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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-18.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 . . . . . . . . . . . . . . . . . . . . . . . . 7 70 3.5. Communication Workflow . . . . . . . . . . . . . . . . . . 7 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 . . . . . . . 10 75 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 76 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 77 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 78 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 79 8.1. Normative References . . . . . . . . . . . . . . . . . . . 14 80 8.2. Informative References . . . . . . . . . . . . . . . . . . 14 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 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 persistent connections [RFC2616] allow multiple interactions to 153 take place on the same HTTP connection. However, neither HTTP nor 154 this protocol are designed to correlate messages on the same 155 connection in any meaningful way; persistent connections are only a 156 performance optimization. In particular, intermediaries can do 157 things like mix connections from different clients into one 158 "upstream" connections, terminate persistent connections and forward 159 requests as non-persistent requests, etc. As such, implementations 160 MUST NOT infer that requests on the same connection come from the 161 same client (e.g., for correlating PKI messages with ongoing 162 transactions); every message is to be evaluated in isolation. 164 3.3. General Form 166 A DER-encoded PKIMessage is sent as the entity-body of an HTTP POST 167 request. If this HTTP request is successful, the server returns the 168 CMP response in the body of the HTTP response. The HTTP response 169 status code in this case MUST be 200; other "Successful 2xx" codes 170 MUST NOT be used for this purpose. HTTP responses to pushed CMP 171 Announcement messages (i.e., CA Certificate Announcement, Certificate 172 Announcement, Revocation Announcement, and CRL Announcement) utilize 173 the status codes 201 and 202 to identify whether the received 174 information was processed. 176 While "Redirection 3xx" status codes MAY be supported by 177 implementations, clients should only be enabled to automatically 178 follow them after careful consideration of possible security 179 implications. 181 All applicable "Client Error 4xx" or "Server Error 5xx" status codes 182 may be used to inform the client about errors. 184 3.4. Media Type 186 The Internet Media Type "application/pkixcmp" MUST be set in the HTTP 187 header when conveying a PKIMessage. 189 3.5. Communication Workflow 191 In CMP most communication is initiated by the end entities where 192 every CMP request triggers a CMP response message from the CA or RA. 194 The CMP Announcement messages described in Section 3.7 are an 195 exception. Their creation may be triggered by certain events or done 196 on a regular basis by a CA. The recipient of the Announcement only 197 replies with an HTTP status code acknowledging the receipt or 198 indicating an error but not with a CMP response. 200 If the receipt of an HTTP request is not confirmed by receiving an 201 HTTP response, it MUST be assumed that the transported CMP message 202 was not successfully delivered to its destination. 204 3.6. HTTP Request-URI 206 The Request-URI is formed as specified in [RFC3986]. 208 A server implementation MUST handle Request-URI paths with or without 209 a trailing slash as identical. 211 An example of a Request-Line and a Host header field in an HTTP/1.1 212 header, sending a CMP request to a server, located in the "/cmp" path 213 of the host "example.com", would be 215 POST /cmp HTTP/1.1 216 Host: example.com 218 or in the absoluteURI form 220 POST http://example.com/cmp/ HTTP/1.1 221 Host: example.com 223 3.7. Pushing of Announcements 225 A CMP server may create event-triggered announcements or generate 226 them on a regular basis. It MAY utilize HTTP transport to convey 227 them to a suitable recipient. As no request messages are specified 228 for those announcements they can only be pushed to the recipient. 230 If an EE wants to poll for a potential CA Key Update Announcement or 231 the current CRL, a PKI Information Request using a General Message as 232 described in E.5 of [RFC4210] can be used. 234 When pushing Announcement messages, PKIMessage structures are sent as 235 the entity-body of an HTTP POST request. 237 Suitable recipients for CMP announcements might e.g. be repositories 238 storing the announced information such as directory services. Those 239 listen for incoming messages, utilizing the same HTTP Request-URI 240 scheme as defined in Section 3.6. 242 The following PKIMessages are announcements that may be pushed by a 243 CA. The prefixed numbers reflect ASN.1 numbering of the respective 244 element. 246 [15] CA Key Update Announcement 247 [16] Certificate Announcement 248 [17] Revocation Announcement 249 [18] CRL Announcement 251 CMP Announcement messages do not require any CMP response. However, 252 the recipient MUST acknowledge receipt with a HTTP response having an 253 appropriate status code and an empty body. When not receiving such 254 response it MUST be assumed that the delivery was not successful and 255 if applicable the sending side may retry sending the Announcement 256 after waiting for an appropriate time span. 258 If the announced issue was successfully stored in a database or was 259 already present, the answer MUST be an HTTP response with a "201 260 Created" status code and empty message body. 262 In case the announced information was only accepted for further 263 processing, the status code of the returned HTTP response MAY also be 264 "202 Accepted". After an appropriate delay, the sender may then try 265 to send the Announcement again and may repeat this until it receives 266 a confirmation that it had been successfully processed. The 267 appropriate duration of the delay and the option to increase it 268 between consecutive attempts should be carefully considered. 270 A receiver MUST answer with a suitable 4xx or 5xx HTTP error code 271 when a problem occurs. 273 3.8. HTTP Considerations 275 While implementations MAY make use of all defined features of the 276 HTTP protocol, they SHOULD keep the protocol utilization as simple as 277 possible. E.g. there is no benefit in using chunked Transfer- 278 Encoding as the length of an ASN.1 sequence is know when starting to 279 send it. 281 There is no need for the clients to send an "Expect" request-header 282 field with the "100-continue" expectation and wait for a "100 283 Continue" status as described in chapter 8.2.3 of [RFC2616]. The CMP 284 payload sent by a client is relatively small, so having extra 285 messages exchanged is more inefficient as the server will anyway only 286 seldom reject a message without evaluating the body. 288 4. Compatibility Issues with Legacy Implementations 290 As this document was subject of multiple changes during the long 291 period of time it was created in, implementations using a different 292 approach for HTTP transport may exist. While only those 293 implementations according to this specification are compliant, 294 implementers should to be aware that there might be existing ones 295 which behave differently. 297 Legacy implementations might also use an unregistered "application/ 298 pkixcmp-poll" MIME type as it was specified in earlier drafts of this 299 document. Here, the entity-body of an HTTP POST request contains the 300 DER-encoded PKIMessage prefixed by an additional so-called TCP- 301 Message field. The "TCP-Based Management Protocol" specifying those 302 TCP-Messages has been described in draft versions of this document 303 but was removed. 305 5. Security Considerations 307 The following aspects need to be considered by implementers and 308 users: 310 1. There is the risk for denial of service attacks through resource 311 consumption by opening many connections to an HTTP server. 312 Therefore idle connections should be terminated after an 313 appropriate timeout, maybe also depending on the available free 314 resources. After sending a CMP Error Message, the server should 315 close the connection even if the CMP transaction is not yet fully 316 completed. 318 2. Without being encapsulated in effective security protocols such 319 as TLS [RFC5246] there is no integrity protection at the HTTP 320 protocol level. Therefore information from the HTTP protocol 321 should not be used to change state of the transaction. 323 3. Client users should be aware that storing the target location of 324 a HTTP response with the "301 Moved Permanently" status code 325 could be exploited by a man-in-the-middle attacker to block them 326 permanently from contacting the correct server. 328 4. If no measures to authenticate and protect the HTTP responses to 329 pushed Announcement messages are in place their information 330 regarding the Announcement's processing state may not be trusted. 331 In that case the overall design of the PKI system must not depend 332 on the Announcements being reliably received and processed by 333 their destination. 335 5. CMP provides inbuilt integrity protection and authentication. 336 The information communicated unencrypted in CMP messages does not 337 contain sensitive information endangering the security of the PKI 338 when intercepted. However, it might be possible for an 339 eavesdropper to utilize the available information to gather 340 confidential technical or business critical information. 341 Therefore users of the HTTP transport for CMP might want to 342 consider using HTTP over TLS according to [RFC2818] or virtual 343 private networks created e.g. by utilizing Internet Protocol 344 Security according to [RFC4301]. 346 6. IANA Considerations 348 The IANA has already registered the MIME media type "application/ 349 pkixcmp" for identifying CMP sequences due to an request made in 350 connection with [RFC2510]. 352 No further action by the IANA is necessary for this document or any 353 anticipated updates. 355 7. Acknowledgments 357 Until the fifth draft version of this document, released on November 358 24th 2000, the sole authors were Amit Kapoor and Ronald Tschlaer from 359 Certicom. Up to this point the now removed TCP-Based transport was 360 described in detail. They are not available for this working on this 361 document anymore at the time it is entering the "Authors Final Review 362 state AUTH48". As they therefore cannot approve this document as it 363 would be necessary, their names were moved to this section. Their 364 contact data as originally stated by them is as follows: 366 Amit Kapoor 367 Certicom 368 25801 Industrial Blvd 369 Hayward, CA 370 US 371 Email: amit@trustpoint.com 373 Ronald Tschalaer 374 Certicom 375 25801 Industrial Blvd 376 Hayward, CA 377 US 378 Email: ronald@trustpoint.com 380 The authors gratefully acknowledge the contributions of various 381 members of the IETF PKIX Working Group and the ICSA CA-talk mailing 382 list (a list solely devoted to discussing CMP interoperability 383 efforts). 385 By providing ideas, giving hints and doing invaluable review work, 386 the following alphabetically listed individuals have significantly 387 contributed to this document: 389 Tomas Gustavsson, Primekey 390 Peter Gutmann, University of Auckland 391 Wolf-Dietrich Moeller, Nokia Siemens Networks 393 8. References 395 8.1. Normative References 397 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 398 Requirement Levels", BCP 14, RFC 2119, March 1997. 400 [RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key 401 Infrastructure Certificate Management Protocols", 402 RFC 2510, March 1999. 404 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 405 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 406 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 408 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 409 Resource Identifier (URI): Generic Syntax", STD 66, 410 RFC 3986, January 2005. 412 [RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen, 413 "Internet X.509 Public Key Infrastructure Certificate 414 Management Protocol (CMP)", RFC 4210, September 2005. 416 8.2. Informative References 418 [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext 419 Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. 421 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 423 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 424 Internet Protocol", RFC 4301, December 2005. 426 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 427 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 429 Authors' Addresses 431 Tomi Kause 432 Tectia Corporation 433 Kumpulantie 3 434 Helsinki 00520 435 Finland 437 Email: toka@tectia.com 439 Martin Peylo 440 Nokia Siemens Networks 441 Linnoitustie 6 442 Espoo 02600 443 Finland 445 Email: martin.peylo@nsn.com