From: Jim Choate <ravage@einstein.ssz.com>
Date: Thu, 29 Oct 1998 21:54:54 +0800
To: cypherpunks@einstein.ssz.com (Cypherpunks Distributed Remailer)
Subject: Re: Shuffling (fwd)
Message-ID: <199810291325.HAA19001@einstein.ssz.com>
MIME-Version: 1.0
Content-Type: text



Forwarded message:

> Date: Wed, 28 Oct 1998 22:10:08 -0800
> From: Alex Alten <Alten@home.com>
> Subject: Re: Shuffling

> The concept of swapping to get a random string of bits is very interesting.
> >From what I understand when one shuffles a deck of 52 cards 7 or more times
> the card order becomes unpredictable e.g. random.

Only if it is a 'fair' shuffle. There are poker players I've met who could
put a given card anywhere in the deck after 4-5 shuffles.

>  The shuffle must be
> what is called a "near perfect" shuffle.

Perfect for who? Idealy the 'perfect' shuffle (if I understand your meaning
of perfect) would be for each card in each deck-half to interleave 1-to-1.
This does not produce random anything, it does make it very hard for people
to count cards, which is why you shuffle - not to create a necessarily
random ordering of the cards, just so mis-ordered nobody can remember what
the sequence was and predict reliably what the sequence will be. This is
incredibly important in games like poker or rummie where the cards pile up
and players can see the sequence (and if they can remember it use it).

This is also the reason that all games involving shuffled cards strictly
call for a neutral party to shuffle and deal, falling back to the players
only for 'friendly' games. Really smart 'amateur' players as you call them
also make sure that he who deals is not he who anties first.

I've never quite understood where this 'shuffle equal random' theory so 
many people have comes from (historicaly). But it is fun to play against
them because they also (usualy) only shuffle the cards once to twice before
a deal.

Even un-even shuffles aren't prevention from short-sequence card counters.
I impliment this when I play poker, it's helpfull to figure out how many
cards to draw because it's possible to estimate the 'distance' between a
short set of cards (eg a royal flush) after the shuffle.

> In other words the cards can't
> strictly alternate from each hand (with a half deck each), but must be 
> slightly random, in the sense that sometimes 2 or 3 cards may drop from a
> hand before a card drops from the other hand.

Unfortunately, professional croupie's don't practice for this. They practice
for a perfect inter-leave.

>  An amateur shuffle, like
> the one I perform, where the cards clump as they drop, may require 100's 
> of iterations before the order becomes totally unpredictable.  BTW, if
> I remember correctly the number of people in the world who can execute a 
> perfect shuffle at a professional rate (about 8 times a minute?) 
> consistently is somewhat less than 30.

8 time a minute? That's a pretty slow shuffle. Where did you get this number
from? A really quick proffessional shuffle doesn't take 3 seconds.


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