When a fingerprint is stored on a card (or such) I am assuming that a
message digest of key points is stored rather than a bitmap image of
the full print. Does anyone know how many bits such a digest has to be
at minimum to guarantee uniqueness? Or, alternately a more proper group
to ask at? (All the security sites google listed seemed OS/network
specific.)

-Chris

Chris Williams wrote:
> When a fingerprint is stored on a card (or such) I am assuming that a
> message digest of key points is stored rather than a bitmap image of
> the full print. Does anyone know how many bits such a digest has to be
> at minimum to guarantee uniqueness? Or, alternately a more proper group
> to ask at? (All the security sites google listed seemed OS/network
> specific.)
> 
> -Chris
> 

IIRC there is a system for (manually) indexing fingerpronts, based on 
the "characteristic points" (like Y . O) and their relative posistions.
You can never guarantee uniqueness, not even for random numbers.

HTH,
AvK

"Chris Williams" writes:

> When a fingerprint is stored on a card (or such) I am assuming that a
> message digest of key points is stored rather than a bitmap image of
> the full print. Does anyone know how many bits such a digest has to be
> at minimum to guarantee uniqueness? Or, alternately a more proper group
> to ask at? (All the security sites google listed seemed OS/network
> specific.)

I suppose you already have an answer based on the clue provided by moi.  I 
find this an interesting topic too and fiddled a bit.  It seems to be that 
they store about 12 interesting points in the form of 300-500 bytes.

I found these links helpful.

http://www.esiee.fr/~coupriem/Sdi_eng/finger.html
http://members.tripod.com/edward.nygma/fingerprints.htm
http://www.fme.fujitsu.com/products/biometric/pdf/Find_FPS.pdf

I have been reading a bit on DNA lately and according to my source the FBI 
accepts 13 markers as a kind of standard, very similar to the 12 fingerprint 
points accepted in Holland   The author says that (13) is overkill.

osmium wrote:
> I suppose you already have an answer based on the clue provided by
moi.  I
> find this an interesting topic too and fiddled a bit.  It seems to be
that
> they store about 12 interesting points in the form of 300-500 bytes.

Cool, that's what I needed to know. Thank you both for answering.

-Chris