Re: Blinded Identities [was Re: exporting signatures only/CAPI]

[azur@netcom.com (Steve Schear)]

>>> >Steve Shear <azur@netcom.com> writes:
>>> 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.
>
>At 04:28 PM 10/13/96 -0400, "Michael Froomkin - U.Miami School of Law"
><froomkin@law.miami.edu> wrote:
>>Stefan Brands has a protocol that probably does what you want.
>....
>>http://www.law.miami.edu/~froomkin/articles/oceanno.htm#ENDNOTE286
>
>Looks like a really nice paper on anonymity issues; at 485K, it'll take
>a little while to read :-)

Yes, it was quite a load, but very good material.

>
>The fundamental difficulty in this problem is that you need some
>demonstrable proof of uniqueness for human users; if you don't have that,
>you can't transform it into a unique-but-anonymous identity.*
>The issues are similar to privacy-protecting voter registration problems.
>
>Brands's protocol starts with the user going to the bank with proof of ID,
>and getting a numerical ID which can be blinded and signed.
>It's a nice approach; you can do cruder approaches by hashing your
>universal-citizen-unit-ID-number or whatever, but that can be
>dictionary-searched
>by feeding all the possible ID numbers through the hash.
>
>For some applications, mapping back to a unique human isn't necessary;
>if you do something like map back to a bank account which has a high
>minimum balance for setup, this discourages the type of users who
>don't want to spend $100 just to send spam.
>
>Blinding a Verisign signature isn't enough, though - they support
>personna certificates without proof of identity.

Is it possible to determine the level of Verisign signature to screen out
personna certificates?

>
>[ * There are non-universal-identifier methods for preventing double-use.
>Voter registration in many places just depends on identification and
>affidavit, and is often abused (e.g. Chicago graveyard voters and
>Nevada absentee ballots), but usually not massively abused.
>Some third-world countries don't even require registration or literacy -
>they dip your thumb in ink after you vote, using a kind of ink that
>won't come off for a couple of days.  Attacks against this protocol
>include better solvents :-) ]

Of course, if elections were very infrequent, they could cut off a finger
each time you vote :-)

You all have given me much to think about.

Thanks.