matrix-spec-proposals/proposals/3813-obfuscated-events.md

MSC3813: Obfuscated events

Currently, event content can be end-to-end encrypted, but the metadata cannot. This means that if someone inspects the Matrix homeservers, they can see in what rooms one is most active, and at what time they are most active.

We propose that clients send "dummy" events from time to time, at random intervals and times, in random rooms to obfuscate the user's online times and relationships. It is mainly intended to imitate the structure of two-sided conversations.

Proposal

TBD

Introduction

TBD

Events

We add the following types of events:

m.obfuscate.request

Initiates a request to send obfuscated events to the other party.

Content attributes:

Name	Type	Comments
version	string	Must be v0.
min_interval	number	Minimum interval, in seconds, between two keepalive events.
max_interval	number	Maximum interval, in seconds, between two keepalive events.
retries	number	The number of retries that can be sent in keepalive events if the other party does not respond in a timely manner.
payload	string	Can be arbitrary content.

The attributes min_interval, max_interval and retries indicates the parameters this party will stick to, not the parameters it expects the other party to stick to.

m.obfuscate.accept

Indicates that this party is willing to exchange obfuscated events with the other party.

Name	Type	Comments
version	string	Must be v0.
min_interval	number	Minimum interval, in seconds, between two keepalive events.
max_interval	number	Maximum interval, in seconds, between two keepalive events.
retries	number	The number of retries that can be sent in keepalive events if the other party does not respond in a timely manner.
payload	string	Can be arbitrary content.

The attributes min_interval, max_interval and retries indicates the parameters this party will stick to, not the parameters it expects the other party to stick to.

m.obfuscate.reject

Indicates that this party is not willing to exchange obfuscated events with the other party, or wants to stop doing so.

Name	Type	Comments
version	string	Must be v0.
duration	number	Tells the other party how long, in seconds, they should not send a request again. -1 means they should never send requests again. 0 means they can send again immediately.
payload	string	Can be arbitrary content.

m.obfuscate.keepalive

The keepalive message that imitates the structure of a conversation.

Name	Type	Comments
version	string	Must be v0.
payload	string	Can be arbitrary content.

Client behaviour

Clients MUST negotiate to exchange obfuscated events before sending the keepalive messages.

Server behaviour

TBD

Potential issues

TBD

Alternatives

TBD

Security considerations

The events MUST be sent in end-to-end encrypted rooms.

The payload SHOULD be randomly generated, and with random lengths. It SHOULD ideally be similar in length to other non-obfuscated events in the room.

Unstable prefix

Please use moe.kazv.mxc.msc.obfuscated-events as the unstable prefix.

Dependencies

No hard dependencies.