forked from s434650/CatOrNot
99 lines
2.6 KiB
Python
99 lines
2.6 KiB
Python
|
# -*- coding: utf-8 -*-
|
||
|
|
#
|
||
|
|
# Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
|
||
|
|
#
|
||
|
|
# Licensed under the Apache License, Version 2.0 (the "License");
|
||
|
|
# you may not use this file except in compliance with the License.
|
||
|
|
# You may obtain a copy of the License at
|
||
|
|
#
|
||
|
|
# https://www.apache.org/licenses/LICENSE-2.0
|
||
|
|
#
|
||
|
|
# Unless required by applicable law or agreed to in writing, software
|
||
|
|
# distributed under the License is distributed on an "AS IS" BASIS,
|
||
|
|
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
||
|
|
# See the License for the specific language governing permissions and
|
||
|
|
# limitations under the License.
|
||
|
|
|
||
|
|
"""Functions for generating random numbers."""
|
||
|
|
|
||
|
|
# Source inspired by code by Yesudeep Mangalapilly <yesudeep@gmail.com>
|
||
|
|
|
||
|
|
import os
|
||
|
|
|
||
|
|
from rsa import common, transform
|
||
|
|
from rsa._compat import byte
|
||
|
|
|
||
|
|
|
||
|
|
def read_random_bits(nbits):
|
||
|
|
"""Reads 'nbits' random bits.
|
||
|
|
|
||
|
|
If nbits isn't a whole number of bytes, an extra byte will be appended with
|
||
|
|
only the lower bits set.
|
||
|
|
"""
|
||
|
|
|
||
|
|
nbytes, rbits = divmod(nbits, 8)
|
||
|
|
|
||
|
|
# Get the random bytes
|
||
|
|
randomdata = os.urandom(nbytes)
|
||
|
|
|
||
|
|
# Add the remaining random bits
|
||
|
|
if rbits > 0:
|
||
|
|
randomvalue = ord(os.urandom(1))
|
||
|
|
randomvalue >>= (8 - rbits)
|
||
|
|
randomdata = byte(randomvalue) + randomdata
|
||
|
|
|
||
|
|
return randomdata
|
||
|
|
|
||
|
|
|
||
|
|
def read_random_int(nbits):
|
||
|
|
"""Reads a random integer of approximately nbits bits.
|
||
|
|
"""
|
||
|
|
|
||
|
|
randomdata = read_random_bits(nbits)
|
||
|
|
value = transform.bytes2int(randomdata)
|
||
|
|
|
||
|
|
# Ensure that the number is large enough to just fill out the required
|
||
|
|
# number of bits.
|
||
|
|
value |= 1 << (nbits - 1)
|
||
|
|
|
||
|
|
return value
|
||
|
|
|
||
|
|
|
||
|
|
def read_random_odd_int(nbits):
|
||
|
|
"""Reads a random odd integer of approximately nbits bits.
|
||
|
|
|
||
|
|
>>> read_random_odd_int(512) & 1
|
||
|
|
1
|
||
|
|
"""
|
||
|
|
|
||
|
|
value = read_random_int(nbits)
|
||
|
|
|
||
|
|
# Make sure it's odd
|
||
|
|
return value | 1
|
||
|
|
|
||
|
|
|
||
|
|
def randint(maxvalue):
|
||
|
|
"""Returns a random integer x with 1 <= x <= maxvalue
|
||
|
|
|
||
|
|
May take a very long time in specific situations. If maxvalue needs N bits
|
||
|
|
to store, the closer maxvalue is to (2 ** N) - 1, the faster this function
|
||
|
|
is.
|
||
|
|
"""
|
||
|
|
|
||
|
|
bit_size = common.bit_size(maxvalue)
|
||
|
|
|
||
|
|
tries = 0
|
||
|
|
while True:
|
||
|
|
value = read_random_int(bit_size)
|
||
|
|
if value <= maxvalue:
|
||
|
|
break
|
||
|
|
|
||
|
|
if tries % 10 == 0 and tries:
|
||
|
|
# After a lot of tries to get the right number of bits but still
|
||
|
|
# smaller than maxvalue, decrease the number of bits by 1. That'll
|
||
|
|
# dramatically increase the chances to get a large enough number.
|
||
|
|
bit_size -= 1
|
||
|
|
tries += 1
|
||
|
|
|
||
|
|
return value
|