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+# ===================================================================
+#
+# 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 Cryptodome.Util.py3compat import _copy_bytes
+from Cryptodome.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)