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I have encrypted a disk on my Ubuntu machine using

sudo cryptsetup luksOpen /dev/sdb1 sdb1

I'm wondering how difficult is it to decrypt this disk using bruteforce password guessing? What does the success rate depend on?

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I'm wondering how difficult is it to decrypt this disk using bruteforce password guessing?

It's not difficult, but it's time consuming. You only need the LUKS header and a lot of processing power. The default KDF is aes-cbc-essiv:sha256, and that means around 4k hashes per second on a RTX 2070 or around 200 in an i7-9700.

What does the success rate depend on?

It will depend on the password strength and KDF parameters choosen. If the password is random, long (16+ chars), the iteration count is high (to take 10 seconds or more) and WHIRLPOOL is selected as the hashing function for the KDF, the chances of breaking it are almost zero.

If the password can be attacked using a dictionary, or is found on a password leak, your chances are better. If the user have the same password for his email and LUKS, and the password already leaked, you can decrypt it in one try.

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As far as we know, chances of brute-forcing the LUKS header are fairly low.

LUKS uses resource-consuming key derivation functions that will force every password attempt to consume a significant time (e.g. 0.1s on a modern CPU).

You can yourself calculate how much passwords can be tried in a day or a week.

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It's depending on the iteration Count and the amount and performance of your Hardware, better said the performance of your CPU(s) and GPU(s).

For example a GTX 1080 TI can try about 14k passwords per second. Source (mode 14600, 163044 iterations).

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