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Date: Wed, 27 Jun 2012 01:35:06 -0700 (PDT)
From: deepika dutta <>
To: "" <>
Subject: Re: mschap-v2 conversion

Hi magnum,

I dont have any practical experience with bitslicing and i think solar can give better answer for expected speedup with bitslicing. I don't find even in literature somebody giving any figure on how much speedup bitslicing can achieve, I feel it all depends on how much one can optimize. 


 From: magnum <>
Sent: Wednesday, June 27, 2012 5:14 AM
Subject: Re: [john-dev] mschap-v2 conversion
On 2012-06-26 15:02, Solar Designer wrote:
> On Tue, Jun 26, 2012 at 10:06:47AM +0200, magnum wrote:
>> Solar may respond much better when he gets some more time.
> I'm sorry, but my opinion is that tuning OpenMP performance with the
> current early/experimental bitslicing implementation for this format is
> premature.

This is my fault, I just noticed she broke OMP and she went off fixing
it. Anyway, even if it's not time to really *tune* it, it should
definitely not be slower than running one core.

> Notice that the speedup from bitslicing without OpenMP is quite low,
> compared to what we're seeing for purely DES formats (much higher
> speedup there).  I guess this might be because of the uses of MD4 and
> the conversions to/from bitslice representation, but that does not
> explain the low speed for the "many salts" case (the uses of MD4 are in
> key setup only).  We need to seriously look into this and see what can
> be done about it.

I presume Deepika is not really interested in this particular format but
in bit-slicing, so using SSE2 for MD4 might be out of scope. I could add
SSE2 for MD4 at some point if it helps. I just need to understand the
context. If we always have 32 or 64 (or 128) keys at a time, it should
be a walk in the park.

I just know the basic theory of BS. Deepika, what is the expected
speedup from just BS (no OMP) if this had been a straight format with no
MD4 and stuff involved? If we run 64-bit, we do 64 items at a time,
right? But it's not 64x faster of course. How much faster, in general,
should it be?

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