def TruncLeakyInRing(a, k, m, signed):
"""
Returns a >> m.
Requires a < 2^k and leaks a % 2^m (needs to be constant or random).
"""
if k == m:
return 0
assert k > m
assert int(program.options.ring) >= k
from .types import sint, intbitint, cint, cgf2n
n_bits = k - m
n_shift = int(program.options.ring) - n_bits
if n_bits > 1:
r, r_bits = MaskingBitsInRing(n_bits, True)
else:
r_bits = [sint.get_random_bit() for i in range(n_bits)]
r = sint.bit_compose(r_bits)
if signed:
a += (1 << (k - 1))
shifted = ((a << (n_shift - m)) + (r << n_shift)).reveal()
masked = shifted >> n_shift
u = sint()
BitLTL(u, masked, r_bits[:n_bits], 0)
res = (u << n_bits) + masked - r
if signed:
res -= (1 << (n_bits - 1))
return res
def get_bits_loop():
# How can we do this with a vectorized load of the bits? XXXX
tbits = [sint(0)]*bit_length
for i in range(bit_length):
tbits[i] = sint.get_random_bit()
tbits[i].store_in_mem(i)
c = regint(BitLTFull(tbits, pbits, bit_length).reveal())
return (c!=1)
def MaskingBitsInRing(m, strict=False):
from Compiler.types import sint
if program.use_edabit():
return sint.get_edabit(m, strict)
elif program.use_dabit:
r, r_bin = zip(*(sint.get_dabit() for i in range(m)))
else:
r = [sint.get_random_bit() for i in range(m)]
r_bin = r
return sint.bit_compose(r), r_bin
def Mod2mRing(a_prime, a, k, m, signed):
assert (int(program.options.ring) >= k)
from Compiler.types import sint, intbitint, cint
shift = int(program.options.ring) - m
r = [sint.get_random_bit() for i in range(m)]
r_prime = sint.bit_compose(r)
tmp = a + r_prime
c_prime = (tmp << shift).reveal() >> shift
u = sint()
BitLTL(u, c_prime, r, 0)
res = (u << m) + c_prime - r_prime
if a_prime is not None:
movs(a_prime, res)
return res
def get_random_bit(size=None):
return sint.get_random_bit(size=size)
def get_random_bit(size=None):
return sint.get_random_bit(size=size)
