http://hg.viff.dk/viff/rev/d522f9b14b49
changeset: 1148:d522f9b14b49
user: Marcel Keller <[email protected]>
date: Thu Feb 26 19:35:08 2009 +0100
summary: Added possibility to share multiple random bits in GF256 with less
calls of the PRF.
diffstat:
4 files changed, 51 insertions(+), 4 deletions(-)
viff/aes.py | 5 ++---
viff/passive.py | 25 ++++++++++++++++++++++++-
viff/prss.py | 13 +++++++++++++
viff/test/test_runtime_prss.py | 12 ++++++++++++
diffs (102 lines):
diff -r 5ac7a2c23337 -r d522f9b14b49 viff/aes.py
--- a/viff/aes.py Wed Feb 25 21:14:30 2009 +0100
+++ b/viff/aes.py Thu Feb 26 19:35:08 2009 +0100
@@ -34,9 +34,8 @@
assert isinstance(share, Share) and share.field == GF256, \
"Parameter must be GF256 share."
- r_bits = [share.runtime.prss_share_random(GF256, binary=True) \
- for i in range(8)]
-
+ r_bits = share.runtime.prss_share_random_multi(GF256, 8, binary=True)
+
if (use_lin_comb):
r = share.runtime.lin_comb([2 ** i for i in range(8)], r_bits)
else:
diff -r 5ac7a2c23337 -r d522f9b14b49 viff/passive.py
--- a/viff/passive.py Wed Feb 25 21:14:30 2009 +0100
+++ b/viff/passive.py Thu Feb 26 19:35:08 2009 +0100
@@ -21,7 +21,7 @@
from viff import shamir
from viff.runtime import Runtime, increment_pc, Share, ShareList, gather_shares
-from viff.prss import prss, prss_lsb, prss_zero
+from viff.prss import prss, prss_lsb, prss_zero, prss_multi
from viff.field import GF256, FieldElement
from viff.util import rand, profile
@@ -352,6 +352,29 @@
return result
@increment_pc
+ def prss_share_random_multi(self, field, quantity, binary=False):
+ """Does the same as calling *quantity* times :meth:`prss_share_random`,
+ but with less calls to the PRF. Sampling of a binary element is only
+ possible if the field is :class:`GF256`.
+
+ Communication cost: none.
+ """
+ assert not binary or field == GF256, "Binary sampling not possible " \
+ "for this field, use prss_share_random()."
+
+ if field is GF256 and binary:
+ modulus = 2
+ else:
+ modulus = field.modulus
+
+ # Key used for PRSS.
+ prss_key = tuple(self.program_counter)
+ prfs = self.players[self.id].prfs(modulus ** quantity)
+ shares = prss_multi(self.num_players, self.id, field, prfs, prss_key,
+ modulus, quantity)
+ return [Share(self, field, share) for share in shares]
+
+ @increment_pc
def prss_share_zero(self, field):
"""Generate shares of the zero element from the field given.
diff -r 5ac7a2c23337 -r d522f9b14b49 viff/prss.py
--- a/viff/prss.py Wed Feb 25 21:14:30 2009 +0100
+++ b/viff/prss.py Thu Feb 26 19:35:08 2009 +0100
@@ -120,6 +120,19 @@
rep_shares = random_replicated_sharing(j, prfs, key)
return convert_replicated_shamir(n, j, field, rep_shares)
+def prss_multi(n, j, field, prfs, key, modulus, quantity):
+ """Does the same as :meth:`prss`, but multiple times in order to
+ call the PRFs less frequently.
+ """
+ prf_results = random_replicated_sharing(j, prfs, key)
+ rep_shares_list = [[] for i in range(quantity)]
+ for subset, result in prf_results:
+ for i in range(quantity):
+ rep_shares_list[i].append((subset, result % modulus))
+ result /= modulus
+ return [convert_replicated_shamir(n, j, field, rep_shares)
+ for rep_shares in rep_shares_list]
+
@fake(lambda n, j, field, prfs, key: (field(7), GF256(1)))
def prss_lsb(n, j, field, prfs, key):
"""Share a pseudo-random number and its least significant bit.
diff -r 5ac7a2c23337 -r d522f9b14b49 viff/test/test_runtime_prss.py
--- a/viff/test/test_runtime_prss.py Wed Feb 25 21:14:30 2009 +0100
+++ b/viff/test/test_runtime_prss.py Thu Feb 26 19:35:08 2009 +0100
@@ -116,6 +116,18 @@
return opened_a
@protocol
+ def test_prss_share_random_multi_bit(self, runtime):
+ """Tests the sharing of several 0/1 GF256 elements using PRSS."""
+ a_list = runtime.prss_share_random_multi(field=GF256, quantity=8,
binary=True)
+
+ for a in a_list:
+ self.assert_type(a, Share)
+ opened_a = runtime.open(a)
+ opened_a.addCallback(self.assertIn, [GF256(0), GF256(1)])
+
+ return gather_shares(a_list)
+
+ @protocol
def test_prss_share_zero_bit(self, runtime):
"""Tests the sharing of a zero GF256 element using PRSS."""
a = runtime.prss_share_zero(GF256)
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