Well irssinotifier uses Google cloud messaging (is that the current name? The Google push service). It encrypts messages on the server and decrypts them in the client, using a passphrase. It's a technically neat solution but a bit annoying to set up.

It has a script for weechat (and of course irssi), not sure about other clients.

Or you can use pushbullet /..., there should be scripts for any popular scriptable client

For quassel there seem to be options: https://news.ycombinator.com/item?id=12065792