Re: Members of Parliament Problem

["Mark M." <markm@voicenet.com>]

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On Thu, 14 Nov 1996, Peter Hendrickson wrote:

> I read awhile ago that certain members of Parliament do not speak
> their mind regarding the situation in Northern Ireland.  The reason
> they give is that they have children and they fear the IRA.
> 
> There are times when one wishes to speak anonymously, yet speak
> as a member of a group.
> 
> 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?

One way would be to have some trusted third party issue a signature for any
key that belongs to a member of the group.  The problem with this method is
that the certificate issuer knows which keys belong to which members.  This
can be solved by blind-signing the keys.  A single secret key could be
distributed to every member, but this is vulnerable to security problems.
Also, it would be impossible to determine if a group of messages were each
issued by different people or if it was the same person.

I don't know if there is any better cryptographic protocol to handle a
situation like this.  Oblivious signatures might be a possibility, but I don't
know how they work and if they could be used in such a protocol.

Mark
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