Create ChaCha20.py
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Evan Su
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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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from Crypto.Random import get_random_bytes
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from Crypto.Util.py3compat import _copy_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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c_uint8_ptr, c_ulong,
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is_writeable_buffer)
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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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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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def _HChaCha20(key, nonce):
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assert(len(key) == 32)
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assert(len(nonce) == 16)
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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):
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"""ChaCha20 (or XChaCha20) cipher object.
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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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"""
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block_size = 1
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def __init__(self, key, nonce):
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"""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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# XChaCha20 requires a key derivation with HChaCha20
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# See 2.3 in https://tools.ietf.org/html/draft-arciszewski-xchacha-03
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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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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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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)))
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if result:
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raise ValueError("Error %d instantiating a %s cipher" % (result,
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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):
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"""Encrypt a piece of data.
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Args:
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plaintext(bytes/bytearray/memoryview): The data to encrypt, of any size.
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Keyword Args:
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output(bytes/bytearray/memoryview): The location where the ciphertext
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is written to. If ``None``, the ciphertext is returned.
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Returns:
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If ``output`` is ``None``, the ciphertext is returned as ``bytes``.
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Otherwise, ``None``.
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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, output)
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def _encrypt(self, plaintext, output):
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"""Encrypt without FSM checks"""
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if output is None:
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ciphertext = create_string_buffer(len(plaintext))
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else:
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ciphertext = output
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if not is_writeable_buffer(output):
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raise TypeError("output must be a bytearray or a writeable memoryview")
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if len(plaintext) != len(output):
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raise ValueError("output must have the same length as the input"
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" (%d bytes)" % len(plaintext))
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result = _raw_chacha20_lib.chacha20_encrypt(
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self._state.get(),
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c_uint8_ptr(plaintext),
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c_uint8_ptr(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 %s" % (result, self._name))
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if output is None:
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return get_raw_buffer(ciphertext)
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else:
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return None
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def decrypt(self, ciphertext, output=None):
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"""Decrypt a piece of data.
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Args:
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ciphertext(bytes/bytearray/memoryview): The data to decrypt, of any size.
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Keyword Args:
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output(bytes/bytearray/memoryview): The location where the plaintext
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is written to. If ``None``, the plaintext is returned.
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Returns:
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If ``output`` is ``None``, the plaintext is returned as ``bytes``.
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Otherwise, ``None``.
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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, output)
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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 to a certain position in the key stream.
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Args:
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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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position, offset = divmod(position, 64)
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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 %s" % (result, self._name))
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def _derive_Poly1305_key_pair(key, nonce):
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"""Derive a tuple (r, s, nonce) for a Poly1305 MAC.
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If nonce is ``None``, a new 12-byte nonce is generated.
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"""
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if len(key) != 32:
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raise ValueError("Poly1305 with ChaCha20 requires a 32-byte key")
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if nonce is None:
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padded_nonce = nonce = get_random_bytes(12)
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elif len(nonce) == 8:
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# See RFC7538, 2.6: [...] ChaCha20 as specified here requires a 96-bit
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# nonce. So if the provided nonce is only 64-bit, then the first 32
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# bits of the nonce will be set to a constant number.
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# This will usually be zero, but for protocols with multiple senders it may be
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# different for each sender, but should be the same for all
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# invocations of the function with the same key by a particular
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# sender.
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padded_nonce = b'\x00\x00\x00\x00' + nonce
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elif len(nonce) == 12:
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padded_nonce = nonce
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else:
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raise ValueError("Poly1305 with ChaCha20 requires an 8- or 12-byte nonce")
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rs = new(key=key, nonce=padded_nonce).encrypt(b'\x00' * 32)
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return rs[:16], rs[16:], nonce
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def new(**kwargs):
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"""Create a new ChaCha20 or XChaCha20 cipher
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Keyword Args:
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key (bytes/bytearray/memoryview): The secret key to use.
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It must be 32 bytes long.
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nonce (bytes/bytearray/memoryview): A mandatory value that
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must never be reused for any other encryption
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done with this key.
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For ChaCha20, it must be 8 or 12 bytes long.
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For XChaCha20, it must be 24 bytes long.
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If not provided, 8 bytes will be randomly generated
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(you can find them back in the ``nonce`` attribute).
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:Return: a :class:`Crypto.Cipher.ChaCha20.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/XChaCha20 key must be 32 bytes long")
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if len(nonce) not in (8, 12, 24):
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raise ValueError("Nonce must be 8/12 bytes(ChaCha20) or 24 bytes (XChaCha20)")
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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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