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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: July 13, 2012 January 10, 2012 8 Internet X.509 Public Key Infrastructure -- HTTP Transport for CMP 9 draft-ietf-pkix-cmp-transport-protocols-15.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 July 13, 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. HTTP-Based Protocol . . . . . . . . . . . . . . . . . . . . . 5 66 3.1. HTTP Versions . . . . . . . . . . . . . . . . . . . . . . 5 67 3.2. Persistent Connections . . . . . . . . . . . . . . . . . . 5 68 3.3. General Form . . . . . . . . . . . . . . . . . . . . . . . 5 69 3.4. Media Type . . . . . . . . . . . . . . . . . . . . . . . . 5 70 3.5. Communication Workflow . . . . . . . . . . . . . . . . . . 5 71 3.6. HTTP Request-URI . . . . . . . . . . . . . . . . . . . . . 6 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. Information Security Considerations . . . . . . . . . . . . . 11 77 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 78 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 79 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 80 9.1. Normative References . . . . . . . . . . . . . . . . . . . 14 81 9.2. Informative References . . . . . . . . . . . . . . . . . . 14 82 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 84 1. Introduction 86 The Certificate Management Protocol (CMP) [RFC4210] requires a well 87 defined transport mechanism to enable End Entities (EEs), 88 Registration Authorities (RAs) and Certificate Authorities (CAs) to 89 pass PKIMessage sequences between them. This document defines the 90 transport mechanism which was removed from the main CMP specification 91 with the second release and referred to be in a separate document. 93 The first version of the CMP specification [RFC2510] included a brief 94 description of a simple transport protocol layer on top of TCP. Its 95 features was simple transport level error-handling and a mechanism to 96 poll for outstanding PKI messages. Additionally it was mentioned 97 that PKI messages could also be conveyed using file-, E-mail- and 98 HTTP-based transport, but those were not specified in detail. 100 The current version of the CMP specification [RFC4210] incorporated 101 an own polling mechanism and thus the need for a transport protocol 102 providing this functionality vanished. The remaining features CMP 103 requires from its transport protocols are connection and error 104 handling. 106 During the long time it existed as draft, this RFC was undergoing 107 drastic changes. The "TCP-Based Management Protocol" was enhanced 108 and a TCP-Messages-over-HTTP transport specification appeared. As 109 both proved to be needless and cumbersome, implementers preferred to 110 use plain HTTP transport. This document now reflects that by 111 exclusively describing HTTP as transport protocol for CMP. 113 HTTP transport is generally easy to implement, traverses network 114 borders utilizing ubiquitous proxies and is already commonly found in 115 existing implementations. 117 With its status codes HTTP provides needed error reporting 118 capabilities. General problems on the server side as well as those 119 directly caused by the respective request can be reported to the 120 client. 122 As CMP implements a transaction ID, identifying transactions spanning 123 over more than just a single request/response pair, the statelessness 124 of HTTP is not blocking its usage as transport protocol for CMP 125 messages. 127 2. Requirements 129 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 130 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 131 document are to be interpreted as described in [RFC2119]. 133 3. HTTP-Based Protocol 135 For direct interaction between two entities, where a reliable 136 transport protocol like TCP is available, HTTP SHOULD be utilized for 137 conveying CMP messages. 139 3.1. HTTP Versions 141 Either HTTP/1.0 as described in [RFC1945] or HTTP/1.1 as in [RFC2616] 142 MAY be used. Server implementations SHOULD be able to interact with 143 counterparts utilizing either HTTP protocol version. 145 3.2. Persistent Connections 147 HTTP permits to reuse a connection for subsequent requests. 148 Implementations may use this functionality for messages within the 149 same transaction but MUST NOT rely on that as e.g. intermediate HTTP 150 proxies might terminate the connection after each request/response 151 pair. 153 3.3. General Form 155 An ASN.1 DER-encoded PKIMessage is sent as the entity-body of an HTTP 156 POST request. If this HTTP request is successful, the server returns 157 the CMP reply in the body of the HTTP response. The response status 158 code in this case MUST be 200; other 2xx codes MUST NOT be used for 159 this purpose. HTTP responses to pushed CMP Announcement messages 160 utilize the status codes 201 and 202 to identify whether the received 161 information was processed. 163 All applicable 4xx or 5xx status codes may be used to inform the 164 client about errors. 166 3.4. Media Type 168 The Internet Media Type "application/pkixcmp" MUST be set in the HTTP 169 header when conveying a PKIMessage. 171 3.5. Communication Workflow 173 In CMP most communication is initiated by the end entities where 174 every CMP request triggers a CMP response message from the CA or RA. 176 The CMP Announcement messages described in Section 3.7 are an 177 exception. Their creation may be triggered by certain events or done 178 on a regular basis by a CA. The recipient of the Announcement only 179 replies with an HTTP status code acknowledging the receipt or 180 indicating an error but not with a CMP response. 182 If the receipt of an HTTP request is not confirmed by receiving an 183 HTTP response, it MUST be assumed that the transported CMP message 184 was not successfully delivered to its destination. 186 3.6. HTTP Request-URI 188 The Request-URI is formed as specified in [RFC3986]. 190 Client requests containing a PKI message MUST be directed to an 191 Request-URI depicting a directory. A server implementation MUST 192 handle Request-URIs with or without a trailing slash as identical. 193 The following list contains all such CMP message types. The prefixed 194 numbers reflect the ASN.1 numbering of the respective element. 196 [0] Initialization Request 197 [2] Certification Request 198 [4] PKCS-10 Request 199 [6] pop Response 200 [7] Key Update Request 201 [9] Key Recovery Request 202 [11] Revocation Request 203 [13] Cross-Certification Request 204 [15] CA Key Update Announcement 205 [16] Certificate Announcement 206 [17] Revocation Announcement 207 [18] CRL Announcement 208 [20] Nested Message 209 [21] General Message 210 [23] Error Message 211 [24] Certificate Confirmation 212 [25] Polling Request 214 An example of a Request-Line and a Host header field in an HTTP/1.1 215 header, sending a CMP request to a server, located in the "/cmp" 216 directory of the host example.com, would be 218 POST /cmp HTTP/1.1 219 Host: example.com 221 or in the absoluteURI form 223 POST http://example.com/cmp/ HTTP/1.1 224 Host: example.com 226 A CMP server may be logically located either inside the root- or 227 within subdirectories of an HTTP server domain. 229 3.7. Pushing of Announcements 231 A CMP server may create event-triggered announcements or generate 232 them on a regular basis. It MAY utilize HTTP transport to convey 233 them to a suitable recipient. No request message for is specified, 234 so they can only be pushed to the recipient. If an EE wants to poll 235 for a potential CA Key Update Announcement or the current CRL, a PKI 236 Information Request using a General Message as described in E.5 of 237 [RFC4210] can be used. 239 When pushing Announcements, ASN.1 encoded structures are sent as the 240 entity-body of an HTTP POST request. 242 Suitable recipients for CMP announcements might e.g. be repositories 243 storing the announced information such as directory services. Those 244 listen for incoming messages, utilizing the same HTTP Request-URI 245 scheme as defined in Section 3.6. 247 The following PKIMessages are announcements that may be pushed by a 248 CA. The prefixed numbers reflect ASN.1 numbering of the respective 249 element. 251 [15] CA Key Update Announcement 252 [16] Certificate Announcement 253 [17] Revocation Announcement 254 [18] CRL Announcement 256 CMP Announcement messages do not require any CMP response. However, 257 the recipient MUST acknowledge receipt with a HTTP response having an 258 appropriate status code and an empty body. When not receiving such 259 response it MUST be assumed that the delivery was not successful and 260 if applicable the sending side may retry sending the Announcement 261 after waiting for an appropriate time span. 263 If the announced issue was successfully stored in a database or was 264 already present, the answer MUST be an HTTP response with a "201 265 Created" status code and empty message body. 267 In case the announced information was only accepted for further 268 processing, the status code of the returned HTTP response MAY also be 269 "202 Accepted". After an appropriate delay, the sender may then try 270 to send the Announcement again and may repeat this until it receives 271 a confirmation that it had been successfully processed. The 272 appropriate duration of the delay and the option to increase it 273 between consecutive attempts should be carefully considered. 275 A receiver MUST answer with a suitable 4xx or 5xx HTTP error code 276 when a problem occurs. 278 3.8. HTTP Considerations 280 In general CMP messages are not cachable. HTTP headers of requests 281 and responses MUST include "Cache-Control: no-cache" and, in case of 282 HTTP/1.0, additionally "Pragma: no-cache" to protect the client from 283 getting cached responses. 285 Connection management is based on the HTTP provided mechanisms 286 ("Connection" and "Proxy-Connection" header fields). 288 While implementations MAY make use of all defined features of the 289 HTTP protocol, they SHOULD keep the protocol utilization as simple as 290 possible. E.g. there is no benefit in using chunked Transfer- 291 Encoding as the length of an ASN.1 sequence is know when starting to 292 send it. 294 There is no need for the clients to send an "Expect" request-header 295 field with the "100-continue" expectation and wait for a "100 296 Continue" status as described in chapter 8.2.3 of [RFC2616]. The CMP 297 payload sent by a client is relatively small, so having extra 298 messages exchanged is more inefficient as the server will anyway only 299 seldom reject a message without evaluating the body. 301 Content codings MAY be applied. 303 4. Compatibility Issues with Legacy Implementations 305 As this document was subject of multiple changes during the long 306 period of time it was created in, implementations using a different 307 approach for HTTP transport may exist. While only those 308 implementations according to this specification are compliant, 309 implementers should to be aware that there might be existing ones 310 which behave differently. 312 Legacy implementations might also use an unregistered "application/ 313 pkixcmp-poll" MIME type as it was specified in earlier drafts of this 314 document. Here, the entity-body of an HTTP POST request contains the 315 DER-encoded PKIMessage prefixed by an additional so-called TCP- 316 Message field. The "TCP-Based Management Protocol" specifying those 317 TCP-Messages has been described in draft versions of this document 318 but was removed. 320 5. Security Considerations 322 The following aspects need to be considered by server side 323 implementers: 325 1. There is the risk for denial of service attacks through resource 326 consumption by opening many connections. Therefore idle 327 connections should be terminated after an appropriate timeout, 328 maybe also depending on the available free resources. After 329 sending a CMP Error Message, the server should close the 330 connection even if the CMP transaction is not yet fully 331 completed. 333 2. There is no security at the HTTP protocol level (unless tunneled 334 via TLS) and thus information from the HTTP protocol SHOULD NOT 335 be used to change state of the transaction. Change of state 336 SHOULD be triggered by signed PKIMessages only. Likewise, the 337 clients SHOULD NOT support the 301 HTTP status code which could 338 otherwise be used by an man-in-the-middle attacker to block them 339 permanently from contacting the correct server. 341 3. If no measures to authenticate and protect the HTTP responses to 342 pushed Announcement messages are in place their information 343 regarding the Announcement's processing state may not be trusted. 344 In that case the overall design of the PKI system must not depend 345 on the Announcements being reliably received and processed by 346 their destination. 348 6. Information Security Considerations 350 CMP provides inbuilt integrity protection and authentication. Due to 351 the nature of a PKI, from a security perspective the information 352 communicated unencrypted does not contain sensitive information. 354 However, it might be possible for an interceptor to utilize the 355 available information to gather confidential technical or business 356 critical information. Therefore users of the HTTP CMP transport 357 might want to use HTTP over TLS according to [RFC2818] or should 358 consider to use virtual private networks created e.g. by utilizing 359 Internet Protocol Security according to [RFC4301]. 361 7. IANA Considerations 363 The IANA has already registered the MIME media type "application/ 364 pkixcmp" for identifying CMP sequences due to an request made in 365 connection with [RFC2510]. 367 No further action by the IANA is necessary for this document or any 368 anticipated updates. 370 8. Acknowledgments 372 Until the fifth draft version of this document, released on November 373 24th 2000, the sole authors were Amit Kapoor and Ronald Tschlaer from 374 Certicom. Up to this point the now removed TCP-Based transport was 375 described in detail. They are not available for this working on this 376 document anymore at the time it is entering the "Authors Final Review 377 state AUTH48". As they therefore cannot approve this document as it 378 would be necessary, their names were moved to this section. Their 379 contact data as originally stated by them is as follows: 381 Amit Kapoor 382 Certicom 383 25801 Industrial Blvd 384 Hayward, CA 385 US 386 Email: amit@trustpoint.com 388 Ronald Tschalaer 389 Certicom 390 25801 Industrial Blvd 391 Hayward, CA 392 US 393 Email: ronald@trustpoint.com 395 The authors gratefully acknowledge the contributions of various 396 members of the IETF PKIX Working Group and the ICSA CA-talk mailing 397 list (a list solely devoted to discussing CMP interoperability 398 efforts). 400 By providing ideas, giving hints and doing invaluable review work, 401 the following alphabetically listed individuals have significantly 402 contributed to this document: 404 Tomas Gustavsson, Primekey 405 Peter Gutmann, University of Auckland 406 Wolf-Dietrich Moeller, Nokia Siemens Networks 408 9. References 410 9.1. Normative References 412 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 413 Requirement Levels", BCP 14, RFC 2119, March 1997. 415 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 416 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 417 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 419 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 420 Resource Identifier (URI): Generic Syntax", STD 66, 421 RFC 3986, January 2005. 423 [RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen, 424 "Internet X.509 Public Key Infrastructure Certificate 425 Management Protocol (CMP)", RFC 4210, September 2005. 427 9.2. Informative References 429 [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext 430 Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. 432 [RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key 433 Infrastructure Certificate Management Protocols", 434 RFC 2510, March 1999. 436 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 438 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 439 Internet Protocol", RFC 4301, December 2005. 441 Authors' Addresses 443 Tomi Kause 444 Tectia Corporation 445 Kumpulantie 3 446 Helsinki 00520 447 Finland 449 Email: toka@tectia.com 451 Martin Peylo 452 Nokia Siemens Networks 453 Linnoitustie 6 454 Espoo 02600 455 Finland 457 Email: martin.peylo@nsn.com