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Melnikov 3 Internet-Draft Isode Ltd 4 Intended status: Standards Track 10 September 2021 5 Expires: 14 March 2022 7 S/MIME signature verification extension to JMAP 8 draft-ietf-jmap-smime-08 10 Abstract 12 This document specifies an extension to JMAP for returning S/MIME 13 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 14 March 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 to Email/get for S/MIME signature verification . . 3 52 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 53 5.1. JMAP capability registration for "smimeverify" . . . . . 8 54 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 55 7. Normative References . . . . . . . . . . . . . . . . . . . . 8 56 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9 57 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 59 1. Introduction 61 JMAP [RFC8621] is a JSON based application protocol for synchronising 62 email data between a client and a server. 64 This document describes an extension to JMAP for returning S/MIME 65 [RFC8551] signature verification status, without requiring a JMAP 66 client to download the signature body part and all signed body parts 67 (when the multipart/signed media type is used) or to download and 68 decode CMS (when the application/pkcs7-mime media type is used). 69 This JMAP extension assumes that JMAP client trusts JMAP server's S/ 70 MIME signature verification code and configuration. This extension 71 is suitable for cases where reduction in network bandwidth and client 72 side code complexity outweigh security concerns about trusting JMAP 73 server to perform S/MIME signature verifications. One possible use 74 case is when the same organization controls both the JMAP server and 75 the JMAP client. 77 2. Conventions Used in This Document 79 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 80 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 81 "OPTIONAL" in this document are to be interpreted as described in BCP 82 14 [RFC2119] [RFC8174] when, and only when, they appear in all 83 capitals, as shown here. 85 Type signatures, examples, and property descriptions in this document 86 follow the conventions established in Section 1.1 of [RFC8620]. Data 87 types defined in the core specification are also used in this 88 document. 90 3. Addition to the capabilities object 92 The capabilities object is returned as part of the standard JMAP 93 Session object; see [RFC8620]. Servers supporting _this_ 94 specification MUST add a property called 95 "urn:ietf:params:jmap:smimeverify" to the capabilities object. 97 The value of this property is an empty object in both the JMAP 98 session _capabilities_ property and an account's 99 _accountCapabilities_ property. 101 4. Extension to Email/get for S/MIME signature verification 103 [RFC8621] defines the Email/get method for retrieving message 104 specific information. This document defines the following pseudo 105 values in the _properties_ argument: 107 * *smimeStatus*: If "smimeStatus" is included in the list of 108 requested properties, it MUST be interpreted by the server as a 109 request to return the "smimeStatus" response property. 111 * *smimeErrors*: If "smimeErrors" is included in the list of 112 requested properties, it MUST be interpreted by the server as a 113 request to return the "smimeErrors" response property. 115 * *smimeVerifiedAt*: If "smimeVerifiedAt" is included in the list of 116 requested properties, it MUST be interpreted by the server as a 117 request to return the "smimeVerifiedAt" response property. 119 * *smimeStatusAtDelivery*: If "smimeStatusAtDelivery" is included in 120 the list of requested properties, it MUST be interpreted by the 121 server as a request to return the "smimeStatusAtDelivery" response 122 property. (It is effectively the same as the "smimeStatus" value 123 calculated at the date/time of delivery, as specified by 124 "receivedAt".) 126 The "smimeStatus" response property is defined as follows: 128 smimeStatus: "String|null". null signifies that the message doesn't 129 contain any signature. Otherwise, this property contains the S/MIME 130 signature and certificate verification status calculated according to 131 [RFC8551] and [RFC8550]. Possible string values of the property are 132 listed below. Servers MAY return other values not defined below. 133 Clients MUST treat unrecognized values as "unknown" or "signed/ 134 failed". Note that the value of this property might change over 135 time. 137 unknown S/MIME message, but it is neither signed nor encrypted. 139 This can also be returned for a multipart/signed message which 140 contains an unrecognized signing protocol (for example OpenPGP). 142 signed S/MIME signed message, but the signature was not yet 143 verified. Some servers might not attempt to verify a signature 144 until a particular message is requested by the client. JMAP 145 servers compliant with this document SHOULD return "signed/ 146 verified" or "signed/failed" instead of this signature status. 148 signed/verified S/MIME signed message and the sender's signature was 149 successfully verified, the sender matches the From header field, 150 and the sender's certificate (and the certificate chain) is 151 trusted for signing. 153 signed/failed S/MIME signed message, but the signature failed to 154 verify. This might be a policy related decision (message signer 155 doesn't match the From header field), message was modified, the 156 signer's certificate has expired or was revoked, etc. 158 The "smimeStatusAtDelivery" response property has the same syntax as 159 "smimeStatus" but is calculated at the "receivedAt" date/time. 160 Unlike "smimeStatus", the "smimeStatusAtDelivery" response property 161 value is immutable. "smimeStatusAtDelivery" allows clients to compare 162 the S/MIME signature verification status at delivery with the current 163 status as returned by "smimeStatus", for example to help to answer 164 questions like "was the signature valid at the time of delivery?". 166 The "smimeErrors" response property is defined as follows: 168 smimeErrors: "String[]|null". null signifies that the message doesn't 169 contain any signature or that there were no errors when verifying the 170 S/MIME signature. (I.e., this property is non null only when the 171 corresponding "smimeStatus" response property value is "signed/ 172 failed".) Each string in the array is a human readable description 173 (in the language specified in the Content-Language header field, if 174 any) of a problem with the signature, the signing certificate or the 175 signing certificate chain. (See Section 3.8 of [RFC8620] in regards 176 to how this is affected by the language selection.) For example, the 177 signing certificate might be expired and the message From email 178 address might not correspond to any of the email addresses in the 179 signing certificate. Or the certificate might be expired and the 180 JMAP server might be unable to retrieve a CRL for the certificate. 181 In both of these cases there would be 2 elements in the array. 183 The "smimeVerifiedAt" response property is defined as follows: 185 smimeVerifiedAt: "UTCDate|null" (server-set). null signifies that the 186 message doesn't contain any S/MIME signature or that there is a 187 signature, but there was no attempt to verify it. In all other cases 188 it is set to the date and time of when the S/MIME signature was most 189 recently verified. Note that a request to fetch "smimeStatus" and/or 190 "smimeErrors" would force this response property to be set to a non 191 null value, if an S/MIME signature exists. 193 "smimeStatus" and "smimeErrors" values are calculated at the time the 194 corresponding JMAP request was processed (but see below about result 195 caching), not at the time when the message was generated (according 196 to its Date header field value). In all cases "smimeVerifiedAt" is 197 set to time when "smimeStatus" and "smimeErrors" were last updated. 198 As recalculating these values is expensive for the server, they MAY 199 be cached for up to 10 minutes from the moment when they were 200 calculated. 202 Example 1: Retrieval of minimal information about a message, 203 including its From, Subject and Date header fields, as well as S/MIME 204 signature verification status at delivery and date/time when the 205 message was received. 207 ["Email/get", { 208 "ids": [ "f123u987" ], 209 "properties": [ "mailboxIds", "from", "subject", "date", 210 "smimeStatusAtDelivery", "receivedAt" ] 211 }, "#1"] 213 This will result in the following response: 215 [["Email/get", { 216 "accountId": "abc", 217 "state": "41234123231", 218 "list": [ 219 { 220 "id": "f123u457", 221 "mailboxIds": { "f123": true }, 222 "from": [{"name": "Joe Bloggs", "email": "joe@bloggs.example.net"}], 223 "subject": "Dinner tonight?", 224 "date": "2020-07-07T14:12:00Z", 225 "smimeStatusAtDelivery": "signed/verified", 226 "receivedAt": "2020-07-07T14:15:18Z" 227 } 228 ] 229 }, "#1"]] 231 Example 2: Retrieval of minimal information about a message, 232 including its From, Subject and Date header fields, as well as the 233 latest S/MIME signature verification status, S/MIME verification 234 errors (if any) and when was the S/MIME signature status last 235 verified. 237 ["Email/get", { 238 "ids": [ "af123u123" ], 239 "properties": [ "mailboxIds", "from", "subject", "date", 240 "smimeStatus", "smimeErrors", "smimeVerifiedAt" ] 241 }, "#1"] 243 This will result in the following response: 245 [["Email/get", { 246 "accountId": "abc", 247 "state": "41234123231", 248 "list": [ 249 { 250 "id": "af123u123", 251 "mailboxIds": { "f123": true }, 252 "from": [{"name": "Jane Doe", 253 "email": "jdoe@example.com"}], 254 "subject": "Company takeover", 255 "date": "2020-01-31T23:00:00Z", 256 "smimeStatus": "signed/failed", 257 "smimeErrors": [ 258 "From email address doesn't match the certificate", 259 "Can't retrieve CRL from the CRL URL"], 260 "smimeVerifiedAt": "2020-03-01T12:11:19Z" 261 } 262 ] 263 }, "#1"]] 265 [RFC8621] defines the Email/query method for searching for messages 266 with specific properties. This document defines the following 267 properties of the *FilterCondition* object: 269 * *hasSmime*: "Boolean". If "hasSmime" has the value true, only 270 messages with "smimeStatus" other than null match the condition. 271 If "hasSmime" has the value false, only messages with 272 "smimeStatus" equal to null match the condition. 274 * *hasVerifiedSmime*: "Boolean". If "hasVerifiedSmime" has the 275 value true, only messages with "smimeStatus" equal to "signed/ 276 verified" match the condition. If "hasVerifiedSmime" has the 277 value false, only messages with "smimeStatus" not equal to 278 "signed/verified" (including the value null) match the condition. 280 5. IANA Considerations 281 5.1. JMAP capability registration for "smimeverify" 283 IANA is requested to register the "smime" JMAP Capability as follows: 285 Capability Name: "urn:ietf:params:jmap:smimeverify" 287 Specification document: this document 289 Intended use: common 291 Change Controller: IETF 293 Security and privacy considerations: this document, Section 6 295 6. Security Considerations 297 Use of server-side S/MIME signature verification JMAP extension 298 requires the client to trust the server verification code and 299 configuration to perform S/MIME signature verification. For example, 300 if the server is not configured with some Trust Anchors, some 301 messages will have "signed/failed" status instead of "signed/ 302 verified". 304 Constant recalculation of S/MIME signature status can result in a 305 Denial-of-Service condition. For that reason, it is RECOMMENDED to 306 cache results of signature verification for 10 minutes. 308 7. Normative References 310 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 311 Requirement Levels", BCP 14, RFC 2119, 312 DOI 10.17487/RFC2119, March 1997, 313 . 315 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 316 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 317 May 2017, . 319 [RFC8550] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ 320 Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 321 Certificate Handling", RFC 8550, DOI 10.17487/RFC8550, 322 April 2019, . 324 [RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ 325 Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 326 Message Specification", RFC 8551, DOI 10.17487/RFC8551, 327 April 2019, . 329 [RFC8620] Jenkins, N. and C. Newman, "The JSON Meta Application 330 Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July 331 2019, . 333 [RFC8621] Jenkins, N. and C. Newman, "The JSON Meta Application 334 Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621, 335 August 2019, . 337 Appendix A. Acknowledgements 339 This document is a product of JMAP Working Group. Special thank you 340 to Bron Gondwana, Neil Jenkins, Murray Kucherawy and Peter Yee for 341 suggestions, comments and corrections on this document. 343 Author's Address 345 Alexey Melnikov 346 Isode Ltd 347 14 Castle Mews 348 Hampton 349 TW12 2NP 350 United Kingdom 352 Email: Alexey.Melnikov@isode.com