From: peter honeyman <honey@citi.umich.edu>
Date: Wed, 6 Oct 93 21:25:34 PDT
To: cypherpunks@toad.com
Subject: Re: Start up costs and paying for speech...
Message-ID: <9310070421.AA06096@toad.com>
MIME-Version: 1.0
Content-Type: text/plain


> I wouldn't worry about either.  I don't see how enforcement of  
> copyright will be possible under crypto-anarchy any more than  
> taxation will be.  If one person pays for a posting, what's to keep  
> him from sharing it anonymously with whomever he wants?  Is there any  
> way that crypto-anarcy won't bring the death of "intellectual  
> property"?

well, i wouldn't equate reading with spending (if i may simplify).

i think the thing that mystifies me about off-line digicash is the
cryptographic protocol that constitutes spending.  other people are
asking about it, too.  it seems to be on everyone's mind.

so here, for the very first time on cpunx ;-) well maybe not
but who's counting is the protocol from chaum's crypto '88
paper "untraceable electronic cash":

   to pay bob one dollar, alice and bob proceed as follows:
   
   1.  alice sends C to bob
   2.  bob chooses a random binary string z sub 1, z sub 2, ... ,
       z sub {k over 2}
   3.  alice responds as follows forall 1 <= i <= {k over 2}
       a.  if s sub i = 1, then alice sends bob a sub i, c sub i,
           and y sub i.
       b.  if z sub i = 0, then alice sends bob x sub i, d sub i,
	   and a sub i xor ( u || (v + i)).
   4.  bob verifies that C is of the proper form and that alice's
       responses fit C.
   5.  bob later sends C and alice's responses to the bank, which
       verifies their correctness and credits his account.

not very illuminating so far ... let's go on.

   the bank must store C, the binary string z sub 1, z sub 2, ... ,
   z sub k and the values a sub i (for z sub i = 1)
   and a sub i xor (u || v) (for z sub i = 0).

gee, what is that "||" operator, anyway?  ah, concatenation.  ok.
going on ...

   if alice uses the same coin C twice, then she has a high
   probablility of being traced: with high probability, two
   different shopkeeprs will send complementary binary values
   for at least one bit z sub i for which B sub i was of the
   proper form.  the bank can easily search its records to
   ensure that C has not been used before.  If alice uses C
   twice, then, with high probability, the bank has both
   a sub i and a sub i xor (u || (v +i)) with high probability. 
   thus the bank can isolate u and trace the payment to alice's
   account.

hmmm.   hmmm.  well, this is very complicated.  with high probability,
i mean.  i'm going to have to study this paper.

	peter

ps:  what are the B sub i you ask?  don't ask.  oh golly, they are
blinded candidates, formed by alice and sent to the bank.  hmmm.
hmmmmmm sup k mod 1/p.