Mercurial > viff
changeset 643:84d720a9ed4b
Added double_share_random method to Runtime.
This method uses a hyper-invertible matrix to efficiently generate
shares of a number of random values unknown to all parties. The values
are shared using two different degrees.
author | Martin Geisler <mg@daimi.au.dk> |
---|---|
date | Sat, 05 Apr 2008 00:00:24 +0200 |
parents | 885828ebed92 |
children | cc58a62d507c |
files | viff/runtime.py |
diffstat | 1 files changed, 52 insertions(+), 1 deletions(-) [+] |
line wrap: on
line diff
--- a/viff/runtime.py Sat Apr 05 00:00:24 2008 +0200 +++ b/viff/runtime.py Sat Apr 05 00:00:24 2008 +0200 @@ -40,7 +40,8 @@ from viff import shamir from viff.prss import prss from viff.field import GF256, FieldElement -from viff.util import wrapper +from viff.matrix import Matrix, hyper +from viff.util import wrapper, rand from twisted.internet import reactor from twisted.internet.defer import Deferred, DeferredList @@ -952,6 +953,56 @@ normal L{Runtime} class and is thus I{not} yet secure. """ + def __init__(self, player, threshold, options=None): + """Initialize runtime.""" + + #: A hyper-invertible matrix. + #: + #: It should be suitable for L{self.num_players} players, but + #: since we don't know the total number of players yet, we set + #: it to C{None} here and update it as necessary. + self._hyper = None + Runtime.__init__(self, player, threshold, options) + + @increment_pc + def double_share_random(self, T, d1, d2, field): + """Double-shares a randoms secret by using two polynomials. + + The guarantee is that a number of shares are made and out of + those, the T that are returned by this method will be correct + double-sharings of a random number using d1 and d2 as the + polynomial degrees. + + @param T: The number of double-shares output. + @param d1: The degree of the first polynomial. + @param d2: The degree of the second polynomial. + @param field: The field over which to share the secret. + """ + inputters = range(1, self.num_players + 1) + if self._hyper is None: + self._hyper = hyper(self.num_players, field) + + # Generate a random element. + si = rand.randint(0, field.modulus - 1) + + # Every player shares the random value with two thresholds. + d1_shares = self.shamir_share(inputters, field, si, d1) + d2_shares = self.shamir_share(inputters, field, si, d2) + + # Turn the shares into a column vector. + svec1 = Matrix([d1_shares]).transpose() + svec2 = Matrix([d2_shares]).transpose() + + # Apply the hyper-invertible matrix to svec1 and svec2. + rvec1 = (self._hyper * svec1).transpose() + rvec2 = (self._hyper * svec2).transpose() + + # TODO: verify sharings + + # Return the first T shares (the ones that was not opened in + # the verifying step. + return rvec1.rows[0][:T], rvec2.rows[0][:T] + @increment_pc def _broadcast(self, sender, message=None): """Perform a Bracha broadcast.