[viff-devel] VIFF and large scale programs -- is VIFF really asynchronous?

[Ivan Bjerre Damgård]

Folks,

I think your precious time is better spent on figuring out a brilliant
solution to handling memory issues with VIFF, than on discussions about what
"asynchronous" really means :-)

regards, Ivan

Quoting Marcel Keller <mkeller at cs.au.dk>:

>> A really unpleasant thought has occurred to me: Is VIFF really properly
>> asynchronous? (Yes, this question is intended to provoke you into thinking
>> about the issue below. Of course VIFF is asynchronous in the sense that
>> there are no rounds.)
>>
>>
>>
>> If I understand/remember correctly, VIFF is 100% single threaded. This
>> means that if we have a small program:
>>
>> x, y = runtime.shamir_share([1, 2], Zp, input)
>> z = x*y
>> for i in xrange(100):
>>   z=z*z
>>
>> 1) We first share two values (returning immediately).
>
> There's a pitfall here: What do you mean with "share"? At this point, the
> shares are only scheduled to be sent, the real communication doesn't occur
> until step 3. The FAQ of Twisted says so:
> http://twistedmatrix.com/trac/wiki/FrequentlyAskedQuestions#WhydoesittakealongtimefordataIsendwithtransport.writetoarriveattheothersideoftheconnection
> Since I discussed this issue last week with Martin, I also looked at the
> source of Twisted 8.1.0 to confirm it.
>
>> 2) We start doing a lot of multiplications. However, as we don't have
>> the actual shares yet, we just get deferreds.
>>
>> 3) Once the for-loop terminates, we return control to the
>> surroundings. At this point we notice that the shares of x and y are
>> there and start the actual multiplication protocols.
>>
>>
>>
>> Is my interpretation above correct? Because if it is, then this really
>> explains the memory issues I've been seeing. And more importantly, it
>> tells us how to actually use VIFF for large-scale computation: put in
>> explicit "stops".
>
> As Mikkel wrote, I had the same issues and I solved them by calling parts of
> my code (one AES round at a time) as a callback of some trigger shares.
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