NIP-17
======

Private Direct Messages
-----------------------

`draft` `optional` `relay`

This NIP defines an encrypted chat scheme which uses [NIP-44](44.md) encryption and [NIP-59](59.md) gift-wrapping.

By convention, `kind 14` direct messages, `kind 15` file messages, and [`kind 7` reactions](./25.md) may be sent to an encrypted chat. See [Message Rumor Definitions](#message-rumor-definitions) below.

## Chat Rooms

The most common use case is a room with only two peers, but more than one person per room is supported.

The set of `pubkey` + `p` tags defines a chat room. If a new `p` tag is added or a current one is removed, a new room is created with a clean message history.

An optional `subject` tag defines the current name/topic of the conversation. Any member can change the topic by simply submitting a new `subject` to an existing `pubkey` + `p` tags room. There is no need to send `subject` in every message. The newest `subject` in the chat room is the subject of the conversation.

## Encrypting

Following [NIP-59](59.md), the **unsigned** chat messages must be sealed (`kind:13`) and then gift-wrapped (`kind:1059`) to each receiver and the sender individually.

```js
{
  "id": "<usual hash>",
  "pubkey": wrapperPublicKey,
  "created_at": randomTimeUpTo2DaysInThePast,
  "kind": 1059, // gift wrap
  "tags": [
    ["p", receiverPublicKey, "<relay-url>"] // receiver
  ],
  "content": nip44.encrypt(
    {
      "id": "<usual hash>",
      "pubkey": senderPublicKey,
      "created_at": randomTimeUpTo2DaysInThePast,
      "kind": 13, // seal
      "tags": [], // no tags
      "content": nip44.encrypt(
        unsignedMessageRumor,
        nip44.compute_conversation_key(senderPrivateKey, receiverPublicKey)
      ),
      "sig": "<signed by senderPrivateKey>"
    },
    nip44.compute_conversation_key(wrapperPrivateKey, receiverPublicKey)
  ),
  "sig": "<signed by randomPrivateKey>"
}
```

`unsignedMessageRumor` is a rumor (an unsigned event, as per [NIP-59](59.md)), usually a `kind:14`, but could also be a different kind, see [Message Rumor Definitions](#message-rumor-definitions) below.

`wrapperPrivateKey` and `wrappedPublicKey` are a new keypair, generated randomly anew for each message sent.

Clients MUST verify if pubkey of the `kind:13` is the same pubkey as that of the `unsignedMessageRumor`, otherwise any sender can impersonate any other by simply changing the pubkey on the rumor.

Clients SHOULD randomize `created_at` in up to two days in the past in both the seal and the gift wrap to make sure grouping by `created_at` doesn't reveal any metadata.

## Publishing

Kind `10050` indicates the user's preferred relays to receive DMs. The event MUST include a list of `relay` tags with relay URIs.

```yaml
{
  "kind": 10050,
  "tags": [
    ["relay", "wss://inbox.nostr.wine"],
    ["relay", "wss://myrelay.nostr1.com"],
  ],
  "content": "",
  // other fields...
}
```

Clients MUST only publish events to the relays listed in the recipient’s kind 10050 event. If such a list is not found that indicates the user is not ready to receive messages and clients shouldn't try.

## Relays

Relays SHOULD protect message metadata by only serving `kind:1059` events to users p-tagged on the event (enforced using [NIP-42 AUTH](./42.md)).

Clients SHOULD guide users to keep `kind:10050` lists small (1-3 relays) and SHOULD spread them to as many relays as viable.

## Delete, edit and disappearing messages

In addition to the deletion behavior specified in [NIP 59](59.md), in which gift wraps can be deleted by the `p`-tagged recipient, clients MAY also allow users to delete messages by wrapping a `kind:5` delete event in a `kind:1059` gift wrap and sending it to the recipient as part of the conversation. Clients SHOULD remove deleted messages from the conversation, or indicate whether a message has been deleted.

Clients MAY implement edit by deleting an event and publishing another one with the same timestamp.

Clients MAY offer disappearing messages by setting an `expiration` tag in the gift wrap of each receiver or by not generating a gift wrap to the sender's public key. This tag SHOULD be included on the `kind:13` seal as well, in case it leaks.

## Benefits & Limitations

This NIP offers the following privacy and security features:

1. **No Metadata Leak**: Participant identities, each message's real date and time, event kinds, and other event tags are all hidden from the public. Senders and receivers cannot be linked with public information alone.
2. **No Public Group Identifiers**: There is no public central queue, channel or otherwise converging identifier to correlate or count all messages in the same group.
3. **No Moderation**: There are no group admins: no invitations or bans.
4. **No Shared Secrets**: No secret must be known to all members that can leak or be mistakenly shared
5. **Fully Recoverable**: Messages can be fully recoverable by any client with the user's private key
6. **Optional Forward Secrecy**: Users and clients can opt-in for "disappearing messages".
7. **Uses Public Relays**: Messages can flow through public relays without loss of privacy. Private relays can increase privacy further, but they are not required.
8. **Cold Storage**: Users can unilaterally opt-in to sharing their messages with a separate key that is exclusive for DM backup and recovery.

The main limitation of this approach is having to send a separate encrypted event to each receiver. Group chats with more than 10 participants should find a more suitable messaging scheme.

## Spam

Since the wrapper events use random keys, relays cannot apply traditional anti-spam based on pubkey reputation, WoT, etc, therefore a naïve implementation of this NIP is an spam target. The recommended approach for spam mitigation is described in the [Spam Protection section of NIP-59](59.md#spam-protection).

## Message Rumor Definitions

### Chat Message

Kind `14` is a chat message. `p` tags identify one or more receivers of the message.

```yaml
{
  "pubkey": "<sender-pubkey>",
  "created_at": "<current-time>",
  "kind": 14,
  "tags": [
    ["p", "<receiver-1-pubkey>", "<relay-url>"],
    ["p", "<receiver-2-pubkey>", "<relay-url>"],
    ["e", "<kind-14-id>", "<relay-url>"] // if this is a reply
    ["subject", "<conversation-title>"],
    // rest of tags...
  ],
  "content": "<message-in-plain-text>",
}
```

`.content` MUST be plain text. Fields `id` and `created_at` are required.

An `e` tag denotes the direct parent message this post is replying to.

`q` tags MAY be used when citing events in the `.content` with [NIP-21](21.md).

```json
["q", "<event-id> or <event-address>", "<relay-url>", "<pubkey-if-a-regular-event>"]
```

## File Message

```yaml
{
  "pubkey": "<sender-pubkey>",
  "created_at": "<current-time>",
  "kind": 15,
  "tags": [
    ["p", "<receiver-1-pubkey>", "<relay-url>"],
    ["p", "<receiver-2-pubkey>", "<relay-url>"],
    ["e", "<kind-14-id>", "<relay-url>", "reply"], // if this is a reply
    ["subject", "<conversation-title>"],
    ["file-type", "<file-mime-type>"],
    ["encryption-algorithm", "<encryption-algorithm>"],
    ["decryption-key", "<decryption-key>"],
    ["decryption-nonce", "<decryption-nonce>"],
    ["x", "<the SHA-256 hexencoded string of the file>"],
    // rest of tags...
  ],
  "content": "<file-url>"
}
```

Kind `15` is used for sending encrypted file event messages:

- `file-type`: Specifies the MIME type of the attached file (e.g., `image/jpeg`, `audio/mpeg`, etc.) before encryption.
- `encryption-algorithm`: Indicates the encryption algorithm used for encrypting the file. Supported algorithms: `aes-gcm`.
- `decryption-key`: The decryption key that will be used by the recipient to decrypt the file.
- `decryption-nonce`: The decryption nonce that will be used by the recipient to decrypt the file.
- `content`: The URL of the file (`<file-url>`).
- `x` containing the SHA-256 hexencoded string of the encrypted file.
- `ox` containing the SHA-256 hexencoded string of the file before encryption.
- `size` (optional) size of the encrypted file in bytes
- `dim` (optional) size in pixels in the form `<width>x<height>`
- `thumbhash`(optional) the [thumbhash](https://evanw.github.io/thumbhash/) to show while the client is loading the file
- `blurhash`(optional) the [blurhash](https://github.com/woltapp/blurhash) to show while the client is loading the file
- `thumb` (optional) URL of thumbnail with same aspect ratio (encrypted with the same key, nonce)
- `fallback` (optional) zero or more fallback file sources in case `url` fails (encrypted with the same key, nonce)


## Examples

This example sends the message `Hola, que tal?` from `nsec1w8udu59ydjvedgs3yv5qccshcj8k05fh3l60k9x57asjrqdpa00qkmr89m` to `nsec12ywtkplvyq5t6twdqwwygavp5lm4fhuang89c943nf2z92eez43szvn4dt`.

The two final GiftWraps, one to the receiver and the other to the sender, respectively, are:

```json
{
   "id":"2886780f7349afc1344047524540ee716f7bdc1b64191699855662330bf235d8",
   "pubkey":"8f8a7ec43b77d25799281207e1a47f7a654755055788f7482653f9c9661c6d51",
   "created_at":1703128320,
   "kind":1059,
   "tags":[
      ["p", "918e2da906df4ccd12c8ac672d8335add131a4cf9d27ce42b3bb3625755f0788"]
   ],
   "content":"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",
   "sig":"a3c6ce632b145c0869423c1afaff4a6d764a9b64dedaf15f170b944ead67227518a72e455567ca1c2a0d187832cecbde7ed478395ec4c95dd3e71749ed66c480"
}
```

```json
{
   "id":"162b0611a1911cfcb30f8a5502792b346e535a45658b3a31ae5c178465509721",
   "pubkey":"626be2af274b29ea4816ad672ee452b7cf96bbb4836815a55699ae402183f512",
   "created_at":1702711587,
   "kind":1059,
   "tags":[
      ["p", "44900586091b284416a0c001f677f9c49f7639a55c3f1e2ec130a8e1a7998e1b"]
   ],
   "content":"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",
   "sig":"c94e74533b482aa8eeeb54ae72a5303e0b21f62909ca43c8ef06b0357412d6f8a92f96e1a205102753777fd25321a58fba3fb384eee114bd53ce6c06a1c22bab"
}
```