If I have a partition like /dev/hd1 that is unencrypted and want it to be encrypted, but want to keep everything currently in that partition, how can I do that?
There does not seem to be an solution to do that in place. Truecrypt offers the system encryption only for windows, dm-crypt overwrites partitions.
Your best bet would be to move everything from that partition into a backup with
cp -a, create an encrypted partition with luks/dm-crypt and move everything back.
Since this comes up near the top of google results, adding solution:
LUKS in place encryption via http://www.johannes-bauer.com/linux/luksipc/
This is trivial if you choose plain
dm-crypt. It's risky - if it fails part-way through (power cut or whatever) then you're stuffed!
Ensure the raw device isn't mounted then create an encrypted device for it and use
dd to copy from the raw device to the encrypted one:
$ cryptsetup open /dev/sda sda-crypt --type plain $ dd if=/dev/sda of=/dev/mapper/sda-crypt bs=512
The plaintext data is read from
/dev/sda and written to the device mapper,
/dev/mapper/sda-crypt, which encrypts it and writes it back to
/dev/sda, overwriting the plaintext data that was read.
It will likely take some time due to it reading and writing the entire disk.
Encrypt LUKS2 device (in-place). Make sure last 32 MiB on /dev/plaintext is unused (e.g.: does not contain filesystem data):
cryptsetup reencrypt --encrypt --type luks2 --reduce-device-size 32m /dev/plaintext_device
The documentation has more examples such as initializing the device at first and taking the device online, encrypting it while it is in use. Furthermore the reencryption seems to be resilient in that it can be stopped and restarted, allowing for elaborate use-cases.
Note that the luks header still needs to be written and thus size restrictions apply, meaning that you should be very careful and ideally test your specific scenario (for instance on another device with plausible test data) before attempting this. The
--reduce-device-size option has more information on this.
While reencrypting the tool will output information about size, speed, and ETA, making it very user friendly IMHO.
The general workflow would be as follows:
- resize the existing filesystem/data to be 32MiB smaller than the surrounding blockdevice (e.g. on btrfs run
btrfs fi resize -32m /mnt)
- make absolutely 100% sure that the device is not mounted or opened in any other way (if you have mdadm running on top of the device that'd be an issue as it would be trying to recover while the device is written to)
- reencrypt the device (e.g.
cryptsetup reencrypt --encrypt --type luks2 --reduce-device-size 32m /dev/sda4)
- that's it, you can now
cryptsetup openlike usual, and use the UUID of the blockdevice (the blockdevice itself now has a UUID derived from the luks layer) as usual, for instance in your boot process/initrd
Actually you can convert from a plain filesystem partition to dm-crypt.
But it's risky and cumbersome.
There is an out-dated tutorial here: https://help.ubuntu.com/community/EncryptedFilesystemHowto7
Dm-crypt maps one block to one block, so in theory it is doable. Luks is a user-friendly container that uses dm-crypt inside it. A luks partition contains a header and a dm-crypt partition inside it, where the encrypted filesystem really lives.
If you choose to go Luks then your task is even harder, and you will need to know exactly how much ahead the dm-crypt data should be with respect to the begining of the official partition.
In any case, if your system crashes or halts during the procedure you loose your data