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(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 122 instances of too long lines in the document, the longest one being 19 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 292: '...error the answer MUST be signed as spe...' RFC 2119 keyword, line 302: '... TSIG MUST be included on the first ...' RFC 2119 keyword, line 304: '...y header, but it SHOULD be placed on a...' RFC 2119 keyword, line 312: '...ails, the client MUST close the connec...' RFC 2119 keyword, line 313: '...uently enough it SHOULD assume the con...' (12 more instances...) Miscellaneous warnings: ---------------------------------------------------------------------------- == Line 156 has weird spacing: '...hm Name doma...' == Line 161 has weird spacing: '...re Size u_in...' == Line 162 has weird spacing: '... stream defi...' == Line 165 has weird spacing: '... stream unde...' == Line 177 has weird spacing: '... RdLen as ap...' == (1 more instance...) == 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 (May 1998) is 9478 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 443 looks like a reference -- Missing reference section? 'RFC1035' on line 446 looks like a reference -- Missing reference section? 'RFC2065' on line 456 looks like a reference -- Missing reference section? 'RFC2136' on line 463 looks like a reference -- Missing reference section? 'RFC2137' on line 467 looks like a reference -- Missing reference section? 'RFC1321' on line 449 looks like a reference -- Missing reference section? 'RFC2104' on line 459 looks like a reference -- Missing reference section? 'RFC1750' on line 452 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 May 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 learn the current status of any Internet-Draft, please check the 24 ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow 25 Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), 26 munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or 27 ftp.isi.edu (US West Coast). 29 Abstract 31 This protocol allows for transaction level authentication using 32 shared secrets and one way hashing. It can be used to authenticate 33 dynamic updates as coming from an approved client, or to authenticate 34 responses as coming from an approved recursive name server. 36 No provision has been made here for distributing the shared secrets; 37 it is expected that a network administrator will statically configure 38 name servers and clients using some out of band mechanism such as 39 sneaker-net until a secure automated mechanism for key distribution 40 is available. 42 1 - Introduction 44 1.1. The Domain Name System (DNS) [RFC1034, RFC1035] is a replicated 45 hierarchical distributed database system that provides information 46 fundamental to Internet operations, such as name <=> address translation 47 and mail handling information. DNS has recently been extended [RFC2065] 48 to provide for data origin authentication, and public key distribution, 49 all based on public key cryptography and public key based digital 50 signatures. To be practical, this form of security generally requires 51 extensive local caching of keys and tracing of authentication through 52 multiple keys and signatures to a pre-trusted locally configured key. 54 1.2. One difficulty with the [RFC2065] scheme is that common DNS 55 implementations include simple ``stub'' resolvers which do not have 56 caches. Such resolvers typically rely on a caching DNS server on 57 another host. It is impractical for these stub resolvers to perform 58 general [RFC2065] authentication and they would naturally depend on 59 their caching DNS server to perform such services for them. To do so 60 securely requires secure communication of queries and responses. 61 [RFC2065] provides public key transaction signatures to support this but 62 such signatures are very expensive computationally to generate. In 63 general, these require the same complex public key logic that is 64 impractical for stubs. This document specifies an efficient secret key 65 based transaction signature that avoids these difficulties. 67 1.3. A second area where use of straight [RFC2065] public key based 68 mechanisms may be impractical is authenticating dynamic update [RFC2136] 69 requests. [RFC2065] provides for request signatures but with [RFC2065] 70 they, like transaction signatures, require computationally expensive 71 public key cryptography and complex authentication logic. Secure Domain 72 Name System Dynamic Update ([RFC2137]) describes how different keys are 73 used in dynamically updated zones. This document's secret key based 74 signatures can be used to authenticate DNS update requests as well as 75 transaction responses, providing a lightweight alternative to the 76 protocol described by [RFC2137]. 78 1.4. A further use of this mechanishm is to protect zone transfers. In 79 this case the data covered would be the whole zone transfer including 80 any glue records sent. The protocol described by [RFC2065] does not 81 protect glue records and unsigned records unless SIG(0) (transaction 82 signature) is used. 84 1.5. The signature mechanism proposed in this document uses shared 85 secret keys to establish trust relationship between two entities. Such 86 keys must be protected in a fashion similar to private keys, lest a 87 third party masquerade as one of the intended parties (forge 88 signatures). There is an urgent need to provide simple and efficient 89 authentication between clients and local servers and this proposal 90 addresses that need. This proposal is unsuitable for general server to 91 server authentication for servers which speak with many other servers, 92 since key management would become unwieldy with the number of shared 93 keys going up quadratically. But it is suitable for many resolvers on 94 hosts that only talk to few recursive servers. 96 1.6. A server acting as an indirect caching resolver -- a ``forwarder'' 97 in common usage -- might use transaction signatures when communicating 98 with its small number of preconfigured ``upstream'' servers. Other uses 99 of DNS secret key signatures and possible systems for automatic secret 100 key distribution may be proposed in separate future documents. 102 1.7. New Assigned Numbers 104 RRTYPE = TSIG (250) 105 ERROR = 0..15 (a DNS RCODE) 106 ERROR = 16 (BADSIG) 107 ERROR = 17 (BADKEY) 108 ERROR = 18 (BADTIME) 110 2 - TSIG RR Format 112 2.1 TSIG RR Type 114 To provide secret key signatures, we use a new RR type whose mnemonic is 115 TSIG and whose type code is 250. TSIG is a meta-RR and can not be 116 stored. TSIG RRs can be used for authentication between DNS entities 117 that have established a shared secret key. TSIG RRs are dynamically 118 computed to cover a particular DNS transaction and are not DNS RRs in 119 the usual sense. 121 2.2 TSIG Calculation 123 As the TSIG RRs are related to one DNS request/response, there is no 124 value in storing or retransmitting them, thus the TSIG RR should be 125 discarded once it has been used to authenticate DNS message. The only 126 Message Digest algorithm specified in this document is ``HMAC-MD5'' (see 127 [RFC1321], [RFC2104]). Other algorithms can be specified at later date. 128 Names and definitions of new algorithms should be registered with IANA. 129 All multi-octet integers in TSIG Record are sent in network byte order 130 (see [RFC1035 2.3.2]). 132 2.3. Record Format 134 NAME A domain-like name of the key used. The name should reflect 135 the names of the hosts and uniquely identify the key among a 136 set of keys these two hosts may share at any given time. If 137 hosts A and B in same zone share a key then the key name could 138 be A-B-.. If two host in different zone share the 139 key the key name could be .A..B. It should 140 be possible for more than one key to be in simultaneous use 141 among a set of interacting hosts. The name only needs to be 142 meaningful to the communicating hosts but a meaningful 143 mnemonic name as above is strongly recommended. 145 TYPE TSIG (250: Transaction SIGnature) 147 CLASS ANY 149 TTL 0 151 RdLen (variable) 152 RDATA 154 Field Name Data Type Notes 155 ------------------------------------------------------------------------------ 156 Algorithm Name domain-name points to an RP RR giving the 157 algorithm definer's address. 158 Time Signed u_int32_t seconds since 1-Jan-70 UTC. 159 Expire u_int32_t Time Signed + estimate of 160 RTT/2+fudge. 161 Signature Size u_int16_t number of octets in Signature. 162 Signature octet stream defined by Algorithm Name. 163 Error u_int16_t expanded RCODE covering signature processing. 164 Other Len u_int16_t length, in octets, of Other Data. 165 Other Data octet stream undefined by this protocol. 167 2.4. Example 169 NAME GW-DENVAX-0042.HOME.VIX.COM. 171 TYPE TSIG 173 CLASS ANY 175 TTL 0 177 RdLen as appropriate 179 RDATA 181 Field Name Contents 182 ------------------------------------ 183 Algorithm Name HMAC-MD5.IANA.ORG. 184 Time Signed 853804800 185 Expire 853805400 186 Signature Size as appropriate 187 Signature as appropriate 188 Error 0 (NOERROR) 189 Other Len 0 190 Other Data empty 192 3 - Protocol Operation 194 3.1. Effects of adding TSIG to outgoing message 196 Once the outgoing message has been constructed, the keyed message digest 197 operation can be performed. The resulting message digest will then be 198 stored in a TSIG which is appended to the additional data section. 199 Appending a transaction signature to an DNS message is not allowed to 200 result in a truncated response; a TCP connection must be used to prevent 201 the truncation. To force a TCP connection, the server is permitted to 202 return an answer with no data only TSIG attached and TC bit set and 203 RCODE 0 (NOERROR). The client should at this point retry the request 204 using TCP (per [RFC1035 4.2.2]). 206 3.2. TSIG processing on incoming messages 208 Upon receipt of a message with a TSIG RR, the TSIG RR is copied to a 209 safe location, removed from the DNS Message, and decremented out of the 210 DNS Message Headers ARCOUNT. At this point the keyed message digest 211 operation is performed. If the algorithm name or key name is unknown to 212 the recipient, or if the message digests do not match, the whole DNS 213 Message must be discarded. A response with RCODE 9 (NOTAUTH) should be 214 sent back to the originator with TSIG ERROR 17 (BADKEY). A message to 215 the system operations log should to be generated, to warn the operations 216 staff of a possible security incident in progress. Care should be taken 217 to ensure that logging of this type of event does not open the system to 218 a denial of service attack. 220 3.3. Expire value considerations 222 If the value of expire field is in the past this transaction should be 223 assumed to be an replay attack, and RCODE 9 (NOTAUTH) should returned 224 with TSIG ERROR 18 (BADTIME). For expire to work correctly it is 225 recommended that all machines using TSIG signatures use clock 226 synchronization. If clock synchronization is not used the ``Fudge'' has 227 to be larger but ``Fudge'' should always be less than or equal to the 228 smallest TTL of the RR in the message. If the smallest TTL is 0 or 229 other very small value fudge may be set to a larger value but not 230 greater than 300. In any case ``Fudge'' should always be set to a value 231 that is less than half the reuse time of request ID's. 233 3.4. Time values used in TSIG calculations 235 The data digested includes the two timer values in the TSIG header in 236 order to prevent replay attacks. If this were not done an attacker 237 could replay old messages but update the ``Time Signed'' and ``Expire'' 238 fields to make the message look new. This data is named ``TSIG 239 Timers'', and for the purpose of digest calculation they are invoked in 240 their ``on the wire'' format, in the following order: first Time Signed, 241 then Expire. For example: 243 Field Name Decimal Value Wire Format Actual Date 244 ------------------------------------------------------------------------- 245 Time Signed 853804800 32 e4 07 00 Tue Jan 21 00:00:00 1997 246 Expire 853805400 32 e4 09 58 Tue Jan 21 00:10:00 1997 248 4 - Protocol Details 250 4.1. TSIG generation on requests 252 Client performs the message digest operation and appends TSIG to 253 additional data section and transmits request to server. The data 254 digested is the whole outgoing DNS message in wire format, before the 255 TSIG RR has been added to the additional data section and before the DNS 256 Message Headers ARCOUNT field has been incremented to contain the TSIG 257 RR. The data digested is: 259 DNSmessage | TSIG Timers 261 The client must store the message digest from the request while waiting 262 for an answer. Note that some older name servers will not accept 263 requests with a nonempty additional data section, but clients should 264 only attempt signed transactions against servers who are known to 265 support TSIG and share some secret key with the client -- so, this is 266 not a problem in practice. 268 4.2. TSIG on Answers 270 When a server has generated a response to a signed request, it 271 calculates the keyed digest over the concatenation of the Signature 272 field of the request's TSIG and the whole outgoing DNS answer message in 273 wire format before the answer TSIG RR has been added and before the 274 ARCOUNT field has been incremented for it. That is, the data to be 275 digested is: 277 Signature field from the TSIG on the request | dnsANSWER | TSIG Timers 279 TSIG is appended and the response is sent. The inclusion of the message 280 digest from the request binds the response to the request. 282 4.3. TSIG on TSIG Error returns 284 When a server detects an error in TSIG checks, and the server shares a 285 secret with the client, the server should send back a signed error 286 message. This message should be digested over the following: 288 dnsANSWER | TSIG Timers 290 The reason that the request is not included in this digest is to make it 291 possible for the client to verify the error. If the error is not a TSIG 292 error the answer MUST be signed as specified in section in 4.2. If the 293 server has multiple secrets with that host, the server should use the 294 secret the client used if the problem was not a signature error in the 295 request. 297 4.4. TSIG on TCP connection 299 A DNS TCP transfer can include multiple DNS headers. This is, for 300 example commonly used by AXFR. TSIG on such a connection can be used to 301 protect the connection from hijacking and provide data integrity. The 302 TSIG MUST be included on the first and last DNS header. It can be 303 optionally placed on any intermediary header. It is expensive to 304 include it on every header, but it SHOULD be placed on at least every 305 100'th header. The first envelope is processed as a standard answer, 306 subsequent envelopes will be covering: 308 Previous TSIG digest | DNS answers | TSIG timers 310 This allows client to rapidly detect when a transfer has been altered 311 and it can close the connection at that point and retry. Once client 312 TSIG check fails, the client MUST close the connection. If the client 313 does not get TSIG frequently enough it SHOULD assume the connection has 314 been hijacked and it SHOULD close the connection. Client should treat 315 this the same way as any other interrupted transfer. 317 4.5. Server TSIG checks 319 Upon receipt of a message, server will check if there is a TSIG RR. If 320 one exists, the server is required to return a TSIG RR in the response. 321 The server MUST perform the following checks in the following order, 322 check KEY, check TIME values, check Signature. 324 4.5.1. KEY check and error handling 326 If a non-forwarding server does not recognize the key used by the client 327 the server MUST generate an error response with RCODE 9 (NOTAUTH) and 328 TSIG ERROR 17 (BADKEY). If the server and client share another key the 329 server should use the one of the other keys to sign the error message as 330 specified in section 4.3. If server does not share any secret with 331 client the server should log the error. 333 4.5.2. TIME check and Error handling 335 If the server time is outside the time interval in the request, the 336 server MUST generate an error response with RCODE 9 (NOTAUTH) and TSIG 337 ERROR 18 (BADTIME). This response MUST be signed by the same key and 338 MUST include the servers current time in the time signed field. The 339 data signed is specified in section 4.3. 341 4.5.3. Signature check and error handling 343 If TSIG fails to verify, the server MUST generate an error response as 344 specified in section 4.3 with RCODE of 9 (NOTAUTH) and TSIG ERROR 16 345 (BADSIG). The server MUST sign this error response with the same key 346 the client used. 348 4.6. Client processing of answer 350 When a client receives a response from a server it expects a TSIG from, 351 it first checks if the TSIG RR is present in the response. Otherwise 352 the response is treated as having a format error and discarded. The 353 client then extracts the TSIG, adjusts the ARCOUNT, and calculates the 354 keyed digest in the same way as the server. If the TSIG does not 355 validate, that response must be discarded, unless the RCODE is 9 356 (NOTAUTH), in which case the client should attempt to verify the 357 response as it was TSIG error as specified in section 4.3. 359 4.6.1. Key error handling 361 If an RCODE on a response is 9 (NOTAUTH), and the response TSIG 362 validates, and the TSIG key is different from the key used on the 363 request, then this is a key error. Client should retry the request 364 using the key specified by server. 366 4.6.2. Time error handling 368 If the response RCODE is 9 (NOTAUTH), and TSIG ERROR is 18 (BADTIME) or 369 the TSIG times in request and answer do not overlap, then this is a TIME 370 error. This is an indication that client and server are not clock 371 synchronized. In this case the client should log the event. DNS 372 resolvers MUST not adjust any clocks in the client based on BADTIME 373 errors. 375 4.6.3. Signature error handling 377 If the response RCODE is 9 (NOTAUTH) and TSIG ERROR is 16 (BADSIG), this 378 is a signature error, and client MAY retry the request with a new 379 request ID but it would be better to try a different shared key if one 380 is available. Client SHOULD keep track of how many times each key has 381 Signature errors. Clients should log this event. 383 4.7. Special considerations for Forwarding Server 385 A server acting as a Forwarding Server of a DNS message, should check 386 for the existence of the TSIG record. If the name on the TSIG is not of 387 a secret that the server shares with the originator the server will 388 forward the message unchanged including the TSIG. If the name of the 389 TSIG is of a key this server shares with the originator it processes the 390 TSIG. If the TSIG passes all checks, the forwarding server has the 391 obligation of including a TSIG of his own, to the destination or the 392 next forwarder. If no transaction security is available to the 393 destination and response has the AD flag (see [RFC2065]), the forwarder 394 MUST unset the AD flag before adding the TSIG to the answer. 396 5 - Shared Secrets 398 5.1. Secret keys are very sensitive information and all available steps 399 should be taken to protect them on every host on which they are stored. 400 Generally such hosts need to be physically protected. If they are 401 multi-user machines, great care should be taken that unprivileged users 402 have no access to keying material. Resolvers usually run unprivileged, 403 which means all users of a host will usually be able to see whatever 404 configuration data is used by the resolver. 406 5.2. A name server usually runs privileged, which means its 407 configuration data need not be visible to all users of the host. For 408 this reason, a host that implements transaction signatures should 409 probably be configured with a ``stub resolver'' and a local caching and 410 forwarding name server. This presents a special problem for [RFC2136] 411 which otherwise depends on clients to communicate only with a zone's 412 authoritative name servers. 414 5.3. Use of strong random shared secrets is essential to the security of 415 TSIG. See [RFC1750] for a discussion of this issue. The secret should 416 be at least as long as the keyed message digest digest, i.e., 16 bytes 417 for HMAC-MD5 or 20 bytes for HMAC-SHA1. 419 6 - Security Considerations 421 6.1. The approach specified here is computationally much less expensive 422 than the signatures specified in [RFC2065]. As long as the shared 423 secret key is not compromised, strong authentication is provided for the 424 last hop from a local name server to the user resolver. 426 6.2. Secret keys should be changed periodically. If the client host has 427 been compromised, the server should suspend the use of all secrets known 428 to that client. If possible, secrets should be stored in encrypted 429 form. Secrets should never be transmitted in the clear over any 430 network. This document does not address the issue on how to distribute 431 secrets. 433 6.3. This mechanism does not authenticate source data, only its 434 transmission between two parties who share some secret. The original 435 source data can come from a compromised zone master or can be corrupted 436 during transit from an authentic zone master to some ``caching 437 forwarder.'' However, if the server is faithfully performing the full 438 [RFC2065] security checks, then only security checked data will be 439 available to the client. 441 7 - References 443 [RFC1034] P. Mockapetris, ``Domain Names - Concepts and Facilities,'' 444 RFC 1034, ISI, November 1987. 446 [RFC1035] P. Mockapetris, ``Domain Names - Implementation and 447 Specification,'' RFC 1034, ISI, November 1987. 449 [RFC1321] R. Rivest, ``The MD5 Message-Digest Algorithm,'' RFC 1321, 450 MIT LCS & RSA Data Security, Inc., April 1992. 452 [RFC1750] D. Eastlake, S. Crocker, J. Schiller, ``Randomness 453 Recommendations for Security,'' RFC 1750, DEC, CyberCash & 454 MIT, December 1995. 456 [RFC2065] D. Eastlake , C Kaufman, ``Domain Name System Security 457 Extensions,'' RFC 2065, CyberCash & Iris, January 1997. 459 [RFC2104] H. Krawczyk, M. Bellare, R. Canetti, ``HMAC-MD5: Keyed-MD5 460 for Message Authentication,'' RFC 2104 , IBM, UCSD & IBM, 461 February 1997. 463 [RFC2136] P. Vixie (Ed.), S. Thomson, Y. Rekhter, J. Bound ``Dynamic 464 Updates in the Domain Name System,'' RFC 2136, ISC & Bellcore 465 & Cisco & DEC, April 1997. 467 [RFC2137] D. Eastlake 3rd ``Secure Domain Name System Dynamic Update,'' 468 CyberCash, April 1997. 470 9 - Author's Addresses 471 Paul Vixie Olafur Gudmundsson 472 Internet Software Consortium Trusted Information Systems 473 950 Charter Street 3060 Washington Road, Route 97 474 Redwood City, CA 94063 Glenwood, MD 21738 475 +1 650 779 7001 +1 301 854 6889 476 478 Donald E. Eastlake 3rd. 479 CyberCash, Inc. 480 318 Acton Street 481 Carlisle, MA 01741 482 +1 978 287 4877 483