From: owen@autodesk.com (D. Owen Rowley)
Date: Wed, 24 Nov 93 18:43:22 PST
To: karn@qualcomm.com
Subject: Re: Give me your password- OR ELSE!
Message-ID: <9311250200.AA04695@lux.YP.acad>
MIME-Version: 1.0
Content-Type: text/plain



 > > From: karn@qualcomm.com (Phil Karn)
  > >Car alarms and security systems didn't convince the criminals who make their
 > >living ripping off cars that the *Good ole days were over* and it was time
 > >to get a  job at Burger Sri, it spurred them to find new methods to ply
 > >their trade.
 
 > How do you know this? Clearly some crooks may have just moved to more
 > violent methods, but it's quite probable that others moved off to
 > other fields where it's easier to make a buck, either legal or
 > illegal.

Watch the nightly news or if you want to be really anal about it look up 
statistics about the increase in violent carjacking.
Walk down the street in any San Francisco neighborhood, and count the piles 
of tempered glass that used to be car windows.

So OK, you don't have a criminal mind, and it makes sense to you
that it might be a good time to go legit, but let me offer you my
sincere advice not to move into a bad neighborhood, you are at a natural 
disadvantage.

 > Although widely deployed strong cryptography may well cause an
 > increase in violent, rubber-hose cryptanalysis, this technique is
 > likely to be useful only for stored encrypted records and for
 > encrypted communications whose protocols are not secure against this
 > type of attack, e.g., PGP encrypted email.

tightly focused linear thinkers are perfect targets for criminally minded
predators, they are assured that you will leave them a wide arena from
which to operate undetected.

 > 
 > But much better protocols exist where online two-way communication is
 > possible, e.g., signed Diffie-Hellman key exchange, with periodic
 > automatic rekeying. Once you rekey in such a system, no amount of
 > rubber hosing will obtain prior session keys; they're gone even to the
 > participants.


Recently a Cash machine was installed in a building which I frequent.
It was placed 10 feet inside a plate glass window, and has easy access
for a small truck to drive up and haul it away. It even has wheels.

I noted that this presented a danger to those of us who were in the building
late at night, since it was apparently so vulnerable.

I was concerned that the unarmed security guard was a sitting duck,
and perhaps target practice, for theives intent on driving through the window 
and quickly hauling the whole shebang away.

The cash machine installer informed me that the unit had a cel phone and GPS
that would call and give its location if tampered with, but he didn't have
an answer when I remarked that this would be littel comfort to anyone
shot or injured by thieves unaware of this factor.

and please don't tell me that posting signs telling would-be criminals
about these security precautions will do any good.
They won't.

 > And even if you rubber-hose one of the participants into revealing the
 > RSA key he uses to sign his DH exchanges, this will only let you
 > masquerade as him in future conversations. In order to tap his future
 > conversations surreptitiously, you'd have to rubberhose him without
 > his knowledge, or hypnotize him into forgetting the incident. I'd say
 > this is difficult. More so than secretly hacking the machine he uses
 > to capture his secrets. Once again, it comes down to some level of
 > physical security, at least while the machine is in actual use.
 
You are making an error if you think that any locks keep out anything
but honest people.

Necesity is the mother of invention.

The point is that these issues are not linear, when implemented in real
world situations you must consider the real world implications and 
provide real world solutions.

LUX ./. owen