1y ago

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

[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:

 bash

    
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:

 bash

    
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 :)

75 comments

we really ain't making any jokes on the name of the drives? okay...
- Actually the bottomLuks generates most of the power.
  
  Speed has everything to do with it.
- Well considdering it was posted by a user with the username "communism" i will assume bottomLuks
  
  Communism doesn't have hierarchy tho
- Yes, perhaps I should have named them outerLuks and innerLuks... oh well lol
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.
- You wouldn’t LUKS a floppy?
  
  I absolutely will, if I can find one
- 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.
It would be good if you wanted to have a system that two people need to be present to unlock. Like those nuke launch locks that need two keys.
- You can also just split the password for a single LUKS into two parts and give one each to the two people :D
  
  Yeah, you’re right. That’s better.
  
  But then you know both parts of the password and so must be killed to keep the machine secure
- Tbf this would enforce the order in which the two people decrypt it, which may not be good if you expect these two people to "arrive" asyncrhonously and you don't want them to have to wait for the other before entering their password/key. But maybe that's too specific of a use case.
  
  You're a programmer, aren't you? Always thinking about those race conditions and edge cases.
  
  What about this: Top layer encrypted by Alice Middle layer encrypted by Bob Bottom layer encrypted by Alice
  If Alice arrives first, she decrypts the top layer and has to wait for Bob to arrive. She cannot go because she has to decrypt the last layer. If Bob arrives first, he has to wait for Alice to arrive. He cannot go because he hasn't decrypted anything yet.
  Not really a solution but kind of helps.
- I don't think that's how its done. I see where your going with this.
Never apologize for enjoying the discovery of new things. That's awesome, enjoy it.
Now recursively create more layers until you have barely any free space left on the disk, then do some performance benchmarks. ;)
top / bottom
( ͡° ͜ʖ ͡°)
- This guy LUKS!!
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.
- not really if you have a hardware chip that does the encrypt/decrypting
  
  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.
  
  Does cryptsetup/luks do that? I thought that was only software encryption.
Great! Although I think that security actually goes down that way. Something something about statistics. A crypto expert could probably explain that properly and we could pretend to understand it.
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)
- 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.
I guess your...Luks not running out.
- Take my angry upvote, you heathen.
Might be a way to enforce multiple algorithms or enforce two factor unlocking (say TPM AND password).
- You guys are going to blow your top when you hear about DFC (Distributed Fragment Cryptography)
  
  Any good reading the subject?!
That's cool and I hope I never see that in the wild
- Why not?
  
  Seems like it would be fairly inefficient having to encrypt and decrypt data twice.
- Yo dog I heard you like cryptography
If you think about, it makes sense, but I didn't know this! Really cool indeed - do you have any use case for that or you were just poking around?
- I have an SSD and an HDD—I was considering on my next distro hop to put the root partition on the SSD and home partition on the HDD, decrypt the SSD and top level of the HDD upon boot, then decrypt the bottom level of the HDD upon user login. I'm sure many will think that's overkill or silly, but hey, if you have full disk encryption you'll have to enter two passwords to get into your computer anyway, just means your personal files get protected with two passwords. I would agree it's mostly gimmicky but I still want to try it out lol
  
  Amazing! How do you setup the decryption on login? systemd-home or something like that?
  
  Wouldn't it be easier to just use a longer password and or a longer hash
Is it possible to.. boot into a LUKS in a LUKS?
- Have fun with the initramfs.
  
  I will thanks
Where's the ZFS love...
- Why not? Even my physical door have top-locks and bottom-locks... get your mind out of the gutter! :)

75 comments