One of the largest holes in encrypted communication is still the fact that the vast majority of email is still neither digitally signed, nor encrypted. And even if they are, the usual schemes do not encrypt the subject line. I wish there was something like Let's encrypt but for email. Just make it trivial to sign and encrypt your mail. Also, mail clients should give a huge warning for unencrypted and/or unsigned mail…
I think Latacora's (famous?) post[1] sums the situation up here nicely: email is designed in such a way that precludes an encryption scheme that actually works for ordinary users. Even power users consistently fail to use email encryption correctly. If we care about secure communication, then we should be nudging users towards protocols that enable encryption, rather than fighting against it. For 99% of cases, that p…
This creates two problems: (1) is that Signal functionally operates as "trust on first use", and (2) Signal has no system by which you can communicate to "conceptual entities" - i.e. companies. There's no way in Signal to talk to say, a bank or a government agency as an entity (IMO: to turn a profit, this is the business Signal actually need to be in).
Which makes it a bit of stochastic security measure: encrypt enough communications and probably when something important does come up, the window to intercept it has failed - except of course, that those verification number messages nobody knows what to do with and so they ignore them.