NIP-4B
======

nsec Transfer
--------------------

`draft` `optional`

This NIP defines how to accomplish nsec transfer from client to client including browser extensions or signers.

## Terminology

- **Source client**: A client that holds the user's nsec.
- **Destination client**: A client that doesn't have the user's nsec and wants it.
- **Ephemeral pubkey**: A pubkey of a key pair generated for one-time use only.

## Flow

### 1. The destination client creates a transfer request URL.

1. The client generates an ephemeral pubkey.
2. The client creates a transfer request URL, which includes the ephemeral pubkey and relay URLs.
3. The client shows the user the URL. The client MAY show the user a QR code.
4. The client subscribes to the relays and waits for the kind-1059 response, which includes the `["p", "<destination client's ephemeral pubkey>"]` tag.


#### Transfer request URL

```
transfer://<destination client's ephemeral pubkey>?relay=<relay URL>&relay=<relay URL>
```

### 2. The source client responds with gift-wrapped ncryptsec.

1. The user enters the transfer request URL.
2. The client parses the URL.
3. The client generates an ncryptsec ([NIP-49](./49.md)) from the user's nsec and a random 6-digit PIN.
4. The client creates an ncryptsec rumor ([NIP-59](./59.md)) event.
5. The client seals and gift-wraps the rumor event.
6. The client publishes the gift-wrapped event to the destination's relays.
7. The client shows the user the PIN.

#### ncryptsec rumor event

`kind: 24144`

This event MUST NOT be signed.

```jsonc
{
    "kind": 24144,
    "pubkey": "<source client's ephemeral pubkey A>",
    "content": "<ncryptsec>",
    // ...
}
```

#### Sealed event

```jsonc
{
  "pubkey": "<source client's ephemeral pubkey A>",
  "content": "<NIP-44 encrypted ncryptsec rumor event>",
  "kind": 13,
  "sig": "<source client's ephemeral pubkey A signature>"
  // ...
}
```

#### Gift-wrapped event

`source client's ephemeral pubkey B` MUST NOT be the same as `A` described above.

```jsonc
{
  "pubkey": "<source client's ephemeral pubkey B>",
  "content": "<NIP-44 encrypted sealed event>",
  "kind": 1059,
  "tags": [["p", "<destination client's ephemeral pubkey>"]],
  "sig": "<source client's ephemeral pubkey B signature>"
  // ...
}
```

### 3. The destination client fetches the response.

1. The client fetches and validates the gift-wrapped event.
2. The client prompts the user to enter the PIN.
3. If the PIN is valid, the client retrieves the user's nsec from the ncryptsec.