def ModExp(a, b, c):
"""Uses openssl, if available, to do a^b mod c where a,b,c are longs."""
if not _FOUND_SSL:
return pow(a, b, c)
# convert arbitrary long args to bytes
bytes_a = number.LongToBytes(a)
bytes_b = number.LongToBytes(b)
bytes_c = number.LongToBytes(c)
# convert bytes to (pointer to) Bignums.
bn_a = ssl.BN_bin2bn(bytes_a, len(bytes_a), 0)
bn_b = ssl.BN_bin2bn(bytes_b, len(bytes_b), 0)
bn_c = ssl.BN_bin2bn(bytes_c, len(bytes_c), 0)
bn_result = ssl.BN_new()
ctx = ssl.BN_CTX_new()
# exponentiate and convert result to long
ssl.BN_mod_exp(bn_result, bn_a, bn_b, bn_c, ctx)
num_bytes_in_result = _NumBytesBn(bn_result)
bytes_result = ctypes.create_string_buffer(num_bytes_in_result)
ssl.BN_bn2bin(bn_result, bytes_result)
long_result = number.BytesToLong(bytes_result.raw)
# clean up
ssl.BN_CTX_free(ctx)
ssl.BN_free(bn_a)
ssl.BN_free(bn_b)
ssl.BN_free(bn_c)
ssl.BN_free(bn_result)
return long_result
def testBytesToLong(self):
self.assertEqual(205, number.BytesToLong('\xcd'))
self.assertEqual(64, number.BytesToLong('\x00\x00\x00\x40'))
self.assertEqual(64, number.BytesToLong('\x40'))
self.assertEqual(4294967295 + 1,
number.BytesToLong('\x01\x00\x00\x00\x00'))
self.assertEqual(
18446744069414584320,
number.BytesToLong('\xff\xff\xff\xff\x00\x00\x00\x00'))
self.assertEqual(3, number.BytesToLong(struct.pack('>I', 3)))
self.assertEqual(4294967303,
number.BytesToLong(struct.pack('>2I', 1, 7)))
self.assertEqual(2**64, number.BytesToLong(struct.pack('>3I', 1, 0,
0)))
self.assertEqual(
2**160 + 2**128 + 2**96 + 2**64 + 2**32 + 7,
number.BytesToLong(struct.pack('>6I', 1, 1, 1, 1, 1, 7)))
def Decrypt(self, ciphertext):
"""Takes ciphertext and decrypts to a float.
Args:
ciphertext: a string which is an encrypted float, converted to bytes,
and base64 encoded.
Returns:
decrypted float.
Raises:
ValueError: when ciphertext is not a string.
"""
if not isinstance(ciphertext, str):
raise ValueError('Expected type data str but got: %s' % type(ciphertext))
return self._paillier.DecryptFloat(
number.BytesToLong(base64.b64decode(ciphertext)))