You never want to share keys if you can get away with it.<p>Your suggestion also doesn&#x27;t solve the problem of lost, compromised or destroyed devices.<p>If I have one phone and one computer, no algorithmic solution can determine if the person holding my phone is me, and the person holding my laptop is a thief, or if the person holding my phone is a thief and the person holding my laptop is me.<p>Honestly, even majority vote is insufficient: is there any reason to trust the person holding my phone and laptop over the person holding my computer? What if my home just burned down?<p>What&#x27;s needed is for each device to have its own keys, and for messages to &#x27;you&#x27; to really be sent to each device. And when you lose a device, you have to let your friends know, and they have to manually verify which of your devices to no longer trust. This can be presented in a pleasing fashion, but you can&#x27;t eliminate the need for human judgement.