[Cryptech Core] modexp optimization plans

[Joachim Strömbergson]

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Aloha!

Peter Stuge wrote:
> 4194304 / 65536 = factor 64 doesn't seem huge to me. Typo?

64 is huge increase in performance. It is difference in number of
operations, not cycles.


> Different size moduli still have different number of words. I think 
> completely data-independent constant-time execution is highly
> desirable.

Are you suggesting that all operations should fake a max size modulus
(8192) and always do that many operations. Jakob can probably answer,
bit I would find that solution to be very uncommon even in $$$$ and
certified HSMs.


>> One could further optimize to find the MSB one of the exponent and
>> set the size to that. And then you could end up with data
>> dependent execution time.
> 
> It seems that this is already the case?

No, not at all.

- -- 
Med vänlig hälsning, Yours

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