Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Informational                         15 September 2023
Expires: 18 March 2024


            JMAP extension for S/MIME signing and encryption
           draft-melnikov-jmap-smime-sender-extensions-alt-01

Abstract

   This document specifies an extension to JMAP for sending S/MIME
   signed and/or S/MIME encrypted messages, as well as automatic
   decryption of received S/MIME messages.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 18 March 2024.

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   Copyright (c) 2023 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
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised 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/set for S/MIME signing and/or
           encryption  . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Extension to Email/get and Email/query for S/MIME
           decryption  . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  JMAP capability registration for "smime-advanced" . . . .   9
     6.2.  JMAP Error Codes Registry Updates . . . . . . . . . . . .   9
       6.2.1.  signedSenderNotAllowed error code . . . . . . . . . .   9
       6.2.2.  validEncryptionKeyNotFound error code . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  11
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

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/or encrypted messages, as well as automatic decryption of
   received S/MIME 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.






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4.  Extension to Email/set for S/MIME signing and/or encryption

   smimeOperations: SmimeOperation[]|null (default: null).  The list of
   S/MIME operations to perform, in the order specified.  If none are
   specified, or if this property is omitted, no S/MIME operation is
   performed.  [RFC8621] defines Email/set method for creating new email
   messages.  This document defines the following additional request
   argument that can be used to create S/MIME signed and/or encrypted
   messages:

   The SmimeOperation object contains the following attributes:

   *  operation: "String".  S/MIME operation to perform.  This document
      only defines 2 possible values: "sign" and "encrypt".  Future
      documents might add further values.

   *  options: "SignOptions"|"EncryptOptions"|null (default: null).
      Options controlling aspects of S/MIME signing or S/MIME
      encryption.  If this attributes includes SignOptions when the
      operation attribute has the value "encrypt" or if this attributes
      includes EncryptOptions when the operation attribute has the value
      "sign", then JMAP server ignores content of this attribute.  [[Or
      should we define a new error code instead?]]

   The SignOptions object contains the following attributes:

   *  algorithm: "String"|null (default: null).  The value represents
      the signature algorithm that the JMAP server should use to sign
      this message.  If the algorithm is unspecified, this property is
      omitted, or an unrecognized algorithm string is specified, the
      JMAP server chooses the most appropriate algorithm to use.
      [[Alternatively make this an error and define a new error code.]]
      Currently specified algorithms are "ecdsa_secp256r1_sha256",
      "ed25519", "rsa_pkcs1_sha256", "rsa_pss_pss_sha256".  [[Alexey:
      probably need to define a new IANA registry or reference an
      existing one.]]

   *  opaque: "Boolean" (default: true).  If the value is "true", this
      requests the JMAP server to use application/pkcs7-mime [RFC8551]
      media type for S/MIME signing, otherwise multipart/signed
      [RFC1847] media type.










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   *  headersToProtect: "String[]"|"all"|"none"|null (default: null).
      The list of header fields which should be protected by the
      smimeOperations specified.  If the value is "all", all header
      fields of the original message should be protected.  If the value
      is "none", no header fields should be protected.  If the value is
      null, or if this property is omitted, the set of header fields to
      be protected is left up to the JMAP server.

   The EncryptOptions object contains the following attributes:

   *  keyEncryptionAlgorithm: "String"|null (default: null).  The value
      represents the key encryption algorithm that the JMAP server
      should use when encrypting this message.  If the algorithm is
      unspecified, this property is omitted, or an unrecognized
      algorithm string is specified, the JMAP server chooses the most
      appropriate algorithm to use.  [[Need a new IANA registry or a
      link to an existing one here.]]

   *  contentEncryptionAlgorithm: "String"|null (default: null).  The
      value represents the data encryption algorithm that the JMAP
      server should use when encrypting this message.  If the algorithm
      is unspecified, this property is omitted, or an unrecognized
      algorithm string is specified, the JMAP server chooses the most
      appropriate algorithm to use.  [[Need a new IANA registry or a
      link to an existing one here.]]

   *  [[For the following attribute: is this the right object or should
      it be moved to SignOptions (or even directly into the Email/set)?
      Logically it is related to encryption.  But the result of this
      attribute is going to be in the inner S/MIME signed object.]]

   *  headersToObscure: "String[String]"|"none"|null (default: null).
      If smimeOperations contains an "encrypt" operation, this specifies
      the list of header fields to obscure, as well as their obscured
      representation (see [draft-ietf-lamps-header-protection]).  If the
      value is the string "none", no header field should be obscured.
      If the value is null, or if this property is omitted, the set of
      header fields to be protected is left up to the JMAP server.  If
      any header fields are explicitly specified in this attribute, the
      headersToProtect attribute of the SignOptions object MUST also
      contain that header field, or be set to "none" or null.

   When the operation attribute value is "sign", JMAP server constructs
   the S/MIME signed message from the original message (if this is the
   first operation) or the result of the previous operation, taking into
   considerations the SignOptions object (if present) or its defaults.
   The signature's private key/certificate is associated with the email
   address in the Sender header field, if present; otherwise, it is



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   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.

   When the operation is "encrypt", JMAP server constructs the S/MIME
   encrypted message from the original message (if this is the first
   operation) or the result of the previous operation, taking into
   considerations the EncryptOptions object (if present) or its
   defaults.  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.

   (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",
              "smimeOperations": [{
                  "operation": "sign",



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                  "options": {
                    "opaque": false,
                    "headersToProtect": "all"
                  }
                },
                {
                  "operation": "encrypt"
                }
              ],
              "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",
          "created": {
            "k192": {
              "id": "Mf40b5f831efa7233b9eb1c7f",
              "blobId": "Gf40b5f831efa7233b9eb1c7f8f97d84eeeee64f7",
              "threadId": "Td957e72e89f516dc",
              "size": 5096
            }
          },
          ...
        }, "0" ]]

                           Figure 1: Example 1:








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5.  Extension to Email/get and Email/query 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:


   [RFC8621] defines Email/query method for searching for email
   messages.  This document defines the following additional request
   arguments to the *FilterCondition* object that can be used to search
   for S/MIME encrypted messages:

   *  isEncrypted: "Boolean" (default: false) If isEncrypted is true,
      then an Email matches this condition if its top level body part
      has content type "application/pkcs7-mime" with smime-type
      parameter that has the case-insensitive value "enveloped-data" or
      "authEnveloped-data".  [[Alexey: Do we want to limit this to S/
      MIME encryption and not OpenPGP?]]






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   *  isNotEncrypted: "Boolean" (default: false) If isNotEncrypted is
      true, then an Email matches this condition if its top level body
      part has any content type other than "application/pkcs7-mime", or
      its top level body part has content type "application/pkcs7-mime"
      but the smime-type parameter has the case-insensitive value other
      than "enveloped-data" or "authEnveloped-data".  [[Alexey: what if
      smime-type is absent?  It is defined as optional!  Shall we make
      compliant server implementations test the inner CMS structure
      type?]]

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

   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



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   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

   [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>.



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   [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-16, 13 September 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
              header-protection-16>.

Appendix A.  Acknowledgements

   Thank you to Phillip Tao for suggestions, comments and corrections on
   this document.

Author's Address

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





























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