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audit/Poly1305.py
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# -*- coding: utf-8 -*-
#
# Hash/Poly1305.py - Implements the Poly1305 MAC
#
# ===================================================================
# The contents of this file are dedicated to the public domain. To
# the extent that dedication to the public domain is not available,
# everyone is granted a worldwide, perpetual, royalty-free,
# non-exclusive license to exercise all rights associated with the
# contents of this file for any purpose whatsoever.
# No rights are reserved.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
# ===================================================================
from binascii import unhexlify
from Crypto.Util.py3compat import bord, tobytes, _copy_bytes
from Crypto.Hash import BLAKE2s
from Crypto.Random import get_random_bytes
from Crypto.Util._raw_api import (load_pycryptodome_raw_lib,
VoidPointer, SmartPointer,
create_string_buffer,
get_raw_buffer, c_size_t,
c_uint8_ptr)
_raw_poly1305 = load_pycryptodome_raw_lib("Crypto.Hash._poly1305",
"""
int poly1305_init(void **state,
const uint8_t *r,
size_t r_len,
const uint8_t *s,
size_t s_len);
int poly1305_destroy(void *state);
int poly1305_update(void *state,
const uint8_t *in,
size_t len);
int poly1305_digest(const void *state,
uint8_t *digest,
size_t len);
""")
class Poly1305_MAC(object):
"""An Poly1305 MAC object.
Do not instantiate directly. Use the :func:`new` function.
:ivar digest_size: the size in bytes of the resulting MAC tag
:vartype digest_size: integer
"""
digest_size = 16
def __init__(self, r, s, data):
if len(r) != 16:
raise ValueError("Parameter r is not 16 bytes long")
if len(s) != 16:
raise ValueError("Parameter s is not 16 bytes long")
self._mac_tag = None
state = VoidPointer()
result = _raw_poly1305.poly1305_init(state.address_of(),
c_uint8_ptr(r),
c_size_t(len(r)),
c_uint8_ptr(s),
c_size_t(len(s))
)
if result:
raise ValueError("Error %d while instantiating Poly1305" % result)
self._state = SmartPointer(state.get(),
_raw_poly1305.poly1305_destroy)
if data:
self.update(data)
def update(self, data):
"""Authenticate the next chunk of message.
Args:
data (byte string/byte array/memoryview): The next chunk of data
"""
if self._mac_tag:
raise TypeError("You can only call 'digest' or 'hexdigest' on this object")
result = _raw_poly1305.poly1305_update(self._state.get(),
c_uint8_ptr(data),
c_size_t(len(data)))
if result:
raise ValueError("Error %d while hashing Poly1305 data" % result)
return self
def copy(self):
raise NotImplementedError()
def digest(self):
"""Return the **binary** (non-printable) MAC tag of the message
authenticated so far.
:return: The MAC tag digest, computed over the data processed so far.
Binary form.
:rtype: byte string
"""
if self._mac_tag:
return self._mac_tag
bfr = create_string_buffer(16)
result = _raw_poly1305.poly1305_digest(self._state.get(),
bfr,
c_size_t(len(bfr)))
if result:
raise ValueError("Error %d while creating Poly1305 digest" % result)
self._mac_tag = get_raw_buffer(bfr)
return self._mac_tag
def hexdigest(self):
"""Return the **printable** MAC tag of the message authenticated so far.
:return: The MAC tag, computed over the data processed so far.
Hexadecimal encoded.
:rtype: string
"""
return "".join(["%02x" % bord(x)
for x in tuple(self.digest())])
def verify(self, mac_tag):
"""Verify that a given **binary** MAC (computed by another party)
is valid.
Args:
mac_tag (byte string/byte string/memoryview): the expected MAC of the message.
Raises:
ValueError: if the MAC does not match. It means that the message
has been tampered with or that the MAC key is incorrect.
"""
secret = get_random_bytes(16)
mac1 = BLAKE2s.new(digest_bits=160, key=secret, data=mac_tag)
mac2 = BLAKE2s.new(digest_bits=160, key=secret, data=self.digest())
if mac1.digest() != mac2.digest():
raise ValueError("MAC check failed")
def hexverify(self, hex_mac_tag):
"""Verify that a given **printable** MAC (computed by another party)
is valid.
Args:
hex_mac_tag (string): the expected MAC of the message,
as a hexadecimal string.
Raises:
ValueError: if the MAC does not match. It means that the message
has been tampered with or that the MAC key is incorrect.
"""
self.verify(unhexlify(tobytes(hex_mac_tag)))
def new(**kwargs):
"""Create a new Poly1305 MAC object.
Args:
key (bytes/bytearray/memoryview):
The 32-byte key for the Poly1305 object.
cipher (module from ``Crypto.Cipher``):
The cipher algorithm to use for deriving the Poly1305
key pair *(r, s)*.
It can only be ``Crypto.Cipher.AES`` or ``Crypto.Cipher.ChaCha20``.
nonce (bytes/bytearray/memoryview):
Optional. The non-repeatable value to use for the MAC of this message.
It must be 16 bytes long for ``AES`` and 8 or 12 bytes for ``ChaCha20``.
If not passed, a random nonce is created; you will find it in the
``nonce`` attribute of the new object.
data (bytes/bytearray/memoryview):
Optional. The very first chunk of the message to authenticate.
It is equivalent to an early call to ``update()``.
Returns:
A :class:`Poly1305_MAC` object
"""
cipher = kwargs.pop("cipher", None)
if not hasattr(cipher, '_derive_Poly1305_key_pair'):
raise ValueError("Parameter 'cipher' must be AES or ChaCha20")
cipher_key = kwargs.pop("key", None)
if cipher_key is None:
raise TypeError("You must pass a parameter 'key'")
nonce = kwargs.pop("nonce", None)
data = kwargs.pop("data", None)
if kwargs:
raise TypeError("Unknown parameters: " + str(kwargs))
r, s, nonce = cipher._derive_Poly1305_key_pair(cipher_key, nonce)
new_mac = Poly1305_MAC(r, s, data)
new_mac.nonce = _copy_bytes(None, None, nonce) # nonce may still be just a memoryview
return new_mac