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Diffstat (limited to 'lib/Crypto/Cipher/_mode_ofb.py')
| -rw-r--r-- | lib/Crypto/Cipher/_mode_ofb.py | 282 |
1 files changed, 282 insertions, 0 deletions
diff --git a/lib/Crypto/Cipher/_mode_ofb.py b/lib/Crypto/Cipher/_mode_ofb.py new file mode 100644 index 0000000..958f6d0 --- /dev/null +++ b/lib/Crypto/Cipher/_mode_ofb.py @@ -0,0 +1,282 @@ +# -*- coding: utf-8 -*- +# +# Cipher/mode_ofb.py : OFB mode +# +# =================================================================== +# The contents of this file are dedicated to the public domain. To +# the extent that dedication to the public domain is not available, +# everyone is granted a worldwide, perpetual, royalty-free, +# non-exclusive license to exercise all rights associated with the +# contents of this file for any purpose whatsoever. +# No rights are reserved. +# +# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, +# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF +# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND +# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS +# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN +# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN +# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE +# SOFTWARE. +# =================================================================== + +""" +Output Feedback (CFB) mode. +""" + +__all__ = ['OfbMode'] + +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_ofb_lib = load_pycryptodome_raw_lib("Crypto.Cipher._raw_ofb", """ + int OFB_start_operation(void *cipher, + const uint8_t iv[], + size_t iv_len, + void **pResult); + int OFB_encrypt(void *ofbState, + const uint8_t *in, + uint8_t *out, + size_t data_len); + int OFB_decrypt(void *ofbState, + const uint8_t *in, + uint8_t *out, + size_t data_len); + int OFB_stop_operation(void *state); + """ + ) + + +class OfbMode(object): + """*Output FeedBack (OFB)*. + + This mode is very similar to CBC, but it + transforms the underlying block cipher into a stream cipher. + + The keystream is the iterated block encryption of the + previous ciphertext block. + + An Initialization Vector (*IV*) is required. + + See `NIST SP800-38A`_ , Section 6.4. + + .. _`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 OFB 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 a nonce, to to be reused for any other + message**. It shall be a nonce or a random value. + + Reusing the *IV* for encryptions performed with the same key + compromises confidentiality. + """ + + self._state = VoidPointer() + result = raw_ofb_lib.OFB_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 OFB 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_ofb_lib.OFB_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 = [ self.encrypt, self.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) + + This function does not add any padding to the plaintext. + + :Parameters: + plaintext : bytes/bytearray/memoryview + The piece of data to encrypt. + It can be of any length. + :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 self.encrypt not in self._next: + raise TypeError("encrypt() cannot be called after decrypt()") + self._next = [ self.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_ofb_lib.OFB_encrypt(self._state.get(), + c_uint8_ptr(plaintext), + c_uint8_ptr(ciphertext), + c_size_t(len(plaintext))) + if result: + raise ValueError("Error %d while encrypting in OFB 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. + It can be of any length. + :Keywords: + output : bytearray/memoryview + The location where the plaintext is written to. + If ``None``, the plaintext is returned. + :Return: + If ``output`` is ``None``, the plaintext is returned as ``bytes``. + Otherwise, ``None``. + """ + + if self.decrypt not in self._next: + raise TypeError("decrypt() cannot be called after encrypt()") + self._next = [ self.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_ofb_lib.OFB_decrypt(self._state.get(), + c_uint8_ptr(ciphertext), + c_uint8_ptr(plaintext), + c_size_t(len(ciphertext))) + if result: + raise ValueError("Error %d while decrypting in OFB mode" % result) + + if output is None: + return get_raw_buffer(plaintext) + else: + return None + + +def _create_ofb_cipher(factory, **kwargs): + """Instantiate a cipher object that performs OFB encryption/decryption. + + :Parameters: + factory : module + The underlying block cipher, a module from ``Crypto.Cipher``. + + :Keywords: + iv : bytes/bytearray/memoryview + The IV to use for OFB. + + 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 OFB: %s" % str(kwargs)) + + return OfbMode(cipher_state, iv) |