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'ITU.X690.1994' ** Downref: Normative reference to an Informational RFC: RFC 1945 ** Obsolete normative reference: RFC 2510 (Obsoleted by RFC 4210) ** Obsolete normative reference: RFC 2616 (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235) -- Obsolete informational reference (is this intentional?): RFC 2818 (Obsoleted by RFC 9110) -- Obsolete informational reference (is this intentional?): RFC 5246 (Obsoleted by RFC 8446) Summary: 3 errors (**), 0 flaws (~~), 1 warning (==), 10 comments (--). 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: January 25, 2013 July 24, 2012 8 Internet X.509 Public Key Infrastructure -- HTTP Transfer for CMP 9 draft-ietf-pkix-cmp-transport-protocols-20.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 January 25, 2013. 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. Conventions Used in This Document . . . . . . . . . . . . . . 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. Implementation Considerations . . . . . . . . . . . . . . . . 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 transfer mechanism to enable End Entities (EEs), Registration 87 Authorities (RAs) and Certification Authorities (CAs) to pass 88 PKIMessage sequences between them. 90 The first version of the CMP specification [RFC2510] included a brief 91 description of a simple transfer protocol layer on top of TCP. Its 92 features was simple transfer level error-handling and a mechanism to 93 poll for outstanding PKI messages. Additionally it was mentioned 94 that PKI messages could also be conveyed using file-, E-mail- and 95 HTTP-based transfer, but those were not specified in detail. 97 The current version of the CMP specification [RFC4210] incorporated 98 its own polling mechanism and thus the need for a transfer protocol 99 providing this functionality vanished. The remaining features CMP 100 requires from its transfer protocols are connection and error 101 handling. 103 Before this document was published as an RFC, the draft version 104 underwent drastic changes during the long-lasting work process. The 105 so-called "Direct TCP-Based Management Protocol" specified in 106 [RFC2510] was enhanced and at some point a version existed where this 107 protocol was again transferred over HTTP. As both approaches proved 108 to be needless and cumbersome, implementers preferred to use plain 109 HTTP transfer following [RFC1945] or [RFC2616]. This document now 110 reflects that by exclusively describing HTTP as transfer protocol for 111 CMP. 113 The usage of HTTP for transferring CMP messages exclusively uses POST 114 method for requests, effectively tunneling CMP over HTTP. While this 115 is generally considered as bad practice and should not be emulated, 116 there are good reasons to do so for transferring CMP. HTTP is used 117 as it is generally easy to implement and able to traverse network 118 borders utilizing ubiquitous proxies. Most importantly, HTTP is 119 already commonly used in existing CMP implementations. Other HTTP 120 request methods such as GET are not used as PKI management operations 121 can only be triggered using CMP's PKI messages which need to be 122 transferred using a POST request. 124 With its status codes HTTP provides needed error reporting 125 capabilities. General problems on the server side as well as those 126 directly caused by the respective request can be reported to the 127 client. 129 As CMP implements a transaction ID, identifying transactions spanning 130 over more than just a single request/response pair, the statelessness 131 of HTTP is not blocking its usage as transfer protocol for CMP 132 messages. 134 2. Conventions Used in This Document 136 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 137 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 138 document are to be interpreted as described in [RFC2119]. 140 3. HTTP-Based Protocol 142 For direct interaction between two entities, where a reliable 143 transport protocol like TCP is available, HTTP SHOULD be utilized for 144 conveying CMP messages. 146 3.1. HTTP Versions 148 Implementations MUST support HTTP/1.0 [RFC1945], and SHOULD support 149 HTTP/1.1 [RFC2616]. 151 3.2. Persistent Connections 153 HTTP persistent connections [RFC2616] allow multiple interactions to 154 take place on the same HTTP connection. However, neither HTTP nor 155 the protocol specified in this document are designed to correlate 156 messages on the same connection in any meaningful way; persistent 157 connections are only a performance optimization. In particular, 158 intermediaries can do things like mix connections from different 159 clients into one "upstream" connections, terminate persistent 160 connections and forward requests as non-persistent requests, etc. As 161 such, implementations MUST NOT infer that requests on the same 162 connection come from the same client (e.g., for correlating PKI 163 messages with ongoing transactions); every message is to be evaluated 164 in isolation. 166 3.3. General Form 168 A DER-encoded [ITU.X690.1994] PKIMessage [RFC4210] is sent as the 169 entity-body of an HTTP POST request. If this HTTP request is 170 successful, the server returns the CMP response in the body of the 171 HTTP response. The HTTP response status code in this case MUST be 172 200; other "Successful 2xx" codes MUST NOT be used for this purpose. 173 HTTP responses to pushed CMP Announcement messages (i.e., CA 174 Certificate Announcement, Certificate Announcement, Revocation 175 Announcement, and CRL Announcement) utilize the status codes 201 and 176 202 to identify whether the received information was processed. 178 While "Redirection 3xx" status codes MAY be supported by 179 implementations, clients should only be enabled to automatically 180 follow them after careful consideration of possible security 181 implications. As described in Section 5, "301 Moved Permanently" 182 could be misused for permanent denial of service. 184 All applicable "Client Error 4xx" or "Server Error 5xx" status codes 185 MAY be used to inform the client about errors. 187 3.4. Media Type 189 The Internet Media Type "application/pkixcmp" MUST be set in the HTTP 190 Content-Type header field when conveying a PKIMessage. 192 3.5. Communication Workflow 194 In CMP most communication is initiated by the end entities where 195 every CMP request triggers a CMP response message from the CA or RA. 197 The CMP Announcement messages described in Section 3.7 are an 198 exception. Their creation may be triggered by certain events or done 199 on a regular basis by a CA. The recipient of the Announcement only 200 replies with an HTTP status code acknowledging the receipt or 201 indicating an error but not with a CMP response. 203 If the receipt of an HTTP request is not confirmed by receiving an 204 HTTP response, it MUST be assumed that the transferred CMP message 205 was not successfully delivered to its destination. 207 3.6. HTTP Request-URI 209 The Request-URI is formed as specified in [RFC3986]. 211 A server implementation MUST handle Request-URI paths with or without 212 a trailing slash as identical. 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" path 216 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 3.7. Pushing of Announcements 228 A CMP server may create event-triggered announcements or generate 229 them on a regular basis. It MAY utilize HTTP transfer to convey them 230 to a suitable recipient. As no request messages are specified for 231 those announcements they can only be pushed to the recipient. 233 If an EE wants to poll for a potential CA Key Update Announcement or 234 the current CRL, a PKI Information Request using a General Message as 235 described in E.5 of [RFC4210] can be used. 237 When pushing Announcement messages, PKIMessage structures are sent as 238 the entity-body of an HTTP POST request. 240 Suitable recipients for CMP announcements might e.g. be repositories 241 storing the announced information such as directory services. Those 242 listen for incoming messages, utilizing the same HTTP Request-URI 243 scheme as defined in Section 3.6. 245 The following PKIMessages are announcements that may be pushed by a 246 CA. The prefixed numbers reflect ASN.1 numbering of the respective 247 element. 249 [15] CA Key Update Announcement 250 [16] Certificate Announcement 251 [17] Revocation Announcement 252 [18] CRL Announcement 254 CMP Announcement messages do not require any CMP response. However, 255 the recipient MUST acknowledge receipt with a HTTP response having an 256 appropriate status code and an empty body. When not receiving such 257 response it MUST be assumed that the delivery was not successful and 258 if applicable the sending side MAY retry sending the Announcement 259 after waiting for an appropriate time span. 261 If the announced issue was successfully stored in a database or was 262 already present, the answer MUST be an HTTP response with a "201 263 Created" status code and empty message body. 265 In case the announced information was only accepted for further 266 processing, the status code of the returned HTTP response MAY also be 267 "202 Accepted". After an appropriate delay, the sender may then try 268 to send the Announcement again and may repeat this until it receives 269 a confirmation that it had been successfully processed. The 270 appropriate duration of the delay and the option to increase it 271 between consecutive attempts should be carefully considered. 273 A receiver MUST answer with a suitable 4xx or 5xx HTTP error code 274 when a problem occurs. 276 3.8. HTTP Considerations 278 While all defined features of the HTTP protocol are available to 279 implementations, they SHOULD keep the protocol utilization as simple 280 as possible. E.g. there is no benefit in using chunked Transfer- 281 Encoding as the length of an ASN.1 sequence is know when starting to 282 send it. 284 There is no need for the clients to send an "Expect" request-header 285 field with the "100-continue" expectation and wait for a "100 286 Continue" status as described in chapter 8.2.3 of [RFC2616]. The CMP 287 payload sent by a client is relatively small, so having extra 288 messages exchanged is more inefficient as the server will anyway only 289 seldom reject a message without evaluating the body. 291 4. Implementation Considerations 293 Implementors should be aware that implementations might exist that 294 use a different approach for transferring CMP over HTTP because this 295 document has been under development for more than a decade. Further, 296 implementations based on earlier drafts of this document might use an 297 unregistered "application/pkixcmp-poll" MIME type. 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 transfer 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]. Compliant implementations MUST 339 support TLS with the option to authenticate both server and 340 client. 342 6. IANA Considerations 344 The IANA has already registered the MIME media type "application/ 345 pkixcmp" for identifying CMP sequences due to an request made in 346 connection with [RFC2510]. 348 No further action by the IANA is necessary for this document or any 349 anticipated updates. 351 7. Acknowledgments 353 Amit Kapoor and Ronald Tschlaer were the original authors of this 354 document and their version focused on the so-called "TCP-Based 355 Management Protocol", which has been removed from this document. 356 Their contact data as originally stated by them is as follows: 358 Amit Kapoor 359 Certicom 360 25801 Industrial Blvd 361 Hayward, CA 362 US 363 Email: amit@trustpoint.com 365 Ronald Tschalaer 366 Certicom 367 25801 Industrial Blvd 368 Hayward, CA 369 US 370 Email: ronald@trustpoint.com 372 The authors gratefully acknowledge the contributions of various 373 members of the IETF PKIX Working Group and the ICSA CA-talk mailing 374 list (a list solely devoted to discussing CMP interoperability 375 efforts). 377 By providing ideas, giving hints and doing invaluable review work, 378 the following alphabetically listed individuals have significantly 379 contributed to this document: 381 Tomas Gustavsson, Primekey 382 Peter Gutmann, University of Auckland 383 Wolf-Dietrich Moeller, Nokia Siemens Networks 385 8. References 387 8.1. Normative References 389 [ITU.X690.1994] 390 International Telecommunications Union, "Information 391 Technology - ASN.1 encoding rules: Specification of Basic 392 Encoding Rules (BER), Canonical Encoding Rules (CER) and 393 Distinguished Encoding Rules (DER)", ITU-T Recommendation 394 X.690, 1994. 396 [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext 397 Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. 399 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 400 Requirement Levels", BCP 14, RFC 2119, March 1997. 402 [RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key 403 Infrastructure Certificate Management Protocols", 404 RFC 2510, March 1999. 406 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 407 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 408 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 410 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 411 Resource Identifier (URI): Generic Syntax", STD 66, 412 RFC 3986, January 2005. 414 [RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen, 415 "Internet X.509 Public Key Infrastructure Certificate 416 Management Protocol (CMP)", RFC 4210, September 2005. 418 8.2. Informative References 420 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 422 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 423 Internet Protocol", RFC 4301, December 2005. 425 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 426 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 428 Authors' Addresses 430 Tomi Kause 431 Tectia Corporation 432 Kumpulantie 3 433 Helsinki 00520 434 Finland 436 Email: toka@tectia.com 438 Martin Peylo 439 Nokia Siemens Networks 440 Linnoitustie 6 441 Espoo 02600 442 Finland 444 Email: martin.peylo@nsn.com