Since I hate typing passwords all the time, I looked for a way to automatically unlock my SSH keys at login. This guide focuses on KDE Plasma 5 and SDDM, but it should be easy to implement it for KDE Plasma 4 and other display managers as well.
1. Start ssh-agent during login. This can be done in /etc/plasma/startup/agent-startup.sh
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2. Install and enable the kwallet PAM module to automatically unlock your KDE wallet during login.