Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1990-07-16
1991-02-19
Buczinski, Stephen C.
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
380 10, 380 20, H04L 908, H04N 7167
Patent
active
049950800
ABSTRACT:
A method of operating a pay per view (PPV) television system includes transmitting global data packets alternately encrypted with two different session keys. Subscriber terminals store three session keys, and automatically sequence through the session keys in an ateempt to decrypt the data packets. A program tag in the global data packet identifies a television program and a memory location in the subscriber authorization memory and may also include a tag identifying an upcoming program for which the subscriber may self-authorize his terminal by accessing the memory location identified by the PPV tag. The program tag is required to enable the subscriber terminal descrambling means to descramble the accompanying television program. Subscriber terminals are periodically polled by addressed data packets whereupon the contents of their authorization memories are sent to the cable heat-end for billing purposes. After successful polling, a new session key is downloaded to the subscriber in an addressed data packet. After polling of all subscribers, the memory location identified by the PPV tag is cleared by means of a global data packet encrypted in the new session key which only polled subscriber terminals have. An unpolled subscriber terminal needs to be polled before it receives the new session key.
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patent: 4771458 (1988-09-01), Citta et al.
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patent: 4803725 (1989-02-01), Horne et al.
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Bestler Caitlin B.
Citta Richard W.
Long Michael E.
Buczinski Stephen C.
Gregory Bernarr Earl
Zenith Electronics Corporation
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