> The saying that stuck with me was "defenders have to be right 100% of the time, while attackers only have to be right once".

> You are suggesting this isn't correct?

The intuition behind that is applicable only when correctness is stochastic. If you need to be waved in by a security guard, then one fake mustache might be the difference between being granted or denied entry. However, a keypad either works or it doesn't; entering the wrong PIN is guaranteed refusal.

The other breach of that intuition is defense in depth. Secure systems don't generally rely on a single binary trusted/untrusted status; the classified building still locks its interior doors. This is the part that has – in my view temporarily – changed most with frontier models, in that they are much more skilled at chaining together vulnerabilities than previous models (and much faster about it than human experts, even if potentially less skilled). If a system has a latent (0-day) vulnerability 50% of the time, then 10 independent layers would imply a ≈ 1/1000 chance that a critical compromise is possible.

However, these independent layers don't currently happen in practice because it's easier to write insecure code than secure code. With luck, modest discipline, and defensive use of frontier models I think that this gap will narrow with time, in much the same way that it would be plainly crazy to deploy root access via telnet today.

It's correct but defenders also choose where that happens. 100% of the time on the locations and conditions that the defenders choose / allow. As a defender i need to be right 100% of the time, sure, but i can make it so that the things i have to be right about are very well known to me, unknown to others, maybe even extremely unlikely to be to known by others, difficult to get to know, (...). So that saying is true but over simplifies the situation. I know monkey brain likes simple phrase. But monkey not live in savannah anymore. Need to adapt and open mind to complex.

This is the same mentality that drives companies to sue cybersecurity researchers for exposing vulnerabilities in their software instead of fixing the software, or to insist on keeping software closed source for "security reasons".

If AI makes finding software vulnerabilities easier, then we should deploy it widely to find as many vulnerabilities as possible and fix them, not bury our heads in the sand and pretend the vulnerabilities don't exist as long as nobody knows about them. That's just the same "security by obscurity" strategy that has been tried and failed time and time again.

> "defenders have to be right 100% of the time, while attackers only have to be right once"

If you have an adaptive system that can react to attacks flexible (say, your own AI agent), then no, that's not correct. It is correct in the classical conception of cybersecurity where the defender is basically static.