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Melnikov 3 Internet-Draft Isode Ltd 4 Intended status: Standards Track 30 September 2021 5 Expires: 3 April 2022 7 S/MIME signature verification extension to JMAP 8 draft-ietf-jmap-smime-09 10 Abstract 12 This document specifies an extension to JMAP for Mail (RFC 8621) for 13 returning S/MIME signature verification status. 15 Status of This Memo 17 This Internet-Draft is submitted in full conformance with the 18 provisions of BCP 78 and BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF). Note that other groups may also distribute 22 working documents as Internet-Drafts. The list of current Internet- 23 Drafts is at https://datatracker.ietf.org/drafts/current/. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 30 This Internet-Draft will expire on 3 April 2022. 32 Copyright Notice 34 Copyright (c) 2021 IETF Trust and the persons identified as the 35 document authors. All rights reserved. 37 This document is subject to BCP 78 and the IETF Trust's Legal 38 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 39 license-info) in effect on the date of publication of this document. 40 Please review these documents carefully, as they describe your rights 41 and restrictions with respect to this document. Code Components 42 extracted from this document must include Simplified BSD License text 43 as described in Section 4.e of the Trust Legal Provisions and are 44 provided without warranty as described in the Simplified BSD License. 46 Table of Contents 48 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 49 2. Conventions Used in This Document . . . . . . . . . . . . . . 2 50 3. Addition to the capabilities object . . . . . . . . . . . . . 3 51 4. Extension for S/MIME signature verification . . . . . . . . . 3 52 4.1. Extension to Email/get . . . . . . . . . . . . . . . . . 3 53 4.2. Extension to Email/query . . . . . . . . . . . . . . . . 7 54 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 55 5.1. JMAP capability registration for "smimeverify" . . . . . 8 56 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 57 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 58 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 59 7.2. Informative References . . . . . . . . . . . . . . . . . 9 60 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9 61 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 63 1. Introduction 65 JMAP for Mail [RFC8621] is a JSON based application protocol for 66 synchronising email data between a client and a server. 68 This document describes an extension to JMAP for returning S/MIME 69 [RFC8551] signature verification status, without requiring a JMAP 70 client to download the signature body part and all signed body parts 71 (when the multipart/signed media type [RFC1847] is used) or to 72 download and decode CMS (when the application/pkcs7-mime media type 73 (Section 3.2 of [RFC8551]) is used). The use of the extension 74 implies the client trusts the JMAP server's S/MIME signature 75 verification code and configuration. This extension is suitable for 76 cases where reduction in network bandwidth and client side code 77 complexity outweigh security concerns about trusting JMAP server to 78 perform S/MIME signature verifications. One possible use case is 79 when the same organization controls both the JMAP server and the JMAP 80 client. 82 2. Conventions Used in This Document 84 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 85 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 86 "OPTIONAL" in this document are to be interpreted as described in BCP 87 14 [RFC2119] [RFC8174] when, and only when, they appear in all 88 capitals, as shown here. 90 Type signatures, examples, and property descriptions in this document 91 follow the conventions established in Section 1.1 of [RFC8620]. Data 92 types defined in the core specification are also used in this 93 document. 95 3. Addition to the capabilities object 97 The capabilities object is returned as part of the standard JMAP 98 Session object; see Section 2 of [RFC8620]. Servers supporting 99 _this_ specification MUST add a property called 100 "urn:ietf:params:jmap:smimeverify" to the capabilities object. 102 The value of this property is an empty object in both the JMAP 103 session _capabilities_ property and an account's 104 _accountCapabilities_ property. 106 4. Extension for S/MIME signature verification 108 4.1. Extension to Email/get 110 [RFC8621] defines the Email/get method for retrieving message 111 specific information. This document defines the following pseudo 112 values in the _properties_ argument: 114 * *smimeStatus*: If "smimeStatus" is included in the list of 115 requested properties, it MUST be interpreted by the server as a 116 request to return the "smimeStatus" response property. 118 * *smimeStatusAtDelivery*: If "smimeStatusAtDelivery" is included in 119 the list of requested properties, it MUST be interpreted by the 120 server as a request to return the "smimeStatusAtDelivery" response 121 property. (It is effectively the same as the "smimeStatus" value 122 calculated at the date/time of delivery, as specified by 123 "receivedAt".) 125 * *smimeErrors*: If "smimeErrors" is included in the list of 126 requested properties, it MUST be interpreted by the server as a 127 request to return the "smimeErrors" response property. 129 * *smimeVerifiedAt*: If "smimeVerifiedAt" is included in the list of 130 requested properties, it MUST be interpreted by the server as a 131 request to return the "smimeVerifiedAt" response property. 133 The "smimeStatus" response property is defined as follows: 135 smimeStatus: "String|null". null signifies that the message doesn't 136 contain any signature. Otherwise, this property contains the S/MIME 137 signature and certificate verification status calculated according to 138 [RFC8551] and [RFC8550]. Possible string values of the property are 139 listed below. Servers MAY return other values not defined below, as 140 defined in extensions to this document. All values (defined below or 141 in extensions to this document) MUST be in ASCII. (Note that this 142 response property contains tokens, thus it is not subject to 143 Internationalization or Localization). Clients MUST treat 144 unrecognized values as "unknown" or "signed/failed". Note that the 145 value of this property might change over time. 147 unknown: S/MIME message, but it was neither signed nor encrypted. 148 This can also be returned for a multipart/signed message which 149 contains an unrecognized signing protocol (for example OpenPGP). 151 signed: S/MIME signed message, but the signature was not yet 152 verified. Some servers might not attempt to verify a signature 153 until a particular message is requested by the client. JMAP 154 servers compliant with this document SHOULD return "signed/ 155 verified" or "signed/failed" instead of this signature status. 157 signed/verified: S/MIME signed message and the sender's signature 158 was successfully verified, the sender matches the From header 159 field, and the sender's certificate (and the certificate chain) is 160 trusted for signing. 162 signed/failed: S/MIME signed message, but the signature failed to 163 verify. This might be a policy related decision (message signer 164 doesn't match the From header field), message was modified, the 165 signer's certificate has expired or was revoked, etc. 167 The "smimeStatusAtDelivery" response property has the same syntax as 168 "smimeStatus" but is calculated at the "receivedAt" date/time. 169 Unlike "smimeStatus", the "smimeStatusAtDelivery" response property 170 value is immutable. "smimeStatusAtDelivery" allows clients to compare 171 the S/MIME signature verification status at delivery with the current 172 status as returned by "smimeStatus", for example to help to answer 173 questions like "was the signature valid at the time of delivery?". 175 The "smimeErrors" response property is defined as follows: 177 smimeErrors: "String[]|null". null signifies that the message doesn't 178 contain any signature or that there were no errors when verifying the 179 S/MIME signature. (I.e., this property is non null only when the 180 corresponding "smimeStatus" response property value is "signed/ 181 failed".) Each string in the array is a human readable description 182 (in the language specified in the Content-Language header field, if 183 any) of a problem with the signature, the signing certificate or the 184 signing certificate chain. (See Section 3.8 of [RFC8620] in regards 185 to how this is affected by the language selection.) In one example, 186 the signing certificate might be expired and the message From email 187 address might not correspond to any of the email addresses in the 188 signing certificate. In another example the certificate might be 189 expired and the JMAP server might be unable to retrieve a CRL for the 190 certificate. In both of these cases there would be 2 elements in the 191 array. 193 The "smimeVerifiedAt" response property is defined as follows: 195 smimeVerifiedAt: "UTCDate|null" (server-set). null signifies that the 196 message doesn't contain any S/MIME signature or that there is a 197 signature, but there was no attempt to verify it. In all other cases 198 it is set to the date and time of when the S/MIME signature was most 199 recently verified. Note that a request to fetch "smimeStatus" and/or 200 "smimeErrors" would force this response property to be set to a non 201 null value, if an S/MIME signature exists. 203 "smimeStatus" and "smimeErrors" values are calculated at the time the 204 corresponding JMAP request was processed (but see below about result 205 caching), not at the time when the message was generated (according 206 to its Date header field value). In all cases "smimeVerifiedAt" is 207 set to the time when "smimeStatus" and "smimeErrors" were last 208 updated. As recalculating these values is expensive for the server, 209 they MAY be cached for up to 10 minutes from the moment when they 210 were calculated. 212 Example 1: Retrieval of minimal information about a message, 213 including its From, Subject and Date header fields, as well as S/MIME 214 signature verification status at delivery and date/time when the 215 message was received. 217 ["Email/get", { 218 "ids": [ "f123u457" ], 219 "properties": [ "mailboxIds", "from", "subject", "date", 220 "smimeStatusAtDelivery", "receivedAt" ] 221 }, "#1"] 223 This might result in the following response: 225 [["Email/get", { 226 "accountId": "abc", 227 "state": "41234123231", 228 "list": [ 229 { 230 "id": "f123u457", 231 "mailboxIds": { "f123": true }, 232 "from": [{"name": "Joe Bloggs", "email": "joe@bloggs.example.net"}], 233 "subject": "Dinner tonight?", 234 "date": "2020-07-07T14:12:00Z", 235 "smimeStatusAtDelivery": "signed/verified", 236 "receivedAt": "2020-07-07T14:15:18Z" 237 } 238 ] 239 }, "#1"]] 241 Example 2: Retrieval of minimal information about a message, 242 including its From, Subject and Date header fields, as well as the 243 latest S/MIME signature verification status, S/MIME verification 244 errors (if any) and when was the S/MIME signature status last 245 verified. The response contains 2 S/MIME errors related to S/MIME 246 signature verification. 248 ["Email/get", { 249 "ids": [ "af123u123" ], 250 "properties": [ "mailboxIds", "from", "subject", "date", 251 "smimeStatus", "smimeErrors", "smimeVerifiedAt" ] 252 }, "#1"] 254 This might result in the following response: 256 [["Email/get", { 257 "accountId": "abc", 258 "state": "41234123231", 259 "list": [ 260 { 261 "id": "af123u123", 262 "mailboxIds": { "f123": true }, 263 "from": [{"name": "Jane Doe", 264 "email": "jdoe@example.com"}], 265 "subject": "Company takeover", 266 "date": "2020-01-31T23:00:00Z", 267 "smimeStatus": "signed/failed", 268 "smimeErrors": [ 269 "From email address doesn't match the certificate", 270 "Can't retrieve CRL from the CRL URL"], 271 "smimeVerifiedAt": "2020-03-01T12:11:19Z" 272 } 273 ] 274 }, "#1"]] 276 4.2. Extension to Email/query 278 [RFC8621] defines the Email/query method for searching for messages 279 with specific properties. This document defines the following 280 properties of the *FilterCondition* object: 282 * *hasSmime*: "Boolean". If "hasSmime" has the value true, only 283 messages with "smimeStatus" other than null match the condition. 284 If "hasSmime" has the value false, only messages with 285 "smimeStatus" equal to null match the condition. 287 * *hasVerifiedSmime*: "Boolean". If "hasVerifiedSmime" has the 288 value true, only messages with "smimeStatus" equal to "signed/ 289 verified" match the condition. If "hasVerifiedSmime" has the 290 value false, only messages with "smimeStatus" not equal to 291 "signed/verified" (including the value null) match the condition. 293 5. IANA Considerations 294 5.1. JMAP capability registration for "smimeverify" 296 IANA is requested to register the "smimeverify" JMAP Capability as 297 follows: 299 Capability Name: "urn:ietf:params:jmap:smimeverify" 301 Specification document: this document 303 Intended use: common 305 Change Controller: IETF 307 Security and privacy considerations: this document, Section 6 309 6. Security Considerations 311 Use of server-side S/MIME signature verification JMAP extension 312 requires the client to trust the server signature verification code 313 and configuration to perform S/MIME signature verification. For 314 example, if the server is not configured with some Trust Anchors, 315 some messages will have "signed/failed" status instead of "signed/ 316 verified". 318 Constant recalculation of S/MIME signature status can result in a 319 Denial-of-Service condition. For that reason, it is RECOMMENDED to 320 cache results of signature verification for 10 minutes. 322 7. References 324 7.1. Normative References 326 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 327 Requirement Levels", BCP 14, RFC 2119, 328 DOI 10.17487/RFC2119, March 1997, 329 . 331 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 332 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 333 May 2017, . 335 [RFC8550] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ 336 Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 337 Certificate Handling", RFC 8550, DOI 10.17487/RFC8550, 338 April 2019, . 340 [RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ 341 Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 342 Message Specification", RFC 8551, DOI 10.17487/RFC8551, 343 April 2019, . 345 [RFC8620] Jenkins, N. and C. Newman, "The JSON Meta Application 346 Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July 347 2019, . 349 [RFC8621] Jenkins, N. and C. Newman, "The JSON Meta Application 350 Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621, 351 August 2019, . 353 7.2. Informative References 355 [RFC1847] Galvin, J., Murphy, S., Crocker, S., and N. Freed, 356 "Security Multiparts for MIME: Multipart/Signed and 357 Multipart/Encrypted", RFC 1847, DOI 10.17487/RFC1847, 358 October 1995, . 360 Appendix A. Acknowledgements 362 This document is a product of JMAP Working Group. Special thank you 363 to Bron Gondwana, Neil Jenkins, Murray Kucherawy, Kirsty Paine and 364 Peter Yee for suggestions, comments and corrections to this document. 366 Author's Address 368 Alexey Melnikov 369 Isode Ltd 370 14 Castle Mews 371 Hampton 372 TW12 2NP 373 United Kingdom 375 Email: Alexey.Melnikov@isode.com