[116977] in Cypherpunks
On Resisting the Jackbooted Thugs
daemon@ATHENA.MIT.EDU (William Hugh Murray)
Tue Aug 24 19:10:58 1999
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Date: Tue, 24 Aug 1999 18:53:23 -0400
From: William Hugh Murray <whmurray@sprynet.com>
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Tim May writes:
>>>My conclusion is that the key and the encryption engine need to be stored in
a tamper resistant module, such as a PCMCIA card. The module can zeroize
itself if someone tries a brute force attack. Fortezza is close but it
relies on a PIN that can be captured by the bad guys. How do you create
a
trusted path between the legitimate user and the module? You could have
an
integrated keypad, but that is susceptible to video surveillance.<<<
Key-board grabbers make a good attack when the private key is stored on
board. One reason for using a PCMCIA is that one can protect it from
clue less thugs by taking it, along with the only copy of the key,
away. Access to the pass-phrase is necessary but not sufficient.
>>>The other
possibility is biometrics, an iris or retina scan would work. The
problem is
that you can't "forget" your eyes like you can "forget" a PIN.<<<
This demonstrates why strong authentication requires two kinds of
evidence; a biometric which is difficult to forge, and a pass-phrase
which can be conveniently forgotten if necessary. Now the thugs must
have a copy of the encrypted key, a copy of the pass-phrase, and the
ability to forge your biometric. While all of these are possible, in
combination they are difficult. Assuming that the biometric is
implemented in such a way as to resist replay, getting sufficient
information to forge the biometric without your knowledge may be
particularly irksome.
>>>Besides, it would be too bulky and expensive.<<<
I assume that by "it," Tim is referring to the biometric, and more
specifically, the biometric implemented on the PCMCIA (or other smart
token). If the pass-phrase is checked on the token and the biometric is
otherwise resistant to replay, then the biometric can be implemented on
the computer. Computers shipping today come with two biometric devices
standard and built in. These are a microphone and a camera. The
microphone can be used to implement speaker recognition with built in
challenge-response to resist replays. The camera can be used to
implement visage recognition. This too can be implemented to resist
re-play but it is beyond my skill to demonstrate.
Now, it is easy to dismiss these measures in theory. Moreover, it is
not possible to say that what is possible in theory is beyond the
capability of a nation state that is prepared to invade the homes of its
citizens. We may not be able to make all homes resistant but it is
certainly within the skill and resources of those here to make many
homes resistant.
William Hugh Murray
New Canaan, CT
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