KDE: What are gpg-agent and ssh-agent?

I updated gentoo today and noticed:

>>> Installing (226 of 226) kde-base/kdebase-startkde-4.11.22::gentoo
* Updating desktop mime database ...
* Updating shared mime info database ...
* Updating desktop mime database ...
* Updating shared mime info database ...

* To enable gpg-agent and/or ssh-agent in KDE sessions,
* edit /etc/kde/startup/agent-startup.sh and
* /etc/kde/shutdown/agent-shutdown.sh

* The name of the session script has changed.
* If you currently have XSESSION="kde-4.11" in your
* configuration files, you will need to change it to
* XSESSION="KDE-4"

=> I have no idea what gpg-agent and ssh-agent are, why would I want to enable them, etc.
The message should link to a wiki page giving a clear introduction on the topic, and more.