plus/minus epsilonTagged: Message Layer Security
MLS with Hidden Members17 Dec 2020
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Recently I was asked about the possibility of using MLS in groups with “hidden members”. That is, groups where the creator is known to all participants but the participants don’t know each other. This is the use-case of broadcast TV, private Twitter accounts, Instagram stories. The answer is no, MLS doesn’t work here.
The main issue is that MLS isn’t secure against malicious insiders, and therefore isn't suitable for most broadcast use-cases. A lesser issue is that MLS is designed for homogeneous groups, and would be wasteful to use in a scenario where one member has special authority.