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proposals/3813-obfuscated-events.md

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+# MSC3813: Obfuscated events
+
+## Introduction
+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.
+### 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.
+
+## Potential issues
+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.