This is an oldie but goodie from rdiff-backup:
In the backup file directory, test the gzip file integrity with this:
find . -name 'duplicity-full-signatures.*.gz' | while read a; do echo -n "$a: "; gzip --test "$a"; done or this: find . -name 'duplicity-*-signatures.*.gz' | while read a; do echo -n "$a: "; gzip --test "$a"; done | grep in
If you can afford to loose those files, (and data), you could try removing them and re-running the restore / check.
Here is the original link for reference (and attribution): http://rdiff-backup.nongnu.org/FAQ.html#crc
Just want to find if a dir is in an non encrypted archive?
find . duplicity*.difftar.gz -exec tar -tf {} \; | grep somedir