Dispute Chat

The dispute chat uses the same shared key encryption scheme as the Peer-to-peer Chat. Instead of computing a shared key between buyer and seller, each party computes an independent shared key with the admin who took the dispute.

Establishing the shared key

When an admin takes a dispute, Mostro sends an admin-took-dispute message to each party (buyer and seller) containing the admin's pubkey:

[
  {
    "order": {
      "version": 1,
      "id": "<Order Id>",
      "action": "admin-took-dispute",
      "payload": {
        "peer": {
          "pubkey": "<Admin's pubkey>"
        }
      }
    }
  },
  null
]

Upon receiving this message, the client computes the shared key using ECDH:

Shared Key = ECDH(tradeKey.private, adminPubkey)

The admin computes the same shared key from their side:

Shared Key = ECDH(adminPrivateKey, tradeKey.public)

Each party (buyer and seller) has its own independent shared key with the admin. A session can have both a peer shared key (for the P2P chat) and an admin shared key (for the dispute chat) simultaneously.

Sending and receiving messages

Messages are wrapped and unwrapped using the same simplified NIP-59 scheme described in Peer-to-peer Chat. The inner event is a kind 1 event signed by the sender's key, encrypted with NIP-44 and placed inside a kind 1059 Gift Wrap event.

The p tag in the wrapper event points to the admin shared key's pubkey, not the trade key:

{
  "content": "<Encrypted content>",
  "kind": 1059,
  "created_at": 1703021488,
  "pubkey": "<Ephemeral pubkey>",
  "id": "<Event Id>",
  "sig": "<Ephemeral key signature>",
  "tags": [["p", "<Admin Shared Pubkey>"]]
}

Subscribing to messages

Clients subscribe to kind 1059 events filtered by the admin shared key's pubkey:

{
  "kinds": [1059],
  "#p": ["<Admin Shared Pubkey>"]
}

Clients should discard any messages received from pubkeys other than the Mostro node or the dispute solver.