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Diffstat (limited to 'rsa/transform.py')
| -rw-r--r-- | rsa/transform.py | 224 |
1 files changed, 224 insertions, 0 deletions
diff --git a/rsa/transform.py b/rsa/transform.py new file mode 100644 index 0000000..16061a9 --- /dev/null +++ b/rsa/transform.py @@ -0,0 +1,224 @@ +# -*- 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. + +"""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(b'\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) + b'\x07[\xcd\x15' + >>> bytes2int(_int2bytes(123456789)) + 123456789 + + >>> _int2bytes(123456789, 6) + b'\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() |