Evolution of Receiving Addresses in Signal, Simplex Chat, and Keychat A receiving address is indispensable to any chat application—just as an envelope needs only the recipient’s address. Because this address is exposed plaintext metadata, its design determines how much metadata privacy the user enjoys. Signal each user has a single receiving address that is also their ID. For Bob and Carl alike, Alice’s address is always the same—simply A—and it never changes. Simplex Chat Here, the receiving address (smp://<queueKey>@<relay-host>/<queueId>) is different for every contact. Alice has one fixed address for Bob, A(b), and another for Carl, A(c). Having separate—but constant—addresses for each contact is already a significant improvement over Signal’s single, global address. Keychat Keychat goes a step further: the address not only differs per contact but also rotates over time. Alice begins with A(b1)for Bob and A(c1) for Carl; after she replies, they become A(b2) and A(c2), and so on. Each time Alice responds to Bob, her address is refreshed. This dynamic, per-contact rotation provides even stronger privacy than Simplex’s static per-contact addresses.