nips/704.md

NIP-704
======

Key derivation for Encrypted Direct Messages
-----------------------------------

`draft` `optional` `author:motorina0`

This NIP defines a way for two clients to derive `one-use-only` keys for sending and recieving `kind:4` events.

## Motivation
The content of `Direct Messages` [NIP-04](https://github.com/nostr-protocol/nips/blob/master/04.md) is encrypted, but everyone can see who is chatting with whom. This is far from ideal from a privacy perspective. 

This NIP describes a way to obfuscate DM communications from the "general public", it does not deal with the relay tracking of clients (for that see [NIP XXX](xxx)).

## Suggestion
For the maximum of privacy the two participants of a `Direct Message` exchange SHOULD use a different public key for **each** `kind:4` event.
This means that each participant has to:
 - build a `direct message parent key` from which it will derive keys to send and keys to recieve (listen for) `kind:4` events
 - share this `direct message parent key` with its DM peer

Each client has a `master` key (denoted with `m`). This key can be the profile `nsec...`, but it is not mandatory.

## Deriving the direct message parent key
[BIP32](https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki) is used to derive the paths. A client can generate multiple `direct message parent keys`, one for each peer that it is communicating with.

 Nostr `coin_type'` is `1237'` (see [NIP-06](https://github.com/nostr-protocol/nips/blob/master/06.md)). This NIP defines purpose `25709'` (`dm` -> `0x646d` -> `25709`) for deriving `Direct Messages` related keys.
 
 
`m/25709'/1237'/[<account>']`