# SPDX-FileCopyrightText: 2014 Legrandin # SPDX-License-Identifier: BSD-2-Clause """ Ciphertext Block Chaining (CBC) mode. """ from __future__ import annotations from typing import Optional, Union, overload __all__ = ["CbcMode"] from Crypto.Cipher._state_machine import Method from Crypto.Random import get_random_bytes from Crypto.Util._raw_api import ( SmartPointer, VoidPointer, c_size_t, c_uint8_ptr_len, c_uint8_ptr_out, create_output_buffer, get_raw_buffer, is_writeable_buffer, load_pycryptodome_raw_lib, ) Buffer = Union[bytes, bytearray, memoryview] 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: """*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 """ def __init__(self, block_cipher: SmartPointer, iv: Buffer) -> None: """Create a new block cipher, configured in CBC mode. Args: 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. """ state = VoidPointer() iv_ptr, iv_len = c_uint8_ptr_len(iv) result = raw_cbc_lib.CBC_start_operation( block_cipher.get(), iv_ptr, c_size_t(iv_len), 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(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 = bytes(iv) """The Initialization Vector originally used to create the object. The value does not change.""" self.IV = self.iv """Alias for `iv`""" self._next = [Method.ENCRYPT, Method.DECRYPT] @overload def encrypt(self, plaintext: Buffer) -> bytes: ... @overload def encrypt(self, plaintext: Buffer, output: Union[bytearray, memoryview]) -> None: ... def encrypt( self, plaintext: Buffer, output: Optional[Union[bytearray, memoryview]] = None ) -> Optional[bytes]: """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. Args: plaintext (bytes/bytearray/memoryview): The piece of data to encrypt. Its length must be multiple of the cipher block size. Keyword Args: output (bytearray/memoryview): The location where the ciphertext must be written to. If ``None``, the ciphertext is returned. Returns: If ``output`` is ``None``, the ciphertext is returned as ``bytes``. Otherwise, ``None``. """ if Method.ENCRYPT not in self._next: raise TypeError("encrypt() cannot be called after decrypt()") self._next = [Method.ENCRYPT] if output is None: ciphertext = create_output_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)) with c_uint8_ptr_out(ciphertext) as ciphertext_ptr: plaintext_ptr, plaintext_len = c_uint8_ptr_len(plaintext) # Check the lengths of the buffers that C code gets if len(ciphertext_ptr) != plaintext_len: raise ValueError("output must have the same length as the input (%d bytes)" % plaintext_len) result = raw_cbc_lib.CBC_encrypt( self._state.get(), plaintext_ptr, ciphertext_ptr, c_size_t(plaintext_len) ) 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 @overload def decrypt(self, ciphertext: Buffer) -> bytes: ... @overload def decrypt(self, ciphertext: Buffer, output: Union[bytearray, memoryview]) -> None: ... def decrypt( self, ciphertext: Buffer, output: Optional[Union[bytearray, memoryview]] = None ) -> Optional[bytes]: """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. Args: ciphertext (bytes/bytearray/memoryview): The piece of data to decrypt. Its length must be multiple of the cipher block size. Keyword Args: output (bytearray/memoryview): The location where the plaintext must be written to. If ``None``, the plaintext is returned. Returns: If ``output`` is ``None``, the plaintext is returned as ``bytes``. Otherwise, ``None``. """ if Method.DECRYPT not in self._next: raise TypeError("decrypt() cannot be called after encrypt()") self._next = [Method.DECRYPT] if output is None: plaintext = create_output_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)) with c_uint8_ptr_out(plaintext) as plaintext_ptr: ciphertext_ptr, ciphertext_len = c_uint8_ptr_len(ciphertext) # Check the lengths of the buffers that C code gets if len(plaintext_ptr) != ciphertext_len: raise ValueError("output must have the same length as the input (%d bytes)" % ciphertext_len) result = raw_cbc_lib.CBC_decrypt( self._state.get(), ciphertext_ptr, plaintext_ptr, c_size_t(ciphertext_len) ) 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. Args: factory (module): The underlying block cipher, a module from ``Crypto.Cipher``. Keyword Args: 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 (iv, IV) == (None, None): 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)