Function open_message 

pub(crate) fn open_message(
    qt: &CxxQtThread<Sioul>,
    shared: &Arc<Shared>,
    key: &str,
    typed: String,
)

Opens a message encrypted to your security key (“Open with your security key”); its session key then stays in memory until Sioul closes, so that it opens again, with its attachments and its answer, without the key.