[sporkenfang]

I've never done this with UUCP, but if you don't care about anonymity you could do two-way authenticated TLS (both client and server have and present certs).

Maybe you could do a ratcheting protocol like Signal does, instead, which might be better.

There's a couple ways to do this that might be sensible depending on whatever constraints there might be in a deployment.

[stargrave]

Anonymity is not the goal, because it is another separate task.

NNCP contains nncp-daemon and nncp-caller that work with online protocol. It uses Noise protocol: http://noiseprotocol.org/ (Noise-IK). So ratcheting as Signal does is already applied. http://www.nncpgo.org/Sync.html

[sporkenfang]

Wonderful, I had no idea what Noise was, or Signal for that matter, or NNCP despite reading the article. Thanks for the links! Guess I'll get back to my punch cards.