# [rc5] stats and philosophy

Michael Driscoll fenris at frob.ml.org
Sun Oct 12 23:02:05 EDT 1997

```>Huha?  What is the difference?  Since the probability for each key is
>1/2^56, then (.5*2^56)*1/2^56=.5.  So when half of the keyspace is
>completed, there is a 50% chance that The Key will have been hit.

Actually it's a little more complicated, from what I understand.
When we started, there was a 50% chance that we would hit it in
the first 50%.  However, now that we have actually shown some 40%
to not contain the key, there is no longer a 50% chance that the
key is in the next 10%.  The way to do it is take the remaining
keyspace (60%) and half that.  So there is now a 50% chance that
we will hit it in the next 30%.

To take this to the extreme, say there were two keys left.  You
pick one key to check (50% of the remaining keyspace) and there
is a 50% chance that it is the winning key.

Jokes about Schrodinger's Key will now be presented.
Mike
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