Cancel and resume a duplicity backup

Duplicity 0.6+ will attempt to resume a previously aborted/failed/partial backup (source). The rsync options will not help, as duplicity encrypts each tardiff file as it it created, and deletes these not yet transferred files on failure.

The rsync options will allow it to resume a transfer if no encryption is in use.

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