US006069957A [ii] Patent Number: 6,069,957  Date of Patent: May 30,2000
"Applied Cryptography," 2nd Edition, by Bruce Schneier (1995).
Primary Examiner—Gail O. Hayes
Assistant Examiner—Hrayr A. Sayadian
An encryption system for restricted-access television systems. Decryption keys, which are used to decrypt program material, are transmitted to customers in a restricted-access television system. The keys are transmitted as a hierarchy, wherein one key unlocks another key, and the last key unlocked is used to decrypt program material. Such a hierarchy is sometimes called "key-upon-key" encryption. The system transmits a second key that produces a first key from a cipher text (which first key decrypts a first program material) and wherein the second key also decrypts a second program material.
2 Claims, 30 Drawing Sheets