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+# ===================================================================
+#
+# Copyright (c) 2018, Helder Eijs <helderijs@gmail.com>
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in
+# the documentation and/or other materials provided with the
+# distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+# ===================================================================
+
+from ._IntegerNative import IntegerNative
+
+from Cryptodome.Util.number import long_to_bytes, bytes_to_long
+
+from Cryptodome.Util._raw_api import (load_pycryptodome_raw_lib,
+ create_string_buffer,
+ get_raw_buffer, backend,
+ c_size_t, c_ulonglong)
+
+
+from Cryptodome.Random.random import getrandbits
+
+c_defs = """
+int monty_pow(const uint8_t *base,
+ const uint8_t *exp,
+ const uint8_t *modulus,
+ uint8_t *out,
+ size_t len,
+ uint64_t seed);
+"""
+
+
+_raw_montgomery = load_pycryptodome_raw_lib("Cryptodome.Math._modexp", c_defs)
+implementation = {"library": "custom", "api": backend}
+
+
+class IntegerCustom(IntegerNative):
+
+ @staticmethod
+ def from_bytes(byte_string):
+ return IntegerCustom(bytes_to_long(byte_string))
+
+ def inplace_pow(self, exponent, modulus=None):
+ exp_value = int(exponent)
+ if exp_value < 0:
+ raise ValueError("Exponent must not be negative")
+
+ # No modular reduction
+ if modulus is None:
+ self._value = pow(self._value, exp_value)
+ return self
+
+ # With modular reduction
+ mod_value = int(modulus)
+ if mod_value < 0:
+ raise ValueError("Modulus must be positive")
+ if mod_value == 0:
+ raise ZeroDivisionError("Modulus cannot be zero")
+
+ # C extension only works with odd moduli
+ if (mod_value & 1) == 0:
+ self._value = pow(self._value, exp_value, mod_value)
+ return self
+
+ # C extension only works with bases smaller than modulus
+ if self._value >= mod_value:
+ self._value %= mod_value
+
+ max_len = len(long_to_bytes(max(self._value, exp_value, mod_value)))
+
+ base_b = long_to_bytes(self._value, max_len)
+ exp_b = long_to_bytes(exp_value, max_len)
+ modulus_b = long_to_bytes(mod_value, max_len)
+
+ out = create_string_buffer(max_len)
+
+ error = _raw_montgomery.monty_pow(
+ out,
+ base_b,
+ exp_b,
+ modulus_b,
+ c_size_t(max_len),
+ c_ulonglong(getrandbits(64))
+ )
+
+ if error:
+ raise ValueError("monty_pow failed with error: %d" % error)
+
+ result = bytes_to_long(get_raw_buffer(out))
+ self._value = result
+ return self