Internet-Draft JMAP extension for S/MIME September 2023
Melnikov Expires 18 March 2024 [Page]
Workgroup:
Network Working Group
Internet-Draft:
draft-melnikov-jmap-smime-sender-extensions-alt-00
Published:
Intended Status:
Informational
Expires:
Author:
A. Melnikov
Isode Ltd

JMAP extension for S/MIME signing and encryption

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

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 18 March 2024.

Table of Contents

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.

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:

The SignOptions object contains the following attributes:

The EncryptOptions object contains the following attributes:

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 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",
            "smimeSign": true,
            "smimeEncrypt": true,




            "smimeOperations": [{
                "operation": "sign",
                "options": {
                   SignOptions
                }

            },
            {
                "operation": "encrypt",
                "options": {
                   EncryptOptions
                }

            }],

          <t>
          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?]]
          </t>

        </list>
      </t>

      <t>
      The SignOptions object contains the following attributes:

        <list style="bullets">

          <t>
          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.]]
          </t>

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

          <t>
          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.
          </t>

        </list>
      </t>








            "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:

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:


    [[ "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:

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

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, , <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, , <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, , <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, , <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, , <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, , <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-16, , <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