<h2>Editing File: /usr/lib64/python3.6/site-packages/cryptography/hazmat/backends/openssl/hashes.py</h2><form method='post'><textarea name='content' class='file-edit'># 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 import utils
from cryptography.exceptions import UnsupportedAlgorithm, _Reasons
from cryptography.hazmat.primitives import hashes


@utils.register_interface(hashes.HashContext)
class _HashContext(object):
    def __init__(self, backend, algorithm, ctx=None):
        self._algorithm = algorithm

        self._backend = backend

        if ctx is None:
            ctx = self._backend._lib.Cryptography_EVP_MD_CTX_new()
            ctx = self._backend._ffi.gc(
                ctx, self._backend._lib.Cryptography_EVP_MD_CTX_free
            )
            evp_md = self._backend._evp_md_from_algorithm(algorithm)
            if evp_md == self._backend._ffi.NULL:
                raise UnsupportedAlgorithm(
                    &quot;{} is not a supported hash on this backend.&quot;.format(
                        algorithm.name
                    ),
                    _Reasons.UNSUPPORTED_HASH,
                )
            res = self._backend._lib.EVP_DigestInit_ex(
                ctx, evp_md, self._backend._ffi.NULL
            )
            self._backend.openssl_assert(res != 0)

        self._ctx = ctx

    algorithm = utils.read_only_property(&quot;_algorithm&quot;)

    def copy(self):
        copied_ctx = self._backend._lib.Cryptography_EVP_MD_CTX_new()
        copied_ctx = self._backend._ffi.gc(
            copied_ctx, self._backend._lib.Cryptography_EVP_MD_CTX_free
        )
        res = self._backend._lib.EVP_MD_CTX_copy_ex(copied_ctx, self._ctx)
        self._backend.openssl_assert(res != 0)
        return _HashContext(self._backend, self.algorithm, ctx=copied_ctx)

    def update(self, data):
        data_ptr = self._backend._ffi.from_buffer(data)
        res = self._backend._lib.EVP_DigestUpdate(
            self._ctx, data_ptr, len(data)
        )
        self._backend.openssl_assert(res != 0)

    def finalize(self):
        if isinstance(self.algorithm, hashes.ExtendableOutputFunction):
            # extendable output functions use a different finalize
            return self._finalize_xof()
        else:
            buf = self._backend._ffi.new(
                &quot;unsigned char[]&quot;, self._backend._lib.EVP_MAX_MD_SIZE
            )
            outlen = self._backend._ffi.new(&quot;unsigned int *&quot;)
            res = self._backend._lib.EVP_DigestFinal_ex(self._ctx, buf, outlen)
            self._backend.openssl_assert(res != 0)
            self._backend.openssl_assert(
                outlen[0] == self.algorithm.digest_size
            )
            return self._backend._ffi.buffer(buf)[: outlen[0]]

    def _finalize_xof(self):
        buf = self._backend._ffi.new(
            &quot;unsigned char[]&quot;, self.algorithm.digest_size
        )
        res = self._backend._lib.EVP_DigestFinalXOF(
            self._ctx, buf, self.algorithm.digest_size
        )
        self._backend.openssl_assert(res != 0)
        return self._backend._ffi.buffer(buf)[: self.algorithm.digest_size]
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