Patent ID: 6735312
Filing Date: 2004-05-11
Classification: H04L,H04N

Abstract:
A method for broadcasting an encrypted program comprising the steps of:selecting a set of encryption keys to encrypt a program, wherein the selected set of keys enables a number of unintended broadcast recipients to view the program, thereby requiring fewer encryption keys to broadcast the program to a number of intended broadcast recipients who paid to receive the program than an encryption method which does not enable the number of unintended broadcast recipients to view the program; compiling an f-redundant key cover set establishment keys to encrypt the program from an f-redundant establishment key allocation set using an algorithm defined by the steps of: (a) repeat Î›&LeftArrow;Si&it;:&it;&LeftBracketingBar;Si&it;&it;R&RightBracketingBar;&LeftBracketingBar;(K&Intersection;Si)&it;&it;R&RightBracketingBar;&leq;f;(b)(c) Aâ† Si&egr;A which maximizes |(Kâˆ©Si)R|; (d) Râ† RâˆªA; Câ† Câˆª{A}; (e) until the candidate collection A is empty; (f) return R, C; wherein f is the total number of broadcast system viewers to said number of intended recipients; K denotes said number of the intended broadcast recipients who paid to receive the program; the establishment keys used to encrypt and decrypt are described by a collection of key sets S, wherein S={S1, S2, . . . } such that âˆªSi=U; U represents a set of all viewers who can receive broadcasts from the head-end transmitter, wherein the total number of members of U=n; C is a key cover set; and R a set of recipients of a given key cover set C;encrypting the program using the encryption keys; and broadcasting the encrypted program wherein both the number of encrypted transmissions required to broadcast the program to the intended paying recipients and the number of unintended recipients are reduced by strictly maintaining an inequality for the step (b) of the algorithm for establishment key set having fewer than eight viewers and by permitting a non-strict inequality for the step (b) of the algorithm for establishment key sets having eight or more viewers.