A quick experiment has confirmed the obvious: when a client
reissues a coin at the mint, both the blinded and its unblinded cousin
are valid instruments to the Lucrative mint.
Example: Alice uses the Mint's API to reissue a one-dollar note,
blinding the coin before getting a signature, and unblinding the
signature afterwards. She's left with both a blinded and a non-blinded
version of the coin. The mint believes they are both valid. Instant,
unlimited inflation.
I believe the solution to this is to have the mint track both
spent coins and issued coins (that is, it automatically cancels coins it
issues, before the client receives them). The client is left with no
choice but to go through a blinding and unblinding process in order to
have a usable coin.
This seems to make identity-agnostic cash difficult or
impossible, at least with Lucrative:
http://www.io.com/~cman/agnostic.html,
http://cypherpunks.venona.com/date/1995/09/msg00197.html .
Patrick
The Lucrative Project: http://lucrative.thirdhost.com
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R. A. Hettinga