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'PKCS10') (Obsoleted by RFC 2986) ** Obsolete normative reference: RFC 2459 (Obsoleted by RFC 3280) Summary: 9 errors (**), 0 flaws (~~), 12 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET DRAFT Xiaoyi Liu 2 draft-nourse-scep-05.txt Cheryl Madson 3 expires 11 March 2002 David McGrew 4 Andrew Nourse 5 Cisco Systems 7 Category: Informational 11 September 2001 9 Cisco Systems' Simple Certificate Enrollment Protocol(SCEP): 11 Status of this Memo 13 This document is an Internet-Draft and is NOT offered in 14 accordance with Section 10 of RFC2026, and the author does not 15 provide the IETF with any rights other than to publish as an 16 Internet-Draft 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as 21 Internet-Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six 24 months and may be updated, replaced, or obsoleted by other 25 documents at any time. It is inappropriate to use Internet- 26 Drafts as reference material or to cite them other than as 27 "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This memo provides information for the Internet community. This memo 36 does not specify an Internet standard of any kind. Distribution of 37 this memo is unlimited. 39 Abstract 41 This document specifies the Cisco Simple Certificate Enrollment 42 Protocol, a PKI communication protocol which leverages existing 43 technology by using PKCS#7 and PKCS#10. SCEP is the evolution of the 44 enrollment protocol developed by Verisign, Inc. for Cisco Systems, Inc. 45 It now enjoys wide support in both client and CA implementations. 47 Table of Contents 49 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 2 50 2. The Goal of SCEP . . . . . . . . . . . . . . . . . . . . . 3 51 2.1 SCEP Entity types . . . . . . . . . . . . . . . . . . . . 3 52 2.2 SCEP Operations Overview . . . . . . . . . . . . . . . . . 7 53 2.3 PKI Operation Transactional Behavior . . . . . . . . . . . 10 54 2.4 Security . . . . . . . . . . . . . . . . . . . . . . . . . 12 55 3. Transport Protocol . . . . . . . . . . . . . . . . . . . . 13 56 4. Secure Transportation: PKCS #7 . . . . . . . . . . . . . . 14 57 4.1 SCEP Message Format . . . . . . . . . . . . . . . . . . . 14 58 4.2 Signed Transaction Attributes . . . . . . . . . . . . . . 15 59 5. SCEP Transaction Specification . . . . . . . . . . . . . . 16 60 6. Security Considerations . . . . . . . . . . . . . . . . . 33 61 7. Intellectual Propoerty . . . . . . . . . . . . . . . . . . 33 62 8. References . . . . . . . . . . . . . . . . . . . . . . . . 33 63 Appendix A. Cisco End Entity Subject Name Definition . . . . . 34 64 Appendix B. IPSEC Client Enrollment Certificate Request . . . . 35 65 Appendix C. Private OID Definitions . . . . . . . . . . . . . 36 66 Appendix D. Obtaining CRL by LDAP Query . . . . . . . . . . . . 36 67 Appendix E. SCEP State Transitions . . . . . . . . . . . . . . 37 68 Appendix F. Author Contact Information. . . . . . . . . . . . . 40 69 Appendix G. Copyright Section . . . . . . . . . . . . . . . . . 40 71 Section 1. Introduction 73 Public key technology is becoming more widely deployed and is becoming 74 the basis for standards based security, such as the Internet Engineering 75 Task Force's IPSEC and IKE protocols. With the use of public key 76 certificates in network security protocols comes the need for a 77 certificate management protocol that Public Key Infrastructure (PKI) 78 clients and Certificate Authority servers can use to support certificate 79 life cycle operations such as certificate enrollment and revocation, and 80 certificate and CRL access. 82 In the following, Section 2 gives an overview of the PKI operations, and 83 Section 2.4 describes the security goals of the protocol and the 84 mechanisms used to achieve them. The transport protocol and the 85 security protocol PKCS#7 are described at Section 3 and Section 4, 86 respectively. The last section, Section 5, specifies each PKI operation 87 in terms of the message formats and the data structures of each 88 operation. 90 The appendices provide detailed specifications and examples. End entity 91 subject names are specified in Appendix A, attribute OIDs are specified 92 in Appendix C , and the SCEP state transitions are described in Appendix 93 E. An example of a certificate enrollment request is provided in 94 Appendix B, and an example LDAP query URL encoding is provided in 95 Appendix D. 97 The authors would like to thank Peter William of ValiCert, Inc. 98 (formerly of Verisign, Inc) and Alex Deacon of Verisign, Inc. and 99 Christopher Welles of IRE, Inc. for their contributions to this protocol 100 and to this document. 102 2.0 The Goal of SCEP 103 The goal of SCEP is to support the secure issuance of certificates to 104 network devices in a scalable manner, using existing technology whenever 105 possible. The protocol supports the following operations: 107 CA and RA public key distribution 108 Certificate enrollment 109 Certificate revocation 110 Certificate query 111 CRL query 113 Certificate and CRL access can be achieved by using the LDAP protocol 114 (as specified in Appendix D), or by using the query messages defined in 115 SCEP. The use of HTTP certificate and CRL access, and the support of 116 CDP as specified in RFC2459, will be specified in a future version of 117 this document. In Section 2.1, we first define PKI entity types as well 118 as the properties of each entity type. In Section 2.2, the PKI 119 operations are described at functional level. Section 2.3 describes the 120 transaction behavior of each PKI operations. The complete PKI messages 121 are covered in Section 5. 123 2.1 SCEP Entity types 125 The entity types defined in SCEP are the end entity type (i.e., IPSEC 126 clients), the Certificate Authority (CA) entity type, and the 127 Registration Authority entity type (RA). An end entity is sometimes 128 called a "SCEP client" in the following. 130 2.1.1 End Entities 132 An end entity is an entity whose name is defined in a certificate 133 subject name field and optionally, in SubjectAltName, a X.509 134 certificate V3 extension. As an end entity, a SCEP client is identified 135 by a subject name consisting of the following naming attributes: 137 Fully qualified domain name, for example, router.cisco.com 138 IP address, or 139 Serial number. 141 In the paragraph above , the fully qualified domain name is required for 142 each SCEP client, the IP address and the serial number are optional name 143 attributes. In the certificate enrollment request, the PKCS#10 subject 144 field contains the required and optional name attributes. Based on the 145 PKCS#10 subject name information, the certificate issued to the SCEP 146 client must have the same name attributes set both in the subjectName 147 field and in the SubjectAltName extension. 149 It is important to note that a client named as Alice.cisco.com is 150 different than a client named as Alice.cisco.com plus the IP address 151 name attribute 171.69.1.129. From CA point of view, the Distinguished 152 names assigned in these two cases are distinct names. 154 Entity names which are specified as in the IPSEC profile (i.e., FQDN, IP 155 address and User FQDN) must be presented in certificate's SubjectAltName 156 extension. Multiple IPSEC entity names, (if any) are encoded as multiple 157 values of a single SubjectAltName extension. The CA has the authority 158 to assign a distinguished name to an end entity. The assigned DN should 159 contain the SCEP client names as the relative DN. 161 The attribute identifiers and an example of SCEP client subject name are 162 specified in Appendix A. Appendix B has an example from Cisco VPN Client 163 enrollment request. 165 2.1.1.1 Local Key/Certificate/CRL Storage and Certificate-name uniqueness 167 An end entity is required to generate asymmetric key pairs and to 168 provide storage to store its private keys. If the end entity does not 169 have enough permanent memory to save its certificate, the end entity 170 should be able to query its own certificate from the CA, once the 171 certificate has been issued. The public key pairs can be generated with 172 a specific key usage. The key usage are conveyed to the CA through the 173 certificate enrollment request. All current SCEP client implementations 174 expect that there will be only one pair of keys for a given subject name 175 and key usage combination and CA, at any time. This property is called 176 the certificate-name uniqueness property, and it implies that a CA that 177 implements SCEP will enforce the unique mapping between a SCEP client 178 subject name and its key pairs with a given key usage. At any time, if 179 the subject name is changed, or if the key is updated, the existing 180 certificate would have to be revoked before a new one could be issued. 182 It is desirable that the CA enforce certificate-name uniqueness, but 183 it is not mandatory. However a CA that does not enforce uniqueness 184 must provide some other mechanism to prevent the re-transmission of an 185 enrollment request by a SCEP client from creating a second certificate 186 or certificate request, nor can the second request merely be rejected. 187 If a client times out from polling for a pending request it can 188 resynchronize by reissuing the original request with the original 189 subject name and transaction ID. This must return the status of the 190 original transaction, including the certificate if it was granted. 191 It must not create a new transaction unless the original cert has been 192 revoked, or the transaction arrives more than halfway through the 193 validity time of the original certificate. 195 An enrollment request that occurs more than halfway through the validity 196 time of an existing certificate for the same subject name and key usage 197 MAY be interpreted as a renewal request and accepted regardless of the 198 duplication of subject name. Certificate renewal can be done this way. 200 2.1.1.2 End entity authentication 202 As with every protocol that uses public-key cryptography, the 203 association between the public keys used in the protocol and the 204 identities with which they are associated must be authenticated in a 205 cryptographically secure manner. This requirement is needed to 206 prevent a "man in the middle" attack, in which an adversary that can 207 manipulate the data as it travels between the protocol participants 208 can subvert the security of the protocol. To satisfy this 209 requirement, SCEP provides two authentication methods: manual 210 authentication, and authentication based on pre-shared secret. In the 211 manual mode, the end entity submitting the request is required to wait 212 until its identity can be verified by the CA operator using any 213 reliable out-of-band method. To prevent a "man-in-the-middle" attack, 214 an MD5 `fingerprint' generated on the PKCS#10 (before PKCS #7 215 enveloping and signing) must be compared out-of-band between the server 216 and the end entity. SCEP clients and CAs (or RAs, if appropriate) 217 must display this fingerprint to a user to enable this verification, 218 if manual mode is used. Failing to provide this information leaves 219 the protocol vulnerable to attack by sophisticated adversaries. When 220 utilizing a pre-shared secret scheme, the server should distribute a 221 shared secret to the end entity which can uniquely associate the 222 enrollment request with the given end entity. The distribution of the 223 secret must be private: only the end entity should know this 224 secret. The actual binding mechanism between the end entity and the 225 secret is subject to the server policy and implementation. When 226 creating enrollment request, the end entity is asked to provide a 227 challenge password. When using the pre-shared secret scheme, the end 228 entity must type in the re-distributed secret as the password. In the 229 manual authentication case, the challenge password is also required 230 since the server may challenge an end entity with the password before 231 any certificate can be revoked. Later on, this challenge password 232 will be included as a PKCS#10 attribute, and is sent to the server as 233 encrypted data. The PKCS#7 envelope protects the privacy of the 234 challenge password with DES encryption. 236 2.1.1.3 Self-Signed Certificates 238 In this protocol, the communication between the end entity and the 239 certificate authority is secured by using PKCS#7 as the messaging 240 protocol. PKCS#7, however, is a protocol which assumes the communicating 241 entities already possess the peer's certificates and requires both 242 parties use the issuer names and issuer assigned certificate serial 243 numbers to identify the certificate in order to verify the signature and 244 decrypt the message. When using PKCS#7 as a secure protocol for SCEP 245 transactions this assumption may not be valid. To solve this problem, 246 an end entity generates a self-signed certificate for its own public 247 key. In this self-signed certificate, the issuer name is the end entity 248 subject name (the same name later used in the PKCS#10). During the 249 certificate enrollment, the end entity will first post itself as the 250 signing authority by attaching the self-signed certificate to the signed 251 certificate request. When the Certificate Authority makes the envelope 252 on the issued certificate using the public key included in the 253 self-signed certificate, it should use the same issuer name and serial 254 number as conveyed in the self-signed certificate to inform the end 255 entity on which private key should be used to open the envelope. 257 Note that when a client enrolls for separate encryption and signature 258 certificates, it may use the signature certificate to sign both 259 requests, and then expect its signature key to be used to encrypt 260 both responses. In any case, the recipientinfo on the envelope should 261 reflect the key used to encrypt the request. 263 2.1.2 Certificate Authority 265 A Certificate Authority(CA) is an entity whose name is defined in the 266 certificate issuer name field. Before any PKI operations can begin, 267 the CA generates its own public key pair and creates a self-signed CA 268 certificate. Associated with the CA certificate is a fingerprint 269 which will be used by the end entity to authenticate the received CA 270 certificate. The fingerprint is created by calculating a MD5 hash on 271 the whole CA certificate. Before any end entity can start its 272 enrollment, this root certificate has to be configured at the entity 273 side securely. For IPSEC clients, the client certificates must have 274 SubjectAltName extension. To utilize LDAP as a CRL query protocol, 275 the certificates must have CRL Distribution Point. Key usage is 276 optional. Without key usage, the public key is assumed as a general 277 purpose public key and it can be used for all the purposes. 279 A Certificate Authority may enforce certain name policy. When using 280 X.500 directory name as the subject name, all the name attributes 281 specified in the PKCS#10 request should be included as Relative DN. All 282 the name attributes as defined in RFC2459 should be specified in the 283 SubjectAltName. An example is provided in Appendix A. 285 If there is no LDAP query protocol support, the Certificate Authority 286 should answer certificate and CRL queries, and to this end it should be 287 online all the time. 289 The updating of the CA's public key is not addressed within the SCEP 290 protocol. An SCEP client can remove its copy of a CA's public key and 291 re-enroll under the CA's new public key. 293 2.1.3 Registration Authorities 295 In the environment where a RA is present, an end entity performs 296 enrollment through the RA. In order to setup a secure channel with RA 297 using PKCS#7, the RA certificate(s) have to be obtained by the client 298 in addition to the CA certificate(s). 300 In the following, the CA and RA are specified as one entity in the 301 context of PKI operation definitions. 303 2.1.4 Trusted Root Store 305 To support interoperability between IPSEC peers whose certificates are 306 issued by different CA, SCEP allows the users to configure multiple 307 trusted roots. A root is a trusted root when its certificate has been 308 configured as such in the client. An SCEP client that supports multiple 309 roots must associate with each root the information needed to query a 310 CRL from each root. 312 Once a trusted root is configured in the client, the client can verify 313 the signatures of the certificates issued by the given root. 315 2.2 SCEP Operations Overview 317 In this section, we give a high level overview of the PKI operations as 318 defined in SCEP. 320 2.2.1 End Entity Initialization 322 The end entity initialization includes the key pair generation and the 323 configuring of the required information to communicate with the 324 certificate authority. 326 2.2.1.1 Key Pair Generation 328 Before an end entity can start PKI transaction, it first generates 329 asymmetric key pairs, using the selected algorithm (the RSA algorithm is 330 required in SCEP, and is the only algorithm in current implementations). 332 An end entity can create one or more asymmetric key pairs, for different 333 key usage. The key pairs can be created for encryption only, signing 334 only, or for all purposes. For the same key usage, there can be only 335 one key pair at any time. 337 The key pairs are saved by the client in NVRAM or other non-volatile 338 media. The identification of a key pair is based on the FQDN assigned to 339 the client and the selected key usage. Every time a new key pair is 340 generated to replace the old key pair, the existing certificates have to 341 be revoked from the CA and a new enrollment has to be completed. 343 2.2.1.2 Required Information 345 An end entity is required to have the following information configured 346 before starting any PKI operations: 348 1. the certificate authority IP address or fully qualified domain name, 349 2. the certificate authority HTTP CGI script path, and 350 the HTTP proxy information in case there is no direct Internet 351 connection to the server, 352 3. the CRL query URL, if the CRL is to be obtained by from a directory 353 server by means of LDAP. 355 2.2.2 CA/RA Certificate Distribution 357 Before any PKI operation can be started, the end entity needs to get 358 the CA/RA certificates. At this time, since no public key has been 359 exchanged between the end entity and the CA/RA, the message to get the 360 CA/RA certificate can not be secured using PKCS#7 protocol. Instead, the 361 CA/RA certificate distribution is implemented as a clear HTTP Get 362 operation. After the end entity gets the CA certificate, it has to 363 authenticate the CA certificate by comparing the finger print with the 364 CA/RA operator. Since the RA certificates are signed by the CA, there is 365 no need to authenticate the RA certificates. 367 This operation is defined as a transaction consisting of one HTTP Get 368 message and one HTTP Response message: 370 END ENTITY CA SERVER 371 Get CA/RA Cert: HTTP Get message 372 -----------------------------> 373 CA/RA Cert download: HTTP Response message 374 <--------------------------------------- 375 Compute finger print and 376 call CA operator. 377 Receive call and check finger print 379 If an RA is in use, a degenerated PKCS#7 with a certificate chain 380 consisting of both RA and CA certificates is sent back to the end 381 entity. Otherwise the CA certificate is directly sent back as the 382 HTTP response payload. 384 2.2.3 Certificate Enrollment 386 An end entity starts an enrollment transaction by creating a certificate 387 request using PKCS#10 and send it to the CA/RA enveloped using the 388 PKCS#7. After the CA/RA receives the request, it will either 389 automatically approve the request and send the certificate back, or it 390 will require the end entity to wait until the operator can manually 391 authenticate the identity of the requesting end entity. Two attributes 392 (defined in PKCS#6) are included in the PKCS#10 certificate request - a 393 Challenge Password attribute and an optional ExtensionReq attribute 394 which will be a sequence of extensions the end entity would like to be 395 included in its V3 certificate extensions. The Challenge Password is 396 used for revocation and may be used (at the option of the CA/RA) 397 additionally as a one-time password for automatic enrollment. 399 In the automatic mode, the transaction consists of one PKCSReq PKI 400 Message, and one CertRep PKI message. In the manual mode, the end entity 401 enters into polling mode by periodically sending GetCertInitial PKI 402 message to the server, until the server operator completes the manual 403 authentication, after which the CA will respond to GetCertInitial by 404 returning the issued certificate. 406 The transaction in automatic mode: 408 END ENTITY CA SERVER 410 PKCSReq: PKI cert. enrollment msg 411 --------------------------------> CertRep: pkiStatus = SUCCESS 412 certificate 413 attached 414 <------------------------------ 415 Receive issued certificate. 417 The transaction in manual mode: 419 END ENTITY CA SERVER 420 PKCSReq: PKI cert. enrollment msg 421 --------------------------------> CertRep: pkiStatus = PENDING 422 <------------------------------ 423 GetCertInitial: polling msg 424 --------------------------------> CertRep: pkiStatus = PENDING 425 <------------------------------ 426 ................. CertRep: pkiStatus = SUCCESS 430 certificate 431 attached 432 <------------------------------ 433 Receive issued certificate. 435 2.2.4 End Entity Certificate Revocation 437 An end entity should be able to revoke its own certificate. Currently 438 the revocation is implemented as a manual process. In order to revoke a 439 certificate, the end entity make a phone call to the CA server 440 operator. The operator will come back asking the ChallangePassword 441 (which has been send to the server as an attribute of the PKCS#10 442 certificate request). If the ChallangePassword matches, the certificate 443 is revoked. The reason of the revocation is documented by CA/RA. 445 2.2.5 Certificate Access 447 There are two methods to query certificates. The first method is to use 448 LDAP as a query protocol. Using LDAP to query assumes the client 449 understand the LDAP scheme supported by the CA. The SCEP client assumes 450 that the subject DN name in the certificate is used as URL to query the 451 certificate. The standard attributes (userCertificate and caCertificate) 452 are used as filter. 454 For the environment where LDAP is not available, a certificate query 455 message is defined to retrieve the certificates from CA. 457 To query a certificate from the certificate authority, an end entity 458 sends a request consisting of the certificate's issuer name and the 459 serial number. This assumes that the end entity has saved the issuer 460 name and the serial number of the issued certificate from the previous 461 enrollment transaction. The transaction to query a certificate consists 462 of one GetCert PKI message and one CertRep PKI message: 464 END ENTITY CA SERVER 465 GetCert: PKI cert query msg 466 -------------------------------> CertRep: pkiStatus = SUCCESS 467 certificate 468 attached 469 <----------------------------- 470 Receive the certificate. 472 2.2.6 CRL Distribution 474 The CA/RA will not "push" the CRL to the end entities. The query of the 475 CRL can only be initialized by the end entity. 477 There are three methods to query CRL. 479 The CRL may be retrieved by a simple HTTP GET. If the CA supports this 480 method, it should encode the URL into a CRL Distribution Point extension 481 in the certificates it issues. Support for this method should be 482 incorporated in new and updated clients, but may not be in older 483 versions. 485 The second method is to query CRL using LDAP. This assumes the CA server 486 supports CRL LDAP publishing and issues the CRL Distribution Point in 487 the certificate. The CRL Distribution Point is encoded as a DN. Please 488 refer to Appendix D for the examples of CRL Distribution Point. 490 The third method is implemented for the CA which does not support LDAP 491 CRL publishing or does not implement the CRL Distribution Point. In this 492 case, a CRL query is composed by creating a message consists of the CA 493 issuer name and the CA's certificate serial number. This method is 494 deprecated because it does not scale well and requires the CA to be a 495 high-availability service. 497 The message is send to the CA in the same way as the other SCEP 498 requests: The transaction to query CRL consists of one GetCRL PKI 499 message and one CertRep PKI message which have no certificates but CRL. 501 END ENTITY CA SERVER 502 GetCRL: PKI CRL query msg 503 ----------------------------------> CertRep: CRL attached 504 <-------------------------------- 506 2.3 PKI Operation Transactional Behavior 508 As described before, a PKI operation is a transaction consisting of the 509 messages exchanged between an end entity and the CA/RA. This section 510 will specify the transaction behavior on both the end entity and the 511 certificate authority server. Because the protocol is basically a two 512 way communication protocol without a confirmation message from the 513 initiating side, state and state resynchronization rules have to be 514 defined, in case any error happens at either side. Before the state 515 transition can be defined, the notion of transaction identifier has to 516 be defined first. 518 2.3.1 Transaction Identifier 520 A transaction identifier is a string generated by the entity when 521 starting a transaction. Since all the PKI operations defined in this 522 protocol are initiated by the end entity, it is the responsibility of 523 the end entity to generate a unique string as the transaction 524 identifier. All the PKI messages exchanged for a given PKI operations 525 must carry the same transaction identifier. The transaction identifier 526 is generated as a MD5 hash on the public key value for which the 527 enrollment request is made. This allows the SCEP client to reuse the 528 same transaction identifier if it is reissuing a request for the same 529 certificate (i.e. a certificate with the same subject, issuer, and key). 530 The SCEP protocol requires that transaction identifiers be unique, so 531 that queries can be matched up with transactions. For this reason, in 532 those cases in which separate signing and encryption certificates are 533 issued to the same end entity, the keys must be different. 535 2.3.2 State Transitions in Certificate Enrollment 537 The end entity state transitions during enrollment operation is 538 indicated in the diagram below: 539 +-<------+ 540 | | 541 GetCertInitial triggered by timeout or 542 | | manual authentication 543 | | 544 [CERT-NONEXISTANT] ------> [CERT-REQ-PENDING] ---> [CERT-ISSUED] 545 | PKCSReq | CertRep with SUCCESS 546 | | 547 | | 548 +--------<-------------------+ 549 request rejected, timeout, or error 551 As described in the section 2.2.3, certificate enrollment starts at the 552 state CERT-NONEXISTANT. Sending PKCSReq changes the state to 553 CERT-REQ-PENDING. Receiving CertRep with SUCCESS status changes the 554 state to CERT-ISSUED. In the case the server sending back the response 555 with pending status, the end entity will keep polling certificate 556 response by sending GetCertInitial to the server, until either a CertRep 557 with SUCCESS status is received, or the maximum polling number has been 558 exceeded. 560 If an error or timeout occurs in the CERT-REQ-PENDING state, the end 561 entity will transition to the CERT-NONEXISTANT state. 563 The client administrator will, eventually, start up another enrollment 564 request. It is important to note that, as long as the end entity does 565 not change its subject name or keys, the same transaction id will be 566 used in the "new" transaction. This is important because based on this 567 transaction id, the certificate authority server can recognize this as 568 an existing transaction instead of a new one. 570 2.3.3 Transaction Behavior of Certificate/CRL Access 572 There is no state maintained during certificate access and CRL access 573 transaction. When using the certificate query and CRL query messages 574 defined in this protocol, the transaction identifier is still required 575 so that the end entity can match the response message with the 576 upstanding request message. When using LDAP to query the certificate and 577 the CRL, the behavior is specified by the LDAP protocol. 579 2.4 Security 581 The security goals of SCEP are that no adversary can: 583 o subvert the public key/identity binding from that intended, 584 o discover the identity information in the enrollment requests and 585 issued certificates, 586 o cause the revocation of certificates with any non-negligible 587 probability. 589 Here an adversary is any entity other than the end entity and the CA 590 (and optionally the RA) participating in the protocol that is 591 computationally limited, but that can manipulate data during 592 transmission (that is, a man-in-the-middle). The precise meaning of 593 'computationally limited' depends on the implementer's choice of 594 cryptographic hash functions and ciphers. The required algorithms are 595 RSA, DES, and MD5. 597 The first and second goals are met through the use of PKCS#7 and PKCS#10 598 encryption and digital signatures using authenticated public keys. The 599 CA's public key is authenticated via the checking of the CA fingerprint, 600 as specified in Section 2.1.2, and the SCEP client's public key is 601 authenticated through the manual authentication or pre-shared secret 602 authentication, as specified in Section 2.1.1.2. The third goal is met 603 through the use of a Challenge Password for revocation, that is chosen 604 by the SCEP client and communicated to the CA protected by the PKCS#7 605 encryption, as specified in Section 2.2.4. 607 The motivation of the first security goal is straightforward. The 608 motivation for the second security goal is to protect the identity 609 information in the enrollment requests and certificates. For example, 610 two IPSEC hosts behind a firewall may need to exchange certificates, and 611 may need to enroll certificates with a CA that is outside of a firewall. 612 Most networks with firewalls seek to prevent IP addresses and DNS 613 information from the trusted network leaving that network. The second 614 goal enables the hosts in this example to enroll with a CA outside the 615 firewall without revealing this information. The motivation for the 616 third security goal is to protect the SCEP clients from denial of 617 service attacks. 619 Section 3 Transport Protocol 621 In the SCEP protocol, HTTP is used as the transport protocol for the PKI 622 messages. 624 3.1 HTTP "GET" Message Format 626 In the PKI protocol, CA/RA certificates are send to the end entity in 627 clear, whereas the end entity certificates are send out using the PKCS#7 628 secure protocol. This results in two types of GET operations. The type 629 of GET operation is specified by augmenting the GET message with 630 OPERATION and MESSAGE parameters in the Request-URL. OPERATION 631 identifies the type of GET operation, and MESSAGE is actually the PKI 632 message encoded as a text string. 634 The following is the syntax definition of a HTTP GET message send from 635 an end entity to a certificate authority server: 637 Request = "GET " CGI-PATH CGI-PROG "?operation=" OPERATION "&message=" MESSAGE 638 where: 639 CGI-PATH defines the actual CGI path to invoke the CGI program which 640 parses the request. 641 | CGI-PROG is set to be the string "pkiclient.exe". This is intended 642 | to be the program that the CA will use to handle the SCEP transactions, 643 | though the CA may ignore CGI-PROG and use only the CGI-PATH. 644 OPERATION is set to be the string "PKIOperation" when the GET message 645 carries a PKI message to request certificates or CRL; OPERATION is set 646 | to be the string "GetCACert" or "GetCACertChain" when the GET operation 647 | is used to get CA/RA certificate or the CA Cert chain (respectively). 648 When OPERATION is "PKIOperation", MESSAGE is a base64-encoded PKI 649 message 650 | when OPERATION is "GetCACert" or "GetCACertChain", MESSAGE is a string 651 | which represents the certificate authority issuer identifier. 653 For example. An end entity may submit a message via HTTP to the server 654 as follows: 656 GET /cgi-bin/pkiclient.exe?operation=PKIOperation&message=MIAGCSqGSIb3D 657 QEHA6CAMIACAQAxgDCBzAIBADB2MGIxETAPBgNVBAcTCE ......AAAAAA== 659 3.2 Response Message Format 661 For each GET operation, the CA/RA server will return a MIME object via 662 HTTP. For a GET operation with PKIOperation as its type, the response is 663 tagged as having a Content Type of application/x-pki-message. The body 664 of this message is a BER encoded binary PKI message. The following is an 665 example of the response: 667 "Content-Type:application/x-pki-message\n\n" 669 In the case of GET operation with a type of GetCACert, the MIME content 670 type returned will depend on whether or not an RA is in use. If there 671 is no RA, only the CA certificate is send back in the response, and the 672 response has the content type tagged as application/x-x509-ca-cert. the 673 body of the response is a DER encoded binary X.509 certificate. For 674 example: 676 "Content-Type:application/x-x509-ca-cert\n\n" 678 If there is an RA, the RA certificates are send back together with the 679 CA certificates, a certificate-only PKCS#7 SignedData is send back in 680 the response where the SignerInfo is empty. Section 5 has the detailed 681 definition of the message format in this case. The content type is 682 application/x-x509-ca-ra-cert. 684 Section 4 Secure Transportation: PKCS#7 686 PKCS#7 is a general enveloping mechanism that enables both signed and 687 encrypted transmission of arbitrary data. It is widely implemented and 688 included in the RSA tool kit. 690 In this section, the general PKCS#7 enveloped PKI message format is 691 specified. The complete PKCS#7 message format for each PKI transaction 692 will be covered in Section 5. 694 4.1 SCEP Message Format 696 As a transaction message, a SCEP message has a set of transaction 697 specific attributes and an information portion. Employing PKCS#7 698 protocol, the transaction specific attributes are encoded as a set of 699 authenticated attributes of the SignedData. The information portion will 700 first be encrypted to become Enveloped Data, and then the digest of the 701 enveloped information portion is included as one of the message digest 702 attributes and being signed together with the other transaction specific 703 attributes. 705 By applying both enveloping and signing transformations, a SCEP message 706 is protected both for the integrity of its end-end-transition 707 information and the confidentiality of its information portion. The 708 advantage of this technique over the conventional transaction message 709 format is that, the signed transaction type information and the status 710 of the transaction can be determined prior to invoke security handling 711 procedures specific to the information portion being processed. 713 The following is an example of a SCEP message with its enveloped and 714 signed data portion represented by pkcsPKISigned and 715 pkcsPKIEnveloped. The out-most of any PKI message is a blob of 716 ContentInfo, with its content type set to SignedData and the actual 717 signed data as the content. 719 pkiMessage ContentInfo ::= { 720 contentType {pkcs-7 signedData(2)} 721 content pkcsPKISigned 722 } 723 pkcsPKISigned SignedData ::= { 724 version 1 725 digestAlgorithm { iso(1) member-body(2) US(840) rsadsi(113549) 726 digestAlgorithm(2) 5} 727 contentInfo { 728 contentType {pkcs-7 1} -- data content identifier 729 content pkcsPKIEnvelope -- enveloped information portion 730 } 731 certificates -- signer certificate chain 732 signerInfo -- including signed transaction info and the digest 733 -- of the enveloped information portion as the 734 -- authenticated attributes 735 } 736 pkcsPKIEnveloped EnvelopedData ::= { 737 version 0 738 recipientInfos -- information required to open the envelop 739 encryptedContentInfo { 740 contentType {pkcs-7 1} -- data content identifier 741 contentEncryptionAlgorithm 742 encryptedContent -- encrypted information portion 743 } 744 } 746 4.2 Signed Transaction Attributes 748 The following transaction attributes are encoded as authenticated 749 attributes. Please refer to Appendix B for the OID definitions. 751 transactionID PrintableString -- Decimal value as a string 752 messageType PrintableString -- Decimal value as a string 753 pkiStatus PrintableString -- Decimal value as a string 754 failinfo PrintableString -- Decimal value as a string 755 senderNonce Octet String 756 recipientNonce Octet String 758 where: 760 The transactionID is an attribute which uniquely identify a 761 transaction. This attribute is required in all PKI messages. 763 The messageType attribute specify the type of operation performed by the 764 transaction. This attribute is required in all PKI 765 messages. Currently, the following message types are defined: 767 PKCSReq (19) -- Permits use of PKCS#10 certificate request 768 CertRep (3) -- Response to certificate or CRL request 769 GetCertInitial (20) -- Certificate polling in manual enrollment 770 GetCert (21) -- Retrieve a certificate 771 GetCRL (22) -- Retrieve a CRL 773 All response message will include transaction status information which 774 is defined as pkiStatus attribute: 776 SUCCESS (0) -- request granted 777 FAILURE (2) -- request rejected 778 PENDING (3) -- request pending for manual approval. 780 If the status in the response is FAILURE, the failinfo attribute will 781 contain one of the following failure reasons: 783 badAlg (0) -- Unrecognized or unsupported algorithm ident 784 badMessageCheck (1) -- integrity check failed 785 badRequest (2) -- transaction not permitted or supported 786 badTime (3) -- Message time field was not sufficiently close 787 to the system time 788 badCertId (4) -- No certificate could be identified matching 789 the provided criteria 791 The attributes of senderNonce and recipientNonce are the 16 byte 792 random numbers generated for each transaction to prevent the replay 793 attack. 795 When an end entity sends a PKI message to the server, a senderNonce is 796 included in the message. After the server processes the request, it will 797 send back the end entity senderNonce as the recipientNonce and generates 798 another nonce as the senderNonce in the response message. Because the 799 proposed pki protocol is a two-way communication protocol, it is clear 800 that the nonce can only be used by the end entity to prevent the 801 replay. The server has to employ extra state related information to 802 prevent a replay attack. 804 Section 5. SCEP Transaction Specification 806 In this section each SCEP transaction is specified in terms of the 807 complete messages exchanged during the transaction. 809 5.1 Certificate Enrollment 811 The certificate enrollment transaction consists of one PKCSReq message 812 send to the certificate authority from an end entity, and one CertRep 813 message send back from the server. The pkiStatus returned in the 814 response message is either SUCCESS, or FAILURE, or PENDING. The 815 information portion of a PKCSReq message is a PKCS#10 certificate 816 request, which contains the subject Distinguished Name, the subject 817 public key, and two attributes, a ChallangePassword attribute to be used 818 for revocation, and an optional ExtensionReq attribute which will be a 819 sequence of extensions the end entity expects to be included in its V3 820 certificate extensions. One of the extension attribute specifies the key 821 usage. The pkiStatus is set to SUCCESS when the certificate is send 822 back in CertRep; the pkiStatus is set to FAILURE when the certificate 823 request is rejected; the pkiStatus is set to PENDING when the server has 824 decided to manually authenticate the end entity. The messages exchanged 825 in the manual authentication mode is further specified in Section 5.2. 827 Precondition: 828 Both the end entity and the certificate authority have completed their 829 initialization process. The end entity has already been configured 830 with the CA/RA certificate. 832 Postcondition: 833 Either the certificate is received by the end entity, or the end 834 entity is notified to do the manual authentication, or the request 835 is rejected. 837 5.1.1 PKCSReq Message Format 839 A PKCSReq message is created by following the steps defined below: 841 1. Create a PKCS#10 certificate request which is signed by the end 842 entity's private key, corresponding to the public key included in 843 the PKCS#10 certificate request. This constitutes the information 844 portion of PKCSReq. 846 2. Encrypt the PKCS#10 certificate request using a randomly generated 847 content-encryption key. This content-encryption key is then 848 encrypted by the CA's* public key and included in the recipientInfo. 849 This step completes the "envelope" for the PKCS#10 certificate 850 request. 852 3. Generate a unique string as the transaction id. 854 4. Generate a 16 byte random number as senderNonce. 856 5. Generate message digest on the enveloped PKCS#10 certificate request 857 using the selected digest algorithm. 859 6. Create SignedData by adding the end entity's self-signed certificate 860 as the signer's public key certificate. Include the message type, 861 transaction id, the senderNonce and the message digest as the 862 authenticated attributes and sign the attributes using the end 863 entity's private key. This completes the SignedData. 865 7. The SignedData is prepended with the ContenInfo blob which indicates 866 a SignedData object. This final step completes the create of a 867 complete PKCSReq PKI message. 869 In the following, the PKCSReq message is defined following the ASN.1 870 notation. 872 For readability, the values of a field is either represented by a quoted 873 string which specifies the intended value, or a constant when the value 874 is known. 876 -- PKCSReq information portion 877 pkcsCertReq CertificationRequest ::= { -- PKCS#10 878 version 0 879 subject "the end entity's subject name" 880 subjectPublicKeyInfo { 881 algorithm {pkcs-1 1} -- rsa encryption 882 subjectPublicKey "DER encoding of the end entity's public key" 883 } 884 attributes { 885 challengePassword {{pkcs-9 7} "password string" } 886 extensions 887 } 888 signatureAlgorithm {pkcs-1 4} -- MD5WithRSAEncryption 889 signature "bit string which is created by signing inner content 890 of the defined pkcsCertReq using end entity's private 891 key, corresponding to the public key included in 892 subjectPublicKeyInfo." 893 } 894 -- Enveloped information portion 895 pkcsCertReqEnvelope EnvelopeData ::= { -- PKCS#7 896 version 0 897 recipientInfo { 898 version 0 899 issuerAndSerialNumber { 900 issuer "the CA issuer name" 901 serialNumber "the CA certificate serial number" 902 } 903 keyEncryptionAlgorithm {pkcs-1 1} -- rsa encryption 904 encryptedKey "content-encryption key 905 encrypted by CA public key" 906 } 907 encryptedContentInfo { 908 contentType {pkcs-7 1} -- data content 909 contentEncryptionAlgorithm "object identifier 910 for DES encryption" 911 encryptedContent "encrypted pkcsCertReq using the content- 912 encryption key" 913 } 914 } 915 -- Signed PKCSReq 916 pkcsCertReqSigned SignedData ::= { -- PKCS#7 917 version 1 918 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 919 digestAlgorithm(2) 5} 920 contentInfo { 921 contentType {pkcs-7 1} -- data content identifier 922 content pkcsCertReqEnvelope 923 } 924 certificate { -- the end entity's self-signed certificate 925 version 3 926 serialNumber "the transaction id associated with enrollment" 927 signature {pkcs-1 4} -- md5WithRSAEncryption 929 issuer " the end entity's subject name" 930 validity { 931 notBefore "a UTC time" 932 notAfter "a UTC time" 933 } 934 subject "the end entity's subject name" 935 subjectPublicKeyInfo { 936 algorithm {pkcs-1 1} 937 subjectPublicKey "DER encoding of end entity's public key" 938 } 939 signatureAlgorithm {pkcs-1 4} 940 signature "the signature generated by using the end entity's 941 private key corresponding to the public key in 942 this certificate." 943 } 944 signerInfo { 945 version 1 946 issuerAndSerialNumber { 947 issuer "the end entity's subject name" 948 serialNumber "the transaction id associated 949 with the enrollment" 950 } 951 digestAlgorithm {iso(0) member-body(2) US(840) rsadsi(113549) 952 digestAlgorithm(2) 5} 953 authenticateAttributes { 954 contentType {{pkcs-9 3} {pkcs-7 1}} 955 messageDigest {{pkcs-9 4} "an octet string"} 956 transaction-id {{id-attributes transId(7)} "printable 957 string"} 958 -- this transaction id will be used 959 -- together with the subject name as 960 -- the identifier of the end entity's key 961 -- pair during enrollment 962 messageType {{id-attributes messageType(2)} "PKCSReq"} 963 senderNonce {{id-attributes senderNonce(5)} 964 "a random number encoded as a string"} 965 } 966 digestEncryptionAlgorithm {pkcs-1 1} -- rsa encryption 967 encryptedDigest "encrypted digest of the authenticated 968 attributes using end entity's private key" 969 } 970 } 971 pkcsReq PKIMessage ::= { 972 contentType {pkcs-7 2} 973 content pkcsCertRepSigned 974 } 976 5.1.2 CertRep Message Format 978 The response to an SCEP enrollment request is a CertRep message. 980 5.1.2.1 PENDING Response 982 When the CA is configured to manually authenticate the end entity, 983 the CertRep is returned with the attribute pkiStatus set to PENDING. 984 The data portion for this message is null. Only the transaction 985 required attributes are sent back. 987 CertRepSigned SignedData ::= { -- PKCS#7 988 version 1 989 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 990 digestAlgorithm(2) 5} 991 contentInfo {contentType {pkcs-7 1} -- empty content 992 } 993 signerInfo { 994 version 1 995 issuerAndSerialNumber { 996 | issuer "name of CA that issued the CA [RA] cert" 997 | serialNumber "the serial number of the CA [RA] cert" 998 } 999 digestAlgorithm (iso(1) member-body(2) US(840) rsadsi(113549) 1000 digestAlgorithm(2) 5} 1001 authenticateAttributes { 1002 contentType {{pkcs-9 3} {pkcs-7 1}} 1003 messageDigest {{pkcs-9 4} NULL} 1004 messageType {{id-attribute messageType(0)} "CertRep"} 1005 transaction-id {{id-attributes transid(7)} "printablestring"} 1006 --- same transaction id used in PKCSReq 1007 pkiStatus {{id-attributes pkiStatus(3)} "PENDING"} 1008 recipientNonce {{id-attributes recipientNonce(6)}<16 bytes>} 1009 senderNonce {{id-attributes senderNonce(5)} <16 bytes>} 1010 } 1011 digestEncrytionAlgorithm {pkcs-1 1} 1012 encryptedDigest "encrypted message digest of the authenticated 1013 | attributes using the CA's [RA's] private key" 1014 } 1015 } 1016 CertRep PKIMessage ::= { 1017 contentType {pkcs-7 2} 1018 content CertRepSigned 1019 } 1021 5.1.2.2 Failure Response 1023 In this case, the CertRep sent back to the end entity is same as in 1024 the PENDING case, except that the pkiStatus attribute is set to FAILURE, 1025 and the failInfo attribute should be included: 1027 pkistatus {{id-attributes pkiStatus(3)} "FAILURE"} 1028 failInfo {{id-attributes failInfo(4)} "the reason to reject"} 1030 5.1.2.3 SUCCESS response 1032 In this case, the information portion of CertRep will be a degenerated 1033 PKCS#7 which contains the end entity's certificate. It is then enveloped 1034 and signed as below: 1036 pkcsCertRep SignedData ::= { -- PKCS#7 1037 version 1 1038 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 1039 digestAlgorithm(2) 5} 1040 contentInfo { -- empty content since this is degenerated PKCS#7 1041 contentType {pkcs-7 1} 1042 } 1043 certificates { 1044 certificate { -- issued end entity's certificate 1045 version 3 1046 serialNumber "issued end entity's certificate serial number" 1047 signature {pkcs-1 4} -- md5WithRSAEncryption 1048 issuer "the certificate authority issuer name" 1049 validity { 1050 notBefore "UTC time" 1051 notAfter "UTC time" 1052 } 1053 subject "the end entity subject name as given in PKCS#10" 1054 subjectPublicKeyInfo { 1055 algorithm {pkcs-1 1} 1056 subjectPublicKey "a DER encoding of end entity public 1057 key as given in PKCS#10" 1058 } 1059 extensions " the extensions as given in PKCS#10" 1060 signatureAlgorithm {pkcs-1 4} 1061 signature " the certificate authority signature" 1062 } 1063 certificate "the certificate authority certificate" 1064 | certificate "the registration authority certificate (if applicable)" 1065 } 1066 } 1067 pkcsCertRepEnvelope EnvelopedData ::= { -- PKCS#7 1068 version 0 1069 recipientInfo { 1070 version 0 1071 issuerAndSerialNumber { -- use issuer name and serial number as 1072 -- conveyed in end entity's self-signed 1073 -- certificate, included in the PKCSReq 1074 issuer "the end entity's subject name" 1075 serialNumber "the serial number defined by the end entity in 1076 its self-signed certificate" 1077 } 1078 keyEncryptionAlgorithm {pkcs-1 1} 1079 encryptedKey "content-encrypt key encrypted by the end entity's 1080 public key which is same key as authenticated in 1081 the end entity's certificate" 1082 } 1083 encryptedContentInfo { 1084 contentType {pkcs-7 1} -- data content identifier 1085 contentEncryptionAlgorithm "OID for DES encryption" 1086 encryptedContent "encrypted pkcsCertRep using content encryption 1087 key" 1088 } 1089 } 1090 pkcsCertRepSigned SignedData ::= { -- PKCS#7 1091 version 1 1092 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 1093 digestAlgorithm(2) 5} 1094 contentInfo { 1095 contentType {pkcs-7 1} 1096 content pkcsCertRepEnvelope 1097 } 1098 signerInfo { 1099 version 1 1100 issuerAndSerialNumber { 1101 issuer "the certificate authority issuer name" 1102 serialNumber "the CA certificate's serial number" 1103 } 1104 digestAlgorithm {iso(1), member-body(2) US(840) rsadsi(113549) 1105 digestAlgorithm(2) 5} 1106 authenticateAttributes { 1107 contentType {{pkcs-9 3} {pkcs-7 1}} 1108 messageDigest {{pkcs-9 4} "a octet string"} 1109 messageType {{id-attribute messageType(2)} "CertRep"} 1110 transaction-id {{id-attributes transId(7)} "printable 1111 string"} 1112 -- same transaction id as given in PKCSReq 1113 pkiStatus {{id-attributes pkiStatus(3) "SUCCESS"} 1114 recipientNonce {{id-attribute recipientNonce(6)}<16 bytes>} 1115 senderNonce {{ id-attributes senderNonce(5) <16 bytes>} 1116 } 1117 digestEncryptionAlgorithm {pkcs-1 1} 1118 encryptedDigest "encrypted digest of authenticate attributes 1119 using CA's private key " 1120 } 1121 } 1122 CertRep PKIMessage ::= { 1123 contentType {pkcs-7 2} 1124 content pkcsCertRepSigned 1125 } 1127 5.2 Poll for End Entity Initial Certificate 1129 Either triggered by the PENDING status received from the CertRep, or by 1130 the non-response timeout for the previous PKCSReq, an end entity will 1131 enter the polling state by periodically sending GetCertInitial to the 1132 server, until either the request is granted and the certificate is sent 1133 back, or the request is rejected, or the the configured time limit for 1134 polling is exceeded. 1136 Since GetCertInitial is part of the enrollment, the messages exchanged 1137 during the polling period should carries the same transaction identifier 1138 as the previous PKCSReq. 1140 PreCondition 1141 Either the end entity has received a CertRep with pkiStatus set to be 1142 PENDING, or the previous PKCSReq has timed out. 1144 PostContition 1145 The end entity has either received the certificate, or be rejected of 1146 its request, or the polling period ended as a failure. 1148 5.2.1 GetCertInitial Message Format 1150 |Since at this time the certificate has not been issued, the end entity 1151 |can only use the end entity's subject name, combined with the 1152 |transaction identifier, to identify the polled certificate request. 1154 |The certificate authority server must be able to uniquely identify the 1155 |polled certificate request. A subject name can have more than one 1156 |outstanding certificate request (with different key usage attributes). 1158 -- Information portion 1160 pkcsGetCertInitial issuerAndSubject ::= { 1161 issuer "the certificate authority issuer name" 1162 subject "the end entity subject name as given in PKCS#10" 1163 } 1164 pkcsGetCertInitialEnvelope EnvelopedData ::= { 1165 version 0 1166 recipientInfo { 1167 version 0 1168 issuerAndSerialNumber { 1169 issuer "the CA issuer name" 1170 serialNumber "the CA certificate serial number" 1171 } 1172 keyEncryptionAlgorithm {pkcs-1 1} 1173 encryptedKey "content-encrypt key encrypted by CA's public key" 1174 } 1175 encryptedContentInfo { 1176 contentType {pkcs-7 1} -- data content 1177 contentEncryptionAlgorithm "OID for DES encryption" 1178 encryptedContent "encrypted getCertInital" 1179 } 1180 } 1181 pkcsGetCertInitialSigned SignedData ::= { -- PKCS#7 1182 version 1 1183 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 1184 digestAlgorithm(2) 5} 1185 contentInfo { 1186 contentType {pkcs-7 1} 1187 content pkcsGetCertIntialEnvelope 1188 } 1189 certificate { -- the end entity's self-signed certificate 1190 version 3 1191 serialNumber "the transaction id associated with enrollment" 1192 signature {pkcs-1 4} -- md5WithRSAEncryption 1193 issuer " the end entity's subject name" 1194 validity { 1195 notBefore "a UTC time" 1196 notAfter "a UTC time" 1197 } 1198 subject "the end entity's subject name" 1199 subjectPublicKeyInfo { 1200 algorithm {pkcs-1 1} 1201 subjectPublicKey "DER encoding of end entity's public key" 1202 } 1203 signatureAlgorithm {pkcs-1 4} 1204 signature "the signature generated by using the end entity's 1205 private key corresponding to the public key in 1206 this certificate." 1207 } 1208 signerInfo { 1209 version 1 1210 issuerAndSerialNumber { 1211 issuer "end entity's subject name" 1212 serialNumber "the transaction id used in previous PKCSReq" 1213 } 1214 digestAlgorithm {iso(1), member-body(2) US(840) rsadsi(113549) 1215 digestAlgorithm(2) 5} 1216 authenticateAttributes { 1217 contentType {{pkcs-9 3} {pkcs-7 1}} 1218 messageDigest {{pkcs-9 4} "an octet string"} 1219 -- digest of getCertInitial 1220 messageType {{id-attribute messageType(2)} "GetCertInitial"} 1221 transaction-id {{id-attributes transId(7)} "printable 1222 string"} 1223 -- same transaction idused in previous PKCSReq 1224 senderNonce {{id-attribute senderNonce(3)} 0x<16 bytes>} 1225 } 1226 digestEncryptionAlgorithm {pkcs-1 1} 1227 encryptedDigest "encrypted digest of authenticateAttributes" 1228 } 1229 } 1230 GetCertInitial PKIMessage ::= { 1231 contentType {pkcs-7 2} 1232 content pkcsGetCertInitialSigned 1233 } 1235 5.2.2 GetCertInitial Response Message Format 1237 The response messages for GetCertInitial are the same as for PKCSReq. 1239 5.3 Certificate Access 1241 The certificate query message defined in this section is an option when 1242 the LDAP server is not available to provide the certificate query. An 1243 end entity should be able to query an issued certificate from the 1244 certificate authority, as long as the issuer name and the issuer 1245 assigned certificate serial number is known to the requesting end 1246 entity. This transaction is not intended to provide the service as a 1247 certificate directory service. A more complicated query mechanism would 1248 have to be defined in order to allow an end entity to query a certificate 1249 using various different fields. 1251 This transaction consists of one GetCert message send to the server by 1252 an end entity, and one CertRep message send back from the server. 1254 PreCondition 1255 The queried certificate have been issued by the certificate authority 1256 and the issuer assigned serial number is known. 1258 PostContition 1259 Either the certificate is send back or the request is rejected. 1261 5.3.1 GetCert Message Format 1263 The queried certificate is identified by its issuer name and the issuer 1264 assigned serial number. If this is a query for an arbitrary end entity's 1265 certificate, the requesting end entity should includes its own CA issued 1266 certificate in the signed envelope. If this is a query for its own 1267 certificate (assume the end entity lost the issued certificate, or does 1268 not have enough non-volatile memory to save the certificate), then the 1269 self-signed certificate has to be included in the signed envelope. 1271 pkcsGetCert issuerAndSerialNumber ::= { 1272 issuer "the certificate issuer name" 1273 serialNumber "the certificate serial number" 1274 } 1275 pkcsGetCertEnvelope EnvelopedData ::= { 1276 version 0 1277 recipientInfo { 1278 version 0 1279 issuerAndSerialNumber { 1280 issuer "the CA [RA] issuer name" 1281 serialNumber "the CA [RA] certificate serial number" 1282 } 1283 keyEncryptionAlgorithm {pkcs-1 1} 1284 encryptedKey "content-encrypt key encrypted 1285 by CA [RA] public key" 1286 } 1287 encryptedContentInfo { 1288 contentType {pkcs-7 1} -- data content 1289 contentEncryptionAlgorithm "OID for DES encryption" 1290 encryptedContent "encrypted pkcsGetCert using the content 1291 encryption key" 1292 } 1293 } 1294 pkcsGetCertSigned SignedData ::= { 1295 version 1 1296 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 1297 digestAlgorithm(2) 5} 1298 contentInfo { 1299 contentType {pkcs-7 1} 1300 content pkcsGetCertEnvelope 1301 } 1302 certificates { 1303 certificate "CA issued certificate" 1304 or "self-signed certificate" 1305 } 1306 signerInfo { 1307 version 1 1308 issuerAndSerialNumber { 1309 issuer "the end entity's subject name" 1310 serialNumber "end entity's certificate serial number" 1311 } 1312 digestAlgorithm {iso(1), member-body(2) US(840) rsadsi(113549) 1313 digestAlgorithm(2) 5} 1314 authenticateAttributes { 1315 contentType {{pkcs-9 3} {pkcs-7 1}} 1316 messageDigest {{pkcs-9 4} "an octet string"} 1317 -- digest of pkcsGetCertEnvelope 1318 messageType {{id-attribute messageType(2)} "GetCert"} 1319 transaction-id {{id-attributes transId(7)} "printable 1320 string"} 1321 senderNonce {{id-attribute senderNonce(3)} <16 bytes>} 1322 } 1323 digestEncryptionAlgorithm {pkcs-1 1} 1324 encryptedDigest "encrypted digest of authenticateAttributes" 1325 } 1326 } 1327 GetCert PKIMessage ::= { 1328 contentType {pkcs-7 2} 1329 content pkcsGetCertSigned 1330 } 1332 5.3.2 CertRep Message Format 1334 In this case, the CertRep from the server is same as the CertRep for the 1335 PKCSReq, except that the server will only either grant the request or 1336 reject the request. Also, the recipientInfo should use the CA issuer 1337 name and CA assigned serial number to identify the end entity's key pair 1338 since at this time, the end entity has received its own certificate. 1340 5.4 CRL Access 1342 The CRL query message defined in this section is an option when the LDAP 1343 server is not available to provide the CRL query. In the PKI protocol 1344 proposed here, only the end entity can initiate the transaction to 1345 download CRL. An end entity send GetCRL request to the server and the 1346 server send back CertRep whose information portion is a degenerated 1347 PKCS#7 which contains only the most recent CRL. The size of CRL included 1348 in the CertRep should be determined by the implementation. 1350 PreCondition 1351 The certificate authority certificate has been downloaded to the end 1352 entity. 1354 PostCondition 1355 CRL send back to the end entity. 1357 5.4.1 GetCRL Message format 1359 The CRL is identified by using both CA's issuer name and the CA 1360 certificate's serial number: 1362 pkcsGetCRL issuerAndSerialNumber { 1363 issuer "the certificate authority issuer name" 1364 serialNumber "certificate authority certificate's serial number" 1365 } 1367 When the CRLDistributionPoint is supported, the pkcsGetCRL is defined as 1368 the following: 1370 pkcsGetCRL SEQUENCE { 1371 crlIssuer issuerAndSerialNumber 1372 distributionPoint CE-CRLDistPoints 1373 } 1375 where CE-CRLDisPoints is defined in X.509, but must contain only one 1376 CRL distribution point. 1378 pkcsGetCRLEnvelope EnvelopedData ::= { 1379 version 0 1380 recipientInfo { 1381 version 0 1382 issuerAndSerialNumber { 1383 issuer "the certificate authority (or RA) issuer name" 1384 serialNumber "the CA (RA) certificate's serial number" 1385 } 1386 keyEncryptionAlgorithm {pkcs-1 1} 1387 encryptedKey "content-encrypt key encrypted by CA (RA) public key" 1388 } 1389 encryptedContentInfo { 1390 contentType {pkcs-7 1} -- data content 1391 contentEncryptionAlgorithm "OID for DES encryption" 1392 encryptedContent "encrypted pkcsGetCRL" 1393 } 1394 } 1395 pkcsGetCRLSigned SignedData ::= { 1396 version 1 1397 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 1398 digestAlgorithm(2) 5} 1399 contentInfo { 1400 contentType {pkcs-7 1} 1401 content pkcsGetCRLEnvelope 1402 } 1403 certificates { 1404 certificate "CA-issued or self-signed end entity's certificate" 1405 } 1406 signerInfo { 1407 version 1 1408 issuerAndSerialNumber { 1409 issuer "the end entity's issuer name" 1410 serialNumber "the end entity's certificate serial number" 1411 } 1412 digestAlgorithm {iso(1), member-body(2) US(840) rsadsi(113549) 1413 digestAlgorithm(2) 5} 1414 authenticateAttributes { 1415 contentType {{pkcs-9 3} {pkcs-7 1}} 1416 messageDigest {{pkcs-9 4} 0x<16/20 bytes>} 1417 -- digest of pkcsGetCRLEnvelope 1418 messageType {{id-attribute messageType(2)} "CertCRL"} 1419 transaction-id {{id-attributes transId(7)} "printable 1420 string"} 1421 senderNonce {{id-attribute senderNonce(3)} <16 bytes>} 1422 } 1423 digestEncryptionAlgorithm {pkcs-1 1} 1424 encryptedDigest "encrypted digest of authenticateAttributes" 1425 } 1426 } 1427 GetCRL PKIMessage ::= { 1428 contentType {pkcs-7 2} 1429 content pkcsGetCRLSigned 1430 } 1432 5.4.2 CertRep Message Format 1434 The CRL is send back to the end entity through CertRep message. The 1435 information portion of this message is a degenerated PKCS#7 SignedData 1436 which contains only a CRL. 1438 pkcsCertRep SignedData ::= { 1439 version 1 1440 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 1441 digestAlgorithm(2) 5} 1442 contentInfo { 1443 contentType {pkcs-7 1} 1444 } 1445 crl { 1446 signature {pkcs-1 4} 1447 issuer "the certificate authority issuer name" 1448 lastUpdate "UTC time" 1449 nextUpdate "UTC time" 1450 revokedCertificate { 1451 -- the first entry 1452 userCertificate "certificate serial number" 1453 revocationData "UTC time" 1454 .... 1455 -- last entry 1456 userCertificate "certificate serial number" 1457 revocationData "UTC time" 1458 } 1459 } 1460 pkcsCertRepEnvelope EnvelopedData ::= { 1461 version 0 1462 recipientInfo { 1463 version 0 1464 issuerAndSerialNumber { 1465 issuer "the end entity's issuer name" 1466 serialNumber "the end entity certificate serial number" 1467 } 1468 keyEncryptionAlgorithm {pkcs-1 1} 1469 encryptedKey "content-encrypt key encrypted by end entity's 1470 public key " 1471 } 1472 encryptedContentInfo { 1473 contentType {pkcs-7 1} -- data content 1474 contentEncryptionAlgorithm "OID for DES encryption" 1475 encryptedContent "encrypted pkcsCertRep using end entity's 1476 public key" 1477 } 1478 } 1479 pkcsCertRepSigned SignedData ::= { -- PKCS#7 1480 version 1 1481 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 1482 digestAlgorithm(2) 5} 1483 contentInfo { 1484 contentType {pkcs-7 1} 1485 content pkcsCertRepEnvelope 1486 } 1487 signerInfo { 1488 version 1 1489 issuerAndSerialNumber { 1490 issuer "the certificate authority issuer name" 1491 serialNumber "the CA certificate's serial number" 1492 } 1493 digestAlgorithm {iso(1), member-body(2) US(840) rsadsi(113549) 1494 digestAlgorithm(2) 5} 1495 authenticateAttributes { 1496 contentType {{pkcs-9 3} {pkcs-7 1}} 1497 messageDigest {{pkcs-9 4} "an octet string"} 1498 -- digest of pkcsCertRepEnvelope 1499 messageType {{id-attribute messageType(2)} "CertRep"} 1500 transaction-id {{id-attributes transId(7)} "printable 1501 string"} 1502 -- same transaction id as given in PKCSReq 1503 pkiStatus {{id-attributes pkiStatus(3) "SUCCESS"} 1504 recipientNonce{{id-attribute recipientNonce(6)}<16 bytes>} 1505 senderNonce {{id-attribute senderNonce (5) 0x<16 bytes>} 1506 } 1507 digestEncryptionAlgorithm {pkcs-1 1} 1508 encryptedDigest "encrypted digest of authenticatedAttributes 1509 using CA private key" 1510 } 1511 } 1513 NOTE:The PKCS#7 EncryptedContent is specified as an octet string, but 1514 SCEP entities must also accept a sequence of octet strings as a valid 1515 alternate encoding. 1517 This alternate encoding must be accepted wherever PKCS #7 Enveloped 1518 Data is specified in this document. 1520 5.5 Get Certificate Authority Certificate 1522 Before any transaction begins, end entities have to get the CA (and 1523 possibly RA) certificate(s) first. Since no public keys have been 1524 exchanged, the message can not be encrypted and the response must be 1525 authenticated by out-of-band means. These certs are obtained by means 1526 of an HTTP GET message. To get the CA certificate, the end entity does a 1527 "HTTP GET" and receives a plain X.509 certificate in response. In the 1528 request, the URL identifies a CGI script on the server and passes the CA 1529 issuer identifier as the parameter to the CGI script. Once the CA 1530 certificate is received by the end entity, a fingerprint is generated 1531 using MD5 hash algorithm on the whole CA certificate. This fingerprint 1532 is verified by some positive out-of-band means, such as a phone call. 1534 5.5.1 GetCACert HTTP Message Format 1535 "GET" CGI-PATH CGI-PROG "?operation=GetCACert" "&message=" CA-IDENT 1536 where: 1537 CGI-PATH defines the actual CGI path to invoke the CGI program 1538 which parses the request. 1539 CGI-PROG is set to be the string "pkiclient.exe" and this is 1540 expected to be the program that the CA will use to handle the 1541 SCEP transactions. 1542 CA-IDENT is any string which is understood by the CA. 1543 For example, it could be a domain name like ietf.org. 1544 If a certificate authority has multiple root certificates 1545 this field can be used to distinguish which is required. 1546 Otherwise it may be ignored. 1548 5.5.2 Response 1550 The response for GetCACert is different between the case where the CA 1551 directly communicated with the end entity during the enrollment, and the 1552 case where a RA exists and the end entity communicates with the RA 1553 during the enrollment. 1555 5.5.2.1 CA Certificate Only Response 1557 A binary X.509 CA certificate is send back as a MIME object with a 1558 Content-Type of application/x-x509-ca-cert. 1560 5.5.2.2 CA and RA Certificates Response 1562 When an RA exists, both CA and RA certificates must be sent back in 1563 the response to the GetCACert request. The RA certificate(s) must be 1564 signed by the CA. A certificates-only PKCS#7 SignedData is used to 1565 carry the certificates to the end entity, with a Content-Type of 1566 application/x-x509-ca-ra-cert. 1568 |5.6 Get Certificate Authority Certificate Chain 1569 | 1570 |In order to support Certificate Authority hierarchies, it is necessary 1571 |to have a way to get the entire certificate chain. The following message 1572 |has been added to SCEP for this purpose. 1573 | 1574 |5.6.1 GetCACertChain HTTP Message Format 1575 | 1576 | "GET" CGI-SCRIPT "?" "operation=GetCACertChain" "&" "message" CA-IDENT 1577 | where CGI-SCRIPT and CA-IDENT are as described for GetCACert. 1578 | 1579 |5.6.2 Response 1580 | 1581 |The response for GetCACertChain is a certificates-only PKCS#7 SignedData 1582 |to carry the certificates to the end entity, with a Content-Type of 1583 |application/x-x509-ca-ra-cert-chain. 1584 | 1585 |5.6.3 Backwards Compatability 1586 | 1587 |Versions of SCEP prior to revision 3 do not support GetCACertChain. 1588 |Certificate Authorities written to these prior versions will not be 1589 |able to process the message and may return an HTML error. 1590 | 1591 |To avoid this, clients should send the GetCACert message first. If the 1592 |returned certificate is self-signed or is signed by a Certificate 1593 |Authority that is trusted by the client, then it is not necessary to 1594 |send the GetCACertChain message and it should not be sent. 1595 | 1596 |If a Certificate Authority is configured with a certificate that is 1597 |not either self-signed or has a self-signed issuer, then it should 1598 |support this message. In other words, it should be supported if the 1599 |CA hierarchy is more than two-deep. 1600 | 1601 |An old CA in a two-deep hierarchy might still get this message from 1602 |a client if the client did not trust either that CA or its issuer. 1603 |In that event, the certificate cannot be trusted anyway. In any case 1604 |the CA must not crash or hang upon the receipt of the message and the 1605 |client must be able to handle whatever error is returned by the CA, 1606 |including an HTML error or an ungraceful disconnect. 1608 The following is the ASN.1 definition of Cert-Only PKCS#7: 1610 certOnly SignedData ::= { 1611 version 1 1612 digestAlgorithm {iso(1) member-body(2) US(840) rsadsi(113549) 1613 digestAlgorithm(2) 5} 1615 contentInfo { 1616 contentType {pkcs-7 1} -- data content identifier 1617 content -- NULL 1618 } 1619 certificates -- the RA and CA certificates. 1620 } 1622 CARACerts PKIMessage ::= { -- special pki message sent in the clear 1623 contentType {pkcs-7 2} 1624 content certOnly 1625 } 1627 6.0 Security Considerations 1629 This entire document is about security. Common security considerations 1630 such as keeping private keys truly private and using adequate lengths 1631 for symmetric and asymmetric keys must be followed in order to maintain 1632 the security of this protocol. 1634 7.0 Intellectual Property 1636 This protcol includes the optional use of Certificate Revocation List 1637 Distribution Point (CRLDP) technology, which is a patented technology 1638 of Entrust Technologies, Inc. (Method for Efficient Management of 1639 Certificate Revocation Lists and Update Information (U.S. Patent 1640 5,699,431)). Please contact Entrust Technologies, Inc. 1641 (www.entrust.com) for more information on licensing CRLDP technology. 1643 8.0 References 1645 [PKCS7] Kaliski, B., "PKCS #7: Cryptographic Message Syntax Version 1646 1.5", RFC 2315, March 1998. 1648 [PKCS10] Kaliski, B., "PKCS #10: Certification Request Syntax Version 1649 1.5", RFC 2314, March 1998. 1651 [RFC2459] Housley, R., ec. al., "Internet X.509 Public Key 1652 Infrastructure Certificate and CRL Profile", RFC 2459, January 1999. 1654 Appendix A: Cisco End Entity Subject Name Definition 1656 The ip address and the FQDN of a SCEP client should be included in the 1657 V3 extension subjectAltName. When the subjectAltName extension attribute 1658 is present, both the subjectAltName fields and the subjectName field could 1659 have the IP address and the FQDN information. 1661 When the X.500 directory is used by the CA to define the name space, the 1662 subject name defined above become a RDN which is part of DN binded to 1663 the end entity's public key in the certificate. 1665 A sample of DN assigned by Entrust CA is given below (assume the same 1666 ciscoRouterAlice is used as the end entity defined subject name): 1668 OU = InteropTesting, O = Entrust Technologies, C = CA 1669 RDN = {"alice.cisco.com", "172.21.114.67", "22334455"} 1671 Appendix B: IPSEC Client Enrollment Certificate Request 1673 The following is the certificate enrollment request (PKCS#10) as created 1674 by Cisco VPN Client: 1676 -----END NEW CERTIFICATE REQUEST----- 1677 0 30 439: SEQUENCE { 1678 4 30 288: SEQUENCE { 1679 8 02 1: INTEGER 0 1680 11 30 57: SEQUENCE { 1681 13 31 55: SET { 1682 15 30 53: SEQUENCE { 1683 17 06 3: OBJECT IDENTIFIER commonName (2 5 4 3) 1684 22 13 46: PrintableString 1685 : 'For Xiaoyi, IPSEC attrs in alternate name 1686 extn' 1687 : } 1688 : } 1689 : } 1690 70 30 158: SEQUENCE { 1691 73 30 13: SEQUENCE { 1692 75 06 9: OBJECT IDENTIFIER rsaEncryption (1 2 840 113549 1 1693 1 1) 1694 86 05 0: NULL 1695 : } 1696 88 03 140: BIT STRING 0 unused bits 1697 : 30 81 88 02 81 80 73 DB 1D D5 65 AA EF C7 D4 8E 1698 : AA 6E EB 46 AC 91 2A 0F 50 51 17 AD 50 A2 2A F2 1699 : CE BE F1 E4 22 8C D7 61 A1 6C 87 61 62 92 CB A6 1700 : 80 EA B4 0F 09 9D 18 5F 39 A3 02 0E DB 38 4C E4 1701 : 8A 63 2E 72 8B DC BE 9E ED 6C 1A 47 DE 13 1B 0F 1702 : 83 29 4D 3E 08 86 FF 08 2B 43 09 EF 67 A7 6B EA 1703 : 77 62 30 35 4D A9 0F 0F DF CC 44 F5 4D 2C 2E 19 1704 : E8 63 94 AC 84 A4 D0 01 E1 E3 97 16 CD 86 64 18 1705 : [ Another 11 bytes skipped ] 1706 : } 1707 231 A0 63: [0] { 1708 233 30 61: SEQUENCE { 1709 235 06 9: OBJECT IDENTIFIER extensionReq (1 2 840 113549 1 9 1710 14) 1711 246 31 48: SET { 1712 248 30 46: SEQUENCE { 1713 250 30 44: SEQUENCE { 1714 252 06 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17) 1715 257 04 37: OCTET STRING 1716 30 23 87 04 01 02 03 04 81 0D 65 6D 61 69 1717 6C 40 69 72 65 2E 63 6F 6D 82 0C 66 71 64 1718 6E 2E 69 72 65 2E 63 6F 6D 1719 : } 1720 : } 1721 : } 1722 : } 1723 : } 1724 : } 1726 296 30 13: SEQUENCE { 1727 298 06 9: OBJECT IDENTIFIER md5withRSAEncryption (1 2 840 113549 1728 1 1 4) 1729 309 05 0: NULL 1730 : } 1731 311 03 129: BIT STRING 0 unused bits 1732 : 19 60 55 45 7F 72 FD 4E E5 3F D2 66 B0 77 13 9A 1733 : 87 86 75 6A E1 36 C6 B6 21 71 68 BD 96 F0 B4 60 1734 : 95 8F 12 F1 65 33 16 FD 46 8A 63 19 90 40 B4 B7 1735 : 2C B5 AC 63 17 50 28 F0 CD A4 F0 00 4E D2 DE 6D 1736 : C3 4F F5 CB 03 4D C8 D8 31 5A 7C 01 47 D2 2B 91 1737 : B5 48 55 C8 A7 0B DD 45 D3 4A 8D 94 04 3A 6C B0 1738 : A7 1D 64 74 AB 8A F7 FF 82 C7 22 0A 2A 95 FB 24 1739 : 88 AA B6 27 83 C1 EC 5E A0 BA 0C BA 2E 6D 50 C7 1740 : } 1742 Appendix C: Private OID Definitions 1744 The OIDs used in defining pkiStatus are VeriSign self-maintained 1745 OIDs. Please note, work is in progress to replace the VeriSign owned 1746 object identifiers with the standard object identifiers. Once the 1747 standarlization is completed, this documentation will be updated. 1749 id-VeriSign OBJECT_IDENTIFIER ::= {2 16 US(840) 1 VeriSign(113733)} 1750 id-pki OBJECT_IDENTIFIER ::= {id-VeriSign pki(1)} 1751 id-attributes OBJECT_IDENTIFIER ::= {id-pki attributes(9)} 1752 id-messageType OBJECT_IDENTIFIER ::= {id-attributes messageType(2)} 1753 id-pkiStatus OBJECT_IDENTIFIER ::= {id-attributes pkiStatus(3)} 1754 id-failInfo OBJECT_IDENTIFIER ::= {id-attributes failInfo(4)} 1755 id-senderNonce OBJECT_IDENTIFIER ::= {id-attributes senderNonce(5)} 1756 id-recipientNonce OBJECT_IDENTIFIER ::= {id-attributes recipientNonce(6)} 1757 id-transId OBJECT_IDENTIFIER ::= {id-attributes transId(7)} 1758 id-extensionReq OBJECT_IDENTIFIER ::= {id-attributes extensionReq(8)} 1759 Appendix D: CRL Query by means of LDAP 1761 In order to retrieve the CRL by means of LDAP, the client needs to know 1762 where in the directory it is stored. The certificate must contain a 1763 CRL Distribution Point extension encoded as a DN or as an LDAP URI. 1765 For example, the certificate issued by Entrust VPN contains 1766 the following DN as the CRL distribution point: 1768 CN = CRL1, O = cisco, C = US. 1770 The asn.1 encoding of this distribution point is: 1772 30 2C 31 0B 30 09 06 03 55 04 06 13 02 55 53 31 0E 30 0C 06 1773 03 55 04 0A 13 05 63 69 73 63 6F 31 0D 30 0B 06 03 55 04 03 1774 13 04 43 52 4C 31 1776 The ldap form would be: 1778 ldap://servername/CN=CRL1,O=cisco,C=US 1780 Appendix E: SCEP State Transitions 1782 SCEP state transitions are based on transaction identifier. The design 1783 goal is to ensure the synchronization between the CA and the end entity 1784 under various error situations. 1786 An identity is defined by the combination of FQDN, the IP address and 1787 the client serial number. FQDN is the required name attribute. It is 1788 important to notice that, a client named as Alice.cisco.com is different 1789 from the client named as Alice.cisco.com plus IPAddress 171.69.1.129. 1791 Each enrollment transaction is uniquely associated with a transaction 1792 identifier. Because the enrollment transaction could be interrupted by 1793 various errors, including network connection errors or client reboot, 1794 the SCEP client generates a transaction identifier by calculating MD5 1795 hash on the public key value for which the enrollment is requested. This 1796 retains the same transaction identifier throughout the enrollment 1797 transaction, even if the client has rebooted or timed out, and issues a 1798 new enrollment request for the same key pair. It also provides the way 1799 for the CA to uniquely identify a transaction in its database. At the 1800 end entity side, it generates a transaction identifier which is included 1801 in PKCSReq. If the CA returns a response of PENDING, the end entity 1802 will poll by periodically sending out GetCertInitial with the same 1803 transaction identifier until either a response other than PENDING is 1804 obtained, or the configured maximum time has elapsed. 1806 If the client times out or the client reboots, the client administrator 1807 will start another enrollment transaction with the same key pair. The 1808 second enrollment will have the transaction idenifier. At the server 1809 side, instead of accepting the PKCSReq as a new enrollment request, it 1810 should respond as if another GetCertInitial message had been sent with 1811 that transaction ID. In another word, the second PKCSReq should be 1812 taken as a resynchronization message to allow the enrollment resume as 1813 the same transaction. 1815 It is important to keep the transaction id unique since CEP requires the 1816 same policy and same identity be applied to the same subject name and 1817 key pair binding. In the current implementation, an SCEP client can 1818 only assume one identity. At any time, only one key pair, with a given 1819 key usage, can be associated with the same identity. 1821 The following gives several example of client to CA transactions. 1823 Client actions are indicated in the left column, CA actions are 1824 indicated in the right column. A blank action signifies that no message 1825 was received. Note that these examples assume that the CA enforces the 1826 certificate-name uniqueness property defined in Section 2.1.1.1. 1828 The first transaction, for example, would read like this: 1829 "Client Sends PKCSReq message with transaction ID 1 to the 1830 CA. The CA signs the certificate and constructs a CertRep Message 1831 containing the signed certificate with a transaction ID 1. The client 1832 receives the message and installs the cert locally." 1834 Successful Enrollment Case: no manual authentication 1835 PKCSReq (1) ----------> CA Signs Cert 1836 Client Installs Cert <---------- CertRep (1) SIGNED CERT 1838 Successful Enrollment Case: manual authentication required 1839 PKCSReq (10) ----------> Cert Request goes into Queue 1840 Client Polls <---------- CertRep (10) PENDING 1841 GetCertInitial (10) ----------> Still pending 1842 Client Polls <---------- CertRep (10) PENDING 1843 GetCertInitial (10) ----------> Still pending 1844 Client Polls <---------- CertRep (10) PENDING 1845 GetCertInitial (10) ----------> Still pending 1846 Client Polls <---------- CertRep (10) PENDING 1847 GetCertInitial (10) ----------> Cert has been signed 1848 Client Installs Cert <---------- CertRep (10) SIGNED CERT 1850 Resync Case - CA Receive and Signs PKCSReq, Client Did not receive 1851 CertRep: 1853 PKCSReq (3) ----------> Cert Request goes into queue 1854 <---------- CertRep (3) PENDING 1855 GetCertInitial (3) ----------> 1856 <---------- CertRep (3) PENDING 1857 GetCertInitial (3) -----------> 1858 <----------- CA signed Cert and send back 1859 CertRep(3) 1860 (Time Out) 1861 PKCSReq (3) ----------> Cert already signed, send back to 1862 client 1863 Client Installs Cert <---------- CertRep (3) SIGNED CERT 1864 Case when NVRAM is lost and client has to generate a new key pair, there 1865 is no change of name information: 1867 PKCSReq (4) ----------> CA Signs Cert 1868 Client Installs Cert <---------- CertRep (4) SIGNED CERT 1869 (Client looses Cert) 1870 PKCSReq (5) ----------> There is already a valid cert with 1871 this DN. 1872 Client Admin Revokes <---------- CertRep (5) OVERLAPPING CERT ERROR 1873 PKCSReq (5) ----------> CA Signs Cert 1874 Client Installs Cert <---------- CertRep (5) SIGNED CERT 1876 Case when client admin resync the enrollment using a different PKCS#10: 1877 PKCSReq (6) ----------> CA Signs Cert 1878 <---------- CertRep (6) SIGNED CERT 1879 (Client timeout and admin starts another enrollment with a different 1880 PKCS#10, but the same transaction id) 1881 PKCSReq (6) with different PKCS#10 1882 ----------> There is already a valid cert with 1883 this entity (by checking FQDN). 1884 <---------- CertRep (6) INVALID PKCS#10 CERT 1885 ERROR 1886 Client admin either revokes the existing cert 1887 or corrects the error by enrolling with 1888 the same PKCS#10 as the first PKCSReq(6) 1889 PKCSReq (6) ----------> CA find the existing Cert 1890 Client Installs Cert <---------- CertRep (6) SIGNED CERT 1892 Resync case when server is slow in response: 1893 PKCSReq (13) ----------> Cert Request goes into Queue 1894 <---------- CertRep (13) PENDING 1895 GetCertInitial ----------> Still pending 1896 <---------- CertRep (13) PENDING 1897 GetCertInitial ----------> Still pending 1898 <---------- CertRep (13) PENDING 1899 GetCertInitial ----------> Still pending 1900 <---------- CertRep (13) PENDING 1901 GetCertInitial ----------> Still pending 1902 (TimeOut) <---------- CertRep (13) PENDING 1903 * Case 1 1904 PKCSReq (13) ----------> Still pending 1905 Client polls <---------- CertRep (13) PENDING 1906 CertCertInitial ----------> Cert has been signed 1907 Client Installs Cert <---------- CertRep (13) SIGNED CERT 1908 * Case 2 1909 PKCSReq (13) ----------> Cert has been signed 1910 Client Installs Cert <---------- CertRep (13) SIGNED CERT 1911 Appendix F. Author Contact Information 1913 Xiaoyi Liu Cheryl Madson 1914 Cisco Cisco 1915 170 West Tasman Drive 170 West Tasman Drive 1916 San Jose, CA 94134 San Jose, CA 94134 1917 xliu@cisco.com cmadson@cisco.com 1919 David McGrew Andrew Nourse 1920 Cisco Cisco 1921 170 West Tasman Drive 101 Cooper Street 1922 San Jose, CA 94134 Santa Cruz, CA 95060 1923 mcgrew@cisco.com nourse@cisco.com 1925 Appendix G. Copyright Section 1927 Copyright (C) The Internet Society (2000). All Rights Reserved. 1929 This document and translations of it may be copied and furnished 1930 to others, and derivative works that comment on or otherwise 1931 explain it or assist in its implmentation may be prepared, copied, 1932 published and distributed, in whole or in part, without 1933 restriction of any kind, provided that the above copyright notice 1934 and this paragraph are included on all such copies and derivative 1935 works. However, this document itself may not be modified in any 1936 way, such as by removing the copyright notice or references to the 1937 Internet Society or other Internet organizations, except as needed 1938 for the purpose of developing Internet standards in which case the 1939 procedures for copyrights defined in the Internet Standards 1940 process must be followed, or as required to translate it into 1941 languages other than English. 1943 The limited permissions granted above are perpetual and will not 1944 be revoked by the Internet Society or its successors or assigns. 1946 This document and the information contained herein is provided on 1947 an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET 1948 ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR 1949 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1950 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1951 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1953 This draft expires 11 September 2001 1955 [End of draft-nourse-scep-04.txt]