Members of Parliament Problem

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?

Peter Hendrickson
ph@netcom.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
- --   
finger -l for PGP key
PGP encrypted mail prefered.

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Most of the usual arguments about disallowing anonymity
actually apply to a Parliment.  There is a responsibility involved in
the execution of power.  

	This is not to condone attacking children, or killing ones
political opponents.  For an MP to imply that something he wants to
say will likely get him/his kids killed probably means that he wants
to use the power of the state in some way likely to quite upset at
least a few people.  If this is the case, then allowing him to
anonymously, and without responsibility, direct the power of the state
is congruent to tyranny.

	To answer the technical end of your question, you could build
a DC net where joining required a signed key, or build a mix which
will only accept messages signed by a member of the group.  If the
mixmasters all agree to only accept messages signed by the group, then
each mixmaster can be made a member of the group, and sign its
outbound messages as being recieved with a signature, allowing
anonymous chaining.

Adam

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?

-- 
"It is seldom that liberty of any kind is lost all at once."
					               -Hume

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 to implement this would be to set up a remailer that only 
accepts input signed by a key on its ring.

Or just share a secret key. It would have to be timestamped, i.e., 
"104th Congress Key."

You either need to trust a shared server to know and then blind your 
identity, or trust the people with whom you share a secret key not to 
give that key to non-group members.

-rich

On Fri, 15 Nov 1996, Rich Graves wrote:

> Peter Hendrickson wrote:
> > 
> > 
> > There are times when one wishes to speak anonymously, yet speak
> > as a member of a group.
> 
> You either need to trust a shared server to know and then blind your 
> identity, or trust the people with whom you share a secret key not to 
> give that key to non-group members.

Why not use  blinding for obtaining the certificate? 

Create a number up public/private key pairs, blind them, then do the
cut-and-choose thing with the security officer. He signs the blinded key,
then returns it. Unblind the remaining pubic key, and you've got a public
key with the appropriate signature on it. 

Simon

 ---
If I can get my key back,   it's Key Recovery
If you can get my key back, it's Key Escrow

Simon Spero <ses@tipper.oit.unc.edu> writes:
> On Fri, 15 Nov 1996, Rich Graves wrote:
> 
> > Peter Hendrickson wrote:
> > > 
> > > 
> > > There are times when one wishes to speak anonymously, yet speak
> > > as a member of a group.
> > 
> > You either need to trust a shared server to know and then blind your 
> > identity, or trust the people with whom you share a secret key not to 
> > give that key to non-group members.
> 
> Why not use  blinding for obtaining the certificate? 
> 
> Create a number up public/private key pairs, blind them, then do the
> cut-and-choose thing with the security officer. He signs the blinded key,
> then returns it. Unblind the remaining pubic key, and you've got a public
> key with the appropriate signature on it. 

Reasonable, except that it's linkable.  You may not want it to be
linkable, because the more messages signed with the key, the greater
the chance that speech paterns give away the speaker.

Adam
--
print pack"C*",split/\D+/,`echo "16iII*o\U@{$/=$z;[(pop,pop,unpack"H*",<>
)]}\EsMsKsN0[lN*1lK[d2%Sa2/d0<X+d*lMLa^*lN%0]dsXx++lMlN/dsM0<J]dsJxp"|dc`

On Sun, 17 Nov 1996, Adam Back wrote:

> Simon Spero <ses@tipper.oit.unc.edu> writes:
> 
> Reasonable, except that it's linkable.  You may not want it to be
> linkable, because the more messages signed with the key, the greater
> the chance that speech paterns give away the speaker.

How about using ephemerialish keys (keys issued in big batches, etc)? 
All you need is a quick way to generate a few hundred or thousand RSA keys...

Simon