Edit File: _mode_openpgp.py
# =================================================================== # # Copyright (c) 2014, Legrandin <helderijs@gmail.com> # All rights reserved. # # Redistribution and use in source and binary forms, with or without # modification, are permitted provided that the following conditions # are met: # # 1. Redistributions of source code must retain the above copyright # notice, this list of conditions and the following disclaimer. # 2. Redistributions in binary form must reproduce the above copyright # notice, this list of conditions and the following disclaimer in # the documentation and/or other materials provided with the # distribution. # # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS # FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, # BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; # LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER # CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE # POSSIBILITY OF SUCH DAMAGE. # =================================================================== """ OpenPGP mode. """ __all__ = ['OpenPgpMode'] from Crypto.Util.py3compat import _copy_bytes from Crypto.Random import get_random_bytes class OpenPgpMode(object): """OpenPGP mode. This mode is a variant of CFB, and it is only used in PGP and OpenPGP_ applications. If in doubt, use another mode. An Initialization Vector (*IV*) is required. Unlike CFB, the *encrypted* IV (not the IV itself) is transmitted to the receiver. The IV is a random data block. For legacy reasons, two of its bytes are duplicated to act as a checksum for the correctness of the key, which is now known to be insecure and is ignored. The encrypted IV is therefore 2 bytes longer than the clean IV. .. _OpenPGP: http://tools.ietf.org/html/rfc4880 :undocumented: __init__ """ def __init__(self, factory, key, iv, cipher_params): #: The block size of the underlying cipher, in bytes. self.block_size = factory.block_size self._done_first_block = False # True after the first encryption # Instantiate a temporary cipher to process the IV IV_cipher = factory.new( key, factory.MODE_CFB, IV=b'\x00' * self.block_size, segment_size=self.block_size * 8, **cipher_params) iv = _copy_bytes(None, None, iv) # The cipher will be used for... if len(iv) == self.block_size: # ... encryption self._encrypted_IV = IV_cipher.encrypt(iv + iv[-2:]) elif len(iv) == self.block_size + 2: # ... decryption self._encrypted_IV = iv # Last two bytes are for a deprecated "quick check" feature that # should not be used. (https://eprint.iacr.org/2005/033) iv = IV_cipher.decrypt(iv)[:-2] else: raise ValueError("Length of IV must be %d or %d bytes" " for MODE_OPENPGP" % (self.block_size, self.block_size + 2)) self.iv = self.IV = iv # Instantiate the cipher for the real PGP data self._cipher = factory.new( key, factory.MODE_CFB, IV=self._encrypted_IV[-self.block_size:], segment_size=self.block_size * 8, **cipher_params) def encrypt(self, plaintext): """Encrypt data with the key and the parameters set at initialization. A cipher object is stateful: once you have encrypted a message you cannot encrypt (or decrypt) another message using the same object. The data to encrypt can be broken up in two or more pieces and `encrypt` can be called multiple times. That is, the statement: >>> c.encrypt(a) + c.encrypt(b) is equivalent to: >>> c.encrypt(a+b) This function does not add any padding to the plaintext. :Parameters: plaintext : bytes/bytearray/memoryview The piece of data to encrypt. :Return: the encrypted data, as a byte string. It is as long as *plaintext* with one exception: when encrypting the first message chunk, the encypted IV is prepended to the returned ciphertext. """ res = self._cipher.encrypt(plaintext) if not self._done_first_block: res = self._encrypted_IV + res self._done_first_block = True return res def decrypt(self, ciphertext): """Decrypt data with the key and the parameters set at initialization. A cipher object is stateful: once you have decrypted a message you cannot decrypt (or encrypt) another message with the same object. The data to decrypt can be broken up in two or more pieces and `decrypt` can be called multiple times. That is, the statement: >>> c.decrypt(a) + c.decrypt(b) is equivalent to: >>> c.decrypt(a+b) This function does not remove any padding from the plaintext. :Parameters: ciphertext : bytes/bytearray/memoryview The piece of data to decrypt. :Return: the decrypted data (byte string). """ return self._cipher.decrypt(ciphertext) def _create_openpgp_cipher(factory, **kwargs): """Create a new block cipher, configured in OpenPGP mode. :Parameters: factory : module The module. :Keywords: key : bytes/bytearray/memoryview The secret key to use in the symmetric cipher. IV : bytes/bytearray/memoryview The initialization vector to use for encryption or decryption. For encryption, the IV must be as long as the cipher block size. For decryption, it must be 2 bytes longer (it is actually the *encrypted* IV which was prefixed to the ciphertext). """ iv = kwargs.pop("IV", None) IV = kwargs.pop("iv", None) if (None, None) == (iv, IV): iv = get_random_bytes(factory.block_size) if iv is not None: if IV is not None: raise TypeError("You must either use 'iv' or 'IV', not both") else: iv = IV try: key = kwargs.pop("key") except KeyError as e: raise TypeError("Missing component: " + str(e)) return OpenPgpMode(factory, key, iv, kwargs)
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