Thread by @JohnCantrell97

I’m sure you’re aware that the main purpose of the lightning network is to help Bitcoin scale by enabling faster and cheaper payments.

Did you know it’s possible to use it to send arbitrary data along with a payment?

Why might you do that?

Should you?

Let me break it down 👇

Normally when you make a payment using the lightning network the receiver has to create an invoice for the specific amount and then get that invoice to you somehow.

You then instruct your wallet or node to pay that specific invoice and the money is routed to the recipient.

There’s a feature called ‘keysend’ that allows you to send money directly to a node's public key without an invoice.

This means instead of having to communicate with the recipient in order to send a payment you can now do so spontaneously as long as you have their public key.

This is useful for sending tips and is currently used by the podcasting 2.0 apps you might have heard about so you can stream money directly to the podcaster’s node as you listen.

Keysend is pretty useful for sending money but it can be used to do much more.

Because of the way payments are routed through the network it turns out there’s a bunch of random data that is added to the payment as it is routed around the network.

This data provides privacy by making it impossible for a routing node to know where it is along the route.

If Alice is trying to route a payment to Dave and has to route through Bob and Charlie to get to Dave then it means Bob has no idea that he is the first hop and he has no idea if Charlie is the final destination or not. The same is true for Charlie.

This means your payment has to have a lot of this random data to be able to support enough hops to navigate the entire network.

It also means that you can use this space to embed additional data in the payment that the recipient can access.

This is how apps like Sphinx and Zion are able to implement messaging over the lightning network.

When you send a message to your friend you use keysend to send them a 1 sat payment and use the extra data to include an encrypted message they can decrypt when they receive it.

This is pretty interesting at first glance because you can now utilize the lightning network to enable end-to-end encrypted onion-routed messaging.

It’s really the first time that you can atomicly send data and a payment in the same request.

It enables a new set of applications

It’s not to say it doesn’t raise some important questions though.

Most importantly, just because you can do it, does it mean you should?

Some would argue that it’s an abuse of the network because you are routing tons of messages when it was intended to route actual payments.

On a network where there is already liquidity and max payments-in-flight concerns should we really be overloading it with arbitrary messages?

Some other folks would argue that it’s not abuse or spam because the users are still paying fees in order to send their messages.

As long as routing nodes set their fee rates appropriately and the users are paying them then who’s to say what payment is spam or not?

It’s a bit of an open debate and it’s hard to know where it will settle as there’s new related functionality coming called Onion Messages.

Onion Messages are a topic for another thread but they are being developed as part of the new Bolt 12 specification that will allow nodes to negotiate on-demand invoices.

This will enable a whole new mechanism for sending and receiving money on the lightning network.

I hope this helped you understand keysend payments and how they can be used to send arbitrary data in an end-to-end encrypted fashion over the lightning network.

Do you think this is an abuse of the lightning network?

Let me know below!