From: Michael Froomkin <froomkin@law.miami.edu>
Date: Sun, 3 Dec 1995 11:57:38 +0800
To: Ian Goldberg <iang@cory.EECS.Berkeley.EDU>
Subject: Re: Questions/Comments on ecash protocol
In-Reply-To: <199512030127.RAA03496@cory.EECS.Berkeley.EDU>
Message-ID: <Pine.SUN.3.91.951202223133.3336H-100000@viper.law.miami.edu>
MIME-Version: 1.0
Content-Type: text/plain


thank you for the sterling analysis.  I for one am following this with 
enormous interest, even though some of the details are lost on me right now.

I can't recall if you were party to the earlier thread on "digital coin 
launderies", and I know some of it was off line.  I hope you will keep 
some of the following in mind as you go.

One of the major questions about digicash/MTB$ is whether and how money
might be laundered.  The question subsumes the following (among others): 

1) What information about Charlie/customer is encoded onto the coin? 
(There must be some, right, since the serial number is blinded?)  Since the
bank doesn't know what serial number it is signing, it needs to put info 
about Charlie onto the coin so that it can track him down if he double 
spends.  Lacking such info, the bank can refuse to honor a double-spent 
coin, but has no way to know who the double-spender is.

2) How does Charlie (customer) software store the coin internally?

3) Is there a way [how hard is it] for charlie to extract a coin and 
either 
   (i) copy it and/or 

   (ii) send it to David [3rd party] in such a way 
that David could insert it into David's MTB software and then spend it to 
Sam without Sam or the Bank noticing that anything was wrong.  If Charlie 
and David do this, David now has a coin that is from his point of view 
both payee and payor anonymous, although Charlie has a risk that David 
will double-spend and expose Charlie to the bank's wrath.

4) what information if any is encoded onto a coin when Charlie spends it 
to Sam?


A. Michael Froomkin        | +1 (305) 284-4285; +1 (305) 284-6506 (fax)
Associate Professor of Law | 
U. Miami School of Law     | froomkin@law.miami.edu
P.O. Box 248087            | http://www.law.miami.edu/~froomkin
Coral Gables, FL 33124 USA | It's warm here.