Yesterday I tried to convert my home-partition on the laptop to an encrypted filesystem. But it failed and all Data were lost. So I set up a new partition (xfs) and encrypt it. And now it works.
You need to have cryptoloop and loopback-support compiled in your kernel, also you need a crypto-algo. I will prefer aes, it is fast and secure.
losetup -e aes-256 /dev/loop0 /dev/partition mkfs.xfs -f /dev/loop0 losetup -d /dev/loop0
Add this to your /etc/fstab:
/dev/partition /mnt/encrypted xfs defaults,loop=/dev/loop0,encryption=aes-256 0 0
But backup your data before doing it. I dissuade from using aespipe to encrypt the partition on-the-fly. It seems to be unstable.