Patent ID: 7450722

Claim:
An improvement to a subset-difference method, the subset-difference method using a plurality of difference keys to encrypt a content key, each of the plurality of difference keys being generated by using a corresponding label, the improvement comprising: generating during a first rekeying each of the plurality of difference keys L I,J by applying a one-way function G M to the corresponding current label, LABEL I,J and a first current content key, CK P ; generating during a next rekeying each of the plurality of difference keys L I,J by applying a one-way function G M to the corresponding current label, LABEL I,J and the next current content key, CK P+1 ; and wherein the next sequential content key, CK P+2 generated by applying a one-way function G M to the corresponding current label, LABEL I,J and content key, CK P+1 , is used to ensure continued delivery of contents.