From: Adam Back <aba@dcs.ex.ac.uk>
Date: Wed, 15 Oct 1997 02:42:53 +0800
To: frantz@netcom.com
Subject: Re: proposal: commercial data recovery
In-Reply-To: <v0300780cb06943af6a1f@[207.94.249.37]>
Message-ID: <199710141811.TAA04798@server.test.net>
MIME-Version: 1.0
Content-Type: text/plain




Bill Frantz <frantz@netcom.com> writes:
> At 2:37 AM -0700 10/14/97, Adam Back wrote:
> >...
> >2. second crypto recipients on encrypted communications are not
> >   used to allow access to third parties who are not messaging
> >   recipients manually selected by the sender
> >...
> >
> >Included in 2) is the principle of not re-transmitting over
> >communication channels keys or data re-encrypted to third parties
> >after receipt -- that is just structuring -- and violates design
> >principle 2.
> 
> This requirement tries to enforce something which can not be enforced by
> technical means.  That is, when you send another person some data, there is
> no technical way you can prevent them from using it however they want.  For
> example, a user can always program his filters (given something like
> procmail) to send decrypted data anywhere he wants.

I agree with that statement entirely.

The principle has deeper meaning than your point.  It acknowledges
that there are limits to what can be done to enforce things in
software.  What it argues is that you should enforce what you can
where this helps you to make your software less useful to GAKkers
without modifications.  So if this means that the GAKkers can't use
your software with out getting you to re-write it, or without making
the modifications themselves this is good because fielded systems have
intertia.  It takes time and costs money to make software updates,
doubly so where people will be hostile to those updates.  People who
would otherwise not care about GAK will suddenly "care" because they
are too lazy to update their system, or becaues the update will cost
them money.


Btw. Lest it is not clear, when I say "should" in this discussion of
the anti-GAK protocol design process I mean "should" according to my
CDR or "anti-GAK" protocol design principles.  If following these
principles causes you to have non functioning or unsaleable designs,
and when this occurs you should still try to violate as few of the
design principles as possible.


So for your .procmail filter example: what the principle says is that
you should make it as non-automatable as possible in your software to
do this redirection in electronic form.  The danger about automated
redirection in electronic form is that there will be a nice little box
saying for you to type: "recovery@lazarus", where lazarus is the
address of the recovery machine on your LAN, but then the GAKkers can
pass laws and all the people who bought your software will be
automatically able to comply by filling in that box with
"thoughtpolice@nsa.gov"; alternately the GAKkers may buy your software
for re-sale in Iraq and then fill in the field with or
"thoughtpolice@mil.iq", with the result that Iraqis.

So for example with your .procmail example: the email client should
decrypt the traffic with short lived keys to provide forward secrecy,
and re-encrypt the plaintext for storage in your mail folder with a
recoverable key (presuming you want corporate data recovery of your
mail folder in case your dog chews your smart card key token).

Forwarding of email at the .procmail level won't help the GAKkers in
this case because the email is still encrypted; and the anti-GAK
protocol design principles state that the encrypted message should be
encrypted to one recipient only: you.

The anti-GAK design principles also mean that you should offer no
tools to decrypt from the command line.  This ensures that GAKkers
will be hindered from using software provided by you to cobble
together a GAK system, without writing and distributing software
themselves.

Think of the CDR or anti-GAK software principles as attempting to
codify your natural predilections as a GAK hating protocol designer.
They codify how best to design your software to hinder GAKkers.


Clearly the GAKkers can pass a law saying that you must manually
forward each of your emails after decryption to them, but if the
software provides no easy way to automate this process they are asking
the impossible if there are 10 million US citizens using the software.

Contrast this to PGP Inc's CMR design where all that is required is a
change to one field for completely automated over the wire key word
searches.

> N.B. I applaud Adam's direction of building the data recovery businesses
> need without helping 3rd parties engage in undetected snooping.  Keeping
> the decryption keys (if data is not stored in the clear) near the
> legitimate copies seems to be a useful step in this direction.

I like your locality point.

It is something I had not earlier considered had more than binary
meaning (communicated or not ever communicated).  However it does.
The Frantz corollary to the anti-GAK protocol design principles is
then:

i)  recovery information should be kept as close to the data as possible

ii) if recovery information is moved it should in preference not be
    transferred using over communications networks, and should
    not be transferred automatically by the software without requiring
    human interaction.


You can see that this design principle leads to some at first
apparently absurd requirements, but actually they are all sensible and
pertinent.  If the software requires user interaction to transmit
recovery information this means therefore that it should not be
possible with the software as is to write automatic scripts; this
contributes to the uselessness of the software to the GAKkers.

Of course there are ways around everything (eg. scripting software
which allows mouse and keyboard actions to be automated); but we are
trying to avoid easy cobbling together actions by the GAKkers allowing
them to convert our software designed under anti-GAK principles into
one which can then becomes automated GAK system.


Also clearly there is some user intelligence required in the design
process to work out functionalities it is worth forgoing where it
comes to this by comparing their potential value to the GAKker against
the ergonomic or utility advantage to the user.

Adam
-- 
Now officially an EAR violation...
Have *you* exported RSA today? --> http://www.dcs.ex.ac.uk/~aba/rsa/

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