[Search] [txt|html|xml|pdf|bibtex] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11            Standards Track
Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Standards Track                        18 November 2021
Expires: 22 May 2022


            S/MIME signature verification extension to JMAP
                        draft-ietf-jmap-smime-11

Abstract

   This document specifies an extension to JMAP for Mail (RFC 8621) 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 22 May 2022.

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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.







Melnikov                   Expires 22 May 2022                  [Page 1]


Internet-Draft          JMAP extension for S/MIME          November 2021


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  Addition to the capabilities object . . . . . . . . . . . . .   3
   4.  Extension for S/MIME signature verification . . . . . . . . .   3
     4.1.  Extension to Email/get  . . . . . . . . . . . . . . . . .   3
       4.1.1.  "smimeStatus" response property extensibility . . . .   7
     4.2.  Extension to Email/query  . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  JMAP capability registration for "smimeverify"  . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   JMAP for Mail [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 the multipart/signed media type [RFC1847] is used) or to
   download and decode CMS (when the application/pkcs7-mime media type
   (Section 3.2 of [RFC8551]) is used).  The use of the extension
   implies the client trusts the JMAP server's S/MIME signature
   verification code and configuration.  This extension is suitable for
   cases where reduction in network bandwidth and client-side code
   complexity outweigh security concerns about trusting the JMAP server
   to perform S/MIME signature verifications.  One possible use case is
   when the same organization controls both the JMAP server and the JMAP
   client.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.







Melnikov                   Expires 22 May 2022                  [Page 2]


Internet-Draft          JMAP extension for S/MIME          November 2021


   Type signatures, examples, and property descriptions in this document
   follow the conventions established in Section 1.1 of [RFC8620].  Data
   types defined in the core specification are also used in this
   document.

3.  Addition to the capabilities object

   The capabilities object is returned as part of the standard JMAP
   Session object; see Section 2 of [RFC8620].  Servers supporting
   _this_ specification MUST add a property called
   "urn:ietf:params:jmap:smimeverify" 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 for S/MIME signature verification

4.1.  Extension to Email/get

   [RFC8621] defines the Email/get method for retrieving message
   specific information.  This document defines the following pseudo
   values in the _properties_ argument:

   *  *smimeStatus*: If "smimeStatus" is included in the list of
      requested properties, it MUST be interpreted by the server as a
      request to return the "smimeStatus" response property.

   *  *smimeStatusAtDelivery*: If "smimeStatusAtDelivery" is included in
      the list of requested properties, it MUST be interpreted by the
      server as a request to return the "smimeStatusAtDelivery" response
      property.  (It is effectively the same as the "smimeStatus" value
      calculated at the date/time of delivery, as specified by
      "receivedAt".)

   *  *smimeErrors*: If "smimeErrors" is included in the list of
      requested properties, it MUST be interpreted by the server as a
      request to return the "smimeErrors" response property.

   *  *smimeVerifiedAt*: If "smimeVerifiedAt" is included in the list of
      requested properties, it MUST be interpreted by the server as a
      request to return the "smimeVerifiedAt" response property.

   The "smimeStatus" response property is defined as follows:

   smimeStatus: "String|null". null signifies that the message doesn't
   contain any signature.  Otherwise, this property contains the S/MIME
   signature and certificate verification status calculated according to



Melnikov                   Expires 22 May 2022                  [Page 3]


Internet-Draft          JMAP extension for S/MIME          November 2021


   [RFC8551] and [RFC8550].  Possible string values of the property are
   listed below.  Servers MAY return other values not defined below, as
   defined in extensions to this document.  Clients 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 was neither signed nor encrypted.
      This can also be returned for a multipart/signed message which
      contains an 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 a signature
      until a particular message is requested by the client.  (This is a
      useful optimization for a JMAP server to avoid doing work until
      exact information is needed.  A JMAP client that only needs to
      display an icon that signifies presence of an S/MIME signature can
      still use this value.)  JMAP servers compliant with this document
      SHOULD attempt signature verification and 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 according to [RFC8551] and [RFC8550].
      Additionally the signer email address extracted from the S/MIME
      certificate matches the From header field value, and the signer
      certificate SHOULD be checked for revocation.

   signed/failed:  S/MIME signed message, but the signature failed to
      verify according to [RFC8551] and [RFC8550].  This might be a
      policy related decision (e.g. the message signer email address
      doesn't match the From header field value), message was modified,
      the signer's certificate has expired or was revoked, etc.

   encrypted+signed/verified:  This value is reserved for future use.
      It is typically handled in the same way as "signed/verified".

   encrypted+signed/failed:  This value is reserved for future use.  It
      is typically handled in the same way as "signed/failed".














Melnikov                   Expires 22 May 2022                  [Page 4]


Internet-Draft          JMAP extension for S/MIME          November 2021


   The "smimeStatusAtDelivery" response property has the same syntax as
   "smimeStatus" but is calculated in relationship to the "receivedAt"
   date/time.  Unlike "smimeStatus", the "smimeStatusAtDelivery"
   response property value doesn't change, unless Trust Anchors are
   added.  (For example, addition of a Trust Anchor can change the value
   of a message "smimeStatusAtDelivery" property from "signed/failed" to
   "signed/verified".)  The "smimeStatusAtDelivery" allows clients to
   compare the S/MIME signature verification status at delivery with the
   current status as returned by "smimeStatus", for example to help to
   answer questions like "was the signature valid at the time of
   delivery?".

   Note that the "smimeStatusAtDelivery" response property value doesn't
   have to be calculated at delivery time.  A JMAP server can defer its
   calculation until it is explicitly requested, but once calculated its
   value is remembered for later use.

   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 the
   S/MIME signature.  (I.e., this property is non null only when the
   corresponding "smimeStatus" response property value is "signed/
   failed" or "encrypted+signed/failed".  Note that future extensions to
   this document can specify other smimeStatus values that can be used
   with smimeErrors.)  Each string in the array is a human readable
   description (in the language specified in the Content-Language header
   field, if any) of a problem with the signature, the signing
   certificate or the signing certificate chain.  (See Section 3.8 of
   [RFC8620] in regards to how this is affected by the language
   selection.)  In one 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.  In another example the
   certificate might be expired and the JMAP server might be unable to
   retrieve a 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.  (Retrieval of the
   smimeStatus value can be used to distinguish these 2 cases).  In all
   other cases it is set to the date and time of when the S/MIME
   signature was most recently verified.  Note that a request to fetch
   "smimeStatus", "smimeStatusAtDelivery" and/or "smimeErrors" would
   force this response property to be set to a non null value, if an S/
   MIME signature exists.



Melnikov                   Expires 22 May 2022                  [Page 5]


Internet-Draft          JMAP extension for S/MIME          November 2021


   "smimeStatus" and "smimeErrors" values are calculated at the time the
   corresponding JMAP request was processed (but see below about the
   effect of result caching), not at the time when the message was
   generated (according to its Date header field value).  In all cases
   "smimeVerifiedAt" is set to the time when "smimeStatus" and
   "smimeErrors" were last updated.  As recalculating these values is
   expensive for the server, they MAY be cached for up to 24 hours from
   the moment when they were calculated.

   Example 1: Retrieval of minimal information about a message,
   including its From, Subject and Date header fields, as well as S/MIME
   signature verification status at delivery and date/time when the
   message was received.

      ["Email/get", {
      "ids": [ "fe123u457" ],
      "properties": [ "mailboxIds", "from", "subject", "date",
       "smimeStatusAtDelivery", "receivedAt" ]
      }, "#1"]

This might result in the following response:

      [["Email/get", {
         "accountId": "abc",
         "state": "51234123231",
         "list": [
           {
             "id": "fe123u457",
             "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 2: Retrieval of minimal information about a message,
   including its From, Subject and Date header fields, as well as the
   latest S/MIME signature verification status, S/MIME verification
   errors (if any) and when was the S/MIME signature status last
   verified.  The response contains 2 S/MIME errors related to S/MIME
   signature verification.






Melnikov                   Expires 22 May 2022                  [Page 6]


Internet-Draft          JMAP extension for S/MIME          November 2021


         ["Email/get", {
         "ids": [ "ag123u123" ],
         "properties": [ "mailboxIds", "from", "subject", "date",
          "smimeStatus", "smimeErrors", "smimeVerifiedAt" ]
         }, "#1"]

   This might result in the following response:

         [["Email/get", {
            "accountId": "abc",
            "state": "47234123231",
            "list": [
              {
                "id": "ag123u123",
                "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"]]


4.1.1.  "smimeStatus" response property extensibility

   Future extensions to this document can specify extra allowed values
   for the smimeStatus response property.  All values (defined in this
   document or in extensions to this document) MUST be in ASCII.  (Note
   that this response property contains tokens, thus it is not subject
   to Internationalization or Localization).

   New smimeStatus response property values defined in extensions may
   affect behaviour of properties such as smimeErrors response property
   of Email/get (see Section 4.1) or hasVerifiedSmime property of Email/
   query (see Section 4.2).  In particular the new values can be treated
   similar to values defined in this document.

   For example a putative JMAP extension for automatically decrypting S/
   MIME messages can specify two additional values, one specifying that
   a message is both encrypted and signed with a valid S/MIME signature
   and another one specifying that a message is both encrypted and
   signed with an invalid S/MIME signature.  The former value can be



Melnikov                   Expires 22 May 2022                  [Page 7]


Internet-Draft          JMAP extension for S/MIME          November 2021


   treated as "signed/verified" (and would thus affect hasVerifiedSmime)
   and the latter can be treated as "signed/failed" (and thus can be
   used with smimeErrors).

4.2.  Extension to Email/query

   [RFC8621] defines the Email/query method for searching for messages
   with specific properties.  This document defines the following
   properties of the *FilterCondition* object:

   *  *hasSmime*: "Boolean".  If "hasSmime" has the value true, only
      messages with "smimeStatus" other than null match the condition.
      If "hasSmime" has the value false, only messages with
      "smimeStatus" equal to null match the condition.

   *  *hasVerifiedSmime*: "Boolean".  If "hasVerifiedSmime" has the
      value true, only messages with "smimeStatus" equal to "signed/
      verified" or "encrypted+signed/verified" (*), match the condition.
      If "hasVerifiedSmime" has the value false, only messages with
      "smimeStatus" not equal to "signed/verified" and not equal to
      "encrypted+signed/verified" (*) (including the value null) match
      the condition.  Note that use of this attribute is potentially
      expensive for a JMAP server, as it forces calculation of
      smimeStatus property value for each message.  However caching of
      smimeStatus values should ameliorate this cost somewhat.

      (*) as well as "smimeStatus" values added by future extensions to
      this document that are explicitly specified as having similar
      effect to "signed/verified" as far as "hasVerifiedSmime"
      calculation is concerned.

   *  *hasVerifiedSmimeAtDelivery*: "Boolean".  The
      "hasVerifiedSmimeAtDelivery" property is handled similar to
      "hasVerifiedSmime" property, but the value of
      "smimeStatusAtDelivery" is used instead of "smimeStatus" to assess
      whether a particular message matches the condition.

5.  IANA Considerations

5.1.  JMAP capability registration for "smimeverify"

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

   Capability Name: "urn:ietf:params:jmap:smimeverify"

   Specification document: this document




Melnikov                   Expires 22 May 2022                  [Page 8]


Internet-Draft          JMAP extension for S/MIME          November 2021


   Intended use: common

   Change Controller: IETF

   Security and privacy considerations: this document, Section 6

6.  Security Considerations

   Use of the server-side S/MIME signature verification JMAP extension
   requires the client to trust the server signature verification code,
   server configuration and its operational practices to perform S/MIME
   signature verification, as well as to trust that the channel between
   the client and the server is integrity protected.  (For example, if
   the server is not configured with some Trust Anchors, some messages
   will have "signed/failed" status instead of "signed/verified".)  A
   malicious or compromised server could return false verification
   status to a client.  A successful verification could be conveyed to a
   client for a forged or altered message.  A properly signed message
   could be signaled as having a failed signature verification or no
   signature at all.  In the case of the latter attack, no new attack
   surface is presented with this extension above what malicious or
   compromised server could already do by stripping or tampering with
   the S/MIME information in the message.  In the case of the former
   attack, client software capable of performing S/MIME signature
   verification could detect this attack.  Local configuration of the
   client should determine if this client-side verification should
   occur.  For clients without local verification capabilities, such an
   attack would be difficult to detect.

   Integrity protection of the channel between the client and the server
   is provided by use of TLS, as required by JMAP specification (see
   Section 8.1 of [RFC8620]).

   Constant recalculation of S/MIME signature status can result in a
   Denial-of-Service condition.  For that reason, it is RECOMMENDED to
   cache results of signature verification for up to 24 hours.

7.  References

7.1.  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>.






Melnikov                   Expires 22 May 2022                  [Page 9]


Internet-Draft          JMAP extension for S/MIME          November 2021


   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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>.

7.2.  Informative 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>.

Appendix A.  Acknowledgements

   This document is a product of JMAP Working Group.  Special thank you
   to Bron Gondwana, Neil Jenkins, Murray Kucherawy, Kirsty Paine,
   Benjamin Kaduk, Roman Danyliw, Peter Yee, Robert Wilton and Erik
   Kline for suggestions, comments and corrections to this document.

Author's Address

   Alexey Melnikov
   Isode Ltd
   14 Castle Mews
   Hampton
   TW12 2NP
   United Kingdom

   Email: Alexey.Melnikov@isode.com





Melnikov                   Expires 22 May 2022                 [Page 10]