Internet DRAFT - draft-ralston-mimi-linearized-matrix
draft-ralston-mimi-linearized-matrix
More Instant Messaging Interoperability T. Ralston
Internet-Draft M. Hodgson
Intended status: Standards Track The Matrix.org Foundation C.I.C.
Expires: 14 July 2024 11 January 2024
Linearized Matrix
draft-ralston-mimi-linearized-matrix-04
Abstract
This document specifies Linearized Matrix (LM). LM is an extensible
protocol for interoperability between messaging providers, using
Matrix's (matrix.org (https://matrix.org)) decentralized room model.
LM simplifies the Directed Acyclic Graph (DAG) persistence of Matrix
while maintaining compatibility with non-linearized servers within a
room. It does this by using a doubly-linked list of events/messages
per room with hub and spoke fanout.
LM's extensibility enables a wide range of transport protocol and
end-to-end encryption possibilities. This document uses Matrix's
room access control semantics supported by Messaging Layer Security
(MLS), transported via HTTPS and JSON. The details of which server-
to-server transport to use and what is put over MLS are replaceable.
The threat model of LM does not place trust in a central owning
server for each conversation. Instead, it defines a hub server which
handles maintaining linearized room history for other servers in the
room. This model permits transparent interconnection between LM
servers and Matrix servers, in the same room.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://turt2live.github.io/ietf-mimi-linearized-matrix/draft-
ralston-mimi-linearized-matrix.html. Status information for this
document may be found at https://datatracker.ietf.org/doc/draft-
ralston-mimi-linearized-matrix/.
Discussion of this document takes place on the More Instant Messaging
Interoperability Working Group mailing list (mailto:mimi@ietf.org),
which is archived at https://mailarchive.ietf.org/arch/browse/mimi/.
Subscribe at https://www.ietf.org/mailman/listinfo/mimi/.
Source for this draft and an issue tracker can be found at
https://github.com/turt2live/ietf-mimi-linearized-matrix.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 5
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Server Names . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Rooms . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2.1. Room Versions . . . . . . . . . . . . . . . . . . . . 9
3.3. Users . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4. Devices . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Events . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5.1. Linearized PDU . . . . . . . . . . . . . . . . . . . 16
3.5.2. State Events . . . . . . . . . . . . . . . . . . . . 16
3.5.3. Event Types . . . . . . . . . . . . . . . . . . . . . 18
4. MLS Considerations . . . . . . . . . . . . . . . . . . . . . 21
4.1. Device Credentials . . . . . . . . . . . . . . . . . . . 23
4.2. Group Creation . . . . . . . . . . . . . . . . . . . . . 24
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4.3. Updating Group State . . . . . . . . . . . . . . . . . . 24
4.4. Key Packages . . . . . . . . . . . . . . . . . . . . . . 26
4.5. Room Event Types . . . . . . . . . . . . . . . . . . . . 26
4.5.1. m.mls.commit . . . . . . . . . . . . . . . . . . . . 26
4.5.2. m.room.encrypted . . . . . . . . . . . . . . . . . . 27
5. Processing Events . . . . . . . . . . . . . . . . . . . . . . 27
5.1. Receiving Events/PDUs . . . . . . . . . . . . . . . . . . 28
5.2. Authorization Rules . . . . . . . . . . . . . . . . . . . 29
5.2.1. Auth Events Selection . . . . . . . . . . . . . . . . 29
5.2.2. Calculating Power Levels . . . . . . . . . . . . . . 30
5.2.3. Auth Rules Algorithm . . . . . . . . . . . . . . . . 30
6. Signing . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.1. Signing Events . . . . . . . . . . . . . . . . . . . . . 35
6.2. Signing Arbitrary Objects . . . . . . . . . . . . . . . . 36
6.3. Checking Signatures . . . . . . . . . . . . . . . . . . . 36
7. Canonical JSON . . . . . . . . . . . . . . . . . . . . . . . 36
8. Event Redactions . . . . . . . . . . . . . . . . . . . . . . 37
9. Hashes . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
9.1. Content Hash Calculation . . . . . . . . . . . . . . . . 38
9.2. Reference Hash Calculation . . . . . . . . . . . . . . . 38
10. Unpadded Base64 . . . . . . . . . . . . . . . . . . . . . . . 38
11. Hub Selection . . . . . . . . . . . . . . . . . . . . . . . . 39
11.1. Hub Transfers . . . . . . . . . . . . . . . . . . . . . 39
12. Transport . . . . . . . . . . . . . . . . . . . . . . . . . . 39
12.1. TLS Certificates . . . . . . . . . . . . . . . . . . . . 40
12.2. API Standards . . . . . . . . . . . . . . . . . . . . . 40
12.2.1. Requests and Responses . . . . . . . . . . . . . . . 40
12.2.2. Errors . . . . . . . . . . . . . . . . . . . . . . . 41
12.2.3. Unsupported Endpoints . . . . . . . . . . . . . . . 42
12.2.4. Malformed Requests . . . . . . . . . . . . . . . . . 42
12.2.5. Transaction Identifiers . . . . . . . . . . . . . . 42
12.2.6. Rate Limiting . . . . . . . . . . . . . . . . . . . 42
12.3. Resolving Server Names . . . . . . . . . . . . . . . . . 43
12.3.1. GET /.well-known/matrix/server . . . . . . . . . . . 45
12.4. Request Authentication . . . . . . . . . . . . . . . . . 46
12.4.1. Retrieving Server Keys . . . . . . . . . . . . . . . 48
12.5. Sending Events . . . . . . . . . . . . . . . . . . . . . 53
12.5.1. PUT /_matrix/federation/v2/send/:txnId . . . . . . . 54
12.6. Event and State APIs . . . . . . . . . . . . . . . . . . 57
12.6.1. GET /_matrix/federation/v2/event/:eventId . . . . . 57
12.6.2. GET /_matrix/federation/v1/state/:roomId . . . . . . 58
12.6.3. GET /_matrix/federation/v1/state_ids/:roomId . . . . 60
12.6.4. GET /_matrix/federation/v2/backfill/:roomId . . . . 60
12.7. Room Membership . . . . . . . . . . . . . . . . . . . . 62
12.7.1. Make and Send Handshake . . . . . . . . . . . . . . 64
12.7.2. Invites . . . . . . . . . . . . . . . . . . . . . . 66
12.7.3. Joins . . . . . . . . . . . . . . . . . . . . . . . 72
12.7.4. Knocks . . . . . . . . . . . . . . . . . . . . . . . 75
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12.8. Content Repository . . . . . . . . . . . . . . . . . . . 78
12.9. Ephemeral Data Units (EDUs) . . . . . . . . . . . . . . 78
12.10. MLS . . . . . . . . . . . . . . . . . . . . . . . . . . 79
12.10.1. Device Info Publishing . . . . . . . . . . . . . . 79
12.10.2. To-Device Messaging . . . . . . . . . . . . . . . . 81
12.10.3. One Time Key Claiming . . . . . . . . . . . . . . . 81
12.11. TODO: Remainder of Transport . . . . . . . . . . . . . . 83
12.11.1. Open Questions . . . . . . . . . . . . . . . . . . 83
13. User Privacy . . . . . . . . . . . . . . . . . . . . . . . . 83
14. Spam Prevention . . . . . . . . . . . . . . . . . . . . . . . 84
15. Security Considerations . . . . . . . . . . . . . . . . . . . 84
16. MIMI Protocol Comparison . . . . . . . . . . . . . . . . . . 85
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 85
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 85
18.1. Normative References . . . . . . . . . . . . . . . . . . 85
18.2. Informative References . . . . . . . . . . . . . . . . . 88
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 89
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 89
1. Introduction
Linearized Matrix derives from Matrix (matrix.org
(https://matrix.org)). Matrix is an interoperable decentralized
communications protocol with an open specification. Matrix uses a
Directed Acyclic Graph (DAG) to persist rooms, synchronizing the DAG
between servers. Linearized Matrix uses an append-only doubly-linked
list. A hub server is present in each room to persist the linked
list, and to handle linearization of events (user/application
messages, as well as room configuration changes) from other servers.
The hub server in a room does not act as an owner for the room. All
rooms support the doubly-linked list and a DAG at the same time. The
precise details of DAG and linked list interconnection are not
covered by this document; they are out of scope for the More Instant
Messaging Interoperability (MIMI) working group. Full details are
available within the Matrix specification process as [MSC3995].
Where applicable, this document covers the mandatory components.
As rooms support these two representations, this permits a variable
threat model. Messaging providers who want to deliver all their
messages/don't trust other servers to deliver their messages would
choose the DAG representation, at the cost of implementation
complexity. Providers using the Linearized Matrix representation
place trust in the hub server to deliver the messages. Those
providers attach verifiable hashes and signatures to each event as a
safeguard against the hub server modifying the events.
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The primary exports of Linearized Matrix are the room model and the
rules which govern how a room accepts events. This document
specifies a server-centric approach, where one or more servers
perform access control. With some changes, it can become client-
centric too. This document also specifies a transport for
synchronizing the doubly-linked list to other servers. More
efficient and scalable transport methods should replace this example.
In a similar fashion, this document specifies how Messaging Layer
Security (MLS) [I-D.ietf-mls-protocol] [I-D.ietf-mls-architecture]
could run over a Linearized Matrix room. User messages use MLS,
while state events (room configuration information) are plain-text in
this iteration of the document. Clients synchronize room and MLS
group membership, while servers verify those memberships. This
ensures that users who are not in the room are unable to gain access
to encrypted messages.
A key component for interoperability is consistent access control
semantics. Where a single server 'owns' a room, it can establish
arbitrary measures. For example, an owning provider might decide
that a different kind of password is required to join a room. This
diminishes the user experience on providers who do not (or can not)
support those custom measures. With decentralization, all
participating servers must use the same consistent set of access
controls. Linearized Matrix uses a decentralized room model for this
reason, with linear room history for ease of implementation.
Linearized Matrix also supports transferring a hub to a different
server in the room. This enables two major features: a hub server
that wishes to leave the room can do so, as it is no longer
responsible for handling events for the room, and because the hub
could change at any time, access control semantics must remain
consistent. As a bonus, hub transfers make it possible for a (non-
linearized) Matrix server to take hub status. When it becomes the
hub, it takes responsibility for linearizing the room's DAG for other
Linearized Matrix servers in the room. The DAG linearization
algorithm is not specified in this document; it is out of scope for
the MIMI working group.
2. Conventions and Definitions
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.
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This document uses [I-D.ralston-mimi-terminology] for the majority of
terminology.
This document additionally defines:
*Rejection*: An event which is "rejected" is not relayed to any local
clients and is not appended to the room in any way.
*Soft Failure*: An event which is "soft-failed" SHOULD NOT be relayed
to any local clients, nor be used as in auth_events if possible. The
event is otherwise appended to the room as per usual.
Further terms are introduced in-context within this document.
*TODO*: We should move/copy those definitions up here anyways.
3. Architecture
For a given conversation/room:
.------------. .------------.
| Client A | | Client B |
'---------+--' '---------+--'
^ | ^ |
| | Client-Server API | |
| V | V
+-----+------------+ +-----+------------+
| +----------( events )------->| |
| Provider/Server | | Provider/Server |
| A |<---------( events )--------+ B |
+-----+------------+ Server-Server Protocol +------------------+
| ^
| | +------------------+
| +----( events )--------+ |
| | Provider/Server |
+----------( events )------->| C |
+------------+-----+
^ |
| |
| V
.--+---------.
| Client C |
'------------'
In this diagram, events (Section 3.5) are objects which carry
information about the room as well as messages between users within
that room.
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Server A is acting as a hub for the other two servers in the diagram.
Servers B and C do not converse directly when sending events to the
room: those events are instead sent to the hub which then distributes
them back out to all participating servers. Servers communicate with
each other using the API surface described by Section 12.
Clients are shown in the diagram here for demonstrative purposes
only. No Client-Server API or other requirements of clients are
specified in this document.
This leads to two distinct roles:
* *Hub server*: the server responsible for holding conversation
history on behalf of other servers in the room.
* *Participant server*: any non-hub server. This server MAY persist
conversation history or rely on the hub server instead.
*OPEN QUESTION*: Should we support having multiple hubs for increased
trust between participant and hub? (participant can pick the hub it
wants to use rather than being forced to use a single hub)
*OPEN QUESTION*: Should we instead require that each server persist
events they create, with the hub being responsible for purely
distribution/fetching? It'd be in the hub's best interest to store
all history, but equally if it can rebuild the room by reaching out
to origin servers then it might be fine enough (it'd only be storing
event IDs rather than whole events).
3.1. Server Names
Each messaging provider is referred to as a "server" and has a
"domain name" or "server name" to uniquely identify it. This server
name is then used to namespace user IDs, room IDs/aliases, etc.
A server name MUST be compliant with Section 2.1 of [RFC1123].
Improper server names MUST be considered "uncontactable" by a server.
A server MUST NOT use a literal IPv4 or IPv6 address as a server
name. Doing so reduces the ability for the server to move to another
internet address later, and IP addresses are generally difficult to
acquire a certificate for (required in Section 12). Additionally,
servers SHOULD NOT use an explicit port in their server name for
similar portability reasons.
The approximate ABNF [RFC5234] grammar for a server name is:
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server_name = hostname [ ":" port ]
port = 1*5DIGIT
hostname = 1*255dns-char
dns-char = DIGIT / ALPHA / "-" / "."
Server names MUST be treated as case sensitive (eXaMpLe.OrG,
example.org, and EXAMPLE.ORG are 3 different servers). Server names
SHOULD be lower case (example.org) and SHOULD NOT exceed 230
characters for ease of use. The 230 characters specifically gives
room for a suitably long localpart while being within the 255
allowable characters from Section 2.1 of [RFC1123].
Examples:
* example.org (DNS host name)
* example.org:5678 (DNS host name with explicit port)
3.2. Rooms
Rooms hold the same definition under [I-D.ralston-mimi-terminology]:
a conceptual place where users send and receive events. All users
with sufficient access to the room receive events sent to that room.
The different chat types are represented by rooms through state
events (Section 3.5.2), which ultimately change how the different
algorithms in the room version (Section 3.2.1) behave.
Rooms have a single internal "Room ID" to identify them from another
room. The ABNF [RFC5234] grammar for a room ID is:
room_id = "!" room_id_localpart ":" server_name
room_id_localpart = 1*opaque
opaque = DIGIT / ALPHA / "-" / "." / "~" / "_"
server_name is inherited from Section 3.1.
room_id MUST NOT exceed 255 characters and MUST be treated as case
sensitive.
Example: !abc:example.org.
The server_name for a room ID does _NOT_ indicate the room is
"hosted" or served by that domain. The domain is used as a namespace
to prevent another server from maliciously taking over a room. The
server represented by that domain may no longer be participating in
the room.
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The entire room ID after the ! sigil MUST be treated as opaque. No
part of the room ID should be parsed, and cannot be assumed to be
human-readable.
3.2.1. Room Versions
*TODO*: We should consider naming this something else.
Each room declares which room version it's using, and each room
version (identified by a single string) describes the specific
algorithms a server needs to follow in order to particpate in rooms
with that version. Room versions are immutable once specified, as
otherwise a change in algorithms could cause a split-brain between
servers participating in affected rooms.
Room versions prefixed with I. MUST only be used within the IETF
specification process. Room versions consisting solely of 0-9 and .
MUST only be used by the Matrix protocol.
This document as a whole describes I.1 as a room version.
Servers MUST implement support for I.1 at a minimum. Servers SHOULD
use I.1 when creating new rooms.
*Implementation note*: Currently I.1 is not a real thing. Use
org.matrix.i-d.ralston-mimi-linearized-matrix.02 when testing against
other Linearized Matrix implementations. This string may be updated
later to account for breaking changes.
*Implementation note*: org.matrix.i-d.ralston-mimi-linearized-
matrix.00 also exists in the wild, defining a set of algorithms which
exist in a prior version of this document (00 and 01).
*TODO*: Remove implementation notes.
There is no implicit ordering or hierarchy to room versions. Future
room versions, such as an I.2, can choose to build upon I.1's
algorithms or start completely from scratch if they prefer.
A room version has the following algorithms defined:
* Event authorization - Rules which govern when events are accepted,
rejected, or soft-failed by a server. For I.1, this is
Section 5.2.
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* Redaction - Description of which fields to keep on an event during
redaction. Redaction is used by the signing and hash algorithms,
meaning they need to be consistent across implementations. For
I.1, this is Section 8.
* Event format - Which fields are expected to be present on an
event, and the schema for each. For I.1, this is Section 3.5.
* Canonical JSON - Specific details about how to canonicalize an
event as JSON. This is used by the signing algorithm and must be
consistent between implementations. For I.1, this is Section 7.
* Hub selection - Rules around picking the hub server and
transferring to a new hub. For I.1, this is Section 11.
* Identifier grammar - All identifiers (room IDs, user IDs, event
IDs, etc) can change grammar within a room version. As such, they
SHOULD generally be treated as opaque as possible over a
transport. For I.1, these details are described in Section 3.1,
Section 3.2, Section 3.3, Section 3.4, and Section 3.5.
The transport between servers is decoupled from the algorithms above.
For example, events are treated as blobs with no specific format over
the wire but have strict schema in the context of a room or room
version. Endpoints MUST be designed with this distinction in mind.
Each room version has a "stable" or "unstable" designation. Stable
room versions SHOULD be used in production by messaging providers.
Unstable room versions might contain bugs or are not yet fully
specified and SHOULD NOT be used in production by messaging
providers.
I.1 shall be considered "stable".
*Implementation note*: org.matrix.i-d.ralston-mimi-linearized-
matrix.02 is considered "unstable".
*TODO*: Remove implementation notes.
*TODO*: Matrix considers a version as stable once accepted through
FCP. When would be the process equivalent for the IETF?
The ABNF [RFC5234] grammar for a room version is:
room_version = 1*128room_version_char
room_version_char = DIGIT
/ %x61-7A ; a-z
/ "-" / "."
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Examples:
* 1
* I.1
* org.example.my-room-version
Room versions not formally specified SHOULD be prefixed using reverse
domain name notation, creating a sort of namespace. org.example.my-
room-version is an example of this.
3.3. Users
As described by [I-D.ralston-mimi-terminology], a user is typically a
human which operates a client. Each user has a distinct user ID.
The ABNF [RFC5234] grammar for a user ID is:
user_id = "@" user_id_localpart ":" server_name
user_id_localpart = 1*user_id_char
user_id_char = DIGIT
/ %x61-7A ; a-z
/ "-" / "." / "="
/ "_" / "/" / "+"
server_name is inherited from Section 3.1.
user_id MUST NOT exceed 255 characters and MUST be treated as case
sensitive.
Examples:
* @alice:example.org
* @watch/for/slashes:example.org
user_id_localpart SHOULD be human-readable and notably MUST NOT
contain uppercase letters.
server_name denotes the domain name (Section 3.1) which allocated the
ID, or would allocate the ID if the user doesn't exist yet.
Identity systems and messaging providers SHOULD NOT use a phone
number in a localpart. Using a phone number would mean that when a
human operator's changes their phone number then they'd lose access
to their existing chats and potentially gain access to any chats the
new number is participating in. Providers which use phone numbers
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SHOULD ensure the new user ID is not in chats belonging to a
different logical user. To prevent this case, a GUID (scoped to the
allocating server) or an account ID is recommended as a localpart,
allowing users to change their phone number without losing chats.
This document does not define how a user ID is acquired. It is
expected that an identity specification under MIMI will handle
resolving email addresses, phone numbers, names, and other common
queries to user IDs.
User IDs are sometimes informally referenced as "MXIDs", short for
"Matrix User IDs".
3.4. Devices
Each user can have zero or more devices/active clients. These
devices are intended to be members of the MLS group and thus have
their own key package material associated with them.
Because device IDs are used as "key versions" in a key ID
(Section 6), they have a compatible ABNF [RFC5234] grammar:
device_id = 1*key_version_char
device_id_char = ALPHA / DIGIT / "_"
3.5. Events
All data exchanged over Linearized Matrix is expressed as an "event".
Each client action (such as sending a message) correlates with
exactly one event. All events have a type to distinguish them, and
use reverse domain name notation to namespace custom events (for
example, org.example.appname.eventname).
Event types using m. as a prefix MUST only be used by the protocol.
When events are traversing a transport to another server they are
referred to as a *Persistent Data Unit* or *PDU*. Structurally, an
event and PDU are the same.
An event has the following minimum fields:
* room_id (string; required) - The room ID for where the event is
being sent. This MUST be a valid room ID (Section 3.2).
* type (string; required) - A UTF-8 [RFC3629] string to distinguish
different data types being carried by events. Event types are
case sensitive. This MUST NOT exceed 255 characters.
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* state_key (string; optional) - A UTF-8 [RFC3629] string to further
distinguish an event as a state event (see Section 3.5.2). Can be
an empty string. This MUST NOT exceed 255 characters.
Each event type specifies its own state key requirements. For
m.room.member (Section 3.5.3.3), the state key is the user ID
(Section 3.3) for which the membership applies to. For
m.room.join_rules (Section 3.5.3.2), this is an empty string. For
a custom event type this may be an opaque string such as a UUID or
randomly generated string.
* sender (string; required) - The user ID which is sending this
event. This MUST be a valid user ID (Section 3.3).
* origin_server_ts (64-bit integer; required) - The milliseconds
since the unix epoch for when this event was created.
* hub_server (string; optional) - When a hub server is converting an
LPDU (Section 3.5.1) to a formal event, it MUST specify its own
server name (Section 3.1) here. The value MUST be a valid server
name.
To support interconnection with non-linearized Matrix, as
discussed in Section 1, events created outside of a hub server
MUST NOT populate this field.
* content (object; required) - The event content. The specific
schema depends on the event type. Clients and servers processing
an event MUST NOT assume the content is safe or accurately
represented. Malicious clients and servers are able to send
payloads which don't comply with a given schema, which may cause
unexpected behaviour on the receiving side. For example, a field
marked as "required" might be missing.
* hashes (object; required) - The content hashes (Section 9.1) for
the event. There is a special lpdu key to contain the LPDU
(partial PDU schema; see Section 3.5.1) hashes, which is itself
keyed by hash algorithm and has the encoded hash as the value.
The hashes object, outside of lpdu, similarly is keyed by hash
algorithm with encoded hash values.
Events which specify a hub_server MUST additionally contain an
lpdu hash. All other events MUST NOT contain lpdu hashes. This
is to support interconnection with non-linearized Matrix, as
discussed in Section 1.
* signatures (object; required) - Keyed first by domain name then by
key ID, the signatures for the event.
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* auth_events (array of strings; required) - The event IDs which
prove the sender is able to send this event in the room. Which
specific events are put here are defined by the auth events
selection algorithm (Section 5.2.1).
* prev_events (array of strings; required) - This field is to
support interconnection with non-linearized Matrix, discussed in
Section 1. Events which specify a hub_server are expected to have
exactly 1 entry in this array, while other events MAY have 1 or
more entries.
Note that an event ID is not specified on the schema. Event IDs are
calculated to ensure accuracy and consistency between servers. To
determine the ID for an event, calculate the reference hash
(Section 9.2) then encode it using URL-safe Unpadded Base64
(Section 10) and prefix that with the event ID sigil, $. For example,
$nKHVqt3iyLA_HEE8lT1yUaaVjjBRR-fAqpN4t7opadc.
Using a reference hash in the event ID prevents other servers from
changing what that event ID represents. If an event ID was just a
UUID (or similar), any server along the send or receive path could
swap the actual event payload out for a different event. The hashes
and signatures in this case do nothing to protect the actual event,
as a malicious server can simply generate legal hashes/signatures as
part of their modification. If we add a namespace condition where
the event ID _must_ reference the same server name as the sender
($uuid:example.org) then the sending server is free to re-assign the
event ID to a different payload during the sending of that event,
though all other servers along the send/receive path cannot change
the event. This is particularly problematic if the event's sender is
the hub for the room: the hub can send one copy of an event to half
the room, and a very different copy to the other half while still
maintaining the same event ID for both halves. To fix this, a hash
of the event itself would need to become part of the event ID such
that any modification or reassignment of the event ID is made obvious
to receipient servers. This could be a tuple of (uuid, hash), though
for simplicity this document uses just the reference hash on its own.
With event IDs containing hashes of the events it's theoretically
possible for a sufficiently motivated person to build a database of
event IDs. With that database, they could eventually determine
enough information to identify parts of the event payload itself.
There is not enough anchoring information on an event (or sent over
the transport) for this to be efficient or effective, however.
The ABNF [RFC5234] for an event ID is:
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event_id = "$" reference_hash
reference_hash = 1*urlsafe_unpadded_base64_char
urlsafe_unpadded_base64_char = ALPHA / DIGIT / "-" / "_"
If both the sender and receiver are implementing the algorithms
correctly, the event ID will be the same. When different, the
receiver will have issues accepting the event (none of the
auth_events will make sense, for example). The sender and receiver
will need to review that their implementation matches the
specification in this case.
Events are treated as JSON [RFC8259] within the protocol, but can be
encoded and represented by any binary-compatible format. Additional
overhead may be introduced when converting between formats, however.
An example event is:
{
"room_id": "!abc:example.org",
"type": "m.room.member",
"state_key": "@alice:first.example.org",
"sender": "@bob:second.example.org",
"origin_server_ts": 1681340188825,
"hub_server": "first.example.org",
"content": {
"membership": "invite"
},
"hashes": {
"lpdu": {
"sha256": "<unpadded base64>"
},
"sha256": "<unpadded base64>"
},
"signatures": {
"first.example.org": {
"ed25519:1": "<unpadded base64 signature covering whole event>"
},
"second.example.org": {
"ed25519:1": "<unpadded base64 signature covering LPDU>"
}
},
"auth_events": ["$first", "$second"],
"prev_events": ["$parent"]
}
An event/PDU MUST NOT exceed 65536 bytes when formatted using
Canonical JSON (Section 7). Note that this includes all signatures
on the event.
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Fields have no size limit unless specified above, other than the
maximum 65536 bytes for the whole event.
3.5.1. Linearized PDU
All events generated by participant servers are routed through the
hub, but the participant servers themselves are unable to populate
fields like prev_events because they can't guarantee order and those
fields contribute to the event ID, signatures, and overall validity.
To fix this, participant servers send the hub server a "Linearized
PDU" or "LPDU" which does not include the fields they cannot set
while still ensuring integrity of the event contents themselves.
The participant server MUST NOT populate the following fields on
events (LPDUs) they are sending to the hub:
* auth_events - the participant cannot reliably determine what
allows it to send the event.
* prev_events - the participant cannot reliably know what event
precedes theirs.
* hashes (except hashes.lpdu) - top-level hashes cover the above two
fields.
The participant server MUST populate the hashes.lpdu object, covering
a content hash (Section 9.1) of the partial event, giving
authenticity to the sender's contents. The participant server
additionally signs this partial event before sending it to the hub.
The participant server will receive an echo of the fully-formed event
from the hub once appended to the room.
3.5.2. State Events
State events track metadata for the room, such as name, topic, and
members. State is keyed by a tuple of type and state_key. The state
"at" an event is the set of state events which have the most recent
(in terms of event ordering, not timestamp) state tuple.
For example, consider the following (simplified) room history:
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[
/* in all events, irrelevant fields are not shown for brevity */
/* 0 */ {
"type": "m.room.create", "state_key": ""
},
/* 1 */ {
"type": "m.room.member", "state_key": "@alice:example.org"
},
/* 2 */ {
"type": "m.room.encrypted"
},
/* 3 */ {
"type": "m.room.member", "state_key": "@bob:example.org"
},
/* 4 */ {
"type": "m.room.member", "state_key": "@alice:example.org"
}
]
The state at index 2 consists of Alice's m.room.member event
(Section 3.5.3.3) and the m.room.create event (Section 3.5.3.1) from
the room. The m.room.encrypted event itself is not a state event and
therefore does not get appended to the state "at" any particular
event.
The state at index 4 would have Alice's new m.room.member event,
Bob's m.room.member event, and the m.room.create event from before.
Alice's old membership event is overridden due to having the same
type and state_key as the previous event. Note however that the
state at index 3 still contains the older membership event, as the
new event happens later with respect to event ordering.
"Current state" is the state at the most recent event in the room.
Calculating the state at a given event is needed for the
authorization rules (Section 5.2) and event visibility
(Section 3.5.3.5.1) algorithms. Clients additionally need to know
current state to show accurate room names, topics, avatars, etc.
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3.5.2.1. Stripped State
Stripped state events are extremely simplified state events to
provide context to a user for an invite (Section 12.7.2) or knock
(Section 12.7.4). Servers and clients have no ability to verify the
events outside of the context for a room, so all such fields are
removed. Servers and clients MUST NOT rely on the events being
accurate because they cannot independently verify them.
When generating stripped state for an invite or knock, the following
events SHOULD be included if present in the current room state
itself:
* m.room.create (Section 3.5.3.1)
* m.room.name (*TODO*: Link)
* m.room.avatar (*TODO*: Link)
* m.room.topic (*TODO*: Link)
* m.room.join_rules (Section 3.5.3.2)
* m.room.canonical_alias (*TODO*: Link)
Servers MAY include other event types/state keys. The above set
gives users enough context to determine if they'd like to knock/join
the room, as features such as the name and avatar are generally key
pieces of information for a user.
Stripped state events MUST only have sender, type, state_key, and
content from the event schema (Section 3.5).
Example:
{
"type": "m.room.create",
"sender": "@alice:example.org",
"state_key": "",
"content": {
"room_version": "I.1"
}
}
3.5.3. Event Types
Linearized Matrix defines the following event types. The section
headers are the event type.
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3.5.3.1. m.room.create
The very first event in the room. It MUST NOT have any auth_events
or prev_events, and the domain of the sender MUST be the same as the
domain in the room_id. The state_key MUST be an empty string.
The content for a create event MUST have at least a room_version
field to denote what set of algorithms the room is using.
These conditions are checked as part of the event authorization rules
(Section 5.2).
3.5.3.2. m.room.join_rules
Defines whether users can join without an invite and other similar
conditions. The state_key MUST be an empty string. Any other state
key, including lack thereof, serve no meaning and are treated as
though they were a custom event.
The content for a join rules event MUST have at least a join_rule
field to denote the join policy for the room. Allowable values are:
* public - anyone can join without an invite.
* knock - users must receive an invite to join, and can request an
invite (knock) too.
* invite - users must receive an invite to join.
*TODO*: Describe restricted (and knock_restricted) rooms?
*TODO*: What's the default?
3.5.3.3. m.room.member
Defines the membership for a user in the room. If the user does not
have a membership event then they are presumed to be in the leave
state.
The state_key MUST be a non-empty string denotating the user ID the
membership is affecting.
The content for a membership event MUST have at least a membership
field to denote the membership state for the user. Allowable values
are:
* leave - not participating in the room. If the state_key and
sender do not match, this was a kick rather than voluntary leave.
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* join - participating in the room.
* knock - requesting an invite to the room.
* invite - invited to participate in the room.
* ban - implies kicked/not participating. Cannot be invited or join
the room without being unbanned first (moderator sends a kick,
essentially).
These conditions are checked as part of the event authorization rules
(Section 5.2), as are the rules for moving between membership states.
The content for a membership event MAY additionally have a reason
field containing a human-readable (and usually human-supplied)
description for why the membership change happened. For example, the
reason why a user was kicked/banned or why they are requesting an
invite by knocking.
3.5.3.4. m.room.power_levels
Defines what given users can and can't do, as well as which event
types they are able to send. The enforcement of these power levels
is determined by the event authorization rules (Section 5.2).
The state_key MUST be an empty string.
The content for a power levels event SHOULD have at least the
following:
* ban (integer) - the level required to ban a user. Defaults to 50
if unspecified.
* kick (integer) - the level required to kick a user. Defaults to
50 if unspecified.
* invite (integer) - the level required to invite a user. Defaults
to 0 if unspecified.
* redact (integer) - the level required to redact an event sent by
another user. Defaults to 50 if unspecified.
* events (map) - keyed by event type string, the level required to
send that event type to the room. Defaults to an empty map if
unspecified.
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* events_default (integer) - the level required to send events in
the room. Overridden by the events map. Defaults to 0 if
unspecified.
* state_default (integer) - the level required to send state events
in the room. Overridden by the events map. Defaults to 50 if
unspecified.
* users (map) - keyed by user ID, the level of that user. Defaults
to an empty map if unspecified.
* users_default (integer) - the level for users. Overridden by the
users map. Defaults to 0 if unspecified.
*TODO*: Include notifications for at-room here too?
Note that if no power levels event is specified in the room then the
room creator (sender of the m.room.create state event) has a default
power level of 100.
These conditions are checked as part of the event authorization rules
(Section 5.2).
3.5.3.5. m.room.history_visibility
*TODO*: Describe.
3.5.3.5.1. Calculating Event Visibility
*TODO*: Describe. (when can a server see an event?). Mention that
m.mls.commit is exempt.
*TODO*: This section feels like it's in the wrong place. Bring it
closer to on-receive-event sections.
3.5.3.6. TODO: Other events
*TODO*: m.room.name, m.room.topic, m.room.avatar,
m.room.canonical_alias
4. MLS Considerations
*TODO*: We should consider running [I-D.robert-mimi-delivery-service]
over LM instead. Using something like [I-D.mahy-mimi-group-chat]
would be good for more of a client-side representation of the LM room
model.
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The MIMI working group is chartered to use Messaging Layer Security
(MLS) [I-D.ietf-mls-protocol] [I-D.ietf-mls-architecture] for
encryption in chats, and this document specifies no different. Each
room has a single MLS Group associated with it, both identified by
the room ID (Section 3.2).
Rooms additionally track membership at a per-user level while MLS
tracks group membership at a per-device level. With this
consideration, commits to the MLS Group MUST use PublicMessage,
giving the hub server an ability to inspect MLS group membership
changes for illegal joins and leaves.
Encryption can only be enabled at the time the room is created. This
prevents the room having encryption disabled or downgraded without an
entirely new room being created. The exact ciphersuite and other
algorithmic details are contained in the content for the
m.room.create event (Section 3.5.3.1):
{
"encryption": {
"algorithm": "m.mls.v1.dhkemx25519-aes128gcm-sha256-ed25519"
}
}
algorithm denotes which specific algorithm clients MUST use for
sending and receiving encrypted events in the room. If a received
event is encrypted using a different algorithm, it MUST be treated as
undecryptable (even if the client has sufficient key information to
decrypt it).
m.mls.v1. as a prefix describes the behaviour for encrypted clients,
with the remainder of the algorithm string covering the exact
ciphersuite. This document uses the same mandatory ciphersuite as
MLS: MLS_128_DHKEMX25519_AES128GCM_SHA256_Ed25519. Thus, this is
encoded as m.mls.v1.dhkemx25519-aes128gcm-sha256-ed25519. Other
ciphersuites can be represented similarly, though are considered to
be entirely new encryption algorithms for the purposes of this
document.
Custom or non-standard encryption algorithms are possible with this
approach, however out of scope for MIMI. If such an algorithm is
used, it SHOULD be prefixed using reverse domain name notation. For
example, org.example.my-encryption.
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Mentioned in the introduction (Section 1), this document does not
explore the details for what is needed to interconnect Linearized
Matrix and Matrix's existing room model. However, for
interconnection to be successful, extensions to MLS are needed to
support decentralization. One possible extension is "Decentralised
MLS" [DMLS].
4.1. Device Credentials
Under Section 5.3 of [I-D.ietf-mls-protocol], each MLS group member
(a device, Section 3.4) has a "credential" or signing key associated
with it. These are published to each client's local server and
available over federation (Section 12.10).
This document relies upon out-of-band verification and therefore uses
basic credentials. The format for the credential is:
struct {
opaque user_id<V>;
opaque device_id<V>;
opaque signature_key<V>;
} BasicCredential;
user_id is as described by Section 3.3, and device_id is as described
by Section 3.4. signature_key is from MLS.
The device then constructs the following object, signs it using each
of the listed keys, and publishes it through its local server
(Section 12.10.1):
{
"device_id": "ABCDEF",
"user_id": "@alice:example.org",
"algorithms": [
"m.mls.v1.dhkemx25519-aes128gcm-sha256-ed25519"
],
"keys": {
"m.mls.v1.credential.ed25519:ABCDEF":
"<unpadded base64 BasicCredential>"
},
"signatures": {
"@alice:example.org": {
"m.mls.v1.credential.ed25519:ABCDEF":
"<unpadded base64 signature>"
}
}
}
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device_id is the client's device ID (Section 3.4). user_id is the
user ID (Section 3.3) to which the device ID belongs. algorithms are
the encryption algorithms the device supports, and SHOULD contain at
least m.mls.v1.dhkemx25519-aes128gcm-sha256-ed25519.
When a device supports m.mls.v1.dhkemx25519-aes128gcm-sha256-ed25519,
it MUST specify its basic credential with the
m.mls.v1.credential.ed25519 key algorithm.
keys is an object containing each algorithm-specific key (or keys)
for the device. The fields for the object form a key ID, with the
device ID representing the "key version", as per Section 6.
All top-level fields in the object above MUST be supplied.
For each of the device's keys, a valid signature MUST be produced.
If there is a missing signature from any of the keys, or from the
user_id, the device information is considered invalid. Invalid
devices MUST NOT be members of the MLS group, and are removed if
already members prior to the device information becoming invalid.
4.2. Group Creation
After the m.room.create event and other initial state events for the
room are sent, the room creator MUST establish the appropriate MLS
group. This is sent as an m.mls.commit event (Section 4.5.1).
Afterwards, the remaining devices are added as normal (Section 4.3).
Ideally, the m.room.create event would also contain the initial
public group state, however doing so would mean either tracking an
independent MLS group ID or allowing the client to specify the room
ID. While servers MAY allow the client to specify the room ID,
servers usually have better context for which localparts (see
Section 3.2) are already claimed by other rooms. Having independent
group IDs and room IDs can lead to confusion and a similar sort of
namespacing issue (a room creator can create a conflicting group ID).
Instead, the server (usually) creates the room on behalf of the
client, allowing the client to then send the initial public group
state to the room for other MLS members.
4.3. Updating Group State
This document does not provide a way to send proposals to the MLS
group, meaning all commits MUST only contain proposals which are sent
by the same member (see Section 12 of [I-D.ietf-mls-protocol]).
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All commits are encoded as m.mls.commit events (Section 4.5.1) and
are sent to the room. These commits are additionally encoded using
PublicMessage, giving servers visibility on the contents of the
commits. Upon receiving the event (see Section 5.1), the hub server
MUST additionally validate that any membership changes match what is
possible with the room membership:
* Devices can only be added to the group if they belong to a user
which is joined to the room, or if the room is "world readable"
(Section 3.5.3.5.1). It is generally not enough to be invited,
knocking, etc on the room - the user ID must usually be in the
join state.
* Devices can be removed in two ways:
- A device can remove another device if they both belong to the
same user ID.
- A device can be removed by anyone if the user ID to which it
belongs is no longer in the join state. This condition is
required to satisfy a case in MLS where a device cannot self-
remove itself from the group.
If this validation fails, the hub server MUST reject the request if
it's shaped as an LPDU (Section 3.5.1) and soft-fail the event if
it's a PDU (Section 3.5).
Welcome messages are sent to devices over to-device messaging
(Section 12.10.2). The message_type for the message is
m.room.encrypted [*TODO*: Rename to avoid confusion with room event?]
and message of:
{
"algorithm": "m.mls.v1.welcome.[ciphersuite]",
"ciphertext": "<unpadded base64 encoded welcome message>",
"commit_event_id": "<event ID of the m.mls.commit event>"
}
algorithm is the ciphersuite, dhkemx25519-aes128gcm-sha256-ed25519,
prefixed with m.mls.v1.welcome.
The remaining fields are as described in the example. See Section 10
for "unpadded base64".
All fields MUST be supplied. Note that the sender's user ID and
device ID are made available over the to-device messaging endpoints
(Section 12.10.2).
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In all cases, a device remembers the event ID (either from the
m.mls.commit event or commit_event_id from a to-device message) after
decryption to associate it with the MLS epoch. The device can then
do a reverse lookup of epoch to event ID to MLS group state. Note
that a client _always_ has access to m.mls.commit events, even when
hidden by history visibility (Section 3.5.3.5.1).
*TODO*: Is it correct to say all commits are visible as "shared"?
*TODO*: We may need to store the group state in the media repo if it
gets to be too big, or otherwise allow oversized events.
*TODO*: The server also likely needs to prevent devices being added
to the group which don't support the ciphersuite/algorithm.
4.4. Key Packages
Clients "claim" another device's key package through their server
(Section 12.10.3). Clients will typically generate several key
packages and upload them to their server, making them available even
if the client goes offline.
The algorithm for a key package is m.mls.v1.key_package.dhkemx25519-
aes128gcm-sha256-ed25519 and is combined with a device-generated key
version, forming a key ID described by Section 6. The key version
SHOULD be generated based upon the key package itself rather than
using an unrelated string, such as a hash or the public key of the
key package.
4.5. Room Event Types
*TODO*: Should these be defined with the other event types rather
than here?
This document describes the following event types for use with MLS-
encrypted rooms. The section headers are the event type. See
Section 3.5 for more information on events.
These event types are non-state events, also called "room events".
4.5.1. m.mls.commit
Represents an MLS commit, which may be rejected by the hub server.
content for the event MUST contain at least the following example:
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{
"message": "<unpadded base64 encoded PublicMessage>",
"public_group_state": "<unpadded base64 encoded public group state>"
}
As mentioned, message is a PublicMessage from MLS. public_group_state
is to enable external joins.
An optional field, prev_commit_event_id, SHOULD be specified when a
parent commit exists. This is to enable clients to find the commit
they have keys for upon joining the room, as the most recent one may
not be decryptable to them. The client can then work forwards from
where they can decrypt the message.
*TODO*: Should we use the RatchetTree extension? It might make the
group state massive...
*TODO*: Which fields from this need to be protected by Section 8?
4.5.2. m.room.encrypted
Represents an encrypted MLS application message. The sender first
encrypts the message per the content format then MUST send an event
with content matching:
{
"algorithm": "m.mls.v1.[ciphersuite]",
"ciphertext": "<unpadded base64 encoded MLS ciphertext>",
"commit_event_id": "<event ID of applicable m.mls.commit event>"
}
Within this document, algorithm will be m.mls.v1.dhkemx25519-
aes128gcm-sha256-ed25519. The other fields are as described in the
example.
Clients SHOULD treat m.room.encrypted events which are improperly
structured as undecryptable events.
*TODO*: Which fields from this need to be protected by Section 8?
5. Processing Events
An event has several authenticity properties:
* Content hashes (Section 9.1) to cover the LPDU (Section 3.5.1) and
event (Section 3.5) contents.
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* Reference hashes (Section 9.2) which double as the event ID,
covering the redacted event.
* Signatures from the direct senders (server name of the sender and
the hub_server if present), ensuring the entities did actually
produce that event.
*TODO*: Does the hub's signature actually guard anything?
These properties are validated throughout this document. Each
property has different behaviour when violated. For example, a
difference in content hash ultimately causes the event to be stored
as a redacted copy.
5.1. Receiving Events/PDUs
*TODO*: This section conflates sending and receiving a bit more than
it should. Split sending out to its own section.
When a hub receives an LPDU from a participant it MUST add the
missing fields to create a fully formed PDU then MUST send that PDU
back out to all participants, including the original sender.
A server is considered to have "received" an event when it does not
recognize the event ID. This may be because the event has not yet
been persisted, or the server is not persisting anything (in the case
of a participant server). This includes when the server asks another
server for an event it might be missing.
When a server (hub or participant) receives an event, it MUST:
1. Verify the event matches the schema for the room version
(Section 3.5), without considering type-specific schemas applied
to content. If an event fails to meet this requirement, it is
dropped/ignored.
2. Ensure the required signatures are present and that they are
valid (Section 6.3). If the event has a hub_server field, the
event MUST be signed by that server. The event MUST also be
signed by the server implied by the sender, noting that this will
be an LPDU if hub_server is present. All other signatures MUST
NOT be considered for signature validation, regardless of their
individual validity. If the event fails to meet this
requirement, it is dropped/ignored.
3. Ensure the event has a valid content hashes (Section 9.1). If
the event has a hub_server field, it MUST have a content hash
which covers the LPDU. If either the LPDU or PDU content hash
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doesn't match what the receiving server calculations, the event
is redacted before further processing. The server will
ultimately persist the redacted copy.
Additionally, a hub server MUST complete the following checks.
Participant servers SHOULD also perform the following checks to
validate that the hub server is acting in a compliant manner. If the
hub is not acting appropriately (for example, by sending the
participant an event which never should have been accepted), the
participant server MAY choose to warn its local users that the room
history may have been tampered with.
1. The constraints described by Section 4.3 validated, if the room
is encrypted.
5.2. Authorization Rules
These are the rules which govern whether an event is accepted into
the room, depending on the state events surrounding that event. A
given event is checked against multiple different sets of state.
5.2.1. Auth Events Selection
The auth_events on an event MUST consist of the following state
events, with the exception of an m.room.create event which has no
auth_events.
1. The m.room.create state event.
2. The current m.room.power_levels state event, if any.
3. The sender's current m.room.member state event, if any.
4. If the type is m.room.member:
1. The target's (state_key) current m.room.member state event,
if any.
2. If content.membership is join or invite, the current
m.room.join_rules state event, if any.
*TODO*: Talk about restricted room joins here?
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5.2.2. Calculating Power Levels
A requirement of the authorization rules is being able to determine
the current/future "power level" for a user. All power levels are
calculated with reference to the content of an m.room.power_levels
state event (Section 3.5.3.4).
To calculate a user's current power level:
1. If users is present, use the power level for the user ID, if
present.
2. If users is not present, or the user ID is not present in users,
use users_default.
3. If users_default is not present, use 0.
To calculate the required power level to do an action:
1. If the action (kick, ban, invite, or redact) is present, use that
power level.
2. If not present, use the default for the action (50 for kick, ban,
and redact, 0 for invite).
To calculate the required power level to send an event:
1. If events is present, use the power level for the event type, if
present.
2. If events is not present, or the event type is not present in
events:
1. If state_key is present (including empty), use state_default.
1. If state_default is not specified, use 50.
2. If state_key is not present, use events_default.
1. If events_default is not specified, use 0.
5.2.3. Auth Rules Algorithm
With consideration for default/calculated power levels
(Section 5.2.2), each event MUST pass the following rules. "Current
state" (and "current membership", etc) are the state of the room
_before_ the event being checked is applied.
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*TODO*: should we reference m.federate?
1. Events must be signed (Section 6.3) by the server denoted by the
sender field. Note that this may be an LPDU if the hub_server
is specified and not the same server. If the event is
improperly signed, reject the event.
2. If hub_server is present on the event, the event must be signed
(Section 6.3) by that server. If it is improperly signed,
reject the event.
3. If the event's type is m.room.create:
1. If it has any prev_events, reject the event.
2. If the domain of the room_id is not the same domain as the
sender, reject the event.
3. If content.room_version is not I.1, reject the event.
4. Otherwise, allow the event.
4. Considering the event's auth_events:
*TODO*: Does this check make sense for Linearized Matrix? We
already removed what was #3 because it talked about rejecting
events which reference rejected events.
1. If there are duplicate entries for a given type and
state_key pair, reject the event.
2. If there are entries whose type and state_key do not match
those specified by the auth events selection algorithm
(Section 5.2.1), reject the event.
3. If there is no m.room.create event among the entries,
reject.
5. If the event's type is m.room.member:
1. If there is no state_key property, or no membership in
content, reject the event.
2. If the event content's membership field is join:
1. If the previous event is an m.room.create event and the
state_key is the creator, allow the event.
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2. If sender does not match state_key, reject the event.
3. If the sender is banned, reject the event.
4. If the join_rule for m.room.join_rules is invite or
knock, then allow the event if the current membership
state is invite or join.
5. If the join_rule for m.room.join_rules is public, allow
the event.
6. Otherwise, reject the event.
3. If the event content's membership field is invite:
1. If the sender's current membership state is not join,
reject the event.
2. If the target user's (state_key) membership is join or
ban, reject the event.
3. If the sender's power level is greater than or equal to
the power level needed to send invites, allow the event.
4. Otherwise, reject the event.
4. If the event content's membership field is leave:
1. If the sender matches the state_key, allow the event if
and only if that user's current membership state is
knock, join, or invite.
2. If the sender's current membership state is not join,
reject the event.
3. If the target user's (state_key) current membership
state is ban, and the sender's power level is less than
the power level needed to ban other users, reject the
event.
4. If the sender's power level is greater than or equal to
the power level needed to kick users, and the target
user's (state_key) power level is less than the
sender's, allow the event.
5. Otherwise, reject the event.
5. If the event content's membership field is ban:
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1. If the sender's current membership state is not join,
reject the event.
2. If the sender's power level is greater than or equal to
the power level needed to ban users, and the target
user's (state_key) power level is less than the sender's
power level, allow the event.
3. Otherwise, reject the event.
6. If the event content's membership field is knock:
1. If the join_rule for m.room.join_rules is anything other
than knock, reject the event.
2. If the sender does not match the state_key, reject the
event.
3. If the sender's current membership state is not ban or
join, allow the event.
4. Otherwise, reject the event.
7. Otherwise, the membership is unknown. reject the event.
6. If the sender's current membership state is not join, reject the
event.
7. If the event type's required power level to send it is greater
than the sender's power level, reject the event.
8. If the event has a state_key which starts with an @ and does not
match the sender, reject the event.
*TODO*: Do we care? This is theoretically to allow for owned
state events, but in practice nothing which uses this concept
makes it this far into the auth rules (membership events are
validated above).
9. If the event's type is m.room.power_levels:
1. If any of the fields users_default, events_default,
state_default, ban, redact, kick, or invite in content are
present and not an integer, reject the event.
2. If events in content is present and not an object with
values that are integers, reject the event.
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3. If the users in content is present and not an object with
valid user IDs as keys and integers as values, reject the
event.
4. If there is no previous m.room.power_levels event in the
room, allow the event.
5. For the fields users_default, events_default,
state_default, ban, redact, kick, and invite, check if they
were added, changed, or removed. For each found
alteration:
1. If the current value is higher than the sender's
current power level, reject the event.
2. If the new value is higher than the sender's current
power level, reject the event.
6. For each entry being changed in or removed from events:
1. If the current value is higher than the sender's
current power level, reject the event.
7. For each entry being added to or changed in events:
1. If the new value is greater than the sender's current
power level, reject the event.
8. For each entry being changed in or removed from users,
other than the sender's own entry:
1. If the current value is higher than the sender's
current power level, reject the event.
9. For each entry being added to or changed in users:
1. If the new value is greater than the sender's current
power level, reject the event.
10. Otherwise, allow the event.
10. Otherwise, allow the event.
There are some consequences to these rules:
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* Unless you are already a member of the room, the only permitted
operations (aside from the initial create/join) are being able to
join public rooms, accept invites to rooms, and reject invites to
rooms.
* To unban another user, the sender must have a power level greater
than or equal to both the kick and ban power levels, _and_ greater
than the target user's power level.
*TODO*: If we want to enforce a single hub in a room, we'd do so here
with auth rules.
6. Signing
All servers, including hubs and participants, publish an ed25519
[RFC8032] signing key to be used by other servers when verifying
signatures. These keys can then be fetched over the transport as
needed (Section 12.4.1).
*TODO*: Verify RFC reference. We might be using a slightly different
ed25519 key today? See https://hdevalence.ca/blog/2020-10-04-its-
25519am
Each key ID consists of an algorithm name and version. Signing keys
MUST use an algorithm of ed25519 (and therefore MUST be an ed25519
key). The key version MUST be valid under the following ABNF
[RFC5234]:
key_version = 1*key_version_char
key_version_char = ALPHA / DIGIT / "_"
An algorithm and version combined is a "key ID", deliminated by : as
per the following ABNF [RFC5234]:
key_id = key_algorithm ":" key_version
key_algorithm = "ed25519"
Additional key algorithms may be supported by future documents.
6.1. Signing Events
To sign an event:
1. Redact it (Section 8).
2. Sign the result as an arbitrary object (Section 6.2).
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6.2. Signing Arbitrary Objects
To sign an object:
1. Remove signatures if present.
2. Encode the result with Canonical JSON (Section 7).
3. Using the relevant ed25519 signing key (usually the server's),
sign the object.
4. Encode that signature under signatures using unpadded base64
(Section 10).
Note that signatures is an object with keys being the entity which
did the signing and value being the key ID to encoded signature pair.
See Section 3.5 for details on the signatures structure for events
specifically.
6.3. Checking Signatures
If the signatures field is missing, doesn't contain the entity that
is expected to have done the signing (usually a server name), doesn't
have a known key ID, or is otherwise structurally invalid then the
signature check fails.
If decoding the base64 fails, the check fails.
If the object is an event, redact (Section 8) it before continuing.
If removing the signatures property, canonicalizing the JSON
(Section 7), and verifying the signature fails, the check fails.
Note that to verify the signature the server may need to fetch
another server's key first (Section 12.4.1).
Otherwise, the check passes.
*TODO*: Which specific signatures are required? If a server has
multiple signing keys, possibly a combination of new and old, do we
require all or some of them to sign?
7. Canonical JSON
When signing a JSON object, such as an event, it is important that
the bytes be ordered in the same way for everyone. Otherwise, the
signatures will never match.
To canonicalize a JSON object, use [RFC8785].
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*TODO*: Matrix currently doesn't use RFC8785, but it should (or
similar).
8. Event Redactions
All fields at the top level except the following are stripped from
the event:
* type
* room_id
* sender
* state_key
* content
* origin_server_ts
* hashes
* signatures
* prev_events
* auth_events
* hub_server
Additionally, some event types retain specific fields under the
event's content. All other fields are stripped.
* m.room.create retains all fields in content.
* m.room.member retains membership.
* m.room.join_rules retains join_rule.
* m.room.power_levels retains ban, events, events_default, kick,
redact, state_default, users, users_default, and invite.
* m.room.history_visibility retains history_visibility.
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9. Hashes
An event is covered by two hashes: a content hash and a reference
hash. The content hash covers the unredacted event to ensure it was
not modified in transit. The reference hash covers the essential
fields of the event, including content hashes, and serves as the
event's ID.
9.1. Content Hash Calculation
*TODO*: Describe what this protects, and why it matters.
1. Remove any existing signatures field.
1. If calculating an LPDU's (Section 3.5.1) content hash, remove
any existing hashes field as well.
2. If _not_ calculating an LPDU's content hash, remove any
existing fields under hashes except for lpdu.
2. Encode the object using canonical JSON.
3. Hash the resulting bytes with SHA-256 [RFC6234].
4. Encode the hash using unpadded base64 (Section 10).
9.2. Reference Hash Calculation
*TODO*: Describe what this protects, and why it matters.
1. Redact the event.
2. Remove signatures field.
3. Encode the object using canonical JSON.
4. Hash the resulting bytes with SHA-256 [RFC6234].
5. Encode the hash using URL-safe unpadded base64 (Section 10).
10. Unpadded Base64
Throughout this document, "unpadded base64" is used to represent
binary values as strings. Base64 is as specified by Section 4 of
[RFC4648], and "unpadded base64" simply removes any = padding from
the resulting string.
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Implementations SHOULD accept input with or without padding on base64
values, where possible.
Section 5 of [RFC4648] describes _URL-safe_ base64. The same changes
are adopted here. Namely, the 62nd and 63rd characters are replaced
with - and _ respectively. The unpadded behaviour is as described
above.
11. Hub Selection
*TODO*: Describe impacts of hub transfers
The hub server for a room is the server denoted by the sender of the
m.room.create event (Section 3.5.3.1). Note that this is effectively
the same as the server name contained in the room ID (Section 3.2)
currently, however is deliberately not defined as such. In a future
scenario where hub transfers are possible, the room ID does not
change when the hub server does.
11.1. Hub Transfers
*TODO*: This section, if we want a single canonical hub in the room.
Some expected problems in this area are: who signs the transfer
event? who _sends_ the transfer event? how does a transfer start?
*TODO*: Likely to be done with an m.room.hub state event in the room,
where the "current hub" is either the sender of m.room.hub or
m.room.create if no hub state event is present. Auth rules would
govern what makes for a legal m.room.hub event.
*TODO*: [I-D.kohbrok-mimi-portability] may be of help here.
12. Transport
This document specifies a wire transport which uses JSON [RFC8259]
over HTTPS [RFC9110]. Servers MUST support a minimum of HTTP/2
[RFC9113] and TLS 1.3 [RFC8446].
*TODO*: This transport doesn't scale, and doesn't use RESTful
endpoints. This example transport is heavily inspired by Matrix's
existing Server-Server API, largely acting as a starting point for
testing interoperability of the access control semantics. A better
option might be gRPC, which might change how events are structured
but keep the overall semantics the same.
[I-D.rosenberg-mimi-protocol] might have ideas here as well for REST
APIs.
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12.1. TLS Certificates
Servers MUST provide a TLS certificate signed by a known Certificate
Authority. Requesting servers are ultimately responsible for the
Certificate Authorities they place trust in, however servers SHOULD
trust authorities which would commonly be trusted by an operating
system or web browser.
12.2. API Standards
12.2.1. Requests and Responses
All HTTP POST and PUT endpoints require the sending server to supply
a (potentially empty) JSON object as the request body. Requesting
servers SHOULD supply a Content-Type header of application/json for
such requests.
All endpoints which require a server to respond with a JSON object
MUST include a Content-Type header of application/json.
All JSON data, in requests or responses, MUST be encoded using UTF-8
[RFC3629].
All endpoints in this document do _not_ support trailing slashes on
them. When such a request is encountered, it MUST be handled as an
unknown endpoint (Section 12.2.3). Examples include:
* https://example.org/_matrix/path - valid.
* https://example.org/_matrix/path/ - unknown/invalid.
* https://example.org//_matrix/path - unknown/invalid (domain also
can't have a trailing slash).
* https://example.org//_matrix/path/ - doubly unknown/invalid.
Servers (both hub and participants) MUST implement all endpoints
unless otherwise specified.
Most endpoints have a version number as part of the path. This
version number is that endpoint's version, allowing for breaking
changes to be made to the schema of that endpoint. For clarity, the
version number is _not_ representative of an API version.
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12.2.2. Errors
All errors are represented by an error code defined by this document
and an accompanied HTTP status code. It is possible for a HTTP
status code to map to multiple error codes, and it's possible for an
error code to map to multiple HTTP status codes.
When a server is returning an error to a caller, it MUST use the most
appropriate error response defined by the endpoint. If no
appropriate error response is specified, the server SHOULD use
M_UNKNOWN as the error code and 500 Internal Server Error as the HTTP
status code.
Errors are represented as JSON objects, requiring a Content-Type:
application/json response header:
{
"errcode": "M_UNKNOWN",
"error": "Something went wrong."
}
errcode is required and denotes the error code. error is an optional
human-readable description of the error. error can be as precise or
vague as the responding server desires - the strings in this document
are suggestions.
Some common error codes are:
* M_UNKNOWN - An unknown error has occurred.
* M_FORBIDDEN - The caller is not permitted to access the resource.
For example, trying to join a room the user does not have an
invite for.
* M_NOT_JSON - The request did not contain valid JSON. Must be
accompanied by a 400 Bad Request HTTP status code.
* M_BAD_JSON - The request did contain valid JSON, but it was
missing required keys or was malformed in another way. Must be
accompanied by a 400 Bad Request HTTP status code.
* M_LIMIT_EXCEEDED - Too many requests have been sent. The caller
should wait before trying the request again.
* M_TOO_LARGE - The request was too large for the receiver to
handle.
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12.2.3. Unsupported Endpoints
If a server receives a request for an unsupported or otherwise
unknown endpoint, the server MUST respond with an HTTP 404 Not Found
status code and M_UNRECOGNIZED error code. If the request was for a
known endpoint, but wrong HTTP method, a 405 Method Not Allowed HTTP
status code and M_UNRECOGNIZED error code (Section 12.2.2).
12.2.4. Malformed Requests
If a server is expecting JSON in the request body but receives
something else, it MUST respond with an HTTP status code of 400 Bad
Request and error code M_NOT_JSON (Section 12.2.2). If the request
contains JSON, and is for a known endpoint, but otherwise missing
required keys or is malformed, the server MUST respond with an HTTP
status code of 400 Bad Request and error code M_BAD_JSON
(Section 12.2.2). Where possible, error for M_BAD_JSON should
describe the missing keys or other parsing error.
12.2.5. Transaction Identifiers
Where endpoints use HTTP PUT, it is typical for a "transaction ID" to
be specified in the path parameters. This transaction ID MUST ONLY
be used for making requests idempotent - if a server receives two (or
more) requests with the same transaction ID, it MUST return the same
response for each and only process the request body once. It is
assumed that requests using the same transaction ID also contain the
same request body between calls.
A transaction ID only needs to be unique per-endpoint and per-sending
server. A server's transaction IDs do not affect requests made by
other servers or made to other endpoints by the same server.
12.2.6. Rate Limiting
Servers SHOULD implement rate limiting semantics to reduce the risk
of being overloaded. Endpoints which support being rate limited are
annotated in this document.
If a rate limit is encountered, the server MUST respond with an HTTP
429 Too Many Requests status code and M_LIMIT_EXCEEDED error code
(Section 12.2.2). If applicable, the server should additionally
include a retry_after_ms integer field on the error response to
denote how long the caller should wait before retrying, in
milliseconds.
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{
"errcode": "M_LIMIT_EXCEEDED",
"error": "Too many requests. Try again later.",
"retry_after_ms": 10254
}
The exact rate limit mechanics are left as an implementation detail.
A potential approach may be to prevent repeated requests for the same
resource at a high rate and ensuring a remote server does not request
more than a defined number of resources at a time.
12.3. Resolving Server Names
Before making an API request, the caller MUST resolve a server name
(Section 3.1) to an IP address and port, suitable for HTTPS [RFC9110]
traffic.
A server MAY change the IP/port combination used for API endpoints
using SRV DNS records [RFC2782]. Servers MAY additionally change
which TLS certificate is presented by using .well-known delegation.
.well-known delegation (step 3 below) is recommended for its ease of
configuration over SRV DNS records.
The target server MUST present a valid TLS certificate (Section 12.1)
for the name described in each step. Similarly, the requesting
server MUST use an HTTP Host header matching the description in each
step.
Server developers should note that many of the DNS requirements for
the steps below are typically handled by the software language or
library implicitly. It is rare that a DNS A record needs to be
resolved manually, for example.
Per Section 3.1, a server name consists of <hostname>[:<port>]. The
steps to convert that server name to an IP address and port are:
1. If <hostname> has an explicit <port> is present, resolve
<hostname> to an IP address using CNAME [RFC1034] [RFC2181], AAAA
[RFC3596], or A [RFC1035] DNS records. Requests are made to the
resolved IP address and port number.
TLS certificate: <hostname> (always without port)
Host header: <hostname>:<port>
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2. A regular (non-Matrix) HTTPS request is made to
https://<hostname>/.well-known/matrix/server, expecting the
schema defined by Section 12.3.1. If the response is invalid
(bad/not JSON, missing properties, non-200 response, etc), skip
to Step 4. If the response is valid, the m.server property is
parsed as <delegated_hostname>[:<delegated_port>].
1. If <delegated_hostname> has an explicit <delegated_port> is
present, resolve <delegated_hostname> to an IP address using
CNAME, AAAA, or A DNS records. Requests are made to the
resolved IP address and port number.
TLS certificate: <delegated_hostname> (always without port)
Host header: <delegated_hostname>:<delegated_port>
2. An SRV DNS record is resolved for
_matrix._tcp.<delegated_hostname>. This may result in
another hostname and port to be resolved using AAAA or A DNS
records. Requests are made to the resolved IP address and
port number.
TLS certificate: <delegated_hostname>
Host header: <delegated_hostname> (without port)
3. If no SRV record is found, an IP address is resolved for
<delegated_hostname> is resolved using CNAME, AAAA, or A DNS
records. Requests are made to the resolved IP address with
port number 8448.
TLS certificate: <delegated_hostname>
Host header: <delegated_hostname> (without port)
3. If the .well-known call from Step 2 resulted in an invalid
response, an SRV DNS record is resolved for
_matrix._tcp.<hostname>. This may result in another hostname and
port to be resolved using AAAA or A DNS records. Requests are
made to the resolved IP address and port number.
TLS certificate: <hostname> (always without port)
Host header: <hostname> (without port)
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4. If the .well-known call from Step 3 resulted in an invalid
response, and the SRV record from Step 4 was not found, and IP
address is resolved using CNAME, AAAA, or A DNS records.
Requests are made to the resolved IP address and port 8448.
TLS certificate: <hostname> (always without port)
Host header: <hostname> (without port)
We require <[delegated_]hostname> rather than <srv_hostname> in Steps
2.3 and 3 for the following reasons:
1. DNS is largely insecure (not all domains use DNSSEC [RFC9364]),
so the target of the SRV record must prove it is a valid
delegate/target for <[delegated_]hostname> via TLS.
2. Section 6.2.1 of [RFC6125] recommends this approach, and is
consistent with other applications which use SRV records (such as
Section 13.7.2.1 of [RFC6120]/XMPP).
Server implementations and owners should additionally note that the
target of a SRV record MUST NOT be a CNAME, as per RFC 2782
[RFC2782]:
the name MUST NOT be an alias (in the sense of RFC 1034 or RFC
2181)
[RFC1034] [RFC2181]
12.3.1. GET /.well-known/matrix/server
Used by the server name resolution approach to determine a delegated
hostname for a given server. 30x HTTP redirection MUST be followed,
though loops SHOULD be avoided. Normal X.509 certificate validation
is applied to this endpoint (not the specific validation required by
the server name resolution steps) [RFC5280].
This endpoint MAY be implemented by servers (it is optional).
*Rate-limited*: No.
*Authentication required*: No.
This HTTP endpoint does not specify any request parameters or body.
200 OK response:
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{
"m.server": "delegated.example.org:8448"
}
m.server is a required response field. Responses SHOULD have a
Content-Type HTTP header of application/json, however servers parsing
the response should assume that the body is JSON regardless of
Content-Type header. Failures in parsing the JSON or otherwise
invalid data that prevents parsing MUST NOT result in discovery
failure. Instead, the caller is expected to move on to the next step
of the name resolution approach.
Cache control headers SHOULD be respected on a 200 OK response.
Callers SHOULD impose a maximum cache time of 48 hours, regardless of
cache control headers. A default of 24 hours SHOULD be used when no
cache control headers are present.
Error responses (non-200) SHOULD be cached for no longer than 1 hour.
Callers SHOULD exponentially back off (to a defined limit) upon
receiving repeated error responses.
12.4. Request Authentication
Most endpoints in this document require authentication to prove which
server is making the request. This is done using public key digital
signatures.
The request method, target, and body are represented as a JSON
object, signed, and appended as an HTTP Authorization header with an
auth scheme of X-Matrix.
The object to be signed is:
{
"method": "GET",
"uri": "/path/to/endpoint?with_qs=true",
"origin": "requesting.server.name.example.org",
"destination": "target.server.name.example.org",
"content": {"json_request_body": true}
}
method is the HTTP request method, capitalized. uri is the full
request path, beginning with the leading slash and containing the
query string (if present). uri does not contain the https: scheme or
hostname.
*TODO*: Define an ordering algorithm for the query string (if we need
to?).
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origin and destination are the sender and receiver server names
(Section 3.1), respectively.
content is the JSON-encoded request body. When a request doesn't
contain a body, such as in GET requests, use an empty JSON object.
That object is then signed (Section 6.2) by the requesting server.
The resulting signature is appended as an Authentication HTTP header
on the request:
GET /path/to/endpoint?with_qs=true
Authorization: X-Matrix origin="requesting.server.name.example.org",
destination="target.server.name.example.org",
key="ed25519:0",
sig="<unpadded base64 encoded signature>"
Content-Type: application/json
{"json_request_body": true}
Linebreaks within Authorization are for clarity and are non-
normative.
The format of the Authorization header matches Section 11.4 of
[RFC9110]. The header begins with an authorization scheme of
X-Matrix, followed by one or more spaces, followed by an (unordered)
comma-separated list of parameters written as name=value pairs. The
names are case insensitive, though the values are. The values must
be enclosed in quotes if they contain characters which are not
allowed in a token, as defined by Section 5.6.2 of [RFC9110]. If a
value is a valid token it may not be enclosed in quotes. Quoted
values MAY contain backslash-escaped characters. When parsing the
header, the recipient must unescape the characters.
The exact parameters are:
* origin - The name of the sending server. MUST match the origin in
the signed JSON.
* destination - The name of the receiving server. MUST match the
destination in the signed JSON.
* key - The ID, including algorithm name, of the sending server's
signing key used to sign the request.
* signature - The unpadded base64 (Section 10) encoded signature
from step 2.
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Unknown parameters are ignored and MUST NOT result in authentication
errors.
A receiving server validates the Authorization header by composing
the JSON object represented above and checking the sender's signature
(Section 6.3). Note that to comply with Section 6.3 the receiver may
need to append a signatures field to the JSON object manually. All
signatures MUST use an unexpired key at the time of the request
(Section 12.4.1.1).
A server with multiple signing keys SHOULD include an Authorization
header for each signing key.
If an endpoint requires authentication, servers MUST:
* Validate all presented Authorization headers.
* Ensure at least one Authorization header is present.
If either fails (lack of headers, or any of the headers fail
validation), the request MUST be rejected with an HTTP 401
Unauthorized status code and M_FORBIDDEN error code (Section 12.2.2):
{
"errcode": "M_FORBIDDEN",
"error": "Signature error on request."
}
If an endpoint does _not_ require authentication, Authorization
headers are ignored entirely.
Responses from a server are authenticated using TLS and do not have
additional signing requirements.
12.4.1. Retrieving Server Keys
*TODO*: Explain what notaries are and what they do, if we keep this
section at all.
A server's signing keys are published under /_matrix/key/v2/server
(Section 12.4.1.2) and can be queried through notary servers in two
ways: Section 12.4.1.3 and Section 12.4.1.4. Notary servers
implicitly call /_matrix/key/v2/server when queried, signing and
caching the response for some time. This allows the target server to
be offline without affecting their previously sent events.
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The approach used here is borrowed from the Perspectives Project
[PerspectivesProject], modified to cover the server's ed25519 keys
and to use JSON instead of XML. The advantage of this system is it
allows each server to pick which notaries it trusts, and can contact
multiple notaries to corroborate the keys returned by any given
notary.
Servers SHOULD attempt to contact the target server directly before
using a notary server.
Note that these endpoints operate outside the context of a room: a
server does not need to participate in any shared rooms to be used as
a notary by another server, and does not need to use the hub as a
notary.
12.4.1.1. Validity
A server's keys are only valid for a short time, denoted by
valid_until_ts. Around the valid_until_ts timestamp, a server would
re-fetch the server's keys to discover any changes. In the vast
majority of cases, only valid_until_ts changes between requests (keys
are long-lived, but validated frequently).
valid_until_ts MUST be handled as the lesser of valid_until_ts and 7
days into the future, preventing attackers from publishing long-lived
keys that are unable to be revoked. Servers SHOULD use a timestamp
approximately 12 hours into the future when responding with their
keys.
*TODO*: What does it mean to require events have an origin_server_ts
which is less than that of valid_until_ts? Do we reject the event,
soft-fail it, or do something else? Do we only do this on the hub?
12.4.1.2. GET /_matrix/key/v2/server
Retrieves the server's signing keys. The server can have any number
of active or inactive keys at a time, but SHOULD have at least 1
active key at all times.
*Rate-limited*: No.
*Authentication required*: No.
This HTTP endpoint does not specify any request parameters or body.
200 OK response:
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{
"server_name": "example.org",
"valid_until_ts": 1686776437176,
"m.linearized": true,
"verify_keys": {
"ed25519:0": {
"key": "<unpadded base64 encoded public key>"
}
},
"old_verify_keys": {
"ed25519:bad": {
"expired_ts": 1586776437176,
"key": "<unpadded base64 encoded public key>"
}
},
"signatures": {
"example.org": {
"ed25519:0": "<unpadded base64 encoded signature>"
}
}
}
server_name MUST be the name of the server (Section 3.1) which is
returning the keys.
valid_until_ts is the integer timestamp (milliseconds since Unix
epoch) for when the server's keys should be re-fetched. See
Section 12.4.1.1.
m.linearized is an optional boolean, but SHOULD be set to true.
Semantics for false and not being present apply to contexts outside
of this document.
verify_keys are the current signing keys for the server, keyed by key
ID (Section 6). The object value for each key ID under verify_keys
is simply the key, consisting of the unpadded base64 encoded public
key matching that algorithm and version.
old_verify_keys are similar to verify_keys, but have an additional
required expired_ts property to denote when the key ceased usage.
This overrides valid_until_ts for the purposes of Section 12.4.1.1 at
an individual key level.
*TODO*: What about events sent with old_verify_keys?
For request authentication (Section 12.4), only keys listed under
verify_keys are honoured. If another key is referenced by the
Authorization headers, the request fails authentication.
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Notaries SHOULD cache a 200 OK response for half of its lifetime to
avoid serving stale values. Responding servers SHOULD avoid
returning responses which expire in less than an hour to avoid
repeated requests. Requesting servers SHOULD limit how frequently
they query for keys to avoid flooding a server with requests.
If the server fails to respond to this request, notaries SHOULD
continue to return the last response they received from the server so
that the signatures of old events can still be checked, even if that
response is no longer considered valid (Section 12.4.1.1).
Servers are capable of rotating their keys without populating
old_verify_keys, though this can cause reliability issues if other
servers don't see both keys. Notaries SHOULD cache responses with
distinct key IDs indefinitely. For example, if a server has
ed25519:0 and ed25519:1 on its first response, and a later response
returns ed25519:1 and ed25519:2, the notary should cache both
responses. This gives servers an ability to validate ed25519:0 for
old events in a room.
12.4.1.3. GET /_matrix/key/v2/query/:serverName
This is one of two endpoints for querying a server's keys through
another server. The notary (receiving) server will attempt to
refresh its cached copy of the target server's keys through
/_matrix/key/v2/server, falling back to any cached values if needed.
*Rate-limited*: No.
*Authentication required*: No.
Path parameters:
* :serverName - the target server's name (Section 3.1) to retrieve
keys for.
Query parameters:
* minimum_valid_until_ts (integer; optional) - The time in
milliseconds since the Unix epoch the target server's keys will
need to be valid until to be useful to the caller. If not
specified the notary server's current time will be used.
Request body: None applicable.
200 OK response:
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{
"server_keys": [
{/* server key */}
]
}
server_keys is the array of keys (see Section 12.4.1.2 response
format) for the target server. If the target server could not be
reached and the notary has no cached keys, this array is empty. If
the keys do not meet minimum_valid_until_ts per Section 12.4.1.1,
they are not included.
The notary server MUST sign each key returned in server_keys by at
least one of its own signing keys. The calling server MUST validate
all signatures on the objects.
12.4.1.4. POST /_matrix/key/v2/query
A bulk version of /_matrix/key/v2/query/:serverName
(Section 12.4.1.3). The same behaviour applies to this endpoint.
*Rate-limited*: No.
*Authentication required*: No.
Path parameters: None applicable.
Query parameters: None applicable.
Request body:
{
"server_keys": {
"example.org": {
"ed25519:0": {
"minimum_valid_until_ts": 1686783382189
}
}
}
}
server_keys is required and is the search criteria. The object value
is first keyed by server name which maps to another object keyed by
Key ID, mapping to the specific criteria. If no key IDs are given in
the request, all of the server's known keys are queried. If no
servers are given in the request, the response MUST contain an empty
server_keys array.
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minimum_valid_until_ts holds the same meaning as in Section 12.4.1.3.
200 OK response:
Same as Section 12.4.1.3 with the following added detail:
Responding servers SHOULD only return signed key objects for the key
IDs requested by the caller, however servers MAY respond with more
keys than requested. The caller is expected to filter the response
if needed.
12.5. Sending Events
Events accepted into the room by a hub server must be sent to all
other servers in that room. Similarly, participant servers need a
way to send partial events through the hub server, as mentioned by
Section 3.5.1.
A single endpoint is used for all rooms on either server, and can
contain both fully-formed PDUs (Section 3.5) or Linearized PDUs
(partial events; Section 3.5.1) depending on the server's role in the
applicable room.
A typical event send path will be:
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+-----+ +---------------+ +---------------+
| Hub | | Participant1 | | Participant2 |
+-----+ +---------------+ +---------------+
| | |
| | Create LPDU |
| +-----------+ |
| | | |
| |<----------+ |
| | |
| PUT /send/:txnId | |
|<--------------------------+ |
| | |
| Append PDU fields | |
+-----------------+ | |
| | | |
|<----------------+ | |
| | |
----------------- Concurrent requests follow -----------------
| | |
| PUT /send/:txnId | |
+-------------------------->| |
| | |
| PUT /send/:txnId | |
+------------------------------------------------>|
| | |
PUT /send/:txnId is shorthand for Section 12.5.1.
Hubs which generate events would skip to the point where they create
a fully-formed PDU and send it out to all other participants.
When a hub is broadcasting events to participant servers, it MUST
include the following targets:
* The server implied by the sender for a kick or ban m.room.member
(Section 3.5.3.3) event, up to the point of that kick or ban.
* All servers which have at least 1 user which is joined to the
room.
12.5.1. PUT /_matrix/federation/v2/send/:txnId
Sends (L)PDUs (Section 3.5, Section 3.5.1) to another server. The
sending server MUST wait for a 200 OK response from the receiver
before sending another request with a different :txnId.
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*Implementation note*: Currently this endpoint doesn't actually
exist. Use PUT /_matrix/federation/unstable/org.matrix.i-d.ralston-
mimi-linearized-matrix.02/send/:txnId when testing against other
Linearized Matrix implementations. This string may be updated later
to account for breaking changes.
*TODO*: Remove implementation notes.
*Rate-limited*: No.
*Authentication required*: Yes.
Path parameters:
* :txnId - the transaction ID (Section 12.2.5) for the request.
Query parameters: None applicable.
Request body:
{
"edus": [
{/* EDU */}
],
"pdus": [
{/* Either an LPDU or PDU */}
]
}
edus are the Ephemeral Data Units (Section 12.9) to send. If no EDUs
are being sent, this field MAY be excluded from the request body.
There MUST NOT be more than 100 entries in edus.
pdus are the events/PDUs (Section 3.5) and LPDUs (Section 3.5.1) to
send to the server. Whether it's an LPDU or PDU depends on the
sending server's role in that room: if they are a non-hub server, it
will be an LPDU. There MUST NOT be more than 50 entries in pdus.
Each event in the pdus array gets processed as such:
1. Identify the room ID for the event. The exact format of the
event can differ between room versions, however currently this
would be done by extracting the room_id property.
1. If that room ID is invalid/not found, the event is rejected.
2. If the server is not participating in the room, the event is
dropped/skipped.
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2. If the event is an LPDU and the receiving server is the hub, the
additional PDU fields are appended before continuing.
3. If the event is an LPDU and the receiving server is not the hub,
the event is dropped/skipped.
4. The checks defined by Section 5.1 are performed.
5. If the event still hasn't been dropped/rejected, it is appended
to the room. For participant servers, this may mean it's queued
for sending to local clients.
Server implementation authors should note that these steps can be
condensed, but are expanded here for specification purposes. For
example, an LPDU's signature can/will fail without ever needing to
append the PDU fields first - the server can skip some extra work
this way.
200 OK response:
{
"failed_pdus": {
"$eventid": {
"error": "Invalid event format"
},
"$eventid": {
"error":
"@alice:example.org cannot send m.room.power_levels"
}
}
}
The receiving server MUST NOT send a 200 OK response until all events
have been processed. Servers SHOULD NOT block responding to this
endpoint on sending accepted events to local clients or other
participant servers, as doing so could lead to a lengthy backlog of
events waiting to be sent.
Sending servers SHOULD apply/expect a timeout and retry the exact
same request with the same transaction ID until they see a 200 OK
response. If the sending server attempts to send a different
transaction ID from the one already in flight, the receiving server
MUST respond with a 400 Bad Request HTTP status code and M_BAD_STATE
error code (Section 12.2.2). Receiving servers SHOULD continue
processing requests to this endpoint even after the sender has
disconnected/timed out, but SHOULD NOT process the request multiple
times due to the transaction ID (Section 12.2.5).
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failed_pdus is an object mapping event ID (Section 3.5) to error
string. Event IDs are based upon the received object, not the final/
complete object. For example, if an LPDU is sent, gets its PDU
fields appended, and fails event authorization, then the error would
be for the event ID of the LPDU, not the fully-formed PDU. This is
to allow the sender to correlate what they sent with errors.
The object for each event ID MUST contain an error string field,
representing the human-readable reason for an event being rejected.
Events which are dropped/ignored or accepted do _not_ appear in
failed_pdus.
*TODO*: Should we also return fully-formed PDUs for the LPDUs we
received?
12.6. Event and State APIs
When a participant in the room is missing an event, or otherwise
needs a new copy of it, it can retrieve that event from the hub
server. Similar mechanics apply for getting state events, current
state of a room, and backfilling scrollback in a room.
All servers are required to implement all endpoints (Section 12.2.1),
however only hub servers are guaranteed to have the full history/
state for a room. While other participant servers might have
history, they SHOULD NOT be contacted due to the high likelihood of a
Not Found-style error.
12.6.1. GET /_matrix/federation/v2/event/:eventId
Retrieves a single event.
*Implementation note*: Currently this endpoint doesn't actually
exist. Use GET /_matrix/federation/unstable/org.matrix.i-d.ralston-
mimi-linearized-matrix.02/event/:eventId when testing against other
Linearized Matrix implementations. This string may be updated later
to account for breaking changes.
*TODO*: Remove implementation notes.
*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters:
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* :eventId - the event ID (Section 3.5) to retrieve. Note that
event IDs are typically reference hashes (Section 9.2) of the
event itself, which includes the room ID. This makes event IDs
globally unique.
Query parameters: None applicable.
Request body: None applicable.
200 OK response:
{
/* the event */
}
The response body is simply the event (Section 3.5) itself, if the
requesting server has reasonable visibility of the event
(Section 3.5.3.5.1). When the server can see an event but not the
contents, the event is served redacted (Section 8) instead.
If the event isn't known to the server, or the requesting server has
no reason to know that the event even exists, a 404 Not Found HTTP
status code and M_NOT_FOUND error code (Section 12.2.2) is returned.
The returned event MUST be checked before being used by the
requesting server (Section 5.1). This endpoint MUST NOT return LPDUs
(Section 3.5.1), instead treating such events as though they didn't
exist.
12.6.2. GET /_matrix/federation/v1/state/:roomId
Retrieves a snapshot of the room state (Section 3.5.2) at the given
event. This is typically most useful when a participant server
prefers to store minimal information about the room, but still needs
to offer context to its clients.
*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters:
* :roomId - the room ID (Section 3.2) to retrieve state in.
Query parameters:
* event_id (string; required) - The event ID (Section 3.5) to
retrieve state at.
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Request body: None applicable.
200 OK response:
{
"auth_chain": [
{/* event */}
],
"pdus": [
{/* event */}
]
}
The returned room state is in two parts: the pdus, consisting of the
events which represent "current state" (Section 3.5.2) prior to
considering state changes induced by the event in the original
request, and auth_chain, consisting of the events which make up the
auth_events (Section 5.2.1) for the pdus and the auth_events of those
events, recursively.
The auth_chain will eventually stop recursing when it reaches the
m.room.create event, as it cannot have any auth_events.
*TODO*: Do we actually need to recurse auth events to get the full
auth chain here? What are participant servers expected to do with
this information? (Do they even care about it?)
For example, if the requested event ID was an m.room.power_levels
event, the returned state would be as if the new power levels were
not applied.
Both auth_chain and pdus contain event objects (Section 3.5).
If the requesting server does not have reasonable visibility on the
room (Section 3.5.3.5.1), or either the room ID or event ID don't
exist, a 404 Not Found HTTP status code and M_NOT_FOUND error code
(Section 12.2.2) is returned. The same error is returned if the
event ID doesn't exist in the requested room ID.
Note that the requesting server will generally always have visibility
of the auth_chain and pdu events, but may not be able to see their
contents. In this case, they are redacted (Section 8) before being
served.
The returned events MUST be checked before being used by the
requesting server (Section 5.1). This endpoint MUST NOT return LPDUs
(Section 3.5.1), instead treating such events as though they didn't
exist.
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If the receiving server is not the hub server for the room ID, an
HTTP status code of 400 Bad Request and error code M_WRONG_SERVER
(Section 12.2.2) is returned.
12.6.3. GET /_matrix/federation/v1/state_ids/:roomId
This performs the same function as Section 12.6.2 but returns just
the event IDs instead.
*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters:
* :roomId - the room ID (Section 3.2) to retrieve state in.
Query parameters:
* event_id (string; required) - The event ID (Section 3.5) to
retrieve state at.
Request body: None applicable.
200 OK response:
{
"auth_chain_ids": ["$event1", "$event2"],
"pdu_ids": ["$event3", "$event4"]
}
See Section 12.6.2 for behaviour. Note that auth_chain becomes
auth_chain_ids when using this endpoint, and pdus becomes pdu_ids.
12.6.4. GET /_matrix/federation/v2/backfill/:roomId
Retrieves a sliding window history of previous events in a given
room.
*Implementation note*: Currently this endpoint doesn't actually
exist. Use GET /_matrix/federation/unstable/org.matrix.i-d.ralston-
mimi-linearized-matrix.02/backfill/:roomId when testing against other
Linearized Matrix implementations. This string may be updated later
to account for breaking changes.
*TODO*: Remove implementation notes.
*Rate-limited*: Yes.
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*Authentication required*: Yes.
Path parameters:
* :roomId - the room ID (Section 3.2) to retrieve events from.
Query parameters:
* v (string; required) - The event ID (Section 3.5) to start
backfilling from.
* limit (integer; required) - The maximum number of events to
return, including v.
Request body: None applicable.
200 OK response:
{
"pdus": [
{/* event */}
]
}
The number of returned pdus MUST NOT exceed the limit provided by the
caller. limit SHOULD have a maximum value imposed by the receiving
server. pdus contains the events (Section 3.5) preceeding the
requested event ID (v), including v. pdus is ordered from oldest to
newest.
If the requesting server does not have reasonable visibility on the
room (Section 3.5.3.5.1), or either the room ID or event ID don't
exist, a 404 Not Found HTTP status code and M_NOT_FOUND error code
(Section 12.2.2) is returned. The same error is returned if the
event ID doesn't exist in the requested room ID.
If the requesting server does have visibility on the returned events,
but not their contents, they are redacted (Section 8) before being
served.
The returned events MUST be checked before being used by the
requesting server (Section 5.1). This endpoint MUST NOT return LPDUs
(Section 3.5.1), instead treating such events as though they didn't
exist.
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12.7. Room Membership
When a server is already participating in a room, it can simply send
m.room.member (Section 3.5.3.3) events with the /send API
(Section 12.5.1) to other servers/the hub directly. When a server is
not already participating however, it needs to be welcomed in by the
hub server.
A typical invite flow would be:
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+-------------+ +-----+ +---------------+
| Participant | | Hub | | TargetServer |
+-------------+ +-----+ +---------------+
| | |
| POST /invite (LPDU) | |
+---------------------->| |
| | |
| | POST /invite (PDU) |
| +----------------------->|
| | |
| | Decide to process the |
| | invite. Can reject due |
| | to spam, or send it to |
| | the recipient user. |
| | +----------------------+
| | | |
| | +--------------------->|
| | |
| | Finish POST /invite |
| |<-----------------------+
| | |
| Finish POST /invite | |
|<----------------------+ |
| | |
-------------------- User decides to accept invite ---------------------
| | |
| | GET /make_join |
| |<-----------------------+
| | |
| | Finish GET /make_join |
| +----------------------->|
| | |
| | Fill event template |
| | +-------------------+
| | | |
| | +------------------>|
| | |
| | POST /send_join |
| |<-----------------------+
| | |
| | Finish POST /send_join |
| +----------------------->|
| | |
POST /invite is shorthand for Section 12.7.2.1. Similarly, GET
/make_join is Section 12.7.3.1 and POST /send_join is
Section 12.7.3.2.
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If the user decided to reject the invite, the TargetServer would use
GET /make_leave (Section 12.7.2.2.1) and POST /send_leave
(Section 12.7.2.2.2) instead of make/send_join.
12.7.1. Make and Send Handshake
When a server is already participating in a room, it can use
m.room.member (Section 3.5.3.3) events and the /send API
(Section 12.5.1) to directly change membership. When the server is
not already involved in the room, such as when being invited for the
first time, the server needs to "make" an event and "send" it through
the hub server to append it to the room.
The different processes which use this handshake are:
* Rejecting Invites (Section 12.7.2.2)
* Joins (Section 12.7.3)
* Knocks (Section 12.7.4)
The "make" portion of the endpoints take the shape of GET
/_matrix/federation/v1/make_CHANGE/:roomId/:userId, where CHANGE is
leave, join, or knock (respective to the list above). This endpoint
will return a partial LPDU (Section 3.5.1) which needs to be turned
into a full LPDU and signed before being sent using POST
/_matrix/federation/v3/send_CHANGE/:txnId.
The flow for this handshake appears as such:
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+----------------+ +-----+
| ExternalServer | | Hub |
+----------------+ +-----+
| |
| GET /_matrix/federation/v1/make_CHANGE/:roomId/:userId |
+-------------------------------------------------------->|
| |
| Reject if event future event |
| would not be allowed by auth rules |
|<--------------------------------------------------------+
| |
| Respond with partial LPDU |
|<--------------------------------------------------------+
| |
| Populate LPDU and sign it |
+-------------------------+ |
| | |
|<------------------------+ |
| |
| POST /_matrix/federation/v3/send_CHANGE/:txnId |
+-------------------------------------------------------->|
| |
| Validate event and append to the room |
| +-------------------------------------+
| | |
| +------------------------------------>|
| |
| Reject if event not allowed by auth rules |
|<--------------------------------------------------------+
| |
| Send new event to all other |
| participants in the room (async) |
| +-------------------------------------+
| | |
| +------------------------------------>|
| |
| 200 OK |
|<--------------------------------------------------------+
| |
Note that the send_CHANGE step re-checks the event against the auth
rules: any amount of time could have passed between the make_CHANGE
and send_CHANGE calls.
*TODO*: Describe how the external server is meant to find the hub.
Invites work by (usually) trying to contact the server which sent the
invite, but knocking is a guess.
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12.7.2. Invites
When inviting a user belonging to a server already in the room,
senders SHOULD use m.room.member (Section 3.5.3.3) events and the
/send API (Section 12.5.1). This section's endpoints SHOULD only be
used when the target server is _not_ participating in the room
already.
Note that being invited does not count as the server "participating"
in the room. This can mean that while a server has a user with a
pending invite in the room, this section's endpoints are needed to
send additional invites to other users on the same server.
The full invite sequence is:
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+-------------+ +-----+ +---------------+
| Participant | | Hub | | TargetServer |
+-------------+ +-----+ +---------------+
| | |
| POST /invite | |
+--------------------->| |
| | |
| Reject if sender | |
| cannot invite other | |
| users | |
|<---------------------+ |
| | |
| | Otherwise, append |
| | PDU fields |
| +------------------+ |
| | | |
| |<-----------------+ |
| | |
| | POST /invite |
| +----------------------->|
| | |
| | Reject if room |
| | version not supported |
| |<-----------------------+
| | |
| | Reject if target user |
| | is ineligible for |
| | invites |
| |<-----------------------+
| | |
| Proxy TargetServer | |
| rejection | |
|<---------------------+ |
| | |
| | Otherwise, queue |
| | sending the invite to |
| | target user |
| | +---------------------+
| | | |
| | +-------------------->|
| | |
| | 200 OK |
| |<-----------------------+
| | |
| 200 OK | |
|<---------------------+ |
| | |
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POST /invite is shorthand for Section 12.7.2.1.
What causes a user to be considered "ineligible" for an invite is
left as an implementation detail. See Section 13 and Section 14 for
suggestions on handling user-level privacy controls and spam invites.
12.7.2.1. POST /_matrix/federation/v3/invite/:txnId
Sends an invite event to a server. If the sender is a participant
server, the receiving server (the hub) will convert the contained
LPDU (Section 3.5.1) to a fully-formed event (Section 3.5) before
sending that event to the intended server.
*Implementation note*: Currently this endpoint doesn't actually
exist. Use POST /_matrix/federation/unstable/org.matrix.i-d.ralston-
mimi-linearized-matrix.02/invite/:txnId when testing against other
Linearized Matrix implementations. This string may be updated later
to account for breaking changes.
*TODO*: Remove implementation notes.
*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters:
* :txnId - the transaction ID (Section 12.2.5) for the request. The
event ID (Section 3.5) of the contained event may be a good option
as a readily-available transaction ID.
Query parameters: None applicable.
Request body:
{
"event": {/* the event */},
"invite_room_state": [/* stripped state events */],
"room_version": "I.1"
}
invite_room_state are the stripped state events (Section 3.5.2.1) for
the room's current state. invite_room_state MAY be excluded from the
request body.
room_version is the room version identifier (Section 3.2.1) the room
is currently using. This will be retrieved from the m.room.create
(Section 3.5.3.1) state event.
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event is the event (LPDU or PDU; Section 3.5) representing the invite
for the user. It MUST meet the following criteria, in addition to
the requirements of an event:
* type MUST be m.room.member.
* membership in content MUST be invite.
When the hub server receives a request from a participant server, it
MUST populate the event fields before sending the event to the
intended recipient. This means running the event through the normal
event authorization steps (Section 5.2). If the invite is not
allowed under the auth rules, the server responds with a 403
Forbidden HTTP status code and M_FORBIDDEN error code
(Section 12.2.2).
The intended recipient of the invite can be identified by the
state_key on the event.
If the invite event is valid, the hub server sends its own POST
/_matrix/federation/v3/invite/:txnId request to the target server (if
the target server is not itself) with the fully-formed event. The
transaction ID does not need to be the same as the original inbound
request.
All responses from the target server SHOULD be proxied verbatim to
the original requesting server through the hub. The hub SHOULD
discard what appears to be excess data before sending a response to
the requesting server, such as extra or large fields. If the target
server does not respond with JSON, an error response (Section 12.2.2)
SHOULD be sent by the hub instead.
The target server then ensures it can support the room version. If
it can't, it responds with an HTTP status code of 400 Bad Request and
error code of M_INCOMPATIBLE_ROOM_VERSION (Section 12.2.2).
Then, the target server runs any implementation-specific checks as
needed, such as those implied by Section 13 and Section 14,
rejecting/erroring the request as needed.
Finally, the target server signs the event and returns it to the hub.
The hub server appends this signed event to the room and sends it out
to all participants in the room. The signed event is additionally
returned to the originating participant server, though it also
receives the event through the /send API (Section 12.5.1).
200 OK response:
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{
"pdu": {/* signed fully-formed event */}
}
Note that by the time a response is received, the event is signed 2-3
times:
1. The LPDU signature from the participant server (Section 3.5.1).
2. The hub's signature on the PDU (Section 3.5).
3. The target server's signature on the PDU.
These signatures are to satisfy the auth rules (Section 5.2).
*TODO*: Do we ever validate the target server's signature? Do we
need to?
12.7.2.2. Rejecting Invites and Leaves
Rejecting an invite is done by making a membership transition of
invite to leave through the user's m.room.member (Section 3.5.3.3)
event. The membership event SHOULD be sent directly when it can and
use the "make and send" handshake (Section 12.7.1) described here
otherwise.
This same approach is additionally used to retract a knock
(Section 12.7.4).
12.7.2.2.1. GET /_matrix/federation/v1/make_leave/:roomId/:userId
Requests an event template from the hub server for a room. The
requesting server will have already been checked to ensure it
supports the room version as part of the invite process prior to
making a call to this endpoint.
*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters:
* :roomId - the room ID (Section 3.2) to get a template for.
* :userId - the user ID (Section 3.3) attempting to leave.
Query parameters: None applicable.
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Request body: None applicable.
200 OK response:
{
"event": {/* partial LPDU */},
"room_version": "I.1"
}
The response body's event MUST be a partial LPDU (Section 3.5.1) with
at least the following fields:
* type of m.room.member.
* state_key of :userId from the path parameters.
* sender of :userId from the path parameters.
* content of {"membership": "leave"}.
The sending server SHOULD remove all other fields before using the
event in a send_leave (Section 12.7.2.2.2).
If the receiving server is not the hub server for the room ID, an
HTTP status code of 400 Bad Request and error code M_WRONG_SERVER
(Section 12.2.2) is returned. If the room ID is not known, 404 Not
Found is used as an HTTP status code and M_NOT_FOUND as an error code
(Section 12.2.2).
If the user does not have permission to leave under the auth rules
(Section 5.2), a 403 Forbidden HTTP status code is returned alongside
an error code of M_FORBIDDEN (Section 12.2.2). For example, if the
user does not have a pending invite, is not a member of the room, or
is banned.
If the sending server does not recognize the returned room_version,
it SHOULD NOT attempt to populate the template or use the send_leave
(Section 12.7.2.2.2) endpoint.
12.7.2.2.2. POST /_matrix/federation/v3/send_leave/:txnId
Sends a leave membership event to the room through a hub server.
*Implementation note*: Currently this endpoint doesn't actually
exist. Use POST /_matrix/federation/unstable/org.matrix.i-d.ralston-
mimi-linearized-matrix.02/send_leave/:txnId when testing against
other Linearized Matrix implementations. This string may be updated
later to account for breaking changes.
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*TODO*: Remove implementation notes.
*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters:
* :txnId - the transaction ID (Section 12.2.5) for the request. The
event ID (Section 3.5) of the contained event may be a good option
as a readily-available transaction ID.
Query parameters: None applicable.
Request body:
{
/* LPDU created from make_leave template */
}
200 OK response:
{/* deliberately empty object */}
The errors responses from /make_leave (Section 12.7.2.2.1) are copied
here. Servers should note that room state MAY change between a
/make_leave and /send_leave, potentially in a way which prevents the
user from leaving the room suddenly. For example, the invited user
may have been banned from the room.
12.7.3. Joins
Joins for users SHOULD be sent directly whenever possible, and
otherwise use the "make and send" handshake (Section 12.7.1) approach
described here.
12.7.3.1. GET /_matrix/federation/v1/make_join/:roomId/:userId
Requests an event template from the hub server for a room. This is
done to ensure the requesting server supports the room's version
(Section 3.2.1), as well as hint at the event format needed to
participate.
Note that this endpoint is extremely similar to /make_leave
(Section 12.7.2.2.1).
*Rate-limited*: Yes.
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*Authentication required*: Yes.
Path parameters:
* :roomId - the room ID (Section 3.2) to get a template for.
* :userId - the user ID (Section 3.3) attempting to join.
Query parameters:
* ver (string; required; repeated) - The room versions
(Section 3.2.1) the sending server supports.
Request body: None applicable.
200 OK response:
{
/* partial LPDU */
}
The response body MUST be a partial LPDU (Section 3.5.1) with at
least the following fields:
* type of m.room.member.
* state_key of :userId from the path parameters.
* sender of :userId from the path parameters.
* content of {"membership": "join"}.
The sending server SHOULD remove all other fields before using the
event in a send_join (Section 12.7.3.2).
If the receiving server is not the hub server for the room ID, an
HTTP status code of 400 Bad Request and error code M_WRONG_SERVER
(Section 12.2.2) is returned. If the room ID is not known, 404 Not
Found is used as an HTTP status code and M_NOT_FOUND as an error code
(Section 12.2.2).
If the user does not have permission to join under the auth rules
(Section 5.2), a 403 Forbidden HTTP status code is returned alongside
an error code of M_FORBIDDEN (Section 12.2.2).
If the room version is not one of the ver strings the sender
supplied, a 400 Bad Request HTTP status code is returned alongside
M_INCOMPATIBLE_ROOM_VERSION error code (Section 12.2.2).
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12.7.3.2. POST /_matrix/federation/v3/send_join/:txnId
Sends a join membership event to the room through a hub server.
Note that this endpoint is extremely similar to /send_leave
(Section 12.7.2.2.2).
*Implementation note*: Currently this endpoint doesn't actually
exist. Use POST /_matrix/federation/unstable/org.matrix.i-d.ralston-
mimi-linearized-matrix.02/send_join/:txnId when testing against other
Linearized Matrix implementations. This string may be updated later
to account for breaking changes.
*TODO*: Remove implementation notes.
*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters:
* :txnId - the transaction ID (Section 12.2.5) for the request. The
event ID (Section 3.5) of the contained event may be a good option
as a readily-available transaction ID.
Query parameters: None applicable.
*TODO*: Incorporate faster joins work.
Request body:
{
/* LPDU created from make_join template */
}
200 OK response:
{
"state": [/* events */],
"auth_chain": [/* events */],
"event": {/* fully-formed event */}
}
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state is the current room state, consisting of the events which
represent "current state" (Section 3.5.2) prior to considering the
membership state change. auth_chain consists of the events which make
up the auth_events (Section 5.2.1) for the state events, and the
auth_events of those events, recursively. event will be the fully-
formed PDU (Section 3.5) that is sent by the hub to all other
participants in the room.
The errors responses from /make_join (Section 12.7.3.1) are copied
here (with the exception of M_INCOMPATIBLE_ROOM_VERSION, as the
server already checked for support). Servers should note that room
state MAY change between a /make_join and /send_join, potentially in
a way which prevents the user from joining the room suddenly.
12.7.4. Knocks
To knock on a room is to request an invite to that room. It is not a
join, nor is it an invite itself. "Approving" the knock is done by
inviting the user, which is typically only allowed by moderators in
these rooms. "Denying" the knock is done through kicking (sending a
leave membership) or banning the user. If the user is kicked, they
may re-send their knock.
Senders should note the reason field on m.room.member events
(Section 3.5.3.3) to provide context for their knock.
To retract a knock, the sending server uses the same APIs as
rejecting an invite (Section 12.7.2.2).
Where possible, knocks from users SHOULD be sent directly, otherwise
using the "make and send" handshake (Section 12.7.1) approach
described here.
12.7.4.1. GET /_matrix/federation/v1/make_knock/:roomId/:userId
Requests an event template from the hub server for a room. This is
done to ensure the requesting server supports the room's version
(Section 3.2.1), as well as hint at the event format needed to
participate.
Note that this endpoint is almost exactly the same as /make_join
(Section 12.7.3.1).
*TODO*: It's so similar to make_join that we should probably just
combine the two endpoints.
*Rate-limited*: Yes.
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*Authentication required*: Yes.
Path parameters:
* :roomId - the room ID (Section 3.2) to get a template for.
* :userId - the user ID (Section 3.3) attempting to knock.
Query parameters:
* ver (string; required; repeated) - The room versions
(Section 3.2.1) the sending server supports.
Request body: None applicable.
200 OK response:
{
/* partial LPDU */
}
The response body MUST be a partial LPDU (Section 3.5.1) with at
least the following fields:
* type of m.room.member.
* state_key of :userId from the path parameters.
* sender of :userId from the path parameters.
* content of {"membership": "knock"}.
The sending server SHOULD remove all other fields before using the
event in a send_knock (Section 12.7.4.2).
If the receiving server is not the hub server for the room ID, an
HTTP status code of 400 Bad Request and error code M_WRONG_SERVER
(Section 12.2.2) is returned. If the room ID is not known, 404 Not
Found is used as an HTTP status code and M_NOT_FOUND as an error code
(Section 12.2.2).
If the user does not have permission to knock under the auth rules
(Section 5.2), a 403 Forbidden HTTP status code is returned alongside
an error code of M_FORBIDDEN (Section 12.2.2).
If the room version is not one of the ver strings the sender
supplied, a 400 Bad Request HTTP status code is returned alongside
M_INCOMPATIBLE_ROOM_VERSION error code (Section 12.2.2).
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12.7.4.2. POST /_matrix/federation/v3/send_knock/:txnId
Sends a knock membership event to the room through a hub server.
*Implementation note*: Currently this endpoint doesn't actually
exist. Use POST /_matrix/federation/unstable/org.matrix.i-d.ralston-
mimi-linearized-matrix.02/send_knock/:txnId when testing against
other Linearized Matrix implementations. This string may be updated
later to account for breaking changes.
*TODO*: Remove implementation notes.
*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters:
* :txnId - the transaction ID (Section 12.2.5) for the request. The
event ID (Section 3.5) of the contained event may be a good option
as a readily-available transaction ID.
Query parameters: None applicable.
Request body:
{
/* LPDU created from make_knock template */
}
200 OK response:
{
"stripped_state": [
/* stripped state events */
]
}
stripped_state are the stripped state events (Section 3.5.2.1) for
the room.
The errors responses from /make_knock (Section 12.7.4.1) are copied
here (with the exception of M_INCOMPATIBLE_ROOM_VERSION, as the
server already checked for support). Servers should note that room
state MAY change between a /make_knock and /send_knock, potentially
in a way which prevents the user from knocking upon the room
suddenly.
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12.8. Content Repository
The content repository, sometimes called the "media repo", is where
user-generated content is stored for referencing within an encrypted
message.
*TODO*: Complete this section. We want auth/event linking from
MSC3911 and MSC3916.
*TODO*: Spell out that content is images, videos, files, etc.
12.9. Ephemeral Data Units (EDUs)
EDUs are sent out of band from rooms and are only persisted for
exactly as long as they are needed. For example, once a to-device
(Section 12.10.2) message is delivered to a client, the server may
easily be able to delete its copy of the message.
EDUs contain the following mandatory fields:
{
"type": "m.room.encrypted",
"sender": "@alice:example.org",
"content": {
/* type-specific content */
}
}
The type is similar to an event type (Section 3.5) and ultimately
describes the schema for the content.
sender_id is the user ID (Section 3.3) which is sending the EDU.
Typically, clients will not generate EDUs directly. Instead, the
server will convert a client's request into an EDU for sending to a
remote server, where that server then unpacks the EDU before
delivering it to local devices.
Because EDUs are not sent in the context of a room, even if an MLS
Welcome message is being sent for a room, servers MUST send the EDUs
directly to the target server with the send API (Section 12.5.1).
In this document, EDUs are only used for to-device messages
(Section 12.10.2) and device list changes (Section 12.10.1), but
could be used for read/delivery receipts, typing notifications, and
more in future. This may necessitate routing EDUs through the hub
rather than using full-mesh fanout.
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*TODO*: Address EDU fanout; Document the implied missing features
(receipts, typing notifs).
12.10. MLS
*TODO*: This section. Talk about to-device messaging, device
management/querying/key claiming, etc.
There are several endpoints required by this document's MLS
implementation (Section 4), largely around device management for each
device's signing key, claiming key packages for those devices, and
sending messages (Welcome in particular) after using a key package.
12.10.1. Device Info Publishing
When a user creates a new encryption-capable device, or removes one,
a "device list update" is sent to all servers the user shares a room
with. The receiving servers then determine which local clients need
to be made aware of the device list change and sends the information
to them. This is primarily used by this document's MLS
implementation (Section 4) to indicate to other devices that either a
new possible device has come online or that another needs to be
removed from some MLS groups due to being deleted.
Typically, a device is created by a user when they log in to a new
session. Similarly, a device is deleted/removed when they log out of
that client.
The device list update takes the shape of an EDU (Section 12.9), as
such:
{
"type": "m.device_list_update",
"sender_id": "@alice:example.org",
"content": {
"changed": [/* Device Objects */],
"removed": [/* Device IDs */]
}
}
The device objects are the same as in the response for /user/:userId/
device/:deviceId (Section 12.10.1.1), indicating that either a new
device was created or that information about a previous device has
changed.
*TODO*: Matrix's m.device_list_update EDU is _very_ different from
this, and relatively complicated. Do we actually need a stream_id,
like in Matrix? Do we then need the /devices endpoint?
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12.10.1.1. GET /_matrix/federation/v1/user/:userId/device/:deviceId
Retrieves information about a specific device for a user. This
request does not go via a hub, instead going directly to the server
which owns the :userId.
*Implementation note*: Currently this endpoint doesn't actually
exist. Use PUT /_matrix/federation/unstable/org.matrix.i-d.ralston-
mimi-linearized-matrix.02/user/:userId/device/:deviceId when testing
against other Linearized Matrix implementations. This string may be
updated later to account for breaking changes.
*TODO*: Remove implementation notes.
*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters:
* :userId - the user ID (Section 3.3) who owns the device.
* :deviceId - the device ID (Section 3.4) to get information about.
Query parameters: None applicable.
Request body: None applicable.
200 OK response:
{
"device_id": "ABCDEF",
"user_id": "@alice:example.org",
"algorithms": [
"m.mls.v1.dhkemx25519-aes128gcm-sha256-ed25519"
],
"keys": {
"m.mls.v1.credential.ed25519:ABCDEF":
"<unpadded base64 BasicCredential>"
},
"signatures": {
"@alice:example.org": {
"m.mls.v1.credential.ed25519:ABCDEF":
"<unpadded base64 signature>"
}
}
}
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Note that the response is the same object the device itself signed/
created in Section 4.1.
If the user ID does not belong the receiving server, a 404 Not Found
HTTP status code is returned with error code M_NOT_FOUND
(Section 12.2.2). The same applies if the user ID does not exist, or
the user does not have the device ID requested.
12.10.2. To-Device Messaging
To-device messaging is an ability to send information directly to
another device, typically to carry MLS Welcome messages and similar.
They are sent as EDUs (Section 12.9), one per receipient device and
payload:
{
"type": "m.direct_to_device",
"sender": "@alice:example.org",
"content": {
"target": "@bob:example.org",
"target_device": "ABCD",
"message_type": "m.room.encrypted",
"message": {
/* message_type-specific schema */
}
}
}
target and target_device denote the destination user ID (Section 3.3)
and device ID (Section 3.4) for that user. This EDU MUST be sent to
the server denoted by the target user ID. If the target user doesn't
exist or doesn't have a device with the ID described, the receiving
server drops/ignores the EDU.
See Section 4.3 for an example of a to-device message being used.
12.10.3. One Time Key Claiming
To enable two devices to communicate, they need to claim a key
package (Section 4.4) for the other device. These key packages are
also called "one time keys". This is done through the following
endpoint.
12.10.3.1. POST /_matrix/federation/v1/user/keys/claim
Claims one time keys for devices. This request does not go via a
hub, instead going directly to the server which owns the given user
IDs.
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*Rate-limited*: Yes.
*Authentication required*: Yes.
Path parameters: None applicable.
Query parameters: None applicable.
Request body:
{
"one_time_keys": {
"@alice:example.org": {
"ABCD":
"m.mls.v1.key_package.dhkemx25519-aes128gcm-sha256-ed25519"
}
}
}
one_time_keys MUST be specified and is a map of user ID (Section 3.3)
to device ID (Section 3.4) to algorithm for the key package to claim.
Currently the only expected algorithm is defined by Section 4.4.
Any user IDs which don't belong to the receiving server, or which
don't exist, are ignored. The same applies for device IDs for which
the user doesn't have.
200 OK response:
{
"one_time_keys": {
"@alice:example.org": {
"ABCD": {
"m.mls.v1.key_package.dhkemx25519-aes128gcm-sha256-ed25519":
"<unpadded base64 encoded key package>"
}
}
}
}
Like the request body, one_time_keys MUST be specified (but MAY be
empty) and is a map of requested user ID to requested device ID to
algorithm name. The value for the algorithm name is dependent on the
algorithm itself. For m.mls.v1.key_package.dhkemx25519-aes128gcm-
sha256-ed25519, this is an unpadded base64 (Section 10) string
representing the key package itself.
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Servers MUST NOT reuse a device's one time key, unless that key
permits it. For example, MLS's "last resort" key MAY be used
multiple times, but SHOULD only be used if no other one time keys
remain for the device. Servers MUST NOT use an expired key.
Typically, the server will inform the device that a key was used so
the device can upload additional keys. See Section 4.4 for further
implementation-related concerns.
12.11. TODO: Remainder of Transport
*TODO*: This section.
Topics:
* More EDUs (typing notifications, receipts, presence)
* Query APIs (alias resolution, profiles)
* Other Encryption APIs??
* Server ACLs? (this probably should become part of the auth rules)
Notably/deliberately missing APIs are:
* get_missing_events - this is used by DAG servers only
* Public room directory
* Timestamp-to-event API
* All of 3rd party invites
* All of Spaces
* OpenID API
12.11.1. Open Questions
* Should we include /_matrix/federation/v1/version in here? It's
used by federation testers, but not really anything else.
13. User Privacy
*TODO*: Fully complete this section.
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Messaging providers may have user-level settings to prevent
unexpected or unwarranted invites, such as automatically blocking
invites from non-contacts. This setting can be upheld by returning
an error on POST /_matrix/federation/v3/invite/:txnId
(Section 12.7.2.1), and by having the server (optionally) auto-
decline any invites received directly through PUT
/_matrix/federation/v2/send/:txnId (Section 12.5.1). See
Section 12.7.2.2 for more information on rejecting invites.
14. Spam Prevention
*TODO*: Fully complete this section.
*TODO*: Talk about how to deal with spammy/unwanted invites.
Servers MAY temporarily or permanently block a room entirely by using
the room ID. Typically, when a room becomes blocked, all local users
will be removed from the room using m.room.member events with
membership of leave (Section 3.5.3.3). Then, any time the server
receives a request for that room ID it can reject it with an error
response (Section 12.2.2).
Blocking a room does not block it from all servers, but does prevent
users on a server from accessing the content within. This is
primarily useful to remove a server from rooms where abusive/illegal
content is shared.
15. Security Considerations
*TODO*: Expand upon this section.
With the combined use of MLS and server-side enforcement, the server
theoretically has an ability to add a malicious device to the MLS
group and receive decryptable messages. Authenticity of devices
needs to be established to ensure a user's devices are actually a
user's devices.
*TODO*: Should we bring Matrix's cross-signing here?
Servers retain the ability to control/puppet their own users due to
no strong cryptographic link between the sending device and the event
which gets emitted.
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16. MIMI Protocol Comparison
[I-D.barnes-mimi-arch], [I-D.ralston-mimi-protocol], and
[I-D.robert-mimi-delivery-service] collectively define a protocol
with similar capabilities to Linearized Matrix, leaning more heavily
into the MLS layering to accomplish interoperable messaging.
Linearized Matrix in contrast provides a signaling layer for which
encryption can operate, using existing open standards as the
foundational piece.
17. IANA Considerations
The m.* namespace likely needs formal registration in some capacity.
The I.* namespace likely needs formal registration in some capacity.
Port 8448 may need formal registration.
The SRV service name matrix may need re-registering, or a new service
name assigned.
The .well-known/matrix namespace is already registered for use by The
Matrix.org Foundation C.I.C.
18. References
18.1. Normative References
[I-D.barnes-mimi-arch]
Barnes, R., "An Architecture for More Instant Messaging
Interoperability (MIMI)", Work in Progress, Internet-
Draft, draft-barnes-mimi-arch-02, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-barnes-mimi-
arch-02>.
[I-D.ietf-mls-architecture]
Beurdouche, B., Rescorla, E., Omara, E., Inguva, S., and
A. Duric, "The Messaging Layer Security (MLS)
Architecture", Work in Progress, Internet-Draft, draft-
ietf-mls-architecture-11, 26 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-mls-
architecture-11>.
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[I-D.ietf-mls-protocol]
Barnes, R., Beurdouche, B., Robert, R., Millican, J.,
Omara, E., and K. Cohn-Gordon, "The Messaging Layer
Security (MLS) Protocol", Work in Progress, Internet-
Draft, draft-ietf-mls-protocol-20, 27 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-mls-
protocol-20>.
[I-D.ralston-mimi-protocol]
Ralston, T., Kohbrok, K., Robert, R., and M. Hodgson,
"More Instant Messaging Interoperability (MIMI) using
HTTPS and MLS", Work in Progress, Internet-Draft, draft-
ralston-mimi-protocol-01, 6 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ralston-mimi-
protocol-01>.
[I-D.ralston-mimi-terminology]
Ralston, T., "MIMI Terminology", Work in Progress,
Internet-Draft, draft-ralston-mimi-terminology-03, 23
October 2023, <https://datatracker.ietf.org/doc/html/
draft-ralston-mimi-terminology-03>.
[I-D.robert-mimi-delivery-service]
Robert, R. and K. Kohbrok, "MIMI Delivery Service", Work
in Progress, Internet-Draft, draft-robert-mimi-delivery-
service-06, 6 November 2023,
<https://datatracker.ietf.org/doc/html/draft-robert-mimi-
delivery-service-06>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/rfc/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/rfc/rfc1035>.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<https://www.rfc-editor.org/rfc/rfc1123>.
[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/rfc/rfc2119>.
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[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<https://www.rfc-editor.org/rfc/rfc2181>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000,
<https://www.rfc-editor.org/rfc/rfc2782>.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", STD 88,
RFC 3596, DOI 10.17487/RFC3596, October 2003,
<https://www.rfc-editor.org/rfc/rfc3596>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/rfc/rfc3629>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/rfc/rfc4648>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/rfc/rfc6125>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/rfc/rfc6234>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/rfc/rfc8032>.
[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/rfc/rfc8174>.
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[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/rfc/rfc8259>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC8785] Rundgren, A., Jordan, B., and S. Erdtman, "JSON
Canonicalization Scheme (JCS)", RFC 8785,
DOI 10.17487/RFC8785, June 2020,
<https://www.rfc-editor.org/rfc/rfc8785>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[RFC9113] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/rfc/rfc9113>.
18.2. Informative References
[DMLS] Chathi, H., "Decentralised MLS", 29 May 2023,
<https://gitlab.matrix.org/matrix-org/mls-ts/-
/blob/48efb972075233c3a0f3e3ca01c4d4f888342205/
decentralised.org>.
[I-D.kohbrok-mimi-portability]
Kohbrok, K. and R. Robert, "MIMI Portability", Work in
Progress, Internet-Draft, draft-kohbrok-mimi-portability-
01, 4 January 2024,
<https://datatracker.ietf.org/doc/html/draft-kohbrok-mimi-
portability-01>.
[I-D.mahy-mimi-group-chat]
Mahy, R., "Group Chat Framework for More Instant Messaging
Interoperability (MIMI)", Work in Progress, Internet-
Draft, draft-mahy-mimi-group-chat-00, 10 July 2023,
<https://datatracker.ietf.org/doc/html/draft-mahy-mimi-
group-chat-00>.
[I-D.rosenberg-mimi-protocol]
Rosenberg, J., Jennings, C. F., and S. Nandakumar, "More
Instant Messaging Interop (MIMI) Transport Protocol", Work
in Progress, Internet-Draft, draft-rosenberg-mimi-
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protocol-00, 13 March 2023,
<https://datatracker.ietf.org/doc/html/draft-rosenberg-
mimi-protocol-00>.
[MSC3995] Ralston, T., "MSC3995: [WIP] Linearized Matrix", 12 April
2023, <https://github.com/matrix-org/matrix-spec-
proposals/pull/3995>.
[PerspectivesProject]
"Perspectives Project", 2 July 2017,
<https://web.archive.org/web/20170702024706/
https://perspectives-project.org/>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
March 2011, <https://www.rfc-editor.org/rfc/rfc6120>.
[RFC9364] Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237,
RFC 9364, DOI 10.17487/RFC9364, February 2023,
<https://www.rfc-editor.org/rfc/rfc9364>.
Acknowledgments
Thanks to the Matrix Spec Core Team (SCT) for exploring methods of
linearizing Matrix's DAG room model, especially Richard van der Hoff
and Erik Johnston. Additional thanks to the Matrix core team as a
whole for general review and input on this document, especially
Patrick Cloke and Jim Mackenzie.
Matrix's crypto team graciously allowed their work-in-progress MLS
considerations to be incorporated in this document. Thanks to Hubert
Chathi for reviewing the MLS work for plausibility.
Thanks are also extended to the wider MIMI working group for
continous review and input on this document.
Authors' Addresses
Travis Ralston
The Matrix.org Foundation C.I.C.
Email: travisr@matrix.org
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Matthew Hodgson
The Matrix.org Foundation C.I.C.
Email: matthew@matrix.org
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