They say how they've attacked the problem. And its as stupid as you would imagine: https://www.virtru.com/how-virtru-works https://www.virtru.com/how-virtru-wor

They say how they've attacked the problem. And its as stupid as you would imagine: https://www.virtru.com/how-virtru-works https://www.virtru.com/how-virtru-works I'm guessing the system works by sending the encrypted item out-of-band. Revocation could be done by the key server. Though there's nothing to prevent designing a client that automatically grabbed the key material when an encrypted message was sent.