rsa_source/rsa/transform.py

   1 # -*- coding: utf-8 -*-
   2 #
   3 #  Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
   4 #
   5 #  Licensed under the Apache License, Version 2.0 (the "License");
   6 #  you may not use this file except in compliance with the License.
   7 #  You may obtain a copy of the License at
   8 #
   9 #      http://www.apache.org/licenses/LICENSE-2.0
  10 #
  11 #  Unless required by applicable law or agreed to in writing, software
  12 #  distributed under the License is distributed on an "AS IS" BASIS,
  13 #  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14 #  See the License for the specific language governing permissions and
  15 #  limitations under the License.
  16
  17 '''Data transformation functions.
  18
  19 From bytes to a number, number to bytes, etc.
  20 '''
  21
  22 import types
  23 import binascii
  24
  25 from rsa import common
  26
  27 def bytes2int(bytes):
  28     r"""Converts a list of bytes or an 8-bit string to an integer.
  29
  30     When using unicode strings, encode it to some encoding like UTF8 first.
  31
  32     >>> (((128 * 256) + 64) * 256) + 15
  33     8405007
  34     >>> bytes2int('\x80@\x0f')
  35     8405007
  36
  37     """
  38
  39     return int(binascii.hexlify(bytes), 16)
  40
  41 def int2bytes(number, block_size=None):
  42     r'''Converts a number to a string of bytes.
  43
  44     @param number: the number to convert
  45     @param block_size: the number of bytes to output. If the number encoded to
  46         bytes is less than this, the block will be zero-padded. When not given,
  47         the returned block is not padded.
  48
  49     @throws OverflowError when block_size is given and the number takes up more
  50         bytes than fit into the block.
  51
  52
  53     >>> int2bytes(123456789)
  54     '\x07[\xcd\x15'
  55     >>> bytes2int(int2bytes(123456789))
  56     123456789
  57
  58     >>> int2bytes(123456789, 6)
  59     '\x00\x00\x07[\xcd\x15'
  60     >>> bytes2int(int2bytes(123456789, 128))
  61     123456789
  62
  63     >>> int2bytes(123456789, 3)
  64     Traceback (most recent call last):
  65     ...
  66     OverflowError: Needed 4 bytes for number, but block size is 3
  67
  68     '''
  69
  70     # Type checking
  71     if type(number) not in (types.LongType, types.IntType):
  72         raise TypeError("You must pass an integer for 'number', not %s" %
  73             number.__class__)
  74
  75     if number < 0:
  76         raise ValueError('Negative numbers cannot be used: %i' % number)
  77
  78     # Do some bounds checking
  79     if block_size is not None:
  80         needed_bytes = common.byte_size(number)
  81         if needed_bytes > block_size:
  82             raise OverflowError('Needed %i bytes for number, but block size '
  83                 'is %i' % (needed_bytes, block_size))
  84
  85     # Convert the number to bytes.
  86     bytes = []
  87     while number > 0:
  88         bytes.insert(0, chr(number & 0xFF))
  89         number >>= 8
  90
  91     # Pad with zeroes to fill the block
  92     if block_size is not None:
  93         padding = (block_size - needed_bytes) * '\x00'
  94     else:
  95         padding = ''
  96
  97     return padding + ''.join(bytes)
  98
  99
 100 if __name__ == '__main__':
 101     import doctest
 102     doctest.testmod()
 103