LVM

Install necessary apps

E.g. on a rescue disc ...

apt-get install cryptsetup

Open encryted lvm partition

cryptsetup luksOpen /dev/sda5 my-crypt

Mount existing volume groups

sudo apt-get install lvm2
sudo modprobe dm-mod
sudo vgchange -a y

Umount existing volume groups and close encrypted container

sudo umount /dev/mapper/whatever
sudo vgchange -a n
sudo cryptsetup luksClose my-crypt