Patent ID: 7529369

Claim:
A method for enciphering data in a data processing means, by means of an algorithm that employs a confidential key, comprising the steps of, applying a secret key and a first random number to a first function to thereby generate a first key in the processing means, prestoring the first key and the first random number in non-volatile memory in the processing means, employing said first key and said first random number stored in said non-volatile memory each time data is enciphered with said algorithm in said data processing means, without reference to said secret key, and for each execution of said algorithm to encipher data, said method comprising the steps of generating a second random number, applying the first key and the second generated random number to a second function in order to produce a second key, and applying the second key and the first prestored random number to a function which is the inverse of the first function in order to produce a third key used for the execution of the algorithm.