digital cash and identity disclosure

[Tom Weinstein]

In article <DGqtsp.1L at sgi.sgi.com>, Holger.Reif at PrakInf.TU-Ilmenau.DE (Holger Reif ) writes:

> Scott Brickner writes:
>> Andreas Bogk writes:
>>> But as far as I got Chaums idea, Alice would not reveal Bobs identity,
>>> but rather her own. Am I missing a point here?
>> 
>> You're right.  Tim's wrong.  Bob can't spend the money Alice gave him
>> without depositing it in the bank and getting new money issued.  Each
>> coin has "This money was issued to Alice" as an invisible imprint which
>> only shows up when two coins with the same serial number are together.

> I don't understand how this could happen? The two coins are identical
> (as I understood it from the tech backgound of ecash). what has a double-
> spended coin what a copied single-spended coin not has?

> Forgive if I missed relevant postings to this subject since I only read
> parts from the list offline.

The process of spending a coin is not simply that of transfering data.
There is a complicated protocol in which Alice decrypts some of the
identity information in the coin.  Let's say that Alice spends the coin
twice, once with Bob and again with Chuck.  Bob and Chuck can pool the
information they got from Alice and reconstruct her identity.  Alice
can't just give them both the same information because the receiver is
the one who determines what information is decrypted.  For a more
detailed explanation, check out Schneier's book.

-- 
Sure we spend a lot of money, but that doesn't mean | Tom Weinstein
we *do* anything.  --  Washington DC motto          | tomw at engr.sgi.com