S/MIME signature verification extension to JMAP
draft-ietf-jmap-smime-02

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Last updated 2020-07-02
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Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Informational                              July 2, 2020
Expires: January 3, 2021

            S/MIME signature verification extension to JMAP
                        draft-ietf-jmap-smime-02

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
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   This Internet-Draft will expire on January 3, 2021.

Copyright Notice

   Copyright (c) 2020 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
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   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.

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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.  Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  JMAP capability registration for "smime"  . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  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:

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   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.
   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.

   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 "smimeErrors" response property is defined as follows:

   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)

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   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.

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      ["Email/get", {
      "ids": [ "f123u987" ],
      "properties": [ "mailboxIds", "from", "subject", "date",
       "smimeStatus" ]
      }, "#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",
             smimeStatus: "signed/verified"
           }
         ]
      }, "#1"]]

                                Example 1:

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         ["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.  Open Issues

   [[This section should be empty before publication]]

   1.  Should a new property be added on requests to allow signature
       verification "at specified time"?

6.  IANA Considerations

6.1.  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

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   Change Controller: IETF

   Security and privacy considerations: this document, Section 7

7.  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.

8.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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, <https://www.rfc-editor.org/info/rfc8550>.

   [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, <https://www.rfc-editor.org/info/rfc8551>.

   [RFC8620]  Jenkins, N. and C. Newman, "The JSON Meta Application
              Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July
              2019, <https://www.rfc-editor.org/info/rfc8620>.

   [RFC8621]  Jenkins, N. and C. Newman, "The JSON Meta Application
              Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621,
              August 2019, <https://www.rfc-editor.org/info/rfc8621>.

Author's Address

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   Alexey Melnikov
   Isode Ltd
   14 Castle Mews
   Hampton, Middlesex  TW12 2NP
   UK

   EMail: Alexey.Melnikov@isode.com

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