[Evans] The answer is there are 41 different positions for the first wheel,
and we multiply that by 31 different positions for the second K wheel.
And so that means that every 1271 letters those wheels would repeat,
and there are only 1271 different possible settings for the K wheels.
Remember that based on the intercepted messages
they had learned enough about the structure of the machine
to know what the bits are around these wheels.
So it's only necessary to figure out the right configuration.
So certainly today, being able to try 1200-some possibilities
would be trivial with a modern computer,
and you might wonder why when they encountered this at Bletchley Park
they didn't just go down to the store and buy a computer to solve it,
but this was 1941. Computers didn't exist yet. They had to invent one first.
And in fact, arguably, the first computer was invented to solve exactly this problem.
Before we get to that, I want to make sure that we actually have enough of an advantage here
that trying these configurations will help.
So let's look at the probability that if we guess the right key
we'll be able to tell that we got the right message.
