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Date: Mon, 25 Nov 2019 16:17:07 +0100
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Subject: Re: [dm-crypt] detached LUKS header size
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To: Milan Broz <gmazyland@gmail.com>, dm-crypt@saout.de

> On 2019-11-25 14:55, Milan Broz wrote:

Hi Milan,

just to make sure there is no misunderstanding:

> Then there is alignment, so the real data offset is aligned by default t=
o
> the 1MB boundary.
>
> With this padding, header size is for 128bit key 2MB, for 256/512 key 4M=
B.

I am actually using 512 bit key:

 --cipher aes-xts-plain64 --key-size 512 --hash sha512

so it would seem I need 4MB header for luks1 with 512 key

> Yes. For reference: for 128bit it is 528384 bytes, for 256bit 1052672
> bytes,
> for 512bit (2x256bits in XTS mode) it is 2068480 bytes.

now I am confused. 2068480 is less than 2MB. So when aligned to 1MB
boundary, 2MB would be enough for luks1 with 512 key.

So is it 2MB or 4MB ?

many thanks,