228 lines
7.9 KiB
Python
228 lines
7.9 KiB
Python
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# The MIT License (MIT)
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#
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# Copyright (c) 2014 Richard Moore
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#
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# Permission is hereby granted, free of charge, to any person obtaining a copy
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# of this software and associated documentation files (the "Software"), to deal
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# in the Software without restriction, including without limitation the rights
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# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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# copies of the Software, and to permit persons to whom the Software is
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# furnished to do so, subject to the following conditions:
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#
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# The above copyright notice and this permission notice shall be included in
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# all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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# THE SOFTWARE.
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from .aes import AESBlockModeOfOperation, AESSegmentModeOfOperation, AESStreamModeOfOperation
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from .util import append_PKCS7_padding, strip_PKCS7_padding, to_bufferable
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# First we inject three functions to each of the modes of operations
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#
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# _can_consume(size)
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# - Given a size, determine how many bytes could be consumed in
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# a single call to either the decrypt or encrypt method
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#
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# _final_encrypt(data, padding = PADDING_DEFAULT)
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# - call and return encrypt on this (last) chunk of data,
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# padding as necessary; this will always be at least 16
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# bytes unless the total incoming input was less than 16
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# bytes
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#
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# _final_decrypt(data, padding = PADDING_DEFAULT)
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# - same as _final_encrypt except for decrypt, for
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# stripping off padding
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#
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PADDING_NONE = 'none'
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PADDING_DEFAULT = 'default'
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# @TODO: Ciphertext stealing and explicit PKCS#7
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# PADDING_CIPHERTEXT_STEALING
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# PADDING_PKCS7
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# ECB and CBC are block-only ciphers
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def _block_can_consume(self, size):
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if size >= 16: return 16
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return 0
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# After padding, we may have more than one block
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def _block_final_encrypt(self, data, padding = PADDING_DEFAULT):
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if padding == PADDING_DEFAULT:
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data = append_PKCS7_padding(data)
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elif padding == PADDING_NONE:
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if len(data) != 16:
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raise Exception('invalid data length for final block')
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else:
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raise Exception('invalid padding option')
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if len(data) == 32:
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return self.encrypt(data[:16]) + self.encrypt(data[16:])
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return self.encrypt(data)
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def _block_final_decrypt(self, data, padding = PADDING_DEFAULT):
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if padding == PADDING_DEFAULT:
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return strip_PKCS7_padding(self.decrypt(data))
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if padding == PADDING_NONE:
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if len(data) != 16:
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raise Exception('invalid data length for final block')
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return self.decrypt(data)
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raise Exception('invalid padding option')
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AESBlockModeOfOperation._can_consume = _block_can_consume
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AESBlockModeOfOperation._final_encrypt = _block_final_encrypt
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AESBlockModeOfOperation._final_decrypt = _block_final_decrypt
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# CFB is a segment cipher
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def _segment_can_consume(self, size):
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return self.segment_bytes * int(size // self.segment_bytes)
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# CFB can handle a non-segment-sized block at the end using the remaining cipherblock
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def _segment_final_encrypt(self, data, padding = PADDING_DEFAULT):
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if padding != PADDING_DEFAULT:
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raise Exception('invalid padding option')
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faux_padding = (chr(0) * (self.segment_bytes - (len(data) % self.segment_bytes)))
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padded = data + to_bufferable(faux_padding)
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return self.encrypt(padded)[:len(data)]
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# CFB can handle a non-segment-sized block at the end using the remaining cipherblock
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def _segment_final_decrypt(self, data, padding = PADDING_DEFAULT):
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if padding != PADDING_DEFAULT:
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raise Exception('invalid padding option')
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faux_padding = (chr(0) * (self.segment_bytes - (len(data) % self.segment_bytes)))
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padded = data + to_bufferable(faux_padding)
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return self.decrypt(padded)[:len(data)]
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AESSegmentModeOfOperation._can_consume = _segment_can_consume
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AESSegmentModeOfOperation._final_encrypt = _segment_final_encrypt
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AESSegmentModeOfOperation._final_decrypt = _segment_final_decrypt
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# OFB and CTR are stream ciphers
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def _stream_can_consume(self, size):
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return size
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def _stream_final_encrypt(self, data, padding = PADDING_DEFAULT):
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if padding not in [PADDING_NONE, PADDING_DEFAULT]:
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raise Exception('invalid padding option')
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return self.encrypt(data)
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def _stream_final_decrypt(self, data, padding = PADDING_DEFAULT):
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if padding not in [PADDING_NONE, PADDING_DEFAULT]:
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raise Exception('invalid padding option')
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return self.decrypt(data)
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AESStreamModeOfOperation._can_consume = _stream_can_consume
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AESStreamModeOfOperation._final_encrypt = _stream_final_encrypt
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AESStreamModeOfOperation._final_decrypt = _stream_final_decrypt
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class BlockFeeder(object):
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'''The super-class for objects to handle chunking a stream of bytes
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into the appropriate block size for the underlying mode of operation
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and applying (or stripping) padding, as necessary.'''
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def __init__(self, mode, feed, final, padding = PADDING_DEFAULT):
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self._mode = mode
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self._feed = feed
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self._final = final
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self._buffer = to_bufferable("")
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self._padding = padding
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def feed(self, data = None):
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'''Provide bytes to encrypt (or decrypt), returning any bytes
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possible from this or any previous calls to feed.
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Call with None or an empty string to flush the mode of
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operation and return any final bytes; no further calls to
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feed may be made.'''
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if self._buffer is None:
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raise ValueError('already finished feeder')
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# Finalize; process the spare bytes we were keeping
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if data is None:
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result = self._final(self._buffer, self._padding)
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self._buffer = None
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return result
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self._buffer += to_bufferable(data)
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# We keep 16 bytes around so we can determine padding
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result = to_bufferable('')
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while len(self._buffer) > 16:
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can_consume = self._mode._can_consume(len(self._buffer) - 16)
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if can_consume == 0: break
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result += self._feed(self._buffer[:can_consume])
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self._buffer = self._buffer[can_consume:]
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return result
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class Encrypter(BlockFeeder):
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'Accepts bytes of plaintext and returns encrypted ciphertext.'
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def __init__(self, mode, padding = PADDING_DEFAULT):
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BlockFeeder.__init__(self, mode, mode.encrypt, mode._final_encrypt, padding)
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class Decrypter(BlockFeeder):
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'Accepts bytes of ciphertext and returns decrypted plaintext.'
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def __init__(self, mode, padding = PADDING_DEFAULT):
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BlockFeeder.__init__(self, mode, mode.decrypt, mode._final_decrypt, padding)
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# 8kb blocks
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BLOCK_SIZE = (1 << 13)
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def _feed_stream(feeder, in_stream, out_stream, block_size = BLOCK_SIZE):
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'Uses feeder to read and convert from in_stream and write to out_stream.'
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while True:
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chunk = in_stream.read(block_size)
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if not chunk:
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break
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converted = feeder.feed(chunk)
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out_stream.write(converted)
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converted = feeder.feed()
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out_stream.write(converted)
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def encrypt_stream(mode, in_stream, out_stream, block_size = BLOCK_SIZE, padding = PADDING_DEFAULT):
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'Encrypts a stream of bytes from in_stream to out_stream using mode.'
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encrypter = Encrypter(mode, padding = padding)
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_feed_stream(encrypter, in_stream, out_stream, block_size)
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def decrypt_stream(mode, in_stream, out_stream, block_size = BLOCK_SIZE, padding = PADDING_DEFAULT):
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'Decrypts a stream of bytes from in_stream to out_stream using mode.'
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decrypter = Decrypter(mode, padding = padding)
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_feed_stream(decrypter, in_stream, out_stream, block_size)
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