Re: "privmsg is not private", IRC is a great medium for public discussion of topics where it's fine for anyone to join and listen, & the limitations of the medium help to remind of that. It's not a suitable medium for secrets.
Conversation
Public chat rooms act as a starting point for private discussions. It's natural to direct message people in the room as a way of starting a private discussion.
Needing to move to another platform for private discussions draws into question the use of IRC for the public channels.
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Yes, this is a client failing though. They could/should just do e2ee for private one on one chats over IRC transport.
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I guess DCC used to be the hotness to solve that stuff back in the days.
But yeah, no particular reason, beside standardizing a common way for clients to do it.
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Yep. That was back when ISPs weren't dragnet spy infrastructure. Nowadays there's no need for DCC; the server transport is fine as long as you use e2ee. Not sure how OTR works but Noise handshake over IRC would be low overhead and trivial to implement.
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It can be painful due to lack of persistent state on the server though. The sessions need to keep being re-synchronized, etc. It was always a pain to use IRC OTR.
Element's session verification and cross-signing is now smoother than any other E2E encrypted chat apps I've used.
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Does OTR have signing (nonrepudiation)? That would be so awful for IRC. Big advantage of authenticated DH handshake over signing here is that it doesn't provide nonrepudiation.
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OTR avoids this via the forward secrecy approach as does the more modern Signal protocol. Signal protocol was essentially a successor for OTR designed around making it into a proper asynchronous communication protocol. Matrix gives it proper multi-session support.
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Cross-signing in Element means that after you verify your own sessions on the same account from each other, they can bootstrap trust for each other.
For example, if you have a desktop and mobile session and verify with someone else from mobile, it verifies the desktop one too.
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You can use separate accounts when you want them to be separate or multiple sessions on the same account when you want it to be transparent to other people.
If you add a session, you verify from an existing one and it ends up being verified by other people through you doing it.
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Everyone can see that you have multiple sessions though, and they can choose if they want to rely on the cross-signing to verify them. It's really nice to have this transparent by default though. Element has the most usable experience that I've seen for non-technical users.