[clug] Biometrics and Linux

[Alex Satrapa]

On 22 Feb 2004, at 21:45, Andrew Pollock wrote:

> The other thing is, does anyone know how they work? Are the identifying
> features of the fingerprints stored in the reader itself, or does it 
> just
> spit out the equivalent of a checksum to the application for
> comparison/verification?

How Stuff Works: http://travel.howstuffworks.com/fingerprint-scanner.htm

They don't mention the infrared scanners that were at one time used at 
the ACT Legislative Assembly buildings. The problem with infrared 
scanners is that they are typically designed for indoor ("controlled" 
environment) use. They're useless for outdoors gates since, as the ACT 
MLAs found out, on a cold day (or a hot day) the infrared "signature" 
of your thumb changes significantly.

But all fingerprint scanners simply send your application a report of 
some features that they find. The features may be different every time 
- the device will report on eg 6 of 10 features, and may not 
predictably detect the same 6 features each time the finger is 
presented.

There are also "palm scanners" which are actually "hand shape 
scanners". You place your palm on a metal plate that has pins in it to 
guide the placement of your fingers. A raster-imager then measures your 
hand and calculates key features such as digit length ratio, and 
possibly the width of key digits (and digit count!). As with the 
fingerprint scanner, it detects a number of features and reports those 
features to your application.

When "training" a system for fingerprint or palmprint scanning, you 
would typically take three measurements to maximise your chances of 
getting consistent feature reports.

Some finger and palm print scanners are smart enough to check for 
things like temperature and even heart beat (is the hand alive, or a 
plaster cast?)

I'm not a big fan of biometric identification, since it's impossible to 
revoke such ID should it be compromised. It's also impossible to store 
your fingerprints securely, since anyone who wants a copy only has to 
hand you a (clean) glass of (room temperature) wine. We've all seen 
Charlie's Angels, right?

Alex Satrapa

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Fingerprint: 8B0E B92F 28A5 5CEC FF21  B760 A86E 868B 9DB4 5403
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