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Refers to:

Disk Partition Encryption

Steps for encryption of vdb1:

# dd if=/dev/urandom of=/root/vdb_secret_key bs=512 count=8
# cryptsetup -v luksAddKey /dev/vdb1 /root/vdb_secret_key
# cryptsetup luksDump /dev/vdb1 | grep "Key Slot"
# cryptsetup -v luksOpen /dev/vdb1 vdb1_crypt --key-file=/root/vdb_secret_key 
# cryptsetup -v luksClose vdb1_crypt

Add following line for auto decryption:

# vim /etc/crypttab
vdb1_crypt UUID=43740d4f-df91-492e-8d06-b32f461a633e /root/vdb_secret_key luks

While UUID is generated via following command:

# cryptsetup luksDump /dev/vdb1  | grep "UUID"

Add lines into /etc/fstab:

/dev/mapper/vdb1_crypt	/media/vdb1	ext4	defaults	0	 2

Volume Encryption

For storing contents in an encrypted file, do following steps:

# dd if=/dev/zero of=/root/luks.vol bs=1M count=1024
# cryptsetup --cipher aes-xts-plain64 --key-size 512 --hash sha512 --iter-time 10000 luksFormat /root/luks.vol
# cryptsetup luksOpen /root/luks.vol file
# ls /dev/mapper/
# mkfs.ext4 /dev/mapper/file

Now we begin to use keyfile for unlock this partition:

# dd if=/dev/urandom of=/root/file_key bs=512 count=8
# cryptsetup -v luksAddKey /root/luks.vol /root/file_key
# cryptsetup -v luksOpen /root/luks.vol vol_crypt --key-file=/root/file_key 
# cryptsetup -v luksClose vol_crypt

Get the UUID of the luks.vol:

# cryptsetup luksDump /root/luks.vol  | grep "UUID"

Now you could add following lines into /etc/rc.local:

cryptsetup -v luksOpen /root/luks.vol vol_crypt --key-file=/root/file_key
mount /dev/mapper/vol_crypt /media/vol