Authorization-based Group-oriented Secure Broadcasting System

This paper presents an authorization-based group-oriented secure broadcasting sys-tem based on the ID-based system proposed by Tsujii and Itoh. In the proposed system, anybroadcasting secret in ciphertext form is addressed to figroupfl instead of fiindividualfl. Firstof all, the broadcaster defines the message authorization strategy among the individuals inthe destination group by considering the characteristics or restrictions of the secret, such astimeliness, integrity, or importance etc. Afterwards, the broadcaster broadcasts the secret inciphertext form to the destination group such that the individuals in the destination grouponly can recover the secret by means of authentication, following a predefined messageauthorization strategy. In general, the broadcaster can define the message authorizationstrategy for a secure broadcast as one of the following: (1) restricted 1-out-of- n, so that onlythe specified individual in the destination group can recover it; (2) unrestricted 1-out-of-n,so that any individual in the destination group can recover it; (3) n-out-of-n, so that allindividuals in the destination group should collaborate together to recover it; (4) restrictedt-out-of-n, so that only the specified t individuals in the destination group should collabo-rate together to recover it; and (5) unrestricted t-out-of-n, so that any t individuals in thedestination group can collaborate together to recover it. The security of the proposed sys-tem is based on the difficulty of computing discrete logarithms over GF(p). Also, somepossible conspiracy attacks on the proposed system are analyzed.Keywords: secure broadcasting, authorization-based, group-oriented, ID-based system,authentication, discrete logarithms