Join Log in
Score:1
avatar Crypto

Are brute-force attacks made more difficult by removing the LUKS header?

lk flag
kytebucks000

If the LUKS header is removed from the LUKS partition, will this make the brute-force attack much more difficult? Can software tell which type of partition is it?

60
0 + 0
Score:1
kelalaka avatar Crypto
in flag
kelalaka

If we look at a sample Luks header ( The tables taken from here )

  1. Luks Partition Header (PHDR) consists of the necessary information to decrypt/encrypt the luks device as followings,
-------------------------------+-----------------------------
|   Partition Header Contents  |      Output by luksDump    |
-------------------------------+-----------------------------
|  Magic Byte                  | LUKS                       |
-------------------------------+-----------------------------
| Luks version                 | 1                          |
-------------------------------+-----------------------------
| Cipher Name                  | serpent                    |
-------------------------------+-----------------------------
| Cipher Mode                  | xts-plain64                |
-------------------------------+-----------------------------
| Hash Type                    | whirpool                   |
-------------------------------+-----------------------------
| Payload offset               | 4096                       |
-------------------------------+-----------------------------
| Master Key Bits              | 512                        |
-------------------------------+-----------------------------
| Master Key Digest            | 8a 90 77 7e ...            |
-------------------------------+-----------------------------
| Master Key Salt              | ca f3 40 fc ...            |
-------------------------------+-----------------------------
| Master Key Digest Iteration  | 23250                      |
-------------------------------+-----------------------------
| Partition UUID               | 46927c7d-7f17-4312-...     |
-------------------------------+-----------------------------
                          Table - 1


2. 2nd portion of partition header (PHDR) consists of 8 key-slot descriptors i.e information about key-slot as following,

------------------------------+------------------------------
| Key Descriptors             |      Output by luksDump     |
+-----------------------------+------------------------------
| Activation status           | Enabled                     |
+-----------------------------+------------------------------
| Iteration                   | 146285                      |
+-----------------------------+------------------------------
| Salt                        | 1e c1 94 24 36 4c 98..      |
+-----------------------------+------------------------------
| Key Material Offset         | 8                           |
+-----------------------------+------------------------------
| AF Stripes                  | 4000                        |
------------------------------+------------------------------
                         Table - 2

will this make the bruteforce crack much more difficult?

One will see that an attacker will lose a lot of information about the header like cipher name, cipher mode, iteration, hash, key slots, etc.

The easy attack on the LUKS is brute-forcing the password (hashcat can do this) if the password is weak. When the LUKS header is lost, the attacker cannot test the password anymore; the user passwords decrypt the related key slot to release the Master Key (MK). If there is no data to decrypt, it is a random process that is not better than brute0force.

The rest is brute-forcing the MK. For 128-bit encryption algorithms, except for a foreseeable Cryptographic Quantum Computer (CQC), it is infeasible. When one uses a cipher with a 256-bit key it is safe from all targets including CQC.

Can softwares tell which type of the partition is?

No!

And, make sure that you removed the header without leaving a trace, i.e. secure erase.

0 + 0
forest avatar
vn flag
forest
Note that this particular header indicates a 256-bit cipher in XTS mode, which means the effective security is actually 384 bits (not 512, but that's due to a meet-in-the-middle attack).
1
Reply
lk flag
kytebucks000
So I guess if the attacker gets the LUKS disk without LUKS header, he/she/they have to guess to rebuild the LUKS header first, but it is hard to test every try, and every try leads so many tries... Is it also work for quantum computer in the future? They say quantum computer crack the algorithm and encryption.
0
Reply
kelalaka avatar
in flag
kelalaka
@kytebucks000 Rebuilding is not really possible since there is no encrypted MK anymore. As I said, quantum attacks really depend on the key size though even 128-bit is arguable since it is not clear how one can run the sequential calls of Grover's machine..
0
Reply
lk flag
kytebucks000
brilliant answers!
0
Reply
kelalaka avatar
in flag
kelalaka
@kytebucks000 well, in SO network, upvote (10Pts)is used to show that ( you need 15 points for this and If you edit a post, you will get +2 points) and accepting the answer (15pts to the answerer and 20pts to you) is performed by clicking the checkmark. This indicates the other that the problem is solved. Have fun.
0
Reply
ธงชาติไทย
Elon Musk
I sit in a Tesla and translated this thread with Ai:

mangohost

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.