[E-Lang] Ownership certificates via capabilities?

[Ben Laurie]

hal@finney.org wrote:
> The question was, could this be done in an offline way, since players
> often get together at a place where there is no Internet connection.
> Perhaps they could each bring a portable computer and hook them together
> directly or via an IR connection.

Oops. Managed to miss this bit in my previous reply. However...

> The cryptographers said they were trying to find a way to do it with
> capabilities.  Each card would be represented by a capability.  I thought
> about that and it seemed that the problem would be that when you used
> your card in a game, the other player could see its value and steal it
> by copying the capability.  So it does not appear that it can be done.

The capability could be one that allowed you to play the card _on behalf
of a particular player_ - so stealing it would not give you the card,
though you would get the ability to play it inappropriately - however,
you can fix that by setting things up such that only the player whose
turn it is can play at all (which can be done by handing out "turn"
capabilities to the "game process") - then if someone tried to exercise
their capability out-of-turn, they wouldn't be able to (their turn
capability would not yet be valid), and in-turn, it wouldn't work (their
card capability would be linked to the wrong player).

Howzat?

Cheers,

Ben.

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