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Message-ID: <CA+TsHUAb_YOqH6ZnP59ZoRvTkeZXibYP-YF6SZbzR5cAsaa1+g@mail.gmail.com>
Date: Mon, 27 Aug 2012 01:06:52 +0530
From: Sayantan Datta <std2048@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: bitslice DES on GPU
On Mon, Aug 27, 2012 at 12:44 AM, Sayantan Datta <std2048@...il.com> wrote:
> Hi solar,
>
>
> On Sun, Aug 26, 2012 at 2:23 PM, Solar Designer <solar@...nwall.com>wrote:
>
>> So let's suppose DES_BS_EXPAND=1. In that case, you could do the
>> expansion on CPU side, but the reason why you won't is that you want to
>> keep the key setup finalization on GPU. That's fine. However, all you
>> need on GPU to perform the expansion is that constant array of 768
>> indices; you don't need any pointers, and you don't want to use pointers
>> for the same reason that would apply in the DES_BS_EXPAND=0 case (the
>> pointers would differ between work-items and thus would require a lot
>> more memory total).
>>
>
> #if DES_BS_EXPAND
> {
> int index;
> for (index = 0; index < 0x300; index++)
>
> vst(*(kvtype *)&opencl_DES_bs_all[section].KS.v[index], 0,
> *(kvtype *)opencl_DES_bs_all[section].KSp[index]);
>
> }
> #endif
>
> So you are saying that I should do this portion of the code on cpu. I
> think I could do it in the DES_bs_init() and get rid of KSp all
> together(Right?). Also it would be easier this way.
>
> There is another bigger problem than the previous one. I see that address
> stored in E.E[] array is aliased with the B[] array. Transferring data to
> gpu would change the location of B[] array and result in same kind of
> problem as above. The most complex part being the initialization of E.E[]
> array in the set_salt() function. I could port both DES_bs_init() and
> set_salt() to GPU(as different kernel) but it would then result in same
> problem as I would need to transfer data to and from GPU in order
> to synchronize it with the CPU in between the kernel calls. Whenever I
> transfer data from CPU to GPU the address of B[] will change.
>
> One more thing I would like to know that immediately after set_salt()
> function which function is called? If it is the crypt_all() then maybe I
> could transfer some portion of the required code from DES_bs_init to
> set_salt() and port set_salt() to GPU. And if the crypt_all() function is
> called just after set_salt() then there would be no need for CPU to GPU
> data transfer and the address of B[] would remain the same for set_salt()
> and DES_bs_crypt_25() kernels.
>
> P.S: I assume that the GPU buffer remains at the same global memory
> location unless we write the buffer explicitly.
>
Also is there any way I could convert E.E[] into indices of B[] array?
>
>
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