The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 13, 1988
Filed:
Mar. 12, 1987
Richard W Citta, Oak Park, IL (US);
Paul M Gosc, Buffalo Grove, IL (US);
Dennis M Mutzabaugh, Mount Prospect, IL (US);
Gary J Sgrignoli, Mount Prospect, IL (US);
Zenith Electronics Corporation, Glenview, IL (US);
Abstract
A bit packet communication system includes a head end having a software implemented 16 bit shift register with a plurality of feed-forward taps and a different plurality of feedback taps for simultaneously dividing and multiplying the input data bit packet to provide an output bit packet that is both encrypted and error protected. Dynamic encryption is provided by utilizing an initial preset for the software corresponding to a preset encryption key for the shift register. Authorized subscriber terminals are provided with memories and decryption keys are downloaded. The bit packets are assembled with a global bit packet encrypted with a global encryption key and subsequent individually addressed bit packets encrypted with address keys. The address keys and terminal addresses are permanently stored in the subscriber terminal memories. The global encryption keys are changed periodically. Means are provided in each subscriber terminal for storing a number of global decryption keys which are cycled through in attempts to decrypt the global packets. One of the global decryption keys is a permanent default key associated with the subscriber terminal to assure that communication with that terminal is possible despite a lack of knowledge of the terminal address or the other global decryption keys in its memory.