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Fully specify room versions (#3432)

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* Fully specify room versions

* Misc typo clarifications

* Try to clarify redactions a bit

* Update content/client-server-api/_index.md

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* Update content/rooms/v6.md

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* Update content/rooms/v6.md

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* Better describe client considerations

* Doc template params

* Move redaction "new stuff" to v3

* Remove unhelpful sentences about "here follows unchanged stuff"

* Simplify event signing text

* Clean up handling redactions sections

* Move v4's event schema to unchanged section

* Update content/rooms/v4.md

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
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@ -1598,7 +1598,9 @@ content from the databases. Servers should include a copy of the
when serving the redacted event to clients. when serving the redacted event to clients.
The exact algorithm to apply against an event is defined in the [room The exact algorithm to apply against an event is defined in the [room
version specification](/rooms). version specification](/rooms), as are the criteria homeservers should
use when deciding whether to accept a redaction event from a remote
homeserver.
When a client receives an `m.room.redaction` event, it should change When a client receives an `m.room.redaction` event, it should change
the affected event in the same way a server does. the affected event in the same way a server does.

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The types of state events that affect authorization are:
- `m.room.create`
- `m.room.member`
- `m.room.join_rules`
- `m.room.power_levels`
- `m.room.third_party_invite`
{{% boxes/note %}}
Power levels are inferred from defaults when not explicitly supplied.
For example, mentions of the `sender`'s power level can also refer to
the default power level for users in the room.
{{% /boxes/note %}}
The rules are as follows:
1. If type is `m.room.create`:
1. If it has any previous events, reject.
2. If the domain of the `room_id` does not match the domain of the
`sender`, reject.
3. If `content.room_version` is present and is not a recognised
version, reject.
4. If `content` has no `creator` field, reject.
5. Otherwise, allow.
2. Reject if event has `auth_events` that:
1. have duplicate entries for a given `type` and `state_key` pair
2. have entries whose `type` and `state_key` don't match those
specified by the [auth events
selection](/server-server-api#auth-events-selection)
algorithm described in the server specification.
3. If event does not have a `m.room.create` in its `auth_events`,
reject.
4. If type is `m.room.aliases`:
1. If event has no `state_key`, reject.
2. If sender's domain doesn't matches `state_key`, reject.
3. Otherwise, allow.
5. If type is `m.room.member`:
1. If no `state_key` key or `membership` key in `content`, reject.
2. If `membership` is `join`:
1. If the only previous event is an `m.room.create` and the
`state_key` is the creator, allow.
2. If the `sender` does not match `state_key`, reject.
3. If the `sender` is banned, reject.
4. If the `join_rule` is `invite` then allow if membership
state is `invite` or `join`.
5. If the `join_rule` is `public`, allow.
6. Otherwise, reject.
3. If `membership` is `invite`:
1. If `content` has `third_party_invite` key:
1. If *target user* is banned, reject.
2. If `content.third_party_invite` does not have a `signed`
key, reject.
3. If `signed` does not have `mxid` and `token` keys,
reject.
4. If `mxid` does not match `state_key`, reject.
5. If there is no `m.room.third_party_invite` event in the
current room state with `state_key` matching `token`,
reject.
6. If `sender` does not match `sender` of the
`m.room.third_party_invite`, reject.
7. If any signature in `signed` matches any public key in
the `m.room.third_party_invite` event, allow. The public
keys are in `content` of `m.room.third_party_invite` as:
1. A single public key in the `public_key` field.
2. A list of public keys in the `public_keys` field.
8. Otherwise, reject.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If *target user*'s current membership state is `join` or
`ban`, reject.
4. If the `sender`'s power level is greater than or equal to
the *invite level*, allow.
5. Otherwise, reject.
4. If `membership` is `leave`:
1. If the `sender` matches `state_key`, allow if and only if
that user's current membership state is `invite` or `join`.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If the *target user*'s current membership state is `ban`,
and the `sender`'s power level is less than the *ban level*,
reject.
4. If the `sender`'s power level is greater than or equal to
the *kick level*, and the *target user*'s power level is
less than the `sender`'s power level, allow.
5. Otherwise, reject.
5. If `membership` is `ban`:
1. If the `sender`'s current membership state is not `join`,
reject.
2. If the `sender`'s power level is greater than or equal to
the *ban level*, and the *target user*'s power level is less
than the `sender`'s power level, allow.
3. Otherwise, reject.
6. Otherwise, the membership is unknown. Reject.
6. If the `sender`'s current membership state is not `join`, reject.
7. If type is `m.room.third_party_invite`:
1. Allow if and only if `sender`'s current power level is greater
than or equal to the *invite level*.
8. If the event type's *required power level* is greater than the
`sender`'s power level, reject.
9. If the event has a `state_key` that starts with an `@` and does not
match the `sender`, reject.
10. If type is `m.room.power_levels`:
1. If `users` key in `content` is not a dictionary with keys that
are valid user IDs with values that are integers (or a string
that is an integer), reject.
2. If there is no previous `m.room.power_levels` event in the room,
allow.
3. For the keys `users_default`, `events_default`, `state_default`,
`ban`, `redact`, `kick`, `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.
2. If the new value is higher than the `sender`'s current power
level, reject.
4. For each entry being added, changed or removed in both the
`events` and `users` keys:
1. If the current value is higher than the `sender`'s current
power level, reject.
2. If the new value is higher than the `sender`'s current power
level, reject.
5. For each entry being changed under the `users` key, other than
the `sender`'s own entry:
1. If the current value is equal to the `sender`'s current
power level, reject.
6. Otherwise, allow.
11. If type is `m.room.redaction`:
1. If the `sender`'s power level is greater than or equal to the
*redact level*, allow.
2. If the domain of the `event_id` of the event being redacted is
the same as the domain of the `event_id` of the
`m.room.redaction`, allow.
3. Otherwise, reject.
12. Otherwise, allow.
{{% boxes/note %}}
Some consequences of these rules:
- Unless you are a member of the room, the only permitted operations
(apart from the initial create/join) are: joining a public room;
accepting or rejecting an invitation to a room.
- To unban somebody, you must have power level greater than or equal
to both the kick *and* ban levels, *and* greater than the target
user's power level.
{{% /boxes/note %}}

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Servers MUST NOT strictly enforce the JSON format specified in the
[appendices](/appendices#canonical-json) for the reasons
described there.

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Upon receipt of a redaction event, the server must strip off any keys
not in the following list:
- `event_id`
- `type`
- `room_id`
- `sender`
- `state_key`
- `content`
- `hashes`
- `signatures`
- `depth`
- `prev_events`
- `prev_state`
- `auth_events`
- `origin`
- `origin_server_ts`
- `membership`
The content object must also be stripped of all keys, unless it is one
of one of the following event types:
- `m.room.member` allows key `membership`.
- `m.room.create` allows key `creator`.
- `m.room.join_rules` allows key `join_rule`.
- `m.room.power_levels` allows keys `ban`, `events`, `events_default`,
`kick`, `redact`, `state_default`, `users`, `users_default`.
- `m.room.aliases` allows key `aliases`.
- `m.room.history_visibility` allows key `history_visibility`.

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The room state *S*′(*E*) after an event *E* is defined in terms of the
room state *S*(*E*) before *E*, and depends on whether *E* is a state
event or a message event:
- If *E* is a message event, then *S*′(*E*) = *S*(*E*).
- If *E* is a state event, then *S*′(*E*) is *S*(*E*), except that its
entry corresponding to *E*'s `event_type` and `state_key` is
replaced by *E*'s `event_id`.
The room state *S*(*E*) before *E* is the *resolution* of the set of
states {*S*′(*E*<sub>1</sub>), *S*′(*E*<sub>2</sub>), …} consisting of
the states after each of *E*'s `prev_event`s
{*E*<sub>1</sub>, *E*<sub>2</sub>, …}, where the resolution of a set of
states is given in the algorithm below.
#### Definitions
The state resolution algorithm for version 2 rooms uses the following
definitions, given the set of room states
{*S*<sub>1</sub>, *S*<sub>2</sub>, …}:
Power events
A *power event* is a state event with type `m.room.power_levels` or
`m.room.join_rules`, or a state event with type `m.room.member` where
the `membership` is `leave` or `ban` and the `sender` does not match the
`state_key`. The idea behind this is that power events are events that
might remove someone's ability to do something in the room.
Unconflicted state map and conflicted state set
The *unconflicted state map* is the state where the value of each key
exists and is the same in each state *S*<sub>*i*</sub>. The *conflicted
state set* is the set of all other state events. Note that the
unconflicted state map only has one event per `(event_type, state_key)`,
whereas the conflicted state set may have multiple events.
Auth difference
The *auth difference* is calculated by first calculating the full auth
chain for each state *S*<sub>*i*</sub>, that is the union of the auth
chains for each event in *S*<sub>*i*</sub>, and then taking every event
that doesn't appear in every auth chain. If *C*<sub>*i*</sub> is the
full auth chain of *S*<sub>*i*</sub>, then the auth difference is
 ∪ *C*<sub>*i*</sub> −  ∩ *C*<sub>*i*</sub>.
Full conflicted set
The *full conflicted set* is the union of the conflicted state set and
the auth difference.
Reverse topological power ordering
The *reverse topological power ordering* of a set of events is the
lexicographically smallest topological ordering based on the DAG formed
by auth events. The reverse topological power ordering is ordered from
earliest event to latest. For comparing two topological orderings to
determine which is the lexicographically smallest, the following
comparison relation on events is used: for events *x* and *y*,
*x* &lt; *y* if
1. *x*'s sender has *greater* power level than *y*'s sender, when
looking at their respective `auth_event`s; or
2. the senders have the same power level, but *x*'s `origin_server_ts`
is *less* than *y*'s `origin_server_ts`; or
3. the senders have the same power level and the events have the same
`origin_server_ts`, but *x*'s `event_id` is *less* than *y*'s
`event_id`.
The reverse topological power ordering can be found by sorting the
events using Kahn's algorithm for topological sorting, and at each step
selecting, among all the candidate vertices, the smallest vertex using
the above comparison relation.
Mainline ordering
Given an `m.room.power_levels` event *P*, the *mainline of* *P* is the
list of events generated by starting with *P* and recursively taking the
`m.room.power_levels` events from the `auth_events`, ordered such that
*P* is last. Given another event *e*, the *closest mainline event to*
*e* is the first event encountered in the mainline when iteratively
descending through the `m.room.power_levels` events in the `auth_events`
starting at *e*. If no mainline event is encountered when iteratively
descending through the `m.room.power_levels` events, then the closest
mainline event to *e* can be considered to be a dummy event that is
before any other event in the mainline of *P* for the purposes of
condition 1 below.
The *mainline ordering based on* *P* of a set of events is the ordering,
from smallest to largest, using the following comparison relation on
events: for events *x* and *y*, *x* &lt; *y* if
1. the closest mainline event to *x* appears *before* the closest
mainline event to *y*; or
2. the closest mainline events are the same, but *x*'s
`origin_server_ts` is *less* than *y*'s `origin_server_ts`; or
3. the closest mainline events are the same and the events have the
same `origin_server_ts`, but *x*'s `event_id` is *less* than *y*'s
`event_id`.
Iterative auth checks
The *iterative auth checks algorithm* takes as input an initial room
state and a sorted list of state events, and constructs a new room state
by iterating through the event list and applying the state event to the
room state if the state event is allowed by the [authorization
rules](/server-server-api#authorization-rules).
If the state event is not allowed by the authorization rules, then the
event is ignored. If a `(event_type, state_key)` key that is required
for checking the authorization rules is not present in the state, then
the appropriate state event from the event's `auth_events` is used if
the auth event is not rejected.
#### Algorithm
The *resolution* of a set of states is obtained as follows:
1. Take all *power events* and any events in their auth chains,
recursively, that appear in the *full conflicted set* and order them
by the *reverse topological power ordering*.
2. Apply the *iterative auth checks algorithm*, starting from the
*unconflicted state map*, to the list of events from the previous
step to get a partially resolved state.
3. Take all remaining events that weren't picked in step 1 and order
them by the mainline ordering based on the power level in the
partially resolved state obtained in step 2.
4. Apply the *iterative auth checks algorithm* on the partial resolved
state and the list of events from the previous step.
5. Update the result by replacing any event with the event with the
same key from the *unconflicted state map*, if such an event exists,
to get the final resolved state.
#### Rejected events
Events that have been rejected due to failing auth based on the state at
the event (rather than based on their auth chain) are handled as usual
by the algorithm, unless otherwise specified.
Note that no events rejected due to failure to auth against their auth
chain should appear in the process, as they should not appear in state
(the algorithm only uses events that appear in either the state sets or
in the auth chain of the events in the state sets).
{{% boxes/rationale %}}
This helps ensure that different servers' view of state is more likely
to converge, since rejection state of an event may be different. This
can happen if a third server gives an incorrect version of the state
when a server joins a room via it (either due to being faulty or
malicious). Convergence of state is a desirable property as it ensures
that all users in the room have a (mostly) consistent view of the state
of the room. If the view of the state on different servers diverges it
can lead to bifurcation of the room due to e.g. servers disagreeing on
who is in the room.
Intuitively, using rejected events feels dangerous, however:
1. Servers cannot arbitrarily make up state, since they still need to
pass the auth checks based on the event's auth chain (e.g. they
can't grant themselves power levels if they didn't have them
before).
2. For a previously rejected event to pass auth there must be a set of
state that allows said event. A malicious server could therefore
produce a fork where it claims the state is that particular set of
state, duplicate the rejected event to point to that fork, and send
the event. The duplicated event would then pass the auth checks.
Ignoring rejected events would therefore not eliminate any potential
attack vectors.
{{% /boxes/rationale %}}
Rejected auth events are deliberately excluded from use in the iterative
auth checks, as auth events aren't re-authed (although non-auth events
are) during the iterative auth checks.

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---
# unused frontmatter - just fixing a hugo issue where it doesn't parse
# shortcodes at the start of a file.
---
{{% added-in this=true %}} In room versions 1 and 2, events need a
signature from the domain of the `event_id` in order to be considered
valid. This room version does not include an `event_id` over federation
in the same respect, so does not need a signature from that server.
The event must still be signed by the server denoted by the `sender`,
however.
The types of state events that affect authorization are:
- `m.room.create`
- `m.room.member`
- `m.room.join_rules`
- `m.room.power_levels`
- `m.room.third_party_invite`
{{% boxes/note %}}
Power levels are inferred from defaults when not explicitly supplied.
For example, mentions of the `sender`'s power level can also refer to
the default power level for users in the room.
{{% /boxes/note %}}
The complete list of rules, as of room version 3, is as follows:
1. If type is `m.room.create`:
1. If it has any previous events, reject.
2. If the domain of the `room_id` does not match the domain of the
`sender`, reject.
3. If `content.room_version` is present and is not a recognised
version, reject.
4. If `content` has no `creator` field, reject.
5. Otherwise, allow.
2. Reject if event has `auth_events` that:
1. have duplicate entries for a given `type` and `state_key` pair
2. have entries whose `type` and `state_key` don't match those
specified by the [auth events
selection](/server-server-api#auth-events-selection)
algorithm described in the server specification.
3. If event does not have a `m.room.create` in its `auth_events`,
reject.
4. If type is `m.room.aliases`:
1. If event has no `state_key`, reject.
2. If sender's domain doesn't matches `state_key`, reject.
3. Otherwise, allow.
5. If type is `m.room.member`:
1. If no `state_key` key or `membership` key in `content`, reject.
2. If `membership` is `join`:
1. If the only previous event is an `m.room.create` and the
`state_key` is the creator, allow.
2. If the `sender` does not match `state_key`, reject.
3. If the `sender` is banned, reject.
4. If the `join_rule` is `invite` then allow if membership
state is `invite` or `join`.
5. If the `join_rule` is `public`, allow.
6. Otherwise, reject.
3. If `membership` is `invite`:
1. If `content` has `third_party_invite` key:
1. If *target user* is banned, reject.
2. If `content.third_party_invite` does not have a `signed`
key, reject.
3. If `signed` does not have `mxid` and `token` keys,
reject.
4. If `mxid` does not match `state_key`, reject.
5. If there is no `m.room.third_party_invite` event in the
current room state with `state_key` matching `token`,
reject.
6. If `sender` does not match `sender` of the
`m.room.third_party_invite`, reject.
7. If any signature in `signed` matches any public key in
the `m.room.third_party_invite` event, allow. The public
keys are in `content` of `m.room.third_party_invite` as:
1. A single public key in the `public_key` field.
2. A list of public keys in the `public_keys` field.
8. Otherwise, reject.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If *target user*'s current membership state is `join` or
`ban`, reject.
4. If the `sender`'s power level is greater than or equal to
the *invite level*, allow.
5. Otherwise, reject.
4. If `membership` is `leave`:
1. If the `sender` matches `state_key`, allow if and only if
that user's current membership state is `invite` or `join`.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If the *target user*'s current membership state is `ban`,
and the `sender`'s power level is less than the *ban level*,
reject.
4. If the `sender`'s power level is greater than or equal to
the *kick level*, and the *target user*'s power level is
less than the `sender`'s power level, allow.
5. Otherwise, reject.
5. If `membership` is `ban`:
1. If the `sender`'s current membership state is not `join`,
reject.
2. If the `sender`'s power level is greater than or equal to
the *ban level*, and the *target user*'s power level is less
than the `sender`'s power level, allow.
3. Otherwise, reject.
6. Otherwise, the membership is unknown. Reject.
6. If the `sender`'s current membership state is not `join`, reject.
7. If type is `m.room.third_party_invite`:
1. Allow if and only if `sender`'s current power level is greater
than or equal to the *invite level*.
8. If the event type's *required power level* is greater than the
`sender`'s power level, reject.
9. If the event has a `state_key` that starts with an `@` and does not
match the `sender`, reject.
10. If type is `m.room.power_levels`:
1. If `users` key in `content` is not a dictionary with keys that
are valid user IDs with values that are integers (or a string
that is an integer), reject.
2. If there is no previous `m.room.power_levels` event in the room,
allow.
3. For the keys `users_default`, `events_default`, `state_default`,
`ban`, `redact`, `kick`, `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.
2. If the new value is higher than the `sender`'s current power
level, reject.
4. For each entry being added, changed or removed in both the
`events` and `users` keys:
1. If the current value is higher than the `sender`'s current
power level, reject.
2. If the new value is higher than the `sender`'s current power
level, reject.
5. For each entry being changed under the `users` key, other than
the `sender`'s own entry:
1. If the current value is equal to the `sender`'s current
power level, reject.
6. Otherwise, allow.
11. Otherwise, allow.
{{% boxes/note %}}
Some consequences of these rules:
- Unless you are a member of the room, the only permitted operations
(apart from the initial create/join) are: joining a public room;
accepting or rejecting an invitation to a room.
- To unban somebody, you must have power level greater than or equal
to both the kick *and* ban levels, *and* greater than the target
user's power level.
{{% /boxes/note %}}

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---
# unused frontmatter - just fixing a hugo issue where it doesn't parse
# shortcodes at the start of a file.
---
{{% added-in this=true %}} In room versions 1 and 2, redactions were
explicitly part of the [authorization rules](/rooms/v1/#authorization-rules)
under Rule 11. As of room version 3, these conditions no longer exist as
represented by the above rules.
While redactions are always accepted by the authorization rules for
events, they should not be sent to clients until both the redaction
event and the event the redaction affects have been received, and can
be validated. If both events are valid and have been seen by the server,
then the server applies the redaction if one of the following conditions
is met:
1. The power level of the redaction event's `sender` is greater than or
equal to the *redact level*.
2. The domain of the redaction event's `sender` matches that of the
original event's `sender`.
If the server would apply a redaction, the redaction event is also sent
to clients. Otherwise, the server simply waits for a valid partner event
to arrive where it can then re-check the above.

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The event ID is the [reference
hash](/server-server-api#calculating-the-reference-hash-for-an-event) of
the event encoded using a variation of [Unpadded
Base64](/appendices#unpadded-base64) which replaces the 62nd and
63rd characters with `-` and `_` instead of using `+` and `/`. This
matches [RFC4648's definition of URL-safe
base64](https://tools.ietf.org/html/rfc4648#section-5). Event IDs are
still prefixed with `$` and may result in looking like
`$Rqnc-F-dvnEYJTyHq_iKxU2bZ1CI92-kuZq3a5lr5Zg`.
Just like in room version 3, event IDs should not be sent over
federation to servers when the room uses this room version. On the
receiving end of an event, the server should compute the relevant event
ID for itself. Room version 3 also changes the format of `auth_events`
and `prev_events` in a PDU.

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When validating event signatures, servers MUST enforce the
`valid_until_ts` property from a key request is at least as large as the
`origin_server_ts` for the event being validated. Servers missing a copy
of the signing key MUST try to obtain one via the [GET
/\_matrix/key/v2/server](/server-server-api#get_matrixkeyv2serverkeyid)
or [POST
/\_matrix/key/v2/query](/server-server-api#post_matrixkeyv2query)
APIs. When using the `/query` endpoint, servers MUST set the
`minimum_valid_until_ts` property to prompt the notary server to attempt
to refresh the key if appropriate.
Servers MUST use the lesser of `valid_until_ts` and 7 days into the
future when determining if a key is valid. This is to avoid a situation
where an attacker publishes a key which is valid for a significant
amount of time without a way for the homeserver owner to revoke it.

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Servers MUST strictly enforce the JSON format specified in the
[appendices](/appendices#canonical-json). This translates to a
400 `M_BAD_JSON` error on most endpoints, or discarding of events over
federation. For example, the Federation API's `/send` endpoint would
discard the event whereas the Client Server API's `/send/{eventType}`
endpoint would return a `M_BAD_JSON` error.

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Upon receipt of a redaction event, the server must strip off any keys
not in the following list:
- `event_id`
- `type`
- `room_id`
- `sender`
- `state_key`
- `content`
- `hashes`
- `signatures`
- `depth`
- `prev_events`
- `prev_state`
- `auth_events`
- `origin`
- `origin_server_ts`
- `membership`
The content object must also be stripped of all keys, unless it is one
of one of the following event types:
- `m.room.member` allows key `membership`.
- `m.room.create` allows key `creator`.
- `m.room.join_rules` allows key `join_rule`.
- `m.room.power_levels` allows keys `ban`, `events`, `events_default`,
`kick`, `redact`, `state_default`, `users`, `users_default`.
- `m.room.history_visibility` allows key `history_visibility`.

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@ -9,40 +9,12 @@ building blocks for other room versions.
## Client considerations ## Client considerations
Clients may need to consider some algorithms performed by the server for Clients which implement the redaction algorithm locally should refer to the
their own implementation. [redactions](#redactions) section below.
### Redactions ### Redactions
Upon receipt of a redaction event, the server must strip off any keys {{% rver-fragment name="v1-redactions" %}}
not in the following list:
- `event_id`
- `type`
- `room_id`
- `sender`
- `state_key`
- `content`
- `hashes`
- `signatures`
- `depth`
- `prev_events`
- `prev_state`
- `auth_events`
- `origin`
- `origin_server_ts`
- `membership`
The content object must also be stripped of all keys, unless it is one
of one of the following event types:
- `m.room.member` allows key `membership`.
- `m.room.create` allows key `creator`.
- `m.room.join_rules` allows key `join_rule`.
- `m.room.power_levels` allows keys `ban`, `events`, `events_default`,
`kick`, `redact`, `state_default`, `users`, `users_default`.
- `m.room.aliases` allows key `aliases`.
- `m.room.history_visibility` allows key `history_visibility`.
## Server implementation components ## Server implementation components
@ -127,150 +99,7 @@ affected are said to be *conflicting* events.
### Authorization rules ### Authorization rules
The types of state events that affect authorization are: {{% rver-fragment name="v1-auth-rules" %}}
- `m.room.create`
- `m.room.member`
- `m.room.join_rules`
- `m.room.power_levels`
- `m.room.third_party_invite`
{{% boxes/note %}}
Power levels are inferred from defaults when not explicitly supplied.
For example, mentions of the `sender`'s power level can also refer to
the default power level for users in the room.
{{% /boxes/note %}}
The rules are as follows:
1. If type is `m.room.create`:
1. If it has any previous events, reject.
2. If the domain of the `room_id` does not match the domain of the
`sender`, reject.
3. If `content.room_version` is present and is not a recognised
version, reject.
4. If `content` has no `creator` field, reject.
5. Otherwise, allow.
2. Reject if event has `auth_events` that:
1. have duplicate entries for a given `type` and `state_key` pair
2. have entries whose `type` and `state_key` don't match those
specified by the [auth events
selection](/server-server-api#auth-events-selection)
algorithm described in the server specification.
3. If event does not have a `m.room.create` in its `auth_events`,
reject.
4. If type is `m.room.aliases`:
1. If event has no `state_key`, reject.
2. If sender's domain doesn't matches `state_key`, reject.
3. Otherwise, allow.
5. If type is `m.room.member`:
1. If no `state_key` key or `membership` key in `content`, reject.
2. If `membership` is `join`:
1. If the only previous event is an `m.room.create` and the
`state_key` is the creator, allow.
2. If the `sender` does not match `state_key`, reject.
3. If the `sender` is banned, reject.
4. If the `join_rule` is `invite` then allow if membership
state is `invite` or `join`.
5. If the `join_rule` is `public`, allow.
6. Otherwise, reject.
3. If `membership` is `invite`:
1. If `content` has `third_party_invite` key:
1. If *target user* is banned, reject.
2. If `content.third_party_invite` does not have a `signed`
key, reject.
3. If `signed` does not have `mxid` and `token` keys,
reject.
4. If `mxid` does not match `state_key`, reject.
5. If there is no `m.room.third_party_invite` event in the
current room state with `state_key` matching `token`,
reject.
6. If `sender` does not match `sender` of the
`m.room.third_party_invite`, reject.
7. If any signature in `signed` matches any public key in
the `m.room.third_party_invite` event, allow. The public
keys are in `content` of `m.room.third_party_invite` as:
1. A single public key in the `public_key` field.
2. A list of public keys in the `public_keys` field.
8. Otherwise, reject.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If *target user*'s current membership state is `join` or
`ban`, reject.
4. If the `sender`'s power level is greater than or equal to
the *invite level*, allow.
5. Otherwise, reject.
4. If `membership` is `leave`:
1. If the `sender` matches `state_key`, allow if and only if
that user's current membership state is `invite` or `join`.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If the *target user*'s current membership state is `ban`,
and the `sender`'s power level is less than the *ban level*,
reject.
4. If the `sender`'s power level is greater than or equal to
the *kick level*, and the *target user*'s power level is
less than the `sender`'s power level, allow.
5. Otherwise, reject.
5. If `membership` is `ban`:
1. If the `sender`'s current membership state is not `join`,
reject.
2. If the `sender`'s power level is greater than or equal to
the *ban level*, and the *target user*'s power level is less
than the `sender`'s power level, allow.
3. Otherwise, reject.
6. Otherwise, the membership is unknown. Reject.
6. If the `sender`'s current membership state is not `join`, reject.
7. If type is `m.room.third_party_invite`:
1. Allow if and only if `sender`'s current power level is greater
than or equal to the *invite level*.
8. If the event type's *required power level* is greater than the
`sender`'s power level, reject.
9. If the event has a `state_key` that starts with an `@` and does not
match the `sender`, reject.
10. If type is `m.room.power_levels`:
1. If `users` key in `content` is not a dictionary with keys that
are valid user IDs with values that are integers (or a string
that is an integer), reject.
2. If there is no previous `m.room.power_levels` event in the room,
allow.
3. For the keys `users_default`, `events_default`, `state_default`,
`ban`, `redact`, `kick`, `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.
2. If the new value is higher than the `sender`'s current power
level, reject.
4. For each entry being added, changed or removed in both the
`events` and `users` keys:
1. If the current value is higher than the `sender`'s current
power level, reject.
2. If the new value is higher than the `sender`'s current power
level, reject.
5. For each entry being changed under the `users` key, other than
the `sender`'s own entry:
1. If the current value is equal to the `sender`'s current
power level, reject.
6. Otherwise, allow.
11. If type is `m.room.redaction`:
1. If the `sender`'s power level is greater than or equal to the
*redact level*, allow.
2. If the domain of the `event_id` of the event being redacted is
the same as the domain of the `event_id` of the
`m.room.redaction`, allow.
3. Otherwise, reject.
12. Otherwise, allow.
{{% boxes/note %}}
Some consequences of these rules:
- Unless you are a member of the room, the only permitted operations
(apart from the initial create/join) are: joining a public room;
accepting or rejecting an invitation to a room.
- To unban somebody, you must have power level greater than or equal
to both the kick *and* ban levels, *and* greater than the target
user's power level.
{{% /boxes/note %}}
### Event format ### Event format
@ -280,6 +109,4 @@ Events in version 1 rooms have the following structure:
### Canonical JSON ### Canonical JSON
Servers MUST NOT strictly enforce the JSON format specified in the {{% rver-fragment name="v1-canonical-json" %}}
[appendices](/appendices#canonical-json) for the reasons
described there.

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@ -4,9 +4,15 @@ type: docs
weight: 20 weight: 20
--- ---
This room version builds off of [version 1](/rooms/v1) with an improved This room version builds on [version 1](/rooms/v1) with an improved
state resolution algorithm. state resolution algorithm.
## Client considerations
There are no client considerations introduced in this room version. Clients
which implement the redaction algorithm locally should refer to the
[redactions](#redactions) section below for a full overview of the algorithm.
## Server implementation components ## Server implementation components
{{% boxes/warning %}} {{% boxes/warning %}}
@ -21,168 +27,29 @@ changing only the state resolution algorithm.
### State resolution ### State resolution
The room state *S*′(*E*) after an event *E* is defined in terms of the {{% added-in this=true %}}
room state *S*(*E*) before *E*, and depends on whether *E* is a state
event or a message event: {{% rver-fragment name="v2-state-res" %}}
- If *E* is a message event, then *S*′(*E*) = *S*(*E*). ## Unchanged from v1
- If *E* is a state event, then *S*′(*E*) is *S*(*E*), except that its
entry corresponding to *E*'s `event_type` and `state_key` is The following sections have not been modified since v1, but are included for
replaced by *E*'s `event_id`. completeness.
The room state *S*(*E*) before *E* is the *resolution* of the set of ### Authorization rules
states {*S*′(*E*<sub>1</sub>), *S*′(*E*<sub>2</sub>), …} consisting of
the states after each of *E*'s `prev_event`s {{% rver-fragment name="v1-auth-rules" %}}
{*E*<sub>1</sub>, *E*<sub>2</sub>, …}, where the resolution of a set of
states is given in the algorithm below. ### Event format
#### Definitions Events in rooms of this version have the following structure:
The state resolution algorithm for version 2 rooms uses the following {{% definition path="api/server-server/definitions/pdu" %}}
definitions, given the set of room states
{*S*<sub>1</sub>, *S*<sub>2</sub>, …}: ### Canonical JSON
Power events {{% rver-fragment name="v1-canonical-json" %}}
A *power event* is a state event with type `m.room.power_levels` or
`m.room.join_rules`, or a state event with type `m.room.member` where ### Redactions
the `membership` is `leave` or `ban` and the `sender` does not match the
`state_key`. The idea behind this is that power events are events that {{% rver-fragment name="v1-redactions" %}}
might remove someone's ability to do something in the room.
Unconflicted state map and conflicted state set
The *unconflicted state map* is the state where the value of each key
exists and is the same in each state *S*<sub>*i*</sub>. The *conflicted
state set* is the set of all other state events. Note that the
unconflicted state map only has one event per `(event_type, state_key)`,
whereas the conflicted state set may have multiple events.
Auth difference
The *auth difference* is calculated by first calculating the full auth
chain for each state *S*<sub>*i*</sub>, that is the union of the auth
chains for each event in *S*<sub>*i*</sub>, and then taking every event
that doesn't appear in every auth chain. If *C*<sub>*i*</sub> is the
full auth chain of *S*<sub>*i*</sub>, then the auth difference is
 ∪ *C*<sub>*i*</sub> −  ∩ *C*<sub>*i*</sub>.
Full conflicted set
The *full conflicted set* is the union of the conflicted state set and
the auth difference.
Reverse topological power ordering
The *reverse topological power ordering* of a set of events is the
lexicographically smallest topological ordering based on the DAG formed
by auth events. The reverse topological power ordering is ordered from
earliest event to latest. For comparing two topological orderings to
determine which is the lexicographically smallest, the following
comparison relation on events is used: for events *x* and *y*,
*x* &lt; *y* if
1. *x*'s sender has *greater* power level than *y*'s sender, when
looking at their respective `auth_event`s; or
2. the senders have the same power level, but *x*'s `origin_server_ts`
is *less* than *y*'s `origin_server_ts`; or
3. the senders have the same power level and the events have the same
`origin_server_ts`, but *x*'s `event_id` is *less* than *y*'s
`event_id`.
The reverse topological power ordering can be found by sorting the
events using Kahn's algorithm for topological sorting, and at each step
selecting, among all the candidate vertices, the smallest vertex using
the above comparison relation.
Mainline ordering
Given an `m.room.power_levels` event *P*, the *mainline of* *P* is the
list of events generated by starting with *P* and recursively taking the
`m.room.power_levels` events from the `auth_events`, ordered such that
*P* is last. Given another event *e*, the *closest mainline event to*
*e* is the first event encountered in the mainline when iteratively
descending through the `m.room.power_levels` events in the `auth_events`
starting at *e*. If no mainline event is encountered when iteratively
descending through the `m.room.power_levels` events, then the closest
mainline event to *e* can be considered to be a dummy event that is
before any other event in the mainline of *P* for the purposes of
condition 1 below.
The *mainline ordering based on* *P* of a set of events is the ordering,
from smallest to largest, using the following comparison relation on
events: for events *x* and *y*, *x* &lt; *y* if
1. the closest mainline event to *x* appears *before* the closest
mainline event to *y*; or
2. the closest mainline events are the same, but *x*'s
`origin_server_ts` is *less* than *y*'s `origin_server_ts`; or
3. the closest mainline events are the same and the events have the
same `origin_server_ts`, but *x*'s `event_id` is *less* than *y*'s
`event_id`.
Iterative auth checks
The *iterative auth checks algorithm* takes as input an initial room
state and a sorted list of state events, and constructs a new room state
by iterating through the event list and applying the state event to the
room state if the state event is allowed by the [authorization
rules](/server-server-api#authorization-rules).
If the state event is not allowed by the authorization rules, then the
event is ignored. If a `(event_type, state_key)` key that is required
for checking the authorization rules is not present in the state, then
the appropriate state event from the event's `auth_events` is used if
the auth event is not rejected.
#### Algorithm
The *resolution* of a set of states is obtained as follows:
1. Take all *power events* and any events in their auth chains,
recursively, that appear in the *full conflicted set* and order them
by the *reverse topological power ordering*.
2. Apply the *iterative auth checks algorithm*, starting from the
*unconflicted state map*, to the list of events from the previous
step to get a partially resolved state.
3. Take all remaining events that weren't picked in step 1 and order
them by the mainline ordering based on the power level in the
partially resolved state obtained in step 2.
4. Apply the *iterative auth checks algorithm* on the partial resolved
state and the list of events from the previous step.
5. Update the result by replacing any event with the event with the
same key from the *unconflicted state map*, if such an event exists,
to get the final resolved state.
#### Rejected events
Events that have been rejected due to failing auth based on the state at
the event (rather than based on their auth chain) are handled as usual
by the algorithm, unless otherwise specified.
Note that no events rejected due to failure to auth against their auth
chain should appear in the process, as they should not appear in state
(the algorithm only uses events that appear in either the state sets or
in the auth chain of the events in the state sets).
{{% boxes/rationale %}}
This helps ensure that different servers' view of state is more likely
to converge, since rejection state of an event may be different. This
can happen if a third server gives an incorrect version of the state
when a server joins a room via it (either due to being faulty or
malicious). Convergence of state is a desirable property as it ensures
that all users in the room have a (mostly) consistent view of the state
of the room. If the view of the state on different servers diverges it
can lead to bifurcation of the room due to e.g. servers disagreeing on
who is in the room.
Intuitively, using rejected events feels dangerous, however:
1. Servers cannot arbitrarily make up state, since they still need to
pass the auth checks based on the event's auth chain (e.g. they
can't grant themselves power levels if they didn't have them
before).
2. For a previously rejected event to pass auth there must be a set of
state that allows said event. A malicious server could therefore
produce a fork where it claims the state is that particular set of
state, duplicate the rejected event to point to that fork, and send
the event. The duplicated event would then pass the auth checks.
Ignoring rejected events would therefore not eliminate any potential
attack vectors.
{{% /boxes/rationale %}}
Rejected auth events are deliberately excluded from use in the iterative
auth checks, as auth events aren't re-authed (although non-auth events
are) during the iterative auth checks.

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@ -20,6 +20,10 @@ Clients should expect to see event IDs changed from the format of
`$acR1l0raoZnm60CBwAVgqbZqoO/mYU81xysh1u7XcJk` (note the lack of domain `$acR1l0raoZnm60CBwAVgqbZqoO/mYU81xysh1u7XcJk` (note the lack of domain
and the potentially problematic slash). and the potentially problematic slash).
Though unchanged in this room version, clients which implement the
redaction algorithm locally should refer to the [redactions](#redactions)
section below for a full overview.
## Server implementation components ## Server implementation components
{{% boxes/warning %}} {{% boxes/warning %}}
@ -30,8 +34,8 @@ regarding client considerations is the resource that Client-Server API
use cases should reference. use cases should reference.
{{% /boxes/warning %}} {{% /boxes/warning %}}
Room version 3 uses the state resolution algorithm defined in [room Room version 3 uses the event format described here in addition to
version 2](/rooms/v2), and the event format defined here. all the remaining behaviour described by [room version 2](/rooms/v2).
### Event IDs ### Event IDs
@ -77,24 +81,34 @@ room version during a request.
### Authorization rules for events ### Authorization rules for events
The authorization rules for a given event have changed in this room {{% added-in this=true %}} `m.room.redaction` events are no longer
version due to the change in event format: explicitly part of the auth rules. They are still subject to the
minimum power level rules, but should always fall into "11. Otherwise,
- The event no longer needs to be signed by the domain of the event ID allow". Instead of being authorized at the time of receipt, they are
(as there is no domain in the event ID), but still needs to be authorized at a later stage: see the [Handling Redactions](#handling-redactions)
signed by the sender's domain. section below for more information.
- In past room versions, redactions were only permitted to enter the
DAG if the sender's domain matched the domain in the event ID being <!-- set withVersioning=true so we get all the "new in this version" stuff -->
redacted, or the sender had appropriate permissions per the power {{% rver-fragment name="v3-auth-rules" withVersioning=true %}}
levels. Due to servers now not being able to determine where an
event came from during event authorization, redaction events are ### Handling redactions
always accepted (provided the event is allowed by `events` and
`events_default` in the power levels). However, servers should not <!-- set withVersioning=true so we get all the "new in this version" stuff -->
apply or send redactions to clients until both the redaction event {{% rver-fragment name="v3-handling-redactions" withVersioning=true %}}
and original event have been seen, and are valid. Servers should
only apply redactions to events where the sender's domains match, or ## Unchanged from v2
the sender of the redaction has the appropriate permissions per the
power levels. The following sections have not been modified since v2, but are included for
completeness.
The remaining rules are the same as [room version
1](/rooms/v1#authorization-rules). ### State resolution
{{% rver-fragment name="v2-state-res" %}}
### Canonical JSON
{{% rver-fragment name="v1-canonical-json" %}}
### Redactions
{{% rver-fragment name="v1-redactions" %}}

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@ -19,6 +19,10 @@ Clients should expect to see event IDs changed from the format of
`$Rqnc-F-dvnEYJTyHq_iKxU2bZ1CI92-kuZq3a5lr5Zg` (note the lack of `$Rqnc-F-dvnEYJTyHq_iKxU2bZ1CI92-kuZq3a5lr5Zg` (note the lack of
domain). domain).
Though unchanged in this room version, clients which implement the
redaction algorithm locally should refer to the [redactions](#redactions)
section below for a full overview.
## Server implementation components ## Server implementation components
{{% boxes/warning %}} {{% boxes/warning %}}
@ -42,20 +46,37 @@ being interpretted differently by some reverse proxy software, and
generally made administration harder. generally made administration harder.
{{% /boxes/rationale %}} {{% /boxes/rationale %}}
The event ID is the [reference {{% rver-fragment name="v4-event-explainer" %}}
hash](/server-server-api#calculating-the-reference-hash-for-an-event) of
the event encoded using a variation of [Unpadded ## Unchanged from v3
Base64](/appendices#unpadded-base64) which replaces the 62nd and
63rd characters with `-` and `_` instead of using `+` and `/`. This The following sections have not been modified since v3, but are included for
matches [RFC4648's definition of URL-safe completeness.
base64](https://tools.ietf.org/html/rfc4648#section-5). Event IDs are
still prefixed with `$` and may result in looking like ### State resolution
`$Rqnc-F-dvnEYJTyHq_iKxU2bZ1CI92-kuZq3a5lr5Zg`.
{{% rver-fragment name="v2-state-res" %}}
Just like in room version 3, event IDs should not be sent over
federation to servers when the room uses this room version. On the ### Authorization rules
receiving end of an event, the server should compute the relevant event
ID for itself. Room version 3 also changes the format of `auth_events` {{% rver-fragment name="v3-auth-rules" %}}
and `prev_events` in a PDU.
### Handling redactions
{{% rver-fragment name="v3-handling-redactions" %}}
### Canonical JSON
{{% rver-fragment name="v1-canonical-json" %}}
### Redactions
{{% rver-fragment name="v1-redactions" %}}
### Event format
The event format is the same as [room version 3](/rooms/v3#event-ids),
however the event IDs in the following example are updated to reflect
the changes in this room version.
{{% definition path="api/server-server/definitions/pdu_v4" %}} {{% definition path="api/server-server/definitions/pdu_v4" %}}

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@ -9,9 +9,9 @@ key validity periods for events.
## Client considerations ## Client considerations
There are no specific requirements for clients in this room version. There are no client considerations introduced in this room version. Clients
Clients should be aware of event ID changes in [room version which implement the redaction algorithm locally should refer to the
4](/rooms/v4), however. [redactions](#redactions) section below for a full overview of the algorithm.
## Server implementation components ## Server implementation components
@ -28,18 +28,35 @@ Room version 5 uses the same algorithms defined in [room version
### Signing key validity period ### Signing key validity period
When validating event signatures, servers MUST enforce the {{% rver-fragment name="v5-signing-requirements" %}}
`valid_until_ts` property from a key request is at least as large as the
`origin_server_ts` for the event being validated. Servers missing a copy ## Unchanged from v4
of the signing key MUST try to obtain one via the [GET
/\_matrix/key/v2/server](/server-server-api#get_matrixkeyv2serverkeyid) The following sections have not been modified since v4, but are included for
or [POST completeness.
/\_matrix/key/v2/query](/server-server-api#post_matrixkeyv2query)
APIs. When using the `/query` endpoint, servers MUST set the ### State resolution
`minimum_valid_until_ts` property to prompt the notary server to attempt
to refresh the key if appropriate. {{% rver-fragment name="v2-state-res" %}}
Servers MUST use the lesser of `valid_until_ts` and 7 days into the ### Authorization rules
future when determining if a key is valid. This is to avoid a situation
where an attacker publishes a key which is valid for a significant {{% rver-fragment name="v3-auth-rules" %}}
amount of time without a way for the homeserver owner to revoke it.
### Handling redactions
{{% rver-fragment name="v3-handling-redactions" %}}
### Event format
{{% rver-fragment name="v4-event-explainer" %}}
{{% definition path="api/server-server/definitions/pdu_v4" %}}
### Canonical JSON
{{% rver-fragment name="v1-canonical-json" %}}
### Redactions
{{% rver-fragment name="v1-redactions" %}}

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@ -9,10 +9,17 @@ authorization rules performed on events.
## Client considerations ## Client considerations
The redaction algorithm has changed from [room version 1](/rooms/v1) to There are no client considerations introduced in this room version. Clients
remove all rules against events of type `m.room.aliases`. Room versions which implement the redaction algorithm locally should refer to the
2, 3, 4, and 5 all use v1's redaction algorithm. The algorithm is [redactions](#redactions) section below for a full overview of the algorithm.
otherwise unchanged.
### Redactions
{{% added-in this=true %}} All significant meaning for `m.room.aliases`
has been removed from the redaction algorithm. The remaining rules are
the same as past room versions.
{{% rver-fragment name="v6-redactions" %}}
## Server implementation components ## Server implementation components
@ -29,56 +36,180 @@ in [room version 5](/rooms/v5).
### Redactions ### Redactions
As mentioned in the client considerations portion of this specification, [See above](#redactions).
all special meaning has been removed for events of type
`m.room.aliases`. The algorithm is otherwise unchanged.
### Authorization rules for events ### Authorization rules for events
Like redactions, all rules relating specifically to events of type `m.room.redaction` events are not explicitly part of the auth rules.
`m.room.aliases` are removed. They must still pass authorization checks They are still subject to the minimum power level rules, but should always
relating to state events. fall into "10. Otherwise, allow". Instead of being authorized at the time
of receipt, they are authorized at a later stage: see the
[Handling Redactions](#handling-redactions) section below for more information.
Additionally, the authorization rules for events of type {{% added-in this=true %}} Rule 4, which related specifically to events
`m.room.power_levels` now include the content key `notifications`. This of type `m.room.aliases`, is removed. `m.room.aliases` events must still pass
new rule takes the place of the rule which checks the `events` and authorization checks relating to state events.
`users` keys.
For completeness, the changes to the auth rules can be represented as {{% added-in this=true %}} Additionally, the authorization rules for events
follows: of type `m.room.power_levels` now include the content key `notifications`.
This new rule takes the place of rule 10.4, which checked the `events` and
`users` keys.
... Events must be signed by the server denoted by the `sender` key.
The types of state events that affect authorization are:
- `m.room.create`
- `m.room.member`
- `m.room.join_rules`
- `m.room.power_levels`
- `m.room.third_party_invite`
{{% boxes/note %}}
Power levels are inferred from defaults when not explicitly supplied.
For example, mentions of the `sender`'s power level can also refer to
the default power level for users in the room.
{{% /boxes/note %}}
The rules are as follows:
1. If type is `m.room.create`:
1. If it has any previous events, reject.
2. If the domain of the `room_id` does not match the domain of the
`sender`, reject.
3. If `content.room_version` is present and is not a recognised
version, reject.
4. If `content` has no `creator` field, reject.
5. Otherwise, allow.
2. Reject if event has `auth_events` that:
1. have duplicate entries for a given `type` and `state_key` pair
2. have entries whose `type` and `state_key` don't match those
specified by the [auth events
selection](/server-server-api#auth-events-selection)
algorithm described in the server specification.
3. If event does not have a `m.room.create` in its `auth_events`,
reject.
4. If type is `m.room.member`:
1. If no `state_key` key or `membership` key in `content`, reject.
2. If `membership` is `join`:
1. If the only previous event is an `m.room.create` and the
`state_key` is the creator, allow.
2. If the `sender` does not match `state_key`, reject.
3. If the `sender` is banned, reject.
4. If the `join_rule` is `invite` then allow if membership
state is `invite` or `join`.
5. If the `join_rule` is `public`, allow.
6. Otherwise, reject.
3. If `membership` is `invite`:
1. If `content` has `third_party_invite` key:
1. If *target user* is banned, reject.
2. If `content.third_party_invite` does not have a `signed`
key, reject.
3. If `signed` does not have `mxid` and `token` keys,
reject.
4. If `mxid` does not match `state_key`, reject.
5. If there is no `m.room.third_party_invite` event in the
current room state with `state_key` matching `token`,
reject.
6. If `sender` does not match `sender` of the
`m.room.third_party_invite`, reject.
7. If any signature in `signed` matches any public key in
the `m.room.third_party_invite` event, allow. The public
keys are in `content` of `m.room.third_party_invite` as:
1. A single public key in the `public_key` field.
2. A list of public keys in the `public_keys` field.
8. Otherwise, reject.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If *target user*'s current membership state is `join` or
`ban`, reject.
4. If the `sender`'s power level is greater than or equal to
the *invite level*, allow.
5. Otherwise, reject.
4. If `membership` is `leave`:
1. If the `sender` matches `state_key`, allow if and only if
that user's current membership state is `invite` or `join`.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If the *target user*'s current membership state is `ban`,
and the `sender`'s power level is less than the *ban level*,
reject.
4. If the `sender`'s power level is greater than or equal to
the *kick level*, and the *target user*'s power level is
less than the `sender`'s power level, allow.
5. Otherwise, reject.
5. If `membership` is `ban`:
1. If the `sender`'s current membership state is not `join`,
reject.
2. If the `sender`'s power level is greater than or equal to
the *ban level*, and the *target user*'s power level is less
than the `sender`'s power level, allow.
3. Otherwise, reject.
6. Otherwise, the membership is unknown. Reject.
5. If the `sender`'s current membership state is not `join`, reject.
6. If type is `m.room.third_party_invite`:
1. Allow if and only if `sender`'s current power level is greater
than or equal to the *invite level*.
7. If the event type's *required power level* is greater than the
`sender`'s power level, reject.
8. If the event has a `state_key` that starts with an `@` and does not
match the `sender`, reject.
9. If type is `m.room.power_levels`:
1. If `users` key in `content` is not a dictionary with keys that
are valid user IDs with values that are integers (or a string
that is an integer), reject.
2. If there is no previous `m.room.power_levels` event in the room,
allow.
3. For the keys `users_default`, `events_default`, `state_default`,
`ban`, `redact`, `kick`, `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.
2. If the new value is higher than the `sender`'s current power
level, reject.
4. For each entry being added, changed or removed in both the
`events`, `users`, and `notifications` keys:
1. If the current value is higher than the `sender`'s current
power level, reject.
2. If the new value is higher than the `sender`'s current power
level, reject.
5. For each entry being changed under the `users` key, other than
the `sender`'s own entry:
1. If the current value is equal to the `sender`'s current
power level, reject.
6. Otherwise, allow.
10. Otherwise, allow.
{{% boxes/note %}}
Some consequences of these rules:
- Unless you are a member of the room, the only permitted operations
(apart from the initial create/join) are: joining a public room;
accepting or rejecting an invitation to a room.
- To unban somebody, you must have power level greater than or equal
to both the kick *and* ban levels, *and* greater than the target
user's power level.
{{% /boxes/note %}}
-If type is `m.room.aliases`: ### Canonical JSON
-
- a. If event has no `state_key`, reject.
- b. If sender's domain doesn't matches `state_key`, reject.
- c. Otherwise, allow.
... {{% rver-fragment name="v6-canonical-json" %}}
If type is `m.room.power_levels`: ## Unchanged from v5
... The following sections have not been modified since v5, but are included for
completeness.
- * For each entry being added, changed or removed in both the `events` and `users` keys: ### State resolution
+ * For each entry being added, changed or removed in the `events`, `users`, and `notifications` keys:
i. If the current value is higher than the `sender`'s current power level, reject. {{% rver-fragment name="v2-state-res" %}}
ii. If the new value is higher than the `sender`'s current power level, reject. ### Event format
... {{% rver-fragment name="v4-event-explainer" %}}
The remaining rules are the same as in [room version {{% definition path="api/server-server/definitions/pdu_v4" %}}
3](/rooms/v3#authorization-rules-for-events) (the last inherited room
version to specify the authorization rules).
### Canonical JSON ### Handling redactions
Servers MUST strictly enforce the JSON format specified in the {{% rver-fragment name="v3-handling-redactions" %}}
[appendices](/appendices#canonical-json). This translates to a
400 `M_BAD_JSON` error on most endpoints, or discarding of events over
federation. For example, the Federation API's `/send` endpoint would
discard the event whereas the Client Server API's `/send/{eventType}`
endpoint would return a `M_BAD_JSON` error.

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@ -12,6 +12,10 @@ as a possible join rule and membership state.
This is the first room version to support knocking completely. As such, This is the first room version to support knocking completely. As such,
users will not be able to knock on rooms which are not based off v7. users will not be able to knock on rooms which are not based off v7.
Though unchanged in this room version, clients which implement the
redaction algorithm locally should refer to the [redactions](#redactions)
section below for a full overview.
## Server implementation components ## Server implementation components
{{% boxes/warning %}} {{% boxes/warning %}}
@ -26,27 +30,183 @@ Room version 7 adds new authorization rules for events to support knocking.
[Room version 6](/rooms/v6) has details of other authorization rule changes, [Room version 6](/rooms/v6) has details of other authorization rule changes,
as do the versions v6 is based upon. as do the versions v6 is based upon.
{{% added-in this=true %}} For checks perfomed upon `m.room.member` events, the following conditions ### Authorization rules
are added in context:
{{% added-in this=true %}} For checks perfomed upon `m.room.member` events, a
If type is `m.room.member`: new point for `membership=knock` is added.
... Events must be signed by the server denoted by the `sender` key.
* If `membership` is `ban`: `m.room.redaction` events are not explicitly part of the auth rules.
They are still subject to the minimum power level rules, but should always
... fall into "10. Otherwise, allow". Instead of being authorized at the time
of receipt, they are authorized at a later stage: see the
* If `membership` is `knock`: [Redactions](#redactions) section below for more information.
i. If the `join_rule` is anything other than `knock`, reject. The types of state events that affect authorization are:
ii. If `sender` does not match `state_key`, reject. - `m.room.create`
- `m.room.member`
iii. If the `sender`'s current membership is not `ban`, `invite`, or `join`, allow. - `m.room.join_rules`
- `m.room.power_levels`
iv. Otherwise, reject. - `m.room.third_party_invite`
... {{% boxes/note %}}
Power levels are inferred from defaults when not explicitly supplied.
The remaining rules are the same as in [room version 6](/rooms/v6#authorization-rules-for-events). For example, mentions of the `sender`'s power level can also refer to
the default power level for users in the room.
{{% /boxes/note %}}
The rules are as follows:
1. If type is `m.room.create`:
1. If it has any previous events, reject.
2. If the domain of the `room_id` does not match the domain of the
`sender`, reject.
3. If `content.room_version` is present and is not a recognised
version, reject.
4. If `content` has no `creator` field, reject.
5. Otherwise, allow.
2. Reject if event has `auth_events` that:
1. have duplicate entries for a given `type` and `state_key` pair
2. have entries whose `type` and `state_key` don't match those
specified by the [auth events
selection](/server-server-api#auth-events-selection)
algorithm described in the server specification.
3. If event does not have a `m.room.create` in its `auth_events`,
reject.
4. If type is `m.room.member`:
1. If no `state_key` key or `membership` key in `content`, reject.
2. If `membership` is `join`:
1. If the only previous event is an `m.room.create` and the
`state_key` is the creator, allow.
2. If the `sender` does not match `state_key`, reject.
3. If the `sender` is banned, reject.
4. If the `join_rule` is `invite` then allow if membership
state is `invite` or `join`.
5. If the `join_rule` is `public`, allow.
6. Otherwise, reject.
3. If `membership` is `invite`:
1. If `content` has `third_party_invite` key:
1. If *target user* is banned, reject.
2. If `content.third_party_invite` does not have a `signed`
key, reject.
3. If `signed` does not have `mxid` and `token` keys,
reject.
4. If `mxid` does not match `state_key`, reject.
5. If there is no `m.room.third_party_invite` event in the
current room state with `state_key` matching `token`,
reject.
6. If `sender` does not match `sender` of the
`m.room.third_party_invite`, reject.
7. If any signature in `signed` matches any public key in
the `m.room.third_party_invite` event, allow. The public
keys are in `content` of `m.room.third_party_invite` as:
1. A single public key in the `public_key` field.
2. A list of public keys in the `public_keys` field.
8. Otherwise, reject.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If *target user*'s current membership state is `join` or
`ban`, reject.
4. If the `sender`'s power level is greater than or equal to
the *invite level*, allow.
5. Otherwise, reject.
4. If `membership` is `leave`:
1. If the `sender` matches `state_key`, allow if and only if
that user's current membership state is `invite` or `join`.
2. If the `sender`'s current membership state is not `join`,
reject.
3. If the *target user*'s current membership state is `ban`,
and the `sender`'s power level is less than the *ban level*,
reject.
4. If the `sender`'s power level is greater than or equal to
the *kick level*, and the *target user*'s power level is
less than the `sender`'s power level, allow.
5. Otherwise, reject.
5. If `membership` is `ban`:
1. If the `sender`'s current membership state is not `join`,
reject.
2. If the `sender`'s power level is greater than or equal to
the *ban level*, and the *target user*'s power level is less
than the `sender`'s power level, allow.
3. Otherwise, reject.
6. If `membership` is `knock`:
1. If the `join_rule` is anything other than `knock`, reject.
2. If `sender` does not match `state_key`, reject.
3. If the `sender`'s current membership is not `ban`, `invite`,
or `join`, allow.
7. Otherwise, the membership is unknown. Reject.
5. If the `sender`'s current membership state is not `join`, reject.
6. If type is `m.room.third_party_invite`:
1. Allow if and only if `sender`'s current power level is greater
than or equal to the *invite level*.
7. If the event type's *required power level* is greater than the
`sender`'s power level, reject.
8. If the event has a `state_key` that starts with an `@` and does not
match the `sender`, reject.
9. If type is `m.room.power_levels`:
1. If `users` key in `content` is not a dictionary with keys that
are valid user IDs with values that are integers (or a string
that is an integer), reject.
2. If there is no previous `m.room.power_levels` event in the room,
allow.
3. For the keys `users_default`, `events_default`, `state_default`,
`ban`, `redact`, `kick`, `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.
2. If the new value is higher than the `sender`'s current power
level, reject.
4. For each entry being added, changed or removed in both the
`events`, `users`, and `notifications` keys:
1. If the current value is higher than the `sender`'s current
power level, reject.
2. If the new value is higher than the `sender`'s current power
level, reject.
5. For each entry being changed under the `users` key, other than
the `sender`'s own entry:
1. If the current value is equal to the `sender`'s current
power level, reject.
6. Otherwise, allow.
10. Otherwise, allow.
{{% boxes/note %}}
Some consequences of these rules:
- Unless you are a member of the room, the only permitted operations
(apart from the initial create/join) are: joining a public room;
accepting or rejecting an invitation to a room.
- To unban somebody, you must have power level greater than or equal
to both the kick *and* ban levels, *and* greater than the target
user's power level.
{{% /boxes/note %}}
## Unchanged from v6
The following sections have not been modified since v6, but are included for
completeness.
### State resolution
{{% rver-fragment name="v2-state-res" %}}
### Event format
{{% rver-fragment name="v4-event-explainer" %}}
{{% definition path="api/server-server/definitions/pdu_v4" %}}
### Canonical JSON
{{% rver-fragment name="v6-canonical-json" %}}
### Signing key validity period
{{% rver-fragment name="v5-signing-requirements" %}}
### Redactions
{{% rver-fragment name="v3-handling-redactions" %}}
{{% rver-fragment name="v6-redactions" %}}

25
layouts/shortcodes/rver-fragment.html
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@ -0,0 +1,25 @@
{{/*
This template is used to render a "room version fragment". Fragments are blocks of
text which describe a portion of the room version specification. They should be
prefixed with the room version which introduces the fragment, and be reusable for
two or more versions.
The `name` parameter is the file name without extension.
The `withVersioning` parameter is optional and defaults to false. When true, any
mentions of "New in this version" from the `added-in` shortcode are removed prior
to rendering. This is useful if needing to use a fragment where part of it describes
new functionality in a given room version but isn't new for subsequent versions.
*/}}
{{ $name := .Params.name }}
{{ $withVersioning := .Params.withVersioning }}
{{ $page := .Site.GetPage (path.Join .Page.Dir "fragments" (printf "%s%s" $name ".md"))}}
{{ $content := $page.Content }}
{{ if not $withVersioning }}
{{ $content = (replace $content "[New in this version]" "") }}
{{ end }}
{{ $content | safeHTML }}
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