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Melnikov 3 Internet-Draft Isode Ltd 4 Intended status: Standards Track 26 July 2021 5 Expires: 27 January 2022 7 S/MIME signature verification extension to JMAP 8 draft-ietf-jmap-smime-06 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 27 January 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 . . . . . . . . . . . . . 2 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" . . . . . 7 54 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 55 7. Normative References . . . . . . . . . . . . . . . . . . . . 7 56 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 58 1. Introduction 60 [RFC8621] is a JSON based application protocol for synchronising 61 email data between a client and a server. 63 This document describes an extension to JMAP for returning S/MIME 64 [RFC8551] signature verification status, without requiring a JMAP 65 client to download the signature body part and all signed body parts 66 (when multipart/signed media type is used) or to download and decode 67 CMS (when application/pkcs7-mime media type is used). 69 2. Conventions Used in This Document 71 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 72 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 73 document are to be interpreted as described in [RFC2119]. 75 Type signatures, examples, and property descriptions in this document 76 follow the conventions established in Section 1.1 of [RFC8620]. Data 77 types defined in the core specification are also used in this 78 document. 80 3. Addition to the capabilities object 82 The capabilities object is returned as part of the standard JMAP 83 Session object; see the JMAP spec. Servers supporting _this_ 84 specification MUST add a property called 85 "urn:ietf:params:jmap:smimeverify" to the capabilities object. 87 The value of this property is an empty object in both the JMAP 88 session _capabilities_ property and an account's 89 _accountCapabilities_ property. 91 4. Extension to Email/get for S/MIME signature verification 93 o *smimeStatus*: If "smimeStatus" is included in the list of 94 requested properties, it MUST be interpreted by the server as a 95 request to return "smimeStatus" response property. o *smimeErrors*: 96 If "smimeErrors" is included in the list of requested properties, it 97 MUST be interpreted by the server as a request to return 98 "smimeErrors" response property. o *smimeStatusAtDelivery*: If 99 "smimeStatusAtDelivery" is included in the list of requested 100 properties, it MUST be interpreted by the server as a request to 101 return "smimeStatusAtDelivery" response property. (It effectively 102 the same as "smimeStatus" value calculated at the date/time of 103 deliver, as specified by "receivedAt".) [RFC8621] defines Email/get 104 method for retrieving message specific information. This document 105 defines the following pseudo values in the _properties_ argument:o 106 *smimeVerifiedAt*: If "smimeVerifiedAt" is included in the list of 107 requested properties, it MUST be interpreted by the server as a 108 request to return "smimeVerifiedAt" response property. 110 The "smimeStatus" response property is defined as follows: 112 smimeStatus: "String|null". null signifies that the message doesn't 113 contain any signature. This property contains the S/MIME signature 114 and certificate verification status calculated according to [RFC8551] 115 and [RFC8550]. Possible string values of the property are listed 116 below. Servers MAY return other values not defined below. Client 117 MUST treat unrecognized values as "unknown" or "signed/failed". Note 118 that the value of this property might change over time. 120 unknown S/MIME message, but it is neither signed, nor encrypted. 121 This can also be returned for a multipart/signed message which 122 contains unrecognized signing protocol (for example OpenPGP). 124 signed S/MIME signed message, but the signature was not yet 125 verified. Some servers might not attempt to verify signature 126 until a particular message is requested by the client. JMAP 127 servers compliant with this document SHOULD return "signed/ 128 verified" or "signed/failed" instead of this signature status. 130 signed/verified S/MIME signed message and the sender's signature was 131 successfully verified, sender matches the From header field and 132 the sender's certificate (and the certificate chain) is trusted 133 for signing. 135 signed/failed S/MIME signed message, but the signature failed to 136 verify. This might be a policy related decision (message signer 137 doesn't match the From header field), message was modified, the 138 signer's certificate has expired or was revoked, etc. 140 The "smimeStatusAtDelivery" response property has the same syntax as 141 "smimeStatus", but calculated at the "receivedAt" date/time. Unlike 142 "smimeStatus", the "smimeStatusAtDelivery" response property value is 143 immutable. "smimeStatusAtDelivery" allows clients to compare S/MIME 144 signature verification status at delivery with the current status as 145 returned by "smimeStatus", for example it helps to answer questions 146 like "was the signature valid at the time of delivery?". 148 The "smimeErrors" response property is defined as follows: 150 smimeErrors: "String[]|null". null signifies that the message doesn't 151 contain any signature or that there were no errors when verifying S/ 152 MIME signature. (I.e. this property is non null only when the 153 corresponding "smimeStatus" response property value is "signed/ 154 failed".) Each string in the array is a human readable description 155 (in the language specified in Content-Language header field, if any) 156 of a problem with the signature or the signing certificate. (See 157 Section 3.8 of [RFC8620] in regards to how this is affected by the 158 language selection.) For example, the signing certificate might be 159 expired and the message From email address might not correspond to 160 any of the email addresses in the signing certificate. Or the 161 certificate might be expired and the JMAP server might be unable to 162 retrieve CRL for the certificate. In both of these cases there would 163 be 2 elements in the array. 165 The "smimeVerifiedAt" response property is defined as follows: 167 smimeVerifiedAt: "UTCDate|null" (server-set). null signifies that the 168 message doesn't contain any S/MIME signature or that there is a 169 signature, but there was no attempt to verify it. In all other cases 170 it is set to the date and time of when S/MIME signature was most 171 recently verified. Note that a request to fetch "smimeStatus" and/or 172 "smimeErrors" would force this response property to be set to a non 173 null value, if S/MIME signature exists. 175 "smimeStatus" and "smimeErrors" values are calculated at the time the 176 corresponding JMAP request was processed (but see below about result 177 caching), not at the time when the message was generated (according 178 to it's Date header field value). In all cases "smimeVerifiedAt" is 179 set to time when "smimeStatus" and "smimeErrors" were last updated. 180 As recalculating these values is expensive for the server they MAY be 181 cached for up to 10 minutes from the moment when they were 182 calculated. 184 ["Email/get", { 185 "ids": [ "f123u987" ], 186 "properties": [ "mailboxIds", "from", "subject", "date", 187 "smimeStatusAtDelivery", "receivedAt" ] 188 }, "#1"] 190 This will result in the following response: 192 [["Email/get", { 193 "accountId": "abc", 194 "state": "41234123231", 195 "list": [ 196 { 197 "id": "f123u457", 198 "mailboxIds": { "f123": true }, 199 "from": [{"name": "Joe Bloggs", "email": "joe@bloggs.example.net"}], 200 "subject": "Dinner tonight?", 201 "date": "2020-07-07T14:12:00Z", 202 "smimeStatusAtDelivery": "signed/verified", 203 "receivedAt": "2020-07-07T14:15:18Z" 204 } 205 ] 206 }, "#1"]] 208 Figure 1: Example 1: 210 ["Email/get", { 211 "ids": [ "af123u123" ], 212 "properties": [ "mailboxIds", "from", "subject", "date", 213 "smimeStatus", "smimeErrors", "smimeVerifiedAt" ] 214 }, "#1"] 216 This will result in the following response: 218 [["Email/get", { 219 "accountId": "abc", 220 "state": "41234123231", 221 "list": [ 222 { 223 "id": "af123u123", 224 "mailboxIds": { "f123": true }, 225 "from": [{"name": "Jane Doe", 226 "email": "jdoe@example.com"}], 227 "subject": "Company takeover", 228 "date": "2020-01-31T23:00:00Z", 229 "smimeStatus": "signed/failed", 230 "smimeErrors": [ 231 "From email address doesn't match the certificate", 232 "Can't retrieve CRL from the CRL URL"], 233 "smimeVerifiedAt": "2020-03-01T12:11:19Z" 234 } 235 ] 236 }, "#1"]] 238 Figure 2: Example 2: 240 o *hasSmime*: "Boolean". If "hasSmime" has the value true, only 241 messages with "smimeStatus" other than null match the condition. If 242 "hasSmime" has the value false, only messages with "smimeStatus" 243 equal to null match the condition. o *hasVerifiedSmime*: "Boolean". 244 If "hasVerifiedSmime" has the value true, only messages with 245 "smimeStatus" equal to "signed/verified" match the condition. If 246 "hasVerifiedSmime" has the value false, only messages with 247 "smimeStatus" not equal to "signed/verified" (including the value 248 null) match the condition. [RFC8621] defines Email/query method for 249 searching for messages with specific properties. This document 250 defines the following properties of the *FilterCondition* object: 252 5. IANA Considerations 254 5.1. JMAP capability registration for "smimeverify" 256 IANA is requested to register the "smime" JMAP Capability as follows: 258 Capability Name: "urn:ietf:params:jmap:smimeverify" 260 Specification document: this document 262 Intended use: common 264 Change Controller: IETF 266 Security and privacy considerations: this document, Section 6 268 6. Security Considerations 270 Server side S/MIME signature verification requires the client to 271 trust server verification code and configuration to perform S/MIME 272 signature verification. For example, if the server is not configured 273 with some Trust Anchors, some messages will have "signed/failed" 274 status instead of "signed/verified". 276 Constant recalculation of S/MIME signature status can result in 277 Denial-of-Service condition. For that reason it is RECOMMENDED to 278 cache results of signature verification for 10 minutes. 280 7. Normative References 282 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 283 Requirement Levels", BCP 14, RFC 2119, 284 DOI 10.17487/RFC2119, March 1997, 285 . 287 [RFC8550] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ 288 Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 289 Certificate Handling", RFC 8550, DOI 10.17487/RFC8550, 290 April 2019, . 292 [RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ 293 Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 294 Message Specification", RFC 8551, DOI 10.17487/RFC8551, 295 April 2019, . 297 [RFC8620] Jenkins, N. and C. Newman, "The JSON Meta Application 298 Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July 299 2019, . 301 [RFC8621] Jenkins, N. and C. Newman, "The JSON Meta Application 302 Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621, 303 August 2019, . 305 Author's Address 307 Alexey Melnikov 308 Isode Ltd 309 14 Castle Mews 310 Hampton 311 TW12 2NP 312 United Kingdom 314 Email: Alexey.Melnikov@isode.com