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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Kause 3 Internet-Draft Tectia 4 Updates: 4210 (if approved) M. Peylo 5 Intended status: Standards Track NSN 6 Expires: November 8, 2012 May 07, 2012 8 Internet X.509 Public Key Infrastructure -- HTTP Transport for CMP 9 draft-ietf-pkix-cmp-transport-protocols-17.txt 11 Abstract 13 This document describes how to layer the Certificate Management 14 Protocol over HTTP. It is the "CMPtrans" document referenced in RFC 15 4210 and therefore updates the reference given therein. 17 Status of this Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on November 8, 2012. 34 Copyright Notice 36 Copyright (c) 2012 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 This document may contain material from IETF Documents or IETF 50 Contributions published or made publicly available before November 51 10, 2008. The person(s) controlling the copyright in some of this 52 material may not have granted the IETF Trust the right to allow 53 modifications of such material outside the IETF Standards Process. 54 Without obtaining an adequate license from the person(s) controlling 55 the copyright in such materials, this document may not be modified 56 outside the IETF Standards Process, and derivative works of it may 57 not be created outside the IETF Standards Process, except to format 58 it for publication as an RFC or to translate it into languages other 59 than English. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 3. HTTP-Based Protocol . . . . . . . . . . . . . . . . . . . . . 6 66 3.1. HTTP Versions . . . . . . . . . . . . . . . . . . . . . . 6 67 3.2. Persistent Connections . . . . . . . . . . . . . . . . . . 6 68 3.3. General Form . . . . . . . . . . . . . . . . . . . . . . . 6 69 3.4. Media Type . . . . . . . . . . . . . . . . . . . . . . . . 6 70 3.5. Communication Workflow . . . . . . . . . . . . . . . . . . 6 71 3.6. HTTP Request-URI . . . . . . . . . . . . . . . . . . . . . 7 72 3.7. Pushing of Announcements . . . . . . . . . . . . . . . . . 7 73 3.8. HTTP Considerations . . . . . . . . . . . . . . . . . . . 8 74 4. Compatibility Issues with Legacy Implementations . . . . . . . 9 75 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 76 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 77 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 78 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 79 8.1. Normative References . . . . . . . . . . . . . . . . . . . 13 80 8.2. Informative References . . . . . . . . . . . . . . . . . . 13 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 83 1. Introduction 85 The Certificate Management Protocol (CMP) [RFC4210] requires a well 86 defined transport mechanism to enable End Entities (EEs), 87 Registration Authorities (RAs) and Certification Authorities (CAs) to 88 pass PKIMessage sequences between them. This document defines the 89 transport mechanism which was removed from the main CMP specification 90 with the second release and referred to be in a separate document. 92 The first version of the CMP specification [RFC2510] included a brief 93 description of a simple transport protocol layer on top of TCP. Its 94 features was simple transport level error-handling and a mechanism to 95 poll for outstanding PKI messages. Additionally it was mentioned 96 that PKI messages could also be conveyed using file-, E-mail- and 97 HTTP-based transport, but those were not specified in detail. 99 The current version of the CMP specification [RFC4210] incorporated 100 its own polling mechanism and thus the need for a transport protocol 101 providing this functionality vanished. The remaining features CMP 102 requires from its transport protocols are connection and error 103 handling. 105 During the long time it existed as draft, this RFC was undergoing 106 drastic changes. The "TCP-Based Management Protocol" was enhanced 107 and a TCP-Messages-over-HTTP transport specification appeared. As 108 both proved to be needless and cumbersome, implementers preferred to 109 use plain HTTP transport. This document now reflects that by 110 exclusively describing HTTP as transport protocol for CMP. 112 The usage of HTTP for transporting CMP messages exclusively uses POST 113 method for requests, effectively tunneling CMP over HTTP. While this 114 is generally considered as bad practice and should not be emulated, 115 there are good reasons to do so for transporting CMP. HTTP is used 116 as it is generally easy to implement and able to traverse network 117 borders utilizing ubiquitous proxies. Most importantly, HTTP is 118 already commonly used in existing CMP implementations. Other HTTP 119 request methods such as GET are not used as PKI management operations 120 can only be triggered using CMP's PKI messages which need to be 121 transported within a POST request. 123 With its status codes HTTP provides needed error reporting 124 capabilities. General problems on the server side as well as those 125 directly caused by the respective request can be reported to the 126 client. 128 As CMP implements a transaction ID, identifying transactions spanning 129 over more than just a single request/response pair, the statelessness 130 of HTTP is not blocking its usage as transport protocol for CMP 131 messages. 133 2. Requirements 135 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 136 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 137 document are to be interpreted as described in [RFC2119]. 139 3. HTTP-Based Protocol 141 For direct interaction between two entities, where a reliable 142 transport protocol like TCP is available, HTTP SHOULD be utilized for 143 conveying CMP messages. 145 3.1. HTTP Versions 147 Implementations MUST support HTTP/1.0 [RFC1945], and SHOULD support 148 HTTP/1.1 [RFC2616]. 150 3.2. Persistent Connections 152 HTTP permits to reuse a connection for subsequent requests. 153 Implementations may use this functionality but MUST NOT rely on this 154 for messages within the same CMP transaction as e.g. intermediate 155 HTTP proxies might terminate the connection after each request/ 156 response pair. 158 3.3. General Form 160 A DER-encoded PKIMessage is sent as the entity-body of an HTTP POST 161 request. If this HTTP request is successful, the server returns the 162 CMP response in the body of the HTTP response. The HTTP response 163 status code in this case MUST be 200; other "Successful 2xx" codes 164 MUST NOT be used for this purpose. HTTP responses to pushed CMP 165 Announcement messages (i.e., CA Certificate Announcement, Certificate 166 Announcement, Revocation Announcement, and CRL Announcement) utilize 167 the status codes 201 and 202 to identify whether the received 168 information was processed. 170 While "Redirection 3xx" status codes MAY be supported by 171 implementations, clients should only be enabled to automatically 172 follow them after careful consideration of possible security 173 implications. 175 All applicable "Client Error 4xx" or "Server Error 5xx" status codes 176 may be used to inform the client about errors. 178 3.4. Media Type 180 The Internet Media Type "application/pkixcmp" MUST be set in the HTTP 181 header when conveying a PKIMessage. 183 3.5. Communication Workflow 185 In CMP most communication is initiated by the end entities where 186 every CMP request triggers a CMP response message from the CA or RA. 188 The CMP Announcement messages described in Section 3.7 are an 189 exception. Their creation may be triggered by certain events or done 190 on a regular basis by a CA. The recipient of the Announcement only 191 replies with an HTTP status code acknowledging the receipt or 192 indicating an error but not with a CMP response. 194 If the receipt of an HTTP request is not confirmed by receiving an 195 HTTP response, it MUST be assumed that the transported CMP message 196 was not successfully delivered to its destination. 198 3.6. HTTP Request-URI 200 The Request-URI is formed as specified in [RFC3986]. 202 A server implementation MUST handle Request-URI paths with or without 203 a trailing slash as identical. 205 An example of a Request-Line and a Host header field in an HTTP/1.1 206 header, sending a CMP request to a server, located in the "/cmp" path 207 of the host "example.com", would be 209 POST /cmp HTTP/1.1 210 Host: example.com 212 or in the absoluteURI form 214 POST http://example.com/cmp/ HTTP/1.1 215 Host: example.com 217 3.7. Pushing of Announcements 219 A CMP server may create event-triggered announcements or generate 220 them on a regular basis. It MAY utilize HTTP transport to convey 221 them to a suitable recipient. As no request messages are specified 222 for those announcements they can only be pushed to the recipient. 224 If an EE wants to poll for a potential CA Key Update Announcement or 225 the current CRL, a PKI Information Request using a General Message as 226 described in E.5 of [RFC4210] can be used. 228 When pushing Announcement messages, PKIMessage structures are sent as 229 the entity-body of an HTTP POST request. 231 Suitable recipients for CMP announcements might e.g. be repositories 232 storing the announced information such as directory services. Those 233 listen for incoming messages, utilizing the same HTTP Request-URI 234 scheme as defined in Section 3.6. 236 The following PKIMessages are announcements that may be pushed by a 237 CA. The prefixed numbers reflect ASN.1 numbering of the respective 238 element. 240 [15] CA Key Update Announcement 241 [16] Certificate Announcement 242 [17] Revocation Announcement 243 [18] CRL Announcement 245 CMP Announcement messages do not require any CMP response. However, 246 the recipient MUST acknowledge receipt with a HTTP response having an 247 appropriate status code and an empty body. When not receiving such 248 response it MUST be assumed that the delivery was not successful and 249 if applicable the sending side may retry sending the Announcement 250 after waiting for an appropriate time span. 252 If the announced issue was successfully stored in a database or was 253 already present, the answer MUST be an HTTP response with a "201 254 Created" status code and empty message body. 256 In case the announced information was only accepted for further 257 processing, the status code of the returned HTTP response MAY also be 258 "202 Accepted". After an appropriate delay, the sender may then try 259 to send the Announcement again and may repeat this until it receives 260 a confirmation that it had been successfully processed. The 261 appropriate duration of the delay and the option to increase it 262 between consecutive attempts should be carefully considered. 264 A receiver MUST answer with a suitable 4xx or 5xx HTTP error code 265 when a problem occurs. 267 3.8. HTTP Considerations 269 While implementations MAY make use of all defined features of the 270 HTTP protocol, they SHOULD keep the protocol utilization as simple as 271 possible. E.g. there is no benefit in using chunked Transfer- 272 Encoding as the length of an ASN.1 sequence is know when starting to 273 send it. 275 There is no need for the clients to send an "Expect" request-header 276 field with the "100-continue" expectation and wait for a "100 277 Continue" status as described in chapter 8.2.3 of [RFC2616]. The CMP 278 payload sent by a client is relatively small, so having extra 279 messages exchanged is more inefficient as the server will anyway only 280 seldom reject a message without evaluating the body. 282 4. Compatibility Issues with Legacy Implementations 284 As this document was subject of multiple changes during the long 285 period of time it was created in, implementations using a different 286 approach for HTTP transport may exist. While only those 287 implementations according to this specification are compliant, 288 implementers should to be aware that there might be existing ones 289 which behave differently. 291 Legacy implementations might also use an unregistered "application/ 292 pkixcmp-poll" MIME type as it was specified in earlier drafts of this 293 document. Here, the entity-body of an HTTP POST request contains the 294 DER-encoded PKIMessage prefixed by an additional so-called TCP- 295 Message field. The "TCP-Based Management Protocol" specifying those 296 TCP-Messages has been described in draft versions of this document 297 but was removed. 299 5. Security Considerations 301 The following aspects need to be considered by implementers and 302 users: 304 1. There is the risk for denial of service attacks through resource 305 consumption by opening many connections to an HTTP server. 306 Therefore idle connections should be terminated after an 307 appropriate timeout, maybe also depending on the available free 308 resources. After sending a CMP Error Message, the server should 309 close the connection even if the CMP transaction is not yet fully 310 completed. 312 2. Without being encapsulated in effective security protocols such 313 as TLS [RFC5246] there is no integrity protection at the HTTP 314 protocol level. Therefore information from the HTTP protocol 315 should not be used to change state of the transaction. 317 3. Client users should be aware that storing the target location of 318 a HTTP response with the "301 Moved Permanently" status code 319 could be exploited by a man-in-the-middle attacker to block them 320 permanently from contacting the correct server. 322 4. If no measures to authenticate and protect the HTTP responses to 323 pushed Announcement messages are in place their information 324 regarding the Announcement's processing state may not be trusted. 325 In that case the overall design of the PKI system must not depend 326 on the Announcements being reliably received and processed by 327 their destination. 329 5. CMP provides inbuilt integrity protection and authentication. 330 The information communicated unencrypted in CMP messages does not 331 contain sensitive information endangering the security of the PKI 332 when intercepted. However, it might be possible for an 333 eavesdropper to utilize the available information to gather 334 confidential technical or business critical information. 335 Therefore users of the HTTP transport for CMP might want to 336 consider using HTTP over TLS according to [RFC2818] or virtual 337 private networks created e.g. by utilizing Internet Protocol 338 Security according to [RFC4301]. 340 6. IANA Considerations 342 The IANA has already registered the MIME media type "application/ 343 pkixcmp" for identifying CMP sequences due to an request made in 344 connection with [RFC2510]. 346 No further action by the IANA is necessary for this document or any 347 anticipated updates. 349 7. Acknowledgments 351 Until the fifth draft version of this document, released on November 352 24th 2000, the sole authors were Amit Kapoor and Ronald Tschlaer from 353 Certicom. Up to this point the now removed TCP-Based transport was 354 described in detail. They are not available for this working on this 355 document anymore at the time it is entering the "Authors Final Review 356 state AUTH48". As they therefore cannot approve this document as it 357 would be necessary, their names were moved to this section. Their 358 contact data as originally stated by them is as follows: 360 Amit Kapoor 361 Certicom 362 25801 Industrial Blvd 363 Hayward, CA 364 US 365 Email: amit@trustpoint.com 367 Ronald Tschalaer 368 Certicom 369 25801 Industrial Blvd 370 Hayward, CA 371 US 372 Email: ronald@trustpoint.com 374 The authors gratefully acknowledge the contributions of various 375 members of the IETF PKIX Working Group and the ICSA CA-talk mailing 376 list (a list solely devoted to discussing CMP interoperability 377 efforts). 379 By providing ideas, giving hints and doing invaluable review work, 380 the following alphabetically listed individuals have significantly 381 contributed to this document: 383 Tomas Gustavsson, Primekey 384 Peter Gutmann, University of Auckland 385 Wolf-Dietrich Moeller, Nokia Siemens Networks 387 8. References 389 8.1. Normative References 391 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 392 Requirement Levels", BCP 14, RFC 2119, March 1997. 394 [RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key 395 Infrastructure Certificate Management Protocols", 396 RFC 2510, March 1999. 398 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 399 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 400 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 402 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 403 Resource Identifier (URI): Generic Syntax", STD 66, 404 RFC 3986, January 2005. 406 [RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen, 407 "Internet X.509 Public Key Infrastructure Certificate 408 Management Protocol (CMP)", RFC 4210, September 2005. 410 8.2. Informative References 412 [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext 413 Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. 415 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 417 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 418 Internet Protocol", RFC 4301, December 2005. 420 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 421 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 423 Authors' Addresses 425 Tomi Kause 426 Tectia Corporation 427 Kumpulantie 3 428 Helsinki 00520 429 Finland 431 Email: toka@tectia.com 433 Martin Peylo 434 Nokia Siemens Networks 435 Linnoitustie 6 436 Espoo 02600 437 Finland 439 Email: martin.peylo@nsn.com