From: "Michael Froomkin - U.Miami School of Law" <froomkin@law.miami.edu>
Date: Sun, 13 Oct 1996 13:26:14 -0700 (PDT)
To: Steve Schear <azur@netcom.com>
Subject: Blinded Identities [was Re: exporting signatures only/CAPI]
In-Reply-To: <v02130503ae865897f409@[10.0.2.15]>
Message-ID: <Pine.SUN.3.95.961013162235.21791C-100000@viper.law.miami.edu>
MIME-Version: 1.0
Content-Type: text/plain


[cc'd to coderpunks]

On Sun, 13 Oct 1996, Steve Schear wrote:

> >Steve Shear <azur@netcom.com> writes:

[much cut]
> 
> I've been charged with developing an Internet service which needs to assure
> its clients of anonymity.  However, we fear some clients may abuse the
> service and we wish to prevent the abusers from re-enrollment if
> terminated for misbehavior. (In your example, it would be the person(s)
> trying to discover the service host via flood).
> 
> My thought was to base enrollment on some sort of 'blinding' of their
> certified signature (e.g., from Verisign) which produces a unique result
> for each signature but prevents the service from reconstructing the
> signature itself (and thereby reveal the client's identity).  I'm calling
> this negative authentication.
> 
> Have you come across anyone who has considered this problem or
> another one which is mathematically very similar?

Stefan Brands has a protocol that probably does what you want.  And also
would form the basis for anonymous internet "postage stamps"...

It is unpublished, but he kindly allowed to me describe it in a paper I
wrote that discussed whether a bank would ever want to take the risk of
allowing bank accounts where it did not know the identity of the customer.

The protocol is described at 

http://www.law.miami.edu/~froomkin/articles/oceanno.htm#ENDNOTE286

[A frames version of the same paper is at 

http://www.law.miami.edu/~froomkin/articles/ocean.htm

but it's harder to jump straight to the footnote you want in that version]

**Benjamin Bradley Froomkin, b. Sept. 13, 1996, 8 lbs 14.5oz 21.5"**
                  **Age two weeks: 9 lbs 12 oz, 23"**
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