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| from Cryptodome.Random import get_random_bytes
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|
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| from Cryptodome.Util.py3compat import _copy_bytes
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| from Cryptodome.Util._raw_api import (load_pycryptodome_raw_lib,
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| create_string_buffer,
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| get_raw_buffer, VoidPointer,
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| SmartPointer, c_size_t,
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| c_uint8_ptr, c_ulong,
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| is_writeable_buffer)
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|
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| _raw_chacha20_lib = load_pycryptodome_raw_lib("Cryptodome.Cipher._chacha20",
|
| """
|
| int chacha20_init(void **pState,
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| const uint8_t *key,
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| size_t keySize,
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| const uint8_t *nonce,
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| size_t nonceSize);
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|
|
| int chacha20_destroy(void *state);
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|
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| int chacha20_encrypt(void *state,
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| const uint8_t in[],
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| uint8_t out[],
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| size_t len);
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|
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| int chacha20_seek(void *state,
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| unsigned long block_high,
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| unsigned long block_low,
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| unsigned offset);
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|
|
| int hchacha20( const uint8_t key[32],
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| const uint8_t nonce16[16],
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| uint8_t subkey[32]);
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| """)
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|
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| def _HChaCha20(key, nonce):
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|
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| assert(len(key) == 32)
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| assert(len(nonce) == 16)
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|
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| subkey = bytearray(32)
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| result = _raw_chacha20_lib.hchacha20(
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| c_uint8_ptr(key),
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| c_uint8_ptr(nonce),
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| c_uint8_ptr(subkey))
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| if result:
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| raise ValueError("Error %d when deriving subkey with HChaCha20" % result)
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|
|
| return subkey
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|
|
|
|
| class ChaCha20Cipher(object):
|
| """ChaCha20 (or XChaCha20) cipher object.
|
| Do not create it directly. Use :py:func:`new` instead.
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|
|
| :var nonce: The nonce with length 8, 12 or 24 bytes
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| :vartype nonce: bytes
|
| """
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|
|
| block_size = 1
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|
|
| def __init__(self, key, nonce):
|
| """Initialize a ChaCha20/XChaCha20 cipher object
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|
|
| See also `new()` at the module level."""
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|
|
| self.nonce = _copy_bytes(None, None, nonce)
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|
| if len(nonce) == 24:
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| key = _HChaCha20(key, nonce[:16])
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| nonce = b'\x00' * 4 + nonce[16:]
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| self._name = "XChaCha20"
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| else:
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| self._name = "ChaCha20"
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| nonce = self.nonce
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|
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| self._next = ("encrypt", "decrypt")
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|
|
| self._state = VoidPointer()
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| result = _raw_chacha20_lib.chacha20_init(
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| self._state.address_of(),
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| c_uint8_ptr(key),
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| c_size_t(len(key)),
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| nonce,
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| c_size_t(len(nonce)))
|
| if result:
|
| raise ValueError("Error %d instantiating a %s cipher" % (result,
|
| self._name))
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| self._state = SmartPointer(self._state.get(),
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| _raw_chacha20_lib.chacha20_destroy)
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|
|
| def encrypt(self, plaintext, output=None):
|
| """Encrypt a piece of data.
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|
|
| Args:
|
| plaintext(bytes/bytearray/memoryview): The data to encrypt, of any size.
|
| Keyword Args:
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| 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)
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|
|
| def _encrypt(self, plaintext, output):
|
| """Encrypt without FSM checks"""
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|
|
| if output is None:
|
| ciphertext = create_string_buffer(len(plaintext))
|
| else:
|
| ciphertext = output
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|
|
| if not is_writeable_buffer(output):
|
| raise TypeError("output must be a bytearray or a writeable memoryview")
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|
|
| if len(plaintext) != len(output):
|
| raise ValueError("output must have the same length as the input"
|
| " (%d bytes)" % len(plaintext))
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|
|
| result = _raw_chacha20_lib.chacha20_encrypt(
|
| self._state.get(),
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| c_uint8_ptr(plaintext),
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| 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.
|
|
|
| If you want to seek to a certain block,
|
| use ``seek(block_number * 64)``.
|
|
|
| Args:
|
| position (integer):
|
| The absolute position within the key stream, in bytes.
|
| """
|
|
|
| block_number, offset = divmod(position, 64)
|
| block_low = block_number & 0xFFFFFFFF
|
| block_high = block_number >> 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:
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| 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:`Cryptodome.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)
|
|
|
|
|
| block_size = 1
|
|
|
|
|
| key_size = 32
|
|
|
