Re: Is Chaum's System Traceable or Untraceable?

[Matthew Carpenter <mcarpent@mailhost.tcs.tulane.edu>]

bryce@digicash.com writes:
> 
> You know, even though current ecash uses on-line clearing, it is
> only necessary for the _payee_ to be on-line at that time.  Thus
> it is entirely possible with current ecash for a payer to load 
> his portable computer up at home with e-coins and then make a 
> purchase a convenience store on the way to work _without_ having
> a networkable computer.  Well-- I mean the computer needs to 
> communicate with the convenience store, but it doesn't need 
> full-scale Internet access.
> 
> 
> Does anyone on cpunks or ecash have an Apple Newton?  I know
> that they come with infrared-- what are the specs on that
> communications device?  And about the Newton itself:  can it
> compile ANSI C code?  How much RAM?  Permanent storage?  Speed
> of crypto operations?

Don't know about the Newton, but one of the first things I thought of
when I picked up a Pilot a week ago was that it would make an excellent
ecash "wallet".

(For those who don't know, the Pilot is the pocket sized PDA from
Palm/USRobotics: 11.9 x 8.1 x 1.8 cm (4.7 x 3.2 x.7 inches), 165 g (5.7
ounces) with batteries.  See http://www.usr.com/palm or
http://www.webcom.com/cyniche/ppage1.htm for more info).

The Pilot isn't as powerful as the Newton, but it is designed to allow
for painless synchronization/communication with the user's desktop
computer, and it is a lot more convenient to pack around than the Newton
and most other small computing devices.  Below I've outlined a procedure
which seems like it would work very well for the Pilot or other PDA's,
palmtops, etc.

Before I head out to go shopping I stop by the ATM to get some money.
But in this case the 'ATM' is just an application on my home computer
which asks me how much money I want to transfer to my PDA.  The program
generates appropriate ecash coins, like the penny Bryce posted to
cypherpunks a few days back, and automatically downloads a copy of them
to the PDA.  These probably need to be encrypted, so that if my "wallet"
is stolen my money isn't lost.  This is just like using an ATM, just
"Please insert your PDA, and enter your PIN," but done without having to
find an ATM and wait in line.

So now I head out shopping and find something I absolutely must buy.  My
PDA asks me for the amount of the purchase (or is told by the merchant's
system and then asks for confirmation), and the 'PIN' I used to encrypt
the coins.  It then selects the appropriate coin(s) for payment,
decrypts them, and sends them to the merchant's computer using IR, a
smart card emulater, or whatever (the Pilot doesn't have IR built in,
but it does have a RS-232 port so IR could be added).  My PDA receives
back any coins as change if needed, and logs info about the transaction
for my financial records.

When I get back home I 'deposit' my change using the same ATM interface.
This also removes from my home computer the copies of the coins I spent,
and automatically updates the transaction records on my PC.

So are there any flaws with above procedure?  It seems to place minimal
strain on the PDA.  All you need on the PDA is some straight forward
encryption and communications routines, along with a fairly simple user
interface.  Of course, since the SDK for the Pilot isn't out yet, it is
hard to tell how well this would work in reality; and I may be
misunderstanding the ecash protocols.  But I would really, really love
to see something like this available.

> 
> 
> Thanks,
> 
> Bryce
> 
> #include <stddisclaimer.h> /* I don't speak for anyone but myself. */
> - -----BEGIN GOODTIMES VIRUS INNOCULATION-----
> Copy me into your .sig for added protection!
> - ----- END  GOODTIMES VIRUS INNOCULATION-----


--Matt

--
mcarpent@mailhost.tcs.tulane.edu    PGP mail preferred, finger for public key.