For some value of "strictly speaking", this is true; but it's not a very relevant value. You can't be "sure" your counter never produces a duplicate, either--st

For some value of "strictly speaking", this is true; but it's not a very relevant value. You can't be "sure" your counter never produces a duplicate, either--strictly speaking--in reality. The bug-free program or the computer that isn't affected by external factors is like the friction-free surface: sometimes useful to think about but not something that exists in reality. And the likelihood of a cosmic ray causing a bit flip or a race condition in the way your counter updates is a lot higher (as in, we see it happen all the time) than the theoretical likelihood of a collision on a sufficiently large and random key.