient 132 means of point-to-point authentication and integrity checking for DNS 133 transactions. Such transactions include DNS update requests and 134 responses for which this can provide a lightweight alternative to the 135 secure DNS dynamic update protocol described by [RFC3007]. 137 A further use of this mechanism is to protect zone transfers. In 138 this case the data covered would be the whole zone transfer including 139 any glue records sent. The protocol described by DNSSEC ([RFC4033], 140 [RFC4034], [RFC4035]) does not protect glue records and unsigned 141 records unless SIG(0) (transaction signature) is used. 143 The authentication mechanism proposed in this document uses shared 144 secret keys to establish a trust relationship between two entities. 146 Such keys must be protected in a manner similar to private keys, lest 147 a third party masquerade as one of the intended parties (by forging 148 the MAC). There was a need to provide simple and efficient 149 authentication between clients and local servers and this proposal 150 addresses that need. The proposal is unsuitable for general server 151 to server authentication for servers which speak with many other 152 servers, since key management would become unwieldy with the number 153 of shared keys going up quadratically. But it is suitable for many 154 resolvers on hosts that only talk to a few recursive servers. 156 1.2. Protocol Overview 158 Secret Key Transaction Authentication makes use of signatures on 159 messages sent between the parties involved (e.g. resolver and 160 server). These are known as "transaction signatures", or TSIG. For 161 historical reasons, in this document they are referred to as message 162 authentication codes (MAC). 164 Use of TSIG presumes prior agreement between the two parties involved 165 (e.g., resolver and server) as to any algorithm and key to be used. 166 The way that this agreement is reached is outside the scope of the 167 document. 169 A DNS message exchange involves the sending of a query and the 170 receipt of one of more DNS messages in response. For the query, the 171 MAC is calculated based on the hash of the contents and the agreed 172 TSIG key. The MAC for the response is similar, but also includes the 173 MAC of the query as part of the calculation. Where a response 174 comprises multiple packets, the calculation of the MAC associated 175 with the second and subsequent packets includes in its inputs the MAC 176 for the preceding packet. In this way it is possible to detect any 177 interruption in the packet sequence. 179 The MAC is contained in a TSIG resource record included in the 180 Additional Section of the DNS message. 182 1.3. Document History 184 TSIG was originally specified by [RFC2845]. In 2017, two nameservers 185 strictly following that document (and the related [RFC4635]) were 186 discovered to have security problems related to this feature. The 187 implementations were fixed but, to avoid similar problems in the 188 future, the two documents were updated and merged, producing this 189 revised specification for TSIG. 191 While TSIG implemented according to this RFC provides for enhanced 192 security, there are no changes in interoperability. TSIG is on the 193 wire still the same mechanism described in [RFC2845]; only the 194 checking semantics have been changed. See Section 10.1 for further 195 details. 197 2. Key Words 199 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 200 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 201 "OPTIONAL" in this document are to be interpreted as described in BCP 202 14 [RFC2119] [RFC8174] when, and only when, they appear in all 203 capitals, as shown here. 205 3. Assigned Numbers 207 This document defines the following RR type and associated value: 209 TSIG (250) 211 In addition, the document also defines the following DNS RCODEs and 212 associated names: 214 16 (BADSIG) 215 17 (BADKEY) 216 18 (BADTIME) 217 22 (BADTRUNC) 219 (See [RFC6895] Section 2.3 concerning the assignment of the value 16 220 to BADSIG.) 222 These RCODES may appear within the "Error" field of a TSIG RR. 224 4. TSIG RR Format 226 4.1. TSIG RR Type 228 To provide secret key authentication, we use an RR type whose 229 mnemonic is TSIG and whose type code is 250. TSIG is a meta-RR and 230 MUST NOT be cached. TSIG RRs are used for authentication between DNS 231 entities that have established a shared secret key. TSIG RRs are 232 dynamically computed to cover a particular DNS transaction and are 233 not DNS RRs in the usual sense. 235 As the TSIG RRs are related to one DNS request/response, there is no 236 value in storing or retransmitting them, thus the TSIG RR is 237 discarded once it has been used to authenticate a DNS message. 239 4.2. TSIG Record Format 241 The fields of the TSIG RR are described below. As is usual, all 242 multi-octet integers in the record are sent in network byte order 243 (see [RFC1035] 2.3.2). 245 NAME The name of the key used in domain name syntax. The name 246 should reflect the names of the hosts and uniquely identify the 247 key among a set of keys these two hosts may share at any given 248 time. If hosts A.site.example and B.example.net share a key, 249 possibilities for the key name include .A.site.example, 250 .B.example.net, and .A.site.example.B.example.net. It 251 should be possible for more than one key to be in simultaneous 252 use among a set of interacting hosts. 254 The name may be used as a local index to the key involved and 255 it is recommended that it be globally unique. Where a key is 256 just shared between two hosts, its name actually need only be 257 meaningful to them but it is recommended that the key name be 258 mnemonic and incorporates the names of participating agents or 259 resources as suggested above. 261 TYPE This MUST be TSIG (250: Transaction SIGnature) 263 CLASS This MUST be ANY 265 TTL This MUST be 0 267 RdLen (variable) 269 RDATA The RDATA for a TSIG RR consists of a number of fields, 270 described below: 272 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 273 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 1 274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 275 / Algorithm Name / 276 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 277 | | 278 | Time Signed +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 279 | | Fudge | 280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 281 | MAC Size | / 282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MAC / 283 / / 284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 285 | Original ID | Error | 286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 287 | Other Len | / 288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Other Data / 289 / / 290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 292 The contents of the RDATA fields are: 294 * Algorithm Name - a octet sequence identifying the TSIG 295 algorithm name in the domain name syntax. (Allowed names 296 are listed in Table 1.) The name is stored in the DNS name 297 wire format as described in [RFC1034]. As per [RFC3597], 298 this name MUST NOT be compressed. 300 * Time Signed - an unsigned 48-bit integer containing the time 301 signed as seconds since 00:00 on 1970-01-01 UTC, ignoring 302 leap seconds. 304 * Fudge - an unsigned 16-bit integer specifying the allowed 305 time difference in seconds permitted in the Time Signed 306 field. 308 * MAC Size - an unsigned 16-bit integer giving the length of 309 MAC field in octets. Truncation is indicated by a MAC size 310 less than the size of the keyed hash produced by the 311 algorithm specified by the Algorithm Name. 313 * MAC - a sequence of octets whose contents are defined by the 314 TSIG algorithm used, possibly truncated as specified by MAC 315 Size. The length of this field is given by the Mac Size. 316 Calculation of the MAC is detailed in Section 4.3. 318 * Original ID - An unsigned 16-bit integer holding the message 319 ID of the original request message. For a TSIG RR on a 320 request, it is set equal to the DNS message ID. In a TSIG 321 attached to a response - or in cases such as the forwarding 322 of a dynamic update request - the field contains the ID of 323 the original DNS request. 325 * Error - an unsigned 16-bit integer containing the extended 326 RCODE covering TSIG processing. 328 * Other Len - an unsigned 16-bit integer specifying the length 329 of the "Other Data" field in octets. 331 * Other Data - this unsigned 48-bit integer field will be 332 empty unless the content of the Error field is BADTIME, in 333 which case it will contain the server's current time as the 334 number of seconds since 00:00 on 1970-01-01 UTC, ignoring 335 leap seconds (see Section 5.2.3). 337 4.3. MAC Computation 339 When generating or verifying the contents of a TSIG record, the data 340 listed in the rest of this section are passed, in the order listed 341 below, as input to MAC computation. The data are passed in network 342 byte order or wire format, as appropriate, and are fed into the 343 hashing function as a continuous octet sequence with no interfield 344 separator or padding. 346 4.3.1. Request MAC 348 Only included in the computation of a MAC for a response message (or 349 the first message in a multi-message response), the validated request 350 MAC MUST be included in the MAC computation. If the request MAC 351 failed to validate, an unsigned error message MUST be returned 352 instead. (Section 5.3.2). 354 The request's MAC, comprising the following fields, is digested in 355 wire format: 357 Field Type Description 358 ---------- ----------------------- ---------------------- 359 MAC Length Unsigned 16-bit integer in network byte order 360 MAC Data octet sequence exactly as transmitted 362 Special considerations apply to the TSIG calculation for the second 363 and subsequent messages a response that consists of multiple DNS 364 messages (e.g. a zone transfer). These are described in 365 Section 5.3.1. 367 4.3.2. DNS Message 369 A whole and complete DNS message in wire format. When creating a 370 TSIG, this is the message before the TSIG RR has been added to the 371 additional data section and before the DNS Message Header's ARCOUNT 372 field has been incremented to contain the TSIG RR. 374 When verifying an incoming message, this is the message after the 375 TSIG RR and been removed and the ARCOUNT field has been decremented. 376 If the message ID differs from the original message ID, the original 377 message ID is substituted for the message ID. (This could happen, 378 for example, when forwarding a dynamic update request.) 380 4.3.3. TSIG Variables 382 Also included in the digest is certain information present in the 383 TSIG RR. Adding this data provides further protection against an 384 attempt to interfere with the message. 386 Source Field Name Notes 387 ---------- -------------- ----------------------------------------- 388 TSIG RR NAME Key name, in canonical wire format 389 TSIG RR CLASS (Always ANY in the current specification) 390 TSIG RR TTL (Always 0 in the current specification) 391 TSIG RDATA Algorithm Name in canonical wire format 392 TSIG RDATA Time Signed in network byte order 393 TSIG RDATA Fudge in network byte order 394 TSIG RDATA Error in network byte order 395 TSIG RDATA Other Len in network byte order 396 TSIG RDATA Other Data exactly as transmitted 398 The RR RDLEN and RDATA MAC Length are not included in the input to 399 MAC computation since they are not guaranteed to be knowable before 400 the MAC is generated. 402 The Original ID field is not included in this section, as it has 403 already been substituted for the message ID in the DNS header and 404 hashed. 406 For each label type, there must be a defined "Canonical wire format" 407 that specifies how to express a label in an unambiguous way. For 408 label type 00, this is defined in [RFC4034] Section 6.1. The use of 409 label types other than 00 is not defined for this specification. 411 4.3.3.1. Time Values Used in TSIG Calculations 413 The data digested includes the two timer values in the TSIG header in 414 order to defend against replay attacks. If this were not done, an 415 attacker could replay old messages but update the "Time Signed" and 416 "Fudge" fields to make the message look new. This data is named 417 "TSIG Timers", and for the purpose of MAC calculation, they are 418 hashed in their "on the wire" format, in the following order: first 419 Time Signed, then Fudge. 421 5. Protocol Details 423 5.1. Generation of TSIG on Requests 425 Once the outgoing record has been constructed, the client performs 426 the keyed hash (HMAC) computation, appends a TSIG record with the 427 calculated MAC to the Additional Data section (incrementing the 428 ARCOUNT to reflect the additional RR), and transmits the request to 429 the server. This TSIG record MUST be the only TSIG RR in the message 430 and MUST be last record in the Additional Data section. The client 431 MUST store the MAC and the key name from the request while awaiting 432 an answer. 434 The digest components for a request are: 436 DNS Message (request) 437 TSIG Variables (request) 439 Note that some older name servers will not accept requests with a 440 nonempty additional data section. Clients SHOULD only attempt signed 441 transactions with servers who are known to support TSIG and share 442 some algorithm and secret key with the client -- so, this is not a 443 problem in practice. 445 5.2. Server Processing of Request 447 If an incoming message contains a TSIG record, it MUST be the last 448 record in the additional section. Multiple TSIG records are not 449 allowed. If multiple TSIG records are detected or a TSIG record is 450 present in any other position, the DNS message is dropped and a 451 response with RCODE 1 (FORMERR) MUST be returned. Upon receipt of a 452 message with exactly one correctly placed TSIG RR, the TSIG RR is 453 copied to a safe location, removed from the DNS Message, and 454 decremented out of the DNS message header's ARCOUNT. 456 If the TSIG RR cannot be understood, the server MUST regard the 457 message as corrupt and return a FORMERR to the server. Otherwise the 458 server is REQUIRED to return a TSIG RR in the response. 460 To validate the received TSIG RR, the server MUST perform the 461 following checks in the following order: 463 1. Check KEY 464 2. Check MAC 465 3. Check TIME values 466 4. Check Truncation policy 468 5.2.1. Key Check and Error Handling 470 If a non-forwarding server does not recognize the key or algorithm 471 used by the client (or recognises the algorithm but does not 472 implement it), the server MUST generate an error response with RCODE 473 9 (NOTAUTH) and TSIG ERROR 17 (BADKEY). This response MUST be 474 unsigned as specified in Section 5.3.2. The server SHOULD log the 475 error. (Special considerations apply to forwarding servers, see 476 Section 5.5.) 478 5.2.2. MAC Check and Error Handling 480 Using the information in the TSIG, the server should verify the MAC 481 by doing its own calculation and comparing the result with the MAC 482 received. If the MAC fails to verify, the server MUST generate an 483 error response as specified in Section 5.3.2 with RCODE 9 (NOTAUTH) 484 and TSIG ERROR 16 (BADSIG). This response MUST be unsigned as 485 specified in Section 5.3.2. The server SHOULD log the error. 487 5.2.2.1. MAC Truncation 489 When space is at a premium and the strength of the full length of a 490 MAC is not needed, it is reasonable to truncate the keyed hash and 491 use the truncated value for authentication. HMAC SHA-1 truncated to 492 96 bits is an option available in several IETF protocols, including 493 IPsec and TLS. 495 Processing of a truncated MAC follows these rules: 497 1. If "MAC size" field is greater than keyed hash output length: 499 This case MUST NOT be generated and, if received, MUST cause the 500 DNS message to be dropped and RCODE 1 (FORMERR) to be returned. 502 2. If "MAC size" field equals keyed hash output length: 504 The entire output keyed hash output is present and used. 506 3. "MAC size" field is less than the larger of 10 (octets) and half 507 the length of the hash function in use: 509 With the exception of certain TSIG error messages described in 510 Section 5.3.2, where it is permitted that the MAC size be zero, 511 this case MUST NOT be generated and, if received, MUST cause the 512 DNS message to be dropped and RCODE 1 (FORMERR) to be returned. 514 4. Otherwise: 516 This is sent when the signer has truncated the keyed hash output 517 to an allowable length, as described in [RFC2104], taking initial 518 octets and discarding trailing octets. TSIG truncation can only 519 be to an integral number of octets. On receipt of a DNS message 520 with truncation thus indicated, the locally calculated MAC is 521 similarly truncated and only the truncated values are compared 522 for authentication. The request MAC used when calculating the 523 TSIG MAC for a reply is the truncated request MAC. 525 5.2.3. Time Check and Error Handling 527 If the server time is outside the time interval specified by the 528 request (which is: Time Signed, plus/minus Fudge), the server MUST 529 generate an error response with RCODE 9 (NOTAUTH) and TSIG ERROR 18 530 (BADTIME). The server SHOULD also cache the most recent time signed 531 value in a message generated by a key, and SHOULD return BADTIME if a 532 message received later has an earlier time signed value. A response 533 indicating a BADTIME error MUST be signed by the same key as the 534 request. It MUST include the client's current time in the time 535 signed field, the server's current time (an unsigned 48-bit integer) 536 in the other data field, and 6 in the other data length field. This 537 is done so that the client can verify a message with a BADTIME error 538 without the verification failing due to another BADTIME error. In 539 addition, the fudge field MUST be set to the fudge value received 540 from the client. The data signed is specified in Section 5.3.2. The 541 server SHOULD log the error. 543 Caching the most recent time signed value and rejecting requests with 544 an earlier one could lead to valid messages being rejected if transit 545 through the network led to UDP packets arriving in a different order 546 to the one in which they were sent. Implementations should be aware 547 of this possibility and be prepared to deal with it, e.g. by 548 retransmitting the rejected request with a new TSIG once outstanding 549 requests have completed or the time given by their time signed plus 550 fudge value has passed. 552 5.2.4. Truncation Check and Error Handling 554 If a TSIG is received with truncation that is permitted under 555 Section 5.2.2.1 above but the MAC is too short for the local policy 556 in force, an RCODE 9 (NOTAUTH) and TSIG ERROR 22 (BADTRUNC) MUST be 557 returned. The server SHOULD log the error. 559 5.3. Generation of TSIG on Answers 561 When a server has generated a response to a signed request, it signs 562 the response using the same algorithm and key. The server MUST NOT 563 generate a signed response to a request if either the KEY is invalid 564 (e.g. key name or algorithm name are unknown), or the MAC fails 565 validation: see Section 5.3.2 for details of responding in these 566 cases. 568 It also MUST NOT not generate a signed response to an unsigned 569 request, except in the case of a response to a client's unsigned TKEY 570 request if the secret key is established on the server side after the 571 server processed the client's request. Signing responses to unsigned 572 TKEY requests MUST be explicitly specified in the description of an 573 individual secret key establishment algorithm [RFC3645]. 575 The digest components used to generate a TSIG on a response are: 577 Request MAC 578 DNS Message (response) 579 TSIG Variables (response) 581 (This calculation is different for the second and subsequent message 582 in a multi-message answer, see below.) 584 If addition of the TSIG record will cause the message to be 585 truncated, the server MUST alter the response so that a TSIG can be 586 included. This response consists of only the question and a TSIG 587 record, and has the TC bit set and an RCODE of 0 (NOERROR). The 588 client SHOULD at this point retry the request using TCP (as per 589 [RFC1035] 4.2.2). 591 5.3.1. TSIG on Zone Transfer Over a TCP Connection 593 A zone transfer over a DNS TCP session can include multiple DNS 594 messages. Using TSIG on such a connection can protect the connection 595 from hijacking and provide data integrity. The TSIG MUST be included 596 on all DNS messages in the response. For backward compatibility, a 597 client which receives DNS messages and verifies TSIG MUST accept up 598 to 99 intermediary messages without a TSIG. The first message is 599 processed as a standard answer (see Section 5.3) but subsequent 600 messages have the following digest components: 602 Prior MAC (running) 603 DNS Messages (any unsigned messages since the last TSIG) 604 TSIG Timers (current message) 606 The "Prior MAC" is the MAC from the TSIG attached to the last message 607 containing a TSIG. "DNS Messages" comprises the concatenation (in 608 message order) of all messages after the last message that included a 609 TSIG and includes the current message. "TSIG timers" comprises the 610 "Time Signed" and "Fudge" fields (in that order) pertaining to the 611 message for which the TSIG is being created: this means that the 612 successive TSIG records in the stream will have non-decreasing "Time 613 Signed" fields. Note that only the timers are included in the second 614 and subsequent messages, not all the TSIG variables. 616 This allows the client to rapidly detect when the session has been 617 altered; at which point it can close the connection and retry. If a 618 client TSIG verification fails, the client MUST close the connection. 619 If the client does not receive TSIG records frequently enough (as 620 specified above) it SHOULD assume the connection has been hijacked 621 and it SHOULD close the connection. The client SHOULD treat this the 622 same way as they would any other interrupted transfer (although the 623 exact behavior is not specified here). 625 5.3.2. Generation of TSIG on Error Returns 627 When a server detects an error relating to the key or MAC in the 628 incoming request, the server SHOULD send back an unsigned error 629 message (MAC size == 0 and empty MAC). It MUST NOT send back a 630 signed error message. 632 If an error is detected relating to the TSIG validity period or the 633 MAC is too short for the local policy, the server SHOULD send back a 634 signed error message. The digest components are: 636 Request MAC (if the request MAC validated) 637 DNS Message (response) 638 TSIG Variables (response) 640 The reason that the request is not included in this MAC in some cases 641 is to make it possible for the client to verify the error. If the 642 error is not a TSIG error the response MUST be generated as specified 643 in Section 5.3. 645 5.4. Client Processing of Answer 647 When a client receives a response from a server and expects to see a 648 TSIG, it performs the same checks as described in Section 5.2, with 649 the following modifications: 651 o If the TSIG RR does not validate, that response MUST be discarded, 652 unless the RCODE is 9 (NOTAUTH), in which case the client SHOULD 653 proceed as described in the following subsections. 655 A message containing an unsigned TSIG record or a TSIG record which 656 fails verification SHOULD NOT be considered an acceptable response; 657 the client SHOULD log an error and continue to wait for a signed 658 response until the request times out. 660 5.4.1. Key Error Handling 662 If an RCODE on a response is 9 (NOTAUTH), but the response TSIG 663 validates and the TSIG key recognised by the client but different 664 from that used on the request, then this is a Key Error. The client 665 MAY retry the request using the key specified by the server. 666 However, this should never occur, as a server MUST NOT sign a 667 response with a different key to that used to sign the request. 669 5.4.2. MAC Error Handling 671 If the response RCODE is 9 (NOTAUTH) and TSIG ERROR is 16 (BADSIG), 672 this is a MAC error, and client MAY retry the request with a new 673 request ID but it would be better to try a different shared key if 674 one is available. Clients SHOULD keep track of how many MAC errors 675 are associated with each key. Clients SHOULD log this event. 677 5.4.3. Time Error Handling 679 If the response RCODE is 9 (NOTAUTH) and the TSIG ERROR is 18 680 (BADTIME), or the current time does not fall in the range specified 681 in the TSIG record, then this is a Time error. This is an indication 682 that the client and server clocks are not synchronized. In this case 683 the client SHOULD log the event. DNS resolvers MUST NOT adjust any 684 clocks in the client based on BADTIME errors, but the server's time 685 in the other data field SHOULD be logged. 687 5.4.4. Truncation Error Handling 689 If the response RCODE is 9 (NOTAUTH) and the TSIG ERROR is 22 690 (BADTRUNC) then this is a Truncation error. The client MAY retry 691 with a lesser truncation up to the full HMAC output (no truncation), 692 using the truncation used in the response as a hint for what the 693 server policy allowed (Section 7). Clients SHOULD log this event. 695 5.5. Special Considerations for Forwarding Servers 697 A server acting as a forwarding server of a DNS message SHOULD check 698 for the existence of a TSIG record. If the name on the TSIG is not 699 of a secret that the server shares with the originator the server 700 MUST forward the message unchanged including the TSIG. If the name 701 of the TSIG is of a key this server shares with the originator, it 702 MUST process the TSIG. If the TSIG passes all checks, the forwarding 703 server MUST, if possible, include a TSIG of its own, to the 704 destination or the next forwarder. If no transaction security is 705 available to the destination and the message is a query then, if the 706 corresponding response has the AD flag (see [RFC4035]) set, the 707 forwarder MUST clear the AD flag before adding the TSIG to the 708 response and returning the result to the system from which it 709 received the query. 711 6. Algorithms and Identifiers 713 The only message digest algorithm specified in the first version of 714 these specifications [RFC2845] was "HMAC-MD5" (see [RFC1321], 715 [RFC2104]). Although a review of its security [RFC6151] concluded 716 that "it may not be urgent to remove HMAC-MD5 from the existing 717 protocols", with the availability of more secure alternatives the 718 opportunity has been taken to make the implementation of this 719 algorithm optional. 721 The use of SHA-1 [FIPS180-4], [RFC3174], (which is a 160-bit hash as 722 compared to the 128 bits for MD5), and additional hash algorithms in 723 the SHA family [FIPS180-4], [RFC3874], [RFC6234] with 224, 256, 384, 724 and 512 bits may be preferred in some cases. This is because 725 increasingly successful cryptanalytic attacks are being made on the 726 shorter hashes. 728 Use of TSIG between two DNS agents is by mutual agreement. That 729 agreement can include the support of additional algorithms and 730 criteria as to which algorithms and truncations are acceptable, 731 subject to the restriction and guidelines in Section 5.2.2.1 above. 732 Key agreement can be by the TKEY mechanism [RFC2930] or some other 733 mutually agreeable method. 735 Implementations that support TSIG MUST also implement HMAC SHA1 and 736 HMAC SHA256 and MAY implement gss-tsig and the other algorithms 737 listed below. SHA-1 truncated to 96 bits (12 octets) SHOULD be 738 implemented. 740 Requirement Name 741 ----------- ------------------------ 742 Optional HMAC-MD5.SIG-ALG.REG.INT 743 Optional gss-tsig 744 Mandatory hmac-sha1 745 Optional hmac-sha224 746 Mandatory hmac-sha256 747 Optional hmac-sha384 748 Optional hmac-sha512 750 Table 1 752 7. TSIG Truncation Policy 754 As noted above, two DNS agents (e.g., resolver and server) must 755 mutually agree to use TSIG. Implicit in such an "agreement" are 756 criteria as to acceptable keys and algorithms and, with the 757 extensions in this document, truncations. Local policies MAY require 758 the rejection of TSIGs, even though they use an algorithm for which 759 implementation is mandatory. 761 When a local policy permits acceptance of a TSIG with a particular 762 algorithm and a particular non-zero amount of truncation, it SHOULD 763 also permit the use of that algorithm with lesser truncation (a 764 longer MAC) up to the full keyed hash output. 766 Regardless of a lower acceptable truncated MAC length specified by 767 local policy, a reply SHOULD be sent with a MAC at least as long as 768 that in the corresponding request. Note if the request specified a 769 MAC length longer than the keyed hash output it will be rejected by 770 processing rules Section 5.2.2.1 case 1. 772 Implementations permitting multiple acceptable algorithms and/or 773 truncations SHOULD permit this list to be ordered by presumed 774 strength and SHOULD allow different truncations for the same 775 algorithm to be treated as separate entities in this list. When so 776 implemented, policies SHOULD accept a presumed stronger algorithm and 777 truncation than the minimum strength required by the policy. 779 8. Shared Secrets 781 Secret keys are very sensitive information and all available steps 782 should be taken to protect them on every host on which they are 783 stored. Generally such hosts need to be physically protected. If 784 they are multi-user machines, great care should be taken that 785 unprivileged users have no access to keying material. Resolvers 786 often run unprivileged, which means all users of a host would be able 787 to see whatever configuration data is used by the resolver. 789 A name server usually runs privileged, which means its configuration 790 data need not be visible to all users of the host. For this reason, 791 a host that implements transaction-based authentication should 792 probably be configured with a "stub resolver" and a local caching and 793 forwarding name server. This presents a special problem for 794 [RFC2136] which otherwise depends on clients to communicate only with 795 a zone's authoritative name servers. 797 Use of strong random shared secrets is essential to the security of 798 TSIG. See [RFC4086] for a discussion of this issue. The secret 799 SHOULD be at least as long as the keyed hash output [RFC2104]. 801 9. IANA Considerations 803 IANA maintains a registry of algorithm names to be used as "Algorithm 804 Names" as defined in Section 4.2. Algorithm names are text strings 805 encoded using the syntax of a domain name. There is no structure 806 required other than names for different algorithms must be unique 807 when compared as DNS names, i.e., comparison is case insensitive. 808 Previous specifications [RFC2845] and [RFC4635] defined values for 809 HMAC MD5 and SHA. IANA has also registered "gss-tsig" as an 810 identifier for TSIG authentication where the cryptographic operations 811 are delegated to the Generic Security Service (GSS) [RFC3645]. 813 New algorithms are assigned using the IETF Consensus policy defined 814 in [RFC8126]. The algorithm name HMAC-MD5.SIG-ALG.REG.INT looks like 815 a fully-qualified domain name for historical reasons; other algorithm 816 names are simple (i.e., single-component) names. 818 IANA maintains a registry of RCODES (error codes), including "TSIG 819 Error values" to be used for "Error" values as defined in 820 Section 4.2. New error codes are assigned and specified as in 821 [RFC6895]. 823 10. Security Considerations 825 The approach specified here is computationally much less expensive 826 than the signatures specified in DNSSEC. As long as the shared 827 secret key is not compromised, strong authentication is provided 828 between two DNS systems, e.g., for the last hop from a local name 829 server to the user resolver, or between primary and secondary 830 nameservers. 832 Recommendations for choosing and maintaining secret keys can be found 833 in [RFC2104]. If the client host has been compromised, the server 834 should suspend the use of all secrets known to that client. If 835 possible, secrets should be stored in encrypted form. Secrets should 836 never be transmitted in the clear over any network. This document 837 does not address the issue on how to distribute secrets except that 838 it mentions the possibilities of manual configuration and the use of 839 TKEY [RFC2930]. Secrets SHOULD NOT be shared by more than two 840 entities. 842 This mechanism does not authenticate source data, only its 843 transmission between two parties who share some secret. The original 844 source data can come from a compromised zone master or can be 845 corrupted during transit from an authentic zone master to some 846 "caching forwarder." However, if the server is faithfully performing 847 the full DNSSEC security checks, then only security checked data will 848 be available to the client. 850 A fudge value that is too large may leave the server open to replay 851 attacks. A fudge value that is too small may cause failures if 852 machines are not time synchronized or there are unexpected network 853 delays. The RECOMMENDED value in most situations is 300 seconds. 855 For all of the message authentication code algorithms listed in this 856 document, those producing longer values are believed to be stronger; 857 however, while there have been some arguments that mild truncation 858 can strengthen a MAC by reducing the information available to an 859 attacker, excessive truncation clearly weakens authentication by 860 reducing the number of bits an attacker has to try to break the 861 authentication by brute force [RFC2104]. 863 Significant progress has been made recently in cryptanalysis of hash 864 functions of the types used here. While the results so far should 865 not affect HMAC, the stronger SHA-1 and SHA-256 algorithms are being 866 made mandatory as a precaution. 868 See also the Security Considerations section of [RFC2104] from which 869 the limits on truncation in this RFC were taken. 871 10.1. Issue Fixed in this Document 873 When signing a DNS reply message using TSIG, the MAC computation uses 874 the request message's MAC as an input to cryptographically relate the 875 reply to the request. The original TSIG specification [RFC2845] 876 required that the TIME values be checked before the request's MAC. 877 If the TIME was invalid, some implementations failed to carry out 878 further checks and could use an invalid request MAC in the signed 879 reply. 881 This document makes it a madatory that the request MAC is considered 882 to be invalid until it has been validated: until then, any answer 883 must be unsigned. For this reason, the request MAC is now checked 884 before the TIME value. 886 10.2. Why not DNSSEC? 888 This section from the original document [RFC2845] analyzes DNSSEC in 889 order to justify the introduction of TSIG. 891 "DNS has recently been extended by DNSSEC ([RFC4033], [RFC4034] and 892 [RFC4035]) to provide for data origin authentication, and public key 893 distribution, all based on public key cryptography and public key 894 based digital signatures. To be practical, this form of security 895 generally requires extensive local caching of keys and tracing of 896 authentication through multiple keys and signatures to a pre-trusted 897 locally configured key. 899 One difficulty with the DNSSEC scheme is that common DNS 900 implementations include simple "stub" resolvers which do not have 901 caches. Such resolvers typically rely on a caching DNS server on 902 another host. It is impractical for these stub resolvers to perform 903 general DNSSEC authentication and they would naturally depend on 904 their caching DNS server to perform such services for them. To do so 905 securely requires secure communication of queries and responses. 906 DNSSEC provides public key transaction signatures to support this, 907 but such signatures are very expensive computationally to generate. 908 In general, these require the same complex public key logic that is 909 impractical for stubs. 911 A second area where use of straight DNSSEC public key based 912 mechanisms may be impractical is authenticating dynamic update 913 [RFC2136] requests. DNSSEC provides for request signatures but with 914 DNSSEC they, like transaction signatures, require computationally 915 expensive public key cryptography and complex authentication logic. 916 Secure Domain Name System Dynamic Update ([RFC3007]) describes how 917 different keys are used in dynamically updated zones." 919 11. References 921 11.1. Normative References 923 [FIPS180-4] 924 National Institute of Standards and Technology, "Secure 925 Hash Standard (SHS)", FIPS PUB 180-4, August 2015. 927 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 928 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 929 . 931 [RFC1035] Mockapetris, P., "Domain names - implementation and 932 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 933 November 1987, . 935 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 936 Requirement Levels", BCP 14, RFC 2119, 937 DOI 10.17487/RFC2119, March 1997, 938 . 940 [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. 941 Wellington, "Secret Key Transaction Authentication for DNS 942 (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000, 943 . 945 [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record 946 (RR) Types", RFC 3597, DOI 10.17487/RFC3597, September 947 2003, . 949 [RFC4635] Eastlake 3rd, D., "HMAC SHA (Hashed Message Authentication 950 Code, Secure Hash Algorithm) TSIG Algorithm Identifiers", 951 RFC 4635, DOI 10.17487/RFC4635, August 2006, 952 . 954 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 955 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 956 May 2017, . 958 11.2. Informative References 960 [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, 961 DOI 10.17487/RFC1321, April 1992, 962 . 964 [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 965 Hashing for Message Authentication", RFC 2104, 966 DOI 10.17487/RFC2104, February 1997, 967 . 969 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 970 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 971 RFC 2136, DOI 10.17487/RFC2136, April 1997, 972 . 974 [RFC2930] Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY 975 RR)", RFC 2930, DOI 10.17487/RFC2930, September 2000, 976 . 978 [RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic 979 Update", RFC 3007, DOI 10.17487/RFC3007, November 2000, 980 . 982 [RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 983 (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001, 984 . 986 [RFC3645] Kwan, S., Garg, P., Gilroy, J., Esibov, L., Westhead, J., 987 and R. Hall, "Generic Security Service Algorithm for 988 Secret Key Transaction Authentication for DNS (GSS-TSIG)", 989 RFC 3645, DOI 10.17487/RFC3645, October 2003, 990 . 992 [RFC3874] Housley, R., "A 224-bit One-way Hash Function: SHA-224", 993 RFC 3874, DOI 10.17487/RFC3874, September 2004, 994 . 996 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 997 Rose, "DNS Security Introduction and Requirements", 998 RFC 4033, DOI 10.17487/RFC4033, March 2005, 999 . 1001 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 1002 Rose, "Resource Records for the DNS Security Extensions", 1003 RFC 4034, DOI 10.17487/RFC4034, March 2005, 1004 . 1006 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 1007 Rose, "Protocol Modifications for the DNS Security 1008 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 1009 . 1011 [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, 1012 "Randomness Requirements for Security", BCP 106, RFC 4086, 1013 DOI 10.17487/RFC4086, June 2005, 1014 . 1016 [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations 1017 for the MD5 Message-Digest and the HMAC-MD5 Algorithms", 1018 RFC 6151, DOI 10.17487/RFC6151, March 2011, 1019 . 1021 [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms 1022 (SHA and SHA-based HMAC and HKDF)", RFC 6234, 1023 DOI 10.17487/RFC6234, May 2011, 1024 . 1026 [RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA 1027 Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895, 1028 April 2013, . 1030 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1031 Writing an IANA Considerations Section in RFCs", BCP 26, 1032 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1033 . 1035 Appendix A. Acknowledgments 1037 This document consolidates and updates the earlier documents by the 1038 authors of [RFC2845] (Paul Vixie, Olafur Gudmundsson, Donald E. 1039 Eastlake 3rd and Brian Wellington) and [RFC4635] (Donald E. Eastlake 1040 3rd). 1042 The security problem addressed by this document was reported by 1043 Clement Berthaux from Synacktiv. 1045 Note for the RFC Editor (to be removed before publication): the first 1046 'e' in Clement is a fact a small 'e' with acute, unicode code U+00E9. 1047 I do not know if xml2rfc supports non ASCII characters so I prefer to 1048 not experiment with it. BTW I am French too so I can help if you 1049 have questions like correct spelling... 1051 Peter van Dijk, Benno Overeinder, Willem Toroop, Ondrej Sury, Mukund 1052 Sivaraman and Ralph Dolmans participated in the discussions that 1053 prompted this document. Mukund Sivaraman and Martin Hoffman made 1054 extremely helpful suggestions concerning the structure and wording of 1055 the updated document. 1057 Appendix B. Change History (to be removed before publication) 1059 RFC EDITOR: Please remove this appendix before publication. 1061 draft-dupont-dnsop-rfc2845bis-00 1063 [RFC4635] was merged. 1065 Authors of original documents were moved to Acknowledgments 1066 (Appendix A). 1068 Section 2 was updated to [RFC8174] style. 1070 Spit references into normative and informative references and 1071 updated them. 1073 Added a text explaining why this document was written in the 1074 Abstract and at the beginning of the introduction. 1076 Clarified the layout of TSIG RDATA. 1078 Moved the text about using DNSSEC from the Introduction to the end 1079 of Security Considerations. 1081 Added the security clarifications: 1083 1. Emphasized that MAC is invalid until it is successfully 1084 validated. 1086 2. Added requirement that a request MAC that has not been 1087 successfully validated MUST NOT be included into a response. 1089 3. Added requirement that a request that has not been validated 1090 MUST NOT generate a signed response. 1092 4. Added note about MAC too short for the local policy to 1093 Section 5.3.2. 1095 5. Changed the order of server checks and swapped corresponding 1096 sections. 1098 6. Removed the truncation size limit "also case" as it does not 1099 apply and added confusion. 1101 7. Relocated the error provision for TSIG truncation to the new 1102 Section 5.2.4. Moved from RCODE 22 to RCODE 9 and TSIG ERROR 1103 22, i.e., aligned with other TSIG error cases. 1105 8. Added Section 5.4.4 about truncation error handling by 1106 clients. 1108 9. Removed the limit to HMAC output in replies as a request 1109 which specified a MAC length longer than the HMAC output is 1110 invalid according to the first processing rule in 1111 Section 5.2.2.1. 1113 10. Promoted the requirement that a secret length should be at 1114 least as long as the HMAC output to a SHOULD [RFC2119] key 1115 word. 1117 11. Added a short text to explain the security issue. 1119 draft-dupont-dnsop-rfc2845bis-01 1121 Improved wording (post-publication comments). 1123 Specialized and renamed the "TSIG on TCP connection" 1124 (Section 5.3.1) to "TSIG on zone transfer over a TCP connection". 1126 Added a SHOULD for a TSIG in each message (was envelope) for new 1127 implementations. 1129 draft-ietf-dnsop-rfc2845bis-00 1131 Adopted by the IETF DNSOP working group: title updated and version 1132 counter reset to 00. 1134 draft-ietf-dnsop-rfc2845bis-01 1136 Relationship between protocol change and principle of assuming the 1137 request MAC is invalid until validated clarified. (Jinmei Tatuya) 1139 Cross reference to considerations for forwarding servers added. 1140 (Bob Harold) 1142 Added text from [RFC3645] concerning the signing behavior if a 1143 secret key is added during a multi-message exchange. 1145 Added reference to [RFC6895]. 1147 Many improvements in the wording. 1149 Added RFC 2845 authors as co-authors of this document. 1151 draft-ietf-dnsop-rfc2845bis-02 1153 Added a recommendation to copy time fields in BADKEY errors. 1154 (Mark Andrews) 1156 draft-ietf-dnsop-rfc2845bis-03 1158 Further changes as a result of comments by Mukund Sivaraman. 1160 Miscellaneous changes to wording. 1162 draft-ietf-dnsop-rfc2845bis-04 1164 Major restructing as a result of comprehensive review by Martin 1165 Hoffman. Amongst the more significant changes: 1167 * More comprehensive introduction. 1169 * Merged "Protocol Description" and "Protocol Details" sections. 1171 * Reordered sections so as to follow message exchange through 1172 "client "sending", "server receipt", "server sending", "client 1173 receipt". 1175 * Added miscellaneous clarifications. 1177 draft-ietf-dnsop-rfc2845bis-05 1179 Make implementation of HMAC-MD5 optional. 1181 Require that the Fudge field in BADTIME response be equal to the 1182 Fudge field received from the client. 1184 Added comment concerning the handling of BADTIME messages due to 1185 out of order packet reception. 1187 draft-ietf-dnsop-rfc2845bis-06 1189 Wording changes and minor corrections after feedback. 1191 Authors' Addresses 1193 Francis Dupont 1194 Internet Software Consortium 1195 950 Charter Street 1196 Redwood City, CA 94063 1197 United States of America 1199 Email: Francis.Dupont@fdupont.fr 1201 Stephen Morris 1202 Internet Software Consortium 1203 950 Charter Street 1204 Redwood City, CA 94063 1205 United States of America 1207 Email: sa.morris8@gmail.com 1209 Paul Vixie 1210 Farsight Security Inc 1211 177 Bovet Road, Suite 180 1212 San Mateo, CA 94402 1213 United States of America 1215 Email: paul@redbarn.org 1216 Donald E. Eastlake 3rd 1217 Futurewei Technologies 1218 155 Beaver Street 1219 Milford, MA 01753 1220 United States of America 1222 Email: d3e3e3@gmail.com 1224 Olafur Gudmundsson 1225 CloudFlare 1226 San Francisco, CA 94107 1227 United States of America 1229 Email: olafur+ietf@cloudflare.com 1231 Brian Wellington 1232 Akamai 1233 United States of America 1235 Email: bwelling@akamai.com