[Cryptography] Real-world crypto/PRNG problem: Bridge
Bill Frantz
frantz at pwpconsult.com
Tue Aug 23 15:38:10 EDT 2016
On 8/23/16 at 1:37 AM, leichter at lrw.com (Jerry Leichter) wrote:
>Given the use case, shuffling a deck of cards and typing in the
>sequence of cards should be sufficient...
I seem to remember reading about an issue that turned up when
duplicate bridge tournaments moved from hand shuffling to
machine shuffling many years ago. People noticed that there were
many more distributional hands with the machine shuffling.
Analysis indicated that the typical hand shuffling wasn't really
mixing the cards enough, so the ordering left from the last hand
presisted into the new hand. Machine shuffling was doing a
better job of mixing.
Typically in rubber bridge, the cards get shuffled 3 or 4 times
before being dealt again. This turned out to be far too few
mixings. I think I remember recommendations for 7 or so mixings,
but I'm not sure even this level is enough.
Moral: Random is hard. :-)
Cheers - Bill
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