From: iang@cs.berkeley.edu (Ian Goldberg)
Date: Wed, 31 Jul 1996 16:57:32 +0800
To: cypherpunks@toad.com
Subject: Re: E-Cash promotion idea
In-Reply-To: <1.5.4.32.19960729084347.00331d14@giasdl01.vsnl.net.in>
Message-ID: <4tmv28$1hn@abraham.cs.berkeley.edu>
MIME-Version: 1.0
Content-Type: text/plain


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In article <1.5.4.32.19960729084347.00331d14@giasdl01.vsnl.net.in>,
Arun Mehta  <amehta@giasdl01.vsnl.net.in> wrote:
>At 05:15 24/07/96 -0500, Matt Carpenter wrote:
>
>>getting change from the merchant.  Ian Goldberg pointed out that
>>with the current ecash protocol, accepting change not only eliminates your
>>anonymity, but that you also have to go online to make sure you aren't being
>>cheated.
But don't forget that you can use a slightly modified protocol to accept
change anonymously, without having to go online!
>
>I'm sure it should be possible for the merchant to electronically
>give you an "IOU" for the amount of change s/he owes you, no
>matter how small, without loss of your anonymity. Next time you
>go to the same merchant, the IOU could automatically be adjusted
>against the new purchase.

An IOU is equivalent to a coupon.  You could even implement it as ecash
issued by the merchant, but why?  Using the "change" protocol, you can
do it with real ecash just as easily.  It's just as hard to get an
HP48 to check the signature on change coins returned by the merchant as it
is to check the signature on the IOU.

An HP48 is unlikely to be able to do 768-bit RSA operations.  However,
it could easily have coins stored on it, transmitted to the store via
a convenient IR port, or an RS232 connection.  It's quite straightforward;
if I had a store, I'd do it myself...

   - Ian

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