def prss_share_bit_double(self, field):
"""Share a random bit over *field* and GF256.
The protocol is described in "Efficient Conversion of
Secret-shared Values Between Different Fields" by Ivan Damgård
and Rune Thorbek available as `Cryptology ePrint Archive,
Report 2008/221 <http://eprint.iacr.org/2008/221>`__.
"""
n = self.num_players
k = self.options.security_parameter
prfs = self.players[self.id].prfs(2**k)
prss_key = self.prss_key()
b_p = self.prss_share_random(field, binary=True)
r_p, r_lsb = prss_lsb(n, self.id, field, prfs, prss_key)
b = self.open(b_p + r_p)
# Extract least significant bit and change field to GF256.
b.addCallback(lambda i: GF256(i.value & 1))
b.field = GF256
# Use r_lsb to flip b as needed.
return (b_p, b ^ r_lsb)
def prss_share_bit_double(self, field):
"""Share a random bit over *field* and GF256.
The protocol is described in "Efficient Conversion of
Secret-shared Values Between Different Fields" by Ivan Damgård
and Rune Thorbek available as `Cryptology ePrint Archive,
Report 2008/221 <http://eprint.iacr.org/2008/221>`__.
"""
n = self.num_players
k = self.options.security_parameter
prfs = self.players[self.id].prfs(2**k)
prss_key = self.prss_key()
b_p = self.prss_share_random(field, binary=True)
r_p, r_lsb = prss_lsb(n, self.id, field, prfs, prss_key)
b = self.open(b_p + r_p)
# Extract least significant bit and change field to GF256.
b.addCallback(lambda i: GF256(i.value & 1))
b.field = GF256
# Use r_lsb to flip b as needed.
return (b_p, b ^ r_lsb)
def test_prss_lsb(self):
(share, bit) = prss.prss_lsb(None, None, self.field, None, None)
self.assertEquals(share, self.field(7))
self.assertEquals(bit, GF256(1))
def test_prss_lsb(self):
(share, bit) = prss.prss_lsb(None, None, self.field, None, None)
self.assertEquals(share, self.field(7))
self.assertEquals(bit, GF256(1))
