221 lines
7.5 KiB
Python
221 lines
7.5 KiB
Python
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# ===================================================================
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#
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# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
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# All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions
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# are met:
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#
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# 1. Redistributions of source code must retain the above copyright
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# notice, this list of conditions and the following disclaimer.
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# 2. Redistributions in binary form must reproduce the above copyright
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# notice, this list of conditions and the following disclaimer in
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# the documentation and/or other materials provided with the
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# distribution.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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# ===================================================================
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"""ChaCha20 stream cipher
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`ChaCha20`_ is a stream cipher designed by Daniel J. Bernstein.
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The key is 256 bits long.
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As an example, encryption can be done as follows:
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>>> from Crypto.Cipher import ChaCha20
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>>>
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>>> key = b'*Thirty-two byte (256 bits) key*'
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>>> cipher = ChaCha20.new(key)
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>>> msg = cipher.nonce + cipher.encrypt(b'Attack at dawn')
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:undocumented: __package__
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.. _ChaCha20: http://http://cr.yp.to/chacha.html
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"""
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from Crypto.Random import get_random_bytes
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from Crypto.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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expect_byte_string, c_ulong)
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_raw_chacha20_lib = load_pycryptodome_raw_lib("Crypto.Cipher._chacha20",
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"""
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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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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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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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""")
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class ChaCha20Cipher:
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"""ChaCha20 cipher object"""
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block_size = 1
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def __init__(self, key, nonce):
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"""Initialize a ChaCha20 cipher object
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See also `new()` at the module level."""
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expect_byte_string(key)
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expect_byte_string(nonce)
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self.nonce = nonce
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self._next = ( self.encrypt, self.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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key,
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c_size_t(len(key)),
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nonce,
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c_size_t(len(nonce)))
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if result:
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raise ValueError("Error %d instantiating a ChaCha20 cipher")
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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):
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"""Encrypt a piece of data.
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:Parameters:
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plaintext : byte string
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The piece of data to encrypt. It can be of any size.
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:Return: the encrypted data (byte string, as long as the
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plaintext).
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"""
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if self.encrypt not in self._next:
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raise TypeError("Cipher object can only be used for decryption")
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self._next = ( self.encrypt, )
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return self._encrypt(plaintext)
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def _encrypt(self, plaintext):
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"""Encrypt without FSM checks"""
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expect_byte_string(plaintext)
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ciphertext = create_string_buffer(len(plaintext))
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result = _raw_chacha20_lib.chacha20_encrypt(
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self._state.get(),
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plaintext,
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ciphertext,
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c_size_t(len(plaintext)))
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if result:
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raise ValueError("Error %d while encrypting with ChaCha20" % result)
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return get_raw_buffer(ciphertext)
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def decrypt(self, ciphertext):
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"""Decrypt a piece of data.
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:Parameters:
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ciphertext : byte string
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The piece of data to decrypt. It can be of any size.
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:Return: the decrypted data (byte string, as long as the
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ciphertext).
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"""
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if self.decrypt not in self._next:
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raise TypeError("Cipher object can only be used for encryption")
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self._next = ( self.decrypt, )
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try:
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return self._encrypt(ciphertext)
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except ValueError as e:
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raise ValueError(str(e).replace("enc", "dec"))
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def seek(self, position):
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"""Seek at a certain position in the key stream.
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:Parameters:
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position : integer
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The absolute position within the key stream, in bytes.
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"""
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offset = position & 0x3f
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position >>= 6
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block_low = position & 0xFFFFFFFF
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block_high = position >> 32
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result = _raw_chacha20_lib.chacha20_seek(
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self._state.get(),
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c_ulong(block_high),
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c_ulong(block_low),
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offset
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)
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if result:
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raise ValueError("Error %d while seeking with ChaCha20" % result)
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def new(**kwargs):
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"""Create a new ChaCha20 cipher
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:Keywords:
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key : byte string
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The secret key to use in the symmetric cipher.
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It must be 32 bytes long.
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nonce : byte string
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A mandatory value that must never be reused for any other encryption
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done with this key. It must be 8 bytes long.
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If not provided, a random byte string will be generated (you can read
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it back via the ``nonce`` attribute).
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:Return: a `ChaCha20Cipher` object
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"""
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try:
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key = kwargs.pop("key")
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except KeyError as e:
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raise TypeError("Missing parameter %s" % e)
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nonce = kwargs.pop("nonce", None)
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if nonce is None:
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nonce = get_random_bytes(8)
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if len(key) != 32:
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raise ValueError("ChaCha20 key must be 32 bytes long")
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if len(nonce) != 8:
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raise ValueError("ChaCha20 nonce must be 8 bytes long")
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if kwargs:
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raise TypeError("Unknown parameters: " + str(kwargs))
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return ChaCha20Cipher(key, nonce)
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#: Size of a data block (in bytes)
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block_size = 1
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#: Size of a key (in bytes)
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key_size = 32
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