[viff-devel] [issue75] Test without local computations

[Ivan Bjerre Damgård]

Hi folks,

Very interesting! I think Martin is right that there is something lost  
in general machinery, but I don't think this means that none of this  
machinery can be removed.
There are bigger lumps of computation that could be done with one call  
to a faster module. Examples:

1) Lagrange interpolation, i.e., reconstructing secret from a set of shares
2) the linear recombination that is done at the end of a multiplication.
3) Secret sharing, i.e., given secret, choose random polynomial and  
evaluate in given points
4) PRSS, which also involves some symmetric crypto.

I guess it would be easy to simply skip 2) in the current code,  
simulating that we have a superfast for linear combination, and see  
what difference that makes..

regards, Ivan


Quoting Martin Geisler <mg at daimi.au.dk>:

> Hi everybody,
>
> I've done some tests where I replaced the normal FieldElement class
> with a new class named FakeFieldElement (rev 464008ada9c2). This class
> fakes all computations by always returning 1.
>
> Timing 10000 multiplications using the real and the fake field
> elements give these results between three machines on the DAIMI LAN:
>
>   +-------------------+----------+----------+------+
>   | Field size (bits) | Real (s) | Fake (s) | Diff |
>   +-------------------+----------+----------+------+
>   |         50        |   14.1   |   13.5   |  4%  |
>   +-------------------+----------+----------+------+
>   |        100        |   14.3   |   13.2   |  8%  |
>   +-------------------+----------+----------+------+
>   |        200        |   14.5   |   13.3   |  8%  |
>   +-------------------+----------+----------+------+
>   |        400        |   15.0   |   13.1   | 13%  |
>   +-------------------+----------+----------+------+
>   |        800        |   16.2   |   13.3   | 18%  |
>   +-------------------+----------+----------+------+
>   |       1600        |   21.4   |   13.5   | 37%  |
>   +-------------------+----------+----------+------+
>
> The results show that there is something to improve for large numbers,
> but for field of size 50-100 bit the difference is quite small. It
> would be interesting to see how the numbers compare when Sigurd
> finishes the patch for using GMPY:
>
>   http://tracker.viff.dk/issue10
>
> It is currently waiting for a reply on my review comments.
>
> These results are from a gigabit LAN, so the time spend on network
> communication is as low as it can possible get. I guess that means
> that the rest of the time is lost in the overall machinery :-(
>
> --
> Martin Geisler
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