plugins/sendinvoiceless

Invoiceless payment plugin

This plugin sends some msatoshis without needing to have an invoice from the receiving node. It uses circular payment: takes the money to the receiving node, pays in the form of routing fee, and brings some change back to close the circle.

Installation

For general plugin installation instructions see the repos main README.md

Usage

Once the plugin is active you can send payment by running:

lightning-cli sendinvoiceless nodeid msatoshi [maxfeepercent] [retry_for] [exemptfee]

If you want to skip/default certain optional parameters but use others, you can use always the lightning-cli -k (key=value) syntax like this:

lightning-cli sendinvoiceless -k nodeid=022368... msatoshi=1000 retry_for=600

Parameters

• The nodeid is the identifier of the receiving node.
• The msatoshi parameter defines the millisatoshi amount to send. Can be denominated in other units, i.e.: 1000000sat, 0.01btc or 10mbtc.
• The maxfeepercent limits the money paid in fees and defaults to 0.5. The maxfeepercent is a percentage of the amount that is to be paid.
• The exemptfee option can be used for tiny payments which would be dominated by the fee leveraged by forwarding nodes. Setting exemptfee allows the maxfeepercent check to be skipped on fees that are smaller than exemptfee (default: 5000 millisatoshi).

The command will keep finding routes and retrying the payment until it succeeds, or the given retry_for seconds pass. retry_for defaults to 60 seconds and can only be an integer.

See also

For a detailed explanation of the optional parameters, see also the manpage of the pay plugin: lightning-pay(7)

List payments

If you want to check if you got paid by using this method, you can call this:

lightning-cli receivedinvoiceless [min_amount]

This will return an array of detected payments using this method. The plugin will filter the results by the optional min_amount parameter (default: 10sat). This will suppress unexpected results caused by route fee fuzzing and changed past channel fees. The results will contain the amount_msat and timestamp of the payments.

NOTE: The plugin currently does not use a database, so it can only assume fees have not changed in the past. It will also apply default fees for already forgotten channels. In both cases result can be slightly off by the changed fee.

Weaknesses

This is kind of hack with some downsides:

• The route is twice as long because of the circular payment. This will increase fees and failure probability.
• The payee receives the money as a routing fee: hard to associate with anything, distinguish from the usual fees.
• If the payment is going on a circular route A-B-C-D-A to pay C, and the same malicious entity controls B and D, the money can be stolen by skipping C.