[viff-devel] Optimizing preprocessing

[Janus Dam Nielsen]

On 21/10/2009, at 20.28, Marcel Keller wrote:
> Martin Geisler wrote:
>> Janus Dam Nielsen <janus.nielsen at alexandra.dk> writes:
>>> Hi Marcel,
>>>
>>> I am not opposed to your suggestion. However I would like to point  
>>> out
>>> that in VIFF you compute on shares and not field elements!
>> Well, we've actually made the outer runtime interfaces in such a way
>> that add, mul, xor, etc... accept both integers, FieldElements and
>> Shares. The methods then wrap their input as needed -- or they *dont*
>> wrap it if that leads to a short cut (e.g., constant multiplication)
>
> I agree (see also my answer).
I would still like to stress that Shares are the basic values in VIFF.  
The interface is then designed in such a way, so that we can do  
various optimizations, but computing on field elements (a particular  
representation of a share) is an optimization, which I am very happy  
that the interface allows us to do. But it is still an optimization.

>>> Computing directly on the field elements is hacking the abstractions
>>> of VIFF. Computation on field elements or rather the  
>>> representation of
>>> a Share can be useful as an optimization, however this optimization
>>> should be confined within applications or runtimes, and should not
>>> progress over interface boundaries as I fear you are suggesting.
>> I think we are in agreement: public methods on the runtimes will keep
>> returning Shares. Methods used internally in runtimes can return  
>> other
>> things as needed. To me it sounds like a better API to require
>> preprocessing functions to return a list of Deferreds:
>>  [D(?), D(?), ...],
>> instead of a Deferred list of tuples containing Deferreds :-)
>> I think it will simplify the interface nicely, at least for  
>> consumers.
>> Using simpler types also leads to less memory usage which has a  
>> positive
>> effect on performance, as Marcel notes. So let's go for it.
>
> So this makes 2 votes in favour of it and 1 against it. Maybe we  
> should have a meeting to discuss it. What do you think?
I can agree on this as well, as long as we don't make field elements  
canonical.

____________________________________________________

Janus Dam Nielsen

Research and Innovationspecialist, PhD.
CENTRE FOR IT-SECURITY

THE ALEXANDRA INSTITUTE LTD.

T +45 42 22 93 56
E janus.nielsen at alexandra.dk
W alexandra.dk
____________________________________________________

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