Is there a way to cancel duplicity (running over rsync and symmetric gpg encryption) without messing up the running backup and resume it later (for example after rebooting the laptop) without problems?Suppose for example that after starting a duplicity backup on my laptop I notice that it will take too long time and that I have to shutdown the laptop in a few minutes. 
Cancel and resume a duplicity backup
backup;rsync;duplicity
According to duplicity and rsync man, you should try this if you stop during the upload (don't know whether it's safe during encryption):duplicity --rsync-options=-P other_args