[fc-discuss] Financial Cryptography Update: On Digital Cash-like Payment Systems

Ian G iang at systemics.com
Sat Oct 22 08:43:50 EDT 2005

R. Hirschfeld wrote:
>>Date: Thu, 20 Oct 2005 11:31:39 -0700
>>From: cyphrpunk <cyphrpunk at gmail.com>
>>> 2. Cash payments are final. After the fact, the paying party has no
>>> means to reverse the payment. We call this property of cash
>>> transactions _irreversibility_.
>>Certainly Chaum ecash has this property. Because deposits are
>>unlinkable to withdrawals, there is no way even in principle to
>>reverse a transaction.
> This is not strictly correct.  The payer can reveal the blinding
> factor, making the payment traceable.  I believe Chaum deliberately
> chose for one-way untraceability (untraceable by the payee but not by
> the payer) in order to address concerns such as blackmailing,
> extortion, etc.  The protocol can be modified to make it fully
> untraceable, but that's not how it is designed.

Huh - first I've heard of that, would be
encouraging if that worked.  How does it
handle an intermediary fall guy?   Say
Bad Guy Bob extorts Alice, and organises
the payoff to Freddy Fall Guy.  This would
mean that Alice can strip her blinding
factors and reveal that she paid to Freddy,
but as Freddy is not to be found, he can't
be encouraged to reveal his blinding factors
so as to reveal that Bob bolted with the


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