[Cryptech Tech] core size in cryptech.h

[Joachim Strömbergson]

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Aloha!

Paul Selkirk wrote:
> Ah, okay. I saw what appeared to be an extra 0: #define
> MODEXP_CORE_SIZE          0x1000
> 
> The actual effect is nil, since it doesn't change MODEXP_ADDR_BASE, 
> and there isn't another math core at the moment, but feel free to 
> revert it.
> 
> Looking ahead, will modexp actually need as many as 4096 addresses?
> I see prefixes from 0x000 to 0x400.

No not 4096 addresses, that is a bit on the high side.

The modulus, message, exponent and result max sizes are all 8192 bits,
or 256 32-bit addresses each. If we want to be able to extract the
residue (in order to speed up key operations), that is another 256
addresses. Finally we need to have a general address area for control,
status, config etc.

In total we should need 6 x 256 addresses or 1536 addresses. So a size
of 0x600 (or even 0x800) is a better fit. I did revert your fix I think,
but drop the size to 0x800.


> Coming at it from another angle, will the math segment need more
> than 2 cores of this size?

Pavel probably has better answers re how much address space the ecdsa
core will occupy.

And the question is then also if/what other math cores we might want to
include in the future. I'm unable to come up with one right now though.
But some oher bignum, dsp functions perhaps?

So, probably not more than two.

- -- 
Med vänlig hälsning, Yours

Joachim Strömbergson - Alltid i harmonisk svängning.
========================================================================
 Joachim Strömbergson          Secworks AB          joachim at secworks.se
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