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this post was submitted on 05 Apr 2025
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I understand how the public key encryption works when you are messaging person to person. Does anyone know how it works with group chats?
Each participant is sent a separate copy of each message encrypted with their own key.
This is one way that signal differs from WhatsApp e2e in groups. In WhatsApp the server replicates the message out to all clients. It can't read the message but it knows the recipient list. In Signal your phone sends the message several times, so only members of the group know who is in the group.
The encryption still works roughly the same, the difference is mostly visible metadata.
Multiple bundles of encrypted message + decryption key & recipient tag for 1 person, or one bundle of the encrypted message and then keys for multiple people & recipients which the server can separate out when relaying the message
(message keys are encrypted to each recipient's keypair*)
*simplified because I can't be bothered to explain how deniability is implemented. Just look up the Signal protocol's ratchet