/usr/lib/python3/dist-packages/Cryptodome/Cipher/ChaCha20.py is in python3-pycryptodome 3.4.7-1ubuntu1.
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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 Cryptodome.Random import get_random_bytes
from Cryptodome.Util._raw_api import (load_pycryptodome_raw_lib,
create_string_buffer,
get_raw_buffer, VoidPointer,
SmartPointer, c_size_t,
expect_byte_string, c_ulong)
_raw_chacha20_lib = load_pycryptodome_raw_lib("Cryptodome.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);
""")
class ChaCha20Cipher:
"""ChaCha20 cipher object. Do not create it directly. Use :py:func:`new` instead.
:var nonce: The nonce with length 8
:vartype nonce: byte string
"""
block_size = 1
def __init__(self, key, nonce):
"""Initialize a ChaCha20 cipher object
See also `new()` at the module level."""
expect_byte_string(key)
expect_byte_string(nonce)
self.nonce = nonce
self._next = ( self.encrypt, self.decrypt )
self._state = VoidPointer()
result = _raw_chacha20_lib.chacha20_init(
self._state.address_of(),
key,
c_size_t(len(key)),
nonce,
c_size_t(len(nonce)))
if result:
raise ValueError("Error %d instantiating a ChaCha20 cipher")
self._state = SmartPointer(self._state.get(),
_raw_chacha20_lib.chacha20_destroy)
def encrypt(self, plaintext):
"""Encrypt a piece of data.
:param plaintext: The data to encrypt, of any size.
:type plaintext: byte string
:returns: the encrypted byte string, of equal length as the
plaintext.
"""
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)
def _encrypt(self, plaintext):
"""Encrypt without FSM checks"""
expect_byte_string(plaintext)
ciphertext = create_string_buffer(len(plaintext))
result = _raw_chacha20_lib.chacha20_encrypt(
self._state.get(),
plaintext,
ciphertext,
c_size_t(len(plaintext)))
if result:
raise ValueError("Error %d while encrypting with ChaCha20" % result)
return get_raw_buffer(ciphertext)
def decrypt(self, ciphertext):
"""Decrypt a piece of data.
:param ciphertext: The data to decrypt, of any size.
:type ciphertext: byte string
:returns: the decrypted byte string, of equal length as the
ciphertext.
"""
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)
except ValueError as e:
raise ValueError(str(e).replace("enc", "dec"))
def seek(self, position):
"""Seek to a certain position in the key stream.
:param integer position:
The absolute position within the key stream, in bytes.
"""
offset = position & 0x3f
position >>= 6
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 ChaCha20" % result)
def new(**kwargs):
"""Create a new ChaCha20 cipher
:keyword key: The secret key to use. It must be 32 bytes long.
:type key: byte string
:keyword nonce:
A mandatory value that must never be reused for any other encryption
done with this key. It must be 8 bytes long.
If not provided, a random byte string will be generated (you can read
it back via the ``nonce`` attribute of the returned object).
:type nonce: byte string
: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 key must be 32 bytes long")
if len(nonce) != 8:
raise ValueError("ChaCha20 nonce must be 8 bytes long")
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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