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Diffstat (limited to 'frozen_deps/Cryptodome/Cipher/_mode_ctr.py')
| -rw-r--r-- | frozen_deps/Cryptodome/Cipher/_mode_ctr.py | 393 |
1 files changed, 393 insertions, 0 deletions
diff --git a/frozen_deps/Cryptodome/Cipher/_mode_ctr.py b/frozen_deps/Cryptodome/Cipher/_mode_ctr.py new file mode 100644 index 0000000..99712d0 --- /dev/null +++ b/frozen_deps/Cryptodome/Cipher/_mode_ctr.py @@ -0,0 +1,393 @@ +# -*- coding: utf-8 -*- +# +# Cipher/mode_ctr.py : CTR 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. +# =================================================================== + +""" +Counter (CTR) mode. +""" + +__all__ = ['CtrMode'] + +import struct + +from Cryptodome.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 Cryptodome.Random import get_random_bytes +from Cryptodome.Util.py3compat import _copy_bytes, is_native_int +from Cryptodome.Util.number import long_to_bytes + +raw_ctr_lib = load_pycryptodome_raw_lib("Cryptodome.Cipher._raw_ctr", """ + int CTR_start_operation(void *cipher, + uint8_t initialCounterBlock[], + size_t initialCounterBlock_len, + size_t prefix_len, + unsigned counter_len, + unsigned littleEndian, + void **pResult); + int CTR_encrypt(void *ctrState, + const uint8_t *in, + uint8_t *out, + size_t data_len); + int CTR_decrypt(void *ctrState, + const uint8_t *in, + uint8_t *out, + size_t data_len); + int CTR_stop_operation(void *ctrState);""" + ) + + +class CtrMode(object): + """*CounTeR (CTR)* mode. + + This mode is very similar to ECB, in that + encryption of one block is done independently of all other blocks. + + Unlike ECB, the block *position* contributes to the encryption + and no information leaks about symbol frequency. + + Each message block is associated to a *counter* which + must be unique across all messages that get encrypted + with the same key (not just within the same message). + The counter is as big as the block size. + + Counters can be generated in several ways. The most + straightword one is to choose an *initial counter block* + (which can be made public, similarly to the *IV* for the + other modes) and increment its lowest **m** bits by one + (modulo *2^m*) for each block. In most cases, **m** is + chosen to be half the block size. + + See `NIST SP800-38A`_, Section 6.5 (for the mode) and + Appendix B (for how to manage the *initial counter block*). + + .. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf + + :undocumented: __init__ + """ + + def __init__(self, block_cipher, initial_counter_block, + prefix_len, counter_len, little_endian): + """Create a new block cipher, configured in CTR mode. + + :Parameters: + block_cipher : C pointer + A smart pointer to the low-level block cipher instance. + + initial_counter_block : bytes/bytearray/memoryview + The initial plaintext to use to generate the key stream. + + It is as large as the cipher block, and it embeds + the initial value of the counter. + + This value must not be reused. + It shall contain a nonce or a random component. + Reusing the *initial counter block* for encryptions + performed with the same key compromises confidentiality. + + prefix_len : integer + The amount of bytes at the beginning of the counter block + that never change. + + counter_len : integer + The length in bytes of the counter embedded in the counter + block. + + little_endian : boolean + True if the counter in the counter block is an integer encoded + in little endian mode. If False, it is big endian. + """ + + if len(initial_counter_block) == prefix_len + counter_len: + self.nonce = _copy_bytes(None, prefix_len, initial_counter_block) + """Nonce; not available if there is a fixed suffix""" + + self._state = VoidPointer() + result = raw_ctr_lib.CTR_start_operation(block_cipher.get(), + c_uint8_ptr(initial_counter_block), + c_size_t(len(initial_counter_block)), + c_size_t(prefix_len), + counter_len, + little_endian, + self._state.address_of()) + if result: + raise ValueError("Error %X while instantiating the CTR 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_ctr_lib.CTR_stop_operation) + + # Memory allocated for the underlying block cipher is now owed + # by the cipher mode + block_cipher.release() + + self.block_size = len(initial_counter_block) + """The block size of the underlying cipher, in bytes.""" + + 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_ctr_lib.CTR_encrypt(self._state.get(), + c_uint8_ptr(plaintext), + c_uint8_ptr(ciphertext), + c_size_t(len(plaintext))) + if result: + if result == 0x60002: + raise OverflowError("The counter has wrapped around in" + " CTR mode") + raise ValueError("Error %X while encrypting in CTR 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 must be 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_ctr_lib.CTR_decrypt(self._state.get(), + c_uint8_ptr(ciphertext), + c_uint8_ptr(plaintext), + c_size_t(len(ciphertext))) + if result: + if result == 0x60002: + raise OverflowError("The counter has wrapped around in" + " CTR mode") + raise ValueError("Error %X while decrypting in CTR mode" % result) + + if output is None: + return get_raw_buffer(plaintext) + else: + return None + + +def _create_ctr_cipher(factory, **kwargs): + """Instantiate a cipher object that performs CTR encryption/decryption. + + :Parameters: + factory : module + The underlying block cipher, a module from ``Cryptodome.Cipher``. + + :Keywords: + nonce : bytes/bytearray/memoryview + The fixed part at the beginning of the counter block - the rest is + the counter number that gets increased when processing the next block. + The nonce must be such that no two messages are encrypted under the + same key and the same nonce. + + The nonce must be shorter than the block size (it can have + zero length; the counter is then as long as the block). + + If this parameter is not present, a random nonce will be created with + length equal to half the block size. No random nonce shorter than + 64 bits will be created though - you must really think through all + security consequences of using such a short block size. + + initial_value : posive integer or bytes/bytearray/memoryview + The initial value for the counter. If not present, the cipher will + start counting from 0. The value is incremented by one for each block. + The counter number is encoded in big endian mode. + + counter : object + Instance of ``Cryptodome.Util.Counter``, which allows full customization + of the counter block. This parameter is incompatible to both ``nonce`` + and ``initial_value``. + + 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) + + counter = kwargs.pop("counter", None) + nonce = kwargs.pop("nonce", None) + initial_value = kwargs.pop("initial_value", None) + if kwargs: + raise TypeError("Invalid parameters for CTR mode: %s" % str(kwargs)) + + if counter is not None and (nonce, initial_value) != (None, None): + raise TypeError("'counter' and 'nonce'/'initial_value'" + " are mutually exclusive") + + if counter is None: + # Cryptodome.Util.Counter is not used + if nonce is None: + if factory.block_size < 16: + raise TypeError("Impossible to create a safe nonce for short" + " block sizes") + nonce = get_random_bytes(factory.block_size // 2) + else: + if len(nonce) >= factory.block_size: + raise ValueError("Nonce is too long") + + # What is not nonce is counter + counter_len = factory.block_size - len(nonce) + + if initial_value is None: + initial_value = 0 + + if is_native_int(initial_value): + if (1 << (counter_len * 8)) - 1 < initial_value: + raise ValueError("Initial counter value is too large") + initial_counter_block = nonce + long_to_bytes(initial_value, counter_len) + else: + if len(initial_value) != counter_len: + raise ValueError("Incorrect length for counter byte string (%d bytes, expected %d)" % (len(initial_value), counter_len)) + initial_counter_block = nonce + initial_value + + return CtrMode(cipher_state, + initial_counter_block, + len(nonce), # prefix + counter_len, + False) # little_endian + + # Cryptodome.Util.Counter is used + + # 'counter' used to be a callable object, but now it is + # just a dictionary for backward compatibility. + _counter = dict(counter) + try: + counter_len = _counter.pop("counter_len") + prefix = _counter.pop("prefix") + suffix = _counter.pop("suffix") + initial_value = _counter.pop("initial_value") + little_endian = _counter.pop("little_endian") + except KeyError: + raise TypeError("Incorrect counter object" + " (use Cryptodome.Util.Counter.new)") + + # Compute initial counter block + words = [] + while initial_value > 0: + words.append(struct.pack('B', initial_value & 255)) + initial_value >>= 8 + words += [ b'\x00' ] * max(0, counter_len - len(words)) + if not little_endian: + words.reverse() + initial_counter_block = prefix + b"".join(words) + suffix + + if len(initial_counter_block) != factory.block_size: + raise ValueError("Size of the counter block (%d bytes) must match" + " block size (%d)" % (len(initial_counter_block), + factory.block_size)) + + return CtrMode(cipher_state, initial_counter_block, + len(prefix), counter_len, little_endian) |