Another friendly reminder:

Mastodon is awesome, but mastodon isn't an appropriate tool if you want private communications. DMs aren't actually private, they can be seen by instance admins and maybe by other people, it isn't at all secure.

Mastodon and GNU social aren't made for private conversations, if you want to have a private conversation there are many tools that are appropriate for that.

I suggest Tox, but Cryptocat and XMPP with OTR are also good. There are others but I have used those

@inmysocks
I suggest XMPP + OMEMO as the stare of the art encryption technology (wich is also used by cryptocat).
OMEMO doesn't require to be online and if multiple clients are online, messages are send to all, and all messages are still end to end encrypted.
Tox is cool for it's p2p approach, but on the other hand, you're required to be online, when another one sends you a message.

@allilengyi when I am wearing my tin foil hat than I have to say that the trade off is using a server to store the messages for XMPP, which can lead to problems with traffic analysis.

But that is only when I am being a tinfoil hat wearing paranoid person.