Patent ID: 7039803

Claim:
A method for broadcast encryption, comprising: assigning each user in a group of users respective private information I u ; selecting at leas one session encryption key K; partitioning use not in a revoked set R into disjoint subsets S i1 , . . . S im having associated subset keys L i1 , . . . , L im ; encrypting the session key K with the subset keys L i1 , . . . , L im to render m encrypted versions of the session key K; partitioning the users into groups S 1 , . . . , S w , wherein “w” is an integer, and the groups establish subtrees in a tree, wherein each subset S i1 , . . . S im includes all leaves in a subtree rooted at some node v i at least each node in the subtree being associated with a respective subset key, wherein content is provided to users in at least one message defining a header, and the header includes at most r*log(N/r) subset keys and encryptions, wherein r is the number of users in the revoked set R and N is the total number of users.