NIP-46
======

Nostr Remote Signing
--------------------

## Changes

`remote-signer-key` is introduced, passed in bunker url, clients must differentiate between `remote-signer-pubkey` and `user-pubkey`, must call `get_public_key` after connect, nip05 login is removed, create_account moved to another NIP.

## Rationale

Private keys should be exposed to as few systems - apps, operating systems, devices - as possible as each system adds to the attack surface.

This NIP describes a method for 2-way communication between a remote signer and a Nostr client. The remote signer could be, for example, a hardware device dedicated to signing Nostr events, while the client is a normal Nostr client.

## Terminology

- **user**: A person that is trying to use Nostr.
- **client**: A user-facing application that _user_ is looking at and clicking buttons in. This application will send requests to _remote-signer_.
- **remote-signer**: A daemon or server running somewhere that will answer requests from _client_, also known as "bunker".
- **client-keypair/pubkey**: The keys generated by _client_. Used to encrypt content and communicate with _remote-signer_.
- **remote-signer-keypair/pubkey**: The keys used by _remote-signer_ to encrypt content and communicate with _client_. This keypair MAY be same as _user-keypair_, but not necessarily.
- **user-keypair/pubkey**: The actual keys representing _user_ (that will be used to sign events in response to `sign_event` requests, for example). The _remote-signer_ generally has control over these keys.

All pubkeys specified in this NIP are in hex format.

## Overview

1. _client_ generates `client-keypair`. This keypair doesn't need to be communicated to _user_ since it's largely disposable. _client_ might choose to store it locally and they should delete it on logout;
2. A connection is established (see below), _remote-signer_ learns `client-pubkey`, _client_ learns `remote-signer-pubkey`.
3. _client_ uses `client-keypair` to send requests to _remote-signer_ by `p`-tagging and encrypting to `remote-signer-pubkey`;
4. _remote-signer_ responds to _client_ by `p`-tagging and encrypting to the `client-pubkey`.
5. _client_ requests `get_public_key` to learn `user-pubkey`.

## Initiating a connection

There are two ways to initiate a connection:

### Direct connection initiated by _remote-signer_

_remote-signer_ provides connection token in the form:

```
bunker://<remote-signer-pubkey>?relay=<wss://relay-to-connect-on>&relay=<wss://another-relay-to-connect-on>&secret=<optional-secret-value>
```

_user_ passes this token to _client_, which then sends `connect` request to _remote-signer_ via the specified relays. Optional secret can be used for single successfully established connection only, _remote-signer_ SHOULD ignore new attempts to establish connection with old secret. 

### Direct connection initiated by the _client_

_client_ provides a connection token in the form: 

```
nostrconnect://<client-pubkey>?relay=<wss://relay-to-connect-on>&metadata=<json metadata: {"name":"...", "url": "...", "description": "...", "perms": "..."}>&secret=<required-secret-value>
```
_user_ passes this token to _remote-signer_, which then sends `connect` *response* event to the `client-pubkey` via the specified relays. Client discovers `remote-signer-pubkey` from connect response author. `secret` value MUST be provided to avoid connection spoofing, _client_ MUST validate the `secret` returned by `connect` response.

## Request Events `kind: 24133`

```js
{
    "kind": 24133,
    "pubkey": <local_keypair_pubkey>,
    "content": <nip04(<request>)>,
    "tags": [["p", <remote-signer-pubkey>]],
}
```

The `content` field is a JSON-RPC-like message that is [NIP-04](04.md) encrypted and has the following structure:

```jsonc
{
    "id": <random_string>,
    "method": <method_name>,
    "params": [array_of_strings]
}
```

- `id` is a random string that is a request ID. This same ID will be sent back in the response payload.
- `method` is the name of the method/command (detailed below).
- `params` is a positional array of string parameters.

### Methods/Commands

Each of the following are methods that the _client_ sends to the _remote-signer_.

| Command                  | Params                                                                        | Result                                                                 |
| ------------------------ | -------------------------------------------------                             | ---------------------------------------------------------------------- |
| `connect`                | `[<remote-signer-pubkey>, <optional_secret>, <optional_requested_permissions>]`        | "ack" OR `<required-secret-value>`                                                                  |
| `sign_event`             | `[<{kind, content, tags, created_at}>]`                                       | `json_stringified(<signed_event>)`                                     |
| `ping`                   | `[]`                                                                          | "pong"                                                                 |
| `get_relays`             | `[]`                                                                          | `json_stringified({<relay_url>: {read: <boolean>, write: <boolean>}})` |
| `get_public_key`         | `[]`                                                                          | `<user-pubkey>`                                                         |
| `nip04_encrypt`          | `[<third_party_pubkey>, <plaintext_to_encrypt>]`                              | `<nip04_ciphertext>`                                                   |
| `nip04_decrypt`          | `[<third_party_pubkey>, <nip04_ciphertext_to_decrypt>]`                       | `<plaintext>`                                                          |
| `nip44_encrypt`          | `[<third_party_pubkey>, <plaintext_to_encrypt>]`                              | `<nip44_ciphertext>`                                                   |
| `nip44_decrypt`          | `[<third_party_pubkey>, <nip44_ciphertext_to_decrypt>]`                       | `<plaintext>`                                                          |

### Requested permissions

The `connect` method may be provided with `optional_requested_permissions` for user convenience. The permissions are a comma-separated list of `method[:params]`, i.e. `nip04_encrypt,sign_event:4` meaning permissions to call `nip04_encrypt` and to call `sign_event` with `kind:4`. Optional parameter for `sign_event` is the kind number, parameters for other methods are to be defined later. Same permission format may be used for `perms` field of `metadata` in `nostrconnect://` string.

## Response Events `kind:24133`

```json
{
    "id": <id>,
    "kind": 24133,
    "pubkey": <remote-signer-pubkey>,
    "content": <nip04(<response>)>,
    "tags": [["p", <client-pubkey>]],
    "created_at": <unix timestamp in seconds>
}
```

The `content` field is a JSON-RPC-like message that is [NIP-04](04.md) encrypted and has the following structure:

```json
{
    "id": <request_id>,
    "result": <results_string>,
    "error": <optional_error_string>
}
```

- `id` is the request ID that this response is for.
- `results` is a string of the result of the call (this can be either a string or a JSON stringified object)
- `error`, _optionally_, it is an error in string form, if any. Its presence indicates an error with the request.

## Example flow for signing an event

- `remote-signer-pubkey` is `fa984bd7dbb282f07e16e7ae87b26a2a7b9b90b7246a44771f0cf5ae58018f52`
- `user-pubkey` is also `fa984bd7dbb282f07e16e7ae87b26a2a7b9b90b7246a44771f0cf5ae58018f52`
- `client-pubkey` is `eff37350d839ce3707332348af4549a96051bd695d3223af4aabce4993531d86`

### Signature request

```js
{
    "kind": 24133,
    "pubkey": "eff37350d839ce3707332348af4549a96051bd695d3223af4aabce4993531d86",
    "content": nip04({
        "id": <random_string>,
        "method": "sign_event",
        "params": [json_stringified(<{
            content: "Hello, I'm signing remotely",
            kind: 1,
            tags: [],
            created_at: 1714078911
        }>)]
    }),
    "tags": [["p", "fa984bd7dbb282f07e16e7ae87b26a2a7b9b90b7246a44771f0cf5ae58018f52"]], // p-tags the remote-signer-pubkey
}
```

### Response event

```js
{
    "kind": 24133,
    "pubkey": "fa984bd7dbb282f07e16e7ae87b26a2a7b9b90b7246a44771f0cf5ae58018f52",
    "content": nip04({
        "id": <random_string>,
        "result": json_stringified(<signed-event>)
    }),
    "tags": [["p", "eff37350d839ce3707332348af4549a96051bd695d3223af4aabce4993531d86"]], // p-tags the client-pubkey
}
```

### Diagram

![signing-example](https://i.nostr.build/P3gW.png)


## Auth Challenges

An Auth Challenge is a response that a _remote-signer_ can send back when it needs the _user_ to authenticate via other means. The response `content` object will take the following form:

```json
{
    "id": <request_id>,
    "result": "auth_url",
    "error": <URL_to_display_to_end_user>
}
```

_client_ should display (in a popup or new tab) the URL from the `error` field and then subscribe/listen for another response from the _remote-signer_ (reusing the same request ID). This event will be sent once the user authenticates in the other window (or will never arrive if the user doesn't authenticate).

### Example event signing request with auth challenge

![signing-example-with-auth-challenge](https://i.nostr.build/W3aj.png)

## Appendix

### Announcing _remote-signer_ metadata

_remote-signer_ MAY publish it's metadata by using [NIP-05](05.md) and [NIP-89](89.md). With NIP-05, a request to `<remote-signer>/.well-known/nostr.json?name=_` MAY return this:
```
{
    "names":{
        "_": <remote-signer-app-pubkey>,
    },
    "nip46": {
        "relays": ["wss://relay1","wss://relay2"...],
        "nostrconnect_url": "https://remote-signer-domain.com/<nostrconnect>"
    }
}
```

The `<remote-signer-app-pubkey>` MAY be used to verify the domain from _remote-signer_'s NIP-89 event (see below). `relays` SHOULD be used to construct a more precise `nostrconnect://` string for the specific `remote-signer`. `nostrconnect_url` template MAY be used to redirect users to _remote-signer_'s connection flow by replacing `<nostrconnect>` placeholder with an actual `nostrconnect://` string.

### Remote signer discovery via NIP-89

_remote-signer_ MAY publish a NIP-89 `kind: 31990` event with `k` tag of `24133`, which MAY also include one or more `relay` tags and MAY include `nostrconnect_url` tag. The semantics of `relay` and `nostrconnect_url` tags are the same as in the section above.

_client_ MAY improve UX by discovering _remote-signers_ using their `kind: 31990` events. _client_ MAY then pre-generate `nostrconnect://` strings for the _remote-signers_, and SHOULD in that case verify that `kind: 31990` event's author is mentioned in signer's `nostr.json?name=_` file as `<remote-signer-app-pubkey>`.