[cryptography] current digital cash / anonymous payment projects?

Ian G iang at iang.org
Wed Dec 1 08:18:30 EST 2010

On 1/12/10 6:12 AM, travis+ml-rbcryptography at subspacefield.org wrote:
> Can anyone give me a good rundown of the current anonymous payment
> systems, technologies and/or algorithms?

OK, there are some issues here.  There is technology, algorithms, 
patents, techniques, protocols, applications, services, business models 
... all lumped into one general term without care.

Anonymous payment systems are a bit of a contradiction, internally. 
What you're probably talking about is untraceable payment systems, which 
typically use Chaum or Brands or Wagner algorithms (there are a handful 
of other variants).  In this model, the "coin" is stripped of its 
identifying information as it transfers from Ivan to Alice to Bob.  When 
Bob deposits the coin to Ivan (issuer) for credit to his account, or for 
rollover to new coins, the chain of traceability is broken.

Then, there is another variation called nymous payment systems.  This 
model is typically done with a client-server public-private key 
arrangement, where the client registers the public key, and signs 
requests (including payments) which are sent to the server.  The privacy 
trick with this one is that the issuer doesn't need to know who holds 
the private key;  so while everything is traceable, it's also nymous.

Now, both of the above have privacy foibles and weaknesses, and both can 
be combined.  Discussing that is ... too much text.

Another variant is the continual slice & combine model.  Somewhat 
echoing the last note below, it all depends what you want to use it for.

> It's just an idea at this point, but I'd be interested in hearing
> about any commercial offerings by companies offering such systems.

It's a tough market because typically there are regulatory, business and 
governance traps that will knock out most players sooner or later.

> Being a cryptonerd, I'd also be interested in hearing about the
> technology generally - I've read Applied Crypto 2e, but wondered about
> the state of the art.  Is there a good locus of such information?

Not really, but one thing is:  if you build it bottom-up, from the 
crypto, you'll have trouble :)  Instead, look to the business, and go 
bottom down.


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