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Message-ID: <CABob6ioqfGFT4qtXkvR7i40KVOWXyLWwqUJJff9KiYCrSyxEcQ@mail.gmail.com>
Date: Wed, 4 Dec 2013 00:31:29 +0100
From: Lukas Odzioba <lukas.odzioba@...il.com>
To: john-users@...ts.openwall.com
Subject: Re: Energy-efficient bcrypt cracking (Passwords^13 slides)
2013/12/3 Solar Designer <solar@...nwall.com>:
> On Tue, Dec 03, 2013 at 10:31:12PM +0100, Lukas Odzioba wrote:
> bull's PSU is officially 85% efficient.
> super's PSUs officially have over 94% efficiency, and there was in fact
> not much difference between AC and 12V DC deltas for GPU load.
PSU efficiency is not constant, so I think there might be hidden 2-5%
estimation error here, but it's still reasonable.
>> Values for gpus looks a bit too small for me.
>
> Actually, before we started measuring, I expected them to be even
> smaller, because bcrypt uses at most 1/4th of HD 7970's computing power.
> My guess was "probably way below 100 W"; in reality, it's around 100 W
> and sometimes even more than that.
When I realized that it was measured under bcrypt load it became clear
to me that it is fine.
> Here's the calculation for HD 7970:
>
> 15 W idle + 95 W delta * 0.85 PSU efficiency = ~96 W
It makes sense now. Thank you very much for clarification.
Lukas
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