[viff-devel] Error when coding with callbacks and reveals

[Martin Geisler]

Tord Ingolf Reistad <tordr at stud.ntnu.no> writes:

> Hello,
>
> Continuing on my previous email about how to code things in VIFF. I
> hereby present the complete test code.
>
> It seems my calculations are done at the same time that the reactor
> is closing down so sometimes my code does not return any printed
> values. This is a mistake, either in my understanding of VIFF or in
> the framework itself.

Yeah, I know what you mean... it takes a bit of time to wrap your head
around how to structure things in VIFF. The solution is often very
simple when someone else points it out, though :-)

But don't worry, after the initial head-ache, you'll be fine...

> See the two runs below.
>
>
> class Protocol:
>
>     def __init__(self, runtime):
>         # Save the Runtime for later use
>         self.runtime = runtime
>         own_id = self.runtime.id
>
>         Zp = GF(43)
>         test_vector = [0, 1, 6, 0]
>         self.value = test_vector[own_id - 1]
>         m1, m2, m3 = runtime.shamir_share([1, 2, 3], Zp, self.value)
>         shares = [m1, m2, m3]
>         r_as_bits = [m1, m2, m1]
>         r = m3
>         mask = m3
>         x = m3
>         result = self.protocol_part_1(r_as_bits, r, mask, x)
>         callback_result = result.addCallback(self.print_answer)
>         #results.addCallback(lambda _: runtime.synchronize())
>         m1.addCallback(lambda _: runtime.shutdown())

This is a problem -- just as soon as m1 arrives from the Shamir
sharing above, runtime.shutdown will be called.

You will want to call runtime.shutdown at a later point when you know
that the protocol is done.

>         #Create_random_bits
>         #Convert_to_test_values
>         #Test_values if useable use random bits otherwise find new bits
>         #c = r + x
>         #Compare (c,r)
>
>     def protocol_part_1(self, r_as_bits, r, mask, x):
> 	test = self.test_not_all_zero(r_as_bits, mask)
> 	self.r = r
> 	self.x = x
> 	return test.addCallback(self.protocol_part_2)
>
>     def protocol_part_2(self, test):
>         if test:
>             c = self.r + self.x
>             c_open = self.runtime.open(c)
>             result = gather_shares([c_open])
>             callback_result = result.addCallback(self.print_answer)
>             return callback_result
>         else:
>             print "No value, False"
>             return False
>
>     def print_answer(self, value):
>         print "Result ", value

I think you want to call self.runtime.shutdown() here since this is
when your result is there.

-- 
Martin Geisler

VIFF (Virtual Ideal Functionality Framework) brings easy and efficient
SMPC (Secure Multiparty Computation) to Python. See: http://viff.dk/.