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1#@!#!123s

: / lib / python3.6 / site-packages / asn1crypto /

Filename : _int.py

back

# coding: utf-8

"""
Function for calculating the modular inverse. Exports the following items:

 - inverse_mod()

Source code is derived from
http://webpages.charter.net/curryfans/peter/downloads.html, but has been heavily
modified to fit into this projects lint settings. The original project license
is listed below:

Copyright (c) 2014 Peter Pearson

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
"""

from __future__ import unicode_literals, division, absolute_import, print_function

import math
import platform

from .util import int_to_bytes, int_from_bytes

# First try to use ctypes with OpenSSL for better performance
try:
    from ._ffi import (
        buffer_from_bytes,
        bytes_from_buffer,
        FFIEngineError,
        LibraryNotFoundError,
        null,
    )

    # Some versions of PyPy have segfault issues, so we just punt on PyPy
    if platform.python_implementation() == 'PyPy':
        raise EnvironmentError()

    try:
        from ._perf._big_num_ctypes import libcrypto

        def inverse_mod(a, p):
            """
            Compute the modular inverse of a (mod p)

            :param a:
                An integer

            :param p:
                An integer

            :return:
                An integer
            """

            ctx = libcrypto.BN_CTX_new()

            a_bytes = int_to_bytes(abs(a))
            p_bytes = int_to_bytes(abs(p))

            a_buf = buffer_from_bytes(a_bytes)
            a_bn = libcrypto.BN_bin2bn(a_buf, len(a_bytes), null())
            if a < 0:
                libcrypto.BN_set_negative(a_bn, 1)

            p_buf = buffer_from_bytes(p_bytes)
            p_bn = libcrypto.BN_bin2bn(p_buf, len(p_bytes), null())
            if p < 0:
                libcrypto.BN_set_negative(p_bn, 1)

            r_bn = libcrypto.BN_mod_inverse(null(), a_bn, p_bn, ctx)
            r_len_bits = libcrypto.BN_num_bits(r_bn)
            r_len = int(math.ceil(r_len_bits / 8))
            r_buf = buffer_from_bytes(r_len)
            libcrypto.BN_bn2bin(r_bn, r_buf)
            r_bytes = bytes_from_buffer(r_buf, r_len)
            result = int_from_bytes(r_bytes)

            libcrypto.BN_free(a_bn)
            libcrypto.BN_free(p_bn)
            libcrypto.BN_free(r_bn)
            libcrypto.BN_CTX_free(ctx)

            return result
    except (LibraryNotFoundError, FFIEngineError):
        raise EnvironmentError()

# If there was an issue using ctypes or OpenSSL, we fall back to pure python
except (EnvironmentError, ImportError):

    def inverse_mod(a, p):
        """
        Compute the modular inverse of a (mod p)

        :param a:
            An integer

        :param p:
            An integer

        :return:
            An integer
        """

        if a < 0 or p <= a:
            a = a % p

        # From Ferguson and Schneier, roughly:

        c, d = a, p
        uc, vc, ud, vd = 1, 0, 0, 1
        while c != 0:
            q, c, d = divmod(d, c) + (c,)
            uc, vc, ud, vd = ud - q * uc, vd - q * vc, uc, vc

        # At this point, d is the GCD, and ud*a+vd*p = d.
        # If d == 1, this means that ud is a inverse.

        assert d == 1
        if ud > 0:
            return ud
        else:
            return ud + p


def fill_width(bytes_, width):
    """
    Ensure a byte string representing a positive integer is a specific width
    (in bytes)

    :param bytes_:
        The integer byte string

    :param width:
        The desired width as an integer

    :return:
        A byte string of the width specified
    """

    while len(bytes_) < width:
        bytes_ = b'\x00' + bytes_
    return bytes_

Name	Size	Last Modified	Owner	Permissions
_perf	Dir	September 10 2020 5:22:33	root	0755
__pycache__	Dir	September 10 2020 5:22:33	root	0755
algos.py	33.296 KB	November 22 2017 4:10:10	root	0644
cms.py	24.529 KB	November 20 2017 12:22:36	root	0644
core.py	153.574 KB	November 21 2017 5:02:30	root	0644
crl.py	15.727 KB	September 15 2017 10:48:38	root	0644
csr.py	2.092 KB	September 15 2017 10:48:44	root	0644
_elliptic_curve.py	9.198 KB	November 07 2017 9:32:35	root	0644
_errors.py	0.944 KB	August 04 2017 2:19:33	root	0644
_ffi.py	0.721 KB	July 15 2016 1:53:18	root	0644
_inet.py	4.552 KB	November 07 2017 9:09:57	root	0644
__init__.py	0.204 KB	January 24 2017 2:23:55	root	0644
_int.py	4.51 KB	January 23 2017 4:49:03	root	0644
_iri.py	8.426 KB	March 03 2017 11:10:52	root	0644
keys.py	34.36 KB	November 22 2017 4:15:11	root	0644
ocsp.py	17.375 KB	September 15 2017 10:49:11	root	0644
_ordereddict.py	4.427 KB	October 08 2015 1:39:26	root	0644
parser.py	8.935 KB	August 04 2017 2:19:37	root	0644
pdf.py	2.197 KB	September 15 2017 10:49:21	root	0644
pem.py	6.001 KB	November 28 2017 4:18:08	root	0644
pkcs12.py	4.459 KB	September 15 2017 10:49:30	root	0644
_teletex_codec.py	4.935 KB	October 08 2015 1:39:30	root	0644
tsp.py	7.644 KB	September 15 2017 10:49:49	root	0644
_types.py	0.917 KB	February 01 2017 12:20:37	root	0644
util.py	17.62 KB	February 01 2017 12:20:37	root	0644
version.py	0.15 KB	December 14 2017 9:01:31	root	0644
x509.py	90.142 KB	December 14 2017 9:01:31	root	0644

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