En root
apt install cryptsetup
Copy your home directory to a temporary directory on a different partition:
mkdir /homebackup cp -a /home/* /homebackup
Encrypt your home partition:
umount /home cryptsetup -h sha512 -c aes-xts-plain64 -s 512 luksFormat /dev/sda5 cryptsetup luksOpen /dev/sda5 chome mkfs.ext4 -m 0 /dev/mapper/chome
Add this line to /etc/crypttab:
chome /dev/sda5 none luks,timeout=30
Set the home partition to this in /etc/fstab (replacing the original home partition line):
/dev/mapper/chome /home ext4 nodev,nosuid,noatime 0 2
Copy your home data back into the encrypted partition:
mount /home cp -a /homebackup/* /home rm -rf /homebackup