Keychat's one-to-one chats and small groups are encrypted using the Signal protocol. Moreover, a small group is a pairwise group; when a member sends a group message, it essentially sends a one-to-one message to the other members. Therefore, the encryption security of small groups is almost equivalent to that of one-to-one chats, but the number of members it can support is limited.
Consequently, our large groups are encrypted with MLS.
The Signal protocol is more suitable for one-to-one chats than MLS because its post-compromise security (PCS) ratcheting occurs more frequently.
Additionally, all Keychat messages (whether one-to-one, small group, or large group) can be intuitively understood using the metaphor of a "letter.” 👇
Keychat uses Signal/MLS protocol to ensure message encryption security and meta-data privacy.
The content of the letter can be exposed easily by opening the envelope. Keychat messages are end-to-end encrypted via Signal/MLS protocol, with a unique encryption key generated for each message. Only the sender and receiver can decrypt the message.
The addresses of both parties on the envelope can be tracked. In theory, this problem is solved if they change addresses daily. So Keychat reuses Signal/MLS protocol to update sending and receiving addresses for nearly every message.
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