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Editing: ChaCha20.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. # =================================================================== from Crypto.Random import get_random_bytes from Crypto.Util.py3compat import _copy_bytes from Crypto.Util._raw_api import (load_pycryptodome_raw_lib, create_string_buffer, get_raw_buffer, VoidPointer, SmartPointer, c_size_t, c_uint8_ptr, c_ulong, is_writeable_buffer) _raw_chacha20_lib = load_pycryptodome_raw_lib("Crypto.Cipher._chacha20", """ int chacha20_init(void **pState, const uint8_t *key, size_t keySize, const uint8_t *nonce, size_t nonceSize); int chacha20_destroy(void *state); int chacha20_encrypt(void *state, const uint8_t in[], uint8_t out[], size_t len); int chacha20_seek(void *state, unsigned long block_high, unsigned long block_low, unsigned offset); int hchacha20( const uint8_t key[32], const uint8_t nonce16[16], uint8_t subkey[32]); """) def _HChaCha20(key, nonce): assert(len(key) == 32) assert(len(nonce) == 16) subkey = bytearray(32) result = _raw_chacha20_lib.hchacha20( c_uint8_ptr(key), c_uint8_ptr(nonce), c_uint8_ptr(subkey)) if result: raise ValueError("Error %d when deriving subkey with HChaCha20" % result) return subkey class ChaCha20Cipher(object): """ChaCha20 (or XChaCha20) cipher object. Do not create it directly. Use :py:func:`new` instead. :var nonce: The nonce with length 8, 12 or 24 bytes :vartype nonce: bytes """ block_size = 1 def __init__(self, key, nonce): """Initialize a ChaCha20/XChaCha20 cipher object See also `new()` at the module level.""" self.nonce = _copy_bytes(None, None, nonce) # XChaCha20 requires a key derivation with HChaCha20 # See 2.3 in https://tools.ietf.org/html/draft-arciszewski-xchacha-03 if len(nonce) == 24: key = _HChaCha20(key, nonce[:16]) nonce = b'\x00' * 4 + nonce[16:] self._name = "XChaCha20" else: self._name = "ChaCha20" nonce = self.nonce self._next = ("encrypt", "decrypt") self._state = VoidPointer() result = _raw_chacha20_lib.chacha20_init( self._state.address_of(), c_uint8_ptr(key), c_size_t(len(key)), nonce, c_size_t(len(nonce))) if result: raise ValueError("Error %d instantiating a %s cipher" % (result, self._name)) self._state = SmartPointer(self._state.get(), _raw_chacha20_lib.chacha20_destroy) def encrypt(self, plaintext, output=None): """Encrypt a piece of data. Args: plaintext(bytes/bytearray/memoryview): The data to encrypt, of any size. Keyword Args: output(bytes/bytearray/memoryview): The location where the ciphertext is written to. If ``None``, the ciphertext is returned. Returns: If ``output`` is ``None``, the ciphertext is returned as ``bytes``. Otherwise, ``None``. """ if "encrypt" not in self._next: raise TypeError("Cipher object can only be used for decryption") self._next = ("encrypt",) return self._encrypt(plaintext, output) def _encrypt(self, plaintext, output): """Encrypt without FSM checks""" 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_chacha20_lib.chacha20_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 with %s" % (result, self._name)) if output is None: return get_raw_buffer(ciphertext) else: return None def decrypt(self, ciphertext, output=None): """Decrypt a piece of data. Args: ciphertext(bytes/bytearray/memoryview): The data to decrypt, of any size. Keyword Args: output(bytes/bytearray/memoryview): The location where the plaintext is written to. If ``None``, the plaintext is returned. Returns: If ``output`` is ``None``, the plaintext is returned as ``bytes``. Otherwise, ``None``. """ if "decrypt" not in self._next: raise TypeError("Cipher object can only be used for encryption") self._next = ("decrypt",) try: return self._encrypt(ciphertext, output) except ValueError as e: raise ValueError(str(e).replace("enc", "dec")) def seek(self, position): """Seek to a certain position in the key stream. Args: position (integer): The absolute position within the key stream, in bytes. """ position, offset = divmod(position, 64) block_low = position & 0xFFFFFFFF block_high = position >> 32 result = _raw_chacha20_lib.chacha20_seek( self._state.get(), c_ulong(block_high), c_ulong(block_low), offset ) if result: raise ValueError("Error %d while seeking with %s" % (result, self._name)) def _derive_Poly1305_key_pair(key, nonce): """Derive a tuple (r, s, nonce) for a Poly1305 MAC. If nonce is ``None``, a new 12-byte nonce is generated. """ if len(key) != 32: raise ValueError("Poly1305 with ChaCha20 requires a 32-byte key") if nonce is None: padded_nonce = nonce = get_random_bytes(12) elif len(nonce) == 8: # See RFC7538, 2.6: [...] ChaCha20 as specified here requires a 96-bit # nonce. So if the provided nonce is only 64-bit, then the first 32 # bits of the nonce will be set to a constant number. # This will usually be zero, but for protocols with multiple senders it may be # different for each sender, but should be the same for all # invocations of the function with the same key by a particular # sender. padded_nonce = b'\x00\x00\x00\x00' + nonce elif len(nonce) == 12: padded_nonce = nonce else: raise ValueError("Poly1305 with ChaCha20 requires an 8- or 12-byte nonce") rs = new(key=key, nonce=padded_nonce).encrypt(b'\x00' * 32) return rs[:16], rs[16:], nonce def new(**kwargs): """Create a new ChaCha20 or XChaCha20 cipher Keyword Args: key (bytes/bytearray/memoryview): The secret key to use. It must be 32 bytes long. nonce (bytes/bytearray/memoryview): A mandatory value that must never be reused for any other encryption done with this key. For ChaCha20, it must be 8 or 12 bytes long. For XChaCha20, it must be 24 bytes long. If not provided, 8 bytes will be randomly generated (you can find them back in the ``nonce`` attribute). :Return: a :class:`Crypto.Cipher.ChaCha20.ChaCha20Cipher` object """ try: key = kwargs.pop("key") except KeyError as e: raise TypeError("Missing parameter %s" % e) nonce = kwargs.pop("nonce", None) if nonce is None: nonce = get_random_bytes(8) if len(key) != 32: raise ValueError("ChaCha20/XChaCha20 key must be 32 bytes long") if len(nonce) not in (8, 12, 24): raise ValueError("Nonce must be 8/12 bytes(ChaCha20) or 24 bytes (XChaCha20)") if kwargs: raise TypeError("Unknown parameters: " + str(kwargs)) return ChaCha20Cipher(key, nonce) # Size of a data block (in bytes) block_size = 1 # Size of a key (in bytes) key_size = 32
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