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1# This file is dual licensed under the terms of the Apache License, Version
2# 2.0, and the BSD License. See the LICENSE file in the root of this repository
3# for complete details.
4
5from __future__ import absolute_import, division, print_function
6
7
8from cryptography import utils
9from cryptography.exceptions import UnsupportedAlgorithm, _Reasons
10from cryptography.hazmat.primitives import hashes
11
12
13@utils.register_interface(hashes.HashContext)
14class _HashContext(object):
15    def __init__(self, backend, algorithm, ctx=None):
16        self._algorithm = algorithm
17
18        self._backend = backend
19
20        if ctx is None:
21            ctx = self._backend._lib.Cryptography_EVP_MD_CTX_new()
22            ctx = self._backend._ffi.gc(
23                ctx, self._backend._lib.Cryptography_EVP_MD_CTX_free
24            )
25            evp_md = self._backend._evp_md_from_algorithm(algorithm)
26            if evp_md == self._backend._ffi.NULL:
27                raise UnsupportedAlgorithm(
28                    "{0} is not a supported hash on this backend.".format(
29                        algorithm.name),
30                    _Reasons.UNSUPPORTED_HASH
31                )
32            res = self._backend._lib.EVP_DigestInit_ex(ctx, evp_md,
33                                                       self._backend._ffi.NULL)
34            self._backend.openssl_assert(res != 0)
35
36        self._ctx = ctx
37
38    algorithm = utils.read_only_property("_algorithm")
39
40    def copy(self):
41        copied_ctx = self._backend._lib.Cryptography_EVP_MD_CTX_new()
42        copied_ctx = self._backend._ffi.gc(
43            copied_ctx, self._backend._lib.Cryptography_EVP_MD_CTX_free
44        )
45        res = self._backend._lib.EVP_MD_CTX_copy_ex(copied_ctx, self._ctx)
46        self._backend.openssl_assert(res != 0)
47        return _HashContext(self._backend, self.algorithm, ctx=copied_ctx)
48
49    def update(self, data):
50        data_ptr = self._backend._ffi.from_buffer(data)
51        res = self._backend._lib.EVP_DigestUpdate(
52            self._ctx, data_ptr, len(data)
53        )
54        self._backend.openssl_assert(res != 0)
55
56    def finalize(self):
57        if isinstance(self.algorithm, hashes.ExtendableOutputFunction):
58            # extendable output functions use a different finalize
59            return self._finalize_xof()
60        else:
61            buf = self._backend._ffi.new("unsigned char[]",
62                                         self._backend._lib.EVP_MAX_MD_SIZE)
63            outlen = self._backend._ffi.new("unsigned int *")
64            res = self._backend._lib.EVP_DigestFinal_ex(self._ctx, buf, outlen)
65            self._backend.openssl_assert(res != 0)
66            self._backend.openssl_assert(
67                outlen[0] == self.algorithm.digest_size
68            )
69            return self._backend._ffi.buffer(buf)[:outlen[0]]
70
71    def _finalize_xof(self):
72        buf = self._backend._ffi.new("unsigned char[]",
73                                     self.algorithm.digest_size)
74        res = self._backend._lib.EVP_DigestFinalXOF(
75            self._ctx, buf, self.algorithm.digest_size
76        )
77        self._backend.openssl_assert(res != 0)
78        return self._backend._ffi.buffer(buf)[:self.algorithm.digest_size]
79