Patent ID: 7552343

Claim:
A secure data processing system including: an unscrambling module disposed on a dedicated hardware part of an integrated circuit and configured to unscramble a stream of data scrambled according to a scrambling key, a module for calculating an unscrambling key disposed on said dedicated hardware part and configured to manipulate data under the control of a so-called calculation program stored on said dedicated hardware part, a processor for at least controlling the functioning of the unscrambling and calculation modules, a read only memory disposed on said dedicated hardware part for storing a secret key, a key manipulation module for calculating supplementary bits from the secret key, and for manipulating the secret key using the supplementary bits to generate a final secret key, said calculation program including instructions for prompting said calculation module to use, internally to said dedicated hardware part, said final secret key and at least two so-called external data items coming from outside the secure data processing system, in order to calculate an unscrambling key, intended to be used internally to said dedicated hardware part, within the unscrambling module, and allowing unscrambling when the unscrambling key corresponds to the scrambling key, said calculation program including instructions for prompting said calculation module to use a first one of said two so-called external data items together with said final secret key to determine an interim result and to prompt said calculation module to utilize said interim result together with a second one of said two so-called external data items to determine said unscrambling key.