The ssss unix utility does this, it's fun to use.<p>Docs at <a href="http://point-at-infinity.org/ssss/" rel="nofollow">http://point-at-infinity.org/ssss/</a>, demo at <a href="http://point-at-infinity.org/ssss/demo.html" rel="nofollow">http://point-at-infinity.org/ssss/demo.html</a> and it can be installed on ubuntu through the 'ssss' package, listed as ssss - Shamir's secret sharing scheme implementation.
It explains how a password can be cut up in pieces and distributed so that each piece individualy can be used to reveal the secret.<p>Skip to >>Shamir’s Algorithm<< section to get to the most interesting part.
hmm.. the article says: "If we encoded our secret with a cubic function and distributed coordinate sub-passwords it would require any combination of four points to determine the intercept and the secret."<p>Maybe I'm missing something here, but, taking any of the cubic function diagrams as example, what if all four coordinates have their "x" between -10 and 0? Those four coordinates will not be enough to generate the whole curve, no?