The Signal Private Group System and Anonymous Credentials Supporting Efficient Verifiable Encryption
Melissa Chase, Trevor Perrin, Greg Zaverucha · 2020
In this paper we present a system for maintaining a membership list of users in a group, designed for use in the Signal Messenger secure messaging app. The goal is to support private groups where membership information is readily available to all group members but hidden from the service provider or anyone outside the group. In the proposed solution, a central server stores the group membership in the form of encrypted entries. Members of the group authenticate to the server in a way that reveals only that they correspond to some encrypted entry, then read and write the encrypted entries.