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# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
from __future__ import absolute_import, division, print_function
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.primitives import constant_time
_POLY1305_TAG_SIZE = 16
_POLY1305_KEY_SIZE = 32
class _Poly1305Context(object):
def __init__(self, backend, key):
self._backend = backend
key_ptr = self._backend._ffi.from_buffer(key)
# This function copies the key into OpenSSL-owned memory so we don't
# need to retain it ourselves
evp_pkey = self._backend._lib.EVP_PKEY_new_raw_private_key(
self._backend._lib.NID_poly1305,
self._backend._ffi.NULL, key_ptr, len(key)
)
self._backend.openssl_assert(evp_pkey != self._backend._ffi.NULL)
self._evp_pkey = self._backend._ffi.gc(
evp_pkey, self._backend._lib.EVP_PKEY_free
)
ctx = self._backend._lib.Cryptography_EVP_MD_CTX_new()
self._backend.openssl_assert(ctx != self._backend._ffi.NULL)
self._ctx = self._backend._ffi.gc(
ctx, self._backend._lib.Cryptography_EVP_MD_CTX_free
)
res = self._backend._lib.EVP_DigestSignInit(
self._ctx, self._backend._ffi.NULL, self._backend._ffi.NULL,
self._backend._ffi.NULL, self._evp_pkey
)
self._backend.openssl_assert(res == 1)
def update(self, data):
data_ptr = self._backend._ffi.from_buffer(data)
res = self._backend._lib.EVP_DigestSignUpdate(
self._ctx, data_ptr, len(data)
)
self._backend.openssl_assert(res != 0)
def finalize(self):
buf = self._backend._ffi.new("unsigned char[]", _POLY1305_TAG_SIZE)
outlen = self._backend._ffi.new("size_t *")
res = self._backend._lib.EVP_DigestSignFinal(self._ctx, buf, outlen)
self._backend.openssl_assert(res != 0)
self._backend.openssl_assert(outlen[0] == _POLY1305_TAG_SIZE)
return self._backend._ffi.buffer(buf)[:outlen[0]]
def verify(self, tag):
mac = self.finalize()
if not constant_time.bytes_eq(mac, tag):
raise InvalidSignature("Value did not match computed tag.")
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