
Mental poker - niyazpk
http://en.wikipedia.org/wiki/Mental_poker
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dminor
Sadly it falls apart as soon as someone decides to quit (or loses
communication) in the middle of a hand, making it unsuitable for internet
poker.

I did run across an interesting "dropout resistant" variation once where the
missing player's cards were (in effect) shuffled back into the deck. This
opens the door to collusion though.

~~~
eru
It's also a hard problem to play Diplomacy like this. (But maybe not as hard
as Poker.)

~~~
avibryant
I'm no crypto expert, but just thinking this through:

In Diplomacy, all that's required is that you commit to your orders before
seeing anyone else's; once everyone has committed, all the orders are
revealed.

What if, for every turn, every player:

1\. Generates a new key 2\. Uses this key to produce an HMAC of their orders
3\. Publishes the HMAC 4\. (once everyone has published the HMAC) Publishes
their orders 5\. Publishes their key so that everyone can verify the HMAC

Would it be feasible for someone to generate two alternative sets of orders
that - given different, carefully chosen keys - produced the same HMAC, and
then choose which combination of orders and key to publish based on what other
moves are revealed? If so, is there some kind of limitation that could be
placed on acceptable keys that would prevent this without allowing the hash to
be brute forced?

~~~
eru
You are basically right. In Diplomacy you need to commit to some secret bits,
and after everyone has committed, reveal them.

But what if I refuse to do step 5? What if I accidentally forgot my key (and
the orders)? Should my units just halt, as if I had not handed in any orders?

~~~
eru
(Sorry, can't reply to your comment directly, yet.)

The problem is, that you do not want give people the option to decide between
using their orders or going into Civil Disorder (by not revealing their keys).
Especially after they've seen the other player's orders.

~~~
avibryant
Good point, though going into Civil Disorder is leaving the game - I guess
this would let them leave it on their terms, possibly screwing over one of the
remaining players in favor of another, but that doesn't strike me as that big
a weakness.

------
jacquesm
The hardest attack to prevent against in a scheme like this is multiple
players playing the game colluding.

It works as long as the number of players is limited to 2.

~~~
dminor
In theory this should be no worse than a game at a brick and mortar casino,
but more of a problem than current online poker sites, who have access to
everyone's hand history and can analyze data after the fact.

If you look at the number one concern among online poker players though, it
isn't whether or not players are colluding -- it's whether or not the dealer
is crooked.

