JMAP extension for S/MIME signing and encryption
draft-melnikov-jmap-smime-sender-extensions-alt-06
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Alexey Melnikov | ||
| Last updated | 2024-03-04 | ||
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draft-melnikov-jmap-smime-sender-extensions-alt-06
Network Working Group A. Melnikov
Internet-Draft Isode Ltd
Intended status: Informational 4 March 2024
Expires: 5 September 2024
JMAP extension for S/MIME signing and encryption
draft-melnikov-jmap-smime-sender-extensions-alt-06
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.
[[This version presents an alternative syntax to revision 04 of
https://datatracker.ietf.org/doc/draft-ietf-jmap-smime-sender-
extensions/]]
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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and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 2
3. Addition to the capabilities object . . . . . . . . . . . . . 3
4. Extension to Email/set for S/MIME signing and/or
encryption . . . . . . . . . . . . . . . . . . . . . . . 3
5. Email/smimeDecrypt method for S/MIME decryption . . . . . . . 7
6. Extension to Email/query for S/MIME decryption . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7.1. JMAP capability registration for "smime-advanced" . . . . 11
7.2. JMAP Error Codes Registry Updates . . . . . . . . . . . . 11
7.2.1. signedSenderNotAllowed error code . . . . . . . . . . 11
7.2.2. validEncryptionKeyNotFound error code . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
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].
This document uses the terms "Cryptographic Layer" and "Cryptographic
Envelope" as defined in [draft-ietf-lamps-e2e-mail-guidance]
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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 Email/set argument
that can be used to create S/MIME signed and/or encrypted messages:
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. If multiple messages are specified in the "create"
argument, these operations apply to each of them.
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.
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 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
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operation attribute has the value "encrypt" or if this attributes
includes EncryptOptions when the operation attribute has the value
"sign", then JMAP server MUST return the invalidArguments error
code.
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 (the value "null")
or this property is omitted, the JMAP server chooses the most
appropriate algorithm to use. If the algorithm name specified is
unrecognized by the server, it MUST return the
unknownSignatureAlgo error code. [[Register unknownSignatureAlgo
error code with IANA.]] 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.
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.]]
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",
"bodyStructure": {
"type": "text/plain",
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"partId": "bd48",
"header:Content-Language": "en"
},
"bodyValues": {
"bd48": {
"value": "I have the most brilliant plan. Let me tell
you all about it.",
"isTruncated": false
}
}
}
},
"smimeOperations": [{
"operation": "sign",
"options": {
"opaque": false,
"headersToProtect": "all"
}
},
{
"operation": "encrypt"
}
]
}, "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. Email/smimeDecrypt method for S/MIME decryption
The new method defined in this section is loosely based on Blob/
upload method defined in [RFC9404]. The Email/smimeDecrypt method
creates new blob(s) with decrypted content of existing blob(s). The
resulting Id can be used in Email/parse method to import the
decrypted message. If the specified blob doesn't specify encrypted
content, the returned Id attribute has the same value as the "blobId"
attribute.
*Parameters*
* accountId: "Id". The id of the account in which the blobs will be
created.
* create: "Id[DecryptObjects]". A map of creation id to
DecryptObjects
*Result*
The result is the same as for Foo/set in [RFC8620], with created and
notCreated objects mapping from the creation id.
The created objects contain:
* id: "Id". The blobId that was created.
* type: "String|null". The media type as given in the creation (if
any). If not provided, the server MAY perform content analysis
and return one of the following: the calculated value,
"application/octet- string", or null.
* size: "UnsignedInt". As per [RFC8620], the size of the created
blob in octets.
The DecryptObjects objects contains:
* data: "DecryptDataSourceObject[]". An array of zero or more octet
sources in order (zero to create an empty blob). The result of
each of these sources is concatenated in order to create the blob.
* type: "String|null" (default: null). A hint for media type of the
data.
The DecryptDataSourceObject objects contains exactly one of:
* data:asBase64: "String|null" (base64 representation of octets)
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* or a blobId source:
* blobId: "Id"
* offset: "UnsignedInt|null" (MAY be zero). If null, then offset is
assumed to be zero.
* length: "UnsignedInt|null" (MAY be zero). If null, then length is
the remaining octets in the blob.
The created objects will also contain any other properties identical
to those that would be returned in the JSON response of the upload
endpoint described in [RFC8620]. This may be extended in the future;
in this document, it is anticipated that implementations will extend
both the upload endpoint and the Email/smimeDecrypt responses in the
same way.
If there is a problem with a creation, then the server will return a
notCreated response with a map from the failed creation id to a
SetError object.
For each successful decryption, servers MUST add an entry to the
createdIds map ([RFC8620], Section 3.3) for the request; even if the
caller did not explicitly pass a createdIds, the value must be
available to later methods defined in the same Request Object. This
allows the blobId to be used via back-reference in subsequent method
calls.
The created blob will have the same lifetime and same expiry
semantics as any other binary object created via the mechanism
specified in [RFC8620], Section 6.
First, find bodyparts that need decrypting:
[[ "Email/get", {
"ids": [ "f123u986" ],
"properties": [ "threadId", "mailboxIds", "from", "subject",
"receivedAt", "bodyStructure" ],
"bodyProperties": [ "partId", "blobId", "size", "type" ]
}, "#1" ]]
This will result in the following response:
[[ "Email/get", {
"accountId": "abc",
"state": "41234123231",
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"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",
"bodyStructure": [{
"partId": "1",
"blobId": "B841623871",
"size": 120537,
"type": "application/pkcs7-mime"
}]
}
]
}, "#1" ]]
Then decrypt the specific body part using the retrieved blobId.
[
"Email/smimeDecrypt",
{
"accountId": "account1",
"create": {
"1": {
"data" : [
{
"blobId": "B841623871"
}
]
}
}
},
"R1"
]
Response:
[
"Email/smimeDecrypt",
{
"accountId" : "account1",
"created" : {
"1": {
"id" : "G4c6751edf9dd6903ff54b792e432fba781271beb",
"type" : "multipart/mixed",
"size" : 1295
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}
}
},
"R1"
]
Figure 2: Example 2:
6. Extension to Email/query for S/MIME decryption
[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 signed and/or encrypted messages:
* isEncrypted: "Boolean" (default: false)
If isEncrypted is true, then an Email matches this condition if it
has a "Cryptographic Envelope" that contains an encryption (PKCS7
enveloped-data or PKCS7 authEnveloped-data) "Cryptographic Layer".
[[Alexey: Do we want to limit this to S/MIME encryption and not
OpenPGP?]]
* isNotEncrypted: "Boolean" (default: false)
If isNotEncrypted is true, then an Email matches this condition if
it doesn't have a "Cryptographic Envelope" or it has a
"Cryptographic Envelope", but it doesn't include any encryption
(PKCS7 enveloped-data or PKCS7 authEnveloped-data) "Cryptographic
Layer".
* isSigned: "Boolean" (default: false)
If isSigned is true, then an Email matches this condition if it
has a "Cryptographic Envelope" that contain a Multipart Signed or
PKCS7 signed-data "Cryptographic Layer". [[Alexey: Do we want to
limit this to S/MIME signing and not OpenPGP?]]
* isNotSigned: "Boolean" (default: false)
If isNotSigned is true, then an Email matches this condition if it
doesn't have a "Cryptographic Envelope" or it has a "Cryptographic
Envelope", but it doesn't include any Multipart Signed or PKCS7
signed-data "Cryptographic Layer".
7. IANA Considerations
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7.1. 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 8
7.2. JMAP Error Codes Registry Updates
7.2.1. 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.
7.2.2. 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.
8. 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.
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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.
9. References
9.1. 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>.
[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-20, 1 March 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
header-protection-20>.
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[draft-ietf-lamps-e2e-mail-guidance]
Gillmor, D. K., Hoeneisen, B., and A. Melnikov, "Guidance
on End-to-End E-mail Security", Work in Progress,
Internet-Draft, draft-ietf-lamps-e2e-mail-guidance-15, 1
March 2024, <https://datatracker.ietf.org/doc/html/draft-
ietf-lamps-e2e-mail-guidance-15>.
9.2. Informative References
[RFC9404] Gondwana, B., Ed., "JSON Meta Application Protocol (JMAP)
Blob Management Extension", RFC 9404,
DOI 10.17487/RFC9404, August 2023,
<https://www.rfc-editor.org/info/rfc9404>.
Appendix A. Acknowledgements
Thank you to Phillip Tao and Neil Jenkins 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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