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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: August 18, 2012 February 15, 2012 8 Internet X.509 Public Key Infrastructure -- HTTP Transport for CMP 9 draft-ietf-pkix-cmp-transport-protocols-16.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 August 18, 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 . . . . . . . . . . . . . . . . . 6 73 3.8. HTTP Considerations . . . . . . . . . . . . . . . . . . . 7 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 With its status codes HTTP provides needed error reporting 113 capabilities. General problems on the server side as well as those 114 directly caused by the respective request can be reported to the 115 client. 117 As CMP implements a transaction ID, identifying transactions spanning 118 over more than just a single request/response pair, the statelessness 119 of HTTP is not blocking its usage as transport protocol for CMP 120 messages. 122 2. Requirements 124 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 125 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 126 document are to be interpreted as described in [RFC2119]. 128 3. HTTP-Based Protocol 130 For direct interaction between two entities, where a reliable 131 transport protocol like TCP is available, HTTP SHOULD be utilized for 132 conveying CMP messages. 134 3.1. HTTP Versions 136 Clients MUST support either HTTP/1.0 [RFC1945] or HTTP/1.1 [RFC2616]. 137 Servers SHOULD support both HTTP versions. 139 3.2. Persistent Connections 141 HTTP permits to reuse a connection for subsequent requests. 142 Implementations may use this functionality for messages within the 143 same transaction but MUST NOT rely on this because intermediate HTTP 144 proxies might terminate the connection after each request/response 145 pair. 147 3.3. General Form 149 A DER-encoded PKIMessage is sent as the entity-body of an HTTP POST 150 request. If this HTTP request is successful, the server returns the 151 CMP response in the body of the HTTP response. The HTTP response 152 status code in this case MUST be 200; other "Successfull 2xx" codes 153 MUST NOT be used for this purpose. HTTP responses to pushed CMP 154 Announcement messages (i.e., CA Certificate Announcement, Certificate 155 Announcement, Revocation Announcement, and CRL Announcement) utilize 156 the status codes 201 and 202 to identify whether the received 157 information was processed. 159 While "Redirection 3xx" status codes MAY be supported by 160 implementations, clients should only be enabled to automatically 161 follow them after careful consideration of possible security 162 implications. 164 All applicable "Client Error 4xx" or "Server Error 5xx" status codes 165 may be used to inform the client about errors. 167 3.4. Media Type 169 The Internet Media Type "application/pkixcmp" MUST be set in the HTTP 170 header when conveying a PKIMessage. 172 3.5. Communication Workflow 174 In CMP most communication is initiated by the end entities where 175 every CMP request triggers a CMP response message from the CA or RA. 177 The CMP Announcement messages described in Section 3.7 are an 178 exception. Their creation may be triggered by certain events or done 179 on a regular basis by a CA. The recipient of the Announcement only 180 replies with an HTTP status code acknowledging the receipt or 181 indicating an error but not with a CMP response. 183 If the receipt of an HTTP request is not confirmed by receiving an 184 HTTP response, it MUST be assumed that the transported CMP message 185 was not successfully delivered to its destination. 187 3.6. HTTP Request-URI 189 The Request-URI is formed as specified in [RFC3986]. 191 Client requests containing a PKI message MUST be directed to an 192 Request-URI depicting a directory. A server implementation MUST 193 handle Request-URIs with or without a trailing slash as identical. 195 An example of a Request-Line and a Host header field in an HTTP/1.1 196 header, sending a CMP request to a server, located in the "/cmp" 197 directory of the host example.com, would be 199 POST /cmp HTTP/1.1 200 Host: example.com 202 or in the absoluteURI form 204 POST http://example.com/cmp/ HTTP/1.1 205 Host: example.com 207 A CMP server may be logically located either inside the root- or 208 within subdirectories of an HTTP server domain. 210 3.7. Pushing of Announcements 212 A CMP server may create event-triggered announcements or generate 213 them on a regular basis. It MAY utilize HTTP transport to convey 214 them to a suitable recipient. As no request messages are specified 215 for those announcements they can only be pushed to the recipient. 217 If an EE wants to poll for a potential CA Key Update Announcement or 218 the current CRL, a PKI Information Request using a General Message as 219 described in E.5 of [RFC4210] can be used. 221 When pushing Announcement messages, PKIMessage structures are sent as 222 the entity-body of an HTTP POST request. 224 Suitable recipients for CMP announcements might e.g. be repositories 225 storing the announced information such as directory services. Those 226 listen for incoming messages, utilizing the same HTTP Request-URI 227 scheme as defined in Section 3.6. 229 The following PKIMessages are announcements that may be pushed by a 230 CA. The prefixed numbers reflect ASN.1 numbering of the respective 231 element. 233 [15] CA Key Update Announcement 234 [16] Certificate Announcement 235 [17] Revocation Announcement 236 [18] CRL Announcement 238 CMP Announcement messages do not require any CMP response. However, 239 the recipient MUST acknowledge receipt with a HTTP response having an 240 appropriate status code and an empty body. When not receiving such 241 response it MUST be assumed that the delivery was not successful and 242 if applicable the sending side may retry sending the Announcement 243 after waiting for an appropriate time span. 245 If the announced issue was successfully stored in a database or was 246 already present, the answer MUST be an HTTP response with a "201 247 Created" status code and empty message body. 249 In case the announced information was only accepted for further 250 processing, the status code of the returned HTTP response MAY also be 251 "202 Accepted". After an appropriate delay, the sender may then try 252 to send the Announcement again and may repeat this until it receives 253 a confirmation that it had been successfully processed. The 254 appropriate duration of the delay and the option to increase it 255 between consecutive attempts should be carefully considered. 257 A receiver MUST answer with a suitable 4xx or 5xx HTTP error code 258 when a problem occurs. 260 3.8. HTTP Considerations 262 In general CMP messages are not cachable. HTTP headers of requests 263 and responses MUST include "Cache-Control: no-cache" and, in case of 264 HTTP/1.0, additionally "Pragma: no-cache" to protect the client from 265 getting cached responses. 267 Connection management is based on the HTTP provided mechanisms 268 ("Connection" and "Proxy-Connection" header fields). 270 While implementations MAY make use of all defined features of the 271 HTTP protocol, they SHOULD keep the protocol utilization as simple as 272 possible. E.g. there is no benefit in using chunked Transfer- 273 Encoding as the length of an ASN.1 sequence is know when starting to 274 send it. 276 There is no need for the clients to send an "Expect" request-header 277 field with the "100-continue" expectation and wait for a "100 278 Continue" status as described in chapter 8.2.3 of [RFC2616]. The CMP 279 payload sent by a client is relatively small, so having extra 280 messages exchanged is more inefficient as the server will anyway only 281 seldom reject a message without evaluating the body. 283 Content codings MAY be applied. 285 4. Compatibility Issues with Legacy Implementations 287 As this document was subject of multiple changes during the long 288 period of time it was created in, implementations using a different 289 approach for HTTP transport may exist. While only those 290 implementations according to this specification are compliant, 291 implementers should to be aware that there might be existing ones 292 which behave differently. 294 Legacy implementations might also use an unregistered "application/ 295 pkixcmp-poll" MIME type as it was specified in earlier drafts of this 296 document. Here, the entity-body of an HTTP POST request contains the 297 DER-encoded PKIMessage prefixed by an additional so-called TCP- 298 Message field. The "TCP-Based Management Protocol" specifying those 299 TCP-Messages has been described in draft versions of this document 300 but was removed. 302 5. Security Considerations 304 The following aspects need to be considered by implementers and 305 users: 307 1. There is the risk for denial of service attacks through resource 308 consumption by opening many connections to an HTTP server. 309 Therefore idle connections should be terminated after an 310 appropriate timeout, maybe also depending on the available free 311 resources. After sending a CMP Error Message, the server should 312 close the connection even if the CMP transaction is not yet fully 313 completed. 315 2. There is no security at the HTTP protocol level and thus 316 information from the HTTP protocol SHOULD NOT be used to change 317 state of the transaction. Change of state SHOULD be triggered by 318 signed PKIMessages only. Likewise, the clients SHOULD NOT 319 support the "301 Moved Permanently" HTTP status code which could 320 otherwise be used by a man-in-the-middle attacker to block them 321 permanently from contacting the correct server. 323 3. If no measures to authenticate and protect the HTTP responses to 324 pushed Announcement messages are in place their information 325 regarding the Announcement's processing state may not be trusted. 326 In that case the overall design of the PKI system must not depend 327 on the Announcements being reliably received and processed by 328 their destination. 330 4. CMP provides inbuilt integrity protection and authentication. 331 The information communicated unencrypted in CMP messages does not 332 contain sensitive information endangering the security of the PKI 333 when intercepted. However, it might be possible for an 334 eavesdropper to utilize the available information to gather 335 confidential technical or business critical information. 336 Therefore users of the HTTP transport for CMP might want to 337 consider using HTTP over TLS according to [RFC2818] or virtual 338 private networks created e.g. by utilizing Internet Protocol 339 Security according to [RFC4301]. 341 6. IANA Considerations 343 The IANA has already registered the MIME media type "application/ 344 pkixcmp" for identifying CMP sequences due to an request made in 345 connection with [RFC2510]. 347 No further action by the IANA is necessary for this document or any 348 anticipated updates. 350 7. Acknowledgments 352 Until the fifth draft version of this document, released on November 353 24th 2000, the sole authors were Amit Kapoor and Ronald Tschlaer from 354 Certicom. Up to this point the now removed TCP-Based transport was 355 described in detail. They are not available for this working on this 356 document anymore at the time it is entering the "Authors Final Review 357 state AUTH48". As they therefore cannot approve this document as it 358 would be necessary, their names were moved to this section. Their 359 contact data as originally stated by them is as follows: 361 Amit Kapoor 362 Certicom 363 25801 Industrial Blvd 364 Hayward, CA 365 US 366 Email: amit@trustpoint.com 368 Ronald Tschalaer 369 Certicom 370 25801 Industrial Blvd 371 Hayward, CA 372 US 373 Email: ronald@trustpoint.com 375 The authors gratefully acknowledge the contributions of various 376 members of the IETF PKIX Working Group and the ICSA CA-talk mailing 377 list (a list solely devoted to discussing CMP interoperability 378 efforts). 380 By providing ideas, giving hints and doing invaluable review work, 381 the following alphabetically listed individuals have significantly 382 contributed to this document: 384 Tomas Gustavsson, Primekey 385 Peter Gutmann, University of Auckland 386 Wolf-Dietrich Moeller, Nokia Siemens Networks 388 8. References 390 8.1. Normative References 392 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 393 Requirement Levels", BCP 14, RFC 2119, March 1997. 395 [RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key 396 Infrastructure Certificate Management Protocols", 397 RFC 2510, March 1999. 399 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 400 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 401 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 403 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 404 Resource Identifier (URI): Generic Syntax", STD 66, 405 RFC 3986, January 2005. 407 [RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen, 408 "Internet X.509 Public Key Infrastructure Certificate 409 Management Protocol (CMP)", RFC 4210, September 2005. 411 8.2. Informative References 413 [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext 414 Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. 416 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 418 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 419 Internet Protocol", RFC 4301, December 2005. 421 Authors' Addresses 423 Tomi Kause 424 Tectia Corporation 425 Kumpulantie 3 426 Helsinki 00520 427 Finland 429 Email: toka@tectia.com 431 Martin Peylo 432 Nokia Siemens Networks 433 Linnoitustie 6 434 Espoo 02600 435 Finland 437 Email: martin.peylo@nsn.com