Keychat emulates a postal system. Each message is a letter; the relay functions as the post office, and every message carries a postage stamp—an ecash sat. The Nostr public key serves as the user’s ID, while the sending address, receiving address, and encryption key are independent of that ID and rotate continuously. For one-to-one and small groups, these components are generated and rotated by the Signal protocol; for large groups, they are generated and rotated by the MLS protocol.