Can we copy trust?

[mheyman at gmail.com]

On Tue, Jun 3, 2008 at 1:05 PM, Ed Gerck <edgerck at nma.com> wrote:
> mheyman at gmail.com wrote:
>
> We see that the trust relationship represented by that SSL cert can be
> copied without any loss, as many times as you wish
>
My understanding is that an SSL certificate is only a method to carry
the assertion that the holder of the private key is the the subject
named in the certificate (with possible limitations on the allowed
uses of the private key). By using the certificate, one does not trust
the subject - one does trust the signer of the certificate as an
entity that verified the subject named in the certificate represents
the actual subject (this is true even for self signed certificates
<grin/>).

Copying the SSL certificate does not copy trust but sometimes copying
some certificates do copy trust.

Say Alice browses around the web looking to buy a widget and when her
browser hits a particular HTTPS protected site, it pops up an
"untrusted certificate" warning. Alice goes "oooo" and moves on to
another site. Bob goes to the same site and his browser doesn't pop up
the warning because Microsoft has automatically updated his computer's
trusted CAs list. Bob's browser trusts the site and Bob trusts his
browser so Bob buys the widget. Alice's browser didn't trust the site,
and Alice, being a remarkable woman, actually paid attention to her
browser and moved on. So we see, the "trusted CA" certificates do
carry trust (heck, "trusted" is part of the name), and, when Microsoft
copied the new trusted CA certificate into Bob's computer, Microsoft
managed to copy trust.

IT departments put corporate trusted CA certificates in employees
computers. The US DoD puts their trusted root certificates in DoD
computers. All these actions copy trust with high fidelity. But this
method rings of an edict from on high, "Thou shalt trust ...". These
methods still don't have the:

   // copy Alice's trust in Charlie to Bob
   Copy(Alice[trust-->Charlie], Bob)

capability. The low fidelity ways of Epinions and eBay seem to be the
only examples I can come up with that allow for that type of trust
copying. For example:

   // copy the trust in Charlie a large group of eBayers has to Bob
   MaybeCopy(eBayClaim.LargeGroup[trust-->Charlie], Bob)

The copy may or may not happen depending on Bob's feelings about the
size of the group or the extent of the trust. Of course, the eBayesque
trust copying happen in wetware. To move it to hardware would require
an online protocol and method to register trust. I can see shades of
the old PGP web-of-trust with added subtleties for timeliness and
dispute resolution.
>
> As to another point of your comment, the problem most people have with PKI
> is not that SSL does not work. SSL does not even need PKI.
>
I meant SSL as we use it - I believe the vast majority of SSL use
involves a hierarchical PKI. I have rarely seen the use of pre-shared
keys or self-signed certificates (which is technically still a PKI).

-Michael Heyman

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