def decrypt_recursive(self, ciphertext, in_range, out_range):
in_size = in_range.size() # M
out_size = out_range.size() # N
in_edge = in_range.start - 1 # d
out_edge = out_range.start - 1 # r
mid = out_edge + int(math.ceil(out_size / 2.0)) # y
assert in_size <= out_size
if in_range.size() == 1:
in_range_min = in_range.start
coins = self.tape_gen(in_range_min)
sampled_ciphertext = stat.sample_uniform(out_range, coins)
if sampled_ciphertext == ciphertext:
return in_range_min
else:
raise InvalidCiphertextError('Invalid ciphertext')
coins = self.tape_gen(mid)
x = stat.sample_hgd(in_range, out_range, mid, coins)
if ciphertext <= mid:
in_range = ValueRange(in_edge + 1, x)
out_range = ValueRange(out_edge + 1, mid)
else:
in_range = ValueRange(x + 1, in_edge + in_size)
out_range = ValueRange(mid + 1, out_edge + out_size)
return self.decrypt_recursive(ciphertext, in_range, out_range)
def encrypt_recursive(self, plaintext, in_range, out_range):
in_size = in_range.size() # M
out_size = out_range.size() # N
in_edge = in_range.start - 1 # d
out_edge = out_range.start - 1 # r
mid = out_edge + int(math.ceil(out_size / 2.0)) # y
assert in_size <= out_size
if in_range.size() == 1:
coins = self.tape_gen(plaintext)
ciphertext = stat.sample_uniform(out_range, coins)
return ciphertext
coins = self.tape_gen(mid)
x = stat.sample_hgd(in_range, out_range, mid, coins)
if plaintext <= x:
in_range = ValueRange(in_edge + 1, x)
out_range = ValueRange(out_edge + 1, mid)
else:
in_range = ValueRange(x + 1, in_edge + in_size)
out_range = ValueRange(mid + 1, out_edge + out_size)
return self.encrypt_recursive(plaintext, in_range, out_range)
def test_uniform():
# Short ranges
value = 10
unit_range = ValueRange(value, value)
assert sample_uniform(unit_range, []) == value
short_range = ValueRange(value, value + 1)
assert sample_uniform(short_range, [0]) == value
assert sample_uniform(short_range, [1]) == value + 1
assert sample_uniform(short_range, [0, 0, 1, 0, 'llama']) == value, "More bits yield no effect"
with pytest.raises(Exception):
sample_uniform(short_range, [])
# Medium ranges
start_range = 20
end_range = start_range + 15
range1 = ValueRange(start_range, start_range + 15)
assert sample_uniform(range1, [0, 0, 0, 0]) == start_range
assert sample_uniform(range1, [0, 0, 0, 1]) == start_range + 1
assert sample_uniform(range1, [1, 1, 1, 1]) == end_range
# Test with a generator object
assert sample_uniform(range1, itertools.repeat(0, 10)) == start_range
# Negative range
start_range = -32
end_range = -17
range = ValueRange(start_range, end_range)
assert sample_uniform(range, [0] * 5) == start_range
assert sample_uniform(range, [1] * 5) == end_range
# Mixed range
start_range = -32
end_range = 31
range = ValueRange(start_range, end_range)
assert sample_uniform(range, [0] * 6) == start_range
assert sample_uniform(range, [1] * 6) == end_range