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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Missing reference section? 'MSP' on line 30 looks like a reference -- Missing reference section? 'SMIME3' on line 1818 looks like a reference -- Missing reference section? 'SMIME2' on line 1814 looks like a reference -- Missing reference section? 'ASN1-1988' on line 1793 looks like a reference -- Missing reference section? 'ESS' on line 298 looks like a reference -- Missing reference section? 'CMS' on line 1799 looks like a reference -- Missing reference section? 'MSG' on line 300 looks like a reference -- Missing reference section? '0' on line 1785 looks like a reference -- Missing reference section? '1' on line 1786 looks like a reference -- Missing reference section? 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Note that other groups may also distribute working documents as 13 Internet-Drafts. 15 Internet-Drafts are draft documents valid for a maximum of six months and 16 may be updated, replaced, or obsoleted by other documents at any time. It 17 is inappropriate to use Internet-Drafts as reference material or to cite 18 them other than as "work in progress." 20 To learn the current status of any Internet-Draft, please check the 21 "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow 22 Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au 23 (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West 24 Coast). 26 1. Introduction 28 This document describes three optional security service extensions for 29 S/MIME. These services provide functionality that is similar to the Message 30 Security Protocol [MSP], but are useful in many other environments, 31 particularly business and finance. The services are: 32 - signed receipts 33 - security labels 34 - secure mailing lists 36 The services described here are extensions to S/MIME version 3 [SMIME3], 37 and some of them can also be added to S/MIME version 2 [SMIME2]. The 38 extensions described here will not cause an S/MIME version 3 recipient to 39 be unable to read messages from an S/MIME version 2 sender. However, some 40 of the extensions will cause messages created by an S/MIME version 3 sender 41 to be unreadable by an S/MIME version 2 recipient. 43 The format of the messages are described in ASN.1:1988 [ASN1-1988]. 45 This draft is being discussed on the "ietf-smime" mailing list. To 46 subscribe, send a message to: 47 ietf-smime-request@imc.org 48 with the single word 49 subscribe 50 in the body of the message. There is a Web site for the mailing list at 51 . 53 1.1 Triple Wrapping 55 Some of the features of each service use the concept of a "triple wrapped" 56 message. A triple wrapped message is one that has been signed, then 57 encrypted, then signed again. The signers of the inner and outer signatures 58 may be different entities or the same entity. Note that the S/MIME 59 specification does not limit the number of nested encapsulations, so there 60 may be more than three wrappings. 62 1.1.1 Purpose of Triple Wrapping 64 Not all messages need to be triple wrapped. Triple wrapping is used when a 65 message must be signed, then encrypted, and then have authenticated 66 attributes bound to the encrypted body. Outer attributes may be added or 67 removed by the message originator or intermediate agents, and may be 68 authenticated by intermediate agents or the final recipient. 70 The inside signature is used for content integrity, non-repudiation with 71 proof of origin, and binding attributes (such as a security label) to the 72 original content. These attributes go from the originator to the recipient, 73 regardless of the number of intermediate entities such as mail list agents 74 that process the message. The authenticated attributes can be used for 75 access control to the inner body. Requests for signed receipts by the 76 originator are carried in the inside signature as well. 78 The encrypted body provides confidentiality, including confidentiality of 79 the attributes that are carried in the inside signature. 81 The outside signature provides authentication and integrity for information 82 that is processed hop-by-hop, where each hop is an intermediate entity such 83 as a mail list agent. The outer signature binds attributes (such as a 84 security label) to the encrypted body. These attributes can be used for 85 access control and routing decisions. 87 1.1.2 Steps for Triple Wrapping 89 The steps to create a triple wrapped message are: 91 1. Start with a message body, called the "original content". 93 2. Encapsulate the original content with the appropriate MIME Content-type 94 headers, such as "Content-type: text/plain". An exception to this MIME 95 encapsulation rule is that a signed receipt is not put in MIME headers. 97 3. Sign the result of step 2 (the inner MIME headers and the original 98 content). The SignedData encapContentInfo eContentType object identifier 99 MUST be id-data. If the structure you create in step 4 is multipart/signed, 100 then the SignedData encapContentInfo eContent MUST be absent. If the 101 structure you create in step 4 is application/pkcs7-mime, then the 102 SignedData encapContentInfo eContent MUST contain the result of step 2 103 above. The SignedData structure is encapsulated by a ContentInfo SEQUENCE 104 with a contentType of id-signedData. 106 4. Add an appropriate MIME construct to the signed message from step 3 as 107 defined in [SMIME3]. The resulting message is called the "inside 108 signature". 110 - If you are signing using multipart/signed, the MIME construct added 111 consists of a Content-type of multipart/signed with parameters, the 112 boundary, the result of step 2 above, the boundary, a Content-type of 113 application/pkcs7-signature, optional MIME headers (such as 114 Content-transfer-encoding and Content-disposition), and a body part that is 115 the result of step 3 above. 117 - If you are instead signing using application/pkcs7-mime, the MIME 118 construct added consists of a Content-type of application/pkcs7-mime with 119 parameters, optional MIME headers (such as Content-transfer-encoding and 120 Content-disposition), and the result of step 3 above. 122 5. Encrypt the result of step 4 as a single block, turning it into an 123 application/pkcs7-mime object. The EnvelopedData encryptedContentInfo 124 contentType MUST be id-data. The EnvelopedData structure is encapsulated by 125 a ContentInfo SEQUENCE with a contentType of id-envelopedData. This is 126 called the "encrypted body". 128 6. Add the appropriate MIME headers: a Content-type of 129 application/pkcs7-mime with parameters, and optional MIME headers such as 130 Content-transfer-encoding and Content-disposition. 132 7. Using the same logic as in step 3 above, sign the result of step 6 (the 133 MIME headers and the encrypted body) as a single block 135 8. Using the same logic as in step 4 above, add an appropriate MIME 136 construct to the signed message from step 7. The resulting message is 137 called the "outside signature", and is also the triple wrapped message. 139 1.2 Format of a Triple Wrapped Message 141 A triple wrapped message has many layers of encapsulation. The structure 142 differs based on the choice of format for the signed portions of the 143 message. Because of the way that MIME encapsulates data, the layers do not 144 appear in order, and the notion of "layers" becomes vague. 146 There is no need to use the multipart/signed format in an inner signature 147 because it is known that the recipient is able to process S/MIME messages 148 (because they decrypted the middle wrapper). A sending agent might choose 149 to use the multipart/signed format in the outer layer so that a non-S/MIME 150 agent could see that the next inner layer is encrypted; however, this is 151 not of great value, since all it shows the recipient is that the rest of 152 the message is unreadable. Because many sending agents always use 153 multipart/signed structures, all receiving agents MUST be able to interpret 154 either multipart/signed or application/pkcs7-mime signature structures. 156 The format of a triple wrapped message that uses multipart/signed for 157 both signatures is: 159 [step 8] Content-type: multipart/signed; 160 [step 8] protocol="application/pkcs7-signature"; 161 [step 8] boundary=outerboundary 162 [step 8] 163 [step 8] --outerboundary 164 [step 6] Content-type: application/pkcs7-mime; ) 165 [step 6] smime-type=enveloped-data ) 166 [step 6] ) 167 [step 4] Content-type: multipart/signed; | ) 168 [step 4] protocol="application/pkcs7-signature"; | ) 169 [step 4] boundary=innerboundary | ) 170 [step 4] | ) 171 [step 4] --innerboundary | ) 172 [step 2] Content-type: text/plain % | ) 173 [step 2] % | ) 174 [step 1] Original content % | ) 175 [step 4] | ) 176 [step 4] --innerboundary | ) 177 [step 4] Content-type: application/pkcs7-signature | ) 178 [step 4] | ) 179 [step 3] inner signedData block (eContent is missing) | ) 180 [step 4] | ) 181 [step 4] --innerboundary | ) 182 [step 8] 183 [step 8] --outerboundary 184 [step 8] Content-type: application/pkcs7-signature 185 [step 8] 186 [step 7] outer signedData block 187 [step 8] 188 [step 8] --outerboundary 190 % = These lines are what the inner signature is computed over. 191 | = These lines are what is encrypted in step 5. This encrypted result 192 is opaque and is a part of an EnvelopedData block. 193 ) = These lines are what the outer signature is computed over. 195 The format of a triple wrapped message that uses application/pkcs7-mime for 196 the both signatures is: 198 [step 8] Content-type: application/pkcs7-mime; 199 [step 8] smime-type=signed-data 200 [step 8] 201 [step 7] outer SignedData block (eContent is present) O 202 [step 6] Content-type: application/pkcs7-mime; ) O 203 [step 6] smime-type=enveloped-data; ) O 204 [step 6] ) O 205 [step 4] Content-type: application/pkcs7-mime; | ) O 206 [step 4] smime-type=signed-data | ) O 207 [step 4] | ) O 208 [step 3] inner SignedData block (eContent is present) I | ) O 209 [step 2] Content-type: text/plain I | ) O 210 [step 2] I | ) O 211 [step 1] Original content I | ) O 213 I = These lines are the inner SignedData block, which is opaque and 214 contains the ASN.1 encoded result of step 2 as well as control 215 information. 216 | = These lines are what is encrypted in step 5. This encrypted result 217 is opaque and is a part of an EnvelopedData block. 218 ) = These lines are what the outer signature is computed over. 219 O = These lines are the outer SignedData block, which is opaque and 220 contains the ASN.1 encoded result of step 6 as well as control 221 information. 223 1.3 Security Services and Triple Wrapping 225 The three security services described in this document are used with triple 226 wrapped messages in different ways. This section briefly describes the 227 relationship of each service with triple wrapping; the other sections of 228 the document go into greater detail. 230 1.3.1 Signed Receipts and Triple Wrapping 232 A signed receipt may be requested in any SignedData object. However, if a 233 signed receipt is requested for a triple wrapped message, the receipt 234 request MUST be in the inside signature, not in the outside signature. A 235 secure mailing list agent may change the receipt policy in the outside 236 signature of a triple wrapped message when that message is processed by the 237 mailing list. 239 Note: the signed receipts and receipt requests described in this draft 240 differ from those described in the work done by the IETF Receipt 241 Notification Working Group. The output of that Working Group, when 242 finished, is not expected to work well with triple wrapped messages as 243 described in this document. 245 1.3.2 Security Labels and Triple Wrapping 247 A security label may be included in the authenticated attributes of any 248 SignedData object. A security label attribute may be included in either the 249 inner signature, outer signature, or both. 251 The inner security label is used for access control decisions related to 252 the plaintext original content. The inner signature provides authentication 253 and cryptographically protects the original signer's security label that is 254 on the inside body. This strategy facilitates the forwarding of messages 255 because the original signer's security label is included in the SignedData 256 block which can be forwarded to a third party that can verify the inner 257 signature which will cover the inner security label. The confidentiality 258 security service can be applied to the inner security label by encrypting 259 the entire inner SignedData block within an EnvelopedData block. 261 A security label may also be included in the authenticated attributes of 262 the outer SignedData block which will include the sensitivities of the 263 encrypted message. The outer security label is used for access control and 264 routing decisions related to the encrypted message. Note that a security 265 label attribute can only be used in an authenticatedAttributes block. An 266 eSSSecurityLabel attribute MUST NOT be used in an EnvelopedData or 267 unauthenticated attributes. 269 1.3.3 Secure Mailing Lists and Triple Wrapping 271 Secure mail list message processing depends on the structure of S/MIME 272 layers present in the message sent to the mail list agent. The agent never 273 changes the data that was hashed to form the inner signature, if such a 274 signature is present. If an outer signature is present, then the agent will 275 modify the data that was hashed to form that outer signature. In all cases, 276 the agent adds or updates an mlExpansionHistory attribute to document the 277 agent's processing, and ultimately adds or replaces the outer signature on 278 the message to be distributed. 280 1.3.4 Placement of Attributes 282 Certain attributes should be placed in the inner or outer SignedData 283 message; some attributes can be in either. Further, some attributes must be 284 authenticated, while authentication is optional for others. The following 285 table summarizes the recommendation of this profile. 287 | |Inner or |MUST be 288 Attribute |OID |outer |authenticated 289 ------------------|-----------------------------|----------|------------- 290 contentHints |id-aa-contentHint [ESS] |either |no 291 contentIdentifier |id-aa-contentIdentifier [ESS]|either |no 292 contentType |id-contentType [CMS] |either |yes 293 counterSignature |id-countersignature [CMS] |either |MUST NOT 294 eSSSecurityLabel |id-aa-securityLabel [ESS] |either |yes 295 messageDigest |id-messageDigest [CMS] |either |yes 296 msgSigDigest |id-aa-msgSigDigest [ESS] |inner only|yes 297 mlExpansionHistory|id-aa-mlExpandHistory [ESS] |outer only|yes 298 receiptRequest |id-aa-receiptRequest [ESS] |inner only|yes 299 signingTime |id-signingTime [CMS] |either |yes 300 smimeCapabilities |sMIMECapabilities [MSG] |either |yes 302 If a counterSignature attribute is present, then it MUST be included in the 303 unauthenticated attributes. It MUST NOT be included in the authenticated 304 attributes. 306 Note that the inner and outer signatures are for different senders, so that 307 the same attribute in the two signatures could lead to very different 308 consequences. 310 ContentIdentifier is an attribute (OCTET STRING) used to carry a unique 311 identifier assigned to the message. 313 1.4 Object Identifiers 315 The object identifiers for many of the objects described in this draft are 316 found in [CMS} and [SMIME3]. Other object identifiers used in S/MIME can be 317 found in the registry kept at . 318 When this draft moves to standards track within the IETF, it is intended 319 that the IANA will maintain this registry. 321 1.5 Criticality of Attributes 323 Authenticated attributes can be marked as critical. In this specification, 324 the only attribute which MUST be marked as critical is eSSSecurityLabel. 326 Note that marking any attribute as critical will make the message 327 unreadable to S/MIME v2 recipients. Because of this, a sending agent should 328 only mark attributes critical if necessary for the agent's application, and 329 at the risk of preventing an S/MIME v2 recipient from verifying (or 330 possibly even being able to read) the message. 332 2. Signed Receipts 334 Returning a signed receipt provides to the originator proof of delivery of 335 a message, and allows the originator to demonstrate to a third party that 336 the recipient was able to verify the signature of the original message. 337 This receipt is bound to the original message through the signature; 338 consequently, this service may be requested only if a message is signed. 339 The receipt sender may optionally also encrypt a receipt to provide 340 confidentiality between the receipt sender and the receipt recipient. 342 2.1 Signed Receipt Concepts 344 The originator of a message may request a signed receipt from the message's 345 recipients. The request is indicated by adding a receiptRequest attribute 346 to the authenticatedAttributes field of the SignerInfo object for which the 347 receipt is requested. The receiving user agent software SHOULD 348 automatically create a signed receipt when requested to do so, and return 349 the receipt in accordance with mailing list expansion options, local 350 security policies, and configuration options. 352 Because receipts involve the interaction of two parties, the terminology 353 can sometimes be confusing. In this section, the "sender" is the agent that 354 sent the original message that included a request for a receipt. The 355 "receiver" is the party that received that message and generated the 356 receipt. 358 The steps in a typical transaction are: 360 1. Sender creates a signed message including a receipt request attribute 361 (Section 2.2). 363 2. Sender transmits the resulting message to the recipient or recipients. 365 3. Recipient receives message and determines if there is a valid signature 366 and receipt request in the message (Section 2.3). 368 4. Recipient creates a signed receipt (Section 2.4). 370 5. Recipient transmits the resulting signed receipt message to the sender 371 (Section 2.5). 373 6. Sender receives the message and validates that it contains a signed 374 receipt for the original message (Section 2.6). This validation relies on 375 the sender having retained either a copy of the original message or 376 information extracted from the original message. 378 The ASN.1 syntax for the receipt request is given in Section 2.7; the ASN.1 379 syntax for the receipt is given in Section 2.8. 381 Note that an agent SHOULD remember when it has sent a receipt so that it 382 can avoid re-sending a receipt each time it processes the message. 384 2.2 Receipt Request Creation 386 Multi-layer S/MIME messages may contain multiple SignedData layers. 387 However, receipts may be requested only for the innermost SignedData layer 388 in a multi-layer S/MIME message, such as a triple wrapped message. Only one 389 receiptRequest attribute can be included in the authenticatedAttributes of 390 a SignerInfo. 392 A ReceiptRequest attribute MUST NOT be included in the attributes of a 393 SignerInfo in a SignedData object that encapsulates a Receipt content. In 394 other words, the user agent MUST NOT request a signed receipt for a signed 395 receipt. 397 A sender requests receipts by placing a receiptRequest attribute in the 398 authenticated attributes of a signerInfo as follows: 400 1. A receiptRequest data structure is created. 402 2. A signed content identifier for the message is created and assigned to 403 the signedContentIdentifier field. The signedContentIdentifier is used to 404 associate the signed receipt with the message requesting the signed 405 receipt. 407 3. The entities requested to return a signed receipt are noted in the 408 receiptsFrom field. 410 4. The message originator MUST populate the receiptsTo field with a 411 GeneralNames for each entity to whom the recipient should send the signed 412 receipt. If the message originator wants the recipient to send the signed 413 receipt to the originator, then the originator MUST include a GeneralNames 414 for itself in the receiptsTo field. GeneralNames is a SEQUENCE OF 415 GeneralName. receiptsTo is a SEQUENCE OF GeneralNames in which each 416 GeneralNames represents an entity. There may be multiple GeneralName 417 instances in each GeneralNames. At a minimum, the message originator MUST 418 populate each entity's GeneralNames with the address to which the signed 419 receipt should be sent. Optionally, the message originator MAY also 420 populate each entity's GeneralNames with other GeneralName instances (such 421 as directoryName). 423 5. The completed receiptRequest attribute is placed in the 424 authenticatedAttributes field of the SignerInfo object. 426 2.2.1 Multiple Receipt Requests 428 There can be multiple SignerInfos within a SignedData object, and each 429 SignerInfo may include authenticatedAttributes. Therefore, a single 430 SignedData object may include multiple SignerInfos, each SignerInfo having 431 a receiptRequest attribute. For example, an originator can send a signed 432 message with two SignerInfos, one containing a DSS signature, the other 433 containing an RSA signature. 435 Each recipient SHOULD return only one signed receipt. 437 Not all of the SignerInfos need to include receipt requests, but in all of 438 the SignerInfos that do contain receipt requests, the receipt requests MUST 439 be identical. 441 2.2.2 Information Needed to Validate Signed Receipts 443 The sending agent MUST retain one or both of the following items to support 444 the validation of signed receipts returned by the recipients. 446 - the original signedData object requesting the signed receipt 448 - the message signature digest value used to generate the original 449 signedData signerInfo signature value and the digest value of the 450 Receipt content containing values included in the original signedData 451 object. If signed receipts are requested from multiple recipients, then 452 retaining these digest values is a performance enhancement because the 453 sending agent can reuse the saved values when verifying each returned 454 signed receipt. 456 2.3 Receipt Request Processing 458 A receiptRequest is associated only with the SignerInfo object in which the 459 receipt request attribute is directly attached. Processing software SHOULD 460 examine the authenticatedAttributes field of each of the SignerInfos for 461 which it verifies a signature in the innermost signedData object to 462 determine if a receipt is requested. This may result in the receiving agent 463 processing multiple receiptRequest attributes included in a single 464 SignedData object. 466 Because all receiptRequest attributes in a SignedData object must be 467 identical, the receiving application fully processes (as described in the 468 following paragraphs) the first receiptRequest that it encounters in a 469 SignerInfo that it can verify, and it then ensures that all other 470 receiptRequests are identical to the first one encountered. If 471 ReceiptRequests which conflict are present, then the processing software 472 MUST NOT return any receipt. 474 If a receiptRequest attribute is absent from the authenticated attributes, 475 then a signed receipt has not been requested from any of the message 476 recipients and MUST NOT be created. If a receiptRequest attribute is 477 present in the authenticated attributes, then a signed receipt has been 478 requested from some or all of the message recipients. Note that in some 479 cases, a receiving agent might receive two almost-identical messages, one 480 with a receipt request and the other without one. In this case, the 481 receiving agent SHOULD send a signed receipt for the message that requests 482 a signed receipt. A receipt SHOULD be returned if any signature containing 483 a receipt request can be validated, even if other signatures containing the 484 same receipt request cannot be validated. 486 If a receiptRequest attribute is present in the authenticated attributes, 487 the following process SHOULD be used to determine if a message recipient 488 has been requested to return a signed receipt. 490 1. If an mlExpansionHistory attribute is present in the outermost 491 signedData block, do one of the following two steps, based on the absence 492 or presence of mlReceiptPolicy: 494 1.1. If an mlReceiptPolicy value is absent from the last MLData 495 element, a Mail List receipt policy has not been specified and the 496 processing software SHOULD examine the receiptRequest attribute value 497 to determine if a receipt should be created and returned. 499 1.2. If an mlReceiptPolicy value is present in the last MLData element, 500 do one of the following two steps, based on the value of 501 mlReceiptPolicy: 503 1.2.1. If the mlReceiptPolicy value is none, then the receipt 504 policy of the Mail List supersedes the originator's request for a 505 signed receipt and a signed receipt MUST NOT be created. 507 1.2.2. If the mlReceiptPolicy value is insteadOf or inAdditionTo, 508 the processing software SHOULD examine the receiptsFrom value from 509 the receiptRequest attribute to determine if a receipt should be 510 created and returned. If a receipt is created, the insteadOf and 511 inAdditionTo fields identify entities that SHOULD be sent the 512 receipt instead of or in addition to the originator. 514 2. If the receiptsFrom value of the receiptRequest attribute is 515 allOrFirstTier, do one of the following two steps based on the value of 516 allOrFirstTier. 518 2.1. If the value of allOrFirstTier is allReceipts, then a signed 519 receipt SHOULD be created. 521 2.2. If the value of allOrFirstTier is firstTierRecipients, do one of 522 the following two steps based on the presence of an mlExpansionHistory 523 attribute in an outer signedData block: 525 2.2.1. If an mlExpansionHistory attribute is present, then this 526 recipient is not a first tier recipient and a signed receipt MUST 527 NOT be created. 529 2.2.2. If an mlExpansionHistory attribute is not present, then a 530 signed receipt SHOULD be created. 532 3. If the receiptsFrom value of the receiptRequest attribute is a 533 receiptList: 535 3.1. If receiptList contains one of the GeneralNames of the recipient, 536 then a signed receipt should be created. 538 3.2. If receiptList does not contain one of the GeneralNames of the 539 recipient, then a signed receipt MUST NOT be created. 541 A flow chart for the above steps to be executed for each signerInfo for 542 which the receiving agent verifies the signature would be: 544 0. Receipt Request attribute present? 545 YES -> 1. 546 NO -> STOP 547 1. Has mlExpansionHistory in outer signedData? 548 YES -> 1.1. 549 NO -> 2. 550 1.1. mlReceiptPolicy absent? 551 YES -> 2. 552 NO -> 1.2. 553 1.2. Pick based on value of mlReceiptPolicy. 554 none -> 1.2.1. 555 insteadOf or inAdditionTo -> 1.2.2. 556 1.2.1. STOP. 557 1.2.2. Examine receiptsFrom to determine if a receipt should be created, 558 create it if required, send it to recipients designated by 559 mlReceiptPolicy, then -> STOP. 560 2. Is value of receiptsFrom allOrFirstTier? 561 YES -> Pick based on value of allOrFirstTier. 562 allReceipts -> 2.1. 563 firstTierRecipients -> 2.2. 564 NO -> 3. 565 2.1. Create a receipt, then -> STOP. 566 2.2. Has mlExpansionHistory in the outer signedData block? 567 YES -> 2.2.1. 568 NO -> 2.2.2. 569 2.2.1. STOP. 570 2.2.2. Create a receipt, then -> STOP. 571 3. Is receiptsFrom value of receiptRequest a receiptList? 572 YES -> 3.1. 573 NO -> STOP. 574 3.1. Does receiptList contain the recipient? 575 YES -> Create a receipt, then -> STOP. 576 NO -> 3.2. 577 3.2. STOP. 579 2.4 Signed Receipt Creation 581 A signed receipt is a signedData object encapsulating a Receipt content 582 (also called a "signedData/Receipt"). Signed receipts are created as 583 follows: 585 1. The signature of the original signedData signerInfo that includes the 586 receiptRequest authenticated attribute MUST be successfully verified before 587 creating the signedData/Receipt. 589 1.1. The content of the original signedData object is digested as 590 described in [CMS]. The resulting digest value is then compared with 591 the value of the messageDigest attribute included in the 592 authenticatedAttributes of the original signedData signerInfo. If these 593 digest values are different, then the signature verification process 594 fails and the signedData/Receipt MUST NOT be created. 596 1.2. The ASN.1 DER encoded authenticatedAttributes (including 597 messageDigest, receiptRequest and, possibly, other authenticated 598 attributes) in the original signedData signerInfo are digested as 599 described in [CMS]. The resulting digest value, called msgSigDigest, is 600 then used to verify the signature of the original signedData 601 signerInfo. If the signature verification fails, then the 602 signedData/Receipt MUST NOT be created. 604 2. A Receipt structure is created. 606 2.1. The value of the Receipt version field is set to 1. 608 2.2. The object identifier from the contentType attribute included in 609 the original signedData signerInfo that includes the receiptRequest 610 attribute is copied into the Receipt contentType. 612 2.3. The original signedData signerInfo receiptRequest 613 signedContentIdentifier is copied into the Receipt 614 signedContentIdentifier. 616 2.4. The signature value from the original signedData signerInfo that 617 includes the receiptRequest attribute is copied into the Receipt 618 originatorSignatureValue. 620 3. The Receipt structure is ASN.1 DER encoded to produce a data stream, D1. 622 4. D1 is digested. The resulting digest value is included as the 623 messageDigest attribute in the authenticatedAttributes of the signerInfo 624 which will eventually contain the signedData/Receipt signature value. 626 5. The digest value (msgSigDigest) calculated in Step 1 to verify the 627 signature of the original signedData signerInfo is included as the 628 msgSigDigest attribute in the authenticatedAttributes of the signerInfo 629 which will eventually contain the signedData/Receipt signature value. 631 6. A contentType attribute including the id-ct-receipt object identifier 632 MUST be created and added to the authenticated attributes of the signerInfo 633 which will eventually contain the signedData/Receipt signature value. 635 7. A signingTime attribute indicating the time that the signedData/Receipt 636 is signed SHOULD be created and added to the authenticated attributes of 637 the signerInfo which will eventually contain the signedData/Receipt 638 signature value. Other attributes (except receiptRequest) may be added to 639 the authenticatedAttributes of the signerInfo. 641 8. The authenticatedAttributes (messageDigest, msgSigDigest, contentType 642 and, possibly, others) of the signerInfo are ASN.1 DER encoded and digested 643 as described in CMS, Section 5.3. The resulting digest value is used to 644 calculate the signature value which is then included in the 645 signedData/Receipt signerInfo. 647 9. The ASN.1 DER encoded Receipt content MUST be directly encoded within 648 the signedData encapContentInfo eContent OCTET STRING defined in [CMS]. The 649 id-ct-receipt object identifier MUST be included in the signedData 650 encapContentInfo eContentType. This results in a single ASN.1 encoded 651 object composed of a signedData including the Receipt content. The Data 652 content type MUST NOT be used. The Receipt content MUST NOT be encapsulated 653 in a MIME header or any other header prior to being encoded as part of the 654 signedData object. 656 10. The signedData/Receipt is then put in an application/pkcs7-mime MIME 657 wrapper with the smime-type parameter set to "signed-receipt". This will 658 allow for identification of signed receipts without having to crack the 659 ASN.1 body. The smime-type parameter would still be set as normal in any 660 layer wrapped around this message. 662 11. If the signedData/Receipt is to be encrypted within an envelopedData 663 object, then an outer signedData object MUST be created that encapsulates 664 the envelopedData object, and a contentHints attribute with contentType set 665 to the id-ct-receipt object identifier MUST be included in the outer 666 signedData SignerInfo authenticatedAttributes. When a receiving agent 667 processes the outer signedData object, the presence of the id-ct-receipt 668 OID in the contentHints contentType indicates that a signedData/Receipt is 669 encrypted within the envelopedData object encapsulated by the outer 670 signedData. 672 2.4.1 MLExpansionHistory Attributes and Receipts 674 An MLExpansionHistory attribute MUST NOT be included in the attributes of a 675 SignerInfo in a SignedData object that encapsulates a Receipt content. This 676 is true because when a SignedData/Receipt is sent to an MLA for 677 distribution, then the MLA must always encapsulate the received 678 SignedData/Receipt in an outer SignedData in which the MLA will include the 679 MLExpansionHistory attribute. The MLA cannot change the 680 authenticatedAttributes of the received SignedData/Receipt object, so it 681 can't add the MLExpansionHistory to the SignedData/Receipt. 683 2.5 Determining the Recipients of the Signed Receipt 685 If a signed receipt was created by the process described in the sections 686 above, then the software MUST use the following process to determine to 687 whom the signed receipt should be sent. 689 1. The receiptsTo field must be present in the receiptRequest attribute. 690 The software initiates the sequence of recipients with the value(s) of 691 receiptsTo. 693 2. If the MlExpansionHistory attribute is present in the outer SignedData 694 block, and the last MLData contains an MLReceiptPolicy value of insteadOf, 695 then the software replaces the sequence of recipients with the value(s) of 696 insteadOf. 698 3. If the MlExpansionHistory attribute is present in the outer SignedData 699 block and the last MLData contains an MLReceiptPolicy value of 700 inAdditionTo, then the software adds the value(s) of inAdditionTo to the 701 sequence of recipients. 703 2.6. Signed Receipt Validation 705 A signed receipt is communicated as a single ASN.1 encoded object composed 706 of a signedData object directly including a Receipt content. It is 707 identified by the presence of the id-ct-receipt object identifier in the 708 encapContentInfo eContentType value of the signedData object including the 709 Receipt content. 711 A signedData/Receipt is validated as follows: 713 1. ASN.1 decode the signedData object including the Receipt content. 715 2. Extract the contentType, signedContentIdentifier, and 716 originatorSignatureValue from the decoded Receipt structure to identify the 717 original signedData signerInfo that requested the signedData/Receipt. 719 3. Acquire the message signature digest value calculated by the sender to 720 generate the signature value included in the original signedData signerInfo 721 that requested the signedData/Receipt. 723 3.1. If the sender-calculated message signature digest value has been 724 saved locally by the sender, it must be located and retrieved. 726 3.2. If it has not been saved, then it must be re-calculated based on 727 the original signedData content and authenticatedAttributes as 728 described in [CMS]. 730 4. The message signature digest value calculated by the sender is then 731 compared with the value of the msgSigDigest authenticatedAttribute included 732 in the signedData/Receipt signerInfo. If these digest values are identical, 733 then that proves that the message signature digest value calculated by the 734 recipient based on the received original signedData object is the same as 735 that calculated by the sender. This proves that the recipient received 736 exactly the same original signedData content and authenticatedAttributes as 737 sent by the sender because that is the only way that the recipient could 738 have calculated the same message signature digest value as calculated by 739 the sender. If the digest values are different, then the signedData/Receipt 740 signature verification process fails. 742 5. Acquire the digest value calculated by the sender for the Receipt 743 content constructed by the sender (including the contentType, 744 signedContentIdentifier, and signature value that were included in the 745 original signedData signerInfo that requested the signedData/Receipt). 747 5.1. If the sender-calculated Receipt content digest value has been 748 saved locally by the sender, it must be located and retrieved. 750 5.2. If it has not been saved, then it must be re-calculated. As 751 described in section 2.4 above, step 2, create a Receipt structure 752 including the contentType, signedContentIdentifier and signature value 753 that were included in the original signedData signerInfo that requested 754 the signed receipt. The Receipt structure is then ASN.1 DER encoded to 755 produce a data stream which is then digested to produce the Receipt 756 content digest value. 758 6. The Receipt content digest value calculated by the sender is then 759 compared with the value of the messageDigest authenticatedAttribute 760 included in the signedData/Receipt signerInfo. If these digest values are 761 identical, then that proves that the values included in the Receipt content 762 by the recipient are identical to those that were included in the original 763 signedData signerInfo that requested the signedData/Receipt. This proves 764 that the recipient received the original signedData signed by the sender, 765 because that is the only way that the recipient could have obtained the 766 original signedData signerInfo signature value for inclusion in the Receipt 767 content. If the digest values are different, then the signedData/Receipt 768 signature verification process fails. 770 7. The ASN.1 DER encoded authenticatedAttributes of the signedData/Receipt 771 signerInfo are digested as described in [CMS]. 773 8. The resulting digest value is then used to verify the signature value 774 included in the signedData/Receipt signerInfo. If the signature 775 verification is successful, then that proves the integrity of the 776 signedData/receipt signerInfo authenticatedAttributes and authenticates the 777 identity of the signer of the signedData/Receipt signerInfo. Note that the 778 authenticatedAttributes include the recipient-calculated Receipt content 779 digest value (messageDigest attribute) and recipient-calculated message 780 signature digest value (msgSigDigest attribute). Therefore, the 781 aforementioned comparison of the sender-generated and recipient-generated 782 digest values combined with the successful signedData/Receipt signature 783 verification proves that the recipient received the exact original 784 signedData content and authenticatedAttributes (proven by msgSigDigest 785 attribute) that were signed by the sender of the original signedData object 786 (proven by messageDigest attribute). If the signature verification fails, 787 then the signedData/Receipt signature verification process fails. 789 The signature verification process for each signature algorithm that is 790 used in conjunction with the CMS protocol is specific to the algorithm. 791 These processes are described in documents specific to the algorithms. 793 2.7 Receipt Request Syntax 795 A receiptRequest attribute value has ASN.1 type ReceiptRequest. Use the 796 receiptRequest attribute only within the authenticated attributes 797 associated with a signed message. 799 ReceiptRequest ::= SEQUENCE { 800 signedContentIdentifier ContentIdentifier, 801 receiptsFrom ReceiptsFrom, 802 receiptsTo SEQUENCE SIZE (1..ub-receiptsTo)) OF GeneralNames } 804 ub-receiptsTo INTEGER ::= 16 806 id-aa-receiptRequest OBJECT IDENTIFIER ::= { iso(1) member-body(2) 807 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 1} 809 ContentIdentifier ::= OCTET STRING 811 id-aa-contentIdentifier OBJECT IDENTIFIER ::= { iso(1) member-body(2) 812 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 7} 814 A signedContentIdentifier MUST be created by the message originator when 815 creating a receipt request. To ensure global uniqueness, the minimal 816 signedContentIdentifier SHOULD contain a concatenation of user-specific 817 identification information (such as a user name or public keying material 818 identification information), a GeneralizedTime string, and a random number. 820 The receiptsFrom field is used by the originator to specify the recipients 821 requested to return a signed receipt. A CHOICE is provided to allow 822 specification of: 823 - receipts from all recipients are requested 824 - receipts from first tier (recipients that did not receive the 825 message as members of a mailing list) recipients are requested 826 - receipts from a specific list of recipients are requested 828 ReceiptsFrom ::= CHOICE { 829 allOrFirstTier [0] AllOrFirstTier, 830 -- formerly "allOrNone [0]AllOrNone" 831 receiptList [1] SEQUENCE OF GeneralNames } 833 AllOrFirstTier ::= INTEGER { -- Formerly AllOrNone 834 allReceipts (0), 835 firstTierRecipients (1) } 837 The receiptsTo field is used by the originator to identify the user(s) to 838 whom the identified recipient should send signed receipts. The message 839 originator MUST populate the receiptsTo field with a GeneralNames for each 840 entity to whom the recipient should send the signed receipt. If the message 841 originator wants the recipient to send the signed receipt to the 842 originator, then the originator MUST include a GeneralNames for itself in 843 the receiptsTo field. 845 2.8 Receipt Syntax 847 Receipts are represented using a new content type, Receipt. The Receipt 848 content type shall have ASN.1 type Receipt. Receipts must be encapsulated 849 within a SignedData message. 851 Receipt ::= SEQUENCE { 852 version Version, -- Version is imported from [CMS] 853 contentType ContentType, 854 signedContentIdentifier ContentIdentifier, 855 originatorSignatureValue OCTET STRING } 857 id-ct-receipt OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) 858 rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-ct(1) 1} 860 The version field defines the syntax version number, which is 1 for this 861 version of the standard. 863 2.9 Content Hints 865 Many applications find it useful to have information that describes the 866 innermost signed content of a multi-layer message available on the 867 outermost signature layer. The contentHints attribute provides such 868 information. 870 Content-hints attribute values have ASN.1 type contentHints. 872 ContentHints ::= SEQUENCE { 873 contentDescription [0] IMPLICIT OCTET STRING SIZE (1..MAX) OPTIONAL, 874 -- If contentDescription is used, its contents MUST be in UTF8 format 875 contentType ContentType } 877 id-aa-contentHint OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) 878 rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 4} 880 The contentDescription field may be used to provide information that the 881 recipient may use to select protected messages for processing, such as a 882 message subject. If this field is set, then the attribute is expected to 883 appear on the signedData object enclosing an envelopedData object and not 884 on the inner signedData object. If a contentDescription is present, it MUST 885 be in UTF8 format, as described in [UTF8]. The SIZE (1..MAX) construct 886 constrains the sequence to have at least one entry. MAX indicates the upper 887 bound is unspecified. Implementations are free to choose an upper bound 888 that suits their environment. 890 Messages which contain a signedData object wrapped around an envelopedData 891 object, thus masking the inner content type of the message, SHOULD include 892 a contentHints attribute, except for the case of the data content type. 893 Specific message content types may either force or preclude the inclusion 894 of the contentHints attribute. For example, when a signedData/Receipt is 895 encrypted within an envelopedData object, an outer signedData object MUST 896 be created that encapsulates the envelopedData object and a contentHints 897 attribute with contentType set to the id-ct-receipt object identifier MUST 898 be included in the outer signedData SignerInfo authenticatedAttributes. 900 2.10 Message Signature Digest Attribute 902 The msgSigDigest attribute can only be used in the authenticated attributes 903 of a signed receipt. It contains the digest of the ASN.1 DER encoded 904 authenticatedAttributes included in the original signedData that requested 905 the signed receipt. Only one msgSigDigest attribute can appear in an 906 authenticated attributes set. It is defined as follows: 908 msgSigDigest ::= OCTET STRING 910 id-aa-msgSigDigest OBJECT IDENTIFIER ::= { iso(1) member-body(2) 911 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 5} 913 3. Security Labels 915 This section describes the syntax to be used for security labels that can 916 optionally be associated with S/MIME encapsulated data. A security label is 917 a set of security information regarding the sensitivity of the content that 918 is protected by S/MIME encapsulation. 920 "Authorization" is the act of granting rights and/or privileges to users 921 permitting them access to an object. "Access control" is a means of 922 enforcing these authorizations. The sensitivity information in a security 923 label can be compared with a user's authorizations to determine if the user 924 is allowed to access the content that is protected by S/MIME encapsulation. 926 Security labels may be used for other purposes such as a source of routing 927 information. The labels are often priority based ("secret", "confidential", 928 "restricted", and so on) or role-based, describing which kind of people can 929 see the information ("patient's health-care team", "medical billing 930 agents", "unrestricted", and so on). 932 3.1 Security Label Processing Rules 934 A sending agent may include a security label attribute in the authenticated 935 attributes of a signedData object. A receiving agent examines the security 936 label on a received message and determines whether or not the recipient is 937 allowed to see the contents of the message. 939 3.1.1 Adding Security Labels 941 A sending agent that is using security labels MUST put the security label 942 attribute in the authenticatedAttributes field of a SignerInfo block. The 943 security label attribute MUST NOT be included in the unauthenticated 944 attributes. Integrity and authentication security services MUST be applied 945 to the security label, therefore it MUST be included as an authenticated 946 attribute, if used. This causes the security label attribute to be part of 947 the data that is hashed to form the SignerInfo signature value. A 948 SignerInfo block MUST NOT have more than one security label authenticated 949 attribute. 951 When there are multiple SignedData blocks applied to a message, a security 952 label attribute may be included in either the inner signature, outer 953 signature, or both. A security label authenticated attribute may be 954 included in a authenticatedAttributes field within the inner SignedData 955 block. The inner security label will include the sensitivities of the 956 original content and will be used for access control decisions related to 957 the plaintext encapsulated content. The inner signature provides 958 authentication of the inner security label and cryptographically protects 959 the original signer's inner security label of the original content. 961 When the originator signs the plaintext content and authenticated 962 attributes, the inner security label is bound to the plaintext content. An 963 intermediate entity cannot change the inner security label without 964 invalidating the inner signature. The confidentiality security service can 965 be applied to the inner security label by encrypting the entire inner 966 signedData object within an EnvelopedData block. 968 A security label authenticated attribute may also be included in a 969 authenticatedAttributes field within the outer SignedData block. The outer 970 security label will include the sensitivities of the encrypted message and 971 will be used for access control decisions related to the encrypted message 972 and for routing decisions. The outer signature provides authentication of 973 the outer security label (as well as for the encapsulated content which may 974 include nested S/MIME messages). 976 There can be multiple SignerInfos within a SignedData object, and each 977 SignerInfo may include authenticatedAttributes. Therefore, a single 978 SignedData object may include multiple eSSSecurityLabels, each SignerInfo 979 having an eSSSecurityLabel attribute. For example, an originator can send a 980 signed message with two SignerInfos, one containing a DSS signature, the 981 other containing an RSA signature. If any of the SignerInfos included in a 982 SignedData object include an eSSSecurityLabel attribute, then all of the 983 SignerInfos in that SignedData object MUST include an eSSSecurityLabel 984 attribute and the value of each MUST be identical. 986 3.1.2 Processing Security Labels 988 Before processing an eSSSecurityLabel authenticatedAttribute, the receiving 989 agent MUST verify the signature of the SignerInfo which covers the 990 eSSSecurityLabel attribute. A recipient MUST NOT process an 991 eSSSecurityLabel attribute that has not been verified. 993 A receiving agent MUST process the eSSSecurityLabel attribute, if present, 994 in each SignerInfo in the SignedData object for which it verifies the 995 signature. This may result in the receiving agent processing multiple 996 eSSSecurityLabels included in a single SignedData object. Because all 997 eSSSecurityLabels in a SignedData object must be identical, the receiving 998 agent processes (such as performing access control) on the first 999 eSSSecurityLabel that it encounters in a SignerInfo that it verifies, and 1000 then ensures that all other eSSSecurityLabels in signerInfos that it 1001 verifies are identical to the first one encountered. If the 1002 eSSSecurityLabels in the signerInfos that it verifies are not all 1003 identical, then the receiving agent MUST warn the user of this condition. 1005 3.2 Syntax of eSSSecurityLabel 1007 The eSSSecurityLabel syntax is derived directly from [MTSABS] ASN.1 module. 1008 (The MTSAbstractService module begins with "DEFINITIONS IMPLICIT TAGS 1009 ::=".) Further, the eSSSecurityLabel syntax is compatible with that used in 1010 [MSP4]. 1012 The eSSSecurityLabel MUST be marked as critical. This means that any 1013 message with an eSSSecurityLabel will be unreadable to S/MIME v2 clients. 1014 Because of this, a sending agent SHOULD apply an eSSSecurityLabel only if 1015 it needs the services this attribute provides. 1017 ESSSecurityLabel ::= SET { 1018 version Version DEFAULT v1, 1019 security-policy-identifier SecurityPolicyIdentifier OPTIONAL, 1020 security-classification SecurityClassification OPTIONAL, 1021 privacy-mark ESSPrivacyMark OPTIONAL, 1022 security-categories SecurityCategories OPTIONAL } 1024 id-aa-securityLabel OBJECT IDENTIFIER ::= { iso(1) member-body(2) 1025 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 2} 1027 SecurityPolicyIdentifier ::= OBJECT IDENTIFIER 1029 SecurityClassification ::= INTEGER { 1030 unmarked (0), 1031 unclassified (1), 1032 restricted (2), 1033 confidential (3), 1034 secret (4), 1035 top-secret (5) } (0..ub-integer-options) 1037 ub-integer-options INTEGER ::= 256 1039 ESSPrivacyMark ::= CHOICE { 1040 pString PrintableString (SIZE (1..ub-privacy-mark-length)), 1041 -- If pString is used, the ESSSecurityLabel version is set to v1 1042 utf8String [0] IMPLICIT OCTET STRING SIZE (1..MAX) 1043 -- If utf8String is used, its contents MUST be in UTF8 format, and 1044 -- the ESSSecurityLabel version is set to v2 1045 } 1047 ub-privacy-mark-length INTEGER ::= 128 1049 SecurityCategories ::= SET SIZE (1..ub-security-categories) OF 1050 SecurityCategory 1052 ub-security-categories INTEGER ::= 64 1054 SecurityCategory ::= SEQUENCE { 1055 type [0] OBJECT IDENTIFIER, 1056 value [1] ANY -- defined by type 1057 } 1059 --Note: The aforementioned SecurityCategory syntax produces identical 1060 --hex encodings as the following SecurityCategory syntax that is 1061 --documented in the X.411 specification: 1062 -- 1063 --SecurityCategory ::= SEQUENCE { 1064 -- type [0] SECURITY-CATEGORY, 1065 -- value [1] ANY DEFINED BY type } 1066 -- 1067 --SECURITY-CATEGORY MACRO ::= 1068 --BEGIN 1069 --TYPE NOTATION ::= type | empty 1070 --VALUE NOTATION ::= value (VALUE OBJECT IDENTIFIER) 1071 --END 1073 3.3 Security Label Components 1075 This section gives more detail on the the various components of the 1076 eSSSecurityLabel syntax. 1078 3.3.1 Security Policy Identifier 1080 A security policy is a set of criteria for the provision of security 1081 services. The eSSSecurityLabel security-policy-identifier is used to 1082 identify the security policy in force to which the security label relates. 1083 It indicates the semantics of the other security label components. Even 1084 though the eSSSecurityLabel security-policy-identifier is an optional 1085 field, all security labels used with S/MIME messages MUST include the 1086 security-policy-identifier. 1088 3.3.2 Security Classification 1090 This specification defines the use of the Security Classification field 1091 exactly as is specified in the X.411 Recommendation, which states in part: 1093 If present, a security-classification may have one of a hierarchical 1094 list of values. The basic security-classification hierarchy is defined 1095 in this Recommendation, but the use of these values is defined by the 1096 security-policy in force. Additional values of security-classification, 1097 and their position in the hierarchy, may also be defined by a 1098 security-policy as a local matter or by bilateral agreement. The basic 1099 security-classification hierarchy is, in ascending order: unmarked, 1100 unclassified, restricted, confidential, secret, top-secret. 1102 This means that the security policy in force (identified by the 1103 eSSSecurityLabel security-policy-identifier) defines the 1104 SecurityClassification integer values and their meanings. 1106 An organization can develop its own security policy that defines the 1107 SecurityClassification INTEGER values and their meanings. However, the 1108 general interpretation of the X.411 specification is that the values of 0 1109 through 5 are reserved for the "basic hierarchy" values of unmarked, 1110 unclassified, restricted, confidential, secret, and top-secret. Note that 1111 X.411 does not provide the rules for how these values are used to label 1112 data and how access control is performed using these values. 1114 There is no universal definition of the rules for using these "basic 1115 hierarchy" values. Each organization (or group of organizations) will 1116 define a security policy which documents how the "basic hierarchy" values 1117 are used (if at all) and how access control is enforced (if at all) within 1118 their domain. 1120 Therefore, the security-classification value MUST be accompanied by a 1121 security-policy-identifier value to define the rules for its use. For 1122 example, a company's "secret" classification may convey a different meaning 1123 than the US Government "secret" classification. In summary, a security 1124 policy SHOULD NOT use integers 0 through 5 for other than their X.411 1125 meanings, and SHOULD instead use other values in a hierarchical fashion. 1127 Note that the set of valid security-classification values MUST be 1128 hierarchical, but these values do not necessarily need to be in ascending 1129 numerical order. Further, the values do not need to be contiguous. 1131 For example, in the Defense Message System 1.0 security policy, the 1132 security-classification value of 11 indicates Sensitive-But-Unclassified 1133 and 5 indicates top-secret. The hierarchy of sensitivity ranks top-secret 1134 as more sensitive than Sensitive-But-Unclassified even though the numerical 1135 value of top-secret is less than Sensitive-But-Unclassified. 1137 (Of course, if security-classification values are both hierarchical and in 1138 ascending order, a casual reader of the security policy is more likely to 1139 understand it.) 1141 An example of a security policy that does not use any of the X.411 values 1142 might be: 1143 10 -- anyone 1144 15 -- Morgan Corporation and its contractors 1145 20 -- Morgan Corporation employees 1146 25 -- Morgan Corporation board of directors 1148 An example of a security policy that uses part of the X.411 hierarchy might 1149 be: 1150 0 -- unmarked 1151 1 -- unclassified, can be read by everyone 1152 2 -- restricted to Timberwolf Productions staff 1153 6 -- can only be read to Timberwolf Productions executives 1155 3.3.3 Privacy Mark 1157 If present, the eSSSecurityLabel privacy-mark is not used for access 1158 control. The content of the eSSSecurityLabel privacy-mark may be defined by 1159 the security policy in force (identified by the eSSSecurityLabel 1160 security-policy-identifier) which may define a list of values to be used. 1161 Alternately, the value may be determined by the originator of the 1162 security-label. 1164 3.3.4 Security Categories 1166 If present, the eSSSecurityLabel security-categories provide further 1167 granularity for the sensitivity of the message. The security policy in 1168 force (identified by the eSSSecurityLabel security-policy-identifier) is 1169 used to indicate the syntaxes that are allowed to be present in the 1170 eSSSecurityLabel security-categories. Alternately, the security-categories 1171 and their values may be defined by bilateral agreement. 1173 4. Mail List Management 1175 Sending agents must create recipient-specific data structures for each 1176 recipient of an encrypted message. This process can impair performance for 1177 messages sent to a large number of recipients. Thus, Mail List Agents 1178 (MLAs) that can take a single message and perform the recipient-specific 1179 encryption for every recipient are often desired. 1181 An MLA appears to the message originator as a normal message recipient, but 1182 the MLA acts as a message expansion point for a Mail List (ML). The sender 1183 of a message directs the message to the MLA, which then redistributes the 1184 message to the members of the ML. This process offloads the per-recipient 1185 processing from individual user agents and allows for more efficient 1186 management of large MLs. MLs are true message recipients served by MLAs 1187 that provide cryptographic and expansion services for the mailing list. 1189 In addition to cryptographic handling of messages, secure mailing lists 1190 also have to prevent mail loops. A mail loop is where one mailing list is a 1191 member of a second mailing list, and the second mailing list is a member of 1192 the first. A message will go from one list to the other in a 1193 rapidly-cascading succession of mail that will be distributed to all other 1194 members of both lists. 1196 To prevent mail loops, MLAs use the mlExpansionHistory attribute of the 1197 outer signature of a triple wrapped message. The mlExpansionHistory 1198 attribute is essentially a list of every MLA that has processed the 1199 message. If an MLA sees its own unique entity identifier in the list, it 1200 knows that a loop has been formed, and does not send the message to the 1201 list again. 1203 4.1 Mail List Expansion 1205 Mail list expansion processing is noted in the value of the 1206 mlExpansionHistory attribute, located in the authenticated attributes of 1207 the MLA's SignerInfo block. The MLA creates or updates the authenticated 1208 mlExpansionHistory attribute value each time the MLA expands and signs a 1209 message for members of a mail list. 1211 The MLA MUST add an MLData record containing the MLA's identification 1212 information, date and time of expansion, and optional receipt policy to the 1213 end of the mail list expansion history sequence. If the mlExpansionHistory 1214 attribute is absent, then the MLA MUST add the attribute and the current 1215 expansion becomes the first element of the sequence. If the 1216 mlExpansionHistory attribute is present, then the MLA MUST add the current 1217 expansion information to the end of the existing MLExpansionHistory 1218 sequence. Only one mlExpansionHistory attribute can be included in the 1219 authenticatedAttributes of a SignerInfo. 1221 Note that if the mlExpansionHistory attribute is absent, then the recipient 1222 is a first tier message recipient. 1224 There can be multiple SignerInfos within a SignedData object, and each 1225 SignerInfo may include authenticatedAttributes. Therefore, a single 1226 SignedData object may include multiple SignerInfos, each SignerInfo having 1227 a mlExpansionHistory attribute. For example, an originator can send a 1228 signed message with two SignerInfos, one containing a DSS signature, the 1229 other containing an RSA signature. Not all of the SignerInfos need to 1230 include mlExpansionHistory attributes, but in all of the SignerInfos that 1231 do contain mlExpansionHistory attributes, the mlExpansionHistory attributes 1232 MUST be identical. 1234 A recipient SHOULD only process an mlExpansionHistory attribute if the 1235 recipient can verify the signature of the SignerInfo which covers the 1236 attribute. A recipient SHOULD NOT use an mlExpansionHistory attribute which 1237 the recipient cannot authenticate. 1239 When receiving a message that includes an outer SignedData object, a 1240 receiving agent that processes mlExpansionHistory attributes MUST process 1241 the mlExpansionHistory attribute, if present, in each SignerInfo in the 1242 SignedData object for which it verifies the signature. This may result in 1243 the receiving agent processing multiple mlExpansionHistory attributes 1244 included in a single SignedData object. Because all mlExpansionHistory 1245 attributes must be identical, the receiving application processes the first 1246 mlExpansionHistory attribute that it encounters in a SignerInfo that it can 1247 verify, and then ensures that all other mlExpansionHistory attributes are 1248 identical to the first one encountered. 1250 4.1.1 Detecting Mail List Expansion Loops 1252 Prior to expanding a message, the MLA examines the value of any existing 1253 mail list expansion history attribute to detect an expansion loop. An 1254 expansion loop exists when a message expanded by a specific MLA for a 1255 specific mail list is redelivered to the same MLA for the same mail list. 1257 Expansion loops are detected by examining the mailListIdentifier field of 1258 each MLData entry found in the mail list expansion history. If an MLA finds 1259 its own identification information, then the MLA must discontinue expansion 1260 processing and should provide warning of an expansion loop to a human mail 1261 list administrator. The mail list administrator is responsible for 1262 correcting the loop condition. 1264 4.2 Mail List Agent Processing 1266 The first few paragraphs of this section provide a high-level description 1267 of MLA processing. The rest of the section provides a detailed description 1268 of MLA processing. 1270 MLA message processing depends on the structure of the S/MIME layers in the 1271 message sent to the MLA for expansion. In addition to sending triple 1272 wrapped messages to an MLA, an entity can send other types of messages to 1273 an MLA, such as: 1275 - a single wrapped signedData or envelopedData message 1276 - a double wrapped message (such as signed and enveloped, enveloped and 1277 signed, or signed and signed, and so on) 1278 - a quadruple-wrapped message (such as if a well-formed triple wrapped 1279 message was sent through a gateway that added an outer SignedData layer) 1281 In all cases, the MLA MUST parse all layers of the received message to 1282 determine if there are any signedData layers that include an 1283 eSSSecurityLabel authenticatedAttribute. This may include decrypting an 1284 EnvelopedData layer to determine if an encapsulated SignedData layer 1285 includes an eSSSecurityLabel attribute. The MLA MUST fully process each 1286 eSSSecurityLabel attribute found in the various signedData layers, 1287 including performing access control checks, before distributing the message 1288 to the ML members. The details of the access control checks are beyond the 1289 scope of this document. The MLA MUST verify the signature of the signerInfo 1290 including the eSSSecurityLabel attribute before using it. 1292 In all cases, the MLA MUST sign the message to be sent to the ML members in 1293 a new "outer" signedData layer. The MLA MUST add or update an 1294 mlExpansionHistory attribute in the "outer" signedData that it creates to 1295 document MLA processing. If there was an "outer" signedData layer included 1296 in the original message received by the MLA, then the MLA-created "outer" 1297 signedData layer MUST include each authenticated attribute present in the 1298 original "outer" signedData layer, unless the MLA explicitly replaces an 1299 attribute (such as signingTime or mlExpansionHistory) with a new value. 1301 When an S/MIME message is received by the MLA, the MLA MUST first determine 1302 which received signedData layer, if any, is the "outer" signedData layer. 1303 To identify the received "outer" signedData layer, the MLA MUST verify the 1304 signature and fully process the authenticatedAttributes in each of the 1305 outer signedData layers (working from the outside in) to determine if any 1306 of them either include an mlExpansionHistory attribute or encapsulate an 1307 envelopedData object. 1309 The MLA's search for the "outer" signedData layer is completed when it 1310 finds one of the following: 1311 - the "outer" signedData layer that includes an mlExpansionHistory 1312 attribute or encapsulates an envelopedData object 1313 - an envelopedData layer 1314 - the original content (that is, a layer that is neither envelopedData nor 1315 signedData). 1317 If the MLA finds an "outer" signedData layer, then the MLA MUST perform 1318 the following steps: 1319 1. Strip off all of the signedData layers that encapsulated the "outer" 1320 signedData layer 1321 2. Strip off the "outer" signedData layer itself (after remembering the 1322 included authenticatedAttributes) 1323 3. Expand the envelopedData (if present) 1324 4. Sign the message to be sent to the ML members in a new "outer" 1325 signedData layer that includes the authenticatedAttributes (unless 1326 explicitly replaced) from the original, received "outer" signedData layer. 1328 If the MLA finds an "outer" signedData layer that includes an 1329 mlExpansionHistory attribute AND the MLA subsequently finds an 1330 envelopedData layer buried deeper with the layers of the received message, 1331 then the MLA MUST strip off all of the signedData layers down to the 1332 envelopedData layer (including stripping off the original "outer" 1333 signedData layer) and MUST sign the expanded envelopedData in a new "outer" 1334 signedData layer that includes the authenticatedAttributes (unless 1335 explicitly replaced) from the original, received "outer" signedData layer. 1337 If the MLA does not find an "outer" signedData layer AND does not find an 1338 envelopedData layer, then the MLA MUST sign the original, received message 1339 in a new "outer" signedData layer. If the MLA does not find an "outer" 1340 signedData AND does find an envelopedData layer then it MUST expand the 1341 envelopedData layer, if present, and sign it in a new "outer" signedData 1342 layer. 1344 4.2.1 Examples of Rule Processing 1346 The following examples help explain the rules above: 1348 1) A message (S1(Original Content)) (where S = SignedData) is sent to the 1349 MLA in which the signedData layer does not include an MLExpansionHistory 1350 attribute. The MLA verifies and fully processes the authenticatedAttributes 1351 in S1. The MLA decides that there is not an original, received "outer" 1352 signedData layer since it finds the original content, but never finds an 1353 envelopedData and never finds an mlExpansionHistory attribute. The MLA 1354 calculates a new signedData layer, S2, resulting in the following message 1355 sent to the ML recipients: (S2(S1(Original Content))). The MLA includes an 1356 mlExpansionHistory attribute in S2. 1358 2) A message (S3(S2(S1(Original Content)))) is sent to the MLA in which 1359 none of the signedData layers includes an MLExpansionHistory attribute. 1360 The MLA verifies and fully processes the authenticatedAttributes in S3, S2 1361 and S1. The MLA decides that there is not an original, received "outer" 1362 signedData layer since it finds the original content, but never finds an 1363 envelopedData and never finds an mlExpansionHistory attribute. The MLA 1364 calculates a new signedData layer, S4, resulting in the following message 1365 sent to the ML recipients: (S4(S3(S2(S1(Original Content))))). The MLA 1366 includes an mlExpansionHistory attribute in S4. 1368 3) A message (E1(S1(Original Content))) (where E = envelopedData) is sent 1369 to the MLA in which S1 does not include an MLExpansionHistory attribute. 1370 The MLA decides that there is not an original, received "outer" signedData 1371 layer since it finds the E1 as the outer layer. The MLA expands the 1372 recipientInformation in E1. The MLA calculates a new signedData layer, S2, 1373 resulting in the following message sent to the ML recipients: 1374 (S2(E1(S1(Original Content)))). The MLA includes an mlExpansionHistory 1375 attribute in S2. 1377 4) A message (S2(E1(S1(Original Content)))) is sent to the MLA in which S2 1378 includes an MLExpansionHistory attribute. The MLA verifies the signature 1379 and fully processes the authenticatedAttributes in S2. The MLA finds the 1380 mlExpansionHistory attribute in S2, so it decides that S2 is the "outer" 1381 signedData. The MLA remembers the authenticatedAttributes included in S2 1382 for later inclusion in the new outer signedData that it applies to the 1383 message. The MLA strips off S2. The MLA then expands the 1384 recipientInformation in E1 (this invalidates the signature in S2 which is 1385 why it was stripped). The MLA calculates a new signedData layer, S3, 1386 resulting in the following message sent to the ML recipients: 1387 (S3(E1(S1(Original Content)))). The MLA includes in S3 the attributes from 1388 S2 (unless it specifically replaces an attribute value) including an updated 1389 mlExpansionHistory attribute. 1391 5) A message (S3(S2(E1(S1(Original Content))))) is sent to the MLA in which 1392 none of the signedData layers include an MLExpansionHistory attribute. The 1393 MLA verifies the signature and fully processes the authenticatedAttributes 1394 in S3 and S2. When the MLA encounters E1, then it decides that S2 is the 1395 "outer" signedData since S2 encapsulates E1. The MLA remembers the 1396 authenticatedAttributes included in S2 for later inclusion in the new outer 1397 signedData that it applies to the message. The MLA strips off S3 and S2. 1398 The MLA then expands the recipientInformation in E1 (this invalidates the 1399 signatures in S3 and S2 which is why they were stripped). The MLA calculates 1400 a new signedData layer, S4, resulting in the following message sent to the 1401 ML recipients: (S4(E1(S1(Original Content)))). The MLA includes in S4 the 1402 attributes from S2 (unless it specifically replaces an attribute value) and 1403 includes a new mlExpansionHistory attribute. 1405 6) A message (S3(S2(E1(S1(Original Content))))) is sent to the MLA in which 1406 S3 includes an MLExpansionHistory attribute. In this case, the MLA verifies 1407 the signature and fully processes the authenticatedAttributes in S3. The MLA 1408 finds the mlExpansionHistory in S3, so it decides that S3 is the "outer" 1409 signedData. The MLA remembers the authenticatedAttributes included in S3 1410 for later inclusion in the new outer signedData that it applies to the 1411 message. The MLA keeps on parsing encapsulated layers because it must 1412 determine if there are any eSSSecurityLabel attributes contained within. 1413 The MLA verifies the signature and fully processes the 1414 authenticatedAttributes in S2. When the MLA encounters E1, then it strips 1415 off S3 and S2. The MLA then expands the recipientInformation in E1 (this 1416 invalidates the signatures in S3 and S2 which is why they were stripped). 1417 The MLA calculates a new signedData layer, S4, resulting in the following 1418 message sent to the ML recipients: (S4(E1(S1(Original Content)))). The MLA 1419 includes in S4 the attributes from S3 (unless it specifically replaces an 1420 attribute value) including an updated mlExpansionHistory attribute. 1422 4.2.3 Processing Choices 1424 The processing used depends on the type of the outermost layer of the 1425 message. There are three cases for the type of the outermost data: 1426 - EnvelopedData 1427 - SignedData 1428 - data 1430 4.2.3.1 Processing for EnvelopedData 1432 1. The MLA locates its own RecipientInfo and uses the information it 1433 contains to obtain the message key. 1435 2. The MLA removes the existing recipientInfos field and replaces it with a 1436 new recipientInfos value built from RecipientInfo structures created for 1437 each member of the mailing list. The MLA also removes the existing 1438 originatorInfo field and replaces it with a new originatorInfo value built 1439 from information describing the MLA. 1441 3. The MLA encapsulates the expanded encrypted message in a SignedData 1442 block, adding an mlExpansionHistory attribute as described in the "Mail 1443 List Expansion" section to document the expansion. 1445 4. The MLA signs the new message and delivers the updated message to mail 1446 list members to complete MLA processing. 1448 4.2.3.2 Processing for SignedData 1450 MLA processing of multi-layer messages depends on the type of data in each 1451 of the layers. Step 3 below specifies that different processing will take 1452 place depending on the type of CMS message that has been signed. That 1453 is, it needs to know the type of data at the next inner layer, which may or 1454 may not be the innermost layer. 1456 1. The MLA verifies the signature value found in the outermost SignedData 1457 layer associated with the signed data. MLA processing of the message 1458 terminates if the message signature is invalid. 1460 2. If the outermost SignedData layer includes an authenticated 1461 mlExpansionHistory attribute the MLA checks for an expansion loop as 1462 described in the "Detecting Mail List Expansion Loops" section. 1464 3. Determine the type of the data that has been signed. That is, look at 1465 the type of data on the layer just below the SignedData, which may or may 1466 not be the "innermost" layer. Based on the type of data, perform either 1467 step 3.1 (EnvelopedData), step 3.2 (SignedData), or step 3.3 (all other 1468 types). 1470 3.1. If the signed data is EnvelopedData, the MLA performs expansion 1471 processing of the encrypted message as described previously. Note that 1472 this process invalidates the signature value in the outermost 1473 SignedData layer associated with the original encrypted message. 1474 Proceed to section 3.2 with the result of the expansion. 1476 3.2. If the signed data is SignedData, or is the result of expanding an 1477 EnvelopedData block in step 3.1: 1479 3.2.1. The MLA strips the existing outermost SignedData layer after 1480 remembering the value of the mlExpansionHistory and all other 1481 authenticated attributes in that layer, if present. 1483 3.2.2. If the signed data is EnvelopedData (from step 3.1), the MLA 1484 encapsulates the expanded encrypted message in a new outermost 1485 SignedData layer. On the other hand, if the signed data is 1486 SignedData (from step 3.2), the MLA encapsulates the signed data in 1487 a new outermost SignedData layer. 1489 3.2.3. The outermost signedData layer created by the MLA replaces 1490 the original outermost signedData layer. The MLA MUST create an 1491 authenticated attribute list for the new outermost signedData layer 1492 which MUST include each authenticated attribute present in the 1493 original outermost signedData layer, unless the MLA explicitly 1494 replaces one or more particular attributes with new value. A 1495 special case is the mlExpansionHistory attribute. The MLA MUST add 1496 an mlExpansionHistory authenticated attribute to the outer 1497 signedData layer as follows: 1499 3.2.3.1. If the original outermost SignedData layer included an 1500 mlExpansionHistory attribute, the attribute's value is copied 1501 and updated with the current ML expansion information as 1502 described in the "Mail List Expansion" section. 1504 3.2.3.2. If the original outermost SignedData layer did not 1505 include an mlExpansionHistory attribute, a new attribute value 1506 is created with the current ML expansion information as 1507 described in the "Mail List Expansion" section. 1509 3.3. If the signed data is not EnvelopedData or SignedData: 1511 3.3.1. The MLA encapsulates the received signedData object in an 1512 outer SignedData object, and adds an mlExpansionHistory attribute 1513 to the outer SignedData object containing the current ML expansion 1514 information as described in the "Mail List Expansion" section. 1516 4. The MLA signs the new message and delivers the updated message to mail 1517 list members to complete MLA processing. 1519 A flow chart for the above steps would be: 1521 1. Has a valid signature? 1522 YES -> 2. 1523 NO -> STOP. 1524 2. Does outermost SignedData layer 1525 contain mlExpansionHistory? 1526 YES -> Check it, then -> 3. 1527 NO -> 3. 1528 3. Check type of data just below outermost 1529 SignedData. 1530 EnvelopedData -> 3.1. 1531 SignedData -> 3.2. 1532 all others -> 3.3. 1533 3.1. Expand the encrypted message, then -> 3.2. 1534 3.2. -> 3.2.1. 1535 3.2.1. Strip outermost SignedData layer, note value of mlExpansionHistory 1536 and other authenticated attributes, then -> 3.2.2. 1537 3.2.2. Encapsulate in new signature, then -> 3.2.3. 1538 3.2.3. Create new signedData layer. Was there an old mlExpansionHistory? 1539 YES -> copy the old mlExpansionHistory values, then -> 4. 1540 NO -> create new mlExpansionHistory value, then -> 4. 1541 3.3. Encapsulate in a SignedData layer and add an mlExpansionHistory 1542 attribute, then -> 4. 1543 4. Sign message, deliver it, STOP. 1545 4.2.3.3 Processing for data 1547 1. The MLA encapsulates the message in a SignedData layer, and adds an 1548 mlExpansionHistory attribute containing the current ML expansion 1549 information as described in the "Mail List Expansion" section. 1551 2. The MLA signs the new message and delivers the updated message to mail 1552 list members to complete MLA processing. 1554 4.3 Mail List Agent Signed Receipt Policy Processing 1556 If a mailing list (B) is a member of another mailing list (A), list B often 1557 needs to propagate forward the mailing list receipt policy of A. As a 1558 general rule, a mailing list should be conservative in propagating forward 1559 the mailing list receipt policy because the ultimate recipient need only 1560 process the last item in the ML expansion history. The MLA builds the 1561 expansion history to meet this requirement. 1563 The following table describes the outcome of the union of mailing list A's 1564 policy (the rows in the table) and mailing list B's policy (the columns in 1565 the table). 1567 | B's policy 1568 A's policy | none insteadOf inAdditionTo missing 1569 ------------------------------------------------------------------------- 1570 none | none none none none 1571 insteadOf | none insteadOf(B) *1 insteadOf(A) 1572 inAdditionTo | none insteadOf(B) *2 inAdditionTo(A) 1573 missing | none insteadOf(B) inAdditionTo(B) missing 1575 *1 = insteadOf(insteadOf(A) + inAdditionTo(B)) 1576 *2 = inAdditionTo(inAdditionTo(A) + inAdditionTo(B)) 1578 4.4 Mail List Expansion History Syntax 1580 An mlExpansionHistory attribute value has ASN.1 type MLExpansionHistory. If 1581 there are more than ub-ml-expansion-history mailing lists in the sequence, 1582 the processing agent should provide notification of the error to a human 1583 mail list administrator. The mail list administrator is responsible for 1584 correcting the overflow condition. 1586 MLExpansionHistory ::= SEQUENCE 1587 SIZE (1..ub-ml-expansion-history) OF MLData 1589 id-aa-mlExpandHistory OBJECT IDENTIFIER ::= { iso(1) member-body(2) 1590 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 3} 1592 ub-ml-expansion-history INTEGER ::= 64 1594 MLData contains the expansion history describing each MLA that has 1595 processed a message. As an MLA distributes a message to members of an ML, 1596 the MLA records its unique identifier, date and time of expansion, and 1597 receipt policy in an MLData structure. 1599 MLData ::= SEQUENCE { 1600 mailListIdentifier EntityIdentifier, 1601 -- EntityIdentifier is imported from [CMS] 1602 expansionTime GeneralizedTime, 1603 mlReceiptPolicy MLReceiptPolicy OPTIONAL } 1605 The receipt policy of the ML can withdraw the originator's request for 1606 the return of a signed receipt. However, if the originator of the 1607 message has not requested a signed receipt, the MLA cannot request a 1608 signed receipt. 1610 When present, the mlReceiptPolicy specifies a receipt policy that 1611 supersedes the originator's request for signed receipts. The policy 1612 can be one of three possibilities: receipts MUST NOT be returned 1613 (none); receipts should be returned to an alternate list of 1614 recipients, instead of to the originator (insteadOf); or receipts 1615 should be returned to a list of recipients in addition to the 1616 originator (inAdditionTo). 1618 MLReceiptPolicy ::= CHOICE { 1619 none [0] NULL, 1620 insteadOf [1] SEQUENCE SIZE (1..MAX) OF GeneralNames, 1621 inAdditionTo [2] SEQUENCE SIZE (1..MAX) OF GeneralNames } 1623 5. Security Considerations 1625 This entire document discusses security. 1627 A. ASN.1 Module 1629 ExtendedSecurityServices 1630 { iso(1) member-body(2) us(840) rsadsi(113549) 1631 pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) } 1633 DEFINITIONS IMPLICIT TAGS ::= 1634 BEGIN 1636 IMPORTS 1638 -- Cryptographic Message Syntax (CMS) 1639 ContentType, EntityIdentifier, SubjectKeyIdentifier, Version 1640 FROM CryptographicMessageSyntax { iso(1) member-body(2) us(840) 1641 rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) cms(1) } 1643 -- X.509 1644 GeneralNames FROM CertificateExtensions 1645 {joint-iso-ccitt ds(5) module(1) certificateExtensions(26) 0}; 1647 -- Extended Security Services 1649 -- The construct "SEQUENCE SIZE (1..MAX) OF" appears in several ASN.1 1650 -- constructs in this module. A valid ASN.1 SEQUENCE can have zero or 1651 -- more entries. The SIZE (1..MAX) construct constrains the SEQUENCE to 1652 -- have at least one entry. MAX indicates the upper bound is unspecified. 1653 -- Implementations are free to choose an upper bound that suits their 1654 -- environment. 1656 -- Section 2.7 1658 ReceiptRequest ::= SEQUENCE { 1659 signedContentIdentifier ContentIdentifier, 1660 receiptsFrom ReceiptsFrom, 1661 receiptsTo SEQUENCE SIZE (1..ub-receiptsTo) OF GeneralNames } 1663 ub-receiptsTo INTEGER ::= 16 1665 id-aa-receiptRequest OBJECT IDENTIFIER ::= { iso(1) member-body(2) 1666 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 1} 1668 ContentIdentifier ::= OCTET STRING 1670 id-aa-contentIdentifier OBJECT IDENTIFIER ::= { iso(1) member-body(2) 1671 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 7} 1673 ReceiptsFrom ::= CHOICE { 1674 allOrFirstTier [0] AllOrFirstTier, 1675 -- formerly "allOrNone [0]AllOrNone" 1676 receiptList [1] SEQUENCE OF GeneralNames } 1678 AllOrFirstTier ::= INTEGER { -- Formerly AllOrNone 1679 allReceipts (0), 1680 firstTierRecipients (1) } 1682 -- Section 2.8 1684 Receipt ::= SEQUENCE { 1685 version Version, -- Version is imported from [CMS] 1686 contentType ContentType, 1687 signedContentIdentifier ContentIdentifier, 1688 originatorSignatureValue OCTET STRING } 1690 id-ct-receipt OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) 1691 rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-ct(1) 1} 1693 -- Section 2.9 1695 ContentHints ::= SEQUENCE { 1696 contentDescription [0] IMPLICIT OCTET STRING SIZE (1..MAX) OPTIONAL, 1697 -- If contentDescription is used, its contents MUST be in UTF8 format 1698 contentType ContentType } 1700 id-aa-contentHint OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) 1701 rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 4} 1703 -- Section 2.10 1705 MsgSigDigest ::= OCTET STRING 1707 id-aa-msgSigDigest OBJECT IDENTIFIER ::= { iso(1) member-body(2) 1708 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 5} 1710 -- Section 3.2 1712 ESSSecurityLabel ::= SET { 1713 version Version DEFAULT v1, 1714 security-policy-identifier SecurityPolicyIdentifier OPTIONAL, 1715 security-classification SecurityClassification OPTIONAL, 1716 privacy-mark ESSPrivacyMark OPTIONAL, 1717 security-categories SecurityCategories OPTIONAL } 1719 id-aa-securityLabel OBJECT IDENTIFIER ::= { iso(1) member-body(2) 1720 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 2} 1722 SecurityPolicyIdentifier ::= OBJECT IDENTIFIER 1724 SecurityClassification ::= INTEGER { 1725 unmarked (0), 1726 unclassified (1), 1727 restricted (2), 1728 confidential (3), 1729 secret (4), 1730 top-secret (5) } (0..ub-integer-options) 1732 ub-integer-options INTEGER ::= 256 1734 ESSPrivacyMark ::= CHOICE { 1735 pString PrintableString (SIZE (1..ub-privacy-mark-length)), 1736 -- If pString is used, the ESSSecurityLabel version is set to v1 1737 utf8String [0] IMPLICIT OCTET STRING SIZE (1..MAX) 1738 -- If utf8String is used, its contents MUST be in UTF8 format, and 1739 -- the ESSSecurityLabel version is set to v2 1740 } 1742 ub-privacy-mark-length INTEGER ::= 128 1744 SecurityCategories ::= SET SIZE (1..ub-security-categories) OF 1745 SecurityCategory 1747 ub-security-categories INTEGER ::= 64 1749 SecurityCategory ::= SEQUENCE { 1750 type [0] OBJECT IDENTIFIER, 1751 value [1] ANY -- defined by type 1752 } 1754 --Note: The aforementioned SecurityCategory syntax produces identical 1755 --hex encodings as the following SecurityCategory syntax that is 1756 --documented in the X.411 specification: 1757 -- 1758 --SecurityCategory ::= SEQUENCE { 1759 -- type [0] SECURITY-CATEGORY, 1760 -- value [1] ANY DEFINED BY type } 1761 -- 1762 --SECURITY-CATEGORY MACRO ::= 1763 --BEGIN 1764 --TYPE NOTATION ::= type | empty 1765 --VALUE NOTATION ::= value (VALUE OBJECT IDENTIFIER) 1766 --END 1768 -- Section 4.4 1770 MLExpansionHistory ::= SEQUENCE 1771 SIZE (1..ub-ml-expansion-history) OF MLData 1773 id-aa-mlExpandHistory OBJECT IDENTIFIER ::= { iso(1) member-body(2) 1774 us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 3} 1776 ub-ml-expansion-history INTEGER ::= 64 1778 MLData ::= SEQUENCE { 1779 mailListIdentifier EntityIdentifier, 1780 -- EntityIdentifier is imported from [CMS] 1781 expansionTime GeneralizedTime, 1782 mlReceiptPolicy MLReceiptPolicy OPTIONAL } 1784 MLReceiptPolicy ::= CHOICE { 1785 none [0] NULL, 1786 insteadOf [1] SEQUENCE SIZE (1..MAX) OF GeneralNames, 1787 inAdditionTo [2] SEQUENCE SIZE (1..MAX) OF GeneralNames } 1789 END -- of ExtendedSecurityServices 1791 B. References 1793 [ASN1-1988] "Recommendation X.208: Specification of Abstract Syntax 1794 Notation One (ASN.1)" 1796 [ASN1-1994] "Recommendation X.680: Specification of Abstract Syntax 1797 Notation One (ASN.1)" 1799 [CMS] "Cryptographic Message Syntax", Internet Draft 1800 draft-ietf-smime-cms-xx. 1802 [MSP4] "Secure Data Network System (SDNS) Message Security Protocol (MSP) 1803 4.0", Specification SDN.701, Revision A, 1997-02-06. 1805 [MTSABS] "1988 International Telecommunication Union (ITU) Data 1806 Communication Networks Message Handling Systems: Message Transfer System: 1807 Abstract Service Definition and Procedures, Volume VIII, Fascicle VIII.7, 1808 Recommendation X.411"; MTSAbstractService {joint-iso-ccitt mhs-motis(6) 1809 mts(3) modules(0) mts-abstract-service(1)} 1811 [PKCS7-1.5] "PKCS #7: Cryptographic Message Syntax", Internet Draft 1812 draft-hoffman-pkcs-crypt-msg-xx. 1814 [SMIME2] "S/MIME Version 2 Message Specification", Internet Draft 1815 draft-dusse-smime-msg-xx, and "S/MIME Version 2 Certificate Handling", 1816 Internet Draft draft-dusse-smime-cert-xx. 1818 [SMIME3] "S/MIME Version 3 Message Specification", Internet Draft 1819 draft-ietf-smime-msg-xx, and "S/MIME Version 3 Certificate Handling", 1820 Internet Draft draft-ietf-smime-cert-xx. 1822 [UTF8] "UTF-8, a transformation format of ISO 10646", RFC 2279. 1824 C. Acknowledgments 1826 The first draft of this work was prepared by David Solo. John Pawling did a 1827 huge amount of very detailed revision work during the many phases of the 1828 document. 1830 Many other people have contributed hard work to this draft, including: 1831 Bengt Ackzell 1832 Blake Ramsdell 1833 Carlisle Adams 1834 Jim Schaad 1835 Russ Housley 1836 Scott Hollenbeck 1837 Steve Dusse 1839 D. Open Issues 1841 There is consensus that contentHints should move to the CMS draft. 1843 E. Changes from draft-ietf-smime-ess-03 to draft-ietf-smime-ess-04 1845 1. Removed mention of redefining UTF8String. 1847 1.1.2, steps 3 and 5: Reworded these to make them clearer. 1849 1.2 Changed both examples to be (hopefully) clearer. Also added MIME 1850 boundaries that were left out. 1852 2.3, step 2.2: added "in the outer signedData block". Also added to the 1853 flow chart in step 1 and step 2.2. 1855 2.3, flow chart: reworded 1.2.1. 1857 2.4, step 1.1: Removed "ASN.1 DER encoded". 1859 2.4, step 2.2: Reworded this step. 1861 2.4, step 2.4: Added this step. 1863 2.4, step 9: Changed "eContent" to "eContentType". 1865 2.4, step 10: added this new step, and renumbered the last step. 1867 2.7: Removed superfluous sentence in the middle of the section. 1869 2.9: Changed definition of contentDescription. Added note about UTF8 1870 format. Also updated Appendix A. 1872 3.1.1: Changed last paragraph to deal with multiple eSSSecurityLabels. 1874 3.1.2: Change two paragraphs to deal with multiple eSSSecurityLabels. 1876 3.2: Added words in the second paragraph about use of eSSSecurityLabel and 1877 S/MIME v2 clients. 1879 3.2: Changed the second option of the ESSPrivacyMark to be an implicit 1880 octet string. Added version number to ESSSecurityLabel. Made same changes 1881 in Appendix A. 1883 4.2: Replaced much of this section with more information about how to find 1884 the outer wrapper. Also renumbered sub-parts of this section. 1886 A: Removed UNIVERSAL 12 definition from top of module. 1888 F. Editor's Address 1890 Paul Hoffman 1891 Internet Mail Consortium 1892 127 Segre Place 1893 Santa Cruz, CA 95060 1894 (408) 426-9827 1895 phoffman@imc.org