Mikkel Krøigård <[EMAIL PROTECTED]> writes:
>> Tomas is right, of course. For the passive case, using the first
>> 2t+1 players always works, and for the active case, we do not use
>> the local-multiply-and-reshare method anyway.
>
> The thing is, I always just assumed that we always used the same set
> of shares, and it is kind of easy to miss if you just read quickly
> through it - it says what you expect. I guess that's why we all
> missed it until now.
When I wrote the code (we're talking about this method in Runtime:
@increment_pc
def _recombine(self, shares, threshold):
"""Shamir recombine a list of deferred (id,share) pairs."""
assert len(shares) > threshold
def filter_good_shares(results):
# Filter results, which is a list of (success, share)
# pairs.
return [result[1] for result in results
if result is not None and result[0]][:threshold+1]
The list comprehension above will return the t+1 first shares to
arrive.
result = ShareList(shares, threshold+1)
result.addCallback(filter_good_shares)
result.addCallback(shamir.recombine)
return result
) I figured that it would be okay to recombine any subset of site t+1
shares... which is normally true, except for the multiplication
protocol. Ups! :-)
Changing the protocol so that only a designated subset of the players
broadcast their shares ought to make it a bit faster too (in addition
to correct).
> The unit tests should not be hardcoded to n=3, t=1 as they are now,
> because that's why we never found the problem in the first place. I
> can rewrite the unit tests to the general setting. It needs to be
> done.
That is why I committed a bunch of tests last night -- you can see the
failed tests here:
http://buildbot.viff.dk/builders/linux-py2.4/builds/30/steps/trial/logs/problems
As we know by now, * and <= fails when n != 3t + 1.
My idea is that we should have unit tests which target one thing only:
The tests using BinaryOperatorTestCase targets coercion between plain
integers, field elements, and Share objects. The tests in
test_thresholds.py target different thresholds.
We can also have some bigger tests which tests multiple things, and
the application tests in test_apps are examples of this. I would like
to see more such application tests -- they will help us avoid breaking
our example applications without noticing (as has happened before).
--
Martin Geisler
VIFF (Virtual Ideal Functionality Framework) brings easy and efficient
SMPC (Secure Multi-Party Computation) to Python. See: http://viff.dk/.
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