From: Jim McCoy <mccoy@communities.com>
Date: Mon, 16 Dec 1996 14:52:17 -0800 (PST)
To: cypherpunks@toad.com
Subject: RE: Securing ActiveX.
In-Reply-To: <01BBEB6C.A6148AA0@bcdev.com>
Message-ID: <v03007805aedb7d667ad1@[205.162.51.35]>
MIME-Version: 1.0
Content-Type: text/plain


Blake Coverett <blake@bcdev.com> wrote:
[...]
>Digitally signed code, a la ActiveX, is another approach to the same
>problem.
>If the digital signatures and infrastructure around them are sound, which
>they
>appear to be for ActiveX, this is also a useful solution.  The built-in
>gotcha
>with this model is the all or nothing nature, either I trust the software
>publisher  to run arbitrary native code on my machine or I don't run it at
>all.

The other problem is that the proposed Authenticode system and other "signed
applet" systems only provide accountability after the fact.  This is little
help when your hard drive is toast and the only proof you had was a logfile
which was the first thing erased...  The illusion that only "trusted software
puslishers" will be given blanket authorization is a pipe dream: users are
sheep who will hit that "OK" dialog box as many times as necessary to get the
tasty treat they are anticipating (and there is actual experimental evidence
to back this up :)  I expect that the first post-Authenticode ActiveX virus
will be one to modify the signature checking routines or add additional keys
to the registry which makes the second round of the attack appear to be a
valid OS update from Microsoft. What exactly does a signature get you other
than someone to point a finger at?  In case you don't read those legal weasel
words in software licenses there is no claim made that the product will work
as intended and the company does warn you that if the product fries your
disk then it is not their fault...

>Specify technical issues follow:
>
>> It can be done under 95 but Microsoft will have to write a Sandbox
>> Virtual Machine (a Virtual x86 session whose API's are filtered to
>> prevent access to certain things like the file system, and disables
>> direct I/O.)  Not that easy under '95, but it already exists for NT.
>
>But of course it's not enough to filter out filesystem calls.  The entire
>windowing system would have to be separated as well.  For example
>a rogue control might watching all edit controls for ones
>that have the ES_PASSWORD style and grabbing the contents.
>
>An equivalent Unix problem would be to allow an open-access guest
>account with the ability to transfer in and execute arbitrary binaries.
>While doing this securely may be possible in theory I don't think the
>state of the art is up to it today.  (I sure wouldn't allow it on my system.)

The state of the art was up to it quite a while ago.  Check out KeyKOS and
other OSes which use capability semantics for access control.  Rather than
the all or nothing approach to security which is currently built into Java
and continued with the code signing initiatives (albeit allowing you to
delegate responsibility regarding trust) what is needed is to extend the
signatures to granting the capability to perform a certain task and nothing
more.  If the signature could express things like "this ActiveX control
needs access to a writable file in C:\WINDOWS\TEMP which will not exceed
1 Megabyte in size" then the system would be flexible enough to succeed
and would allow users to express much more complex trust relationships than
the simple boolean expressions which current code signing mechanisms allow.

jim