From: paul@fatmans.demon.co.uk
Date: Sat, 16 Nov 1996 02:58:59 -0800 (PST)
To: Peter Hendrickson <ph@netcom.com>
Subject: Re: Members of Parliament Problem
Message-ID: <848137382.624190.0@fatmans.demon.co.uk>
MIME-Version: 1.0
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> Is there a way to take published public keys and combine them with
> your own in such a way that your identity is not compromised, but
> it is clear beyond a doubt that you control one of a set of public
> keys?

An obvious solution would be a shared public key/private key pair 
between a number of users then use them for digital signatures and 
route the messages through an anonymous server.


You could also have an arbitrated blind signature protocol whereby 
trent shares a keypair with all users. bob encrypts his comment, M 
with the key he shares with trent. On recieving it trent carries out 
a blind signature on it and publishes it, as trent knows only bob has 
the shared key, K he knows bob said M but as it is a blind sigature 
and he is likely to be signing a lot of messages (trent is of course 
a computer program) he doesn`t know which message came from bob.

Also Chaums group signatures could be used but unfortunately the 
arbitrator can find out who said what, but does not normally know.
Also trent can forge digital signatures with this protocol.
Chaum further mentions protocols for this sort of thing that do not 
even need an arbitrator but I don`t have the papers on this.


  

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  Datacomms Technologies web authoring and data security
       Paul Bradley, Paul@fatmans.demon.co.uk
  Paul@crypto.uk.eu.org, Paul@cryptography.uk.eu.org    
       Http://www.cryptography.home.ml.org/
      Email for PGP public key, ID: 5BBFAEB1
     "Don`t forget to mount a scratch monkey"