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-00
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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This Internet-Draft will expire on 18 March 2024.
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document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. JMAP capability registration for "smime-advanced" . . . . 10
6.2. JMAP Error Codes Registry Updates . . . . . . . . . . . . 10
6.2.1. signedSenderNotAllowed error code . . . . . . . . . . 10
6.2.2. validEncryptionKeyNotFound error code . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Normative References . . . . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
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.
* [[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
associated with the email address in the From header field, if
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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,
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"smimeOperations": [{
"operation": "sign",
"options": {
SignOptions
}
},
{
"operation": "encrypt",
"options": {
EncryptOptions
}
}],
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
media type for S/MIME signing, otherwise multipart/signed media type.
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.
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"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, .
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[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, .
[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, .
[RFC8620] Jenkins, N. and C. Newman, "The JSON Meta Application
Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July
2019, .
[RFC8621] Jenkins, N. and C. Newman, "The JSON Meta Application
Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621,
August 2019, .
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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,
.
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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