Patent ID: 6222923
Filing Date: 2001-04-24
Classification: H04L,H04N

Abstract:
A method for securing at least one system protected by a predefined hierarchy of cryptographic keys against unauthorized users by determining a certain individual cryptographic key assigned to a user, the at least one system including a storage device, the method comprising:assigning an individual cryptographic key to each system user on a lowest hierarchical level;storing the individual cryptographic keys in the storage device;forming at least one higher hierarchical level of cryptographic keys at predefined discrete points in time using a process which includes: combining the cryptographic keys of an immediately lower hierarchical level into a plurality of subsets of a predefined size, an assigned cryptographic key being assigned to each subset; transmitting the assigned cryptographic keys using the respective immediately lower hierarchical level cryptographic keys; and storing the assigned cryptographic key in the storage device; anddetermining the certain individual cryptographic key assigned to a user by performing a set intersection of at least one of the plurality of subsets with another subset formed at a different time and pertaining to a same hierarchical level.