How to use the oscrypto._ffi.deref function in oscrypto

data_len = len(data)
        while data_len:
            write_buffer = buffer_from_bytes(data)
            result = Security.SSLWrite(
                self._session_context,
                write_buffer,
                data_len,
                processed_pointer
            )
            if self._exception is not None:
                exception = self._exception
                self._exception = None
                raise exception
            handle_sec_error(result, TLSError)

            bytes_written = deref(processed_pointer)
            data = data[bytes_written:]
            data_len = len(data)
            if data_len > 0:
                self.select_write()

to_read,
            processed_pointer
        )
        if self._exception is not None:
            exception = self._exception
            self._exception = None
            raise exception
        if result and result not in set([SecurityConst.errSSLWouldBlock, SecurityConst.errSSLClosedGraceful]):
            handle_sec_error(result, TLSError)

        if result and result == SecurityConst.errSSLClosedGraceful:
            self._gracefully_closed = True
            self._shutdown(False)
            self._raise_closed()

        bytes_read = deref(processed_pointer)
        output = self._decrypted_bytes + bytes_from_buffer(read_buffer, bytes_read)

        self._decrypted_bytes = output[max_length:]
        return output[0:max_length]

handle_sec_error(result)

                if disable_auto_validation:
                    result = Security.SSLSetSessionOption(
                        session_context,
                        SecurityConst.kSSLSessionOptionBreakOnServerAuth,
                        True
                    )
                    handle_sec_error(result)

            # Disable all sorts of bad cipher suites
            supported_ciphers_pointer = new(Security, 'size_t *')
            result = Security.SSLGetNumberSupportedCiphers(session_context, supported_ciphers_pointer)
            handle_sec_error(result)

            supported_ciphers = deref(supported_ciphers_pointer)

            cipher_buffer = buffer_from_bytes(supported_ciphers * 4)
            supported_cipher_suites_pointer = cast(Security, 'uint32_t *', cipher_buffer)
            result = Security.SSLGetSupportedCiphers(
                session_context,
                supported_cipher_suites_pointer,
                supported_ciphers_pointer
            )
            handle_sec_error(result)

            supported_ciphers = deref(supported_ciphers_pointer)
            supported_cipher_suites = array_from_pointer(
                Security,
                'uint32_t',
                supported_cipher_suites_pointer,
                supported_ciphers

buffer = buffer_from_bytes(data)
        out_len = new(advapi32, 'DWORD *', len(data))
        res = advapi32.CryptDecrypt(
            key_handle,
            null(),
            # To skip padding, we have to tell the API that this is not
            # the final block
            False if cipher == 'aes' and not padding else True,
            0,
            buffer,
            out_len
        )
        handle_error(res)

        return bytes_from_buffer(buffer, deref(out_len))

    finally:
        if key_handle:
            advapi32.CryptDestroyKey(key_handle)
        if context_handle:
            close_context_handle(context_handle)

))

    out_len = new(bcrypt, 'DWORD *')
    res = bcrypt.BCryptSignHash(
        private_key.key_handle,
        padding_info,
        digest,
        len(digest),
        null(),
        0,
        out_len,
        flags
    )
    handle_error(res)

    buffer_len = deref(out_len)
    buffer = buffer_from_bytes(buffer_len)

    if private_key.algorithm == 'rsa':
        padding_info = cast(bcrypt, 'void *', padding_info_struct_pointer)

    res = bcrypt.BCryptSignHash(
        private_key.key_handle,
        padding_info,
        digest,
        len(digest),
        buffer,
        buffer_len,
        out_len,
        flags
    )
    handle_error(res)

out_len = new(bcrypt, 'ULONG *')
    res = bcrypt.BCryptEncrypt(
        certificate_or_public_key.key_handle,
        data,
        len(data),
        padding_info,
        null(),
        0,
        null(),
        0,
        out_len,
        flags
    )
    handle_error(res)

    buffer_len = deref(out_len)
    buffer = buffer_from_bytes(buffer_len)

    res = bcrypt.BCryptEncrypt(
        certificate_or_public_key.key_handle,
        data,
        len(data),
        padding_info,
        null(),
        0,
        buffer,
        buffer_len,
        out_len,
        flags
    )
    handle_error(res)

buffer = buffer_from_bytes(buffer_len)
    write_to_buffer(buffer, data)

    pointer_set(out_len, len(data))
    res = advapi32.CryptEncrypt(
        certificate_or_public_key.ex_key_handle,
        null(),
        True,
        flags,
        buffer,
        out_len,
        buffer_len
    )
    handle_error(res)

    return bytes_from_buffer(buffer, deref(out_len))[::-1]

res = advapi32.CryptHashData(hash_handle, data, len(data), 0)
        handle_error(res)

        out_len = new(advapi32, 'DWORD *')
        res = advapi32.CryptSignHashW(
            hash_handle,
            Advapi32Const.AT_SIGNATURE,
            null(),
            0,
            null(),
            out_len
        )
        handle_error(res)

        buffer_length = deref(out_len)
        buffer_ = buffer_from_bytes(buffer_length)

        res = advapi32.CryptSignHashW(
            hash_handle,
            Advapi32Const.AT_SIGNATURE,
            null(),
            0,
            buffer_,
            out_len
        )
        handle_error(res)

        output = bytes_from_buffer(buffer_, deref(out_len))

        # CryptoAPI outputs the signature in little endian byte order, so we
        # must swap it for compatibility with other systems

res = bcrypt.BCryptEncrypt(
            key_handle,
            data,
            len(data),
            null(),
            iv_buffer,
            iv_len,
            buffer,
            buffer_len,
            out_len,
            flags
        )
        handle_error(res)

        return bytes_from_buffer(buffer, deref(out_len))

    finally:
        if key_handle:
            bcrypt.BCryptDestroyKey(key_handle)