From: Hal <hfinney@shell.portal.com>
Date: Fri, 10 Nov 1995 10:17:22 +0800
To: cypherpunks@toad.com
Subject: Re: ecash speed
In-Reply-To: <199511090130.UAA13562@jekyll.piermont.com>
Message-ID: <199511090508.VAA05884@jobe.shell.portal.com>
MIME-Version: 1.0
Content-Type: text/plain


"Perry E. Metzger" <perry@piermont.com> writes:

>Hal writes:
>> 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.

>I suspect that as CPU speed exponentiates this will become less and
>less of a problem. It doesn't especially worry me.

Consider, though, what happens in the current ecash system if it were
used to charge a penny per page.  You would click on a link in your web
browser to go to the new page.  It would set the GET request to the
remote server as usual.

The server would fire up a CGI script which will run the shop software.
That software will make a TCP stream connection back to your ecash wallet
software which is running on the system where your client is.  It sends a
request to get payed $.01.  Assuming the wallet is configured to
automatically approve such a payment, it will send a one penny coin to
the shop software along the opened link.  (This may also involve doing a
PK encryption on the coin as an anti-theft measure; this aspect of the
current ecash system is not documented AFAIK.)

The shop software then opens a TCP stream connection to the bank, and
forwards the coin there.  The bank receives it, and checks the public
key signature in the coin.  It then compares the coin against every other
coin which has ever been spent (within the validity period of the coin)
to make sure it is not being doubly spent.  If this all checks out it
sends back some authentication message to the original server.  The shop
software then delivers the new page to the client browser.

This all has to happen whenever you click on a link in your browser.
Even with fast CPU's I think the extra step of connecting to the bank,
having it check against all coins, and getting approval will be
considerable for each link traversal.

Hal