Encrypted group chats are more challenging to implement than one-on-one chats.

Currently, there is no perfect solution for encrypted group chats, and different designs come with various tradeoffs. Keychat will support multiple types of encrypted group chats to meet different scenarios.

Keychat first implemented the pairwise group, which is designed for small groups of close friends. It offers the highest security, but can only support a limited number of group members.

When sending a message to a group, group member simply deliver a pairwise encrypted message to each member of the group. It simulates group chat using multiple one-on-one private chats. Therefore, it maintains the same forward secrecy and backward secrecy as one-on-one chats.

While certainly simple and secure, it’s not without costs. Instead of delivering one message, a client needs to deliver N messages and pay N ecash stamps. https://image.nostr.build/65f444c8097ff72997d57dc7f5a48c1ccb62cd03521bd9b7a89b82a9dcab5379.png  

 Nice, this is somewhat how BBM worked.