Shamir's Secret Sharing Scheme (SSSS) is an implementation of a
threshold scheme for sharing a secret between third parties, and
requiring a threshold of those parties to collaborate to reveal the
secret.

Taken from the Wikipedia article about Secret Sharing:

	In cryptography, a secret sharing scheme is a method for
	distributing a secret amongst a group of participants, each of
	which is allocated a share of the secret.  The secret can only
	be reconstructed when the shares are combined together;
	individual shares are of no use on their own.

Shamir's scheme is provable secure:  in a (t,n) scheme one can prove
that it makes no difference whether an attacker has t-1 valid shares
at his disposal or none at all; as long as he has less than t shares,
there is no better option than guessing to find out the secret.