Patent ID: 7523307

Claim:
A computer-implemented method for securely transmitting multicast data, comprising: encrypting at least one title T with at least title key K T ; and encrypting the title key K T with at least one channel-unique key K cu using at least one encryption function S to render a multicast data channel encrypted as S Kcu (K T ), S KT (T), wherein the channel-unique key K cu is the result of a combination of a channel key K c and a session key K s , wherein the session key K s is encrypted with at least a first encryption scheme B R s1 to render a session key block, further comprising providing at least one player with device keys K d to activate the player and providing the player with the channel key K c and the session key block, wherein the player can determine the session key K s from the session key block using the device keys K d further comprising periodically refreshing the channel key K c to enforce subscriptions, wherein a new channel key K c ′ is encrypted with at least a second encryption scheme B R s2 and wherein the encryption scheme B R s2 includes: assigning each player in a group of players respective private information I u ; partitioning players not in a revoked set R into disjoint subsets S i1 , . . . S im having associated subset keys L i1 , . . . L im ; and encrypting the session key K s with the subset keys L i1 , . . . L im to render m encrypted versions of the session key K s .