From: Matt Blaze <mab@crypto.com>
Date: Sun, 7 Jan 1996 00:34:31 +0800
To: tcmay@got.net (Timothy C. May)
Subject: Re: Revoking Old Lost Keys
In-Reply-To: <ad1366a50002100426f2@[205.199.118.202]>
Message-ID: <199601061626.LAA06345@crypto.com>
MIME-Version: 1.0
Content-Type: text/plain


Timothy May wrote:
> At 7:07 AM 1/6/96, Bruce Baugh wrote:
> 
> >I'd like to bring up a problem I haven't seen addressed much yet, and which
> >I think is going to come up with increasing frequency as PGP use spreads.
> >
> >The problem is this: how can one spread the word that an old key is no
> >longer to be used when one no longer has the pass phrase, and cannot
> >therefore create a revocation certificate?
> 
> Basically, you are screwed. Any revocation you attempt will not be trusted,
> as we will suspect the new "you" to be an attacker, perhaps an agent of the
> NSA or the Illuminati. In the view that "you are your key," the old you no
> longer exists.
> 
...
> 
> Seriously, this is an example where "escrow" works. Seal an envelope with
> your passphrase and any other stuff you want to remember, and leave it with
> your lawyer or escrow agency with instructions to only turn it over to you.
> Same as a safe deposit box, unless you forget the key. (You could forget
> you have a lawyer, so better write that down somewhere, too.)

Escrow is orthogonal to the underlying problem here, which is that the
PGP revocation model is completely wrong.  Since the trust properties
and other semantics of a key originate with the certificates attached to
the key, and not from the key owner per se, it makes little sense to make
the key owner responsible for revoking that trust.  Far more sensible would
be a scheme in which the certificate issuers themselves could revoke their
certificates when they believe a key is no longer trustworthy.  (A practical
decentralized system like PGP could provide a facility for certifiers to
"pre-revoke" their certificates at the time they are issued so that the key
owner could distribute the revocation certificates himself if he discovers
his own key to have been compromised or lost.)

Note that the problem here is in the basic trust model, not just the
certificate distribution model (which is a separate problem).  The lack of
ability for a certifier to revoke his own certification, plus the lack of a
facility to put limits on the duration and meaning of the certification,
make PGP certificates of very limited practical value.

-matt