I can conceive of a level 0, "no one can crack it". I can even believe that potentially, Signal (and possibly nothing else?) falls in this category. But it doesn't matter, because what we already see, specifically with the U.S. government, is that "Signal is currently uncrackable" only means "the difficulty of cracking it is so high that instead of bothering, the threat actor cracks something else which has the ability to read the Signal messages, such as the human at the other end"
oblomov
blaise