-----BEGIN PGP SIGNED MESSAGE----- In my earlier message I said:

...

Cards are not transferrable. In order to make cards transferrable the game company must be able to invalidate cards which have been traded to others. In other words if Alice wants to give a cards to Bob she must:

<snip> Gary Howland said:

This is the double spending problem.

Me again:

...

Since step 3 is so costly to implement, I think it is unlikely that a cryptography-based trading card game will have tradable cards.

Mr. Howland again:

Given that untraceability of cards is less of an issue than with e-cash, why not have a central registry of the owners of the cards (which would consist of the card hashes paired with the public key fingerprint)? Admittedly this means the players must be on line, but then we all know how difficult off line detection of double spenders is.

And herein lies the problem with an implementation of trading card games. In order to detect "double spenders", the system must be on-line. However, I believe going on-line will drive the costs of running such a game out of the range of commercial feasibility. First of all, it requires that all players have Internet access. This reduces marketability. Secondly, it requires that both players make an Internet connection with the game company everytime they want to play a game. This will incur costs to the game company that it invariably will want to pass on to the players. Players, however, will be very resistant to a game that requires a subscription fee as well as costs for purchasing "cards". Especially, if becomes known that the only reason for the game requiring on-line access is to prevent "cheaters". It also raises the question of whether the game program could be "hacked" to avoid checking for authenticity of cards. I think that a more realistic solution to the "double spending" problem is to not allow the transfer of cards between players. -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBMa6cjPBB6nnGJuMRAQGr3wP+K+DXJVM0rX0F6FSqwfTE/YCJbfiJXC7g dAlwBA1URYA96h4su6xRThD2SbL0vJSLhvi3djQiTeshdqgmD8MTzlDsqTDLPp+f Sw0GN7OjHWlt8VO5UOK9686L7u2Ev49EdGqkaR2NOy5qNdj079v0JydRCg3qhvmT 7LqcXhRbH7g= =h3Eq -----END PGP SIGNATURE----- -- David F. Ogren ogren@concentric.net (alternate address: dfogren@msn.com) PGP Key ID: 0xC626E311 PGP Key Fingerprint: 24 23 CD 15 BF 8D D1 DE 81 71 84 C8 2C E0 4B 01 (public key available via server or by sending a message to ogren@concentric.net with a subject of GETPGPKEY)