JMAP extension for S/MIME signing and encryption
draft-ietf-jmap-smime-sender-extensions-03

Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Informational                             13 March 2023
Expires: 14 September 2023

            JMAP extension for S/MIME signing and encryption
               draft-ietf-jmap-smime-sender-extensions-03

Abstract

   This document specifies an extension to JMAP for sending S/MIME
   signed and S/MIME encrypted messages.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 14 September 2023.

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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/set for S/MIME signing and/or
           encryption  . . . . . . . . . . . . . . . . . . . . . . .   2
   5.  Extension to Email/get for S/MIME decryption  . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  JMAP capability registration for "smime-advanced" . . . .   6
     6.2.  JMAP Error Codes Registry Updates . . . . . . . . . . . .   7
       6.2.1.  signedSenderNotAllowed error code . . . . . . . . . .   7
       6.2.2.  validEncryptionKeyNotFound error code . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

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 sending S/MIME
   signed and encrypted messages .  It allows JMAP server to sign/
   encrypt messages on user's behalf.

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-
   advanced" 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/set for S/MIME signing and/or encryption

   [RFC8621] defines Email/set method for creating new email messages.
   This document defines the following additional request arguments that
   can be used to create S/MIME signed and/or encrypted messages:

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   *  smimeSign: "Boolean" (default: false).  If included and has the
      value "true", this requests the JMAP server to create an S/MIME
      signed message from the message constructed according to other
      specified arguments (the "original message").  This is done by
      encapsulating the original message either inside application/
      pkcs7-mime [RFC8551] or multipart/signed [RFC1847] container.
      (smimeSignOpaque argument (see below) controls which of the two
      mechanisms is used.)  The signature's private key/certificate is
      associated with the email address in the Sender header field, if
      present; otherwise, it is associated with the email address in the
      From header field, if present.

      If multiple addresses are present in one of these header fields,
      or there is more than one Sender/From header field, the server
      SHOULD reject the Email/set as invalid with the "invalidEmail"
      error code; otherwise, it MUST take the first address in the last
      Sender/From header field.  If JMAP account is not authorized to
      sign message as the selected sender (as above), it SHOULD return
      "signedSenderNotAllowed" error code.

   *  smimeEncrypt: "Boolean" (default: false).  If included and has the
      value "true", this requests the JMAP server to create an S/MIME
      encrypted message from the constructed message.  This is done by
      encapsulating the message inside application/pkcs7-mime [RFC8551]
      media type.  The message MUST be encrypted to the sender and all
      To/Cc/Bcc recipients.  This extension assumes that there is some
      kind of per user or organizational addressbook, that can be used
      to lookup public keys of recipients.  If lookup of a particular
      public key fails, or results in an expired or revoked certificate,
      the Email/set operation MUST fail with the
      "validEncryptionKeyNotFound" error code.

   *  smimeHeaderProtect: "Boolean" (default: true).  If has the value
      "true", this requests the JMAP server to use S/MIME header
      protection as specified in [draft-ietf-lamps-header-protection]
      when at least one of smimeEncrypt/smimeSign is true.

   *  smimeSignOpaque: "Boolean" (default: true).  If has the value
      "true", this requests the JMAP server to use application/
      pkcs7-mime media type for S/MIME signing, otherwise multipart/
      signed media type.

   If both "smimeSign" and "smimeEncrypt" are set to true, the message
   is first signed and then the signed version is encrypted (in that
   order).

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   (Note that this extension doesn't allow management of private keys/
   certificates.  How private keys are managed or configured for a
   particular user is out of scope for this document.)

        [[ "Email/set", {
          "accountId": "ue150411c",
          "create": {
            "k192": {
              "mailboxIds": {
                "2ea1ca41b38e": true
              },
              "keywords": {
                "$seen": true,
                "$draft": true
              },
              "from": [{
                "name": "Joe Bloggs",
                "email": "joe@example.com"
              }],
              "subject": "World domination",
              "receivedAt": "2021-07-07T01:03:11Z",
              "sentAt": "2021-07-10T11:03:11+10:00",
              "smimeSign": true,
              "smimeEncrypt": true,
              "bodyStructure": {
                "type": "text/plain",
                "partId": "bd48",
                "header:Content-Language": "en"
              },
              "bodyValues": {
                "bd48": {
                  "value": "I have the most brilliant plan.  Let me tell
                    you all about it.",
                  "isTruncated": false
                }
              }
            }
          }
        }, "0" ]]

  This will result in the following response:

        [[ "Email/set", {
          "accountId": "ue150411c",
          "oldState": "780823",
          "newState": "780839",

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          "created": {
            "k192": {
              "id": "Mf40b5f831efa7233b9eb1c7f",
              "blobId": "Gf40b5f831efa7233b9eb1c7f8f97d84eeeee64f7",
              "threadId": "Td957e72e89f516dc",
              "size": 5096
            }
          },
          ...
        }, "0" ]]

                           Figure 1: Example 1:

5.  Extension to Email/get for S/MIME decryption

   [RFC8621] defines Email/get method for retrieving information about
   email messages.  This document defines the following additional
   request arguments of the "bodyProperties" object that can be used to
   facilitate decryption of S/MIME encrypted messages:

   *  smimeBlobId: "Id|null".  The id representing the raw octets of the
      decrypted contents of the part.  When processing this request
      argument, the server first removes the Content-Transfer-Encoding
      (see then "blobId" request argument in RFC 8621).  If the Content-
      Transfer-Encoding is supported by the server, the content is then
      S/MIME decrypted.  The resulting Id can be used in Email/parse
      method to import the decrypted message.  If the body part is not
      encrypted, the returned smimeBlobId attribute has the same value
      as the "blobId" attribute.

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     [[ "Email/get", {
         "ids": [ "f123u986" ],
         "properties": [ "threadId", "mailboxIds", "from", "subject",
           "receivedAt", "htmlBody" ],
         "bodyProperties": [ "partId", "smimeBlobId", "size", "type" ]
       }, "#1" ]]

 This will result in the following response:

     [[ "Email/get", {
      "accountId": "abc",
      "state": "41234123231",
      "list": [
        {
          "id": "f123u986",
          "threadId": "cb1314a",
          "mailboxIds": { "da123c": true },
          "from": [{ "name": "Mice Ace", "email": "mike@example.com" }],
          "subject": "Dinner on Saturday?",
          "receivedAt": "2023-03-09T14:12:00Z",

          "htmlBody": [{
            "partId": "1",
            "smimeBlobId": "B841623871",
            "size": 120537,
            "type": "text/html"
          }]
        }
      ]
    }, "#1" ]]

                          Figure 2: Example 2:

6.  IANA Considerations

6.1.  JMAP capability registration for "smime-advanced"

   IANA is requested to register the "smime" JMAP Capability as follows:

   Capability Name: "urn:ietf:params:jmap:smime-advanced"

   Specification document: this document

   Intended use: common

   Change Controller: IETF

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   Security and privacy considerations: this document, Section 7

6.2.  JMAP Error Codes Registry Updates

6.2.1.  signedSenderNotAllowed error code

   JMAP Error Code: signedSenderNotAllowed

   Intended use: common

   Change controller: IETF

   Reference: This document, Section 4

   Description: JMAP account is not authorized to S/MIME sign message as
   the specified sender.

6.2.2.  validEncryptionKeyNotFound error code

   JMAP Error Code: validEncryptionKeyNotFound

   Intended use: common

   Change controller: IETF

   Reference: This document, Section 4

   Description: S/MIME encrypted message can't be generated because no
   valid certificate (non expired and non revoked) can be found for one
   of recipients.

7.  Security Considerations

   This JMAP extension assumes trust between the user and the JMAP
   server for purposes of signing and encrypting messages on user's
   behalf.

   This JMAP extension also relies on access to user's (or
   organization's) addressbook which contain up-to-date certificates for
   recipients.

   This JMAP extension doesn't support management of user's private keys
   and corresponding certificates.

8.  Normative References

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   [RFC1847]  Galvin, J., Murphy, S., Crocker, S., and N. Freed,
              "Security Multiparts for MIME: Multipart/Signed and
              Multipart/Encrypted", RFC 1847, DOI 10.17487/RFC1847,
              October 1995, <https://www.rfc-editor.org/info/rfc1847>.

   [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>.

   [draft-ietf-lamps-header-protection]
              Gillmor, D. K., Hoeneisen, B., and A. Melnikov, "Header
              Protection for Cryptographically Protected E-mail", Work
              in Progress, Internet-Draft, draft-ietf-lamps-header-
              protection-13, 10 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
              header-protection-13>.

Author's Address

   Alexey Melnikov
   Isode Ltd
   14 Castle Mews
   Hampton
   TW12 2NP
   United Kingdom
   Email: Alexey.Melnikov@isode.com

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