chaum's patent expiry? (Re: Brands' private credentials)

Adam Back adam at
Sun May 9 05:15:59 EDT 2004

Oh yes, my other comment I forgot to mention was that if non-patent
status were a consideration, aside from Wagner's approach, another
approach for which the patent will presently expire is Chaum's
original approach combined with Niels Ferguson's single term offline
coins.  (Don't have citation handy but google will find you both).

Anyone have to hand the expiry date on Chaum's patent?  (Think it is
in patent section of AC for example; perhaps HAC also).

Having an expired patent might be a clearer route to non-patented
status than the putative this is a blind MAC not a blind signature
approach of Wagner's protocol.  But I obviously am not a patent
lawyer, and have avoided reading and participating in the writing of


On Sun, May 09, 2004 at 05:08:09AM -0400, Adam Back wrote:
> [...]
> I looked at Camenisch protocol briefly a couple of years ago and it is
> not based Brands.  It is less efficient computationally, and more
> rounds of communication are required if I recall.

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