Looking for an N -out-of-M split algorithm

[Jill.Ramonsky at Aculab.com]

Hi,
 
I remember reading (many years ago) a description on some web page somewhere
of an algorithm by which an arbitrary file F could be split into M pieces,
such that:
(1) given any N pieces, F can be reconstructed precisely, and
(2) given fewer than N pieces, it is impossible to determine even a single
bit of information about F.
 
Unfortunately, that was many years ago, and -- search as I might -- I
haven't been able to find it on web now.
 
Does anyone have any idea where I might learn about this algorithm - or
indeed any algorithm which does the job.
 
Jill

[Moderator's note: look for "Shamir Sharing" -- the trick is just
turning the secret into a polynomial of degree N so that with enough
points you determine the polynomial uniquely and with too few you
can't determine it. I'm pretty sure that Schneier and all of the other
standard references explain this trick. --Perry]
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