idnits 2.17.1 draft-ietf-dnsind-tsig-05.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** Cannot find the required boilerplate sections (Copyright, IPR, etc.) in this document. Expected boilerplate is as follows today (2024-03-28) according to https://trustee.ietf.org/license-info : IETF Trust Legal Provisions of 28-dec-2009, Section 6.a: This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. IETF Trust Legal Provisions of 28-dec-2009, Section 6.b(i), paragraph 2: Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. IETF Trust Legal Provisions of 28-dec-2009, Section 6.b(i), paragraph 3: This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- ** Missing expiration date. The document expiration date should appear on the first and last page. ** The document seems to lack a 1id_guidelines paragraph about Internet-Drafts being working documents. ** The document seems to lack a 1id_guidelines paragraph about 6 months document validity -- however, there's a paragraph with a matching beginning. Boilerplate error? ** The document seems to lack a 1id_guidelines paragraph about the list of current Internet-Drafts. ** The document seems to lack a 1id_guidelines paragraph about the list of Shadow Directories. == No 'Intended status' indicated for this document; assuming Proposed Standard Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an Introduction section. ** The document seems to lack a Security Considerations section. ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) ** The document seems to lack an Authors' Addresses Section. ** There are 133 instances of too long lines in the document, the longest one being 7 characters in excess of 72. ** The document seems to lack a both a reference to RFC 2119 and the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. RFC 2119 keyword, line 342: '...ror the response MUST be generated as ...' RFC 2119 keyword, line 352: '... TSIG MUST be included on the first ...' RFC 2119 keyword, line 354: '...y header, but it SHOULD be placed on a...' RFC 2119 keyword, line 364: '...ails, the client MUST close the connec...' RFC 2119 keyword, line 365: '...uently enough it SHOULD assume the con...' (12 more instances...) Miscellaneous warnings: ---------------------------------------------------------------------------- == Line 164 has weird spacing: '...hm Name doma...' == Line 169 has weird spacing: '...re Size u_in...' == Line 170 has weird spacing: '... stream defi...' == Line 174 has weird spacing: '... stream unde...' == Line 186 has weird spacing: '... RdLen as ap...' == (4 more instances...) == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: If the response RCODE is 9 (NOTAUTH), and TSIG ERROR is 18 (BADTIME) or the TSIG times in request and answer do not overlap, then this is a TIME error. This is an indication that client and server are not clock synchronized. In this case the client should log the event. DNS resolvers MUST not adjust any clocks in the client based on BADTIME errors. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (June 1998) is 9418 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) -- Missing reference section? 'RFC1034' on line 495 looks like a reference -- Missing reference section? 'RFC1035' on line 498 looks like a reference -- Missing reference section? 'RFC2065' on line 508 looks like a reference -- Missing reference section? 'RFC2136' on line 515 looks like a reference -- Missing reference section? 'RFC2137' on line 519 looks like a reference -- Missing reference section? 'RFC1321' on line 501 looks like a reference -- Missing reference section? 'RFC2104' on line 511 looks like a reference -- Missing reference section? 'RFC1750' on line 504 looks like a reference Summary: 12 errors (**), 0 flaws (~~), 8 warnings (==), 10 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNSIND Working Group Paul Vixie (Ed.) (ISC) 3 INTERNET-DRAFT Olafur Gudmundsson (TIS) 4 Donald Eastlake 3rd (CyberCash) 5 June 1998 7 Amends: RFC 1035 9 Secret Key Transaction Signatures for DNS (TSIG) 11 Status of this Memo 13 This document is an Internet-Draft. Internet-Drafts are working 14 documents of the Internet Engineering Task Force (IETF), its areas, 15 and its working groups. Note that other groups may also distribute 16 working documents as Internet-Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six months 19 and may be updated, replaced, or obsoleted by other documents at any 20 time. It is inappropriate to use Internet-Drafts as reference 21 material or to cite them other than as ``work in progress.'' 23 To view the entire list of current Internet-Drafts, please check 24 the "1id-abstracts.txt" listing contained in the Internet-Drafts 25 Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net 26 (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au 27 (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu 28 (US West Coast). 30 Abstract 32 This protocol allows for transaction level authentication using 33 shared secrets and one way hashing. It can be used to authenticate 34 dynamic updates as coming from an approved client, or to authenticate 35 responses as coming from an approved recursive name server. 37 No provision has been made here for distributing the shared secrets; 38 it is expected that a network administrator will statically configure 39 name servers and clients using some out of band mechanism such as 40 sneaker-net until a secure automated mechanism for key distribution 41 is available. 43 1 - Introduction 45 1.1. The Domain Name System (DNS) [RFC1034, RFC1035] is a replicated 46 hierarchical distributed database system that provides information 47 fundamental to Internet operations, such as name <=> address translation 48 and mail handling information. DNS has recently been extended [RFC2065] 49 to provide for data origin authentication, and public key distribution, 50 all based on public key cryptography and public key based digital 51 signatures. To be practical, this form of security generally requires 52 extensive local caching of keys and tracing of authentication through 53 multiple keys and signatures to a pre-trusted locally configured key. 55 1.2. One difficulty with the [RFC2065] scheme is that common DNS 56 implementations include simple ``stub'' resolvers which do not have 57 caches. Such resolvers typically rely on a caching DNS server on 58 another host. It is impractical for these stub resolvers to perform 59 general [RFC2065] authentication and they would naturally depend on 60 their caching DNS server to perform such services for them. To do so 61 securely requires secure communication of queries and responses. 62 [RFC2065] provides public key transaction signatures to support this but 63 such signatures are very expensive computationally to generate. In 64 general, these require the same complex public key logic that is 65 impractical for stubs. This document specifies an efficient secret key 66 based transaction signature that avoids these difficulties. 68 1.3. A second area where use of straight [RFC2065] public key based 69 mechanisms may be impractical is authenticating dynamic update [RFC2136] 70 requests. [RFC2065] provides for request signatures but with [RFC2065] 71 they, like transaction signatures, require computationally expensive 72 public key cryptography and complex authentication logic. Secure Domain 73 Name System Dynamic Update ([RFC2137]) describes how different keys are 74 used in dynamically updated zones. This document's secret key based 75 signatures can be used to authenticate DNS update requests as well as 76 transaction responses, providing a lightweight alternative to the 77 protocol described by [RFC2137]. 79 1.4. A further use of this mechanishm is to protect zone transfers. In 80 this case the data covered would be the whole zone transfer including 81 any glue records sent. The protocol described by [RFC2065] does not 82 protect glue records and unsigned records unless SIG(0) (transaction 83 signature) is used. 85 1.5. The signature mechanism proposed in this document uses shared 86 secret keys to establish trust relationship between two entities. Such 87 keys must be protected in a fashion similar to private keys, lest a 88 third party masquerade as one of the intended parties (forge 89 signatures). There is an urgent need to provide simple and efficient 90 authentication between clients and local servers and this proposal 91 addresses that need. This proposal is unsuitable for general server to 92 server authentication for servers which speak with many other servers, 93 since key management would become unwieldy with the number of shared 94 keys going up quadratically. But it is suitable for many resolvers on 95 hosts that only talk to few recursive servers. 97 1.6. A server acting as an indirect caching resolver -- a ``forwarder'' 98 in common usage -- might use transaction signatures when communicating 99 with its small number of preconfigured ``upstream'' servers. Other uses 100 of DNS secret key signatures and possible systems for automatic secret 101 key distribution may be proposed in separate future documents. 103 1.7. New Assigned Numbers 105 RRTYPE = TSIG (250) 106 ERROR = 0..15 (a DNS RCODE) 107 ERROR = 16 (BADSIG) 108 ERROR = 17 (BADKEY) 109 ERROR = 18 (BADTIME) 111 2 - TSIG RR Format 113 2.1 TSIG RR Type 115 To provide secret key signatures, we use a new RR type whose mnemonic is 116 TSIG and whose type code is 250. TSIG is a meta-RR and can not be 117 stored. TSIG RRs can be used for authentication between DNS entities 118 that have established a shared secret key. TSIG RRs are dynamically 119 computed to cover a particular DNS transaction and are not DNS RRs in 120 the usual sense. 122 2.2 TSIG Calculation 124 As the TSIG RRs are related to one DNS request/response, there is no 125 value in storing or retransmitting them, thus the TSIG RR should be 126 discarded once it has been used to authenticate DNS message. The only 127 Message Digest algorithm specified in this document is ``HMAC-MD5'' (see 128 [RFC1321], [RFC2104]). Other algorithms can be specified at later date. 129 Names and definitions of new algorithms should be registered with IANA. 130 All multi-octet integers in TSIG Record are sent in network byte order 131 (see [RFC1035 2.3.2]). 133 2.3. Record Format 135 NAME A domain-like name of the key used. The name should reflect 136 the names of the hosts and uniquely identify the key among a 137 set of keys these two hosts may share at any given time. If 138 hosts A and B in same zone share a key then the key name could 139 be A-B-.. If two hosts in different zones share the 140 key the key name could be .A..B. It should 141 be possible for more than one key to be in simultaneous use 142 among a set of interacting hosts. The name only needs to be 143 meaningful to the communicating hosts but a meaningful 144 mnemonic name as above is strongly recommended. 146 The name may be used as a local index to the key involved and 147 it is recommended that it be globally unique. Where a key is 148 just shared between two hosts, its name actually only need 149 only be meaningful to them but it is recommended that the key 150 name be mnemonic and incorporate the resolver and server host 151 names in that order. 153 TYPE TSIG (250: Transaction SIGnature) 155 CLASS ANY 157 TTL 0 159 RdLen (variable) 160 RDATA 162 Field Name Data Type Notes 163 ------------------------------------------------------------------ 164 Algorithm Name domain-name points to an RP RR giving the 165 algorithm definer's address. 166 Time Signed u_int32_t seconds since 1-Jan-70 UTC. 167 Expire u_int32_t Time Signed + estimate of 168 RTT/2+fudge. 169 Signature Size u_int16_t number of octets in Signature. 170 Signature octet stream defined by Algorithm Name. 171 Error u_int16_t expanded RCODE covering 172 signature processing. 173 Other Len u_int16_t length, in octets, of Other Data. 174 Other Data octet stream undefined by this protocol. 176 2.4. Example 178 NAME GW-DENVAX-0042.HOME.VIX.COM. 180 TYPE TSIG 182 CLASS ANY 184 TTL 0 186 RdLen as appropriate 188 RDATA 190 Field Name Contents 191 ------------------------------------------- 192 Algorithm Name HMAC-MD5.SIG-ALG.REG.INT. 193 Time Signed 853804800 194 Expire 853805400 195 Signature Size as appropriate 196 Signature as appropriate 197 Error 0 (NOERROR) 198 Other Len 0 199 Other Data empty 201 3 - Protocol Operation 203 3.1. Effects of adding TSIG to outgoing message 205 Once the outgoing message has been constructed, the keyed message digest 206 operation can be performed. The resulting message digest will then be 207 stored in a TSIG which is appended to the additional data section. 208 Appending a transaction signature to an DNS message is not allowed to 209 result in a truncated response; a TCP connection must be used to prevent 210 the truncation. To force a TCP connection, the server is permitted to 211 return an answer with no data only TSIG attached and TC bit set and 212 RCODE 0 (NOERROR). The client should at this point retry the request 213 using TCP (per [RFC1035 4.2.2]). 215 3.2. TSIG processing on incoming messages 217 Upon receipt of a message with a TSIG RR, the TSIG RR is copied to a 218 safe location, removed from the DNS Message, and decremented out of the 219 DNS Message Headers ARCOUNT. At this point the keyed message digest 220 operation is performed. If the algorithm name or key name is unknown to 221 the recipient, or if the message digests do not match, the whole DNS 222 Message must be discarded. A response with RCODE 9 (NOTAUTH) should be 223 sent back to the originator with TSIG ERROR 17 (BADKEY). A message to 224 the system operations log should to be generated, to warn the operations 225 staff of a possible security incident in progress. Care should be taken 226 to ensure that logging of this type of event does not open the system to 227 a denial of service attack. 229 3.3. Expire value considerations 231 If the value of expire field is in the past this transaction should be 232 assumed to be an replay attack, and RCODE 9 (NOTAUTH) should returned 233 with TSIG ERROR 18 (BADTIME). For expire to work correctly it is 234 recommended that all machines using TSIG signatures use clock 235 synchronization. If clock synchronization is not used the ``Fudge'' has 236 to be larger but ``Fudge'' should always be less than or equal to the 237 smallest TTL of the RR in the message. If the smallest TTL is 0 or 238 other very small value fudge may be set to a larger value but not 239 greater than 300. In any case ``Fudge'' should always be set to a value 240 that is less than half the reuse time of request ID's. 242 3.4. Time values used in TSIG calculations 244 The data digested includes the two timer values in the TSIG header in 245 order to prevent replay attacks. If this were not done an attacker 246 could replay old messages but update the ``Time Signed'' and ``Expire'' 247 fields to make the message look new. This data is named ``TSIG 248 Timers'', and for the purpose of digest calculation they are invoked in 249 their ``on the wire'' format, in the following order: first Time Signed, 250 then Expire. For example: 252 Field Name Decimal Value Wire Format Actual Date 253 ------------------------------------------------------------------------- 254 Time Signed 853804800 32 e4 07 00 Tue Jan 21 00:00:00 1997 255 Expire 853805400 32 e4 09 58 Tue Jan 21 00:10:00 1997 257 3.5. TSIG Variables and Coverage 259 When generating or verifying a transaction signature, the following data 260 are digested, in network byte order or wire format, as appropriate: 262 DNS Message 263 A whole and complete DNS message in wire format, before the TSIG RR 264 has been added to the additional data section and before the DNS 265 Message Header's ARCOUNT field has been incremented to contain the 266 TSIG RR, but substituting 0x0000 as the request ID (due to possible 267 request forwarding). 269 TSIG Variables 271 Source Field Name Notes 272 ------------------------------------------------------------------------ 273 TSIG RR NAME Key name, in canonical wire format 274 TSIG RR CLASS (Always ANY in the current specification) 275 TSIG RR TTL (Always 0 in the current specification) 276 TSIG RDATA Algorythm Name in canonical wire format 277 TSIG RDATA Time Signed in network byte order 278 TSIG RDATA Time Expired in network byte order 279 TSIG RDATA Error in network byte order 280 TSIG RDATA Other Len in network byte order 281 TSIG RDATA Other Data exactly as transmitted 283 The RR RDLEN and RDATA Signature Length are not included in the hash 284 since they are not guaranteed to be knowable before the signature is 285 generated. 287 ``Canonical wire format'' means uncompressed labels shifted to lower 288 case. The use of label types other than 00 is not defined for this 289 specification. 291 Request Signature 292 Response signatures will include the request signature in their 293 digest. The request's signature is digested in wire format, 294 including the following fields: 296 Field Type Description 297 --------------------------------------------------------- 298 Signature Length u_int16_t in network byte order 299 Signature Data octet stream exactly as transmitted 301 Digested components are fed into the hashing function as a continuous 302 octet stream with no interfield padding. 304 4 - Protocol Details 306 4.1. TSIG generation on requests 308 Client performs the message digest operation and appends TSIG to 309 additional data section and transmits request to server. The client 310 must store the message digest from the request while awaiting an answer. 311 Digest components for requests are: 313 DNS Message (request) 314 TSIG Variables (response) 316 Note that some older name servers will not accept requests with a 317 nonempty additional data section, but clients should only attempt signed 318 transactions against servers who are known to support TSIG and share 319 some secret key with the client -- so, this is not a problem in 320 practice. 322 4.2. TSIG on Answers 324 When a server has generated a response to a signed request, it signs the 325 response using the same algorythm and key. Digest components are: 327 Request Signature 328 DNS Message (response) 329 TSIG Variables (response) 331 4.3. TSIG on TSIG Error returns 333 When a server detects an error in TSIG checks, and the server shares a 334 secret with the client, the server should send back a signed error 335 message. Digest components are: 337 DNS Message (response) 338 TSIG Variables (response) 340 The reason that the request is not included in this digest is to make it 341 possible for the client to verify the error. If the error is not a TSIG 342 error the response MUST be generated as specified in section in 4.2. If 343 the server shares multiple secrets with the client, the server should 344 use the secret the client used if the problem was not a signature error 345 in the request, or any available shared secret otherwise. 347 4.4. TSIG on TCP connection 349 A DNS TCP session can include multiple DNS headers. This is, for 350 example commonly used by AXFR. TSIG on such a connection can be used to 351 protect the connection from hijacking and provide data integrity. The 352 TSIG MUST be included on the first and last DNS header. It can be 353 optionally placed on any intermediary header. It is expensive to 354 include it on every header, but it SHOULD be placed on at least every 355 100'th header. The first envelope is processed as a standard answer, 356 and subject messages have the following digests components: 358 Prior Digest (running) 359 DNS Message (current message) 360 TSIG Timers (current message) 362 This allows client to rapidly detect when a transfer has been altered 363 and it can close the connection at that point and retry. Once client 364 TSIG check fails, the client MUST close the connection. If the client 365 does not get TSIG frequently enough it SHOULD assume the connection has 366 been hijacked and it SHOULD close the connection. Client should treat 367 this the same way as any other interrupted transfer. 369 4.5. Server TSIG checks 371 Upon receipt of a message, server will check if there is a TSIG RR. If 372 one exists, the server is required to return a TSIG RR in the response. 373 The server MUST perform the following checks in the following order, 374 check KEY, check TIME values, check Signature. 376 4.5.1. KEY check and error handling 378 If a non-forwarding server does not recognize the key used by the client 379 the server MUST generate an error response with RCODE 9 (NOTAUTH) and 380 TSIG ERROR 17 (BADKEY). If the server and client share another key the 381 server should use the one of the other keys to sign the error message as 382 specified in section 4.3. If server does not share any secret with 383 client the server should log the error. 385 4.5.2. TIME check and Error handling 387 If the server time is outside the time interval in the request, the 388 server MUST generate an error response with RCODE 9 (NOTAUTH) and TSIG 389 ERROR 18 (BADTIME). This response MUST be signed by the same key and 390 MUST include the servers current time in the time signed field. The 391 data signed is specified in section 4.3. 393 4.5.3. Signature check and error handling 395 If TSIG fails to verify, the server MUST generate an error response as 396 specified in section 4.3 with RCODE of 9 (NOTAUTH) and TSIG ERROR 16 397 (BADSIG). The server MUST sign this error response with the same key 398 the client used. 400 4.6. Client processing of answer 402 When a client receives a response from a server it expects a TSIG from, 403 it first checks if the TSIG RR is present in the response. Otherwise 404 the response is treated as having a format error and discarded. The 405 client then extracts the TSIG, adjusts the ARCOUNT, and calculates the 406 keyed digest in the same way as the server. If the TSIG does not 407 validate, that response must be discarded, unless the RCODE is 9 408 (NOTAUTH), in which case the client should attempt to verify the 409 response as it was TSIG error as specified in section 4.3. 411 4.6.1. Key error handling 413 If an RCODE on a response is 9 (NOTAUTH), and the response TSIG 414 validates, and the TSIG key is different from the key used on the 415 request, then this is a key error. Client should retry the request 416 using the key specified by server. 418 4.6.2. Time error handling 420 If the response RCODE is 9 (NOTAUTH), and TSIG ERROR is 18 (BADTIME) or 421 the TSIG times in request and answer do not overlap, then this is a TIME 422 error. This is an indication that client and server are not clock 423 synchronized. In this case the client should log the event. DNS 424 resolvers MUST not adjust any clocks in the client based on BADTIME 425 errors. 427 4.6.3. Signature error handling 429 If the response RCODE is 9 (NOTAUTH) and TSIG ERROR is 16 (BADSIG), this 430 is a signature error, and client MAY retry the request with a new 431 request ID but it would be better to try a different shared key if one 432 is available. Client SHOULD keep track of how many times each key has 433 Signature errors. Clients should log this event. 435 4.7. Special considerations for forwarding servers 437 A server acting as a Forwarding Server of a DNS message, should check 438 for the existence of the TSIG record. If the name on the TSIG is not of 439 a secret that the server shares with the originator the server will 440 forward the message unchanged including the TSIG. If the name of the 441 TSIG is of a key this server shares with the originator it processes the 442 TSIG. If the TSIG passes all checks, the forwarding server has the 443 obligation of including a TSIG of his own, to the destination or the 444 next forwarder. If no transaction security is available to the 445 destination and response has the AD flag (see [RFC2065]), the forwarder 446 MUST unset the AD flag before adding the TSIG to the answer. 448 5 - Shared Secrets 450 5.1. Secret keys are very sensitive information and all available steps 451 should be taken to protect them on every host on which they are stored. 452 Generally such hosts need to be physically protected. If they are 453 multi-user machines, great care should be taken that unprivileged users 454 have no access to keying material. Resolvers usually run unprivileged, 455 which means all users of a host will usually be able to see whatever 456 configuration data is used by the resolver. 458 5.2. A name server usually runs privileged, which means its 459 configuration data need not be visible to all users of the host. For 460 this reason, a host that implements transaction signatures should 461 probably be configured with a ``stub resolver'' and a local caching and 462 forwarding name server. This presents a special problem for [RFC2136] 463 which otherwise depends on clients to communicate only with a zone's 464 authoritative name servers. 466 5.3. Use of strong random shared secrets is essential to the security of 467 TSIG. See [RFC1750] for a discussion of this issue. The secret should 468 be at least as long as the keyed message digest digest, i.e., 16 bytes 469 for HMAC-MD5 or 20 bytes for HMAC-SHA1. 471 6 - Security Considerations 473 6.1. The approach specified here is computationally much less expensive 474 than the signatures specified in [RFC2065]. As long as the shared 475 secret key is not compromised, strong authentication is provided for the 476 last hop from a local name server to the user resolver. 478 6.2. Secret keys should be changed periodically. If the client host has 479 been compromised, the server should suspend the use of all secrets known 480 to that client. If possible, secrets should be stored in encrypted 481 form. Secrets should never be transmitted in the clear over any 482 network. This document does not address the issue on how to distribute 483 secrets. 485 6.3. This mechanism does not authenticate source data, only its 486 transmission between two parties who share some secret. The original 487 source data can come from a compromised zone master or can be corrupted 488 during transit from an authentic zone master to some ``caching 489 forwarder.'' However, if the server is faithfully performing the full 490 [RFC2065] security checks, then only security checked data will be 491 available to the client. 493 7 - References 495 [RFC1034] P. Mockapetris, ``Domain Names - Concepts and Facilities,'' 496 RFC 1034, ISI, November 1987. 498 [RFC1035] P. Mockapetris, ``Domain Names - Implementation and 499 Specification,'' RFC 1034, ISI, November 1987. 501 [RFC1321] R. Rivest, ``The MD5 Message-Digest Algorithm,'' RFC 1321, 502 MIT LCS & RSA Data Security, Inc., April 1992. 504 [RFC1750] D. Eastlake, S. Crocker, J. Schiller, ``Randomness 505 Recommendations for Security,'' RFC 1750, DEC, CyberCash & 506 MIT, December 1995. 508 [RFC2065] D. Eastlake , C Kaufman, ``Domain Name System Security 509 Extensions,'' RFC 2065, CyberCash & Iris, January 1997. 511 [RFC2104] H. Krawczyk, M. Bellare, R. Canetti, ``HMAC-MD5: Keyed-MD5 512 for Message Authentication,'' RFC 2104 , IBM, UCSD & IBM, 513 February 1997. 515 [RFC2136] P. Vixie (Ed.), S. Thomson, Y. Rekhter, J. Bound ``Dynamic 516 Updates in the Domain Name System,'' RFC 2136, ISC & Bellcore 517 & Cisco & DEC, April 1997. 519 [RFC2137] D. Eastlake 3rd ``Secure Domain Name System Dynamic Update,'' 520 CyberCash, April 1997. 522 9 - Author's Addresses 524 Paul Vixie Olafur Gudmundsson 525 Internet Software Consortium Trusted Information Systems 526 950 Charter Street 3060 Washington Road, Route 97 527 Redwood City, CA 94063 Glenwood, MD 21738 528 +1 650 779 7001 +1 301 854 6889 529 531 Donald E. Eastlake 3rd. 532 CyberCash, Inc. 533 318 Acton Street 534 Carlisle, MA 01741 535 +1 978 287 4877 536