nips/47.md

NIP-47

Nostr Wallet Connect

draft optional author:kiwiidb author:bumi author:semisol author:vitorpamplona

Rationale

This NIP describes a way for clients to access a remote Lightning wallet through a standardized protocol. Custodians may implement this, or the user may run a bridge that bridges their wallet/node and the Nostr Wallet Connect protocol.

Terms

• client: Nostr app on any platform that wants to pay Lightning invoices.
• user: The person using the client, and want's to connect their wallet app to their client.
• wallet service: Nostr app that typically runs on an always-on computer (eg. in the cloud or on a Raspberry Pi). This app has access to the APIs of the wallets it serves.

Theory of Operation

1. Users who which to use this NIP to send lightning payments to other nostr users must first acquire a special "connection" URI from their NIP-47 compliant wallet application. The wallet application may provide this URI using a QR screen, or a pasteable string, or some other means.

2. The user should then copy this URI into their client(s) by pasting, or scanning the QR, etc. The client(s) should save this URI and use it later whenever the user makes a payment. The client should then request an info (13194) event from the relay(s) specified in the URI. The wallet service will have sent that event to those relays earlier, and the relays will hold it as a replaceable event.

3. When the user initiates a payment their nostr client create a pay_invoice request, encrypts it using a token from the URI, and sends it (kind 23194) to the relay(s) specified in the connection URI. The wallet service will be listening on those relays and will decrypt the request and then contact the user's wallet application to send the payment. The wallet service will know how to talk to the wallet application because the connection URI specified relay(s) that have access to the wallet app API.

4. Once the payment is complete the wallet service will send an encrypted response (kind 23195) to the user over the relay(s) in the URI.

Events

There are three event kinds:

• NIP-47 info event: 13194
• NIP-47 request: 23194
• NIP-47 response: 23195

The info event should be a replaceable event that is published by the wallet service on the relay to indicate which commands it supports. The content should be a plaintext string with the supported commands, space-separated, eg. pay_invoice get_balance. Only the pay_invoice command is described in this NIP, but other commands might be defined in different NIPs.

Both the request and response events SHOULD contain one p tag, containing the public key of the wallet service if this is a request, and the public key of the user if this is a response. The response event SHOULD contain an e tag with the id of the request event it is responding to.

The content of requests and responses is encrypted with NIP04, and is a JSON-RPCish object with a semi-fixed structure:

Request:

{
    "method": "pay_invoice", // method, string
    "params": { // params, object
        "invoice": "lnbc50n1..." // command-related data
    }
}

Response:

{
    "result_type": "pay_invoice", //indicates the structure of the result field
    "error": { //object, non-null in case of error
        "code": "UNAUTHORIZED", //string error code, see below
        "message": "human readable error message"
    },
    "result": { // result, object. null in case of error.
        "preimage": "0123456789abcdef..." // command-related data
    }
}

The result_type field MUST contain the name of the method that this event is responding to. The error field MUST contain a message field with a human readable error message and a code field with the error code if the command was not successful. If the command was successful, the error field must be null.

Error codes

• RATE_LIMITED: The client is sending commands too fast. It should retry in a few seconds.
• NOT_IMPLEMENTED: The command is not known or is intentionally not implemented.
• INSUFFICIENT_BALANCE: The wallet does not have enough funds to cover a fee reserve or the payment amount.
• QUOTA_EXCEEDED: The wallet has exceeded its spending quota.
• RESTRICTED: This public key is not allowed to do this operation.
• UNAUTHORIZED: This public key has no wallet connected.
• INTERNAL: An internal error.
• OTHER: Other error.

Nostr Wallet Connect URI

client discovers wallet service by scanning a QR code, handling a deeplink or pasting in a URI.

The wallet service generates this connection URI with protocol nostr+walletconnect: and base path it's hex-encoded pubkey with the following query string parameters:

• relay Required. URL of the relay where the wallet service is connected and will be listening for events. May be more than one.
• secret Recommended. 32-byte randomly generated hex encoded string. The client MUST use this if present to sign events and encrypt payloads when communicating with the wallet service.
  • Authorization does not require passing keys back and forth.
  • The user can have different keys for different applications. Keys can be revoked and created at will and have arbitrary constraints (eg. budgets).
  • The key is harder to leak since it is not shown to the user and backed up.
  • It improves privacy because the user's main key would not be linked to their payments.
• lud16 Recommended. A lightning address that clients can use to automatically setup the lud16 field on the user's profile if they have none configured.

The client MAY generate a 32-byte random secret and store it and uses this secret when it wants to perform an action. The corresponding public key must be passed to the wallet service to allow it to authorize the client. The client MUST only use this secret if the wallet service does not return a different secret to the client.

The client should then store this connection and use it when the user wants to perform actions like paying an invoice. Due to this NIP using ephemeral events, it is recommended to pick relays that do not close connections on inactivity to not drop events.

Example connection string

nostr+walletconnect:b889ff5b1513b641e2a139f661a661364979c5beee91842f8f0ef42ab558e9d4?relay=wss%3A%2F%2Frelay.damus.io&secret=71a8c14c1407c113601079c4302dab36460f0ccd0ad506f1f2dc73b5100e4f3c

Commands

pay_invoice

Description: Requests payment of an invoice.

Request:

{
    "method": "pay_invoice",
    "params": {
        "invoice": "lnbc50n1..." // bolt11 invoice
    }
}

Response:

{
    "result_type": "pay_invoice",
    "result": { 
        "preimage": "0123456789abcdef..." // preimage of the payment
    }
}

Errors:

• PAYMENT_FAILED: The payment failed. This may be due to a timeout, exhausting all routes, insufficient capacity or similar.

Example pay invoice flow

0. The user scans the QR code generated by the wallet service with their client application, they follow a nostr+walletconnect: deeplink or configure the connection details manually.
1. client sends an event to the wallet service service with kind 23194. The content is a pay_invoice request. The private key is the secret from the connection string above.
2. wallet service verifies that the author's key is authorized to perform the payment, decrypts the payload and sends the payment.
3. wallet service responds to the event by sending an event with kind 23195 and content being a response either containing an error message or a preimage.

Using a dedicated relay

This NIP does not specify any requirements on the type of relays used. However, if the user is using a custodial service it might make sense to use a relay that is hosted by the custodial service. The relay may then enforce authentication to prevent metadata leaks. Not depending on a 3rd party relay would also improve reliability in this case.