Appeal No. 2000-1508 Page 2
Application No. 08/810,442
Digital signal transmission, which possesses characteristics
different from those of analog signal transmission, is coming
into widespread use. The invention presents modes of encryption
and decryption suited to the unique capabilities of digital
signal transmission. Specifically, multiple decryption keys are
used to decrypt encrypted material transmitted to customers of a
CATV system. For example, a CATV broadcaster encrypts the movie
"The Bells of St. Mary’s" using a segment key (“SK”). The
broadcaster then encrypts the SK using a program key (“PK”) and
encrypts the PK using a customer code key. A customer’s
possession of his customer code allows him to decrypt the PK.
Possession of the PK, in turn, allows the customer to decrypt the
SK, which then allows him to decrypt "The Bells of St. Mary’s."
A further understanding of the invention can be achieved by
reading the following claim:
1. In a decrypting apparatus, usable by a
subscriber to restricted-access television, and which
decrypts digital television programs, the improvement
comprising:
a) first computation means for decrypting
program content which is encrypted by a relatively
weak first key(SK)
b) second computation means, of substantially
similar computational power as the first
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