From: "Chris Adams" <adamsc@io-online.com>
Date: Fri, 7 Jun 1996 22:14:23 +0800
To: "cypherpunks" <cypherpunks@toad.com>
Subject: Fwd: Re: [crypto] crypto-protocols for trading card gam
Message-ID: <199606070508.WAA20921@toad.com>
MIME-Version: 1.0
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>From: "Chris Adams" <adamsc@io-online.com>
>To: "ogren@concentric.net" <ogren@concentric.net>
>Date: Thu, 30 May 96 02:30:30 
>Reply-To: "Chris Adams" <adamsc@io-online.com>
>Priority: Normal
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>Subject: Re: [crypto] crypto-protocols for trading card gam
>

>Disadvantages:
>
>The entire integrity of the system relies on the security of the
>game company's key pair.  If the secret key is comprimised, either by
>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:
I would just have multiple validators w/separate keys. sign w/each. This
would not 
eliminate the problem but could reduce it...

>1. Contact the game company and tell them she wants to give the card
>to Bob. 2. The game company must issue a new card to Bob with a new
>serial number and with Bob's public key rather than Alice's. 3. The
>game company must invalidate Alice's old card.  Since there is no way
>that the game company can make sure all copies of the card have been
>destroyed it must create a "invalid serial number list" and have the
>players dial into that list everytime the game is played.
>
>Since step 3 is so costly to implement, I think it is unlikely that a
>cryptography-based trading card game will have tradable cards.

Much easier - with each card, store its ownership history. EACH time it
is transfered, have 
it be signed by the previous owner.  Originally, the game company signs
it as a valid card. 
On selling it, they record the purchaser's identity (email address,
etc)and seal the card 
with the company key (or set of keys - see above). Repeat as needed.

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