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Recently there was a lot of news coverage of an alleged „backdoor“ in WhatsApp, the proprietary messaging application owned by Facebook. WhatsApp deployed OpenWhisperSystem’s Signal-protocol roughly a year ago. Now a researcher showed, that WhatsApp’s servers are able to register a new device key for a user, so that messages that the user did not read yet (the ones with only one checkmark) are re-encrypted for the new key, so they can be read by WhatsApp (or whoever registered the key). There were a lot of discussions going on about whether this is a security flaw, or careful design.
I also read a lot of articles suggesting alternatives to WhatsApp. Often mentioned was of course Signal, a free open source messenger by OpenWhisperSystems, the creators of the Signal-protocol, which does not suffer from WhatsApps “vulnerability”. Both WhatsApp and Signal share one major flaw: Both create a “walled garden” for their users. That means that you can only write WhatsApp messages to other WhatsApp users. Same goes for Signal. Since Signal depends on proprietary Google libraries, it cannot be used on mobile phones without Google Play services.
Every now and then the news mention another alternative, the XMPP network.
Conversations is a free libre XMPP client for Android, which introduced the OMEMO protocol for end-to-end encryption roughly two years ago. OMEMO is basically the Signal-protocol adapted to XMPP. Since there are many different XMPP servers that can be used with many different clients, the user has a choice, which software they want to use to communicate to their friends. The issue is, there are not too many clients supporting OMEMO at the moment. But what clients are able to do OMEMO at the moment?
For the desktop there is Gajim, an XMPP client written in python, which offers OMEMO support as a plugin. This works well on Linux and Windows. I admit, this is not a lot compared to OTR or GPG – but wait, there is more
Currently I am writing on my bachelors thesis about the OMEMO protocol. As part of this, I am working on a Smack module that hopefully will enable messenger apps based on the Smack library (eg. Xabber, Zom, Jitsi, Kontalk…) to encrypt messages with OMEMO.
Simultaneously another student is developing a Pidgin plugin and yet another one is implementing OMEMO for the console based XMPP client Profanity. You can find a quick overview of the state of OMEMO deployment on https://omemo.top.