From: Jiri Baum <jirib@sweeney.cs.monash.edu.au>
Date: Wed, 3 Jan 1996 20:12:32 +0800
To: perry@piermont.com
Subject: Re: Proxy/Representation?
In-Reply-To: <199512290024.TAA10333@jekyll.piermont.com>
Message-ID: <199601030633.RAA16556@sweeney.cs.monash.edu.au>
MIME-Version: 1.0
Content-Type: text/plain


-----BEGIN PGP SIGNED MESSAGE-----

Hello "David E. Smith" <dsmith@midwest.net>
  and cypherpunks@toad.com
  and "Perry E. Metzger" <perry@piermont.com>

PEM wrote:
> "David E. Smith" writes:
...[about power of attorney and PGP, reply-to-reply]...
> > >standard for "Power of Attorney" documents, and for the entity
> > >receiving something signed in your key that should be signed in
> > >another person's key to also see the digitally signed power of
...
> > That's more of what I was looking for.  I suppose that (I'm still using
> > PGP as my example) there could be a shared PGP key, signed by Helen and
> > myself, where only the two of us know the passphrase,

I don't think that's what was intended. If I understood:

There'd be a document (hereinafter PoA) signed by Helen which would
say "This is a PoA appointing Dave, PGP key X fingerprint Y, to
do A, B, C on my behalf #include<lawyerspeak.h>".

Then, when signing, Dave would sign with his own key X, making sure
that every document has "p.p. Helen" at the end. The recipient checks
Dave's signature on the document and Helen's signature on the PoA.

> Huh? Why? Why would you need [a separate key]? ...

Many automatic systems will assume that a key can only sign for 
one person (though each person may have several keys). Therefore,
it'll confuse "Dave" and "pp. Helen". The RISKS are obvious.

To avoid such confusion, Dave should create a separate key with 
the key ID "Dave pp. Helen" (or similar). However, Helen doesn't need
to (shouldn't) know that key! This is Dave's key, created by Dave
for Dave's use while he is agent for Helen. Helen would probably
sign this key, but doesn't need to since the PoA has the f'print.

In fact, you don't want Helen to know it, so that if Dave oversteps
his authority she can prove that it was him not her. Ie if Helen finds
out the key, Dave should revoke it.


Hope that makes sense...

Jiri
- --
If you want an answer, please mail to <jirib@cs.monash.edu.au>.
On sweeney, I may delete without reading!
PGP 463A14D5 (but it's at home so it'll take a day or two)
PGP EF0607F9 (but it's at uni so don't rely on it too much)

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