this post was submitted on 19 Mar 2024

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I apologise if this is already common knowledge, but I just found out you can have multiple layers of LUKS encryption on a drive! (lemmy.ml)

submitted 8 months ago by [email protected] to c/[email protected]

75 comments fedilink hide all child comments

[Image description:
Screenshot of terminal output:

~ ❯ lsblk
NAME           MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
sda              8:0    1  62.5M  0 disk  
└─topLuks      254:2    0  60.5M  0 crypt 
  └─bottomLuks 254:3    0  44.5M  0 crypt

/end image description]

I had no idea!

If anyone else is curious, it's pretty much what you would expect:

cryptsetup -y -v luksFormat /dev/sda
cryptsetup open /dev/sda topLuks
cryptsetup -y -v luksFormat /dev/mapper/topLuks
cryptsetup open /dev/mapper/topLuks bottomLuks
lsblk

Then you can make a filesystem and mount it:

mkfs.ext4 /dev/mapper/bottomLuks
mount /dev/mapper/bottomLuks ~/mnt/embeddedLuksTest

I've tested putting files on it and then unmounting & re-encrypting it, and the files are indeed still there upon decrypting and re-mounting.

Again, sorry if this is not news to anyone else, but I didn't realise this was possible before, and thought it was very cool when I found it out. Sharing in case other people didn't know and also find it cool :)

(page 2) 26 comments

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[–] [email protected] 40 points 8 months ago

Now recursively create more layers until you have barely any free space left on the disk, then do some performance benchmarks. ;)

[–] [email protected] 60 points 8 months ago (5 children)

Yeah, LUKS and most block level overlays just don't care. That's what good abstraction layers do for you!

You can LUKS on a disk image mounted over SSHFS that itself resides on a Ceph cluster and mounted over iSCSI for all it cares. Is it a block device? Yes? Good to go.

You can even LUKS a floppy if you want. Or a CD.

[–] [email protected] 6 points 8 months ago

I remember years ago investigating alternatives to VMware vSAN and doing hyperconverged storage clusters in Red Hat with glusterFS in top of a couple of other layers. Feels rickety as heck putting it all together but it works well. Hard sell for “normal” people who expect to hit a Next button and get some pretty graphical chart though.

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[–] [email protected] 81 points 8 months ago (3 children)

we really ain't making any jokes on the name of the drives? okay...

[–] [email protected] 11 points 8 months ago

Yes, perhaps I should have named them outerLuks and innerLuks... oh well lol

[–] [email protected] 48 points 8 months ago (1 children)

Actually the bottomLuks generates most of the power.

[–] [email protected] 25 points 8 months ago

Speed has everything to do with it.

[–] [email protected] 17 points 8 months ago (4 children)

Well considdering it was posted by a user with the username "communism" i will assume bottomLuks

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[–] [email protected] 9 points 8 months ago (1 children)

That's cool and I hope I never see that in the wild

[–] [email protected] 3 points 8 months ago (1 children)

Why not?

[–] [email protected] 5 points 8 months ago (1 children)

Seems like it would be fairly inefficient having to encrypt and decrypt data twice.

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[–] [email protected] 25 points 8 months ago (1 children)

You can, sure, but you probably shouldn't. Encrypting and decrypting consume additional cpu time, and you won't gain much in terms of security.

[–] [email protected] 7 points 8 months ago (2 children)

not really if you have a hardware chip that does the encrypt/decrypting

[–] [email protected] 27 points 8 months ago* (last edited 8 months ago) (5 children)

AES has been accelerated on all Intel CPUs since Broadwell, was common as far back as Sandy Bridge, and has been available since Westmere.

AMD has had AES acceleration since Bulldozer.

But the commenter is right that adding a second layer of encryption is useless in everything except very specific circumstances.

[–] [email protected] 6 points 8 months ago

Yes, but as I've found recently AES-NI is only as good as your software support for it. Had a team using an ancient version of winscp and they kept complaining about download speeds on our 10Gb circuit. Couldn't replicate it on any other machine with the newest version of winscp so I installed their exact version. AES-NI support wasn't added until like 2020 and it gave them 5x better download speed after upgrading.

[–] [email protected] 4 points 8 months ago

I've also found about this recently when moving my root from drive to drive which was after I upgraded to 13th gen intel (from various older i5s) and the best cipher changed (cryptsetup benchmark).

[–] [email protected] 4 points 8 months ago (2 children)

agreed that it is useless for most cases but I could see it being useful if you need multiple people to agree on decrypting a file.

[–] [email protected] 11 points 8 months ago (2 children)

multiple people to agree on decrypting a file

For that, you would use Shamir's Secret Sharing algorithm rather than multiple encryption.

https://en.wikipedia.org/wiki/Shamir%27s_secret_sharing

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[–] [email protected] 2 points 8 months ago (1 children)

That's pretty nitty although you can always just partition a long key and distribute the partitions to the different people

[–] [email protected] 4 points 8 months ago

there's always more than one way to skin a rat

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[–] [email protected] 2 points 8 months ago (2 children)

Does cryptsetup/luks do that? I thought that was only software encryption.

[–] [email protected] 4 points 8 months ago

it depends if your hardware supports the algos that cryptsetup/luks use I guess....

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[–] [email protected] 20 points 8 months ago* (last edited 8 months ago) (1 children)

Of course, and you can also add on as many layers of LVM and MDADM as you'd like.

You can also do the same with disk images (including sparse images)

[–] [email protected] 10 points 8 months ago* (last edited 8 months ago)

Above and/or below LUKS!

So these days I use LVMRAID instead of mdraid. Underneath it uses mdraid but it's a bit easier to use since it's self-contained in LVM.

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