From: Hal <hfinney@shell.portal.com>
Date: Thu, 5 Oct 95 21:41:13 PDT
To: cypherpunks@toad.com
Subject: Re: Certificate proposal
Message-ID: <199510060440.VAA23299@jobe.shell.portal.com>
MIME-Version: 1.0
Content-Type: text/plain


Bob Smart <smart@mel.dit.csiro.au> writes:
>Consider the IPSEC case. The current situation is:

>1. We go through some process, let's call it Process A, where we determine
>   that we want to talk to IP address 192.9.8.7.

This would be, say, a DNS lookup on www.egghead.com.

>2. We go through another process where we obtain the public key of 192.9.8.7.

I get it by connecting to that IP address and asking for it, or perhaps
I have it cached or I get it from some public cache.

>3. We then try to decide, based on one or more certificates, whether we
>   trust the public key to be the correct public key for 192.9.8.7.

I see the certificate is signed by someone I trust and it certifies that
this key is good for connections to Egghead Software at www.egghead.com.

>Now consider the key-centric version.

>1. Process A returns a public key which denotes the destination we want to
>   talk to.

OK, maybe this is some DNS variant that given www.egghead.com, returns a
public key 0x12345678.

>2. We then go through a process to obtain the IP address that belongs to
>   that public key. We probably won't use the public key as an index to
>   get that information. We probably use the information that was input
>   to Process A. In fact this information may fall out as a byproduct
>   of Process A. [However if we needed to make a scalable distributed
>   database of RSA public keys then I have a design to do this -
>   available on application.]

OK, so now I do another DNS lookup on www.egghead.com to get the IP
address.  Or maybe I even use key 0x12345678 as an alternative index to
get that address.

>3. We don't need to trust any certificates or anything else at this stage.
>   The fact that the IP address belongs to the Public Key is signed by
>   the Public Key itself.

Now you've lost me.  Are you saying that the key is self-certifying,
saying "I belong to 192.9.8.7"?  That is, it is accompanied by a
signature issued by that key itself on this IP address?  I hate to be
difficult, but this does not provide me with a warm feeling.  Anyone
could have issued that key, claiming to belong to that IP address.  If
the person who did so is able to interpose himself between me and that
address then my messages are not secure.

>The same thing happens with e-mail. If "Process A" gives us an e-mail
>address to send to then we worry about whether we have the right public
>key to go with it. If Process A gives us a Public Key then we can
>have certainty about the associated e-mail address because the association
>is signed by the Public Key.

Again, I don't follow how we gain this certainty.

>And a big win that just falls out of this is that I can have a
>continuous exchange of information with one IP destination even if
>it keeps changing its actual IP address (mobile computing) or I
>can have an e-mail conversation with a person who keeps changing
>their e-mail address. The things you want just fall out instead of
>requiring clever software solutions.

This can be dealt with in the certificate context by having a
certificated key sign a statement that the IP address is now
such-and-such.

>In the key-centric world a certificate binds some attribute as a property
>of a publc key. So an X.509 certificate would say "The owner of this
>public key [i.e. person who knows the corresponding private key] owns
>the following point in the X.500 namespace", rather than that "the
>person identified by this DN owns the following publc key". Experience
>has shown that the latter interpretation is a mine-field. It really
>doesn't work.

I don't really care whether the name is called an attribute, a
distinguished name, or an ooblek.  I just don't see how you're going to
get along without it.  The fact is, we live in a world populated by
people and companies and we use names to identify them.  I will grant
that there are problems with uniqueness but I don't think the solution
can be to just give up on the whole idea of names since they are so
messy.  Pretending that keys are communicating beings is not going to
work.

Hal