Secret sharing
In this method, any t out of the n shares may be used to recover the secret. The idea is that a polynomial of degree t-1 is defined by t points on the polynomial: It takes two points to define a straight line, three to define a quadratic curve, four for a cubic, and so on. It takes t points ot define a polynomial of degree t-1. That way it is possible to build a polynomial, the first coefficient is the secret; there are n randomly picked coefficients. Each player receives one of the n coefficients. If there are at least t players, they can rebuild the original curve, and get the secret.