One of the most popular mechanisms is the Signal protocol, which is used by Signal and WhatsApp (notable for having 1.3 billion users!) I won’t discuss the details of the Signal protocol here, except to say that it’s complicated, but it works pretty well.Ī fly in the ointment is that the standard Signal protocol doesn’t work quite as well for group messaging, primarily because it’s not optimized for broadcasting messages to many users. In pairwise communications ( i.e., Alice communicates with only Bob) this encryption is conducted using a mix of public-key and symmetric key algorithms. With plenty of caveats, this means a corrupt server shouldn’t be able to eavesdrop on the communications. The server has a much more limited role, moving and storing only meaningless ciphertext. The good news is: we’re not stuck with them. One of the most promising advances in the area of secure communications has been the recent widespread deployment of end-to-end (e2e) encrypted messaging protocols.Īt a high level, e2e messaging protocols are simple: rather than sending plaintext to a server - where it can be stolen or read - the individual endpoints (typically smartphones) encrypt all of the data using keys that the server doesn’t possess. In recent years we’ve seen plenty of evidence that centralized messaging servers aren’t a very good place to store confidential information. How do end-to-end encryption and group chats work? (Wired also has a good article.)įirst, some background. But both issues are very avoidable, and tend to undermine the logic of having an end-to-end encryption protocol in the first place. However, the caveat is that these attacks are extremely difficult to pull off in practice, so nobody needs to panic. If all you want is the TL DR, here’s the headline finding: due to flaws in both Signal and WhatsApp (which I single out because I use them), it’s theoretically possible for strangers to add themselves to an encrypted group chat. This result comes from a new paper by Rösler, Mainka and Schwenk from Ruhr-Universität Bochum (affectionately known as “RUB”). The RUB paper paper takes a close look at the problem of group messaging, and finds that while messengers may be doing fine with normal (pairwise) messaging, group messaging is still kind of a hack. If nothing else, today’s post helped disabuse me of that notion. That is, I was starting to believe that most of the interesting problems had finally been solved.
My sadness comes from the fact that lately these systems have been getting too damned good. However, recently I’ve been a bit disappointed.
If you’ve read this blog before, you know that secure messaging is one of my favorite topics.
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