LUKS: Difference between revisions

THIS PAGE IS A DRAFT ! Information on this page is in need of further research and refinement !

This page will need to be split into " difficulty tiers " and since it's the first page this has been needed on , it makes it an excellent test subject to figure out the best way to do so .

This page is written with [[Tiers|Intermediate]] users in mind, but of course everyone is encouraged to try to understand.

For more more info on this topic, check the [https://gitlab.com/cryptsetup/cryptsetup/-/wikis/FrequentlyAskedQuestions cryptsetup FAQ], the [https://wiki.archlinux.org/title/Dm-crypt/Device_encryption Arch Wiki], or the [[Luks (Advanced)|Advanced Guide]].

= Guide to Decent LUKS Security on Linux =

If you just want to know the "best" command to run, you can skip to the bottom. But reading this Guide is encouraged, as it will give you a better understand of what the options do, and how they will affect the security of your data!

== Ciphers ==

Ciphers scramble the files that will be saved, so it's important to pick a good one. Computers have had, for many decades now, built in support for AES, making it the fastest and most secure option for pretty much everyone.

== On-disk Format ==

 

== Initialization Vectors ( IV ) ==

The purpose of IV is to ad some randomness different blocks of the disk , so that overall patterns cannot be discovered . ESSIV ( Encrypted salt-sector initialization vector ) was set as default for CBC to mitigate the fingerprinting issue , but this does not help CBC's issues with malleability . For XTS , plain64 is recommended over plain , since it has no performance impact , and plain has some data leaking vulnerabilities that are viable on disks larger than 2TiB . XTS not being vulnerable to fingerprinitng , does not need the added overhead of ESSIV .

 

The hashing algorithm is intended to make weak passwords harder to break , so a very good password does not really need much hashing . Argon2 is optimized to be impossible to brute-force on devices with limited memory , most notably , graphics cards . The point is to force the attacker to use their CPU , which is not usually not nearly as quick as a GPU for this kind of task . Unless you're primarily concerned about some APT trying to break into your device , it is pretty good tradeoff . If your device is very memory constrained ( like under 4GB ), you ''may'' want to consider using PBKDF2 ( Password-Based Key Derivation Function ) . You will almost certainly want to increase the iteration time more though , as it is far weaker to GPU brute-forcing . For a small note on Argon2 , it has a few different variants . Argon2i is weakest to brute-forcing , but has strong side-channel protection . It's generally not safe to use 2i with anything less than 10 iterations . Conversely , while Argon2d is most secure against brute force attacks , it is more susceptible to side channel timing attacks than Argon2id . Unless you are ''really'' not concerned about side-channel attacks , Argon2id is the most well rounded and therefore the best choice .

 

This defines how long your computer is going to spend hashing the password . More iteration is generally better , and is mostly a question of how long you willing to spend waiting for your computer to initially decrypt the drive . Do note that it doesn't decrease the speed of the drive after the key is decrypted . To be very clear , high iteration count is not an alternative to a secure password ! 2 seconds ( 2000ms ) is generally the recommended default , though of course you are welcome to set it as high as you are willing to tolerate . Make sure your computer is not set to any " low-power mode " when setting up the disk , as this will affect the time it takes to hash .

 

Very important note ! Make sure your password is secure ! Using something short is a very bad idea . Using a string of characters from a well known book is also not a great idea ! Something like a diceware password with at least 6 words is generally a good idea !

 

If you want to see for yourself how fast these various algorithms will run on your computer, you can use <code>cryptsetup benchmark .</code><blockquote>    # Tests are approximate using memory only (no storage IO).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  twofish-xts        512b       221.9 MiB/s       249.3 MiB/s</blockquote>As you can see from this sample output , aes-xts is the fastest ! Assuming you're on an x86 machine , this will almost certainly also be the case for you . You'll also notice Argon2i only has 4 iterations here , making it unsafe to use . You can add <code>-i 5000</code> to test 5000ms as an example , to see how many iterations it achieves .

 

 

There's apparently a lot of debate and conflicting information online about the difference between /dev/random and /dev/urandom online . The main difference is that /dev/random will wait when it estimates that not enough entropy has been gathered . Since it only affects when you initially setup the disk though , waiting for it to gather enough entropy is generally a good idea . Whether its method of ensuring it has gathered enough data is effective , is also somewhat debated , but it certainly doesn't hurt .

 

Unless you have a strong reason to doubt AES-256 ( which is also post-quantum resistant ) , AES should be used . Using CBC even with ESSIV does not have any compelling reasons for consideration , so XTS likely your best choice , especially since it will be significantly faster to encrypt / decrypt on x86 . These options are the default for good reason , and unless you have a particularly special setup or threat model ; like if for example , if your CPU does not have hardware accelerated AES , or if it had a known vulnerability . Lastly , Argon2id is generally your best option for hashing .

Assuming your disk is already correctly partitioned , setting up the disk is as simple as :

As mentioned previously , these settings are the default on the latest cryptsetup ( with the exception of --use-random ) , but setting them manually ensures that they are correct on older versions . You can also check what the defaults are for your system by running cryptsetup --help . You can then verify that it was setup correctly with :

Once it has been setup , it can be opened with :

Note that " dm_name " can be set to whatever you like , and the disk will be available at :

Then you will need to format it , via something like :