When comparing bup vs duplicity, the Slant community recommends duplicity for most people. In the question“What are the best backup programs for Linux?” duplicity is ranked 2nd while bup is ranked 11th. The most important reason people chose duplicity is:
Data is encrypted locally before being sent, and kept encrypted by a key that is never stored on the remote machine. So you might even store your data on a public space, people would still need your key or brute force it.
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Pros
Pro Saves only the minimum amount of data needed
Data is shared between different incremental backups without having to know which backup is based on which. Even for backups that come from different computers that know nothing about each other. Bup simply saves the minimal amount of data needed.
Pro Huge files can be backed up incrementally
Bup splits up files into different chunks. This is especially useful for large files which can then be stored without using a lot of disk space for different versions of the same file.
Pro Encrypted locally before sending (using GnuPG)
Data is encrypted locally before being sent, and kept encrypted by a key that is never stored on the remote machine. So you might even store your data on a public space, people would still need your key or brute force it.
Pro Bandwidth and space efficient
Duplicity uses the rsync algorithm so only the changed parts of files are sent to the archive when doing an incremental backup. For instance, if a long log file increases by just a few lines of text, a small diff will be sent to and saved in the archive. Other backup programs may save a complete copy of the file.
Pro Versioning and incremental backup
You can retrieve older versions or files you recently deleted locally even after having updated your backup.
Pro Free and open-source
Licensed under GNU GPL v2.
Pro Works with scp/ssh, ftp, rsync, Amazon S3...
Duplicity does not make many demands on its archive server. As long as files can be saved to, read from, listed, and deleted from a location, that location can be used as a duplicity backend. Besides increasing choice for the user, it can make a server more secure, as clients only require minimal access.
Pro Has a Dockerized image
Docker allows to run programs on any Linux without having to really install them, and allows to manage versions so it runs exactly the same on different machines.
Cons
Con No GUI
Only available as a command line tool.