How the ThinkPad fingerprint reader works

[beq]

I've been curious about how the fingerprint reader on newer ThinkPads work, if anyone can help:

- Training makes you swipe each finger three times. Should you try to make them represent three different ways you might normally swipe that finger (with variations in angle/tilt -- or even speed, pressure, direction, etc), in the hope that the pattern stored will be the sum total of all the information? Or does the training only check that the three swipes are consistent enough from one to the next, but it might only store the pattern from one of the swipes (be it the first, second, or third)?

- I read somewhere that for training you should swipe your finger a lot slower, but you can swipe at normal speed thereafter?

- Does it matter how much pressure you apply (especially for training)? I was afraid too light might mean it won't read as much of the fingerprint ridge pattern, but too hard might make the ridges too smudged?

- What kind of sensor/technology is used? I recall there were several different technologies used in aftermarket USB fingerprint readers, with different strengths/weaknesses (some read deeper than the outer skin layer and aren't affected by smudge/grease or pressure, some only work with live flesh so that you can't use a dead cut-off finger, etc).

[beq]

I just read from http://forum.thinkpads.com/viewtopic.php?t=16161 (but wanted to keep my fingerprint reader questions all in one thread)

20 fingers can be configured for the BIOS/HD Boot passwords because they have to be stored in the reader or BIOS itself.

More fingers can be used for the Windows login.

You can pick which ones out of all your registered fingers are Approved for power-on.

It's interesting that for power-on you have to initially match each desired fingerprint with the power-on password individually (for the first time), but not so for BIOS/HDD boot. What's the rationale I wonder?

And does the power-on fingerprint initialization match to the specific password used, so that if you change that power-on password in the future you'd have to re-match the fingerprints to the new password again? Also, can you match more than 20 fingerprints to the power-on password, I'm just curious?


Anyways from my experience, it seems the power-on fingerprint matching is stored even if you later disable the power-on password, because when I later re-enabled the power-on (with the same password), I didn't have to re-match the fingerprints I'd already matched previously.

But with the BIOS boot, when I disabled and then re-enabled the password, I had to re-match the whole set of specified fingerprints again (but only one time for the whole set).

I hope what I said makes sense...

[GomJabbar]

I don't have the fingerprint reader so I can't give first hand experience, but I did see the following document that you may find useful. How to configure Fingerprint Reader software