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# Copyright (c) 2015-2021 by Ron Frederick <ronf@timeheart.net> and others.
#
# This program and the accompanying materials are made available under
# the terms of the Eclipse Public License v2.0 which accompanies this
# distribution and is available at:
#
# http://www.eclipse.org/legal/epl-2.0/
#
# This program may also be made available under the following secondary
# licenses when the conditions for such availability set forth in the
# Eclipse Public License v2.0 are satisfied:
#
# GNU General Public License, Version 2.0, or any later versions of
# that license
#
# SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
#
# Contributors:
# Ron Frederick - initial implementation, API, and documentation
"""Chacha20-Poly1305 symmetric encryption handler"""
from ctypes import c_ulonglong, create_string_buffer
from typing import Optional, Tuple
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.backends.openssl import backend
from cryptography.hazmat.primitives.ciphers import Cipher
from cryptography.hazmat.primitives.ciphers.algorithms import ChaCha20
from cryptography.hazmat.primitives.poly1305 import Poly1305
from .cipher import register_cipher
if backend.poly1305_supported():
_CTR_0 = (0).to_bytes(8, 'little')
_CTR_1 = (1).to_bytes(8, 'little')
_POLY1305_KEYBYTES = 32
def chacha20(key: bytes, data: bytes, nonce: bytes, ctr: int) -> bytes:
"""Encrypt/decrypt a block of data with the ChaCha20 cipher"""
return Cipher(ChaCha20(key, (_CTR_1 if ctr else _CTR_0) + nonce),
mode=None).encryptor().update(data)
def poly1305_key(key: bytes, nonce: bytes) -> bytes:
"""Derive a Poly1305 key"""
return chacha20(key, _POLY1305_KEYBYTES * b'\0', nonce, 0)
def poly1305(key: bytes, data: bytes, nonce: bytes) -> bytes:
"""Compute a Poly1305 tag for a block of data"""
return Poly1305.generate_tag(poly1305_key(key, nonce), data)
def poly1305_verify(key: bytes, data: bytes,
nonce: bytes, tag: bytes) -> bool:
"""Verify a Poly1305 tag for a block of data"""
try:
Poly1305.verify_tag(poly1305_key(key, nonce), data, tag)
return True
except InvalidSignature:
return False
chacha_available = True
else: # pragma: no cover
try:
from libnacl import nacl
_chacha20 = nacl.crypto_stream_chacha20
_chacha20_xor_ic = nacl.crypto_stream_chacha20_xor_ic
_POLY1305_BYTES = nacl.crypto_onetimeauth_poly1305_bytes()
_POLY1305_KEYBYTES = nacl.crypto_onetimeauth_poly1305_keybytes()
_poly1305 = nacl.crypto_onetimeauth_poly1305
_poly1305_verify = nacl.crypto_onetimeauth_poly1305_verify
def chacha20(key: bytes, data: bytes, nonce: bytes, ctr: int) -> bytes:
"""Encrypt/decrypt a block of data with the ChaCha20 cipher"""
datalen = len(data)
result = create_string_buffer(datalen)
ull_datalen = c_ulonglong(datalen)
ull_ctr = c_ulonglong(ctr)
_chacha20_xor_ic(result, data, ull_datalen, nonce, ull_ctr, key)
return result.raw
def poly1305_key(key: bytes, nonce: bytes) -> bytes:
"""Derive a Poly1305 key"""
polykey = create_string_buffer(_POLY1305_KEYBYTES)
ull_polykeylen = c_ulonglong(_POLY1305_KEYBYTES)
_chacha20(polykey, ull_polykeylen, nonce, key)
return polykey.raw
def poly1305(key: bytes, data: bytes, nonce: bytes) -> bytes:
"""Compute a Poly1305 tag for a block of data"""
tag = create_string_buffer(_POLY1305_BYTES)
ull_datalen = c_ulonglong(len(data))
polykey = poly1305_key(key, nonce)
_poly1305(tag, data, ull_datalen, polykey)
return tag.raw
def poly1305_verify(key: bytes, data: bytes,
nonce: bytes, tag: bytes) -> bool:
"""Verify a Poly1305 tag for a block of data"""
ull_datalen = c_ulonglong(len(data))
polykey = poly1305_key(key, nonce)
return _poly1305_verify(tag, data, ull_datalen, polykey) == 0
chacha_available = True
except (ImportError, OSError, AttributeError):
chacha_available = False
class ChachaCipher:
"""Shim for Chacha20-Poly1305 symmetric encryption"""
def __init__(self, key: bytes):
keylen = len(key) // 2
self._key = key[:keylen]
self._adkey = key[keylen:]
def encrypt_and_sign(self, header: bytes, data: bytes,
nonce: bytes) -> Tuple[bytes, bytes]:
"""Encrypt and sign a block of data"""
header = chacha20(self._adkey, header, nonce, 0)
data = chacha20(self._key, data, nonce, 1)
tag = poly1305(self._key, header + data, nonce)
return header + data, tag
def decrypt_header(self, header: bytes, nonce: bytes) -> bytes:
"""Decrypt header data"""
return chacha20(self._adkey, header, nonce, 0)
def verify_and_decrypt(self, header: bytes, data: bytes,
nonce: bytes, tag: bytes) -> Optional[bytes]:
"""Verify the signature of and decrypt a block of data"""
if poly1305_verify(self._key, header + data, nonce, tag):
return chacha20(self._key, data, nonce, 1)
else:
return None
if chacha_available: # pragma: no branch
register_cipher('chacha20-poly1305', 64, 0, 1)
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