nips/04.md

NIP-04
======

Encrypted Direct Message
------------------------

`final` `optional` `author:arcbtc`

A special event with kind `4`, meaning "encrypted direct message". It is supposed to have the following attributes:

**`content`** MUST be equal to the base64-encoded, aes-256-cbc encrypted string of anything a user wants to write, encrypted using a shared cipher generated by combining the recipient's public-key with the sender's private-key; this appended by the base64-encoded initialization vector as if it was a querystring parameter named "iv". The format is the following: `"content": "<encrypted_text>?iv=<initialization_vector>"`.

**`tags`** MUST contain an entry identifying the receiver of the message (such that relays may naturally forward this event to them), in the form `["p", "<pubkey, as a hex string>"]`.

**`tags`** MAY contain an entry identifying the previous message in a conversation or a message we are explicitly replying to (such that contextual, more organized conversations may happen), in the form `["e", "<event_id>"]`.

Code sample for generating such an event in JavaScript:

```js
import crypto from 'crypto'
import * as secp from 'noble-secp256k1'

let sharedPoint = secp.getSharedSecret(ourPrivateKey, '02' + theirPublicKey)
let sharedX = sharedPoint.substr(2, 64)

let iv = crypto.randomFillSync(new Uint8Array(16))
var cipher = crypto.createCipheriv(
  'aes-256-cbc',
  Buffer.from(sharedX, 'hex'),
  iv
)
let encryptedMessage = cipher.update(text, 'utf8', 'base64')
encryptedMessage += cipher.final('base64')
let ivBase64 = Buffer.from(iv.buffer).toString('base64')

let event = {
  pubkey: ourPubKey,
  created_at: Math.floor(Date.now() / 1000),
  kind: 4,
  tags: [['p', theirPublicKey]],
  content: encryptedMessage + '?iv=' + ivBase64
}
```