[41625] in Cypherpunks
Re: mental cryptography
daemon@ATHENA.MIT.EDU (Nathan Loofbourrow)
Tue Oct 17 10:01:36 1995
From: Nathan Loofbourrow <loofbour@cis.ohio-state.edu>
Date: Tue, 17 Oct 1995 09:54:15 -0400
To: cypherpunks@toad.com
In-Reply-To: <199510162227.SAA19138@universe.digex.net>
Scott Brickner writes:
> Nathan Loofbourrow writes:
> >It may be that the approach is off anyway. Credit cards have only
> >signature verification -- if the salesperson bothers -- because stolen
> >cards are reported. You don't need a strong authentication technique
> >if a stolen card is easy to cancel.
>
> The card's easy to cancel, but the cash ain't. Credit cards are
> cleared with the issuer. Digital cash with smart cards acting as
> transaction observers don't need this. The thief need only transfer
> the cash from the stolen card to his own, just like he does with
> regular cash.
Er, um, right.
Well, then, perhaps on-line systems need to consider cash
revocation in case of theft. Actually, this is a no-brainer: just
exchange the cash for some new coin, and the old stuff goes
invalid. Admittedly, this means a footrace for the mugger and the
victim, so I guess the mugger is encouraged to knock you out cold.
Maybe you just shouldn't carry too much cash with you. Gee, that
sounds like good advice even without digital protocols.
> >Even with a weak PIN system for authentication, you can always provide
> >a "duress" PIN, right?
>
> Sounds like a better choice.
Duress PINs liberally sprinkled through the keyspace also drop the
efficacy of brute-force PIN search for the thief.
nathan
