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46 lines
2.2 KiB
Markdown
46 lines
2.2 KiB
Markdown
NIP-04
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======
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Encrypted Direct Message
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------------------------
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`final` `optional` `author:arcbtc`
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A special event with kind `4`, meaning "encrypted direct message". It is supposed to have the following attributes:
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**`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>"`.
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**`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>"]`.
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**`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>"]`.
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**Note**: By default in the [libsecp256k1](https://github.com/bitcoin-core/secp256k1) ECDH implementation, the secret is the SHA256 hash of the shared point (both X and Y coordinates). In Nostr, only the X coordinate of the shared point is used as the secret and it is NOT hashed. If using libsecp256k1, a custom function that copies the X coordinate must be passed as the `hashfp` argument in `secp256k1_ecdh`. See [here](https://github.com/bitcoin-core/secp256k1/blob/master/src/modules/ecdh/main_impl.h#L29).
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Code sample for generating such an event in JavaScript:
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```js
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import crypto from 'crypto'
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import * as secp from 'noble-secp256k1'
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let sharedPoint = secp.getSharedSecret(ourPrivateKey, '02' + theirPublicKey)
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let sharedX = sharedPoint.substr(2, 64)
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let iv = crypto.randomFillSync(new Uint8Array(16))
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var cipher = crypto.createCipheriv(
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'aes-256-cbc',
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Buffer.from(sharedX, 'hex'),
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iv
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)
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let encryptedMessage = cipher.update(text, 'utf8', 'base64')
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encryptedMessage += cipher.final('base64')
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let ivBase64 = Buffer.from(iv.buffer).toString('base64')
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let event = {
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pubkey: ourPubKey,
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created_at: Math.floor(Date.now() / 1000),
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kind: 4,
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tags: [['p', theirPublicKey]],
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content: encryptedMessage + '?iv=' + ivBase64
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}
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```
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