How to collaborate across multiple devices whilst protecting your metadata.

Whenever you send a WhatsApp, Telegram, or a Signal message you are making a compromise. It is true that whilst the contents of your messages may be secure an attacker with sufficient knowledge can still deduce a lot by examining the central server and its connection graph. In other words they are still able to deduce who you are talking to and when. In pursuit of making that impossible SimpleX Chat has stumbled upon the concept from military cryptography known as a “unidirectional network” or “simplex network”.

SimpleX doesn’t have a global identity layer! In practical terms this means that your accounts won’t follow you about and each device (client) will have a new database associated with it. This however poses a problem, how do you know which device to message at any given moment in time? To explain this in a more succinct manner Alice will have a different account (database) associated with her phone and her laptop, for example: “alice-laptop” and “alice-phone”.

This problem can easily be solved by adding both “alice-laptop” and “alice-phone” into the same group with bob, we could name this group: #alice_bob. This group would then serve as a primary communication channel between Alice and Bob.

Note: The apps don’t officially support groups just yet.. there is however a hack around using the console that I’m about to share.

Once Bob has invited Alice to #alice_bob and Alice has accepted the corresponding invites you can return to the home screen to be greeted by:

Note: You may have to restart the app for the group to appear.

Problem solved! Bob no longer has to guess which device to message Alice on at any given moment in time. If Bob would like to contact Alice he would message #alice_bob and both “alice-laptop” and “alice-phone” will receive this message!