Importance

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Abstract

A digital broadcast system provides secure transmission of digital programs to in-home digital devices even when some of the devices are unauthorized. A matrix of device keys S.sub.j,i is provided, wherein 'i' is a key index variable indicating a position in a key dimension of the matrix and 'j' is a sets index variable indicating a position in a sets dimension of the matrix. Each in-home device is assigned plural device keys from the matrix, with one and only one device key for each key index variable 'i' being assigned to a device. To generate a session key for a broadcast program, session numbers x.sub.i are encrypted with all device keys S.sub.j,i to generate a session key block which is decrypted by the in-home devices and used to generate a session key for decrypting the program. If one of the devices is a compromised device, at least one of the session numbers is a dummy number that is encrypted and decrypted by the corresponding compromised device key, with the resulting session key being useless in decrypting the program.

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First Claim