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audit/ChaCha20.py
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# ===================================================================
#
# 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 = ( self.encrypt, self.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 self.encrypt not in self._next:
raise TypeError("Cipher object can only be used for decryption")
self._next = ( self.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 self.decrypt not in self._next:
raise TypeError("Cipher object can only be used for encryption")
self._next = ( self.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