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| Science Forum Index » Cryptography Forum » Sliding Window... |
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| Martin... |
 Posted: Mon Oct 19, 2009 10:18 pm |
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Guest
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Hi,
I wonder what are the advantages of the sliding window approach to
implement modular exponentiation. Normally,
I would use the window method where I pre-calculate the powers for a
certain number of bits, e.g. if I have a window size of 4 then I
precalculate the power 2^0 to 2^15 and process then 4 bits of the
exponent at the same time. Maybe someone can exactly point me out how
this sliding window differs from the standard window method.
Many thanks
Martin |
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| Tom St Denis... |
| Posted: Tue Oct 20, 2009 12:06 am |
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Guest
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On Oct 20, 4:18 am, Martin <sportfre... at (no spam) gmx.at> wrote:
[quote]Hi,
I wonder what are the advantages of the sliding window approach to
implement modular exponentiation. Normally,
I would use the window method where I pre-calculate the powers for a
certain number of bits, e.g. if I have a window size of 4 then I
precalculate the power 2^0 to 2^15 and process then 4 bits of the
exponent at the same time. Maybe someone can exactly point me out how
this sliding window differs from the standard window method.
[/quote]
First benefit is you only have to precompute half the values. The
sliding window is such that you're guaranteed to have the msb of your
window set.
The second is you perform marginally fewer multiplications.
Tom |
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