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67 lines
3.3 KiB
Markdown
67 lines
3.3 KiB
Markdown
NIP-704
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======
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Key derivation for Encrypted Direct Messages
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-----------------------------------
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`draft` `optional` `author:motorina0`
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This NIP defines a way for two clients to derive `one-use-only` keys for sending and recieving `kind:4` events.
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## Motivation
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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.
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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)).
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## Suggestion
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For the maximum of privacy the two participants of a `Direct Message` exchange SHOULD use a different public key for **each** `kind:4` event.
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This means that each participant has to:
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- build a `direct message parent key` from which it will derive keys to send and keys to receive (listen for) `kind:4` events
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- share this `direct message parent key` with its DM peer
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Each client has a `master` key (denoted with `m`). This key can be the profile `nsec...`, but it is not mandatory.
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## Derive the direct message parent key
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[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)). In this NIP we define the purpose `25709'` (`dm` -> `0x646d` -> `25709`) for deriving `Direct Messages` related keys.
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When client `Alice` wants to build its `dm parent key` for `Bob` it has to:
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- get the public key of `Bob` (in hex). Eg: `3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d`.
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- split the public key hex string in 8 chunks:
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- `3bf0c63f`, `cb934634`, `07af97a5`, `e5ee64fa`, `883d107e`, `f9e55847`, `2c4eb9aa`, `aefa459d`
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- derive the `dm parent key`: `m/25709'/1237'/p1'/p2'/.../p8'`
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> **Note** the reason for using the peer's public key (`Bob`) in the `dm parent key` derivation is to always arive at the same value even if prio state is lost.
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>
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> **Note** the reason for splitting is that each level of the path can have a max value of 2<sup>32</sup>-1.
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dm/<action>/index
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send, receive, marketplace
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## Exchange the `direct message parent key`
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If `Alice` wants to signal `Bob` that she is ready to use this NIP (for more privacy) she must:
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- build a JSON data of the form:
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```json
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{
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"key": <the direct message parent key>,
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"send_index": <integer (optional), ...>,
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"receive_index": <integer (optional), ...>,
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}
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```
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- publish a `Parameterized Replaceable Event` ([NIP-33](https://github.com/nostr-protocol/nips/blob/master/33.md)) having:
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```json
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{
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...
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"kind": 35709,
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"content": <NIP-04 encrypted content of the JSON data>,
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"tags:" [
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"d": <sha256 of the shared secret as defined in NIP-04>
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]
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}
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```
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> **Note** the reason for using `sha256(shared_secret)` for the `d` tag is so that outside observers do not even know that `Alice` and `Bob` have started to communicate. Any other value for the `d` tag would reveal that the message is intended for `Bob.`
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After both `Alice` and `Bob` have published the `kind: 35709` event, they can start to publish and listen to events using the `one-use-keys`.
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