phc-discussions - Re: [PHC] A review per day

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Date: Mon, 15 Sep 2014 20:06:34 -0400
From: Bill Cox <waywardgeek@...hershed.org>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] A review per day - Catena

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On 09/15/2014 08:19 AM, Dmitry Khovratovich wrote:
> Catena-3 with 128 MB of memory would need 2^21 64-byte SHA blocks,
> so 2^23 compression function calls, i.e. 15mJ within 8/(316/65)=1.5
> seconds. Our tradeoffs have computational penalty 3.75q for the
> memory reduction by q, so, for instance, running it with 16 MB of
> memory would require 30x more energy, or 450mJ within the same 1.5
> seconds.
> 
> The memory will consume far larger. The 128-MB Catena-3
> reads/writes 768 MB of data from/to RAM, and 1.5 GB in tradeoffs.
> If we consider GDDR5, advocated by Bill, and scale it down to 300
> MHz, it would at least consume 0.5W, so its energy consumption
> would be 750mJ, and 94mJ for 16MB.
> 
> Therefore, the attacker will reduce his costs even if the memory is
> reduced 8-fold. And we have not counted the retention energy yet,
> as it will raise the tradeoff efficiency even more.
> 

So, your chip-busting 16MiB on-chip ultra-wide, 30-port cache, from
which you will read 30X more data than I read from external GDDR5 in
the same time... will consume less than 0.1W?  I want some of that
magic memory!  And whatever you're smoking!

I just deleted all my power guestimates that show this is dream-land.
 If you can't figure this out on your own, I'm done talking about it.

Bill
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