Cryptography Reference
In-Depth Information
Another individual human characteristic is the dynamics of
keystrokes
. The
major advantage of this method is that it can continually check whether or
not the 'right' person is still working at a computer. The major downside is
that the error rates are high. A practical use for this method comes from an
entirely different angle: one can derive typed passwords from the keystroke
echo — it works in practice. I don't know whether it would work for mouse
movements, though, considering our keyboard-hostile world.
Figure 6.11:
(
continued
)
Unfortunately, biometric authentication systems have a few problems. Schneier
lists three critical points in his online magazine
Cryptogram
.
1. Biometrics are unique identifiers, but they are not secrets. You leave
your fingerprints on everything you touch, and your iris patterns can be
observed anywhere you look.
2. Biometrics also don't handle failure well. Imagine that Alice is using her
thumbprint as a biometric, and someone steals the digital file. Now what?
This isn't a digital certificate, where some trusted third party can issue
her another one. This is her thumb. She has only two. Once someone
steals your biometric, it remains stolen for life; there's no getting back
to a secure situation.
3. And biometrics are necessarily common across different functions. Just
as you should never use the same password on two different systems, the
same encryption key should not be used for two different applications.
If my fingerprint is used to start my car, unlock my medical records,
and read my electronic mail, then it's not hard to imagine some very
insecure situations arising.
These points are not arguments against biometrics in my opinion. There's a
solution to every problem.
•
First, at least the manufacturers I spoke with know very well that bio-
metrics is not based on secrets. The security concept has to consider this
fact. To use a specific example: suppose the BioID system (the one that
