SESSION KEY UPDATING METHOD, CLIENT DEVICE FOR THE METHOD, KEY UPDATE METHOD FOR THE CLIENT DEVICE, SERVER APPARATUS PROCESSING METHOD, ITS PROGRAM AND RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To reduce the data volume distributed from a server during updating of a decryption session key for decrypting a multicast distributed and encrypted content, or during system subscription.;SOLUTION: A client 200 is divided into a plurality of groups (A), and group variables X₁ to X_g1 are given to each group, and a different hash function is applied to the group variables for each 200 in respective groups, and h₁(X₁)=CV₁, h₂(X₁)=CV₂, and h₃(X₁)=CV₃ are employed as each complementary variable (CV) for 1, 2, and 3 of 200 at a first group, and each 200 maintains all of other 200's CVs within the group it belongs and all of Xs other than the group (B). An IDc (client identification) of 200, to be excluded from the system, is sent to each 200, and each 200 generates a new KS (session key) with the CV and a current KS, using a CV of the IDc, if it exists or creating a CV by performing a hash function determined by the IDc for a X of a group where the IDc belongs, if it does not exist.;COPYRIGHT: (C)2003,JPO