293 lines
11 KiB
Python
293 lines
11 KiB
Python
# ===================================================================
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#
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# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
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# All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions
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# are met:
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#
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# 1. Redistributions of source code must retain the above copyright
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# notice, this list of conditions and the following disclaimer.
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# 2. Redistributions in binary form must reproduce the above copyright
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# notice, this list of conditions and the following disclaimer in
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# the documentation and/or other materials provided with the
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# distribution.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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# ===================================================================
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"""
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Ciphertext Block Chaining (CBC) mode.
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"""
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__all__ = ['CbcMode']
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from Cryptodome.Util.py3compat import _copy_bytes
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from Cryptodome.Util._raw_api import (load_pycryptodome_raw_lib, VoidPointer,
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create_string_buffer, get_raw_buffer,
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SmartPointer, c_size_t, c_uint8_ptr,
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is_writeable_buffer)
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from Cryptodome.Random import get_random_bytes
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raw_cbc_lib = load_pycryptodome_raw_lib("Cryptodome.Cipher._raw_cbc", """
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int CBC_start_operation(void *cipher,
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const uint8_t iv[],
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size_t iv_len,
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void **pResult);
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int CBC_encrypt(void *cbcState,
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const uint8_t *in,
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uint8_t *out,
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size_t data_len);
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int CBC_decrypt(void *cbcState,
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const uint8_t *in,
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uint8_t *out,
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size_t data_len);
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int CBC_stop_operation(void *state);
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"""
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)
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class CbcMode(object):
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"""*Cipher-Block Chaining (CBC)*.
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Each of the ciphertext blocks depends on the current
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and all previous plaintext blocks.
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An Initialization Vector (*IV*) is required.
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See `NIST SP800-38A`_ , Section 6.2 .
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.. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
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:undocumented: __init__
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"""
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def __init__(self, block_cipher, iv):
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"""Create a new block cipher, configured in CBC mode.
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:Parameters:
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block_cipher : C pointer
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A smart pointer to the low-level block cipher instance.
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iv : bytes/bytearray/memoryview
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The initialization vector to use for encryption or decryption.
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It is as long as the cipher block.
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**The IV must be unpredictable**. Ideally it is picked randomly.
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Reusing the *IV* for encryptions performed with the same key
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compromises confidentiality.
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"""
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self._state = VoidPointer()
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result = raw_cbc_lib.CBC_start_operation(block_cipher.get(),
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c_uint8_ptr(iv),
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c_size_t(len(iv)),
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self._state.address_of())
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if result:
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raise ValueError("Error %d while instantiating the CBC mode"
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% result)
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# Ensure that object disposal of this Python object will (eventually)
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# free the memory allocated by the raw library for the cipher mode
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self._state = SmartPointer(self._state.get(),
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raw_cbc_lib.CBC_stop_operation)
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# Memory allocated for the underlying block cipher is now owed
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# by the cipher mode
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block_cipher.release()
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self.block_size = len(iv)
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"""The block size of the underlying cipher, in bytes."""
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self.iv = _copy_bytes(None, None, iv)
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"""The Initialization Vector originally used to create the object.
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The value does not change."""
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self.IV = self.iv
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"""Alias for `iv`"""
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self._next = ["encrypt", "decrypt"]
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def encrypt(self, plaintext, output=None):
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"""Encrypt data with the key and the parameters set at initialization.
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A cipher object is stateful: once you have encrypted a message
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you cannot encrypt (or decrypt) another message using the same
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object.
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The data to encrypt can be broken up in two or
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more pieces and `encrypt` can be called multiple times.
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That is, the statement:
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>>> c.encrypt(a) + c.encrypt(b)
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is equivalent to:
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>>> c.encrypt(a+b)
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That also means that you cannot reuse an object for encrypting
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or decrypting other data with the same key.
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This function does not add any padding to the plaintext.
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:Parameters:
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plaintext : bytes/bytearray/memoryview
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The piece of data to encrypt.
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Its lenght must be multiple of the cipher block size.
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:Keywords:
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output : bytearray/memoryview
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The location where the ciphertext must be written to.
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If ``None``, the ciphertext is returned.
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:Return:
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If ``output`` is ``None``, the ciphertext is returned as ``bytes``.
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Otherwise, ``None``.
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"""
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if "encrypt" not in self._next:
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raise TypeError("encrypt() cannot be called after decrypt()")
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self._next = ["encrypt"]
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if output is None:
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ciphertext = create_string_buffer(len(plaintext))
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else:
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ciphertext = output
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if not is_writeable_buffer(output):
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raise TypeError("output must be a bytearray or a writeable memoryview")
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if len(plaintext) != len(output):
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raise ValueError("output must have the same length as the input"
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" (%d bytes)" % len(plaintext))
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result = raw_cbc_lib.CBC_encrypt(self._state.get(),
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c_uint8_ptr(plaintext),
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c_uint8_ptr(ciphertext),
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c_size_t(len(plaintext)))
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if result:
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if result == 3:
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raise ValueError("Data must be padded to %d byte boundary in CBC mode" % self.block_size)
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raise ValueError("Error %d while encrypting in CBC mode" % result)
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if output is None:
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return get_raw_buffer(ciphertext)
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else:
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return None
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def decrypt(self, ciphertext, output=None):
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"""Decrypt data with the key and the parameters set at initialization.
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A cipher object is stateful: once you have decrypted a message
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you cannot decrypt (or encrypt) another message with the same
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object.
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The data to decrypt can be broken up in two or
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more pieces and `decrypt` can be called multiple times.
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That is, the statement:
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>>> c.decrypt(a) + c.decrypt(b)
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is equivalent to:
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>>> c.decrypt(a+b)
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This function does not remove any padding from the plaintext.
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:Parameters:
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ciphertext : bytes/bytearray/memoryview
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The piece of data to decrypt.
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Its length must be multiple of the cipher block size.
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:Keywords:
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output : bytearray/memoryview
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The location where the plaintext must be written to.
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If ``None``, the plaintext is returned.
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:Return:
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If ``output`` is ``None``, the plaintext is returned as ``bytes``.
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Otherwise, ``None``.
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"""
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if "decrypt" not in self._next:
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raise TypeError("decrypt() cannot be called after encrypt()")
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self._next = ["decrypt"]
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if output is None:
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plaintext = create_string_buffer(len(ciphertext))
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else:
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plaintext = output
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if not is_writeable_buffer(output):
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raise TypeError("output must be a bytearray or a writeable memoryview")
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if len(ciphertext) != len(output):
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raise ValueError("output must have the same length as the input"
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" (%d bytes)" % len(plaintext))
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result = raw_cbc_lib.CBC_decrypt(self._state.get(),
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c_uint8_ptr(ciphertext),
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c_uint8_ptr(plaintext),
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c_size_t(len(ciphertext)))
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if result:
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if result == 3:
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raise ValueError("Data must be padded to %d byte boundary in CBC mode" % self.block_size)
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raise ValueError("Error %d while decrypting in CBC mode" % result)
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if output is None:
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return get_raw_buffer(plaintext)
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else:
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return None
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def _create_cbc_cipher(factory, **kwargs):
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"""Instantiate a cipher object that performs CBC encryption/decryption.
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:Parameters:
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factory : module
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The underlying block cipher, a module from ``Cryptodome.Cipher``.
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:Keywords:
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iv : bytes/bytearray/memoryview
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The IV to use for CBC.
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IV : bytes/bytearray/memoryview
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Alias for ``iv``.
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Any other keyword will be passed to the underlying block cipher.
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See the relevant documentation for details (at least ``key`` will need
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to be present).
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"""
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cipher_state = factory._create_base_cipher(kwargs)
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iv = kwargs.pop("IV", None)
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IV = kwargs.pop("iv", None)
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if (None, None) == (iv, IV):
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iv = get_random_bytes(factory.block_size)
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if iv is not None:
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if IV is not None:
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raise TypeError("You must either use 'iv' or 'IV', not both")
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else:
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iv = IV
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if len(iv) != factory.block_size:
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raise ValueError("Incorrect IV length (it must be %d bytes long)" %
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factory.block_size)
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if kwargs:
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raise TypeError("Unknown parameters for CBC: %s" % str(kwargs))
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return CbcMode(cipher_state, iv)
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