Edit File: _mode_cbc.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. # =================================================================== """ Ciphertext Block Chaining (CBC) mode. """ __all__ = ['CbcMode'] from Crypto.Util.py3compat import _copy_bytes from Crypto.Util._raw_api import (load_pycryptodome_raw_lib, VoidPointer, create_string_buffer, get_raw_buffer, SmartPointer, c_size_t, c_uint8_ptr, is_writeable_buffer) from Crypto.Random import get_random_bytes raw_cbc_lib = load_pycryptodome_raw_lib("Crypto.Cipher._raw_cbc", """ int CBC_start_operation(void *cipher, const uint8_t iv[], size_t iv_len, void **pResult); int CBC_encrypt(void *cbcState, const uint8_t *in, uint8_t *out, size_t data_len); int CBC_decrypt(void *cbcState, const uint8_t *in, uint8_t *out, size_t data_len); int CBC_stop_operation(void *state); """ ) class CbcMode(object): """*Cipher-Block Chaining (CBC)*. Each of the ciphertext blocks depends on the current and all previous plaintext blocks. An Initialization Vector (*IV*) is required. See `NIST SP800-38A`_ , Section 6.2 . .. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf :undocumented: __init__ """ def __init__(self, block_cipher, iv): """Create a new block cipher, configured in CBC mode. :Parameters: block_cipher : C pointer A smart pointer to the low-level block cipher instance. iv : bytes/bytearray/memoryview The initialization vector to use for encryption or decryption. It is as long as the cipher block. **The IV must be unpredictable**. Ideally it is picked randomly. Reusing the *IV* for encryptions performed with the same key compromises confidentiality. """ self._state = VoidPointer() result = raw_cbc_lib.CBC_start_operation(block_cipher.get(), c_uint8_ptr(iv), c_size_t(len(iv)), self._state.address_of()) if result: raise ValueError("Error %d while instantiating the CBC mode" % result) # Ensure that object disposal of this Python object will (eventually) # free the memory allocated by the raw library for the cipher mode self._state = SmartPointer(self._state.get(), raw_cbc_lib.CBC_stop_operation) # Memory allocated for the underlying block cipher is now owed # by the cipher mode block_cipher.release() self.block_size = len(iv) """The block size of the underlying cipher, in bytes.""" self.iv = _copy_bytes(None, None, iv) """The Initialization Vector originally used to create the object. The value does not change.""" self.IV = self.iv """Alias for `iv`""" self._next = ["encrypt", "decrypt"] def encrypt(self, plaintext, output=None): """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) That also means that you cannot reuse an object for encrypting or decrypting other data with the same key. This function does not add any padding to the plaintext. :Parameters: plaintext : bytes/bytearray/memoryview The piece of data to encrypt. Its lenght must be multiple of the cipher block size. :Keywords: output : bytearray/memoryview The location where the ciphertext must be written to. If ``None``, the ciphertext is returned. :Return: If ``output`` is ``None``, the ciphertext is returned as ``bytes``. Otherwise, ``None``. """ if "encrypt" not in self._next: raise TypeError("encrypt() cannot be called after decrypt()") self._next = ["encrypt"] if output is None: ciphertext = create_string_buffer(len(plaintext)) else: ciphertext = output if not is_writeable_buffer(output): raise TypeError("output must be a bytearray or a writeable memoryview") if len(plaintext) != len(output): raise ValueError("output must have the same length as the input" " (%d bytes)" % len(plaintext)) result = raw_cbc_lib.CBC_encrypt(self._state.get(), c_uint8_ptr(plaintext), c_uint8_ptr(ciphertext), c_size_t(len(plaintext))) if result: if result == 3: raise ValueError("Data must be padded to %d byte boundary in CBC mode" % self.block_size) raise ValueError("Error %d while encrypting in CBC mode" % result) if output is None: return get_raw_buffer(ciphertext) else: return None def decrypt(self, ciphertext, output=None): """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. Its length must be multiple of the cipher block size. :Keywords: output : bytearray/memoryview The location where the plaintext must be written to. If ``None``, the plaintext is returned. :Return: If ``output`` is ``None``, the plaintext is returned as ``bytes``. Otherwise, ``None``. """ if "decrypt" not in self._next: raise TypeError("decrypt() cannot be called after encrypt()") self._next = ["decrypt"] if output is None: plaintext = create_string_buffer(len(ciphertext)) else: plaintext = output if not is_writeable_buffer(output): raise TypeError("output must be a bytearray or a writeable memoryview") if len(ciphertext) != len(output): raise ValueError("output must have the same length as the input" " (%d bytes)" % len(plaintext)) result = raw_cbc_lib.CBC_decrypt(self._state.get(), c_uint8_ptr(ciphertext), c_uint8_ptr(plaintext), c_size_t(len(ciphertext))) if result: if result == 3: raise ValueError("Data must be padded to %d byte boundary in CBC mode" % self.block_size) raise ValueError("Error %d while decrypting in CBC mode" % result) if output is None: return get_raw_buffer(plaintext) else: return None def _create_cbc_cipher(factory, **kwargs): """Instantiate a cipher object that performs CBC encryption/decryption. :Parameters: factory : module The underlying block cipher, a module from ``Crypto.Cipher``. :Keywords: iv : bytes/bytearray/memoryview The IV to use for CBC. IV : bytes/bytearray/memoryview Alias for ``iv``. Any other keyword will be passed to the underlying block cipher. See the relevant documentation for details (at least ``key`` will need to be present). """ cipher_state = factory._create_base_cipher(kwargs) 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 if len(iv) != factory.block_size: raise ValueError("Incorrect IV length (it must be %d bytes long)" % factory.block_size) if kwargs: raise TypeError("Unknown parameters for CBC: %s" % str(kwargs)) return CbcMode(cipher_state, iv)