🚀 go-pugleaf

In article <1993Jan3.185628.2976@zip.eecs.umich.edu> positron@quip.eecs.umich.edu (Jonathan Haas) writes:
>I was reading a paper that explained the RSA algorithm
>in layman's terms, and among other things it said, "An
>interesting side benefit of this algorithm is that it
>makes it possible for two people who do not trust each
>other to play poker by telephone." I've thought about
>it, and I can't for the life of me figure out HOW. The
>paper did not elaborate. Can someone explain to me the
>algorithm with which two mutually distrusting players can
>play poker by phone (or, more simply, have a fair coin
>toss)?

OK.  How about this scenerio:  Alice sends Bob a message in which
she describes the situation that the coin toss is going to resolve in
enough detail so as to make it unique, and appends the DES encrypted
output of the privately selected phrase "HEADS" or "TAILS", encrypted
by a random key that she, for the moment, keeps private.  She signs
this entire message.

Bob then takes this message, appends to it his choice "I CHOOSE HEADS"
or "I CHOOSE TAILS", signs the entire thing and sends it back to Alice.

Alice then reveals the random DES key in a signed message to Bob.

If Bob's choice matches Alice's, he wins.  Otherwise, she wins.  Once
Alice receives the reply from Bob, the deed is done.  Both can use the
signed message from the other, plus the DES key, as proof of the
outcome.  If Alice does not or cannot produce the DES key that decrypts
her original choice of "HEADS" or "TAILS", she is adjudicated the de
facto loser.  If Bob never receives the initial message from Alice, or
Alice never receives his reply, well, then the deal was never properly
consummated to begin with.
-- 
Rob Stampfli  rob@colnet.cmhnet.org      The neat thing about standards:
614-864-9377  HAM RADIO: kd8wk@n8jyv.oh  There are so many to choose from.