nips/71.md

NIP-71
======

Restricted Events
-----------------------------------

`draft` `optional`

When the `"+"` tag is present, that means the event is "restricted".

A restricted event is an event which requires [NIP-42 Authentication of Clients to Relays](https://github.com/nostr-protocol/nips/blob/master/42.md) in order to request. These events can only be requested by:

- the author of the event
- a user tagged in the event
- a user who has [NIP-43 Delegated Authentication](https://github.com/nostr-protocol/nips/blob/master/43.md) from the author

The default behavior of a relay MUST be to reject any event that contains `["+"]`.

Relays that want to accept such events MUST first require that clients requesting restricted events perform the [NIP-42](https://github.com/nostr-protocol/nips/blob/master/42.md) `AUTH` flow and check that the authenticated user has the appropriate access for the requested restriced events.

## The tag

The tag is a simple tag with a single item: `["+"]`. It may be added to any event.

## Use Cases

- limiting metadata leakage of private chats
- limiting access to content to only paid subscribers
- limiting metadata leakage of personal events (like a journal or private calendar)

## Requesting

In order to `REQ` for a restricted event, the filter MUST have (a) attibute `"restricted": true` to specify the filter is requesting restricted events AND
(b) either `"authors"` attribute or `"#p"` attribute to establish the pubkey that authentication should be validated for.

If (b) is missing from the filter, the request is invalid and the relay should response with `CLOSED` message with prefix `"invalid"`.

If the filter does not contain the `"restricted": true` attribute, the relay MUST behave as if it does not store any restricted events. Specifically, the relay MUST NOT:

- respond with `CLOSED` and `"auth-required"` prefix
- request authentication
- return any restricted events

in response to a request. Even if there are restricted events that qualify for the filter, if the filter doesn't not have attribute `"restricted": true` the relay should behave as if those events are not stored on the relay. This is so that unauthenticated clients are unable to glean any information on what restricted events might be stored on the relay.

## Access

A user has permission to request any restricted event for which they are the author by:

- authenticating as the author
- authenticating with a delegated authentication token of mode 0-Login from the author


A user has permission to request any restricted event in which their pubkey is tagged by:

- authenticating as the tagged pubkey
- authenticating with a delegated authentication token of mode 0-Login from the tagged pubkey

A user has permission to request any restricted event they have been granted access to by the delegated authentication tokens of mode 1-Restricted Event Permission they authenticate with. The filter used MUST BE narrower in scope than the filter condition of the delegated authentication token.

## Flow

- User `abc...` connects to relay `wss://example.com`:

```jsonc
/* client: */
["REQ", "sub_1", {"authors": ["abc..."], "restricted": true}]
/* relay: */
["AUTH", "challenge_string"]
["CLOSED", "sub_1", "auth-required: cannot serve restricted events to unauthenticated useres"]
/* client: */
["AUTH", {"id": "wxyz...", "pubkey": "abc...", "kind": 22242, "tags": [["relay", "wss://example.com"], ["challenge", "challenge_string"]], ...}]
/* relay: */
["OK", "wxyz...", true, ""]
/* client: */
["REQ", "sub_1", {"authors": ["abc..."], "restricted": true}]
/* relay: */
["EVENT", "sub_1", {...}]
["EVENT", "sub_1", {...}]
["EVENT", "sub_1", {...}]
["EVENT", "sub_1", {...}]
```