221 lines
6.7 KiB
Python
221 lines
6.7 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
|
||
|
|
#
|
||
|
|
# http://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.
|
||
|
|
|
||
|
|
'''Data transformation functions.
|
||
|
|
|
||
|
|
From bytes to a number, number to bytes, etc.
|
||
|
|
'''
|
||
|
|
|
||
|
|
from __future__ import absolute_import
|
||
|
|
|
||
|
|
try:
|
||
|
|
# We'll use psyco if available on 32-bit architectures to speed up code.
|
||
|
|
# Using psyco (if available) cuts down the execution time on Python 2.5
|
||
|
|
# at least by half.
|
||
|
|
import psyco
|
||
|
|
psyco.full()
|
||
|
|
except ImportError:
|
||
|
|
pass
|
||
|
|
|
||
|
|
import binascii
|
||
|
|
from struct import pack
|
||
|
|
from rsa import common
|
||
|
|
from rsa._compat import is_integer, b, byte, get_word_alignment, ZERO_BYTE, EMPTY_BYTE
|
||
|
|
|
||
|
|
|
||
|
|
def bytes2int(raw_bytes):
|
||
|
|
r'''Converts a list of bytes or an 8-bit string to an integer.
|
||
|
|
|
||
|
|
When using unicode strings, encode it to some encoding like UTF8 first.
|
||
|
|
|
||
|
|
>>> (((128 * 256) + 64) * 256) + 15
|
||
|
|
8405007
|
||
|
|
>>> bytes2int('\x80@\x0f')
|
||
|
|
8405007
|
||
|
|
|
||
|
|
'''
|
||
|
|
|
||
|
|
return int(binascii.hexlify(raw_bytes), 16)
|
||
|
|
|
||
|
|
|
||
|
|
def _int2bytes(number, block_size=None):
|
||
|
|
r'''Converts a number to a string of bytes.
|
||
|
|
|
||
|
|
Usage::
|
||
|
|
|
||
|
|
>>> _int2bytes(123456789)
|
||
|
|
'\x07[\xcd\x15'
|
||
|
|
>>> bytes2int(_int2bytes(123456789))
|
||
|
|
123456789
|
||
|
|
|
||
|
|
>>> _int2bytes(123456789, 6)
|
||
|
|
'\x00\x00\x07[\xcd\x15'
|
||
|
|
>>> bytes2int(_int2bytes(123456789, 128))
|
||
|
|
123456789
|
||
|
|
|
||
|
|
>>> _int2bytes(123456789, 3)
|
||
|
|
Traceback (most recent call last):
|
||
|
|
...
|
||
|
|
OverflowError: Needed 4 bytes for number, but block size is 3
|
||
|
|
|
||
|
|
@param number: the number to convert
|
||
|
|
@param block_size: the number of bytes to output. If the number encoded to
|
||
|
|
bytes is less than this, the block will be zero-padded. When not given,
|
||
|
|
the returned block is not padded.
|
||
|
|
|
||
|
|
@throws OverflowError when block_size is given and the number takes up more
|
||
|
|
bytes than fit into the block.
|
||
|
|
'''
|
||
|
|
# Type checking
|
||
|
|
if not is_integer(number):
|
||
|
|
raise TypeError("You must pass an integer for 'number', not %s" %
|
||
|
|
number.__class__)
|
||
|
|
|
||
|
|
if number < 0:
|
||
|
|
raise ValueError('Negative numbers cannot be used: %i' % number)
|
||
|
|
|
||
|
|
# Do some bounds checking
|
||
|
|
if number == 0:
|
||
|
|
needed_bytes = 1
|
||
|
|
raw_bytes = [ZERO_BYTE]
|
||
|
|
else:
|
||
|
|
needed_bytes = common.byte_size(number)
|
||
|
|
raw_bytes = []
|
||
|
|
|
||
|
|
# You cannot compare None > 0 in Python 3x. It will fail with a TypeError.
|
||
|
|
if block_size and block_size > 0:
|
||
|
|
if needed_bytes > block_size:
|
||
|
|
raise OverflowError('Needed %i bytes for number, but block size '
|
||
|
|
'is %i' % (needed_bytes, block_size))
|
||
|
|
|
||
|
|
# Convert the number to bytes.
|
||
|
|
while number > 0:
|
||
|
|
raw_bytes.insert(0, byte(number & 0xFF))
|
||
|
|
number >>= 8
|
||
|
|
|
||
|
|
# Pad with zeroes to fill the block
|
||
|
|
if block_size and block_size > 0:
|
||
|
|
padding = (block_size - needed_bytes) * ZERO_BYTE
|
||
|
|
else:
|
||
|
|
padding = EMPTY_BYTE
|
||
|
|
|
||
|
|
return padding + EMPTY_BYTE.join(raw_bytes)
|
||
|
|
|
||
|
|
|
||
|
|
def bytes_leading(raw_bytes, needle=ZERO_BYTE):
|
||
|
|
'''
|
||
|
|
Finds the number of prefixed byte occurrences in the haystack.
|
||
|
|
|
||
|
|
Useful when you want to deal with padding.
|
||
|
|
|
||
|
|
:param raw_bytes:
|
||
|
|
Raw bytes.
|
||
|
|
:param needle:
|
||
|
|
The byte to count. Default \000.
|
||
|
|
:returns:
|
||
|
|
The number of leading needle bytes.
|
||
|
|
'''
|
||
|
|
leading = 0
|
||
|
|
# Indexing keeps compatibility between Python 2.x and Python 3.x
|
||
|
|
_byte = needle[0]
|
||
|
|
for x in raw_bytes:
|
||
|
|
if x == _byte:
|
||
|
|
leading += 1
|
||
|
|
else:
|
||
|
|
break
|
||
|
|
return leading
|
||
|
|
|
||
|
|
|
||
|
|
def int2bytes(number, fill_size=None, chunk_size=None, overflow=False):
|
||
|
|
'''
|
||
|
|
Convert an unsigned integer to bytes (base-256 representation)::
|
||
|
|
|
||
|
|
Does not preserve leading zeros if you don't specify a chunk size or
|
||
|
|
fill size.
|
||
|
|
|
||
|
|
.. NOTE:
|
||
|
|
You must not specify both fill_size and chunk_size. Only one
|
||
|
|
of them is allowed.
|
||
|
|
|
||
|
|
:param number:
|
||
|
|
Integer value
|
||
|
|
:param fill_size:
|
||
|
|
If the optional fill size is given the length of the resulting
|
||
|
|
byte string is expected to be the fill size and will be padded
|
||
|
|
with prefix zero bytes to satisfy that length.
|
||
|
|
:param chunk_size:
|
||
|
|
If optional chunk size is given and greater than zero, pad the front of
|
||
|
|
the byte string with binary zeros so that the length is a multiple of
|
||
|
|
``chunk_size``.
|
||
|
|
:param overflow:
|
||
|
|
``False`` (default). If this is ``True``, no ``OverflowError``
|
||
|
|
will be raised when the fill_size is shorter than the length
|
||
|
|
of the generated byte sequence. Instead the byte sequence will
|
||
|
|
be returned as is.
|
||
|
|
:returns:
|
||
|
|
Raw bytes (base-256 representation).
|
||
|
|
:raises:
|
||
|
|
``OverflowError`` when fill_size is given and the number takes up more
|
||
|
|
bytes than fit into the block. This requires the ``overflow``
|
||
|
|
argument to this function to be set to ``False`` otherwise, no
|
||
|
|
error will be raised.
|
||
|
|
'''
|
||
|
|
if number < 0:
|
||
|
|
raise ValueError("Number must be an unsigned integer: %d" % number)
|
||
|
|
|
||
|
|
if fill_size and chunk_size:
|
||
|
|
raise ValueError("You can either fill or pad chunks, but not both")
|
||
|
|
|
||
|
|
# Ensure these are integers.
|
||
|
|
number & 1
|
||
|
|
|
||
|
|
raw_bytes = b('')
|
||
|
|
|
||
|
|
# Pack the integer one machine word at a time into bytes.
|
||
|
|
num = number
|
||
|
|
word_bits, _, max_uint, pack_type = get_word_alignment(num)
|
||
|
|
pack_format = ">%s" % pack_type
|
||
|
|
while num > 0:
|
||
|
|
raw_bytes = pack(pack_format, num & max_uint) + raw_bytes
|
||
|
|
num >>= word_bits
|
||
|
|
# Obtain the index of the first non-zero byte.
|
||
|
|
zero_leading = bytes_leading(raw_bytes)
|
||
|
|
if number == 0:
|
||
|
|
raw_bytes = ZERO_BYTE
|
||
|
|
# De-padding.
|
||
|
|
raw_bytes = raw_bytes[zero_leading:]
|
||
|
|
|
||
|
|
length = len(raw_bytes)
|
||
|
|
if fill_size and fill_size > 0:
|
||
|
|
if not overflow and length > fill_size:
|
||
|
|
raise OverflowError(
|
||
|
|
"Need %d bytes for number, but fill size is %d" %
|
||
|
|
(length, fill_size)
|
||
|
|
)
|
||
|
|
raw_bytes = raw_bytes.rjust(fill_size, ZERO_BYTE)
|
||
|
|
elif chunk_size and chunk_size > 0:
|
||
|
|
remainder = length % chunk_size
|
||
|
|
if remainder:
|
||
|
|
padding_size = chunk_size - remainder
|
||
|
|
raw_bytes = raw_bytes.rjust(length + padding_size, ZERO_BYTE)
|
||
|
|
return raw_bytes
|
||
|
|
|
||
|
|
|
||
|
|
if __name__ == '__main__':
|
||
|
|
import doctest
|
||
|
|
doctest.testmod()
|
||
|
|
|