A peer-to-peer, instant messaging protocol has been created for Bitcoin’s Lightning Network, enabling encrypted messages to be sent without the use of a third party, like Facebook or WhatsApp.

The project, called “Whatsat,”—an amalgamation of WhatsApp and satoshi, the smallest unit of value for Bitcoin—piggybacks on the Lightning Network to pass messages around. These are end-to-end encrypted, onion-routed, peer-to-peer and censorship-resistant messages. And, for now, they’re free.

The project was created as a “small pet project” according to Whatsat creator, and current Lighting Labs engineer, Joost Jager. He told Decrypt that he put together the code as a way to use Bitcoin’s micropayment network to talk to an old high school friend who “didn’t trust” WhatsApp.

The project initially received high acclaim at the r/Bitcoin subreddit last week—receiving over 1,100 upvotes. It is based on the Lightning Network, which is is one way that Bitcoin may be able to scale to millions of users. It is known as a second-layer solution that allows participants to make Bitcoin transactions at a much lower cost.

The Netherlands-based engineer said, “The idea of instant messaging over Lightning does seem to resonate and many people acknowledge the potential of it.”

However, he did mention that there are still “plenty of challenges” and that “Lightning, as a payment network, has a whole bunch of them.” It’s, “still very early, just last year it became available on mainnet.”

While he doesn’t see any reasons why a messaging protocol wouldn’t be able to work on a global scale using the Lightning Network, Whatsat might have to adapt to continuing using it.

The current implementation leverages a protocol called “free failures” to send messages between two Lightning nodes. However, in the future, nodes might start charging for this service, or put limits on the number of messages they pass around.

Yesterday, Jager showed off a new demo that supports such an idea, with messages costing tiny fees to be sent around. In his example, messages cost 0.3 satoshis per messages, just $0.00003 a pop. If this were to end up as the standard fee, it would cost an average user around $0.66 to send around 20,000 messages—or one year’s worth of use.

But even this might be problematic. Many nodes don’t support messages being passed around at such low cost. Jager encouraged node operators to set their limits much lower, to allow for more Lightning apps to arrive.