def TruncPrRing(a, k, m, signed=True):
if m == 0:
return a
n_ring = int(program.Program.prog.options.ring)
assert n_ring >= k, '%d too large' % k
if k == n_ring:
for i in range(m):
a += types.sint.get_random_bit() << i
return comparison.TruncLeakyInRing(a, k, m, signed=signed)
else:
from types import sint
if signed:
a += (1 << (k - 1))
if program.Program.prog.use_trunc_pr:
res = sint()
trunc_pr(res, a, k, m)
else:
# extra bit to mask overflow
r_bits = [sint.get_random_bit() for i in range(k + 1)]
n_shift = n_ring - len(r_bits)
tmp = a + sint.bit_compose(r_bits)
masked = (tmp << n_shift).reveal()
shifted = (masked << 1 >> (n_shift + m + 1))
overflow = r_bits[-1].bit_xor(masked >> (n_ring - 1))
res = shifted - sint.bit_compose(r_bits[m:k]) + \
(overflow << (k - m))
if signed:
res -= (1 << (k - m - 1))
return res
def TruncZeroesInRing(a, k, m, signed):
"""
Returns a >> m.
Requires 2^m | a and a < 2^k.
"""
from types import sint, intbitint, cint, cgf2n
n_bits = k - m
n_shift = int(program.options.ring) - n_bits
r_bits = [sint.get_random_bit() for i in range(n_bits)]
r = sint.bit_compose(r_bits)
shifted = ((a << (n_shift - m)) - (r << n_shift)).reveal()
masked = shifted >> n_shift
res_bits = intbitint.bit_adder(r_bits, masked.bit_decompose(n_bits))
res = sint.bit_compose(res_bits)
if signed:
res = sint.conv(res_bits[-1].if_else(res - (sint(1) << n_bits), res))
return res
def TruncZeroesInRing(a, k, m, signed):
"""
Returns a >> m.
Requires 2^m | a and a < 2^k.
"""
from types import sint, intbitint, cint, cgf2n
n_bits = k - m
n_shift = int(program.options.ring) - n_bits
r_bits = [sint.get_random_bit() for i in range(n_bits)]
r = sint.bit_compose(r_bits)
shifted = ((a << (n_shift - m)) - (r << n_shift)).reveal()
masked = shifted >> n_shift
res_bits = intbitint.bit_adder(r_bits, masked.bit_decompose(n_bits))
res = sint.bit_compose(res_bits)
if signed:
res = sint.conv(res_bits[-1].if_else(res - (sint(1) << n_bits),
res))
return res
def TruncPrRing(a, k, m):
if m == 0:
return a
n_ring = int(program.Program.prog.options.ring)
if k == n_ring:
for i in range(m):
a += types.sint.get_random_bit() << i
return comparison.TruncLeakyInRing(a, k, m, True)
else:
from types import sint
# extra bit to mask overflow
r_bits = [sint.get_random_bit() for i in range(k + 1)]
n_shift = n_ring - len(r_bits)
tmp = a + sint.bit_compose(r_bits)
masked = (tmp << n_shift).reveal()
shifted = (masked << 1 >> (n_shift + m + 1))
overflow = r_bits[-1].bit_xor(masked >> (n_ring - 1))
res = shifted - sint.bit_compose(r_bits[m:k]) + (overflow << (k - m))
return res
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 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 TruncLeakyInRing(a, k, m, signed):
"""
Returns a >> m.
Requires a < 2^k and leaks a % 2^m (needs to be constant or random).
"""
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
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, 0)
res = (u << n_bits) + masked - r
if signed:
res -= (1 << (n_bits - 1))
return res