[dm-crypt] How to attached a detached header?

Hi all,

I have a question. I have a detached header for a drive I created years 
ago, where I lost the password for. So, I plan to find the password with 
a brute-force attack. For this I have to attached the header again. I 
thought, this would result in problems - and it did. I build for testing 
purposes the whole situation in a VM. It seems I have to align the data 
offset somehow.

It created the original device as follows:

# cryptsetup luksFormat /dev/sda --hash=sha512 --key-size=512 
--align-payload 4096 --header header.img

# cryptsetup luksDump /dev/sda --header header.img
LUKS header information for header.img

Version:           1
Cipher name:       aes
Cipher mode:       xts-plain64
Hash spec:         sha512
Payload offset:    4096
MK bits:           512
MK digest:         b9 88 28 da e7 ba 60 ee 37 16 44 5b 74 c5 e4 9f 25 20 
01 28
MK salt:           b7 1e 29 73 fe 46 17 a7 02 1f d3 6c 3e ab 9a 27
                    40 3a 05 ce ad 97 99 15 5a 79 a6 0e 4c 84 a5 0f
MK iterations:     149000
UUID:              e7def319-e926-44bf-bf41-2bc850628164

Key Slot 0: ENABLED
     Iterations:             1365332
     Salt:                   de 40 4b a6 e7 69 12 dd b0 dc 8a 7b 82 6d 
6e aa
                               e7 f3 f1 4a 93 9c a4 74 90 ab 9a 1c 8f 86 
a3 d9
     Key material offset:    8
     AF stripes:                4000
Key Slot 1: DISABLED
Key Slot 2: DISABLED
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED

At first I thought to create a new device with the header in front of 
the data. This was a bit naive.

I need help to get data alignment right. Do you have an idea?

Thank you,
Volker

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