CDR: Re: ecash, cut & choose and private credentials (Re: Jim Bell)

[Ben Laurie]

Apologies for indirect routing :-)

> Date: Tue, 28 Nov 2000 22:41:07 -0500
> From: Adam Back <adam at cypherspace.org>
> To: cypherpunks at cyberpass.net
>
> Unfortunately both Brands' and Chaum's ecash and credential schemes
> are patented.  David Wagner et al also had some ideas about an ecash
> coin [3] composed roughly of a public key based MAC (ie the user can't
> verify the validity of the coin directly -- only the bank can do
> that), plus a zero-knowledge proof that the bank hasn't marked the
> coin.  This may be unpatened in that it's not directly a certificate,
> it's a MAC, plus a zero-knowledge proof so it seems like a fairly
> different process.  I don't think you can do efficient offline ecash
> with Wagner et al's mechanism -- I'd guess it's more comparable with
> the functionality offered by Chaum's blind signature.

I'm not sure what you think the requirements for "efficient offline
ecash" are, but I should note that the double-blinded version of lucre
doesn't require the ZKP, and there's also a non-interactive variant of
the ZKP for the single-blinded variant. They are both described in the
current version of the paper (at least, I'm sure the first as, and
somewhat sure the second is).

Cheers,

Ben.

> [3] Ben Laurie has a paper describing Wagner et al's MAC + ZKP ecash /
> credential protocol as theory2.pdf.
> 
> http://anoncvs.aldigital.co.uk/lucre/
> 
> Adam
> 
> Disclaimer: As always my comments are my own.
> 
> --- end forwarded text
> 
> --
> -----------------
> R. A. Hettinga <mailto: rah at ibuc.com>
> The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
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