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