"No. Wizards use magic for locks. Everyone else...I think uses mechanical ones, with keys."

"There's a dath ilani proverb to the effect that a key and a code is more effective than just a key or a code, because keys can be stolen as codes can be spied on.  But maybe that doesn't apply if there's a first-circle spell that makes keys only work in the hands of authorized holders...?"

"...mostly I don't know how you'd do a lock with a...code. I've never heard of that."

"Buttons labeled 0 through 9, you've got to enter six numbers in the correct order to open the lock... I would not have thought that would take a very complicated mechanism, it seems very simple compared to other mechanisms.  Heck, with sixteen buttons, just needing to depress the correct eight buttons in any order, while leaving the eight other buttons raised, would provide significant protection.  That seems very easy to visualize as a lock; though, making it not be externally obvious when you have some of the buttons correct but not others, would take more work..."

"Well, anyways, in dath ilan, there are locks which require a key, or numbers, or both, depending on how strong you want to make them and whether you're more worried about stolen keys or spied-on codes.  And security issues like making sure that somebody can't tell which numbers are being depressed by listening to the sound of the clicks, or not having the interior mechanism of the key be examinable from the outside of the key before it's inserted into the lock, stuff like that."

"Is there such a thing as there being one best code, or one best key, that you could use to fend off the greatest possible number of thieves, and then no better code or better key than that could exist?"

"No," the class choruses. 

"Isn't that, in some sense, contradictory to the very notion of intelligence?  If you can measure intelligence with numbers, and keep going past 20, past 30, past 100, shouldn't there come a point where the greatest possible and most perfect intelligence can determine the one best possible code for a lock?"

"- I guess eventually you could come up with a number so long and hard to specify that no one less smart that you is capable of generating it, and that'd be the best possible code for a lock."

"Well, it's good that you don't just say 'no' and give up on the question!  In dath ilan, once you get past the kind of locks that parents use to keep young children from wandering into the workshop or the," no word for that then where do they do it, "cuddle-room, you get what's called Keeper locks, though they also appear on the more powerful weapons the military is allowed to own.  One component of a Keeper lock is a kind of key that's physically impossible to duplicate, though it has to be refreshed each time it's used; the other component is a game that never plays out the same way twice, with rules of a form that our brains can learn subconsciously without ever figuring them out consciously.  The knowledge that gets you inside consists of you having learned to play the lock's game, after a few days or hours of practice and occasional refreshers; and you don't consciously know what the game's rules are, so you literally can't explain to anybody else how to get inside, even if they drug you."

"But let's say the lock just has ten digits and six numbers."

"Can an entity with Intelligence 100 determine the best possible six-number sequence that every such lock should use?"

"No," they chorus again.

"Well, why not, exactly?"

"The only thing that makes a code good is that no one knows it."

"So use your Intelligence 100 to pick out the best possible code that people are least likely to guess."

"...well, if it's in every lock, then they'll just put a bunch of sl-employees to work trying it on one lock, and once they get it they'll know all the locks."

"Ah, well, perhaps.  Let's look at it from the other side; if there's a ten-digit, six-number lock I need to get through, can I use my 100 Intelligence to discover the single best sequence to try on a lock like that?"

"...yeah, you could mindread the creator and figure out what rule they used to set it."

"Let us suppose that mindreading is not possible; clever guessing is.  You cannot determine a single correct code with certainty, just that some codes are more likely than others.  I put to you, then, that the code which is most likely to open the lock, is the best code to try entering into it."

The students agree with this, but suspiciously.

"Well, for concrete example, if a silly factory makes all its locks with a default code of 012345, and occasionally some silly people forget to change the default code, then 012345 might be the best code to try entering - it may only open one in ten thousand locks, because very few people are that silly, but it will still open more locks than any other code."

"Or if there's a number that's lucky in some religion, so people change their locks to that."

"Wait, so they actively change their lock to one that's...  Can you tell me whether or not you're joking about that being a thing people would really do?  I haven't actually met anyone with Intelligence 10 in my life before and I don't know what that's like."

"- yeah, people do that."

"I mean, we don't have that kind of lock, but people do that sort of thing, they have magic item passwords that are famous magic item passwords, or the names of their kids."

"All right.  Duly noted.  You people seriously need to raise your average intelligence level before somebody accidentally blows up what's left of the planet."

"To resume where we left off:  Having thus determined that 012345 is the best, the most optimal code you can possibly try on a lock, I put to you that, clearly, the optimal strategy for opening a coded lock is to repeatedly try 012345 on it until it opens.  Agreed?"

Suspicious chorus. "Noooo."

"Why not?  Seems reasonable to me.  If you have the optimal best method you should keep using it."