Re: [dm-crypt] Cryptesetup and dm-crypt

[Arno Wagner <arno@wagner.name>]

At the very least, it is a safety issue, as all documentation 
and all relevant help given here says block size is 512 bytes.
It is also a compatibility issue, as volumes done this way 
would only work on your specific system and could not be 
accessed and recovered anywhere else. 

My stance would be sure, shoot yourself in the foot, but do
not call the result "LUKS".

Regards,
Arno

On Wed, Apr 27, 2016 at 14:56:50 CEST, levent demir wrote:
> Hi,
> 
> I am a PhD student and works and I am working with cryptsetup and a hw
> crypto engine. 
> 
> I am using an ATMEL board which is able to do AES-ECB mode for example. 
> 
> We have implemented an XTS version with all operations (XOR, GF
> Multiplication, 2 AES : one for IV one for data...)
> 
> My question is can we use the page size instead of the block size of 512
> bytes ?
> 
> I have read some thread it is written that it could be a security issue
> but I don't agree because : 
> 
> Now to implement XTS I do as follows basically : 
> 
> I take the IV encrypt it with the second part of the key, then I compute
> the 32 tweaks values in -for example- an array tweak_buf[512]. 
> Then I just have to compute the XOR with plaintext. 
> I do a DMA encryption with ECB of the 512 bytes. 
> Again I xor the ciphered data with tweak_buf.
> 
> Then I have ciphered a whole block of 512 bytes.
> 
> Now my question, the hardware is supporting a DMA operation till 4096, 
> is it not interesting to encrypt 8 blocks at a time ? 
> It is exactly the same operation as encrypting each block
> consecutively. 
> 
> Of course I need to pre-compute the 8 tweak_buf in a big
> tweak_buf[4096].Then in only one DMA operation I will be able to encrypt
> 4096 bytes with ECB mode. 
> 
> I hope you understand what I mean.
> 
> Can you tell me if it is possible ? If yes can I use a previous patch, I
> have seen that there are some works on it ?
> 
> Thank you. 
> 
> 
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-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
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