From: Hal <hfinney@shell.portal.com>
Date: Thu, 9 Nov 1995 09:35:07 +0800
To: cypherpunks@toad.com
Subject: ecash speed
Message-ID: <199511082345.PAA02628@jobe.shell.portal.com>
MIME-Version: 1.0
Content-Type: text/plain


A few days ago I got my ecash account set up with the Mark Twain bank.
Presently only one merchant is officially listed at <URL:
http://www.marktwain.com/shops.html>, Delorie Software.  As I understand
it, only people with merchant accounts are eligible to be listed here.
However, you don't have to have a merchant account to receive ecash or to
set up shop software.  If anyone else has set up a shop to receive Mark
Twain ecash using a user account, perhaps they could post here and we
could keep a list of unofficial vendors.

The other thing I wanted to write about is ecash speed.  One idea people
have had is to use ecash for micropayments, such as one cent to read a
web page.  The question is, is the current ecash software sufficiently
fast for this?  Maybe someone could set up a site using either Twain ecash
or DigiCash ecash which actually charged you a penny for each page you
browsed around.  It would be interesting to see how much of an obstacle
it presents in browsing the web.  The impression I've had from the few
times I've used ecash is that in fact it does slow things down way too
much for this to be practical.  But it would be good to actually do the
experiment.

One reason I was thinking about this is reading a new paper by Rivest and
Shamir, <URL:http://theory.lcs.mit.edu/~rivest/RivestShamir-mpay.ps>.  It
is about a couple of proposed systems for micropayments, specifically
oriented towards the penny-per-web-page model.  They are offline systems,
designed so that a minimum of calculation is done by the vendor, user and
bank.  So they should be very efficient.

However, the big problem is that they are not anonymous.  The cash
tokens are recognizable by the bank when spent tokens are sent in by
the vendors - the bank knows who spent them.  Maybe for penny level
transactions that is not a big deal, although if for-pay web browsing
becomes common then it does seem like it would present a privacy
threat.  Every web site you visit (not the specific pages, but the
overall site names) would be known by the bank - quite a significant
piece of marketing data.

The point is that if the anonymity afforded by ecash is too costly in
terms of time, then we may end up stuck with a non-anonymous system
simply because that is the only one efficient enough to work.  It would
be good to find out if that is a serious problem.

Hal Finney