Does not work anymore on Ubuntu 14.04:

$ mount -oencryption=blowfish-256 -ophash=unhashed2 /dev/sdc1 /mnt/backup/
Password: 
ioctl: LOOP_SET_STATUS: No such file or directory


This works:
$ modprobe cryptoloop
$ losetup -e blowfish -k 256 -N /dev/loop0 /dev/sdc1 
Passwort: 
$ mount /dev/loop0 -o loop /mnt/backup/