Digital Cash

[smb at research.att.com]

	 Just a thought on ways to deter all of this multiple spending
	 gunk - when you start off, have a centralized bank server.
	 While traffic is low, you can have each individual certificate
	 cleared with the bank server upon creation and execution.

As someone else noted, ``crypto is all economics''.  In the New York
City subway system, the new fare card readers are all linked to a central
computer, specifically to prevent double spending.  They could have
used smart cards and fancy crypto -- but this is cheaper, especially
because they have an excellent handle on the maximum load -- the number
of subway riders at rush hour.  Fancy technology could get them into
an ``arms race'' with rip-off artists, who reverse-engineer cards,
crack algorithms, etc.

Digital cash -- which provide anonymity, as contrasted against
cryptographically-signed debit card transactions -- will become a
reality if and only if someone finds it more profitable than the
alternative, after deducting the costs for observer chips, licenses
for Chaum's patents, etc.  Some people are willing to pay for privacy --
but are there enough of them to make it pay?


		--Steve Bellovin