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'CERTV2' on line 586 looks like a reference Summary: 4 errors (**), 0 flaws (~~), 2 warnings (==), 15 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Draft Editor: Blake Ramsdell, 3 draft-ietf-smime-rfc2632bis-07.txt Sendmail, Inc. 4 June 4, 2004 5 Expires December 4, 2004 7 S/MIME Version 3.1 Certificate Handling 9 Status of this memo 11 This document is an Internet-Draft and is in full conformance with all 12 provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Engineering Task 15 Force (IETF), its areas, and its working groups. Note that other 16 groups may also distribute working documents as Internet-Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six months 19 and may be updated, replaced, or obsoleted by other documents at any 20 time. It is inappropriate to use Internet-Drafts as reference material 21 or to cite them other than as "work in progress." 23 The list of current Internet-Drafts can be accessed at 24 http://www.ietf.org/ietf/1id-abstracts.txt 26 The list of Internet-Draft Shadow Directories can be accessed at 27 http://www.ietf.org/shadow.html. 29 Abstract 31 This document specifies conventions for X.509 certificate usage by 32 S/MIME (Secure/Multipurpose Internet Mail Extensions) agents. S/MIME 33 provides a method to send and receive secure MIME messages, and 34 certificates are an integral part of S/MIME agent processing. S/MIME 35 agents validate certificates as described in RFC 3280, the Internet 36 X.509 Public Key Infrastructure Certificate and CRL Profile. S/MIME 37 agents must meet the certificate processing requirements in this 38 document as well as those in RFC 3280. 40 1. Overview 42 S/MIME (Secure/Multipurpose Internet Mail Extensions), described in 43 [SMIME-MSG], provides a method to send and receive secure MIME 44 messages. Before using a public key to provide security services, the 45 S/MIME agent MUST verify that the public key is valid. S/MIME agents 46 MUST use PKIX certificates to validate public keys as described in the 47 Internet X.509 Public Key Infrastructure (PKIX) Certificate and CRL 48 Profile [KEYM]. S/MIME agents MUST meet the certificate processing 49 requirements documented in this document in addition to those stated 50 in [KEYM]. 52 This specification is compatible with the Cryptographic Message Syntax 53 [CMS] in that it uses the data types defined by CMS. It also inherits 54 all the varieties of architectures for certificate-based key 55 management supported by CMS. 57 1.1 Definitions 59 For the purposes of this document, the following definitions apply. 61 ASN.1: Abstract Syntax Notation One, as defined in ITU-T X.208. 63 Attribute Certificate (AC): An X.509 AC is a separate structure from a 64 subject's public key X.509 Certificate. A subject may have multiple 65 X.509 ACs associated with each of its public key X.509 Certificates. 66 Each X.509 AC binds one or more Attributes with one of the subject's 67 public key X.509 Certificates. The X.509 AC syntax is defined in 68 [ACAUTH]. 70 BER: Basic Encoding Rules for ASN.1, as defined in ITU-T X.209. 72 Certificate: A type that binds an entity's name to a public key with a 73 digital signature. This type is defined in the Internet X.509 Public 74 Key Infrastructure (PKIX) Certificate and CRL Profile [KEYM]. This 75 type also contains the distinguished name of the certificate issuer 76 (the signer), an issuer-specific serial number, the issuer's signature 77 algorithm identifier, a validity period, and extensions also defined 78 in that document. 80 Certificate Revocation List (CRL): A type that contains information 81 about certificates whose validity an issuer has prematurely revoked. 82 The information consists of an issuer name, the time of issue, the 83 next scheduled time of issue, a list of certificate serial numbers and 84 their associated revocation times, and extensions as defined in 85 [KEYM]. The CRL is signed by the issuer. The type intended by this 86 specification is the one defined in [KEYM]. 88 DER: Distinguished Encoding Rules for ASN.1, as defined in ITU-T 89 X.690. 91 Receiving agent: software that interprets and processes S/MIME CMS 92 objects, MIME body parts that contain CMS objects, or both. 94 Sending agent: software that creates S/MIME CMS objects, MIME body 95 parts that contain CMS objects, or both. 97 S/MIME agent: user software that is a receiving agent, a sending 98 agent, or both. 100 1.2 Compatibility with Prior Practice of S/MIME 102 S/MIME version 3.1 agents should attempt to have the greatest 103 interoperability possible with agents for prior versions of S/MIME. 104 S/MIME version 2 is described in RFC 2311 through RFC 2315, inclusive 105 and S/MIME version 3 is described in RFC 2630 through RFC 2634 106 inclusive. RFC 2311 also has historical information about the 107 development of S/MIME. 109 1.3 Terminology 111 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 112 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 113 document are to be interpreted as described in [MUSTSHOULD]. 115 1.4 Changes Since S/MIME v3 (RFC 2632) 117 Version 1 and Version 2 CRLs MUST be supported. 119 Multiple CA certificates with the same subject and public key, but 120 with overlapping validity periods, MUST be supported. 122 Version 2 attribute certificates SHOULD be supported, and version 1 123 attributes certificates MUST NOT be used. 125 The use of the MD2 digest algorithm for certificate signatures is 126 discouraged, and security language added. 128 Clarified use of email address use in certificates. Certificates that 129 do not contain an email address have no requirements for verifying the 130 email address associated with the certificate. 132 Receiving agents SHOULD display certificate information when 133 displaying the results of signature verification. 135 Receiving agents MUST NOT accept a signature made with a certificate 136 that does not have the digitalSignature or nonRepudiation bit set. 138 Clarifications for the interpretation of the key usage and extended 139 key usage extensions. 141 2. CMS Options 143 The CMS message format allows for a wide variety of options in content 144 and algorithm support. This section puts forth a number of support 145 requirements and recommendations in order to achieve a base level of 146 interoperability among all S/MIME implementations. Most of the CMS 147 format for S/MIME messages is defined in [SMIME-MSG]. 149 2.1 CertificateRevocationLists 151 Receiving agents MUST support the Certificate Revocation List (CRL) 152 format defined in [KEYM]. If sending agents include CRLs in outgoing 153 messages, the CRL format defined in [KEYM] MUST be used. In all cases, 154 both v1 and v2 CRLs MUST be supported. 156 All agents MUST be capable of performing revocation checks using CRLs 157 as specified in [KEYM]. All agents MUST perform revocation status 158 checking in accordance with [KEYM]. Receiving agents MUST recognize 159 CRLs in received S/MIME messages. 161 Agents SHOULD store CRLs received in messages for use in processing 162 later messages. 164 2.2 CertificateChoices 166 Receiving agents MUST support v1 X.509 and v3 X.509 identity 167 certificates as profiled in [KEYM]. End entity certificates MAY 168 include an Internet mail address, as described in section 3. 170 Receiving agents SHOULD support X.509 version 2 attribute 171 certificates. See [ACAUTH] for details about the profile for attribute 172 certificates. 174 2.2.1 Historical Note About CMS Certificates 176 The CMS message format supports a choice of certificate formats for 177 public key content types: PKIX, PKCS #6 Extended Certificates [PKCS6] 178 and PKIX Attribute Certificates. 180 The PKCS #6 format is not in widespread use. In addition, PKIX 181 certificate extensions address much of the same functionality and 182 flexibility as was intended in the PKCS #6. Thus, sending and 183 receiving agents MUST NOT use PKCS #6 extended certificates. 185 X.509 version 1 attribute certificates are also not widely 186 implemented, and have been superseded with version 2 attribute 187 certificates. Sending agents MUST NOT send version 1 attribute 188 certificates. 190 2.3 CertificateSet 192 Receiving agents MUST be able to handle an arbitrary number of 193 certificates of arbitrary relationship to the message sender and to 194 each other in arbitrary order. In many cases, the certificates 195 included in a signed message may represent a chain of certification 196 from the sender to a particular root. There may be, however, 197 situations where the certificates in a signed message may be unrelated 198 and included for convenience. 200 Sending agents SHOULD include any certificates for the user's public 201 key(s) and associated issuer certificates. This increases the 202 likelihood that the intended recipient can establish trust in the 203 originator's public key(s). This is especially important when sending 204 a message to recipients that may not have access to the sender's 205 public key through any other means or when sending a signed message to 206 a new recipient. The inclusion of certificates in outgoing messages 207 can be omitted if S/MIME objects are sent within a group of 208 correspondents that has established access to each other's 209 certificates by some other means such as a shared directory or manual 210 certificate distribution. Receiving S/MIME agents SHOULD be able to 211 handle messages without certificates using a database or directory 212 lookup scheme. 214 A sending agent SHOULD include at least one chain of certificates up 215 to, but not including, a Certificate Authority (CA) that it believes 216 that the recipient may trust as authoritative. A receiving agent 217 MUST be able to handle an arbitrarily large number of certificates 218 and chains. 220 Agents MAY send CA certificates, that is, certificates which can be 221 considered the "root" of other chains, and which MAY be self-signed. 222 Note that receiving agents SHOULD NOT simply trust any self-signed 223 certificates as valid CAs, but SHOULD use some other mechanism to 224 determine if this is a CA that should be trusted. Also note that when 225 certificates contain DSA public keys the parameters may be located in 226 the root certificate. This would require that the recipient possess 227 both the end-entity certificate as well as the root certificate to 228 perform a signature verification, and is a valid example of a case 229 where transmitting the root certificate may be required. 231 Receiving agents MUST support chaining based on the distinguished name 232 fields. Other methods of building certificate chains MAY be supported. 234 Receiving agents SHOULD support the decoding of X.509 attribute 235 certificates included in CMS objects. All other issues regarding the 236 generation and use of X.509 attribute certificates are outside of the 237 scope of this specification. One specification that addresses 238 attribute certificate use is defined in [SECLABEL]. 240 3. Using Distinguished Names for Internet Mail 242 End-entity certificates MAY contain an Internet mail address as 243 described in [RFC-2822]. The address must be an "addr-spec" as defined 244 in Section 3.4.1 of that specification. The email address SHOULD be in 245 the subjectAltName extension, and SHOULD NOT be in the subject 246 distinguished name. 248 Receiving agents MUST recognize and accept certificates that contain 249 no email address. Receiving agents MUST recognize email addresses in 250 the subjectAltName field. Receiving agents MUST recognize email 251 addresses in the Distinguished Name field in the PKCS #9 [PKCS9] 252 emailAddress attribute: 254 pkcs-9-at-emailAddress OBJECT IDENTIFIER ::= 255 {iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 1 } 257 Note that this attribute MUST be encoded as IA5String. 259 Sending agents SHOULD make the address in the From or Sender header in 260 a mail message match an Internet mail address in the signer's 261 certificate. Receiving agents MUST check that the address in the From 262 or Sender header of a mail message matches an Internet mail address, 263 if present, in the signer's certificate, if mail addresses are present 264 in the certificate. A receiving agent SHOULD provide some explicit 265 alternate processing of the message if this comparison fails, which 266 may be to display a message that shows the recipient the addresses in 267 the certificate or other certificate details. 269 A receiving agent SHOULD display a subject name or other certificate 270 details when displaying an indication of successful or unsuccessful 271 signature verification. 273 All subject and issuer names MUST be populated (i.e. not an empty 274 SEQUENCE) in S/MIME-compliant X.509 identity certificates, except that 275 the subject DN in a user's (i.e. end-entity) certificate MAY be an 276 empty SEQUENCE in which case the subjectAltName extension will include 277 the subject's identifier and MUST be marked as critical. 279 4. Certificate Processing 281 A receiving agent needs to provide some certificate retrieval 282 mechanism in order to gain access to certificates for recipients of 283 digital envelopes. There are many ways to implement certificate 284 retrieval mechanisms. X.500 directory service is an excellent example 285 of a certificate retrieval-only mechanism that is compatible with 286 classic X.500 Distinguished Names. Another method under consideration 287 by the IETF is to provide certificate retrieval services as part of 288 the existing Domain Name System (DNS). Until such mechanisms are 289 widely used, their utility may be limited by the small number of 290 correspondent's certificates that can be retrieved. At a minimum, for 291 initial S/MIME deployment, a user agent could automatically generate a 292 message to an intended recipient requesting that recipient's 293 certificate in a signed return message. 295 Receiving and sending agents SHOULD also provide a mechanism to allow 296 a user to "store and protect" certificates for correspondents in such 297 a way so as to guarantee their later retrieval. In many environments, 298 it may be desirable to link the certificate retrieval/storage 299 mechanisms together in some sort of certificate database. In its 300 simplest form, a certificate database would be local to a particular 301 user and would function in a similar way as a "address book" that 302 stores a user's frequent correspondents. In this way, the certificate 303 retrieval mechanism would be limited to the certificates that a user 304 has stored (presumably from incoming messages). A comprehensive 305 certificate retrieval/storage solution may combine two or more 306 mechanisms to allow the greatest flexibility and utility to the user. 307 For instance, a secure Internet mail agent may resort to checking a 308 centralized certificate retrieval mechanism for a certificate if it 309 can not be found in a user's local certificate storage/retrieval 310 database. 312 Receiving and sending agents SHOULD provide a mechanism for the import 313 and export of certificates, using a CMS certs-only message. This 314 allows for import and export of full certificate chains as opposed to 315 just a single certificate. This is described in [SMIME-MSG]. 317 Agents MUST handle multiple valid Certification Authority (CA) 318 certificates containing the same subject name and the same public keys 319 but with overlapping validity intervals. 321 4.1 Certificate Revocation Lists 323 In general, it is always better to get the latest CRL information from 324 a CA than to get information stored away from incoming messages. A 325 receiving agent SHOULD have access to some certificate revocation list 326 (CRL) retrieval mechanism in order to gain access to certificate 327 revocation information when validating certification paths. A 328 receiving or sending agent SHOULD also provide a mechanism to allow a 329 user to store incoming certificate revocation information for 330 correspondents in such a way so as to guarantee its later retrieval. 332 Receiving and sending agents SHOULD retrieve and utilize CRL 333 information every time a certificate is verified as part of a 334 certification path validation even if the certificate was already 335 verified in the past. However, in many instances (such as off-line 336 verification) access to the latest CRL information may be difficult or 337 impossible. The use of CRL information, therefore, may be dictated by 338 the value of the information that is protected. The value of the CRL 339 information in a particular context is beyond the scope of this 340 specification but may be governed by the policies associated with 341 particular certification paths. 343 All agents MUST be capable of performing revocation checks using CRLs 344 as specified in [KEYM]. All agents MUST perform revocation status 345 checking in accordance with [KEYM]. Receiving agents MUST recognize 346 CRLs in received S/MIME messages. 348 4.2 Certification Path Validation 350 In creating a user agent for secure messaging, certificate, CRL, and 351 certification path validation SHOULD be highly automated while still 352 acting in the best interests of the user. Certificate, CRL, and path 353 validation MUST be performed as per [KEYM] when validating a 354 correspondent's public key. This is necessary before using a public 355 key to provide security services such as: verifying a signature; 356 encrypting a content-encryption key (ex: RSA); or forming a pairwise 357 symmetric key (ex: Diffie-Hellman) to be used to encrypt or decrypt a 358 content-encryption key. 360 Certificates and CRLs are made available to the path validation 361 procedure in two ways: a) incoming messages, and b) certificate and 362 CRL retrieval mechanisms. Certificates and CRLs in incoming messages 363 are not required to be in any particular order nor are they required 364 to be in any way related to the sender or recipient of the message 365 (although in most cases they will be related to the sender). Incoming 366 certificates and CRLs SHOULD be cached for use in path validation and 367 optionally stored for later use. This temporary certificate and CRL 368 cache SHOULD be used to augment any other certificate and CRL 369 retrieval mechanisms for path validation on incoming signed messages. 371 4.3 Certificate and CRL Signing Algorithms 373 Certificates and Certificate Revocation Lists (CRLs) are signed by the 374 certificate issuer. A receiving agent MUST be capable of verifying the 375 signatures on certificates and CRLs made with id-dsa-with-sha1 376 [CMSALG]. 378 A receiving agent MUST be capable of verifying the signatures on 379 certificates and CRLs made with md5WithRSAEncryption and 380 sha1WithRSAEncryption signature algorithms with key sizes from 512 381 bits to 2048 bits described in [CMSALG]. 383 Because of the security issues surrounding MD2 [RC95], and in light of 384 current use, md2WithRSAEncryption MAY be supported. 386 4.4 PKIX Certificate Extensions 388 PKIX describes an extensible framework in which the basic certificate 389 information can be extended and how such extensions can be used to 390 control the process of issuing and validating certificates. The PKIX 391 Working Group has ongoing efforts to identify and create extensions 392 which have value in particular certification environments. Further, 393 there are active efforts underway to issue PKIX certificates for 394 business purposes. This document identifies the minimum required set 395 of certificate extensions which have the greatest value in the S/MIME 396 environment. The syntax and semantics of all the identified extensions 397 are defined in [KEYM]. 399 Sending and receiving agents MUST correctly handle the basic 400 constraints, key usage, authority key identifier, subject key 401 identifier, and subject alternative names certificate extensions when 402 they appear in end-entity and CA certificates. Some mechanism SHOULD 403 exist to gracefully handle other certificate extensions when they 404 appear in end-entity or CA certificates. 406 Certificates issued for the S/MIME environment SHOULD NOT contain any 407 critical extensions (extensions that have the critical field set to 408 TRUE) other than those listed here. These extensions SHOULD be marked 409 as non-critical unless the proper handling of the extension is deemed 410 critical to the correct interpretation of the associated certificate. 411 Other extensions may be included, but those extensions SHOULD NOT be 412 marked as critical. 414 Interpretation and syntax for all extensions MUST follow [KEYM], 415 unless otherwise specified here. 417 4.4.1 Basic Constraints Certificate Extension 419 The basic constraints extension serves to delimit the role and 420 position of an issuing authority or end-entity certificate plays in a 421 certification path. 423 For example, certificates issued to CAs and subordinate CAs contain a 424 basic constraint extension that identifies them as issuing authority 425 certificates. End-entity certificates contain an extension that 426 constrains the certificate from being an issuing authority 427 certificate. 429 Certificates SHOULD contain a basicConstraints extension in CA 430 certificates, and SHOULD NOT contain that extension in end entity 431 certificates. 433 4.4.2 Key Usage Certificate Extension 435 The key usage extension serves to limit the technical purposes for 436 which a public key listed in a valid certificate may be used. Issuing 437 authority certificates may contain a key usage extension that 438 restricts the key to signing certificates, certificate revocation 439 lists and other data. 441 For example, a certification authority may create subordinate issuer 442 certificates which contain a key usage extension which specifies that 443 the corresponding public key can be used to sign end user certificates 444 and sign CRLs. 446 If a key usage extension is included in a PKIX certificate, then it 447 MUST be marked as critical. 449 S/MIME receiving agents MUST NOT accept the signature of a message if 450 it was verified using a certificate which contains the key usage 451 extension without either the digitalSignature or nonRepudiation bit 452 set. Sometimes S/MIME is used as a secure message transport for 453 applications beyond interpersonal messaging. In such cases, the 454 S/MIME-enabled application can specify additional requirements 455 concerning the digitalSignature or nonRepudiation bits within this 456 extension. 458 If the key usage extension is not specified, receiving clients MUST 459 presume that the digitalSignature and nonRepudiation bits are set. 461 4.4.3 Subject Alternative Name Extension 463 The subject alternative name extension is used in S/MIME as the 464 preferred means to convey the RFC-2822 email address(es) that 465 correspond to the entity for this certificate. Any RFC-2822 email 466 addresses present MUST be encoded using the rfc822Name CHOICE of the 467 GeneralName type. Since the SubjectAltName type is a SEQUENCE OF 468 GeneralName, multiple RFC-2822 email addresses MAY be present. 470 4.4.4 Extended Key Usage Extension 472 The extended key usage extension also serves to limit the technical 473 purposes for which a public key listed in a valid certificate may be 474 used. The set of technical purposes for the certificate therefore are 475 the intersection of the uses indicated in the key usage and extended 476 key usage extensions. 478 For example, if the certificate contains a key usage extension 479 indicating digital signature and an extended key usage extension which 480 includes the email protection OID, then the certificate may be used 481 for signing but not encrypting S/MIME messages. If the certificate 482 contains a key usage extension indicating digital signature, but no 483 extended key usage extension then the certificate may also be used to 484 sign but not encrypt S/MIME messages. 486 If the extended key usage extension is present in the certificate then 487 interpersonal message S/MIME receiving agents MUST check it contains 488 either the emailProtection or the anyExtendedKeyUsage OID as defined 489 in [KEYM]. S/MIME uses other than interpersonal messaging MAY require 490 the explicit presence of the extended key usage extension or other 491 OIDs to be present in the extension or both. 493 5. Security Considerations 495 All of the security issues faced by any cryptographic application must 496 be faced by a S/MIME agent. Among these issues are protecting the 497 user's private key, preventing various attacks, and helping the user 498 avoid mistakes such as inadvertently encrypting a message for the 499 wrong recipient. The entire list of security considerations is beyond 500 the scope of this document, but some significant concerns are listed 501 here. 503 When processing certificates, there are many situations where the 504 processing might fail. Because the processing may be done by a user 505 agent, a security gateway, or other program, there is no single way to 506 handle such failures. Just because the methods to handle the failures 507 has not been listed, however, the reader should not assume that they 508 are not important. The opposite is true: if a certificate is not 509 provably valid and associated with the message, the processing 510 software should take immediate and noticeable steps to inform the end 511 user about it. 513 Some of the many places where signature and certificate checking might 514 fail include: 516 - no Internet mail addresses in a certificate matches the sender of a 517 message, if the certificate contains at least one mail address 518 - no certificate chain leads to a trusted CA 519 - no ability to check the CRL for a certificate 520 - an invalid CRL was received 521 - the CRL being checked is expired 522 - the certificate is expired 523 - the certificate has been revoked 525 There are certainly other instances where a certificate may be 526 invalid, and it is the responsibility of the processing software to 527 check them all thoroughly, and to decide what to do if the check 528 fails. 530 At the Selected Areas in Cryptography '95 conference in May 1995, 531 Rogier and Chauvaud presented an attack on MD2 that can nearly find 532 collisions [RC95]. Collisions occur when one can find two different 533 messages that generate the same message digest. A checksum operation 534 in MD2 is the only remaining obstacle to the success of the attack. 535 For this reason, the use of MD2 for new applications is discouraged. 536 It is still reasonable to use MD2 to verify existing signatures, as 537 the ability to find collisions in MD2 does not enable an attacker to 538 find new messages having a previously computed hash value. 540 It is possible for there to be multiple unexpired CRLs for a CA. If an 541 agent is consulting CRLs for certificate validation, it SHOULD make 542 sure that the most recently issued CRL for that CA is consulted, since 543 an S/MIME message sender could deliberately include an older unexpired 544 CRL in an S/MIME message. This older CRL might not include recent 545 revoked certificates, which might lead an agent to accept a 546 certificate that has been revoked in a subsequent CRL. 548 When determining the time for a certificate validity check, agents 549 have to be careful to use a reliable time. Unless it is from a trusted 550 agent, this time MUST NOT be the SigningTime attribute found in an 551 S/MIME message. For most sending agents, the SigningTime attribute 552 could be deliberately set to direct the receiving agent to check a CRL 553 that could have out-of-date revocation status for a certificate, or 554 cause an improper result when checking the Validity field of a 555 certificate. 557 A. Normative References 559 [ACAUTH] "An Internet Attribute Certificate Profile for 560 Authorization", RFC 3281 562 [CMS] "Cryptographic Message Syntax (CMS)", 563 draft-ietf-smime-3369bis-04 565 [CMSALG] "Cryptographic Message Syntax (CMS) Algorithms", RFC 3370 567 [KEYM] "Internet X.509 Public Key Infrastructure Certificate and CRL 568 Profile", RFC 3280 570 [KEYMALG] "Algorithms and Identifiers for the Internet X.509 Public 571 Key Infrastructure Certificate and CRL Profile ", RFC 3279 573 [MUSTSHOULD] "Key words for use in RFCs to Indicate Requirement 574 Levels", RFC 2119 576 [PKCS9] "PKCS #9: Selected Object Classes and Attribute Types Version 577 2.0", RFC 2985 579 [RFC-2822], "Internet Message Format", RFC 2822 581 [SMIME-MSG] "S/MIME Version 3 Message Specification ", Internet Draft 582 draft-ietf-smime-msg 584 B. Informative References 586 [CERTV2] "S/MIME Version 2 Certificate Handling", RFC 2312 588 [PKCS6] RSA Laboratories, "PKCS #6: Extended-Certificate Syntax 589 Standard", November 1993 591 [RC95] Rogier, N. and Chauvaud, P., "The compression function of MD2 592 is not collision free," Presented at Selected Areas in Cryptography 593 '95, May 1995 595 [SECLABEL] "Implementing Company Classification Policy with the S/MIME 596 Security Label", RFC 3114 598 [X.500] ITU-T Recommendation X.500 (1997) | ISO/IEC 9594-1:1997, 599 Information technology - Open Systems Interconnection - The Directory: 600 Overview of concepts, models and services 602 [X.501] ITU-T Recommendation X.501 (1997) | ISO/IEC 9594-2:1997, 603 Information technology - Open Systems Interconnection - The Directory: 604 Models 606 [X.509] ITU-T Recommendation X.509 (1997) | ISO/IEC 9594-8:1997, 607 Information technology - Open Systems Interconnection - The Directory: 608 Authentication framework 610 [X.520] ITU-T Recommendation X.520 (1997) | ISO/IEC 9594-6:1997, 611 Information technology - Open Systems Interconnection - The Directory: 612 Selected attribute types. 614 C. Acknowledgements 616 Many thanks go out to the other authors of the S/MIME v2 RFC: Steve 617 Dusse, Paul Hoffman and Jeff Weinstein. Without v2, there wouldn't be 618 a v3. 620 A number of the members of the S/MIME Working Group have also worked 621 very hard and contributed to this document. Any list of people is 622 doomed to omission and for that I apologize. In alphabetical order, 623 the following people stand out in my mind due to the fact that they 624 made direct contributions to this document. 626 Bill Flanigan 627 Trevor Freeman 628 Elliott Ginsburg 629 Paul Hoffman 630 Russ Housley 631 David P. Kemp 632 Michael Myers 633 John Pawling 634 Denis Pinkas 635 Jim Schaad 637 D. Editor's address 639 Blake Ramsdell 640 Sendmail, Inc. 641 704 228th Ave NE #775 642 Sammamish, WA 98074 644 blake@sendmail.com