Method for securing system protected by a key hierarchy
AssigneeDeutsche Telekom AG
InventorJoerg Schwenk
Life of this patent
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Abstract
A method for securing a system protected by a predefined hierarchy of cryptographic keys, and in particular, for securing a pay TV system, against unauthorized users. An individual cryptographic key assigned to a dishonest customer is determined by forming the intersection of at least two predefined subsets formed at different points in time and pertaining to the same hierarchical level.
Claims10
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;
- and
- determining 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.
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 two higher hierarchical levels of cryptographic keys at the same time for the at least one system 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;
- and
- determining 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 pertaining to a same hierarchical level of different key hierarchies of the at least one system.
Dependencies are inferred from the claim text.