Network Working Group A. Melnikov Internet-Draft Isode Ltd Intended status: Informational March 12, 2021 Expires: September 13, 2021 S/MIME signature verification extension to JMAP draft-ietf-jmap-smime-03 Abstract This document specifies an extension to JMAP for returning S/MIME signature verification status. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 13, 2021. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Melnikov Expires September 13, 2021 [Page 1] Internet-Draft JMAP extension for S/MIME March 2021 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions Used in This Document . . . . . . . . . . . . . . 2 3. Addition to the capabilities object . . . . . . . . . . . . . 2 4. Extension to Email/get for S/MIME signature verification . . 2 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5.1. JMAP capability registration for "smime" . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Normative References . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction [RFC8621] is a JSON based application protocol for synchronising email data between a client and a server. This document describes an extension to JMAP for returning S/MIME [RFC8551] signature verification status, without requiring a JMAP client to download the signature body part and all signed body parts (when multipart/signed media type is used) or to download and decode CMS (when application/pkcs7-mime media type is used). 2. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Addition to the capabilities object The capabilities object is returned as part of the standard JMAP Session object; see the JMAP spec. Servers supporting _this_ specification MUST add a property called "urn:ietf:params:jmap:smime" to the capabilities object. The value of this property is an empty object in both the JMAP session _capabilities_ property and an account's _accountCapabilities_ property. 4. Extension to Email/get for S/MIME signature verification [RFC8621] defines Email/get method for retrieving message specific information. This document defines the following pseudo values in the _properties_ argument: o *smimeStatus*: If "smimeStatus" is included in the list of requested properties, it MUST be interpreted by the server as a request to return "smimeStatus" response property. Melnikov Expires September 13, 2021 [Page 2] Internet-Draft JMAP extension for S/MIME March 2021 o *smimeErrors*: If "smimeErrors" is included in the list of requested properties, it MUST be interpreted by the server as a request to return "smimeErrors" response property. o *smimeVerifiedAt*: If "smimeVerifiedAt" is included in the list of requested properties, it MUST be interpreted by the server as a request to return "smimeVerifiedAt" response property. o *smimeStatusAtDelivery*: If "smimeStatusAtDelivery" is included in the list of requested properties, it MUST be interpreted by the server as a request to return "smimeStatusAtDelivery" response property. (It effectively the same as "smimeStatus" value calculated at the date/time of deliver, as specified by "receivedAt".) The "smimeStatus" response property is defined as follows: smimeStatus: "String|null". null signifies that the message doesn't contain any signature. This property contains the S/MIME signature and certificate verification status calculated according to [RFC8551] and [RFC8550]. Possible string values of the property are listed below. Servers MAY return other values not defined below. Client MUST treat unrecognized values as "unknown" or "signed/failed". Note that the value of this property might change over time. unknown S/MIME message, but it is neither signed, nor encrypted. This can also be returned for a multipart/signed message which contains unrecognized signing protocol (for example OpenPGP). signed S/MIME signed message, but the signature was not yet verified. Some servers might not attempt to verify signature until a particular message is requested by the client. JMAP servers compliant with this document SHOULD return "signed/ verified" or "signed/failed" instead of this signature status. signed/verified S/MIME signed message and the sender's signature was successfully verified, sender matches the From header field and the sender's certificate (and the certificate chain) is trusted for signing. signed/failed S/MIME signed message, but the signature failed to verify. This might be a policy related decision (message signer doesn't match the From header field), message was modified, the signer's certificate has expired or was revoked, etc. The "smimeStatusAtDelivery" response property is defined as follows has the same syntax as "smimeStatus", but calculated at the "receivedAt" date/time. Unlike "smimeStatus", the "smimeStatusAtDelivery" response property value is immutable. The "smimeErrors" response property is defined as follows: Melnikov Expires September 13, 2021 [Page 3] Internet-Draft JMAP extension for S/MIME March 2021 smimeErrors: "String[]|null". null signifies that the message doesn't contain any signature or that there were no errors when verifying S/MIME signature. (I.e. this property is non null only when the corresponding "smimeStatus" response property value is "signed/ failed".) Each string in the array is a human readable description (in the language specified in Content-Language header field, if any) of a problem with the signature or the signing certificate. (See Section 3.8 of [RFC8620] in regards to how this is affected by the language selection.) For example, the signing certificate might be expired and the message From email address might not correspond to any of the email addresses in the signing certificate. Or the certificate might be expired and the JMAP server might be unable to retrieve CRL for the certificate. In both of these cases there would be 2 elements in the array. The "smimeVerifiedAt" response property is defined as follows: smimeVerifiedAt: "UTCDate|null" (server-set). null signifies that the message doesn't contain any S/MIME signature or that there is a signature, but there was no attempt to verify it. In all other cases it is set to the date and time of when S/MIME signature was verified the last time. "smimeStatus" and "smimeErrors" values are calculated at the time the corresponding JMAP request was processed, not at the time when the message was generated (according to it's Date header field value). It MAY be calculated at the time the message was delivered to the mailbox. In all cases "smimeVerifiedAt" is set to time when "smimeStatus" and "smimeErrors" were last updated. As recalculating these values is expensive for the server they MAY be cached for up to 10 minutes from the moment when they were calculated. Melnikov Expires September 13, 2021 [Page 4] Internet-Draft JMAP extension for S/MIME March 2021 ["Email/get", { "ids": [ "f123u987" ], "properties": [ "mailboxIds", "from", "subject", "date", "smimeStatusAtDelivery", "receivedAt" ] }, "#1"] This will result in the following response: [["Email/get", { "accountId": "abc", "state": "41234123231", "list": [ { id: "f123u457", mailboxIds: { "f123": true }, from: [{name: "Joe Bloggs", email: "joe@bloggs.example.net"}], subject: "Dinner tonight?", date: "2020-07-07T14:12:00Z", smimeStatusAtDelivery: "signed/verified", receivedAt: "2020-07-07T14:15:18Z" } ] }, "#1"]] Example 1: Melnikov Expires September 13, 2021 [Page 5] Internet-Draft JMAP extension for S/MIME March 2021 ["Email/get", { "ids": [ "af123u123" ], "properties": [ "mailboxIds", "from", "subject", "date", "smimeStatus", "smimeErrors", "smimeVerifiedAt" ] }, "#1"] This will result in the following response: [["Email/get", { "accountId": "abc", "state": "41234123231", "list": [ { id: "af123u123", mailboxIds: { "f123": true }, from: [{name: "Jane Doe", email: "jdoe@example.com"}], subject: "Company takeover", date: "2020-01-31T23:00:00Z", smimeStatus: "signed/failed", smimeErrors: [ "From email address doesn't match the certificate", "Can't retrieve CRL from the CRL URL"], "smimeVerifiedAt": "2020-03-01T12:11:19Z" } ] }, "#1"]] Example 2: 5. IANA Considerations 5.1. JMAP capability registration for "smime" IANA is requested to register the "smime" JMAP Capability as follows: Capability Name: "urn:ietf:params:jmap:smime" Specification document: this document Intended use: common Change Controller: IETF Security and privacy considerations: this document, Section 6 Melnikov Expires September 13, 2021 [Page 6] Internet-Draft JMAP extension for S/MIME March 2021 6. Security Considerations Server side S/MIME signature verification requires the client to trust server verification code and configuration to perform S/MIME signature verification. For example, if the server is not configured with some Trust Anchors, some messages will have "signed/failed" status instead of "signed/verified". Constant recalculation of S/MIME signature status can result in Denial-of-Service condition. For that reason it is RECOMMENDED to cache results of signature verification for 10 minutes. 7. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8550] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Certificate Handling", RFC 8550, DOI 10.17487/RFC8550, April 2019, . [RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Message Specification", RFC 8551, DOI 10.17487/RFC8551, April 2019, . [RFC8620] Jenkins, N. and C. Newman, "The JSON Meta Application Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July 2019, . [RFC8621] Jenkins, N. and C. Newman, "The JSON Meta Application Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621, August 2019, . Author's Address Alexey Melnikov Isode Ltd 14 Castle Mews Hampton, Middlesex TW12 2NP UK EMail: Alexey.Melnikov@isode.com Melnikov Expires September 13, 2021 [Page 7]