ChaCha20_Poly1305.py
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# =================================================================== # # Copyright (c) 2018, Helder Eijs <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 binascii import unhexlify from Crypto.Cipher import ChaCha20 from Crypto.Cipher.ChaCha20 import _HChaCha20 from Crypto.Hash import Poly1305, BLAKE2s from Crypto.Random import get_random_bytes from Crypto.Util.number import long_to_bytes from Crypto.Util.py3compat import _copy_bytes, bord from Crypto.Util._raw_api import is_buffer def _enum(**enums): return type('Enum', (), enums) _CipherStatus = _enum(PROCESSING_AUTH_DATA=1, PROCESSING_CIPHERTEXT=2, PROCESSING_DONE=3) class ChaCha20Poly1305Cipher(object): """ChaCha20-Poly1305 and XChaCha20-Poly1305 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: byte string """ def __init__(self, key, nonce): """Initialize a ChaCha20-Poly1305 AEAD cipher object See also `new()` at the module level.""" self._next = ("update", "encrypt", "decrypt", "digest", "verify") self._authenticator = Poly1305.new(key=key, nonce=nonce, cipher=ChaCha20) self._cipher = ChaCha20.new(key=key, nonce=nonce) self._cipher.seek(64) # Block counter starts at 1 self._len_aad = 0 self._len_ct = 0 self._mac_tag = None self._status = _CipherStatus.PROCESSING_AUTH_DATA def update(self, data): """Protect the associated data. Associated data (also known as *additional authenticated data* - AAD) is the piece of the message that must stay in the clear, while still allowing the receiver to verify its integrity. An example is packet headers. The associated data (possibly split into multiple segments) is fed into :meth:`update` before any call to :meth:`decrypt` or :meth:`encrypt`. If there is no associated data, :meth:`update` is not called. :param bytes/bytearray/memoryview assoc_data: A piece of associated data. There are no restrictions on its size. """ if "update" not in self._next: raise TypeError("update() method cannot be called") self._len_aad += len(data) self._authenticator.update(data) def _pad_aad(self): assert(self._status == _CipherStatus.PROCESSING_AUTH_DATA) if self._len_aad & 0x0F: self._authenticator.update(b'\x00' * (16 - (self._len_aad & 0x0F))) self._status = _CipherStatus.PROCESSING_CIPHERTEXT 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 "encrypt" not in self._next: raise TypeError("encrypt() method cannot be called") if self._status == _CipherStatus.PROCESSING_AUTH_DATA: self._pad_aad() self._next = ("encrypt", "digest") result = self._cipher.encrypt(plaintext, output=output) self._len_ct += len(plaintext) if output is None: self._authenticator.update(result) else: self._authenticator.update(output) return result 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("decrypt() method cannot be called") if self._status == _CipherStatus.PROCESSING_AUTH_DATA: self._pad_aad() self._next = ("decrypt", "verify") self._len_ct += len(ciphertext) self._authenticator.update(ciphertext) return self._cipher.decrypt(ciphertext, output=output) def _compute_mac(self): """Finalize the cipher (if not done already) and return the MAC.""" if self._mac_tag: assert(self._status == _CipherStatus.PROCESSING_DONE) return self._mac_tag assert(self._status != _CipherStatus.PROCESSING_DONE) if self._status == _CipherStatus.PROCESSING_AUTH_DATA: self._pad_aad() if self._len_ct & 0x0F: self._authenticator.update(b'\x00' * (16 - (self._len_ct & 0x0F))) self._status = _CipherStatus.PROCESSING_DONE self._authenticator.update(long_to_bytes(self._len_aad, 8)[::-1]) self._authenticator.update(long_to_bytes(self._len_ct, 8)[::-1]) self._mac_tag = self._authenticator.digest() return self._mac_tag def digest(self): """Compute the *binary* authentication tag (MAC). :Return: the MAC tag, as 16 ``bytes``. """ if "digest" not in self._next: raise TypeError("digest() method cannot be called") self._next = ("digest",) return self._compute_mac() def hexdigest(self): """Compute the *printable* authentication tag (MAC). This method is like :meth:`digest`. :Return: the MAC tag, as a hexadecimal string. """ return "".join(["%02x" % bord(x) for x in self.digest()]) def verify(self, received_mac_tag): """Validate the *binary* authentication tag (MAC). The receiver invokes this method at the very end, to check if the associated data (if any) and the decrypted messages are valid. :param bytes/bytearray/memoryview received_mac_tag: This is the 16-byte *binary* MAC, as received from the sender. :Raises ValueError: if the MAC does not match. The message has been tampered with or the key is incorrect. """ if "verify" not in self._next: raise TypeError("verify() cannot be called" " when encrypting a message") self._next = ("verify",) secret = get_random_bytes(16) self._compute_mac() mac1 = BLAKE2s.new(digest_bits=160, key=secret, data=self._mac_tag) mac2 = BLAKE2s.new(digest_bits=160, key=secret, data=received_mac_tag) if mac1.digest() != mac2.digest(): raise ValueError("MAC check failed") def hexverify(self, hex_mac_tag): """Validate the *printable* authentication tag (MAC). This method is like :meth:`verify`. :param string hex_mac_tag: This is the *printable* MAC. :Raises ValueError: if the MAC does not match. The message has been tampered with or the key is incorrect. """ self.verify(unhexlify(hex_mac_tag)) def encrypt_and_digest(self, plaintext): """Perform :meth:`encrypt` and :meth:`digest` in one step. :param plaintext: The data to encrypt, of any size. :type plaintext: bytes/bytearray/memoryview :return: a tuple with two ``bytes`` objects: - the ciphertext, of equal length as the plaintext - the 16-byte MAC tag """ return self.encrypt(plaintext), self.digest() def decrypt_and_verify(self, ciphertext, received_mac_tag): """Perform :meth:`decrypt` and :meth:`verify` in one step. :param ciphertext: The piece of data to decrypt. :type ciphertext: bytes/bytearray/memoryview :param bytes received_mac_tag: This is the 16-byte *binary* MAC, as received from the sender. :return: the decrypted data (as ``bytes``) :raises ValueError: if the MAC does not match. The message has been tampered with or the key is incorrect. """ plaintext = self.decrypt(ciphertext) self.verify(received_mac_tag) return plaintext def new(**kwargs): """Create a new ChaCha20-Poly1305 or XChaCha20-Poly1305 AEAD cipher. :keyword key: The secret key to use. It must be 32 bytes long. :type key: byte string :keyword nonce: A value that must never be reused for any other encryption done with this key. For ChaCha20-Poly1305, it must be 8 or 12 bytes long. For XChaCha20-Poly1305, it must be 24 bytes long. If not provided, 12 ``bytes`` will be generated randomly (you can find them back in the ``nonce`` attribute). :type nonce: bytes, bytearray, memoryview :Return: a :class:`Crypto.Cipher.ChaCha20.ChaCha20Poly1305Cipher` object """ try: key = kwargs.pop("key") except KeyError as e: raise TypeError("Missing parameter %s" % e) self._len_ct += len(plaintext) if len(key) != 32: raise ValueError("Key must be 32 bytes long") nonce = kwargs.pop("nonce", None) if nonce is None: nonce = get_random_bytes(12) if len(nonce) in (8, 12): chacha20_poly1305_nonce = nonce elif len(nonce) == 24: key = _HChaCha20(key, nonce[:16]) chacha20_poly1305_nonce = b'\x00\x00\x00\x00' + nonce[16:] else: raise ValueError("Nonce must be 8, 12 or 24 bytes long") if not is_buffer(nonce): raise TypeError("nonce must be bytes, bytearray or memoryview") if kwargs: raise TypeError("Unknown parameters: " + str(kwargs)) cipher = ChaCha20Poly1305Cipher(key, chacha20_poly1305_nonce) cipher.nonce = _copy_bytes(None, None, nonce) return cipher # Size of a key (in bytes) key_size = 32
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