How to mount LUKS encrypted file?
Be sure dm-crypt kernel module is loaded.
modprobe dm-crypt
Then I would suggest:
cryptsetup open --type luks /path/to/dump desired-name
This should create a device /dev/mapper/desired-name which you can then mount as used to.
mount /dev/mapper/desired-name /mnt
I'm not sure if this works for a dump. But it's quite possible.