Sphinx Relay

Sphinx Relay is the node-side component of Sphinx, a messaging system that sends messages as Lightning Network payments. Running the relay yourself means your conversations pass through your own node instead of somebody else's server.

The design is unusual and worth understanding. Communication between Relay nodes happens entirely over the Lightning Network, so there is no central messaging server to subpoena, block, or shut down, and messages carry a small payment as they go. Message content is end-to-end encrypted with client public keys in the Sphinx app itself, so the relay handles delivery without being able to read what it delivers.

Because it uses Lightning as transport, the economics of spam invert: sending a message costs a small amount, which is negligible for real conversation and prohibitive for bulk unsolicited messaging. It also means your chat and your payments run over the same channels.

The relay stores what needs to persist between sessions — contact aliases, message history, recurring payment configurations, invites for adding friends, and the media keys used to decrypt attachments, each encrypted per contact. It connects to the LND on your MyNode and needs channels with reasonable capacity to work well.