Subject: Hi-Jacking the VeriSign WebServer CA

From: "Anders Rundgren" <[email-masked]>
Date: Tue, 16 Apr 2002 09:10:13 +0200

Pardon the interesting title :-)  The following is a part of a coming B2B-
standard that I want you PKIXers to comment on.

The scenario
--------------
A multi-party portal supporting potentially millions of small businesses,
will, using the OBI Express B2B-standard, be forced to keep a unique
company-certificate and associated private key for each hosted business-
entity.  AKA a "Digital Company Paper".   The private keys are only
used on the portal-server, and never distributed as OBI Express is based
on organization-level, server-based PKI.

A portal of this kind typically only vouches for the hosted business-entity
as being a customer of the portal with a certain internal customer-ID and
common name.  Mostly because this is a safe thing for the portal to do.

To do this efficiently and securely, the portal usually has an integral
CA-function, with a corresponding CA-cert and key.  A business-
entity's "Digital Company Paper" is automatically created during
the registration of the business entity.  Renewals are performed
automatically in the background.  Revocation does not apply, as
you simply disable or delete the account if a customer is not wanted
anymore.  Private keys are preferably protected by HW-cryptography.

The problem
--------------
All this is great, but it also effectively means that each portal will
become an independent CA-root to be accepted, installed etc. by RPs.
This somewhat defeats the OBI Express goal of plug-and-play operation.
To make the portal-CA a part of an existing and trusted hierarchy is
certainly possible (who's?), but is also likely to cost a minor fortune.

The work-around
--------------------
The portal signs a message containing the local portal-CA certpath using
a web-server certificate issued by a generally known and trusted issuer
like VeriSign  (a web-server certificate is BTW needed anyway, as
OBI Express uses HTTPS for all external communication).  Then the
portal publishes this message for existing and potential RPs to use (OBI
Express' PKI-support functions are capable of performing the dual path-
validations needed).

====================================================
By doing this, the portal-CA gets a certified "home" and can (depending
on local policy) be "auto-accepted" as it was a part of the VeriSign tree.
====================================================

The only difference trustwise is that VeriSign has not sanctioned the portal's
CA-activities.  But for RPs that do not know the portal, that does not mean
much.  This is IMHO a problem with deeply nested PKIs in general.  For a
business operation, the concept of trust is also a bit more complicated than
just a trustworthy digital certificate.  It is more about reputation, and
execution.  To use a web server certificate as a CA-certificate had been
even better, but VeriSign's et al's key-usage constraints for avoiding trust-
anchor hi-jacking (!), make PKIX-conformant path-validation fail.

Is this hi-jacking illegal, unethical, technically broken, or just a "clever"
way to save maybe $25-$100K / installation?

Anders Rundgren
X-OBI

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